Alternatives Development and Evaluation 4-1 CITY OF HAMILTON WASTEWATER FACILITIES PLAN CHAPTER 4 ALTERNATIVES DEVELOPMENT AND EVALUATION

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1 Alternatives Development and Evaluation 4-1 CITY OF HAMILTON WASTEWATER FACILITIES PLAN CHAPTER 4 ALTERNATIVES DEVELOPMENT AND EVALUATION The focus of this chapter is on the development and evaluation of alternatives for improvement and expansion of the Hamilton Wastewater Treatment Plant and for future build-out interceptor projects. Whereas Chapter 3 focused on the existing facilities, Chapter 4 considers plans to address existing system deficiencies, as well as future needs. This is done through the development and evaluation of alternatives. Chapter 2 documented baseline wastewater conditions and established projections of future wastewater flows and loadings. To complete the picture of potential future conditions, consideration must be given to the level of performance required of treatment facilities. That is to say, the facility alternatives must be formulated with not only adequate capacity, but also the ability to adapt to future effluent discharge requirements. Effluent discharge standards are expected to become more stringent in the future and alternatives for improvement and expansion should be considered in that light. To address considerations of sufficient treatment levels for alternatives, Chapter 4 begins with a discussion of potential future effluent discharge requirements. Current effluent discharge conditions in the Bitterroot River are addressed and the potential for future changes considered. Since effluent discharge standards may become more stringent, a general discussion is presented on potential impacts to the Wastewater Treatment Plant and the City of Hamilton. Subsequent sections of Chapter 4 document the development and evaluation of alternatives for improving and expanding the exiting Wastewater Treatment Plant to meet current and projected flows and loadings and collection system expansion. Consideration is given to continuation at current levels of secondary treatment with surface water discharge to the Bitterroot River, as well as advanced levels of treatment. FUTURE EFFLUENT DISCHARGE PERMIT ISSUES Changing water quality regulations may dictate that consideration be given to modifications to improve treated wastewater effluent quality. The Hamilton Wastewater Treatment Plant discharges effluent to the Bitterroot River, a major tributary of the Clark Fork River. The State of Montana Department of Environmental Quality has performed an assessment study of the Clark Fork River Basin and designated the river as a high priority for development of a total maximum daily load (TMDL) for nutrients. The study revealed that nitrogen and phosphorus discharges, primarily from wastewater sources, have a significant deleterious impact on surface water quality. Consequently, the State is developing quality standards and is promoting a voluntary program to reduce nutrient contributions to the river. The purpose of this section is to identify current water quality concerns and define wastewater management techniques to address water quality deficiencies. A goal is to develop an approach for evaluating wastewater treatment process options when receiving water criteria have not been fully defined. Generally, this approach is to identify what is possible to accomplish from a technical standpoint, in terms of key wasteload parameters. By establishing what is feasible, utility managers may continue with facilities planning through definition, comparison, and evaluation of wastewater management alternatives. Meanwhile, the development of receiving water criteria by regulatory agencies, which may later lead to discharge permit limits, may proceed in parallel.

2 4-2 City of Hamilton Wastewater Facilities Plan This section first defines current effluent discharge conditions, Bitterroot River water quality issues, downstream nutrient control issues in the Clark Fork basin, new state nondegradation standards, and new mixing zone rules. This is followed by a discussion of wastewater treatment technology for nutrient removal, and a strategy for wastewater facility planning. CURRENT EFFLUENT DISCHARGE CONDITIONS This section briefly describes the existing Hamilton Wastewater Treatment Plant discharge permit, water quality issues in the Bitterroot River, and water quality issues in the Clark Fork River. Effluent Discharge Permit The Hamilton wastewater utility is operating under a discharge permit which is scheduled to expire on August 31, The current permit establishes maximum limits for biochemical oxygen demand (BOD), total suspended solids (TSS), fecal coliform bacteria, ph, oil and grease, and chlorine residual. Minimum removals of BOD and TSS (85 percent) are also identified. The City of Hamilton is also required to monitor effluent concentrations of total phosphorous, total Kjeldahl nitrogen, total ammonia, nitrate/nitrite and total nitrogen on a monthly basis. Acute toxicity is required to be monitored semi-annually and metals annually. Although previous permits contained load limits for nitrogen and phosphorus, there are currently no limits placed on phosphorous, total nitrogen or ammonia. The Hamilton facility is a conventional secondary treatment facility that uses the air activated sludge process. The facility was not originally designed to remove nutrients; however, during the last upgrade an anoxic selector and the ability to run in an air on/air off mode was provided. This has allowed a large portion of the nitrogen to be removed in the biological process. The treatment facility has also instituted the injection of alum upstream of the secondary clarifiers to enhance settling. This has resulted in approximately a 50% reduction in effluent phosphorus. The Bitterroot River and Montana s Section 303 (d) List The Montana Department of Environmental Quality draft 1998 Section 303(d) list includes 41 water quality limited stream segments on the Bitterroot River system and its tributaries. The Bitterroot River is included on the State of Montana Section 303(d) list as a water quality limited stream segment. Additionally, the Bitterroot River is a key tributary of the Clark Fork River, which is also Section 303(d) listed as water quality impaired. A Voluntary Nutrient Reduction Program (VNRP), the functional equivalent of a total maximum daily load (TMDL), is currently being prepared to control nutrient (nitrogen and phosphorus) enrichment in the Clark Fork (Reference 8). In-stream targets for nitrogen and phosphorus concentrations of 300 ug/l and 39 ug/l respectively, have been established to prevent nuisance algae growth. In-stream concentrations for nitrogen and phosphorus at the mouth of the Bitterroot River immediately upstream of the Clark Fork were 350 ug/l and 16 ug/l, respectively, based upon 1992 sampling data for the critical flow period of August, September and October. This nitrogen concentration is above the limit of the in-stream target established for the Clark Fork River. However, no specific wasteload allocation has been developed for the Bitterroot River. In the absence of a TMDL (Total Maximum Daily Load) and wasteload allocation for the Bitterroot River, MDEQ has been calling for no net increase in loadings for key parameters on water quality limited stream segments. On May 19, 2005, HDR met with representatives from MDEQ to discuss permit issues related to the point discharges to the Bitterroot River and discuss

3 Alternatives Development and Evaluation 4-3 permit renewals and future impacts to discharge permit renewals and future impacts to discharge limits for nutrients and disinfection. Although a specific wasteload allocation has not been developed for the City of Hamilton s Wastewater Treatment Plan, the following is a summary of the findings from the meeting: A TMDL regulation is expected to be completed by 2007 for the Bitterroot River. It appears from preliminary data MDEQ has collected that the main impacts with regard to nutrients are due to non-point sources. The Clark Fork River, which the Bitterroot is a tributary, currently has a TMDL for nutrients. Nutrient standards for the Clark Fork River are expected to be published in approximately 5 years. Numeric water quality standards for total phosphorus and total nitrogen in the reach of the Clark Fork River from the confluence with the Blackfoot River and the confluence with the Flathead River are expected to be 39 ug/l and 300 ug/l respectively. This is expected to equate to an in-stream limit at the end of the mixing zone for discharges to the Bitterroot River of 0.03 to 0.04 mg/l for phosphorus and 0.27 mg/l for total nitrogen. It is understood that these numbers are preliminary, may not be achievable depending upon in-stream water quality, and subject to modification at this time. A mixing zone study should be considered for the City of Hamilton discharge to the Bitterroot River. It is recommended that the City of Hamilton collect available in-stream data for the Bitterroot River and perform a 7Q10 analysis to determine the probable nutrient limits for the Hamilton WWTP. This will be required to determine the necessity of adding a diffuser to the Hamilton outfall. It is also recommended that additional nutrient data be collected upstream from the outfall location to better determine existing in-stream nutrient conditions. Future permit requirements are likely to include year-round disinfection and will not allow a mixing zone for fecal coliform. Since chlorine is currently used for disinfection, dechlorination will likely be required. The total residual chlorine allowed to the Bitterroot River will likely be mg/l. The City of Hamilton should assume that a no net increase policy may be in effect until a TMDL is developed for the Bitterroot River and a wasteload allocation is prepared. This will effectively limit new loadings and growth in existing loadings limits. Discharge Permit Modifications. Future discharge permit conditions are unclear, but in light of the Section 303(d) listing of the Bitterroot River and pending TMDL for the main stem of the Bitterroot River, they are likely to change. In a similar situation downstream on the Clark Fork River, the Montana Department of Environmental Quality staff stated that re-issued permits have established the existing treatment plant flow identified in the new nondegradation standards at current wastewater treatment plant capacity. This is discussed in more detail below. New permits will likely include a re-opener clause that allows the State to revise the permit to include nutrient limits once the TMDL process is complete. Control aspects may be gradually implemented over two, five-year permit cycles. During the first cycle, the discharge permit will have a nutrient removal target (perhaps non-binding). During the second cycle, the discharge permit will have a mandatory removal limit, under which the discharger will be required to remove nutrients or divert the effluent flow.

4 4-4 City of Hamilton Wastewater Facilities Plan Nutrient Control in the Clark Fork Basin A primary environmental feature of western Montana, north Idaho, and eastern Washington is the Clark Fork River/Lake Pend Oreille/Pend Oreille River watershed, of which the Bitterroot River is a tributary. In recent years, there has been public concern about water quality degradation in the basin, particularly eutrophication (enrichment), which is exhibited as excessive growth of nuisance attached algae that impair recreational uses and decrease water clarity. In 1987, Congress responded to the public concerns by authorizing the U.S. Environmental Protection Agency (EPA) to evaluate the sources of cultural pollution within impaired drainage basins and develop recommendations for reducing pollution. This action was authorized under Section 525 of the 1987 Clean Water Act. The planning work began in 1988 and state regulatory agencies were assigned by the EPA, as coordinating agency, to conduct studies within their individual state boundaries. The studies conducted under Section 525 (References 1, 2, and 3) concluded the following: Excessive levels of algae cause water quality impairment in up to 250 miles of the Clark Fork River. High levels of plant nutrients, particularly phosphorus and nitrogen, have been identified as the cause of eutrophication. Excessive algae growth is a seasonal issue that occurs between late June and late September. The proposed management strategy is to reduce in-stream concentrations of nutrients to control attached algae levels. Approximately half of the basin phosphorus load comes from wastewater discharges. Approximately one-quarter of the soluble nitrogen comes from wastewater discharges. Other nutrient sources include agriculture and silviculture, as well as urban stormwater runoff. The largest nonpoint sources are the Bitterroot, Flathead, and Blackfoot rivers which contribute significant nutrient loadings to the Clark Fork River. Nutrient controls or wastewater diversion to land application at wastewater treatment discharges should be implemented, particularly at Missoula, Butte, Stone Container Corporation, and Deer Lodge The sources of up to half of the nitrogen present in the lower Clark Fork River during the summer is from the Missoula urban area ground water seepage contaminated by septic system effluent. During the initial studies, Bitterroot River municipal wastewater dischargers (Hamilton, Stevensville, and Lolo) were not directly monitored. These discharges contribute to the total Bitterroot River loading that enters the Clark Fork River. As noted in previous paragraphs, additional nutrient sampling and modeling is ongoing on the main stem of the Bitterroot River and a TMDL for nutrients is planned for It is likely that, as a result of the TMDL, point source discharges to the Bitterroot River will be required to meet more stringent permit requirements for nutrients and fecal coliform in future permits.

5 Alternatives Development and Evaluation 4-5 Control Approaches for Point Sources. The Department of Environmental Quality is recommending a number of point and nonpoint source controls for reducing nutrient concentrations (Reference 1). Potential point source controls, which may impact the Hamilton Wastewater Treatment Plant discharge, include the following: Evaluate the potential for summer land application of treated municipal wastewater and encourage its implementation. Implement basin-wide bans on the sale of high-phosphorus laundry detergents. (This has already been implemented since the City of Missoula is the main commerce center for the area and has implemented the ban.) Encourage municipalities and industry to adopt additional strategies to curb wastewater nutrient loading to the Clark Fork basin. Potential methods include operational changes, pretreatment requirements, and additional treatment measures. Enforce a consistent and aggressive policy of nondegradation with respect to nutrient loading from new or enlarged point source discharges in the Clark Fork basin. Adopt a whole basin approach to wastewater discharge permits. Permitting would be coordinated so that all renewals are scheduled concurrently on a five-year cycle. Require nutrient monitoring as a wastewater discharge permit requirement. Monitoring would include total and soluble phosphorus, nitrate plus nitrite, ammonia, and Kjeldahl nitrogen for both the wastewater influent and effluent. (Currently being implemented.) Conduct a nutrient wasteload allocation study in the Clark Fork Basin and implement the Total Maximum Daily Load (TMDL) process to control nutrient impacts. From establishment of in-stream concentrations, allowable nutrient loads from point sources would be established. (Currently being implemented as described in paragraphs above.) Preserve long-term protection for in-stream flows in the Clark Fork River and key tributaries, including the Bitterroot River, to provide dilution of wastewater discharges. Typically, regulatory activities have focused first on point source controls, usually because point discharges are easiest to identify and structural approaches are generally appropriate. In the case of the Clark Fork and Bitterroot Rivers, the regulators have expanded the proposed approach and are promoting nonpoint controls, such as best management practices, to limit nutrient releases from silvicultural, agricultural, and industrial activities. Clark Fork River Voluntary Nutrient Control Program (VNRP) The Clark Fork River Voluntary Nutrient Reduction Program submitted by the Tri-State Implementation Council, Nutrient Target Subcommittee has been reviewed for the purpose of identifying considerations related to nutrient discharges. Clark Fork River Nutrient In-Stream Targets. The VNRP establishes in-stream targets for total nitrogen and total phosphorus under the 30 day average low flow river condition expected to occur once in a 10 year period (30-Q-10). Proposed Clark Fork River in-stream targets have been established for the VNRP as 300 µg/l of total nitrogen, and 20 µg/l of total phosphorus

6 4-6 City of Hamilton Wastewater Facilities Plan upstream of Missoula and 39 µg/l of total phosphorus downstream of Missoula. The focus of the initial VNRP targets is on total nutrients, with monitoring for changes in soluble nutrients. Nutrient targets are seasonal and are to apply in the summertime, defined as June 21 to September 21. At three year intervals, the Voluntary Nutrient Reduction Program (VNRP) targets, discharger measures, and river water quality are to be evaluated and revisions made as needed. The Voluntary Nutrient Reduction Program (VNRP) calls for site specific measures to be taken by four key point source dischargers to meet in-stream targets over a 10 year period. Nonpoint Nitrogen Loading on Bitterroot River. Septic tanks drainfields in the south and west portions of the Missoula Valley have been determined to be a significant source of the nitrogen loading to the Bitterroot River and Clark Fork Clark Fork River Basin. Septic tank effluent, which is rich in nitrogen, flows to the aquifer and is carried laterally to discharge along the lower reaches of the Bitterroot River. Half of the total Bitterroot River nitrogen loading enters the river in the lower reaches. The State has attributed all of this loading (half of the total summer river loading) to Missoula aquifer seepage (Reference 3). Nonpoint source nitrogen loadings to the Clark Fork River from Missoula area groundwater have been quantified based upon groundwater flux and shallow groundwater nitrate concentration. Field measurement of groundwater bank seeps to the Bitterroot River have been conducted to substantiate these estimates. Sampling and analysis of the Bitterroot River bank seepage performed during summer 1995 confirmed elevated nitrate concentrations. Modeling of septic tanks sources and ground water flux has been performed to verify the magnitude of this loading. The Missoula area groundwater nonpoint source nitrogen loading has been estimated as 272 kg/d to the Bitterroot River and 49 kg/d to the Clark Fork River for a total of 319 kg/d. The source of nonpoint nitrogen loading is likely a combination of development and land use activities including septic systems, agriculture, urban/suburban land use (stormwater, yard fertilizer, etc.), etc. Groundwater nitrate loadings from 6,780 septic systems in the urbanized area of Missoula result in an estimated 257 kg/d of nitrogen loading to the Clark Fork and Bitterroot rivers. EPA Guidance For Water Quality-Based Decisions EPA has provided guidance for use in wastershed management and the development of nutrient control plans in a document titled Guidance for Water Quality-based Decisions: The TMDL Process, April 1991 (Reference 6). EPA identifies the objective of a total maximum daily load is to allocate allowable loads among different pollutant sources so that the appropriate control actions can be taken and water quality standards achieved. The TMDL process distributes portions of the waterbody s assimilative capacity to various pollution sources - including natural background sources and a margin of safety - so that the waterbody achieves its water quality standards. By optimizing alternative point and nonpoint source control strategies, the cost effectiveness and pollution reduction benefits of allocation tradeoffs may be evaluated. EPA guidance indicates that a phased approach to TMDL development may be necessary if there are not adequate data and predictive tools to characterize and analyze the pollution problem with a known level of uncertainty. The phased approach is required when the TMDL involves both point and nonpoint sources and the point source WLA (wasteload allocation) is based on a LA (load allocation) for which nonpoint source controls need to be implemented. The TMDL, under the phased approach, includes (1) WLAs that confirm existing limits or would lead to new limits for point sources and (2) LAs that confirm existing controls or include implementing new controls for nonpoint sources. (Reference 6). The EPA guidance (Reference 6) cautions that In practice, the terms TMDL and WLA have at times been incorrectly used interchangeably instead of considering both LA (load allocations

7 Alternatives Development and Evaluation 4-7 for nonpoint sources and background sources) and WLA (wasteload allocation to point sources) as components of a TMDL. A TMDL, as referenced in this guidance (Reference 6), includes both WLAs (point source) and LAs (nonpoint source), established in accordance with EPA s regulations. NONDEGRADATION STANDARDS The Administrative Rules of Montana (ARM Sub-Chapter 16.20, Reference 4) categorize the Bitterroot River as water quality classification B-1. Waters under this classification are highquality, suitable for drinking, culinary and food processing purposes, after conventional treatment; bathing, swimming and recreation; growth and propagation of salmonid fishes and associated aquatic life, waterfowl, and furbearers; and agricultural and industrial water supply. Dischargers issued permits are required to conform with the nondegradation rules and may not cause receiving water concentrations to exceed the applicable standards specified in state water quality standards when stream flows equal or exceed the 7-day average flow which may be expected to occur on the average of once in ten years (7Q-10). Nondegradation Standards Degradation has been identified as a change in water quality that, for a given parameter, lowers the quality of high-quality waters. Degradation also means any increase in a discharge that exceeds the limits established under a permit issued by the state prior to April 29, The City of Hamilton is currently operating under permit number MT , dated September 1, 2001, which was issued after the expiration date. The City of Hamilton is allowed to discharge the maximum quantities identified in the permit (30 mg/l of 5-day biochemical oxygen demand (BOD 5 ) and 30 mg/l of total suspended solids. Phosphorus and nitrogen are not currently limited in the MPDES permit. The nondegradation standards apply to new, as well as existing, sources that may affect water quality. Criteria have been established for defining whether or not a proposed change or activity is significant. The regulations state that the following activities have been identified to be nonsignificant: Changes in the quality of water for any harmful parameter for which water quality standards have been adopted, if the changes outside of a mixing zone designated by the Department of Environmental Quality are less than 10 percent of the applicable standard, and existing water quality is less than 40 percent of the standard. Changes in the quality of water for any parameter for which there are only narrative water quality standards, if the changes will not have a measurable effect on any existing or anticipated use, or cause measurable changes in aquatic life or ecological integrity. Changes in existing water quality resulting from treatment of a public sewage system by chlorination or other similar means designed to protect the public health or the environment and approved, authorized, or required by the Department. The meaning of this statement is unclear as it applies to disinfection, or to all wastewater treatment applications. Degradation Permit. If the proposed activity is determined to have a significant impact, then a permit to degrade water quality must be filed with the state. This permit is subject to public review and may not be issued unless it can be demonstrated that the proposed activity has no

8 4-8 City of Hamilton Wastewater Facilities Plan economically, environmentally, and technologically feasible alternative that would result in no degradation. The applicant must also demonstrate that the proposed activity will result in important economic or social development that exceeds the cost to society of allowing the proposed change in water quality. The state must also determine whether the existing and proposed uses of the receiving water will be fully protected. This determination will be based on demonstration that the change will not result in violations of Montana water quality standards outside of a mixing zone, and an analysis of the impacts of the proposed water quality changes. The nondegradation standards are new rules and potential implications may not yet be completely recognized. The City may need to comply with these rules if the quantity of treated wastewater increases significantly in the future. This action could occur if extensive new development is incorporated in the Hamilton service area and connected to the sanitary sewer system. EFFLUENT DISCHARGE MIXING ZONE RULES On August 12, 1994, the State Board of Health implemented regulation MCA (4) which governs effluent discharge mixing zones. A mixing zone is defined as a limited area of a surface water body, or a portion of an aquifer, where initial dilution of a discharge occurs, where water quality changes may occur, and where certain water quality standards may be exceeded. A mixing zone exists at the Hamilton wastewater treatment plant discharge, and is defined as a segment of the Bitterroot River, approximately 6,500 feet down river from the discharge point, to the point where the Bitterroot River crosses the northerly section line of Section 24, T6N, R21W. Narrative water quality standards, standards for harmful substances, numeric acute and chronic standards for aquatic life, and standards for human health must not be exceeded beyond the boundaries of the mixing zone. Within the mixing zone, acute standards for aquatic life may not be violated, unless it will not threaten or impair existing beneficial uses. Potential contaminants of concern that may be present at acute concentrations (toxic to aquatic organisms in a short time) in mixing zones include residual chlorine and un-ionized ammonia. Impact of Nondegradation Standards and Mixing Zones Rules The new nondegradation standards and mixing zone rules may impact considerations for future wastewater treatment. These regulations have considerable impact if the wastewater quantities increase significantly, such as through development and additional connections to the sewer system. For example, the discharge of higher levels of nutrients may require increased treatment to prevent degradation of the river. With a higher discharge flow, the City of Hamilton may be required to construct an outfall diffuser to create an instantaneous mixing zone and preserve standard mixing zone conditions. Improved mixing may also be necessary to prevent acute concentrations of un-ionized ammonia, residual chlorine, and heavy metals in the stream. NUTRIENT CONTROL APPROACHES In the future, the City of Hamilton may be required to reduce or eliminate the discharge of nutrients to the Bitterroot River. The two general approaches to accomplishing this goal are to divert the treated secondary effluent to land application, or to implement advanced methods of wastewater treatment. Advanced wastewater treatment, particularly biological nutrient removal and chemical precipitation, has been widely used in the United States, Canada, Europe, and South Africa. Advanced wastewater treatment is a reliable and effective means for complying with water quality based discharge standards. Natural treatment techniques, such as land application and constructed wetlands, have also been successfully implemented in other

9 Alternatives Development and Evaluation 4-9 locations. This approach is most often used in small, rural communities, where adequate land is available. Adequate land is not available in the vicinity of the Hamilton Wastewater Treatment Plant so land application was not considered further. In 2002, the City of Hamilton completed a significant extension of their wastewater collection to the north to serve the Old Corvallis Road service area and Corixa Corporation. In addition, the City also recently purchased an additional two acres of property adjacent to their wastewater treatment plant site. These actions have shown that the City s preferred approach is to regionalize their wastewater treatment facilities and not promote remote satellite treatment systems. This is consistent with decisions recently made at the Missoula County Lolo Wastewater Treatment Plan and the City of Missoula 2000 Wastewater Facilities Plan Update, where it was shown that satellite systems generally are greater in cost. Advanced wastewater treatment plant technologies are discussed in subsequent sections. WASTEWATER REUSE Wastewater reuse may be considered as a means for avoiding the environmental consequences of additional water supply development or to divert the discharge wastewater effluent from surface water to land. The concept is to substitute reclaimed effluent for potable water in cases where the quality of the supply source is not a critical concern. The most common reuse approach is to use wastewater effluent for irrigation purposes. Montana State Regulations Montana State regulations for water reuse are presented in Circular DEQ-2, Design Standards for Wastewater Facilities, issued by the Montana Department of Health and Environmental Sciences. Appendix F, Standards for the Spray Irrigation of Wastewater, forms the basis for the regulations. Wastewater used for irrigation of fodder, fiber, and seed is required to be oxidized (receive secondary treatment). Wastewater for food crops must be oxidized, disinfected, coagulated, clarified, and filtered. To comply with these requirements, effluent filtration is generally required. Regulations have also been developed for landscape irrigation. Reclaimed water used for irrigation of golf courses, cemeteries, roadway medians, and other landscape with similar public access is required to be oxidized and disinfected. Public access during irrigation is required to be restricted. Reclaimed water used for the irrigation of parks, playgrounds, school yards, unrestricted golf courses, and other areas with similar access is required to be oxidized, disinfected, coagulated, clarified, and filtered. Regulations in Other States Other states have adopted descriptive regulations which identify several categories of reclaimed water. These regulations are usually based on requirements established in California (Title 22), where reclamation is prevalent. For example, the State of Washington has identified Class A, B, C, and D reclaimed water. Class A has the highest level of treatment and quality, requiring oxidation, coagulation, filtration, and disinfection, with a median number of coliform organisms not exceeding 2.2 per 100 milliliters. Reclaimed water classes B, C, and D require oxidation and disinfection, with a median number of coliform organisms not exceeding 2.2, 23, and 240 per 100 milliliters respectively. These guidelines are similar to State of Montana Standards for Spray Irrigation of Wastewater.

10 4-10 City of Hamilton Wastewater Facilities Plan ADVANCED WASTEWATER TREATMENT Advanced treatment techniques using biological, chemical, and physical processes are available for removing nutrients from secondary wastewater effluent. These processes have become much more prevalent in recent years; in some areas of the country nutrient removal is relatively common. The main benefits of advanced treatment are that performance is controllable and predictable, operational strategies can be employed to modify performance, weather impacts on operation are minimized, and compact physical sites can be utilized. Substantial investments in land purchases are reduced when compared to land treatment. The primary disadvantages are that a potentially greater investment in capital facilities is required, along with increased operational costs. This impact applies to not only liquid stream processes, but also to solids stream facilities, which will receive greater quantities of solids. Advanced treatment is the most adaptable alternative for winter nutrient removal, should it become necessary in order to satisfy surface water discharge requirements. Chemical Precipitation in the Secondary Treatment Process The most basic advanced treatment method is to add metal salts, typically aluminum sulfate, to the wastewater for phosphorus removal. When it reacts with phosphates, the alum produces a precipitate which settles in the secondary clarifiers. Capital costs for chemical feed facilities are relatively modest, but annual chemical costs can be significant. The greatest impact of this approach is the increased quantity of sludge generated. Since solids handling facilities at the Hamilton Wastewater Treatment Plant are already at capacity, increased sludge production would require additional capital facilities. Several cities to the west, including Coeur d Alene, Post Falls, Hayden Lake, and Spokane, practice seasonal phosphorus precipitation. In addition, treatment effectiveness of chemical precipitation can consistently meet an effluent phosphorus limit of 1 mg/l total effluent phosphorus concentration. Should total phosphorus concentrations of 0.03 to 0.04 ug/l need to be met, chemical precipitation would need to be followed by an advanced tertiary treatment step, such as effluent filtration. Biological Nutrient Removal Both nitrogen and phosphorus can be removed through biological means. Typically, an aeration basin for this process includes zones with no oxygen (anaerobic) and low oxygen (anoxic), as well as conventional aerated zones. Nitrogen is removed by oxidizing the ammonia compounds to nitrates, then reducing the nitrates to nitrogen gas, which is released into the atmosphere. The anaerobic zones in the oxidation system encourage the growth of specific bacteria that consume high quantities of phosphorus. With this approach, phosphates can be removed from the liquid stream with little or no chemical addition. However, biological nutrient removal plants usually incorporate chemical feed facilities as a backup, and under some circumstances, for the control of nutrient recycle loads. The Kalispell Wastewater Treatment Plant and the City of Missoula Wastewater Treatment Plant are examples of facilities that are designed for biological nutrient removal. The City of Hamilton currently employs biological nitrogen removal at their treatment facility using cyclic aeration within their extended air oxidation ditch system. This treatment process can consistently meet total effluent nitrogen concentrations of 5 ug/l or less and is consistently achieving less than 2 ug/l total effluent nitrogen during the summer months.

11 Alternatives Development and Evaluation 4-11 Effluent Filtration Biological nutrient removal can remove significant amounts of phosphorus and nitrogen. However, increased removals may be required for discharge to sensitive receiving waters. Enhanced effluent quality can be accomplished by filtering the effluent to remove suspended solids that contain nutrients. This filtration system is similar to facilities that treat surface water to potable drinking water standards. For this process to be effective, the major portion of the soluble compounds must be converted to particulate form. Chemical Clarification The most elaborate nutrient removal process would be to construct a chemical clarification facility. In this process, biological nutrient removal effluent would be routed to separate chemical clarifiers. This process would be most effective for phosphorus removal. The City of Columbia Falls Wastewater Treatment Plant is an example of a facility that utilizes chemical clarification for phosphorus removal. TREATMENT PROCESS PERFORMANCE CONSIDERATIONS Nutrient water quality standards for the Clark Fork River Basin have been proposed, but future discharge permit limitations have not yet been established for discharges to the Bitterroot River. In facility planning, when discharge standards are not yet defined, it may be appropriate to evaluate performance of advanced treatment facilities in terms of technically achievable levels. A range of nominal effluent performance characteristics allows consideration of treatment process sizing for facility planning. Phosphorus Precipitation. Nominal effluent quality parameters for phosphorus precipitation in secondary treatment facilities are as follows: Biochemical Oxygen Demand (BOD) Total Suspended Solids Total Nitrogen Ammonia Nitrogen Total Phosphorus Secondary treatment Secondary treatment Secondary treatment Secondary treatment 1 to 2 mg/l Biological Nutrient Removal. Nominal effluent quality parameters for biological nutrient removal facilities are as follows: Biochemical Oxygen Demand (BOD) Total Suspended Solids Total Nitrogen Ammonia Nitrogen Total Phosphorus 10 mg/l 10 mg/l 10 mg/l 1 to 2 mg/l 1 mg/l Biological Nutrient Removal with Effluent Filtration. Effluent quality parameters based upon the limits of biological nutrient removal technology, utilizing additional processing steps and effluent filtration, are approximately as follows: Biochemical Oxygen Demand (BOD) Total Suspended Solids Total Nitrogen Ammonia Nitrogen 5 mg/l 5 mg/l 8 mg/l less than or equal to 1 mg/l

12 4-12 City of Hamilton Wastewater Facilities Plan Total Phosphorus 0.2 to 0.5 mg/l Treatment Process Planning Treatment facility planning involves consideration of a number of factors including receiving water requirements, selection of the treatment process configuration, recycle stream control, utilization of existing facilities, correction of existing system deficiencies, biosolids management, plant site layout, operation and maintenance, budget management, implementation schedule, permitting, and user charges. This multi-dimensional planning process often results in competing priorities. For example, all facility needs may not be able to be satisfied with the resources currently available. Future performance requirements may not be clear, resulting in the need for flexibility to adapt to alternative scenarios. Addressing these issues and choosing a course of action is a large part of the facility planning process. Base Treatment Scenario. Current discharge permit requirements for the Hamilton plant require secondary treatment only. Limits on the overall mass of nitrogen and phosphorus are likely to be imposed in future permits. Phosphate Detergent Ban. A common first step in nutrient control is to implement a phosphate product ban. In recent years, Missoula and the Missoula County area implemented such a ban. Seasonal Phosphorus Removal. Significant amounts of phosphorus could be removed by seasonal chemical precipitation in the secondary treatment process. This approach will not be adequate if both nitrogen and phosphorus controls are required. Biological Nutrient Removal Scenario. Receiving water discharge permit limitations will be key to governing the sizing of biological nutrient removal processes and their performance requirements. Preliminary phosphorus and nitrogen limits for discharge to the Clark Fork Basin have been established. This is proposed to be accomplished within 10 years. Planning for nutrient removal and more restrictive discharge permit conditions to accommodate increased loads may be prudent. In fact, planning for nutrient removal requirements is well advised since regulatory agencies are investigating receiving water conditions, growth in the area is increasing loadings from several point sources, regulators have indicated that MPDES permits may be locked-in at current levels (nondegradation standards), and regulations have indicated a TMDL for the main stem of the Bitterroot River is tentative in Clark Fork River VNRP Effluent Quality Targets. The proposed wasteload allocation from the Clark Fork Voluntary Nutrient Reduction Program (VNRP) (June 15, 1998) results in effluent quality targets for the City of Missoula s wastewater treatment plant discharge as follows: Biochemical Oxygen Demand (BOD) Total Suspended Solids Total Nitrogen Total Phosphorus Secondary treatment Secondary treatment 10 mg/l 1 mg/l These values may serve as a reference for consideration of potential effluent discharge requirements for the Hamilton Wastewater Treatment Plant. FACILITY PLANNING AND EVOLVING NUTRIENT REMOVAL STANDARDS The fact that future discharge permit levels are not defined should not impede planning for possible future conditions. In fact, it may be detrimental to utilities to avoid planning for future discharge standards until permit levels are defined. This approach limits the vision of utility

13 Alternatives Development and Evaluation 4-13 planners and managers, and may prevent them from developing effective strategies for process modifications, arranging for adequate plant site space, developing compatible biosolids management plans, preparing for financial impacts, and understanding the full implications of offers of sewer service to new developments. This is a situation faced by many intermountain communities. Evolution of Discharge Standards As potential wasteload limitations are defined, they can be compared to the levels of technically achievable discharge quality that plant options can produce. In developing this approach, it has been assumed that wasteload allocations (or nutrient management plans, or phased TMDLs) will establish mass discharge loading targets for a variety of parameters (BOD, TSS, Total Nitrogen, Phosphorus) for individual dischargers. Comparing the potential mass discharge limits against plant flow and effluent concentrations provides a forecast of compatibility with receiving water requirements. A number of future scenarios are possible, depending upon receiving water loading limits, the schedule and timing of regulatory limitations, and growth of plant flow and loadings. At some level, mass discharge limits may be exceeded, requiring additional levels of treatment. Treatment plant improvements will need to be implemented to accomplish new objectives. If receiving water standards become stricter (or wasteload thresholds are reduced), or plant loadings increase as a result of growth in the service area, further treatment processing will be required. Staged implementation of successive plant improvements provides an implementation plan for response. Under some scenarios, coupling the best treatment technology with projected flows and loadings, may dictate diversion from receiving waters in order to comply with discharge standards. Conceptualizing this possibility from the inception of planning may allow creative coupling of a wider array of potential alternatives for the utility. This includes seasonal discharge strategies, land acquisition, coupling diversion strategies with treatment for reclaimed water programs, and development of ground water recharge strategies. Objectives of Facility Planning The purpose of a facility plan is to provide utility managers with a vision of the fullest extent of treatment possible, as well as potential diversion strategies, so that utility service can be sustained into the future. If utility managers track the progression of discharge standard development and the growth in plant loadings, a facility plan provides a road map of actions necessary to sustain the viability of the wastewater system. Tracking discharge standard development includes participation in the wasteload allocation process (participative TMDL) and a continuing dialogue with regulatory agencies. Flow and loading development takes on an important meaning, beyond the routine collection of data, as key threshold levels are approached and planned responses implemented. Utility managers can plan proactively for the strategies necessary for implementation of facilities. Such activities include briefing the City of Hamilton Council, coordinating with other agencies (County Health Department), coordinating or planning with other utility services (stormwater discharges, water service/reclaimed water production), preparing the rate payers in the community for change, financial planning (capitalization fee collection, outside grant/loan support, service offers to key developments), and so on. Utility managers can also avoid pitfalls, such as extending services beyond levels that the utility can support or allowing new development into the system without contemplating the full cost impact of offering service.

14 4-14 City of Hamilton Wastewater Facilities Plan NEIGHBORHOOD ISSUES The long-term viability of the existing wastewater treatment plant at Hamilton is based on community acceptance of the utility system in its present location. Consequently, the facility planning effort must consider not only the long-term processing needs of the site, but also the interface between the facility and the surrounding neighborhoods. As older aerial photos demonstrate, the treatment plant was once remotely located away from substantial development. Now the facility is located adjacent to residential development. The City has made a very positive move in purchasing the additional two acres of property to the east of the original treatment plant site. Properties to the north and east of the existing plant site still have the potential for future residential development. As capacity requirements increase and treatment facilities must be built closer and closer to neighboring property owners, the facilities development must: Emphasize that the plant be a good neighbor and pay careful attention to odors, noise, night lighting, hazardous materials handling and vehicle access concerns. Work with the community surrounding the plant to identify issues of concern and ways to improve the facilities and facility operation. Understand the values and expectations of the neighboring stakeholders and, Define other community, development or planning activities impacting the area and adjust tailor expansion to integrate with these activities. WASTEWATER TREATMENT ALTERNATIVES EVALUATION Chapter 3 outlines the existing and projected limitations of the individual process units. This section presents the evaluation of alternatives for improving or expanding the individual process units to address these limitations. The evaluation process included the following basic steps: Summarize the existing and future limitations of the individual process units and identify process improvement or expansion that will be required within the next ten years. List reasonable alternatives for detailed evaluation. Identify criteria to be used for evaluation. Develop alternatives in sufficient detail to permit a reasoned evaluation of their advantages and disadvantages. Develop capital and 20-year life cycle costs for reasonable alternatives. Identify a recommended plan. Evaluation Process Alternatives were identified and evaluated through an interactive process involving City and consultant staff. Major elements of the process are described below. Define Process Methodology and Evaluation Criteria. To provide a consistent planning basis, HDR and City staff developed an evaluation methodology for the wastewater facilities. This process defined evaluation criteria, outlined the decision-making process, and prescribed cost estimating procedures. The evaluation criteria are listed in Table 4-1. Except for cost, these criteria were applied on a non-weighted, qualitative basis.

15 Alternatives Development and Evaluation 4-15 Brainstorm and Screen Ideas. A three-day workshop was conducted to identify any and all potential alternatives for expanding or improving the City of Hamilton facility. Following the initial brainstorm session, an initial screening step was conducted to eliminate ideas that were fatally flawed, technically unproven, excessively expensive or otherwise unworthy of detailed evaluation. Detailed Development and Evaluation. Alternatives surviving the initial screening step were developed in detail. Facility sizing and cost estimating were conducted for modular expansion of plant capacity for 2015, 2025 and 2045 conditions. Alternatives were compared based on cost and non-economic criteria. Based on this analysis, preliminary recommendations for facility improvements were made. Review Workshops. During the development process, meetings were conducted with City Council and wastewater staff to review interim findings and refine the alternatives being evaluated. In addition, a series of meetings were held with members of the City Council s Public Works Committee and City wastewater staff. The workshops presented information on the evaluation process and gained input regarding the technical issues being considered and the planning process used. See a summary of the workshops conducted in Appendix D. Decision Workshop. Based on the results of the evaluation process, and incorporating the comments received during the review workshop, the project team developed final alternatives and recommendations for consideration by the Public Works Committee/City Staff review group. Two workshops were held, on September 8, 2005 and September 15, 2005, to select the elements of the recommended plan for both the liquid stream and solids stream alternatives. Driving Forces Improvements to the Hamilton wastewater treatment facilities are needed to provide reliable treatment capacity, to comply with regulatory requirements, to improve operational efficiency and to enhance the interface with encroaching residential and commercial development. The key driving forces behind the needed improvements are summarized below. Permit Revisions. The current MPDES permit changes may establish more stringent effluent quality requirements for the Hamilton plant. Establishment of more stringent limits for effluent nitrogen and phosphorus is particularly important since the current plant is not designed to remove these contaminants to planned levels. Tougher limits for both bacteriological indicators and residual chlorine also require facility improvements. Age and Condition. A number of the treatment facilities are 20 to 30 years old and have reached their useful life. Some plant components suffer from deteriorated condition, fail to comply with current codes or provide unsatisfactory and possibly unsafe working environments for the operations staff. Service Area Growth. The City of Hamilton s service population is growing at an annual rate of 3 to 5 percent, increasing wastewater loading to the treatment plant (see Chapter 2). At this rate of growth, in addition to the hydraulically-limited components of the plant, the capacity of several major biological treatment components will be reached in 5 to 8 years. Without improvements, the plant could risk permit violations. Process Improvements. Some process improvements will reduce operational costs and/or delay the need for capacity expansions in other portions of the treatment systems.

16 4-16 City of Hamilton Wastewater Facilities Plan Good Neighbor Considerations. Residential and commercial development is encroaching on the City s treatment plant and compost sites (see Chapter 3). To ensure the long-term viability of these facilities for wastewater service, improvements are needed to enhance the interface between the treatment facilities and surrounding areas. Define Process Methodology and Evaluation Criteria To provide a consistent planning basis, HDR developed an evaluation methodology for the wastewater facilities. This process defined evaluation criteria, outlined the decision-making process, and prescribed opinion of probably cost estimating procedures. The evaluation criteria are listed in Table 4-1. Except for the opinion of probable cost, these criteria were applied on a non-weighted qualitative basis when evaluation of alternatives was performed. Regulatory Compliance Meets current NPDES requirements Flexible Allows for potential future NPDES requirements Meets current and anticipated biosolids regulations Operations/Technology Table 4-1. Evaluation Criteria Implementation Criteria Ability to logically phase expansion Ease of construction Ability to maintain operation during construction Permit/approval requirements Proven performance/proven treatment process Community/Environmental Criteria Low complexity Odor potential Operational ease Noise potential Ease of automation Vector potential Reasonable maintenance Air quality impacts (non-odor0 Reliability Truck traffic Longevity Hazardous chemicals Flexible allows for future growth Public safety Compatible with existing facilities Risk Safe/low use of hazardous chemicals Cost Potential for practice to fail due to changes in future regulations, public perception or land use Construction cost/cash flow Compatibility with Site Operations cost Ability to fit on site Land acquisition cost Compatibility with surrounding land uses Life cycle cost Alternatives Brainstorming and Screening Potential alternatives for expanding or improving the Hamilton Wastewater Treatment Plant were identified by City and HDR staff. A full list of the alternatives identified is provided in Table 4-2. Following the initial alternative development, an initial screening step was conducted

17 Alternatives Development and Evaluation 4-17 to eliminate ideas that were fatally flawed, technically unproven, excessively expensive, or otherwise unworthy of detailed evaluation. The screening criteria are described as follows: Compatible with Project Goals. The project goals as described in the objectives discussed in earlier paragraphs of this chapter. Potentially Acceptable to Regulatory Agencies. If it is clear that a management component would not be approved by DEQ or another key regulatory agency, then that component failed the screening. Technically Workable. If the alternative component would not perform as needed, then it failed the screening. Potentially Acceptable to Relevant Land Use. If it was known that a management component would have no chance of being approved, the technique failed the screening. Does Not Involve Extraordinary Costs. A management component failed the screening process if, in the opinion of the team members, the water quality and secondary benefits were expected to be much lower than the costs of comparable approaches that could accomplish the same results. Community Impact Anticipated to be Acceptable. This criterion was used to ensure that the impacts on the community would be acceptable. Examples of community impacts include odor, traffic, recreation, aesthetics and historical/cultural. Environmental Impact Anticipated to be Acceptable. A management alternative component failed the screening process if it was expected to cause adverse impacts on fisheries, wildlife habitat, air quality, water quality, wetland, rare/endangered species, or natural history that were impossible or difficult to mitigate. The initial screening labeled each idea as retain, fail, or feature. These labels are defined as: Retain, In-Scope: Carry idea forward to detailed alternative analysis as part of this facilities plan. Retain, Not-in-Scope: Valid idea, but outside the scope of this study. Address in concurrent or future studies. Fail: Idea is fatally flawed. Do not carry forward to detailed alternative analysis. Feature: Idea should be considered as a component of other ideas generated, or as a component of the pre-design. Table 4-2. Alternative Development Ideas and Initial Screening Results Idea Programmatic Measures: PM1 Identify/reduce potential point sources of ammonia Initial Screening Result Retain but not in current scope of this study. PM2 Implement demand management Retain and include in summary memorandum.

18 4-18 City of Hamilton Wastewater Facilities Plan Idea Initial Screening Result Collection System/Pumping Stations: See subsequent paragraphs of this Chapter. Headworks Influent Screening: IS1 IS2 Install climbing bar screen with washer/compactor Install stair screen with washer/compactor Retain for evaluation. Retain for evaluation. IS3 Install spiral screen Retain for evaluation. IS4 IS5 IS6 Install rotary drum with spiral screen Install traveling rake screen with screenings washer/compactor Install perforated plate screen with screenings washer/compactor Retain for evaluation. Would enable better primary treatment. Retain for evaluation. Retain for evaluation Headworks/Influent Flow Measurement and Grit Removal: HW1 HW2 HW3 Retain existing grit removal facilities and monitor oxidation ditch Upgrade existing flow meter transmitter Install additional aerated grit chamber capacity Retain for evaluation. Feature. Consider during pre-design Retain for evaluation. HW4 Install vortex grit unit Retain for evaluation. HW5 Remove grit from sludge Fail. Substantial existing investment to remove grit from liquid stream. HW6 Install tea cups Fail. Substantial cost associated with existing investment to remove grit from liquid stream. Influent Pumping: IP1 Replace existing influent pumps Retain for evaluation. IP2 Primary Treatment: P1 P2 Construct new submersible pumping station Maintain extended aeration process without primary clarification (No primary clarifiers) Install conventional primary clarifiers Retain for evaluation. Retain for evaluation. Compatible with existing solids handling system. Fail. Not compatible with existing solids handling system and secondary treatment. P3 Install chemical primaries Retain as compatible with phosphorus removal or possible use with secondary treatment option.

19 Alternatives Development and Evaluation 4-19 P4 Idea Use primary screens in lieu of primary clarifiers Retain for evaluation. Initial Screening Result P5 Add tube settlers Fail. Would require new primary clarifiers. Biological/Tertiary Treatment: B1 B2 Extended aeration/cyclical aeration with single stage chemical phosphorus removal Activation sludge and single stage chemical phosphorus removal with parallel extended aeration Retain for evaluation. Retain for evaluation. B3 Biophosphorus treatment system Retain for evaluation. B4 Parallel biophosphorus treatment with extended aeration Retain for evaluation. B5 Effluent filters Retain in case effluent limits get tighter. Add-on feature B6 Microfiltration Fail. Too expensive. B7 Membrane bioreactor Retain for evaluation. B8 Actiflo for phosphorus polishing Retain in case effluent limits get tighter. Add-on feature Disinfection: D1 D2 Retain hypochlorite disinfection and add biosulfite dechlorination Install ultraviolet light disinfection Retain for evaluation. Retain for evaluation. D3 Microfilter Fail. Too expensive. D4 Irradiation Fail. Not proven technology. D5 On-site hypochlorite generation Fail. No driving force to change. D6 Ozone Fail. Too expensive. Flow Measurement/Outfall: E1 Improve effluent metering Feature. Add to disinfection options. E2 Install outfall Feature. Retain should mixing zone regulations require addition of outfall. Disposal/Reuse: DR1 DR2 Limited effluent reuse program on nearby properties (plant site, New York Avenue Boulevard, Cemetery) 100 percent discharge to Bitterroot River Fail. Too expensive for need shown. Retain.

20 4-20 City of Hamilton Wastewater Facilities Plan Recycle Streams: R1 R2 Idea Measure/sample recycle flows to headworks Equalize filtrate from drying beds/dewatering Initial Screening Result Feature. Consider during preliminary design. Retain for evaluation. R3 Sidestream nitrification of filtrate Fail. Increased complexity in similar studies shown to not be cost effective. R4 Sidestream ammonia stripping Fail. Increased complexity, want to avoid lime. Secondary Sludge Thickening: ST1 Expand DAFT systems Retain. ST2 Add gravity belt Fail. Have investment in DAFT thickener. ST3 Add centrifuge Retain for evaluation with centrifuge dewatering. ST4 Add somat thickeners Fail. Have investment in DAFT thickener. ST5 Add rotary drum thickeners Fail. Have investment in DAFT thickener. ST6 Install gravity thickeners Fail. Does not achieve high solids for extended air RAS. Sludge Stabilization: SS1 Expand aerobic digestion Retain for evaluation. SS2 Temperature phased anaerobic digestion Fail. Not necessary expense with existing composting. SS3 Thermophilic digestion Fail. Not necessary expense with existing composting. SS4 High-rate mesophilic digestion Fail. Forecloses ability to produce Class B sludge. Not necessary with composting. SS5 No digestion Fail. Don t want to compost raw sludge. SS6 Recuperation thickening Feature. Only if centrifuge used for sludge thickening. SS7 Anaerobic gas flotation Fail. Not proven technology. SS8 Eliminate sludge storage Retain. Evaluate with SS1 above. Biosolids Management: BM1 BM2 BM3 Retain/expand composting process Land application of Class B sludge Contract handling of dewatered biosolids Retain for evaluation. Fail. Not compatible with existing composting. Too expensive for siting application sites. Retain for evaluation. BM4 Landfill Fail. Too expensive. BM5 Co-composting with yard waste materials Retain for evaluation. BM6 Soil manufacturing Fail. No driving force.

21 Alternatives Development and Evaluation 4-21 Idea Initial Screening Result BM7 Other Class A products Retain. Keep options open that are compatible with baseline digestion option. Dewatering/Drying: DW1 Belt filter press Retain for evaluation. DW2 High solids centrifuge Retain for evaluation. DW3 Vacuum belt press Fail. DW4 Vacuum drying beds Retain for evaluation. DW5 Centrifuge Fail. Expensive, not compatible with objectives. DW6 Direct contact dryer Fail. Too expensive. DW7 Rotary screen press Retain for evaluation. DW8 Plate and frame press Fail. Can be labor intensive to remove sludge. Sludge Storage: STO1 Improve existing storage. Add dewatering to store dewatered material Retain for evaluation. STO2 Build new storage Fail. Too expensive. STO3 Tanker truck storage/transport Fail. Not practical. Support Facilities: SF1 Upgrade existing operations building and lab Retain for evaluation. SF2 New laboratory Fail. Not presently required for processes planned. SF3 Plant Utilities: Expand lab area equipment to handle nutrient removal monitoring Retain. PU1 Expand standby power capability Retain for evaluation. PU2 PU3 Replace standby power capability and plant switch gear Implement energy management plan Retain for evaluation. Retain. Not part of current scope or current facilities planning. Detailed Evaluation of Alternatives Following the initial brainstorming and screening steps, the remaining alternatives were developed in detail and compared against evaluation criteria. This section identifies the alternatives evaluated, presents major design criteria used in development of the alternatives, and describes the cost estimating methodology. Design Criteria An array of design criteria was established to guide development of the treatment alternatives.

22 4-22 City of Hamilton Wastewater Facilities Plan Planning Horizon Rather than selecting a specific timeframe for a planning horizon, alternatives were examined for three incremental increases in influent flow at years 2015, 2025 and Facilities were analyzed for their abilities to convey or treat flow associated with maximum-month low groundwater season flows of 2.17, 3.09 and 6.05 mgd, with the 6.05-mgd case representing the estimated flow at buildout of the service area. Table 4-3 summarizes the flows at other design conditions associated with these nominal values. Table 4-3. Design Flows for Planning Horizon (mgd) Average Daily, mgd Peak Hour, mgd Maximum Month, mgd Minimum Month, mgd Effluent Quality Requirements Development of all unit processes was based on meeting the projected flow and loading conditions presented in Table 3-7 of Chapter 3. Flexibility was provided to meet potential future changes to effluent quality requirements such as limitation on total nitrogen or more stringent limits on phosphorus. Design Criteria Specific design criteria were established for each unit process. Design criteria were based on the following elements: Process Sizing. These criteria specify design loading rates and operating parameters for critical unit treatment processes. Examples include clarifier overflow rates, aeration basin mixed liquor concentrations, filter loading rates, and chlorine contact basin detention times. Reliability/Redundancy. These criteria define reliability and redundancy requirements for unit processes and critical equipment. Reliability/redundancy are discussed in detail in each section of this chapter. Water Quality Parameters. Until a TMDL and wasteload allocation is established for the Bitterroot River, the following effluent quality targets will be used for planning: Biochemical Oxygen Demand (BOD 5 ) Total Suspended Solids (TSS) Total Nitrogen Ammonia Nitrogen Total Phosphorus 10 mg/l 10 mg/l 6-8 mg/l 1 mg/l 1 mg/l Development of Costs Capital costs are expressed in 2005 dollars. The accuracy of all costs is order of magnitude. These estimates are approximations made without detailed engineering or site-specific data.

23 Alternatives Development and Evaluation 4-23 Estimates of this type can be expected to vary from 50 percent less than to 30 percent more than actual final project costs. The sources of construction cost data are: Construction cost data for the recent Missoula area projects and the recent HDR designed expansions at the Coeur d Alene Wastewater Treatment Plant, adjusted to 2005 dollars. Recent construction costs for other, similar facilities, adjusted to regional market conditions and 2005 dollars. Equipment pricing from manufacturers, including installation, structure, and housing costs. All capital costs include allowances for sitework and yard piping; contractor mark-up; contingencies; and engineering, legal and administration costs. The cost estimating procedure is presented in Table 4-4. Table 4-4. Illustration of Cost Estimating Procedure Cost Item Cost ($ thousands) Base Construction Cost $1,000.0 Electrical and Controls $300.0 Subtotal A $1,300.0 Mobilization and Bonds (5% of A) $65.0 Contractor s Overhead and Profit (10% of A) $130.0 Subtotal B $1,495.0 Miscellaneous Costs not Itemized (20% of B) $299.0 Subtotal C $1,794.0 Engineering, Legal, Administration (20% of C) $358.8 Total Capital Cost (Excluding Sitework) $2,152.8 For most treatment processes, the economic comparison of alternatives is strongly driven by capital costs. Consequently, O&M costs were developed only where there was a substantial difference in O&M requirements between the alternatives. Present worth costs are calculated using a 4% discount rate. Present worth O&M costs are based on 20 years of operation. Headworks Influent Screening The influent piping and screening system consists of the influent sewers to the plant, mechanical screening equipment, screenings handling and loadout facilities. A detailed analysis of the alternatives for influent screening is provided below. Driving Forces The driving forces for near-term upgrade and expansion of the influent screenings system are:

24 4-24 City of Hamilton Wastewater Facilities Plan Age and Condition. The existing mechanical bar screen has adequate capacity; however, it is over 20 years old and is at the end of its useful life. Screenings Handling Hygiene. Screenings washing is not provided with the existing facility. Operations staff are required to manually handle the screenings prior to disposal due to high moisture and organic content. Operators temporarily store collected screenings outside during the winter months and spread the screenings in a drying bed during the summer months to dewater. When the material has air-dried, staff then manually re-collects the material and hauls the material to landfill. Impaired Maintenance. The existing equipment is old with significant corrosion and deterioration caused by years of exposure to elevated hydrogen sulfide concentrations. The equipment manufacturer no longer manufactures a similar unit and replacement parts are more difficult to obtain. Alternatives Considered Influent Screening The existing bar screen equipment includes bar racks with spacing of ¾. A more conventional screening spacing in wastewater applications is 1/4 (6 mm) or less. The narrower screen spacing helps eliminate problems with plugging and ragging in downstream treatment units. However, the narrower spacing causes additional organic mater to be collected in the initial screening operation and requires subsequent screenings washing. For the Hamilton WWTP, it is recommended that new screening alternatives considered plan for 1/4 or less screening spacing and incorporate screenings washing/compaction into the design. Screenings washing/compaction will eliminate the need to handle the material multiple times on site in order to dry the screenings prior to landfill disposal. The following headworks screening alternatives were evaluated for installation of automated screening and screenings dewatering/compaction: Climbing Bar Screen Stair Screen Spiral Screen Rotary Drum with Spiral Screen Traveling Rake Screen Perforated Plate Screen It is recommended that the existing mechanical bar screen be replaced with a new fine screen to improve the efficiency of debris removal and replace aging equipment. A fine screen is most often defined as a screen with openings of ¼ (6 mm) or less. Debris not removed in the screening process clogs grit removal equipment, plugs pumps and piping and tends to collect in digesters and sludge holding tanks. The addition of a fine screen will improve the operation and minimize maintenance of downstream equipment, facilities and processes.

25 Alternatives Development and Evaluation 4-25 There are a number of screen options. The alternatives most likely to work in the configuration of the Hamilton facility include climbing bar screen, stair screen, spiral screen, rotary drum screen, traveling rake screen, and perforated plate screen. A description of each alternative evaluated is provided. Install Climbing Bar Screen (IS1) The climbing bar screen alternative consists of a vertical bar screen mechanism with a reciprocating rake assembly that travels along the bar screen periodically clearing debris from the leading edge of the bar rack. Debris is then dumped onto a chute and into a container for disposal. The rake is able to skip over large items on the screen that could jam the rake and damage the motor. The approximate capital cost of a reciprocating rake climber-type mechanical bar screen is $125,000. A climber screen in a 2-0 wide X 7-6 deep channel would handle current and estimated build-out flow and loading to the facility. Maintenance for a climber-type screen consists of the following: Daily maintenance: Observe equipment for normal operation. Weekly maintenance: Grease pin racks and cam tracks, check gearbox for leaks. Monthly maintenance: Check bolts for tightness, inspect follower shaft for wear. Quarterly maintenance: Inspect drive shaft and permalube cartridge. Semi-annual maintenance: Inspect rollers, bushings, sprockets, cam followers and wiper blade. Annual replacement of wiper blade ($100 per wiper blade) Change oil in gear box every 2 years ($200 per year) Replace cam followers every 5 years ($300 for parts) Energy cost for a 1.5 hp motor at 25% usage and 4.5 cents per kilowatt hour is $116/year The screen requires a remote located main control panel and a secondary control station mounted within sight distance of the screen. Two solid-state timers control operation of the climber screen. One controls the frequency of the rake and the other controls the duration of run time. An ultrasonic differential controller would also be used to initiate the operation of the screen based on differential head across the screen. The climber-type screen would not have the capability to wash or dewater screenings without additional equipment. A washer/compactor would be required at the screen discharge to accommodate this function. The climber screen would discharge screenings to the washer/compactor where organic material would be removed and returned to the influent channel. The screenings material would then be compacted, thus removing water from the screenings, and discharge to a receiving dumpster cart. The estimated cost of the washer/compactor is $55,000. Maintenance for a washer/compactor consists of the following: Daily maintenance: Observe equipment for normal operation Weakly maintenance: Flush the pressing area and collection tank Monthly maintenance: Lubricate bearing/ seal assembly,

26 4-26 City of Hamilton Wastewater Facilities Plan inspect cleaning brush for wear Semi-annual maintenance: Check bolts for tightness and check gear reducer oil level Spiral brush replacement every 5 years ($112 for parts) Gear reducer oil change every two years ($35) Spiral replacement every 5 years ($3,125) Energy cost for a 3.0 hp motor at 25% usage and 4.5 cents per kilowatt hour is $232/year The washer/compactor will require a main control panel and a programmable logic controller with timer and counter control logic to control the washer/compactor. The washer/compactor is capable of removing up to 50% of the water contained in the screenings. Install Stair Screen (IS2) A stair screen utilizes a screen surface that looks like a stairway. The screening surface consists of an alternating series of fixed and moveable plates. As headloss is detected across the screen, it advances slowly moving screenings to the top of the assembly where they are discharged onto a chute and into a container for disposal. The approximate cost for this type of screen is $75,000. A stair screen in a 2 wide X 7-6 deep channel would handle current flow and loading and estimated ultimate build-out flow and loading to the facility. Maintenance for a stair screen consists of the following: Daily maintenance: Observe equipment for normal operation. Weekly maintenance: Check tightness of chain, inspect lamellas, lube chain. Monthly maintenance: Inspect chain sprockets, shafts and bearings. Semi-annual maintenance: Check bolts for tightness, inspect plastic chain guides for wear, check gear box oil level Change gear reducer oil every 2 years ($25) Replace chain sprockets every 5 years ($1,120) Replace chain tensioners every 5 years ($510) Replace lamella spacers every 5 years ($938) Energy cost for a 1 hp motor at 25% usage and 4.5 cents per kilowatt hour is $77/year The stair screen requires a remotely located main control panel and a secondary control station mounted within sight of the screen. The stair screen is operated by a single timer to control the frequency of the screen. A differential level controller is used to initiate the operation of the screen.

27 Alternatives Development and Evaluation 4-27 A stair screen would not have the capability to wash or dewater screenings. A washer/compactor would need to be utilized similar to IS1. Install Spiral Screen (IS3) A spiral screen consists of a semi circular screen that sits in the flow stream of the headworks channel. A spiral screw auger clears debris from the screen and conveys it up from the channel in a cylinder into a washing section. Organic material is washed from the screenings and returned to the flow stream. The debris continues up the cylinder via the continuous auger into a compaction zone where it is dewatered. Following dewatering, the compacted screenings are discharged into a receiving dumpster cart. The capital cost of a spiral screen is estimated at $80,000. A 2 wide X 7-6 deep channel would handle the estimated build-out flow and loading to the facility. Maintenance for a spiral screen consists of the following: Daily maintenance: Observe equipment for normal operation Monthly maintenance: Check spiral brush for wear Semi-annual maintenance: Change oil in buddybox, oil motor Annual maintenance: Check lower bearing bar for wear Annual lubrication cost ($20) Replace bearing bar every 3 years ($138) Replace spiral brush every 4 years ($268) Overhaul speed reducer every 5 years ($260) Energy cost for a 2 hp motor at 25% usage and 4.5 cents per kilowatt hour is $155/year The spiral screen requires a local mounted main control panel. An ultrasonic differential controller will be used to initiate the operation of the screen. A spiral screen is capable of removing up to 40% of the water contained in the screenings and a washer compactor unit is not needed. Install Rotary Drum/Spiral Screen (IS4) A rotary drum/ spiral screen is similar to a spiral screen. This alternative utilizes a spiral screen system in series with a channel grinder. The spiral screen portion acts the same as described above. The rotary drum portion takes the influent and runs it through a channel grinder that cuts up large pieces of debris into a smaller size for easier handling by the spiral screen. A 24 wide X 7-6 deep channel would be adequate to handle current flow and loading and estimated buildout flow and loading to the facility. Maintenance for a rotary drum/ spiral screen consists of the following: Daily maintenance: Observe equipment for normal operation Monthly maintenance: Check spiral brush for wear, check cutter stack for play Replace spiral brush every 4 years ($582) Re-build cutter stack every 7 years ($890)

28 4-28 City of Hamilton Wastewater Facilities Plan Energy cost for a 3 hp motor at 100% usage and 4.5 cents per kilowatt hour is $929/year Energy cost for a 2 hp motor at 25% usage and 4.5 cents per kilowatt hour is $155/year The screen requires a local mounted main control panel. The unit is controlled by a differential level controller and a timer to initiate the operation of the screen. A rotary drum/ spiral screen is capable of removing up to 45-50% of the water contained in the screenings. The estimated capital cost for the rotary drum/ spiral screen is $90,000. Once again, a washer compactor would not be required for this unit. Install Traveling Rake Screen (IS5) A traveling rake screen consists of a vertical bar screen with multiple rake assemblies that travel along the bar screen via a chain and sprocket drive periodically clearing debris from the leading edge of the bar rack. Debris is then dumped onto a chute and into a container for disposal. The screen is capable of removing large items. The mechanism is low profile and has a high hydraulic capacity even with small bar spacing The approximate capital cost of a traveling rake screen is $105,000. A traveling rake screen in a 2-0 wide X 7-6 deep channel would handle current flow and loading and estimated ultimate build-out flow and loading to the facility. Maintenance for a traveling rake screen consists of the following: Daily maintenance: Observe equipment for normal operation. Weekly maintenance: Check perforated plate for debris. Monthly maintenance: Check rotary brush for wear. Semi-annual maintenance: Oil motor. Annual replacement of wiper blade ($100 per wiper blade) Change oil in gear box every 2 years ($200 per year) Replace cam followers every 5 years ($300 for parts) Energy cost for a 1.5 hp motor at 25% usage and 4.5 cents per kilowatt hour is $116/year The screen requires a remote located main control panel and a secondary control station mounted within sight distance of the screen. Two solid-state timers control operation of the climber screen. One controls the frequency of the rake and the other controls the duration of run time. An ultrasonic differential controller would also be used to initiate the operation of the screen based on differential head across the screen.

29 Alternatives Development and Evaluation 4-29 A traveling rake screen would not have the capability to wash or dewater screenings. A washer/compactor would need to be utilized, similar to IS1. Install Perforated Plate Screen (IS6) The perforated plate screen is a continuous filter element driven by two conveyor chains. The filter panels are shaped as circular segments cleaned by a rotary brush. The circular segments maximize the cleaning brush s cleaning effectiveness and reduce washwater requirements. Lifting tines allow larger objects, such as stones or wood, to be removed, preventing a build up of larger solids in the bottom of the channel. The screenings are carried upwards by the filter elements and are continuously removed and discharged by the rotary brush as the screen element moves past the brush. The approximate capital cost of a perforated plate screen is $120,000. A perforated plate screen in a 2-0 wide X 7-6 deep channel would handle current flow and loading and estimated ultimate build-out flow and loading to the facility. Maintenance for a perforated plate screen consists of the following: Daily maintenance: Observe equipment for normal operation. Weekly maintenance: Monthly maintenance: Quarterly maintenance: Semi-annual maintenance: Annual replacement of wiper blade ($100 per wiper blade) Change oil in gear box every 2 years ($200 per year) Replace cam followers every 5 years ($300 for parts) Energy cost for a 1.5 hp motor at 25% usage and 4.5 cents per kilowatt hour is $116/year A perforated plate screen would not have the capability to wash or dewater screenings. A washer/compactor would need to be utilized similar to IS1. Alternative Analysis Summary Estimated capital and present worth calculations for each screening alternative are presented in Table 4-5.

30 4-30 City of Hamilton Wastewater Facilities Plan Table 4-5. Costs for Headworks Influent Screening, $ Thousands Description Climbing Bar Screen w/ Washer/ Compactor Stair Screen w/ Washer/ Compactor Spiral Screen Rotary Drum/ Spiral Screen Traveling Rake w/ Washer/ Compactor Perforated Plate w/ Washer/ Compactor Base Construction Cost $180.0 $130.0 $80.0 $90.0 $145.0 $175.0 Electrical & Controls $54.0 $39.0 $24.0 $27.0 $43.5 $52.5 Subtotal A $234.0 $169.0 $104.0 $117.0 $188.5 $227.5 Mobilization & Bonds (5%) Contractor s Overhead & Profit (10%) $11.7 $8.5 $5.2 $5.9 $9.4 $11.4 $23.4 $16.9 $10.4 $11.7 $18.9 $22.8 Subtotal B $269.0 $194.4 $119.6 $133.9 $216.8 $261.7 Miscellaneous Costs Not Itemized (20%) $53.8 $38.8 $23.9 $26.8 $43.4 $52.3 Subtotal C $322.8 $233.2 $143.5 $160.7 $260.2 $314.0 Engineering, Legal, Administration (20%) $64.6 $46.6 $28.7 $32.1 $52.0 $62.8 Total Capital Cost $387.4 $279.8 $172.2 $192.8 $312.2 $376.8 Total O&M Cost/Year $2.2 $4.1 $2.2 $2.2 $2.2 $2.2 Total Present Worth $416.9 $335.5 $202.1 $222.7 $342.1 $406.7 The six headworks influent screening alternatives were evaluated using the criteria outlined at the beginning of this report. The criteria rankings range from 1 to 4 with 1 being poor, 4 being best. Table 4-6 summarizes the evaluation.

31 Alternatives Development and Evaluation 4-31 Table 4-6. Evaluation Summary Evaluation Criteria Climbing Bar Screen w/ Washer/ Compactor Stair Screen w/ Washer/ Compactor Spiral Screen Rotary Drum/ Spiral Screen Traveling Rake w/ Washer/ Compactor Perforated Plate w/ Washer/ Compactor Regulatory Coordination Operations/ Technology Compatibility with Site Implementation Community/ Environmental Risk Cost TOTAL Preliminary Recommendations Replace the existing mechanical bar screen as soon as these facilities can be funded and implemented. Early replacement of the headworks influent screen provides enhanced reliability and operational ease, with improved hygiene for operations personnel. It will also result in significant reduction of site odor potential and improve compatibility with the surrounding area. Replacing the existing screening unit with a spiral screen that includes integral washing and compacting of screenings is the most cost effective screening alternative. It is recommended that the City evaluate both the spiral screen (IS3) and rotary drum/spiral screen (IS4) alternatives further during pre-design to ensure the most appropriate mechanism is installed for long-term maintenance and channel hydraulics. Headworks Influent Flow Measurement and Grit Removal The headworks influent flow measurement and grit removal system is located in the below-grade channels within the existing Preliminary Treatment Building. Flows are directed downstream from the screens through an existing 9-inch Parshall Flume for flow measurement and via influent channels into aerated grit channels. The Parshall Flume is fitted with a bubbler system and associated transmitter for flow measurement. Upgrade of the existing bubbler system and transmitter is recommended during pre-design. An ultrasonic level element and transmitter is recommended.

32 4-32 City of Hamilton Wastewater Facilities Plan The grit removal system removes settleable material, such as racks, sand and other abrasive material that can damage or accumulate in downstream processes. The system includes facilities to process the removed grit, producing a final material that is sufficiently clean and dry to haul to a landfill. A detailed analysis of the alternatives for grit removal is provided below. Driving Forces The driving forces for upgrade and expansion of the grit removal system are: Age and Condition. The existing grit removal system is under-sized; however, grit accumulation in downstream processes has not been a problem at Hamilton. Process Improvement. Detailed hydraulic analysis has shown that the grit removal system appears to have sufficient capacity to handle peak flows associated with nominal plant flows. Use of the oxidation ditch for additional solids removal has not resulted in solids deposition within the ditch. Consequently, in the near term, only minor improvements to the condition of the existing grit pumps and grit cyclone are needed. Growth. As service area growth increases, expansion to the grit removal system should be evaluated against keeping the existing grit removal system as-is. Alternatives Considered The following grit removal alternatives were evaluated for enhancement to the grit removal capability: Retain existing aerated grit system and improve grit handling equipment. Include upgrade of existing flow meter transmitter. Install additional aerated grit chamber capacity to existing grit channel. Install a new vortex-type grit removal unit parallel to the existing aerated grit removal system. Retain Existing Grit Removal Facilities and Monitor Oxidation Ditch (HW 1) This alternative retains the current grit management approach. This alternative has been tested at greater flows since, prior to corrections to significant inflow problems in the City collection system, average and peak flow conditions were at or near projected hydraulic design conditions. This alternative will replace the existing influent flow meter bubbler and level transmitter with a new ultrasonic level element and associated transmitter. This alternative also includes replacing the existing grit pumps and grit cyclone/washer unit and continued monitoring of grit accumulation in the oxidation ditch using a sludge judge probe. Install Additional Aerated Grit Chamber Capacity (HW 3) Under this alternative, a parallel aerated grit channel would be installed to the south of the existing Preliminary Treatment Building. The aerated channel would require construction of additional grit pumping and washer/classifier systems. A new split box would be constructed where influent discharged downstream from the mechanical bar screens would be directed to both the existing and new aerated grit channels. Flows from

33 Alternatives Development and Evaluation 4-33 the grit removal units would be combined following the grit channels for influent transfer pumping. The aerated grit channel would require additional odor control and would need to be configured to enable treatment plant access over the grit channel. Re-location of the existing 24- inch storm drain may also be required for this alternative. This alternative also replaces the influent flow meter as is proposed in HW 1 above. Install Vortex Grit Unit (HW 4) This approach would expand grit removal capacity by constructing a parallel vortex grit removal facility to the south of the existing Preliminary Treatment Building. A second grit cyclone and classifier and grit pumping system would be installed. The vortex grit system would also require installation of the grit unit below the treatment plant access road and would also likely require relocation of the 24-inch storm drain. Similar to the aerated grit removal unit, the vortex grit system would require a flow split box downstream from the mechanical bar screen and recombination of degritted flows for influent transfer pumping. The vortex grit system will result in the use of a second grit removal technology, adding more complexity to the City s preliminary treatment system. This alternative also includes replacing the existing influent flow meter flow element and transmitter as proposed in HW 3 above. Alternative Analysis Summary Although vortex grit units have smaller space requirements and use slightly less energy, the size of the grit removal units evaluated will result in very similar operation and maintenance requirements for all new grit removal units proposed. Therefore, only capital costs were evaluated for the Headworks Influent Flow Measurement and Grit Removal alternatives. Estimated capital cost calculations for each influent flow measurement and grit removal are presented in Table 4-7.

34 4-34 City of Hamilton Wastewater Facilities Plan Table 4-7. Costs for Headworks/Influent Flow Measurement and Grit Removal ($ Thousands) Description Retain Existing Grit Removal Install Parallel Aerated Grit Channel Install Parallel Vortex Grit Unit Base Construction Cost $20.0 $513.7 $376.6 Electrical & Controls $2.0 $154.1 $113.0 Subtotal A $22.0 $667.8 $489.6 Mobilization & Bonds (5%) $1.1 $33.4 $24.5 Contractor s Overhead & $2.2 $66.8 $48.9 Profit (10%) Subtotal B $25.3 $768.0 $563.0 Miscellaneous Costs Not $5.1 $192.0 $141.0 Itemized (20%) Subtotal C $30.4 $ Engineering, Legal, $6.0 $240.0 $176.0 Administration (20%) Total Capital Cost $36.4 $1,200.0 $880.0 The three headworks flow measurement and grit removal alternatives were evaluated using the criteria outlined at the beginning of this report. Table 4-8 summarizes the evaluation. Retaining the existing grit removal system without treatment capacity expansion will be more cost effective and provides a technology with which the plant staff is familiar. There is some risk that grit accumulation may occur in downstream process units, although this has not historically been a problem in Hamilton. Expanding the aerated grit system provides a single technology with which the plant staff is familiar, but will be difficult given the existing site condition. Similarly, the vortex grit removal unit will also be difficult to construct on-site. The vortex grit system provides effective grit removal over a wider range of plant flows than aerated grit systems. Vortex systems also allow easier odor control because they have a smaller surface to cover, do not strip volatile constituents from the wastewater, and avoid off-gas generation produced by aerating the wastewater. Vortex systems preserve volatile fatty acids in the wastewater, which may prove needed should the plant eventually convert to biological phosphorus removal. Vortex units are more susceptible to ragging and are more susceptible to accumulations of grit in their hoppers. Constructibility of the parallel grit unit alternatives will be challenging, primarily due to the constraints for available building area.

35 Alternatives Development and Evaluation 4-35 Description Table 4-8. Evaluation Summary Retain Existing Grit Removal Install Parallel Aerated Grit Channel Install Parallel Vortex Grit Unit Regulatory Coordination Operations/Technology Compatibility with Site Implementation Community/Environmental Risk Cost TOTAL Preliminary Recommendations Retrofitting additional grit removal capacity will be costly and challenging given the site constraints and limited Preliminary Treatment Building area. In addition, historically Hamilton s influent flows have not had a significant amount of grit loading. Previous facility planning efforts have recommended the City consider foregoing installation of additional grit removal capacity and handle any unusual grit loading conditions by removing it from the existing oxidation ditch. It is recommended that the City continue the use of their existing aerated grit channel and install a new influent flow meter and transmitter (HW 1). Construction of additional grit removal facilities would be avoided by consciously planning to address any additional grit removal needs by removing it at the oxidation ditch. Should heavy grit loading conditions become a problem in the future, it is recommended the City re-evaluate expansion of the grit removal facilities using a vortex-type grit removal unit (HW 4). Influent Transfer Pumping The existing influent transfer pumping system consists of two open impeller screw lift pumping units. The firm capacity of these two pumps is sufficient for an extended period of time. However, the pumping units are over 17 years old and are in need of maintenance replacement within the next 5 years. A detailed analysis of the alternatives retained for consideration for influent transfer pumping is provided below. Driving Forces The driving forces for near-term upgrade and expansion of influent transfer pumping are: Age and Condition. The existing pumps are showing significant signs of wear, are heavily corroded, and are in need of major gearbox repairs. The equipment is at the end of their useful life and should be replaced within the next 5 years. The existing pumping unit controls are also worn out and in need of upgrade.

36 4-36 City of Hamilton Wastewater Facilities Plan Impaired Maintenance. The existing equipment is old with significant corrosion and deterioration caused by years of exposure to elevated hydrogen sulfide concentrations. The equipment manufacturer no longer manufactures similar units and replacement parts are more difficult to obtain. Safety. The existing exposed screw impellers are a safety concern for operations personnel and should be protected or replaced with an internal lift type impeller. Alternatives Considered The existing influent transfer pumping screw pumps are very compatible for matching variations in influent flow rate. However, the pumping units and associated controls are at the end of their useful life. The existing impellers are worn significantly and need significant upgrade or replacement. Unfortunately, the Preliminary Treatment Building was originally constructed without an available means for removal of the pumping units or easy installation of replacement units. The existing building roof will likely require removal for equipment replacement. The following influent transfer pumping alternatives were retained for evaluation: Upgrade influent transfer pumping by replacing the existing screw pumps with new internal lift screw pumps. Construct new submersible pumping station to replace the existing transfer pumping station. A description of each alternative evaluated is provided. Replace Existing Influent Pumps (IP 1) Replacing the existing influent transfer pumps will require removal and replacement of a portion of the existing Preliminary Treatment Building roof. The existing exposed screw pumps may be replaced with similar unit with exposed impellers or new internal lift screw pumps that have their impellers enclosed within an external tube or cyclinder. Installation of replacement exposed screws would be less expensive and require minimal structural modifications. Replacement of the existing external screw pumps would handle current and estimated build-out flow to the facility. Replacement with similar equipment would also be easier to implement while maintaining the treatment plant in operation, in lieu of installing internal lift-type pumps. Maintenance for the external-type screw pumps consists of the following: Daily Maintenance: Observe equipment for normal operation. Weekly Maintenance: Grease bearings. Monthly Maintenance: Check bolts for tightness, inspect drive unit gearbox and bearing lubrication unit. Change drive unit oil in gear box every 2 years ($200 per two years). Energy cost for a 40 Hp motor at 100% usage and 4.5 cents per kilowatt hour is $11,800. The screw pump requires level controls for protection of high level alarm or to ensure continuous pumping. Existing controls would also need to be replaced. The Preliminary

37 Alternatives Development and Evaluation 4-37 Treatment Building that houses the influent transfer screw pumps is exposed to severe corrosion conditions due to the exposed nature of the screw pumps. Painting and corrosion protection of interior piping and walls is also recommended if the screw pumps are retained. Because the screw pumps operate at a constant speed, they do require additional energy for operation. Construct New Submersible Pumping Station (IP 2): This alternative consists of construction of a new influent pumping station exterior of the Preliminary Treatment Building downstream from screening and grit removal. The pumping station would consist of a submersible pumping wetwell and dual pumping units. Estimated horsepower required is 60 Hp for the two pumping units. Because the submersible pumping units may be operated from variable frequency drives for flow matching, energy consumption can be better controlled. The submersible pumping station would be configured to provide influent flow metering and would be located south of the existing Preliminary Treatment Building in a location close to the existing New York Avenue Pumping Station. The station design and controls would be similar to the other newer City submersible pumping stations and would be served by standby power. Maintenance for the new submersible influent transfer pumping station consists of the following: Daily Maintenance: Monitor equipment for normal operation. Energy cost for a 60 Hp motor operating from VFD to flow match at 4.5 cents per kilowatt hour is $7,900. Alternative Analysis Summary Estimated capital and present worth calculations for both influent transfer pumping alternatives are presented in Table 4-9. Description Table 4-9. Costs for Influent Transfer Pumping ($ Thousands) Maintain Existing Pumps 1 Replace Existing Influent Pumps Construct New Pumping Station Base Construction Cost $20.0 $180.0 $200.0 Electrical & Controls $6.0 $54.0 $60.0 Subtotal A $26.0 $234.0 $260.0 Mobilization & Bonds (5%) $1.3 $11.7 $13.0 Contractor s Overhead & $2.6 $23.4 $26.0 Profit (10%) Subtotal B $29.9 $269.1 $299.0 Miscellaneous Costs Not $6.0 $53.8 $59.8 Itemized (20%) Subtotal C $35.9 $322.9 $358.8 Engineering, Legal, $7.2 $64.6 $71.8 Administration (20%) Total Capital Cost $43.1 $387.5 $430.6 Total O&M Cost/Year $10.1 $14.1 $10.1 Total Present Worth $180.3 $579.1 $ Added as a no action alternative for comparison of alternatives

38 4-38 City of Hamilton Wastewater Facilities Plan The two influent transfer pumping alternatives were also evaluated using the criteria outlined at the beginning of this report. Table 4-10 summarizes the evaluation. Replacement of the existing screw pumps with similar equipment under a standard maintenance replacement program offers a lower initial capital outlay. However, when annual maintenance requirements are considered, the two alternatives have a much closer present worth value. Installation of the new submersible pumping station would allow system redundancy and would be better for constructability. A new pumping station would also eliminate a significant odor source and reduce the corrosive atmosphere in the Preliminary Treatment Building. The new pumping station would also increase pumping capacity to ultimate buildout (peak) pumping conditions. Description Table Evaluation Summary Replace Existing Influent Pumps Construct New Submersible Pumping Station Regulatory Coordination 4 4 Operations/Technology 2 4 Compatibility with Site 4 3 Implementation 3 4 Community/Environmental 3 4 Risk 4 4 Cost 3 3 TOTAL Preliminary Recommendations It is recommended that the City maximize their use of the existing screw pumps to the greatest extent possible. This would include maintenance of the existing screw impeller to refurbish impeller blades where worn. In addition, careful consideration should be given to re-building existing gear boxes to ensure a minimum of five to seven additional years of operation. As quickly as feasible, the City should then replace the existing pumping units with a separate influent transfer pumping system capable of handling buildout flow conditions and equipped with variable frequency drives to enable energy conservation and smooth flow matching of influent flows. Primary Treatment Primary treatment facilities achieve reductions in CBOD and TSS through removal of settleable and floatable material. Currently, the City of Hamilton s extended air activated sludge system does not include primary treatment. The addition of primary treatment would result in the need for upgrade of additional process units, including solids pumping and digestion, for handling the primary solids generated. Driving Forces The driving forces for incorporation of the primary treatment unit process into the City s current process are:

39 Alternatives Development and Evaluation 4-39 Permit Change. The current Hamilton plant was not designed for biological nutrient removal. There is a possibility that limits on total nitrogen and total phosphorus may require much more stringent treatment performance. Installing an additional primary treatment step prior to the secondary treatment processes may offer advantages for future secondary treatment options. Alternatives Considered The following primary treatment alternatives were considered. Since Alternative P1 involves the no-action alternative for the primary treatment option, only two new alternatives were advanced for detailed evaluation: Maintain extended aeration process without primary clarification (no primary clarifiers) Install primary clarification with chemical addition Install primary screening Maintain Extended Aeration Process without Primary Treatment (P1) This alternative assumes the existing extended aeration activated sludge process will be expanded and primary treatment will not be added. Additional operation and maintenance costs are not associated with this alternative since no new process units are added. However, it can be argued that the absence of primary treatment results in greater maintenance requirements in downstream process units as a result of greater solids loading and other debris that passes through, which would otherwise be retained in a primary treatment unit. Install Primary Clarifiers with Chemical Addition (P3) This alternative would result in construction of the new primary clarifier basins and would also require potential changes to the existing biosolids stabilization process to enable handling of primary sludge without significant odor generation. For projected flow conditions, two 70-foot diameter primary clarifiers, each redundant to the other, would need to be constructed. The overflow rate would be set at 1,000 gpd/sf at annual average flow conditions. Since primary clarification is not currently provided, primary sludge pumping is also not provided and a primary sludge pumping station would also need to be added. Maintenance for new primary clarifiers would include the following: Daily Maintenance: Observe equipment for normal operation Monthly Maintenance: Check scum removal mechanism and scum pumping for wear Annual Maintenance: Replace lubrication for speed reducer ever 3 years ($138) Energy cost for 1 Hp motor at 4.5 cents per kilowatt hour is $295/year Energy cost for sludge pumping at 5 Hp motor and 25% usage and 4.5 cents per kilowatt hour is $390/year

40 4-40 City of Hamilton Wastewater Facilities Plan Use Primary Screening in Lieu of Primary Clarifiers (P4) Installation of primary fine screens would be located immediately following influent transfer pumping and before the secondary treatment processes. In this alternative, all influent flows would be screened by intermediate screening (mechanical bar screen) and then passed to microscreening facilities. The microscreens would be designed to achieve conventional primary treatment removal efficiencies (50% removal of TSS and 35% removal of BOD 5 ). The microscreening station, to be located to the east of the Preliminary Treatment Building, would be self-contained and capable of automatic startup and control. The microscreens would include integral backwashing facilities and would require a 100 gpm backwashing station for removing solids to solids thickening and digestion. The loading rate for the microscreens would be 7.5 gpm/sf of screen area. Two 10- foot diameter by 16-foot long microscreens would be required to handle up to 3.63 mgd of flow at buildout conditions. Alternative Analysis Summary Estimated capital and present worth costs for the Primary Treatment Alternatives are presented in Table The alternative P1 will maintain the extended aeration treatment process and will result in no additional capital or operation and maintenance expenses. The remaining two primary treatment alternatives will both result in significant capital investment to implement. Both processes are evaluated assuming that downstream solids handling systems would be inplace to process the primary solids generated. Description Table Costs for Primary Treatment ($ Thousands) Maintain Existing Aeration w/o Primary Treatment Install Chemical Primary Clarifiers Install Primary Screens Base Construction Cost $0.0 $2,264.0 $941.2 Electrical & Controls $0.0 $679.0 $282.3 Subtotal A $0.0 $2,943.0 $1,223.5 Mobilization & Bonds (5%) Contractor s Overhead & Profit (10%) $0.0 $147.2 $61.2 $0.0 $294.3 $122.4 Subtotal B $0.0 $3,384.5 $ Miscellaneous Costs Not Itemized (20%) $0.0 $676.9 $281.4 Subtotal C $0.0 $4,061.4 $1,688.5 Engineering, Legal, Administration (20%) $0.0 $812.3 $337.7 Total Capital Cost $0.0 $4,873.7 $2,062.2 Total O&M Cost/Year $0.0 $2.6 $2.2 Total Present Worth $0.0 $4,908.6 $2,055.7

41 Alternatives Development and Evaluation 4-41 The three primary treatment alternatives were also evaluated using the established evaluation criteria. Table 4-12 summarizes the evaluation. Although the no action alternative provides the greatest advantage for cost and compatibility with the existing treatment processes, it also carries greater risk associated with more difficulty meeting stringent treatment standards without primary treatment. Description Table Evaluation Summary Maintain Extended Aeration w/o Primary Treatment Install Chemical Primary Clarifiers Install Primary Screens Regulatory Coordination Operations/Technology Compatibility with Site Implementation Community/Environmental Risk Cost TOTAL Preliminary Recommendations The primary advantage of providing primary treatment facilities is to reduce the solids and organic loading to the secondary treatment processes. This will enable the secondary processes to more easily meet more stringent water quality parameters with smaller treatment basins. This advantage comes at considerable capital cost since primary treatment is currently not practiced at the Hamilton WWTP. Since aerobic digestion is already on-site, and no means for primary solids thickening exists, it is recommended that the City continue extended aeration activated sludge the treatment process without primary treatment. Should primary treatment become desirable in the future, consideration should be given to the use of microscreens because of their compact layout and cost advantage when compared to adding new primary clarifiers. Biological/Tertiary Treatment The extended aeration activated sludge system at the Hamilton WWTP utilizes the biological processes to remove carbonaceous BOD, ammonia, nitrate and some phosphorus. In developing alternatives for the activated sludge system, it was recognized that the existing extended air system is also capable of removing some phosphorus and/or total nitrogen. The activated sludge system was defined to include facilities from primary effluent distribution through secondary clarification and of secondary effluent tertiary treatment. Driving Forces The driving forces for biological/tertiary treatment are: Permit Change. The current Hamilton plant was not originally designed to remove phosphorus and ammonia-nitrogen. Although current plant operation is achieving some

42 4-42 City of Hamilton Wastewater Facilities Plan phosphorus reduction and total nitrogen removal, more stringent nutrient limits are expected in future permits. Growth. The plant currently achieves partial removal of ammonia-nitrogen because the biological process (extended air) is relatively lightly loaded. However, when the plant flows exceed 1.0 to 1.5 mgd, the current plant will cease to remove ammonia-nitrogen. Implementation of facilities that achieve nitrification and de-nitrification, as well as phosphorus removal, must be installed. Alternatives Considered Seven alternatives were retained for evaluation to meet design requirements outlined. Two of the seven alternatives were retained in the event effluent limits for phosphorus get even more stringent. The alternatives evaluated were subsequently grouped into two categories relating to the treatment level provided: Category 1: Category 2 o Extended aeration/cyclical aeration with single stage chemical phosphorus removal. o Single-stage chemical phosphorus removal with parallel extended aeration. o Biophosphorus treatment system o Parallel biophosphorus treatment with extended aeration o Membrane bioreactor o Effluent filters for effluent (phosphorus) polishing o Actiflo for effluent (phosphorus) polishing Extended Aeration/Cyclical Aeration with Single Stage Chemical Phosphorus Removal (including Effluent Filtration) (B1) Under this alternative, the existing extended aeration system will be retained and an additional oxidation ditch would be installed for additional process unit capacity. The extended air process would be operated using cyclical aeration for biological nitrogen removal. Aerobic versus anaerobic conditions within the basins would be set at approximately 66% to 33%, respectively. The new extended air oxidation ditch would be located to the east of the existing oxidation ditch and would employ a submersible aeration grid and submersible mixers in lieu of brush aerators. A new flow split structure would be used to split influent flows to each parallel train and alum would be

43 Alternatives Development and Evaluation 4-43 added to a secondary influent junction box upstream form the secondary clarifiers. Alum feed at approximately 130 mg/l would be used for phosphorus reduction and effluent filtration would be added to meet a phosphorus limit of 1 mg/l or less. Figure 4-1 shows the B1 process schematic. As flows increase, a third secondary clarifier with diameter to match two of the large clarifiers would be constructed. This alternative would take best advantage of existing process units and would enable phased implementation of process improvements and expansion. The addition of alum will result in an increase in sludge production. Installation of effluent filtration, required to meet phosphorus limits of 1 mg/l, will result in the need for pumping of plant effluent. The existing RAS/WAS pumping systems would be expanded within existing buildings to accommodate additional capacity needs. Influent from Primary Treatment Influent S p lit Box Existing Anoxic Selector Basin New Anoxic Selector Basin New Secondary S p lit Box Existing Oxidation Ditch 1 Alum Secondary Clarifiers (2) Existing (1) New New Effluent Filters To Disinfection New Oxidation Ditch Return Sludg e Figure 4-1. Extended Aeration with Chemical Phosphorus Removal (B1) Activated Sludge Single Stage Chemical Phosphorus Removal with Parallel Extended Aeration (including Effluent Filtration) (B2) Under this alternative, the existing extended aeration oxidation ditch would be retained and a parallel high-rate activated sludge treatment train would be constructed. The extended aeration basin would be operated using cyclic aeration for nitrogen removal. The new aeration basin would be fitted with anaerobic, anoxic and anaerobic zones to enable biological nitrogen removal. Influent flows would be split to each parallel treatment train and then recombined for alum addition and secondary flow split to the secondary clarifiers. Alum feed at approximately 130 mg/l would be used for phosphorus reduction and effluent filtration would be added to meet a phosphorus limit of 1 mg/l or less. Similar to Alternative B1, a third secondary clarifier would be added when hydraulic capacity requires. Effluent pumping would be added and RAS/WAS pumping would be expanded within existing buildings. Figure 4-2 depicts the B2 process schematic.

44 4-44 City of Hamilton Wastewater Facilities Plan Influent from Primary Treatment Influent S p lit B ox Existing Anoxic Selector Basin Existing Oxidation Ditch 1 Secondary C larifiers New Effluent F ilters Alum New Secondary S p lit B ox (2) E xisting (1) N ew BNR (Nitrogen) To Disinfection New Aeration Basin Return Sludg e Figure 4-2. Activated Sludge Single Stage Phosphorus Removal with Extended Aeration and Effluent Filtration Similar to Alternative B1, this alternative will also take advantage of existing process units but would accomplish secondary treatment and nitrogen removal using a different technology for the aeration basin and nutrient removal cells. The aeration basin would be deeper, include submerged fine bubble diffuser, and would employ submerged mixers and anoxic and aerobic cells for nutrient reduction. Also, similar to Alternative B1, this alternative would require effluent filtration and effluent pumping to meet phosphorus limits of 1 mg/l. Biophosphorus Treatment System (B3) Under this alternative, a new stand-alone biological nutrient removal treatment train would be constructed and the existing oxidation ditch would be removed from service. The influent flow would be directed to the new process train where it would be treated in a high-rate activated sludge treatment process. The treatment process would include anoxic and anaerobic zones with submerged mixers to implement biological phosphorus and nitrogen removal and an aerobic zone fitted with fine bubble diffusers for aeration. A new blower building would be installed and the existing secondary clarifiers and RAS/WAS pumping facilities would be retained. Secondary effluent would be flow split with a new flow split box and a new secondary would be added when plant loading requires. The existing RAS/WAS pumping facilities would be expanded to serve the new treatment capacity. Effluent filtration would not be added unless more stringent water quality limits require effluent phosphorus to limits below 1 mg/l. Figure 4-3 depicts the B3 process schematic.

45 Alternatives Development and Evaluation 4-45 Influent from Primary Treatment BNR (Nitrogen & Phosp horus) New Secondary S p lit B ox Secondary C larifiers (2) E xisting (1) N ew To Disinfection New Aeration Basin Return Sludg e Figure 4-3. Biophosphorus Treatment System with Biological Nitrogen Removal This alternative is the greatest capital cost since it does not incorporate the existing oxidation ditch into the treatment train and primary treatment, such as primary microscreens, would also be necessary to minimize aeration basin size. The aeration basin for biological treatment would be larger and deeper and would include fine bubble air diffusers, submerged mixers and mixed liquor recycle pumping. It is assumed this treatment alternative would not require effluent filtration since all flow would be disinfected to the new BNR process. Parallel Biophosphorus Treatment with Extended Aeration (B4) This alternative has a hybrid alternative from Alternatives B1 and B3. Under this alternative, the existing oxidation ditch would be included in the system as a parallel treatment train. A new biological phosphorus removal cell would be added upstream from the existing oxidation ditch that would also be used to split flows to the existing oxidation ditch and a new parallel oxidation ditch. Both oxidation ditches would be operated in a cyclic aeration mode of operation for nitrogen removal and filament control. The new extended air activated sludge treatment basin would be located to the east of the existing oxidation ditch. The oxidation ditches would be operated with aerobic and anaerobic conditions to promote biological nitrogen and phosphorus removal. Flows from the oxidation ditches would be directed to a post aeration cell and flow split to the secondary clarifiers. A new third secondary clarifier would be added when flows require additional capacity. Effluent filtration would be added to meet a phosphorus limit of 1 mg/l or less. Figure 4-4 shows the B4 process schematic.

46 4-46 City of Hamilton Wastewater Facilities Plan Existing Anoxic Selector Basin Existing Oxidation Ditch Post Aeration and Flow Split Secondary C larifiers (2) E xisting (1) N ew New Effluent F ilters Influent To Disinfection BioP Basin/Flow S plit New BNR Oxidation Ditch Return Sludg e Figure 4-4. Biophosphorus Treatment with Parallel Extended Aeration Similar to Alternative B1, this alternative would take advantage of existing process units and would enable phased implementation of process improvements and expansion. This alternative would not increase solids loadings since phosphorus removal would be done through biological phosphorus removal in lieu of alum addition (chemical precipitation). It is assumed that effluent filtration would be added to meet phosphorus limits of 1 mg/l or less. Pumping of plant effluent would be necessary under this alternative when effluent filtration is added. Membrane Bioreactor Treatment (B7) This alternative has been added as a comparison to baseline conventional biological nutrient removal technologies and for cases where effluent water quality parameters could be the most strict. Under this alternative, the existing oxidation ditch would be maintained as additional aeration basin capacity and a membrane bioreactor treatment train would be added. The bioreactor would add an additional aeration basin, anoxic and anaerobic zones for nutrient removal, and a bioreactor membrane tank and membrane pumps for secondary clarification. With this process alternative, secondary clarifiers and effluent filtration or effluent pumping would not be required. From the existing oxidation ditch and a new aeration basin, flows would be directed to combined membrane basins where permeate from the membranes would be pumped to effluent disinfection and discharged to the Bitterroot River. The existing RAS/WAS pumping system would be retained and a new return pumping system would be added for the membrane bioreactor treatment train. Figure 4-5 shows the membrane bioreactor process schematic.

47 Alternatives Development and Evaluation 4-47 Influent Bar Screen Micro (Fine) Screening Flow Split Box Existing Anoxic Selector Basin Existing Oxidation Ditch A-Basin To Disinfection New MBR Unit Mem brane Basins Figure 4-5. Membrane Bioreactor with Parallel Oxidation Ditch The membrane process requires installation of two stage screening in the influent flow (coarse and fine microscreening technology) to ensure the membranes will not foul from excess debris in the waste stream. Additional process alternatives have been included to be used as add-on tertiary treatment features to the previously discussed alternatives for biological/tertiary treatment. These alternatives have been included as Category 2 alternatives for consideration should more restrictive water quality parameters need to be met in the future. These additional alternatives include: Adding effluent filters following secondary treatment for enhanced solids removal performance and enhanced phosphorus reduction. Adding ballasted flocculation (Actiflo) upstream from effluent filtration for enhanced phosphorus polishing of secondary effluent. The two tertiary polishing treatment processes noted above are not needed to comply with conventional permit limits for CBOD, TSS, ammonia-nitrogen or phosphorus, similar to those proposed at the beginning of this chapter. However, if future permits reduce the effluent phosphorus limit to 0.7 mg/l or lower, effluent polishing will be needed. The following paragraphs present these two viable options for tertiary treatment and present costs associated with these units to meet projected buildout flow conditions. Effluent Filters (B5) Filtration is used to remove suspended solids that do not settle in the secondary clarification process. As discussed in Alternatives B1, B2, B3 and B4, filtration may be needed to meet nondegradation limits for effluent TSS or to meet more stringent effluent phosphorus limits. Regulatory changes and actual plant conditions should be reviewed annually and the schedule for implementing final effluent filtration should be adjusted as needed. In addition to meeting the requirements for TSS removal, effluent filtration complements future phosphorus removal processes by removing filterable particulate matter that contains phosphorus. This effluent enhancement would also enhance downstream disinfection processes by increasing UV transmittance properties and clarity of the effluent. There are many types of filters available for consideration at Hamilton. The alternatives listed below are discussed in more detail and give a good representation of the major types of filter technology available. The following filter types are discussed in greater detail:

48 4-48 City of Hamilton Wastewater Facilities Plan Traveling Bridge Sand Media Filters Traveling Bridge Fabric Media Filters Compressible Media Filters Continuous Backwash Sand Filters Cloth Media Disc Filters Deep Bed Mono-Media Filters Common to all filter applications are that the hydraulic profile of the existing treatment plant and outfall channel indicate that an effluent pumping station would be required, filtration basins and equipment must be housed in a heated space to prevent freezing, facilities for polymer addition will be required, and filtration will not be required if membrane technology replaces traditional secondary clarifiers when the plant process is upgraded to biological nutrient removal. Traveling Bridge Sand Media Filters. Traveling bridge filters utilize shallow (approximately 16 inches) granular media beds configured in long, narrow basins, typically 16 feet x 100 feet maximum width and length. A motorized bridge, located above the water in each filter basin, is equipped with backwash pumps. As the bridge travels the length of the filter, the filter is backwashed. The recommended hydraulic loading rate for this type of filter is 2 gpm/ft 2 at average flow and not over 5 gpm/ft 2 at maximum day flow. This would require approximately 1,260 square feet of filter bed, or two beds, each 16 feet by approximately 50 feet wide. A third filter would be needed, for reliability, when one filter is out of service. Traveling Bridge Fabric Filters. Traveling bridge fabric media filters are also long and narrow. Their filtering concept is entirely different. The filter media consists of large hollow tubes covered with fabric media. The tubes are submerged and run parallel to each other over the long dimension of the filter basin. Hydraulic loading rates can be as much as 3.2 gpm/ft 2 at annual average flow. This would equate to approximately 790 square feet of filter area. Compressible Media Filters. A unique filter media is used in compressible media filters, 1-1/4- inch synthetic fiber balls. A moveable plate with a motor actuator compresses the media to a depth of 30 inches in preparation for operation. Flow is upward at hydraulic loading rates up to 30 gpm/ft 2. Because the hydraulic loading rate is over six times higher than granular media filters or fabric media filters, the footprint space is smaller than for other filtration alternatives. Capacity is limited to 2.8 mgd per tank, thus three filter tanks would be needed to provide adequate filtration capacity while allowing one filter out of serve. When backwashing is required, the moveable plate is raised to decompress the media. Low pressure air is used to scour the media. Continuous Backwash Filters. Continuous backwash filters use a deep (generally 40-inches or more) granular media bed. Upflow and downflow configurations are available from various manufacturers. Continuous backwashing is accomplished by pumping media from the bottom of the filter to the top with an air lift pump. The pumping action is what would scrub the media. The hydraulic loading rate at annual average flow would be 3.4 gpm/ft 2. At this loading rate, approximately 750 square feet of filter is needed, or approximately four filters would be needed when including spare filter area for one unit being out of service. Cloth Media Disc Filters. Cloth media filters consist of several disc shaped frames, approximately 7 feet in diameter by 4 inch thickness, covered with cloth filter media and mounted on a hollow shaft. The entire disc assembly is submerged and backwash on each disc

49 Alternatives Development and Evaluation 4-49 occurs by rotating the discs with reversed flow. Loading rates of up to 6 gpm/ft 2 have been accepted nationally. At that rate, a minimum of three filters would be recommended, with one unit out of service. Deep Bed Mono Media Filters. Deep bed mono media filters are similar in configuration to many of the filters used in potable water treatment plants. Granular media is supported on an underdrain collection system and the direction of flow is downward. Filter media is typically about 72 inches. The filters are backwashed by pumping water from a clearwell or contact basin into the underdrain, reversing the direction of flow. To save cost, the existing chlorine contact chamber at Hamilton could be used if the existing disinfection system is abandoned in favor of UV disinfection. Hydraulic loading rates should not exceed 5 gpm/ft 2. Compared with other filtration alternatives, backwash flows are considerably higher for this technology. Effluent Filtration Evaluation The final effluent filtration alternatives above may be necessary to meet more stringent water quality limits. The biological/tertiary treatment alternatives presented above assume effluent filtration would be required in order to evaluate all alternatives on an equal basis. Each of the filtration options presented above are technically capable of meeting treatment performance requirements and are all comparable for capital costs. Cloth media disc filters and traveling bridge sand media filters typically have capital costs that are typically 15 percent less than the costs of the other options. This is typically due to the lower cost of the equipment for the traveling bridge sand filters and smaller building footprint requirement for cloth media disc filters for housing the equipment. It is recommended that, if final effluent filtration becomes necessary to meet more stringent effluent water quality requirements, a more detailed evaluation of the effluent filtration alternatives be conducted during preliminary design. Since cloth media filters typically have the lowest capital and present worth costs, this effluent filtration alternative will be used for the biological/tertiary treatment alternative analysis. The estimated capital cost for this effluent filtration option is presented in Table The treatment units would include a minimal 4 mgd treatment capacity with a building for housing the filtration and backwash systems.

50 4-50 City of Hamilton Wastewater Facilities Plan Table Costs for Cloth Media Disc Filtration ($ Thousands) Description Cloth Media Disc Filtration Base Construction Cost $421.5 Electrical & Controls $126.5 Subtotal A $548.0 Mobilization & Bonds (5%) $27.4 Contractor s Overhead & Profit (10%) $54.8 Subtotal B $630.2 Miscellaneous Costs Not Itemized $126.1 (20%) Subtotal C $756.3 Engineering, Legal, Administration $151.2 (20%) Total Capital Cost $907.5 Actiflo (Effluent Polishing Filters) (B8) Actiflo is a three-step clarification process marketed by Kruger, which uses chemical injection, flocculation and sedimentation for advanced solids removal. This process would be used in lieu of effluent filtration or in-conjunction with effluent filtration as a preliminary treatment step. The process uses polymer and microsand to enhance flocculation and settling, resulting in clarification facilities with high process loading rates and TSS and total phosphorus removal of percent. Actiflo units are typically sized for overflow rates of 30 gpm/sf under maximumday dry-weather conditions, and 45 gpm/sf under maximum-day wet-weather conditions, with a 5 minute HRT for flocculation and mixing. Because of the higher overflow rates, the footprint of Actiflo units would be significantly smaller than effluent filters. However, the initial capital cost of the equipment and complexity of operation make the Actiflo process less desirable when compared to effluent filters. The Actiflo process can meet more stringent effluent water quality parameters and should be retained for consideration should effluent treatment limits become more stringent. At this time, neither effluent filters nor Actiflo are needed to comply with anticipated water quality requirements over the next 5 to 10 years. The analysis presented in this report above is intended to provide general planning information on the treatment processes should they ever be needed. The choice between effluent filters, Actiflo or other polishing systems, such as membranes, will depend upon the specific effluent quality requirements that must be met and the comparative economics of these options in the future. Alternative Analysis Summary Estimated capital and present worth costs for the biological/tertiary treatment alternatives are presented in Table The capital costs presented do not include additional sitework associated with the process unit expansions and include tertiary (effluent filtration or membrane filtration) even though permit limits may not require that level of treatment. Operation and maintenance costs for each alternative include the estimated cost for annual operation of the existing extended aeration process when this process was retained for use within the process alternative.

51 Alternatives Development and Evaluation 4-51 Description Table Costs for Biological/Tertiary Treatment ($ Thousands) Continue Extended Aeration/ Cyclical Aeration Activated Sludge Single Stage Chemical Phosphorus Removal Biophosphoru s Treatment System Parallel Biophosphorus Treatment with Extended Aeration Membrane Bioreactor Base Construction $2,080.9 $2,163.8 $2,862.5 $2,143.8 $5,283.6 Cost Electrical & $624.3 $649.2 $858.7 $643.2 $1,585.1 Controls Subtotal A $2,705.2 $2,813.0 $3,721.2 $2,787.0 $6,868.7 Mobilization & $135.3 $140.6 $186.1 $139.4 $343.4 Bonds (5%) Contractor s $270.5 $281.4 $372.7 $278.6 $686.4 Overhead & Profit (10%) Subtotal B $3,111.0 $3,235.0 $4,280.0 $3,205.0 $7,899.0 Miscellaneous $622.2 $647.0 $856.0 $641.0 $179.8 Costs Not Itemized (20%) Subtotal C $3,733.2 $3,882.0 $5,136.0 $3,846.0 $8,078.8 Engineering, $746.6 $776.4 $1,027.2 $769.2 $1,615.8 Legal, Administration (20%) Total Capital $4,479.8 $4,658.4 $6,163.2 $4,615.2 $9,694.6 Cost Total O&M $630.8 $630.8 $587.8 $609.3 $488.8 Cost/Year 1 Total Present Worth $13,046.1 $13,224.7 $14,145.5 $12,889.5 $16, O&M costs added to existing O&M expenditures, plus estimated process O&M costs estimated at $293,900 for existing extended aeration process. Costs for 3.63 mgd average annual flow.

52 4-52 City of Hamilton Wastewater Facilities Plan Description Table Evaluation Summary Continue Extende d Aeration / Cyclical Aeration Activated Sludge Single Stage Chemical Phosphoru s Removal Biophosphoru s Treatment System Parallel Biophosphoru s Treatment with Extended Aeration Membran e Bioreactor Regulatory Coordination Operations/Technology Compatibility with Site Implementation Community/Environmental Risk Cost TOTAL The alternatives that retain the use of the existing extended aeration basin (B1, B2 and B4) offer the lowest initial capital cost and operation and maintenance costs. The estimated alum use for an annual average flow of 3.63 mgd, if alum addition were implemented all year long, is 1.05 tons/day, or approximately $43,000/year for polymer at an estimated cost of $120/ton for polymer. As a result, Alternative B4, which plans for installation of a biological/phosphorus removal cell upstream of the existing and planned oxidation ditches, has a present worth cost at or near Alternative B1. Alternatives B3 and B5, which add new biological and membrane treatment trains, are much more expensive and are recommended to be removed from further consideration. The biological treatment alternative (B3) does not take full advantage of the existing oxidation ditch capacity and the membrane bioreactor alternative (B5) is very expensive because of the high cost of the membrane equipment and the need for addition of microfiltration at the preliminary treatment stage of the process. Alternatives B1 and B4 offer the greatest flexibility for phased construction and also take best advantage of existing infrastructure. Alternative B1 would use alum for phosphorous removal that would result in as much as tons of additional solids to manage per year. Alternative B3 would involve a more sophisticated treatment process, using biological nutrient removal technology for both nitrogen and phosphorous removal. Although there is significant advantage in using biological treatment for phosphorous removal (and avoiding the use of alum), the treatment process requires more operator attention to maintain the process and would require significant additional laboratory analyses for process control and monitoring. Preliminary Recommendations It is recommended that the City retain biological/tertiary treatment alternatives B1 Extended Aeration with Chemical Phosphorus Removal and B4 Biophosphorus Removal with Parallel Extended Aeration for further consideration during preliminary design. Depending upon future permit requirements, both alternatives provide distinct advantages. Should only seasonal nutrient removal be required, Alternative B1 would offer a lower cost and less sophisticated treatment process to operate. Alternative B1 also has the lowest initial capital cost. Should more stringent

53 Alternatives Development and Evaluation 4-53 effluent nutrient limits be required, coupled with year-round nutrient removal, Alternative B4 would offer the greatest advantage since operations and maintenance costs would be lower due to the elimination of alum addition and avoidance of the additional solids handling associated with alum. It is also recommended that, pending resolution of future permit requirements, the City plan for future installation of effluent filtration should further nutrient limits require phosphorous removal below 1.0 mg/l. It is likely that cloth membrane disc filtration would be selected for effluent filtration. Disinfection The City of Hamilton s disinfection system was originally designed to utilize gaseous chlorine for effluent disinfection. The current permit requirements for disinfection only require the City to disinfect during the summer months from April 1 to October 31, meeting a fecal coliform bacteria count of no greater than 9,200 organisms per 100 ml (30-day average). Recent discussions indicate that MDEQ will likely be modifying future permit limits to require yearround disinfection and fecal coliform bacteria counts of no greater than 200 organisms per 100 ml. In addition, MDEQ has also indicated they will limit effluent chlorine residuals to no greater than 0.5 mg/l total effluent residual. Given these proposed regulatory changes, the City of Hamilton will be required to upgrade their disinfection facilities. In approximately 2000, the City of Hamilton changed their form of disinfection from gaseous chlorine to liquid chlorine (12.5% sodium hypochlorite) fed from a single chemical metering pump. Because permit requirements will require more stringent disinfection practices, and because the capacity of the existing chlorine contact channel is not sufficient for ultimate buildout of the service area, the City must evaluate alternatives for upgrade of their disinfection facilities. A detailed analysis of the alternatives for disinfection is provided below. Driving Forces Permit Change. The existing MPDES permit will expire in August New permit requirements are likely to be more stringent for both bacteriological indicators and chlorine (the disinfectant used to reduce pathogens in plant effluent). Improve Process. Improved controls will be needed to reduce chemical consumption and increase reliability. Age and Condition. The existing chlorine feed equipment has adequate capacity; however, it will likely require replacement within the next 3 to 5 years. The existing chlorine contact basin does not have sufficient capacity and will require expansion prior to year Growth. The plant currently meets the disinfection requirements of their permit. However, plant influent flows will eventually exceed capacity of the chlorine contact channel. Alternatives Considered Six alternatives were considered for effluent disinfection to meet the more stringent effluent permit limits expected from MDEQ. Two of the six alternatives were retained for detailed evaluation because of their technical feasibility and cost effectiveness. The following effluent disinfection alternatives were evaluated for improving effluent disinfection capability: Retain Hypochlorite disinfection and add bisulfite dechlorination (chemical alternative).

54 4-54 City of Hamilton Wastewater Facilities Plan Install a new ultraviolet light disinfection system. Retain Hypochlorite Disinfection and Add Bisulfite Dechlorination (D1) This alternative retains the existing sodium hypochlorite storage and feed equipment and plans for replacing the existing pumping unit and installation of a redundant unit. This alternative will also expand the capacity of the existing contact channel, under a phased approach when additional capacity is needed, and make provision for installation of a new effluent flow measurement weir. Replacement of the existing Cl 2 leak detector would be implemented. In addition to sodium hypochlorite feed rate control, a sodium bisulfite storage and feed system would be installed. A effluent residual analyzer would be installed and effluent residual and ORP analyzers would be installed to automate the disinfection and dechlorination process. The existing chlorine contact basin is limited in capacity to 3.3 mgd, due to restrictions in the effluent flow measurement weirs. The existing basin has 70,000 gallons of capacity. At a minimum detention time of 15 minutes, capacity of the contact tank is 6.72 mgd at peak flows. For annual average flow conditions, it is recommended that detention times be set for 60 minutes detention. At 60 minutes detention and projected flows of 3.63 mgd, a volume of 150,000 gallons for chlorine contact is required. Therefore, an additional 75,000 gallons of contact basin is needed to retain the existing chemical disinfection system for projected buildout conditions. Install Ultraviolet Light Disinfection (D2) This alternative would include modification of the existing sodium hypochlorite feed system to be used for RAS chlorination and as a backup effluent chlorination system. The existing chlorine contact channel would be retained on-site as a backup system and new ultraviolet light disinfection systems would be installed. Although there is the potential to re-use the chlorine contact basin for some ultraviolet light technologies, the existing circular tankage is not an easy configuration for retrofitting of UV systems. In addition, the existing chlorine contact channel concrete condition would require significant repairs if it were to be re-used. Therefore, this alternative assumes two parallel UV channels would be installed, each with the capacity of approximately 4 mgd annual average flow and 12 mgd peak flow. Level control facilities, lamp removal hoists and monorails, and lamp cleaning systems would be installed. A portion of the existing chlorine storage room would be used for UV lamp maintenance and cleaning purposes, and for installation of the UV electrical service equipment. It is recommended that a building be constructed over the UV channels to provide for weather protection and equipment maintenance. There are several types of UV systems that could be installed at Hamilton. These include the following: Open Channel Low Pressure UV Disinfection. Open channel low pressure systems include UV lamps submerged in the contact channel in both vertical and horizontal arrangements. Low pressure ultraviolet bulbs have the ability to treat between 10 and 180 gallons per minute of wastewater. Based upon average

55 Alternatives Development and Evaluation 4-55 transmissivities that would be concentrated at Hamilton, an estimated 144 low pressure highoutput lamps would be required to handle peak flows at Hamilton. Open Channel Medium Pressure UV Disinfection. Similar to the low pressure ultraviolet light alternative, this option would remove the existing chemical systems for chlorination and install new UV contact channels. Medium pressure ultraviolet light lamps are capable of treating greater amounts of wastewater per lamp. A single medium pressure lamp can treat up to 350 gallons per minute, significantly greater than low pressure lamps. As a result, only 24 medium pressure lamps would be required to accommodate the peak flow condition of 12 mgd. Since the medium pressure systems involve additional headloss with the horizontal, channelized flow pattern, it has been anticipated that effluent pumping would be required for this alternative. Level control facilities, equipment protection building, integral hoist systems and lamp cleaning and maintenance systems would be provided. Similar to the low pressure sub-alternative, the chlorine storage and feed rooms could be dedicated for maintenance and electrical service purposes. Closed Medium Pressure UV Disinfection. This sub-alternative would also include removal of the permanent chemical disinfection systems and would install a closed channel UV technology. The closed channel technology requires directing wastewater flows via pipeline through closed chambers installed on those pipelines. This technology is readily available in modules up to 5 mgd, so multiple modules would be required for peak flows up to 12 mgd. To accommodate the closed channel technology at Hamilton, it has been anticipated that three parallel flow pipelines, each capable of 4 mgd, would be installed. This would serve as an ultraviolet light lamp gallery and would be accessible from ground level. The gallery would be configured with drainage systems to maintain the gallery dry, overhead hoist, and access stairs would be included for personnel access. A canopy would be installed over the gallery to protect the UV equipment from the weather. Once again, the existing chlorine feed and storage rooms would be used for required electrical service equipment associated with the UV system. Control valves and system automation would be installed to bring the multiple parallel systems on line as required by plant flow conditions. Alternative Analysis Summary Key advantages and disadvantages of the alternatives for disinfection are presented in Table 4-16.

56 4-56 City of Hamilton Wastewater Facilities Plan Table Advantages and Disadvantages of Disinfection Alternatives Disinfection Option Advantages Disadvantages Chlorine Chemical Feed, Chemical De-Chlorination (D1) Ultraviolet Light Disinfection (D2) Familiar systems Lower initial capital cost Easier to retrofit existing systems Small footprint for future facilities Minimizes toxic gas and chemicals stored on-site More reliable to meet effluent disinfection limits Less environmental impact Large foot print Complicated controls with chlorine residual analyzers Greater environmental impact Higher initial capital cost New technology, less familiar Higher complexity Based upon the projected flow and loadings presented in Sections 2 and 3, the existing chlorine feed system and chlorine contact channels have sufficient capacity to year 2018 and 2010, respectively. The existing contact channels require retrofits to the effluent weirs to eliminate submergence problems. Degradation of the contact channels concrete also exists. Evaluation of the disinfection alternatives considers expansion of the facilities to ultimate buildout and assumes disinfection will be installed between effluent filtration and effluent pumping at ultimate buildout conditions. Estimated capital and present worth costs for the disinfection alternatives are presented in Table The alternative D1 will maintain the existing chemical disinfection process, but will also add residual control and effluent chemical de-chlorination. This alternative offers the lowest initial capital cost, yet maintains larger quantities of toxic chemicals on-site and carries a greater risk to toxicity concerns than the UV light alternative. The UV light alternative would involve a greater initial capital cost, yet provides a more environmentally acceptable solution. The City would improve site safety considerably by removing the larger quantity of chlorine from the site. In addition to the reduction in the risks associated with handling and transport of hazardous chemicals, the truck traffic to the wastewater treatment plant would be reduced. Traditional low pressure UV systems are ideal for low flow wastewater disinfection on smaller projects, but units for larger wastewater disinfection applications are also available. As flows increase, or higher UV doses are required, multiple low pressure lamps are used. Medium pressure UV systems offer some simplicity in layout. This results in cost effectiveness while meeting the high flow/high dose challenge. Medium pressure systems offer advantages such as fewer lamps to install and maintain, operational flexibility, easier expandability, and a selfcleaning capability. The small number of lamps required for medium pressure systems also lead to problems associated with redundancy at peak flow rates. Medium pressure enclosed channel systems would require similar modifications for installation. Because enclosed channel systems are generally used for lower-flow applications, equipment designs have not been developed for larger flow applications. As such, this technology is less proven than low pressure or open channel medium pressure systems. There are greater operation and maintenance requirements associated with maintaining the low pressure open channel systems due to the large number of lamps associated with the design. Electrical consumption for medium pressure systems is slightly lower than low pressure systems. Implementation of the open channel medium pressure systems is easier than low pressure systems because less infrastructure improvements are required for

57 Alternatives Development and Evaluation 4-57 medium pressure systems. Maintenance, operation and energy consumption costs are similar for open channel and enclosed channel medium pressure systems. Description Table Costs for Disinfection, $ Thousands Retain Hypochlorite Disinfection/Add Biosulfite Dechlorination Install UV Light Disinfection Open Channel Low Pressure Install UV Light Disinfection Open Channel Medium Pressure Install UV Light Disinfection Closed Channel Medium Pressure Base Construction Cost $275.0 $775.5 $834.7 $962.0 Electrical & Controls $7.5 $232.6 $250.4 $288.6 Subtotal A $282.5 $1,008.1 $1,085.1 $1,250.6 Mobilization & Bonds (5%) $14.1 $50.4 $54.3 $62.5 Contractor s Overhead & Profit (10%) $28.3 $100.8 $108.4 $125.0 Subtotal B $324.9 $1,159.3 $1,247.8 $1,438.1 Miscellaneous Costs Not Itemized (20%) $65.0 $231.9 $249.6 $287.6 Subtotal C $389.9 $1,391.2 $1,497.4 $1,725.7 Engineering, Legal, Administration (20%) $78.0 $278.2 $299.5 $345.1 Total Capital Cost $467.9 $1,669.4 $1,796.9 $2,070.8 Total O&M Cost/Year $20.0 $33.6 $28.9 $28.9 Total Present Worth $739.5 $2,125.7 $2,189.4 $2,463.3 The two main disinfection alternatives, including the three sub-alternatives for UV disinfection, were also evaluated using the established evaluation criteria. Table 4-18 summarizes the evaluation. The alternative to retain hypochlorite disinfection, although it offers less initial capital costs, has significant shortfalls when community/environmental and regulatory considerations are taken into account. Installation of the ultraviolet light open channel medium pressure and low pressure alternatives offer cost, implementation and community/environmental benefits.

58 4-58 City of Hamilton Wastewater Facilities Plan Table Evaluation Summary Evaluation Criteria Retain Hypochlorite Disinfection/Add Biosulfite Dechlorination Install UV Light Disinfection Open Channel Low Pressure Install UV Light Disinfection Open Channel Medium Pressure Install UV Light Disinfection Closed Channel Medium Pressure Regulatory Coordination Operations/ Technology Compatibility with Site Implementation Community/ Environmental Risk Cost TOTAL Preliminary Recommendations Although capital costs for installation of UV light disinfection are significantly greater than the chemical disinfection alternative, there are considerable advantages for the City of Hamilton to consider installation of UV light disinfection. UV light is less susceptible to market fluctuations for chemicals, carries less risk for toxic chemical spill, provides greater assurance that future regulatory requirements will be met and allows for easier construction implementation. Since it is likely effluent pumping will be added in the future, it is recommended that the City consider installation of UV disinfection when plant flows reach capacity of existing systems or when disinfection permit requirements change to more stringent requirements. It is also recommended that the City carry both the low pressure open channel and medium pressure open channel technologies for further evaluation in preliminary design. The existing hypochlorite feed system would be retained under either of these alternatives for RAS chlorination and as backup to the UV light disinfection system. The City of Helena, MT recently installed an open channel low pressure system and the City of Missoula, MT recently installed an open channel medium pressure system. Flow Measurement/Outfall Effluent from the City of Hamilton s secondary treatment process is directed from the secondary clarifiers to the chlorine contact basin. At the chlorine contact basin flows are split between two contact channels, each of which are fitted with an effluent weir for flow measurement. Submergence of the weirs occurs at approximately 3.3 mgd, far below the peak flow rate at ultimate buildout. Following overflow from the contact basin, wastewater flows are directed in a

59 Alternatives Development and Evaluation 4-59 single outfall pipeline to an effluent channel. The open top channel then directs plant effluent flows to the Bitterroot River, where the flow is directly introduced to the Bitterroot River at the stream bank. Currently, all flows from the Hamilton wastewater treatment plant are discharged from the plant via gravity. During periods of high flow at projected peak flow conditions, it will be necessary to construct an effluent pumping system with discharge head box to ensure upstream treatment process units are not submerged. When effluent pumping is installed, it is recommended that a new effluent flow weir be constructed to allow flow measurement of the entire projected peak flow of (12) mgd.) Driving Forces Peak Flows. As described in Chapter 3, the effluent outfall and effluent flow metering does not have sufficient capacity for peak flow projections. Consequently, effluent pumping capacity is needed to meet projected conditions. Permit Change - Outfall. The existing outfall for the City of Hamilton does not include a diffuser within the Bitterroot River. Depending upon future permit requirements, the City may need to install an extension to their outfall pipeline and add a diffuser section to enhance dilution at the end of their mixing zone. Should a diffuser section be required, then effluent pumping will also be required. A single 24-inch effluent pipeline would be required. Alternative Analysis Typically, effluent flows are measured using an open channel type overflow weir that is normally found at the end of the disinfection process. After flow measurement, the effluent is then sampled and directed by gravity to the effluent outfall. In locations where insufficient gravity head would exist to convey peak flows, a headbox arrangement is usually configured with automated gate or backflow check gate to enable effluent pumping. It is assumed that for estimating purposes, an open-air pumping station would be installed that would include effluent flow measurement, two redundant high volume mixed flow vertical turbine pumps, and pumping station controls. The estimated cost of effluent pumping is presented in Table 4-19.

60 4-60 City of Hamilton Wastewater Facilities Plan Table Costs for Flow Measurement/Outfall, $ Thousands Description Improve Effluent Metering and Install Effluent Pumping Base Construction Cost $236.5 Electrical & Controls $71.0 Subtotal A $307.5 Mobilization & Bonds (5%) $15.4 Contractor s Overhead & Profit (10%) $30.8 Subtotal B $353.7 Miscellaneous Costs Not Itemized (20%) $70.7 Subtotal C $424.4 Engineering, Legal, Administration (20%) $84.9 Total Capital Cost $509.3 Total O&M Cost/Year $10.0 Total Present Worth $645.1 Preliminary Recommendations Although effluent pumping and effluent diffusers may not be required, there is strong potential that permit limits for effluent disinfection and in-stream dilution may require plant improvements that will force the City to pump their effluent. It is recommended that the City modify the effluent weirs of their existing chlorine contact basin to enable peak flows up to 6.72 mgd to flow through the system unimpeded. To meet higher peak flows of up to 12 mgd, or enable installation of effluent filtration and disinfection, it is recommended that the City install an open-air effluent pumping facility with headbox and effluent gravity check valve. The pumping station would be configured to operate under automated control and pump only when gravity flows cannot sustain due to high river flows and/or high treated water flows. Recycle Streams Currently, recycle streams from the City s digesters and drying beds dewatering are reintroduced to the plant influent stream at the influent transfer pumping station. These recycle streams can detrimentally impact activated sludge treatment processes due to their high ammonia concentrations. The peaks in influent loading, which typically occur during the day when operations is utilizing recycle systems (feeding the drying beds or decanting digesters), can cause stress on the activated sludge process. This stress is exacerbated when trying to perform biological nutrient removal within the process. There are several recycle management alternatives available to Hamilton. The City can continue the no action alternative where recycle streams can be treated as they are now in the extended air activated sludge process or by controlling the timing of the recycle by storing and metering the recycle stream into the process during periods of low influent loading.

61 Alternatives Development and Evaluation 4-61 Driving Forces Permit Change. As described earlier, permit limits for nutrients will likely require installation of biological nutrient removal technologies. The activated sludge will benefit from a more constant influent loading to the plant, making it easier to meet established water quality targets. Improve Process. Alternative approaches to recycle management can achieve greater nutrient removal performance and better plant process control. This can reduce the size and improve the performance of downstream secondary treatment processes. Alternative Analysis The two alternatives for recycle stream management that were considered were to maintain the existing recycle streams that drain to the plant influent or collect and control the filtrate return by storing and metering flows to the influent. The no action alternative would result in the recycle steams from dewatering and biosolids digestion to be returned as is practiced now. This alternative would not require any additional capital investment. An alternative approach, as is practiced at other nutrient removal facilities, such as Coeur d Alene, ID, would be to install a filtrate/centrate pumping station that would deliver recycle streams to a storage basin and then enable plant personnel to meter the flows back to the treatment process during night time to level-out loading to the plant. In Hamilton s case, the recycle flows would be directed by gravity to either the existing small secondary clarifier that is not used for the treatment process or, if taken out of service, the chlorine contact channel. A new filtrate/recycle return submersible pumping station would be installed to pump recycle flows, on a timed basis, back to the treatment plant influent. The pumping station would include timed sequencing on the drives to enable operations to adjust recycle return rates. Table 4-20 shows the estimated capital and operations and maintenance costs for the recycle stream improvements.

62 4-62 City of Hamilton Wastewater Facilities Plan Table Costs for Recycle Streams, $ Thousands Description Equalize Filtrate from Drying Beds/ Dewatering Base Construction Cost $30.0 Electrical & Controls $9.0 Subtotal A $39.0 Mobilization & Bonds (5%) $2.0 Contractor s Overhead & Profit (10%) $3.9 Subtotal B $44.9 Miscellaneous Costs Not Itemized (20%) $9.0 Subtotal C $53.9 Engineering, Legal, Administration (20%) $10.8 Total Capital Cost $64.7 Total O&M Cost/Year $5.9 Total Present Worth $144.9 Preliminary Recommendations Although recycle stream management would serve to improve process performance, it is likely recycle management would have only minor impact on the Hamilton plant. This is largely due to the large aeration basin capacity inherent in the City s activated sludge treatment process. Should the City continue to retain the extended air oxidation ditch unit process with over 15- hour hydraulic retention times in the basin, then installation of recycle stream management would not be recommended. The City will have the opportunity to add this feature should it prove to be needed in the future. Secondary Sludge Thickening The secondary sludge thickening process at Hamilton was added during the 1998 treatment plant upgrades to enhance the City s digestion and sludge storage capacity. The City s plant has a single Dissolved Air Flotation Thickener (DAFT) unit that thickens the secondary sludge that is wasted from the treatment process. Thickened secondary sludge is pumped from the DAFT unit to aerobic digestion. As noted in Chapter 3, the existing DAFT unit has adequate capacity to approximately year A detailed analysis of the alternatives for secondary sludge thickening is provided below.

63 Alternatives Development and Evaluation 4-63 Driving Forces Growth. The firm capacity of the existing DAFT unit is 1,089 lbs per day solids loading capacity. Based upon projected solids loading capacity, the unit has capacity to approximately year Additional thickening capacity will need to be constructed within the next five years. Permit Change. As described earlier, permit limits for total nitrogen and phosphorus are likely to become more stringent. The activated sludge system will generate more sludge per volume of water treated than the current process, increasing the loading on the sludge thickening processes. Improve Process. Alternative approaches to thickening, in lieu of dewatering the aerobic digestion process, would reduce the size and increase the performance of the downstream biosolids treatment processes. Alternatives Considered The treatment process improvements implemented in 1998 evaluated available thickening technologies and selected the DAFT technology for Hamilton. Although the DAFT unit at Hamilton is performing well and is very compatible with current operations, additional treatment processes were evaluated. The following secondary sludge thickening processes were retained for evaluation: Expand the existing DAFT systems Add centrifuge thickening A description of each alternative evaluated is provided below: Expand DAFT Systems (ST1) Expansion of the DAFT system at Hamilton would involve construction of a redundant and duplicate DAFT unit located to the south of the RAS/WAS pumping station. The DAFT support equipment necessary for the new DAFT unit would be installed in the lower level of the RAS/WAS pumping station and the existing WAS sludge pumps would be reused for both the existing and new DAFT units. New thickened sludge pumping units would be installed to replace the aging air diaphragm pumps that currently serve the existing DAFT unit. Both DAFT units would be operated using similar controls to that currently employed at the plant. Maintenance for the DAFT units consists of the following: Daily Maintenance: Observe equipment for normal operation. Calibrate flow and air mixtures. Weekly Maintenance: Grease bearings and cycle redundant drives.

64 4-64 City of Hamilton Wastewater Facilities Plan Monthly Maintenance: Check system for proper operation, clean air charge equipment, change drive unit oil in gear box every 2 years ($100 per year). Energy cost for recycle pump and drive motor at 4.5 cents per kilowatt hour is $2,950. Add Centrifuge Thickening (ST3) This alternative would include keeping the existing DAFT unit in operation. It would require installation of the centrifuge in an enclosed building and installation of waste sludge transfer pumps and a waste sludge storage tank. After an initial look at the costs for this alternative, the capital costs and increased operations and maintenance of the dewatering machine resulted in quick elimination of this alternative as a viable thickening option at Hamilton. Alternative Analysis and Preliminary Recommendation It is recommended that the City continue to plan for expansion of their DAFT treatment process within the next five years (as originally planned in 1998). The addition of a redundant DAFT unit will maintain a common treatment process, result in less intensive operation and maintenance, and be far less expensive as an initial capital investment or long-term present worth basis. The estimated capital and operation and maintenance costs are presented in Table 4-21 for the DAFT expansion and centrifuge dewatering alternatives. Installation of the DAFT unit is far less expensive and, as shown in Table 4-22, is very comparable to centrifuge thickening when compared on a non-monetary basis. Table Costs for Secondary Sludge Thickening, $ Thousands Description Expand DAFT Systems Add Centrifuge Base Construction Cost $138.0 $584.4 Electrical & Controls $41.5 $175.3 Subtotal A $180.0 $759.7 Mobilization & Bonds (5%) $9.0 $38.0 Contractor s Overhead & Profit (10%) $18.0 $76.0 Subtotal B $207.0 $873.7 Miscellaneous Costs Not Itemized (20%) $41.4 $174.7 Subtotal C $248.4 $1,048.4 Engineering, Legal, Administration (20%) $49.7 $209.7 Total Capital Cost $298.1 $1,258.1 Total O&M Cost/Year $11.7 $71.4 Total Present Worth $447.5 $2,227.7

65 Alternatives Development and Evaluation 4-65 Table Evaluation Summary Evaluation Criteria Expand DAFT Systems Add Centrifuge Regulatory Coordination 3 3 Operations/ Technology 4 4 Compatibility with Site 4 3 Implementation 4 3 Community/ Environmental 4 4 Risk 4 4 Cost 4 2 TOTAL Sludge Stabilization Biosolids stabilization at Hamilton is provided by the aerobic digestion method. Waste biosolids from the secondary treatment process are thickened and pumped to two aerobic digestion basins where the material is currently stored under aerated conditions for approximately 66 days for stabilization. In order to meet the minimum 38% reduction in volatile solids (EPA 503 sludge regulations), it is recommended that the retention time be a minimum of 80 days, without additional downstream treatment. The treatment plant s two digesters have a combined volume of 236,500 gallons. Current thickened sludge flows are estimated at 3,600 to 4,000 gallons per day. This equates to the approximately 66 days retention time. Since the City of Hamilton composts its biosolids, full stabilization of their biosolids within the digestion process is not needed. However, additional digestion/storage capacity was added through the use of Secondary Clarifier No. 2 that added an additional 75,000 gallons of aerated storage capacity. The City of Hamilton also has additional liquid sludge storage capacity of 408,500 gallons, making the combined digestion and solids storage volume equal to approximately 720,000 gallons including Secondary Clarifier No. 3 and 645,000 gallons, excluding Secondary Clarifier No. 2. Driving Forces Growth. The capacity of the existing digestion system, when combined with biosolids storage, equates to approximately 2,950 gallons per day. Current conditions are at approximately 3,600 gallons per day of thickened waste sludge. The aerobic digestion system is a bottleneck in the solids handling system. Additional growth will continue to expand the capacity limitations on this unit process. Permit Change. The activated sludge/biological nutrient removal system, needed to meet more stringent nutrient limits, will generate more biosolids per volume of water treated than the current process, increasing loads to the digestion process.

66 4-66 City of Hamilton Wastewater Facilities Plan Alternatives Considered and Analysis The aerobic digestion process at Hamilton is closely tied to the biosolids management plan for the facility. Should the City choose to continue to compost their biosolids, then the amount of time the City must digest their biosolids is less, since stabilization will also occur in the composting process. Should the City decide to discontinue their composting process, then digestion capacity would need to be increased. The aerobic digestion process employed at the Hamilton WWTP is also very closely tied to the biosolids storage facilities. Since composting is performed at Hamilton, there is greater need for solids storage than digestion. Two alternatives have been retained for consideration for Hamilton from the eight alternatives originally identified. These include: Expand the aerobic digestion capacity to meet 80 days minimum suggested detention time needed for volatile solids reduction. Reduce existing sludge storage capacity and increase aerobic digestion capacity within same basin. Expand Aerobic Digestion (SS1) This alternative would add an additional aerobic Digester No. 3 adjacent to Digester No. 2 and the existing sludge storage basin. In order to meet the minimum recommended digester retention time (for aerobic digestion) of 80 days, a total of 1,425,000 gallons of aerobic digestion capacity would be needed. Since only 236,500 gallons currently exist, an additional 1,187,500 gallons of digester storage would be needed. It is assumed that the digester would be constructed as an enclosed top, reinforced concrete basin equipped with coarse bubble aeration and baffling systems. The additional digester capacity would assume that the City would be fully stabilizing their biosolids material for another means of disposition other than composting. Otherwise, this amount of additional digestion capacity would not be warranted. Reduce Sludge Storage and Enhance Digestion Capacity (SS8) This alternative was considered as an alternative to adding additional basins on-site. It assumes that the City will continue composting and enahnced solids dewatering will be added to reduce the amount of biosolids storage to approximately two weeks biosolids storage capacity. This would equate to approximately 250,000 gallons storage capacity. The alternative would require dewatering activities to be conducted every two weeks. Digester No. 1 is a stand-alone digester with approximately 66,000 gallons of capacity. Aerobic Digester No. 2, and the sludge storage basin, are contained in a single covered concrete basin that is 579,000 gallons in total capacity. Of this volume, Digester No. 2 occupies 170,500 gallons and sludge storage occupies the remaining 488,500 gallons. Under this alternative, an additional divider wall would be added, with additional aeration and solids transfer piping, to create an additional Aerobic Digester No. 3. The sludge storage cell would be reduced to 250,000 gallons and an additional 158,500 gallons of digestion capacity would be created. The proposed configuration would increase digestion capacity to 395,000 gallons, or an increase of approximately 50% of digester capacity. At current solids production rates, the digestion detention time would be approximately 109 days. At buildout, approximately 22 days detention time would be provided. The remaining solids stabilization under this alternative would be achieved by composting the biosolids.

67 Alternatives Development and Evaluation 4-67 In comparing digestion capacity provided under this scenario with MDEQ Circular 2 standards, MDEQ requires two cubic feet of storage per equivalent population unit (assuming thickening to 3% solids in the DAFT unit), or approximately 15 gallons digestion capacity per person served. Accordingly, when compared to the planned 395,000 gallons of digestion capacity, approximately 26,300 persons would be the ultimate capacity. This would exceed the projected population of 22,570 people in year The two cubic feet of storage per person served is based upon the City maintaining a minimum of 15 DegC temperature within the basins for 27 days. Although the retention time within the digesters would only be an estimated 22 days at 2045 conditions, the average temperature within these covered and insulated basins (earthen insulation) exceeds 15 DegC. Therefore, assuming liquid solids storage were replaced with dewatering and composting management practices downstream, elimination of solids storage and installation of additional aerobic digestion capacity (using existing basins) would provide sufficient solids stabilization for year 2045 conditions. The estimated capital and present worth costs for the sludge stabilization alternatives are presented in Table The alternative SS1, expansion of aerobic digestion, is far more expensive and would not be necessary should the City continue to compost their biosolids. Table Costs for Sludge Stabilization, $ Thousands Description Expand Aerobic Digestion Reduce Sludge Storage Base Construction Cost $858.0 $33.9 Electrical & Controls $128.7 $10.2 Subtotal A $986.7 $44.1 Mobilization & Bonds (5%) $49.3 $2.2 Contractor s Overhead & Profit (10%) $98.7 $4.4 Subtotal B $1,134.7 $50.7 Miscellaneous Costs Not Itemized (20%) $226.9 $10.1 Subtotal C $1,361.6 $60.8 Engineering, Legal, Administration (20%) $272.3 $12.2 Total Capital Cost $1,633.9 $73.0 Total O&M Cost/Year $17.8 $17.8 Total Present Worth $1,875.6 $314.7 Table 4-25 provides a summary of the alternatives evaluation using the established evaluation criteria. Although the no action alternative was not formally considered, it was determined that additional stabilization should be planned to ensure that odor generation on-site, attributable to

68 4-68 City of Hamilton Wastewater Facilities Plan solids stabilization, would be minimized. Sludge stabilization alternative SS8, reduction in sludge storage and increase in aerobic digestion using existing basin capacity, provided greater advantages to the City of Hamilton. The additional digestion capacity can be provided at minimal cost, since the divider wall can be created using a fabric curtain or low cost concrete wall and only 635 cfm of additional aeration capacity is needed, which may likely be obtained from existing equipment. Table Evaluation Summary Evaluation Criteria Expand Aerobic Digestion Reduce Sludge Storage Regulatory Coordination 4 4 Operations/ Technology 3 4 Compatibility with Site 3 4 Implementation 3 4 Community/ Environmental 4 4 Risk 4 3 Cost 2 4 TOTAL Preliminary Recommendations It is recommended that the City of Hamilton continue to pursue their biosolids dewatering options to reduce the amount of solids storage space required. In addition, it is also recommended that the City re-partition the existing Digester No. 2 and Solids Storage Basin to add an additional 158,500 gallons of digestion capacity to the system. This would require installation of an additional aeration blower, or replacing an exiting aeration blower by approximately 635 SCFM. This would provide sufficient stabilization of the secondary sludge production through year 2025, and would enable the City to use other beneficial reuse strategies for Class B biosolids should the City elect to not continue their Class A biosolids composting program. Biosolids Management The Hamilton WWTP currently produces Class A biosolids under the provisions of the Federal 40 CFR Part 503 regulations for reuse of biosolids. Secondary sludge is thickened in a DAFT thickener. Thickened sludge is aerobically digested and then directed to sludge drying beds for dewatering. Following dewatering, the City produces the Class A product by composting. Final disposition of biosolids is to private landowners within the City of Hamilton service area. Annual biosolids reports required by the US Environmental Protection Agency (USEPA) regarding the disposition history from were reviewed.

69 Alternatives Development and Evaluation 4-69 Due to high population growth in the Hamilton area, there is a concern that the existing biosolids management systems are reaching capacity. This section addresses the general biosolids management alternatives available to the City and provides recommendations on the long-term approach the City should take into the future. Current Regulations The policy of the USEPA is to promote the beneficial use of biosolids while maintaining environmental quality and protecting public health (USEPA, 1999a). The Clean Water Act Amendments of 1987 required the US Environmental Protection Agency to develop new regulations pertaining to biosolids. In February, 1993, EPA published 40 CFR Part 503 (e.g. Part 503). The Part 503 Rule is a complex, risk-based assessment of potential environmental effects of pollutants that may be present in biosolids (USEPA, 1995). These guidelines regulate pollutant and pathogen concentrations as well as vector attraction reduction (VAR). The guideline defines biosolids as Class A or Class B, depending on the potential level of pathogens. Class A biosolids must meet strict pathogen standards and can be used with no restrictions, while Class B biosolids must meet less stringent pathogen requirements, with application restricted to crops with limited human and animal exposure. Biosolids in both classes must meet vector attraction reduction requirements. General Provisions The Part 503 Rule applies to biosolids applied to agricultural and non-agricultural land, biosolids placed in or on surface disposal sites, or biosolids that are incinerated. Biosolids that are landfilled or used as a cover material at a landfill are subject to federal requirements in 40 CFR Part 258. The general provisions of the Part 503 Rule provide basic requirements for biosolids applied to land including pollutant limits, management practices, operational standards, and monitoring, record keeping and reporting. Two approaches to meeting the Part 503 metals limits are allowed: 1) a maximum concentration must be met, or 2) a maximum cumulative amount of metals added to the soil via biosolids must be met. Biosolids meeting the Part 503 requirements by method one are called pollutant concentration (PC) biosolids, and limits are shown in Table If biosolids metals meet these concentrations, no record keeping of cumulative loading to soils is required. If PC biosolids also meet Class A pathogen reduction standards, they are considered exceptional quality (EQ), and may be distributed to the public. Table Pollutant Concentration (PC) Biosolids (Table 3 of 40 CFR ). Pollutant Allowable Concentration (mg/kg monthly average) Arsenic (As) 41 Cadmium (Cd) 39 Copper (Cu) 1,500 Lead (Pb) 300 Mercury (Hg) 17 Nickel (Ni) 420 Selenium (Se) 100 Zinc (Zn) 2,800

70 4-70 City of Hamilton Wastewater Facilities Plan An effective industrial pretreatment program is the key to complying with Part 503 metals limits, as industrial inputs into the collection system are the primary source of metals. The USEPA is currently considering adding 15 additional chemicals to be regulated. Those include acetone, anthracene, barium, beryllium, carbon disulfide, 4-chloroaniline, diazinon, fluoranthene, manganese, methyl ethyl ketone, nitrate, nitrite, phenol, pyrene, and silver. Management practices required by the Part 503 regulations include providing buffer zones around wells, surface water, and property boundaries; nutrient management including only applying biosolids at or below agronomic rates; not causing any adverse impact to threatened or endangered species; and not applying biosolids to flooded, frozen, or snow-covered land. This section also includes requirements on monitoring and reporting. Hamilton currently applies these regulations when evaluating disposition locations and annual biosolids reporting. Pathogen and Vector Attraction Criteria The Part 503 regulations require biosolids that are land applied to meet two distinct criteria in addition to metals limits: pathogen destruction and vector attraction reduction (VAR). As mentioned previously, USEPA divides biosolids into two categories in terms of the potential level of pathogens, Class A and Class B. Part 503 describes several methods for meeting both Class A and Class B criteria. Hamilton currently meets Class A criteria by aerobic digestion and composting. Class A pathogen destruction requirements are more complex, and are discussed in detail in the following section on solids treatment alternatives. Similarly, Part 503 describes several methods for meeting VAR criteria. Hamilton currently meets VAR criteria by providing 38 percent volatile solids destruction during digestion. Phosphorus The general permit for EPA Region VIII has a restriction on sites where the available phosphorus level exceeds an Olson P value of 100 ppm (for soils with a ph above 6.5). Depending upon the nature of the soils, and historical land use, including past fertilizer use and biosolids applications, additional biosolids application may be restricted by the amount of phosphorus already present in the soil. This could limit Hamilton s ability to dispose of composting material to those who apply on land or garden areas repeatedly for long periods of time. The Region VIII general permit allows site specific limits based on the use of a Phosphorus Index. This provision may allow for the development of scientifically based criteria reflecting site specific conditions that are protective of ground water and surface water quality. The Phosphorus Index is a risk management based approach that takes into account Transport Factors (soil erosion, runoff class, subsurface drainage, contributing distance to groundwater or surface water) and Source Factors (soil test, application rates, phosphorus availability). The bioavailability of phosphorus in biosolids differs from fertilizers and manure, and study is needed to develop an appropriate Phosphorus Index. Phosphorus bioavailability and mobility varies in biosolids depending upon a number of factors including the liquid stream treatment process, degree of solids processing and stabilization, and the amount and concentration of metals present such as aluminum and iron. Wastewater utilities with effluent phosphorus limitations, or a total maximum daily load (TMDL) that will require phosphorus removal, as Hamilton will likely need to do, should plan ahead. Liquid stream phosphorus removal will result in biosolids phosphorus concentrations that increase by a factor of 2 to 3 times. Higher biosolids phosphorus concentrations will cause the soil phosphorus levels to increase, making some land unavailable for land application. The Phosphorus Index approach may become increasingly important in maintaining the viability of

71 Alternatives Development and Evaluation 4-71 the land application based management program. Currently, the regulations allow Class A biosolids to be land applied with no restriction based on phosphorus levels in the soil. However, the Part 503 regulations have a provision that allows the regional USEPA biosolids coordinator to impose the phosphorus provisions if they believe that there will be harm to the environment as a result of land application activities. Comprehensive consideration of phosphorus in liquid stream removal, sidestream management, and land application may provide an optimal, system-wide solution to P-management that is most cost effective. Future Regulations The National Academy of Sciences (NAS) recently completed an assessment of the science that supports the Part 503 Rule, and concluded that more research is required to update that science (NRC, 2002). NAS concerns included chemical pollutants and pathogens not considered in the risk assessment of the Part 503 Rule, as well as their synergistic effects. As a result of NAS recommendations, USEPA may begin a review of the Part 503 Rule every five years, as is done for other USEPA-promulgated rules. It is possible that Class B biosolids may not be acceptable for land application or other beneficial reuse in the future due to regulatory changes, or that the pathogen levels for Class B biosolids may be lowered. At a recent Water Environment Research Foundation (WERF) biosolids summit, top industry experts stated that Class B biosolids may be eliminated in the next five years in favor of the Class A process. However, USEPA has reaffirmed its endorsement of biosolids land application in a letter to state biosolids coordinators on October 31, 2003, and will ultimately decide whether Class B biosolids will be viable in the future. Driving Forces Growth. The dewatering and composting processes provide sufficient capacity for the existing treatment plant flow rates. Limitations currently exist with the City s dewatering system. However, future growth will require expansion of both dewatering and composting operations beyond current capacity levels. Permit Change. As described for other solids handling processes, conversion to activated sludge to remove ammonia, nitrogen and phosphorus will increase sludge production. Improve Process. Some dewatering alternatives would allow greater production of a dryer sludge cake, which would improve performance of the compost operation, reduce compost operation costs, delay the need to expand the compost facilities, and require a smaller compost facility at ultimate buildout. Alternatives Considered Alternatives considered and developed in detail for improvements to the Biosolids Management facilities at Hamilton are: Retain and expand the existing City composting facilities. Dispose of biosolids generated on-site by dewatering and contract handling by an off-site contractor. Retain the existing City composting operation and expand to co-compost with the City s yard waste materials.

72 4-72 City of Hamilton Wastewater Facilities Plan Biosolids Quantity The quantity of biosolids generated from the Hamilton wastewater treatment plant is presented in Table 4-26 below. Table Projected Biosolids Production Year Waste Sludge Mass (lbs/day) 1 Dewatered Sludge Mass (lbs/day) 2 Dewatered Sludge Volume (cubic yards/day) Average 889 4, Average 1,376 7, Average 2,036 11, Average 4,453 24, Dry weight basis 2 Based upon 18% solids concentration 3 Based upon unit weight of 60 lbs/ft 3 The dewatering alternatives impact the facility requirements and operating costs for the compost system and/or alternative means for solids disposition. As a means for comparison of biosolids management alternatives, it was assumed that solids concentration of the dewatered biosolids was 18% solids on a dry weight basis. The volume of biosolids produced that are shown in Table 4-26 above reflect this assumption. A description of each alternative evaluated for biosolids management is provided below. Retain/Expand Composting Process (BM1) This alternative assumes the City will continue to process biosolids on-site at the wastewater treatment plant. It also assumes that biosolids will be dewatered to a minimum of 18% solids, regardless whether mechanical dewatering or drying in sludge drying beds are used. The composting process schematic for this alternative is shown in Figure 4-6 below. Sludge (1 volum e) 1/2 Day Mixing 21 Days Aerated Pile 2 Days Drying 1/2 Day Screening 30 Days Curing Compost Reuse! W ood Chips (3.0 volum e) Recycled W ood Chips (85% ) Figure 4-6. Composting with Wood Chips Table 4-27 provides the estimated materials balance for composting facilities at the 2045 design condition, assuming select wood chips are used and screening is added to the process.

73 Alternatives Development and Evaluation 4-73 Table Material Balance, 3.63 mgd, with Select Wood Chips Item Volume (CY/day) Total Weight (lbs) Dry Weight (lbs) Volatile Solids (lbs) Bulk Density (lbs/cy) Solids Content (%) Volatile Solids (%) Sludge ,738 4,452 2,270 1,620 18% 51% New Wood Chips 6.9 4,140 2,277 2, % 95% Recycle ,300 15,015 12, % 80% Compost ,178 21,744 16, % 76% Mix 1 Loss 1,644 1,644 Unscreened ,907 20,100 14, % 73% Recycle ,300 15,015 12, % 80% Compost 6.0 7,874 5,085 2,789 1,312 55% 55% 1 Ratio of woodchips to sludge = Woodchip recovery efficiency = 85% Based upon the above materials balance, and an assumed 2-3 day compost operation each week, the following Table 4-28 indicates expected design conditions for the composting operation at 3.63 mgd.

74 4-74 City of Hamilton Wastewater Facilities Plan Table Compost Design Conditions at 3.63 mgd, with Select Wood Chips Item Amount Compost Area Cubic Yards per Day 61.2 Square Feet Required 1 5,814 (48 x120 ) (two drying beds) Curing Area Cubic Yards per Day 6 Square Feet Required 2 2,680 (22 x120 ) Design for cover over drying bed Bulking Agent Storage Cubic Yards per Day 6.9 Square Feet Required 3 2,760 Recycle Storage Cubic Yards per Day 39.0 Square Feet Required 4 4,290 1 Based on 9 foot pile height, with 1 foot blanket and base, includes slope 2 Based on 6 months storage, 12 foot pile height, includes slope and access 3 Based on 150 days supply, 12 foot pile height, includes slope and access 4 Based on 2 times required recycle, 12 foot pile height The above design shows that at 2045 design, the City should plan for installation of a new compost mixer and recycle screening unit. A cover should be installed over the curing area and composting area should the City choose to compost throughout the year. Otherwise, dewatered cake storage for approximately 720 cubic yards (+/-5,000 square feet covered area) is recommended. The following improvements would be made to the existing composting operation (excluding dewatering) for this alternative: Improvement $ Base Capital Cost Compost Mixer (Bobcat or Pugmill) $30,000 Compost Area Cover (5,814 sf) $87,200 Curing Area Cover (2,680 sf) $40,200 Recycle Screen Unit $30,000 Front End Loader/Bobcat Attachment $20,000 Aeration/Blowers $20,000 Paving and Miscellaneous Equipment $10,000 Total (Excluding electrical and allied costs) $237,000

75 Alternatives Development and Evaluation 4-75 Contract Handling of Dewatered Biosolids (BM3) Under this alternative, the City of Hamilton would deliver their biosolids to EKO Compost, Inc. in Missoula, MT for disposal. For purposes of evaluation, it is assumed the City would dewater the biosolids to 18% dry weight solids and haul to EKO Compost for their treatment and disposition. Total volume of biosolids hauled is 15.3 cubic yards/day, or 5,584.5 cubic yards annually at 3.63 mgd capacity. Truck hauling would include a 10 cubic yard load and 3-hour round-trip. This would involve approximately 11 trips per week and tipping fees at EKO Compost. Co-Composting with Yard Waste Materials and Expansion of Composting Facilities This alternative assumes the City will process their biosolids in conjunction with materials collected through their yard waste program. Currently, the City collects approximately 500 cubic yards of yard waste annually. It is estimated that the wood fraction of that volume that could be shredded into composting wood chips is approximately 20%, or 100 cubic yards. The total cubic yards needed for composting far exceeds the amount of material collected annually. Therefore, it is assumed that all material collected, even if collected volumes increase slightly from current conditions, would be segregated, cleaned, shredded and incorporated into the composting process. The composting process schematic for this alternative is shown in Figure 4-7 below. Sludge (1 volum e) 1/2 Day Mixing 21 Days Aerated Pile 2 Days Drying 1/2 Day Screening 30 Days Curing Compost Reuse! Yard W aste (3.0 volum e) Recycled W ood Chips (70% ) Figure 4-7. Composting with Yard Waste Table 4-29 provides the estimated materials balance for composting facilities using the City s yard waste at the 2045 design condition.

76 4-76 City of Hamilton Wastewater Facilities Plan Table Material Balance, 3.63 mgd, with City Yard Waste & Wood Chips Item Volume (CY/day) Total Weight (lbs) Dry Weight (lbs) Volatile Solids (lbs) Bulk Density (lbs/cy) Solids Content (%) Volatile Solids (%) Sludge ,738 4,452 2,270 1,620 18% 51% Yard Waste w/ Wood Chips (1:5) ,315 5,123 4, % 95% Recycle ,470 12,359 9, % 80% Compost ,523 21,934 17, % 78% Mix 1 Loss 1,700 1,700 Unscreened ,558 20,234 15, % 76% Recycle ,470 12,359 9, % 80% Compost ,088 7,875 5, % 69% 1 Ratio of woodchips to sludge = Woodchip recovery efficiency = 85% Based upon the above materials balance, and an assumed 2-3 day compost operation each week, the following Table 4-30 indicates expected design conditions for the composting operation at 3.63 mgd using yard waste and wood chips.

77 Alternatives Development and Evaluation 4-77 Table Compost Design Conditions at 3.63 mgd using City Yard Waste & Wood Chips Item Amount Compost Area Cubic Yards per Day Square Feet Required 1 5,814 (48 x120 ) (Cover two drying beds) Curing Area Cubic Yards per Day Square Feet Required 2 6,164 (Requires covering two drying beds) Bulking Agent (Yard Waste & Chips) Storage Cubic Yards per Day Square Feet Required 3 5,520 Recycle Storage Cubic Yards per Day Square Feet Required 4 3,531 1 Based on 9 foot pile height, with 1 foot blanket and base, includes slope 2 Based on 6 months storage, 12 foot pile height, includes slope and access 3 Based on 150 days supply, 12 foot pile height, includes slope and access 4 Based on 2 times required recycle, 12 foot pile height The above design, which incorporates the City s yard waste program at current volumes, shows that co-composing increases the required curing and amendment storage requirements. Similar to the base composting alternative, the City would plan for installation of a new compost mixer and recycle unit. In addition, this alternative would plan for purchase of a yard waste shredder. Installation of a cover over the curing and composting areas would be included to enable year-round composting operations. The following improvements would be made to the existing composting operation (excluding dewatering) for this alternative: Improvement $ Base Capital Cost Compost Mixer $30,000 Compost Area Cover (5,814 sf) $87,200 Curing Area Cover (2,680 sf) $92,500 Yard Waste Shredder $20,000 Recycle Screen Unit $30,000 Front End Loader/Bobcat Attachment $20,000 Aeration/Blowers $22,000 Paving and Miscellaneous Equipment $10,000 Total (Excluding electrical and allied costs) $311,700

78 4-78 City of Hamilton Wastewater Facilities Plan Alternative Analysis Summary The alternative for contract handling of dewatered biosolids proved to be far more expensive for the City than continuing the current biosolids program. The City, with only minor investments over time, can effectively expand their compost operation to meet future demands. In order to better handle the additional materials generated, and better address odors at the site, it is recommended that the City transition from static pile composting to aerated static pile composting. It is also recommended that the city install a compost screening system that is capable of recycling their wood chip product. This would reduce the volume of finished product and reduce the volume of new wood chips needed by as much as 80%. The alternative BM5, which involves the use of City yard waste, will require only nominal additional capital cost and annual costs. City staff have indicated that approximately 500 cubic yards of yard waste is collected annually. It is assumed that this volume will not increase significantly over the planning period. However, calculations presented assume all yard waste that is recyclable would be re-directed into the composting process. City personnel involved with the yard waste program indicate a significant amount of solid waste (in the form of plastic bags, garbage, animal waste, etc.) ends up in the yard waste stream. This material would be removed. Estimated capital and present worth calculations for the biosolids management alternatives considered are presented in Table Tipping fees at EKO Compost preclude this alternative from further consideration. Three biosolids management alternatives were also evaluated using the criteria outlined at the beginning of this chapter. Table 4-32 summarizes the evaluation. Both composting alternatives are comparable, with a higher cost associated with composting the City s yard waste material that can be offset by the greater environmental benefits of this alternative.

79 Alternatives Development and Evaluation 4-79 Table Costs for Biosolids Management, $ Thousands Description Retain/Expand Composting Process Contract Handling of Dewatered Biosolids Co- Composting with Yard Waste Materials Base Construction Cost $237.0 $0.0 $311.7 Electrical & Controls $2.0 $0.0 $2.0 Subtotal A $239.0 $0.0 $313.7 Mobilization & Bonds (5%) $12.0 $0.0 $15.7 Contractor s Overhead & Profit (10%) $24.0 $0.0 $31.4 Subtotal B $275.0 $0.0 $350.8 Miscellaneous Costs Not Itemized (20%) $55.0 $0.0 $70.2 Subtotal C $330.0 $0.0 $421.0 Engineering, Legal, Administration (20%) $66.0 $0.0 $84.2 Total Capital Cost $396.0 $0.0 $505.2 Labor Cost $15.6 $42.9 $19.6 Misc. Fuel/Power Costs $5.0 $0.0 $5.0 Haul Vehicle Costs 1 $0.9 $33.3 $0.9 Tipping Fee 2 $0.0 $121.9 $0.0 Bulking Agent 3 $6.0 $0.0 $2.7 Total Annual O&M Costs $27.5 $121.9 $28.2 Total Present Worth O&M $373.5 $1,656.4 $383.0 Total Present Worth $769.5 $1,656.4 $ $ per mile 2 Estimated $150.00/dry ton tipping fee to EKO Compost 3 $8.00/wet ton for select wood chips

80 4-80 City of Hamilton Wastewater Facilities Plan Table Evaluation Summary Evaluation Criteria Retain/Expand Composting Process Contract Handling of Dewatered Biosolids Co-Composting with Yard Waste Materials Regulatory Coordination Operations/ Technology Compatibility with Site Implementation Community/ Environmental Risk Cost TOTAL Preliminary Recommendations It is recommended that the City proceed with phased expansion of their composting operation by adding new pile mixing equipment and a compost screening unit that will recycle the wood chip products. As biosolids quantities increase, it is recommended that the City construct storage for the composting and curing areas of their composting operation and convert to the aerated static pile composting method. Composting of the City s yard waste is economically feasible and offers other environmental advantages, including elimination of burning and less quantity of bulking agent trucked to the site. It is not recommended that the City begin yard waste composting until the treatment process is converted to aerated static pile. This will enable the City to actively address odor generation from the composting process. This is extremely important, as yard waste composting has proven to be a significant odor generator. It is also recommended that, should the City choose to compost their yard waste, a vigorous policy regarding acceptable waste products be put into place and the City actively police for violations. The City will be required to sort and clean the yard waste prior to introduction into the composting treatment train. Co-composting yard waste will generate additional compost product and will result in nominal additional capital and annual operating costs. These costs are primarily associated with the additional labor required for sorting, cleaning and shredding the yard waste material. Dewatering/Drying Dewatering will provide the greatest flexibility for on-site storage and is recommended as an immediate measure to address the currently under-capacity solids drying beds. Several widely used technologies are available. The existing City biosolids drying system consists of a series of 13 sludge drying beds with a total drying surface area of 46,300 square feet. As identified in Chapter 3, the capacity of these beds is rated at 420 to 595 pounds per day dry weight solids,

81 Alternatives Development and Evaluation 4-81 depending upon type of biosolids being dewatered. The current waste sludge mass, roughly 890 pounds per day dry weight solids, now exceeds the rated capacity of the drying bed system. In addition, the City presently has two of the out-of-service drying beds in use as composting and screenings storage. Dewatering of the plant s waste sludge mass is one of the most critical bottlenecks at the City s wastewater treatment plant. The City of Hamilton was recently presented an opportunity to acquire a used belt filter press from the City of Coeur d Alene, Idaho for the cost of the equipment delivery only. Because the City is interested in evaluating mechanical dewatering as an option for their future solids dewatering needs, the City elected to obtain the equipment to conduct pilot operations to determine whether belt filter press dewatering is a viable technology for the City to consider. This used belt filter press (BFP) is a 1.2-meter BFP with a capacity of approximately 700 pounds per hour dry weight solids. This equates to approximately 4,200 to 5,000 pounds per day capacity, assuming operation of the unit would be between 6 to 8 hours per day. At the current solids loading of 889 pounds per day, operations staff could handle the full waste sludge mass from the plant while operating approximately 1.7 hours per day or 11.9 hours per work week. This assumes that the biosolids drying beds would not be in service. At ultimate buildout, with the drying beds again out of service, this machine would be able to handle the waste sludge mass estimated at 4,450 pounds per day dry weight solids. Should the machine prove to meet expected performance, the City s purchase could serve as a good interim dewatering system until a longterm dewatering/drying process is selected and implemented. The City recognizes that if the pilot is to be considered as a longer-term solution, permitting and MDEQ approvals will be required. It is likely that the City will continue to utilize their composting process for solids management. The dewatering process is used to reduce the volume of stabilized biosolids prior to transport to the compost operation. Dewatering can also be used to reduce the required amount of dilute biosolids storage. The City would prefer to continue to convert their dewatered biosolids into a Class A sludge, suitable for distribution to end users. The daily and weekly throughput capacities depend on the number of hours that the dewatering systems are run each day or week and designs are generally based upon the maximum-week loading conditions. Driving Forces Capacity Limitations. The existing biosolids drying beds are rated at a capacity of approximately 50% of current loading conditions. Additional dewatering capacity is needed at the treatment plant immediately. Permit. As described in Chapter 2 and for other solids handling processes, conversion to biological and/or chemical nutrient removal will increase sludge production. Growth. The dewatering and composting processes must grow to support the projected service area expansion. Flows to the Hamilton plant are projected to increase approximately 4% per year. Improve Process. Some dewatering alternatives would allow production of a drier sludge cake, which would improve performance of the compost operation, reduce compost operation costs, delay the need to expand the compost facilities, and require less sludge storage or dewatered sludge/compost storage at ultimate buildout.

82 4-82 City of Hamilton Wastewater Facilities Plan Alternatives Considered The dewatering alternatives impact the facility requirements and operating costs for the selected biosolids management alternative (composting). There were originally eight separate dewatering alternatives evaluated and the following were retained for detailed consideration: Install belt filter press dewatering. Install high solids centrifuge dewatering Install vacuum drying bed dewatering Install Belt Filter Press Dewatering (DW1) Belt filter press (BFP) dewatering technology operates by applying pressure to solids squeezed between two porous belts. The sandwiched solids are passed between various rollers while maintaining tension on the belt. As with a centrifuge, the sludge is initially conditioned with polymer before passing through a gravity drainage zone, which is essentially a single belt conveyor that allows an initial amount of water to drain from the solids, producing a 5-10% solids cake. Next, the solids proceed through a low pressure, or wedge zone in which upper and lower belts begin to squeeze the solids as they are passed between various rollers. The pressure is typically 5-15 psi and can be adjusted by regulating the belt tension. Finally, a high pressure zone with multiple rollers completes the dewatering, which in the case of Hamilton can reach 18% cake solids or greater. BFPs require continuous wash water during operation (unlike a centrifuge, which does not require continuous wash water) at high pressure to clear solids from the belt as it is recycled through the rollers. Thus, of the three dewatering technologies discussed in this section, BFPs will have the highest amount of filtrate to recycle to the front of the plant. Wastewater with high levels of oil and grease can blind the belt filter, despite washing, and raw influent must be adequately screened to avoid sharp objects that can damage the belt fabric. Odors can also be a concern, and require adequate ventilation of the dewatering facility. Belt width can range from approximately meters (1.5 meters is the suggested design for Hamilton) and the unit is typically sized according to the solids and/or hydraulic loading. Presses can be operated in a similar manner to a centrifuge (1-2 shifts per day over multiple days to process the solids production for the week), with a single unit sized to handle peak month conditions along with a redundant unit as a back-up. Start-up and shut-down are more rapid, noise generation is relatively less, and maintenance is not as specialized as for a centrifuge, allowing for plant staff to adequately service the unit and replace belts as needed. Multiple commercial vendors are available, with a typical example shown in Figure 4-8. As can be clearly seen, the unit is open to easy inspection, allowing for visual evaluation of cake quality at various stages of dewatering. As noted above, the City of Hamilton has purchased a 14 meter rebuilt belt filter press that is currently being installed. The City will have the opportunity to test this dewatering technology to determine whether this dewatering unit process will work well for them.

83 Alternatives Development and Evaluation 4-83 Figure 4-8. Example of a belt filter press. Gravity press zone is at the top, the low pressure wedge zone is at the front, and the high pressure zone rollers are in the rear. The belt washing station can be seen on the bottom of the unit. Install High Solids Centrifuge Dewatering (DW2) Centrifuge dewatering is based on the application of centrifugal force to digested solids in order to separate as much liquid from the cake as possible. The digester effluent is spun at rpm in a cylindrical/conical shaped bowl, utilizing the rotational force to pull solids from a clarified centrate. The central bowl contains a conveyor shaft that rotates counter to the centrifugal force, pushing solids toward one end of the unit while centrate is decanted at the opposite end. Polymer is often added prior to the dewatering feed in order to increase the efficiency of the removal process by conglomerating smaller solid particles into larger units more easily separated from the liquid phase. A well designed polymer feed system is essential to dewatering quality. Inadequate mixing, aging, or polymer feed strategies will result in increased costs and lower centrifuge efficiency. Centrate quality will vary from plant to plant, depending on the degree and type of solids processing prior to dewatering. In the case of Hamilton, the post-digestion centrate will likely be high in nitrogen content. This will have a significant impact on upstream liquid processes to which the centrate stream is recycled and must be considered when implementing such a dewatering program. The primary design criteria for sizing a centrifuge unit are the solids feed rate and concentration. The unit is continuous flow, but is often designed to process a full week of peak month solids production during 1-2 shifts, five days a week. A redundant unit with the same capacity is also recommended to be included in the general design; however is not mandatory since Hamilton has drying beds for backup. A redundant unit is not assumed for this analysis. Thus, accounting for approximately an hour to bring the machine up to speed and slow it down for clean out, the unit can be used over 5-7 days in set shifts, or run continuously for fewer days depending on the upstream sludge storage available. Centrifuge units can often produce cake solids in excess of 18% for aerobically digested WAS, making them ideal for solids processing prior to composting as they often outperform belt filter press and screw press units. A solid bowl unit typically requires minimal operator attention

84 4-84 City of Hamilton Wastewater Facilities Plan when running smoothly and has a smaller footprint relative to a belt filter press or a screw press. The device is easy to clean and can often maintain high solids cake content, assuming higher polymer dosing, at and above its design capacity. However, a centrifuge often requires specialized maintenance, is more difficult to monitor with the operator s view of the centrate and solids being blocked, has higher power consumptions and noise generation than a belt filter press, and usually requires operating experience to optimize. High-solids centrifuges (as would be specified for Hamilton s application) have also been shown to produce relative high levels of volatile sulfur compounds which can be a potential source of odor problems during cake storage (WERF, 2003). Commercially available centrifuge designs include disk nozzle, imperforate basket, and solid bowl. Only the latter can perform acceptably with digested solids and will be considered in this report. Humboldt and Sharples are leading manufacturers of solid bowl units. Figure 4-9 shows a section cut of a typical solid bowl centrifuge. Figure 4-9. Example of a solid bowl decanter centrifuge. Feed is introduced through the central shaft, centrate exists on the left of the bowl, and solids exit on the right. Install Vacuum Drying Beds (DW4) Vacuum solids dewatering beds have a long history of use. Earlier applications of this technology experienced problems with bed blinding and efficiently loss. More recent technology improvements have made this technology more viable, including enhanced system controls, better underdrain design using filter plates and better vacuum systems. The vacuum bed drying technology is very similar to the static drying bed technology the City of Hamilton currently operates, only with mechanical assistance and the ability to operate the system year-round. The vacuum drying bed works similar to a gravity drying bed system where sludge is spread over a set of media plates. Prior to this discharge, polymer is injected into the sludge and rapidly mixed. Gravity dewatering begins as the bed is filled. The clear liquid, separated from the flocculated solids, flows down through the porous media and out the bed structure. After the bed is filled to the maximum liquid level, a vacuum pump is started, creating a vacuum in the plenum and media causing a uniform pressure on the top of the sludge cakes. Motorized filtrate drain

85 Alternatives Development and Evaluation 4-85 valves discharge the filtrate from the plenum of the bed. The vacuum drying bed system combines the overall simplicity of conventional sand drying beds with the faster handling of sludges associated with mechanical systems. For most sludges, the result is a liftable cake suitable for handling within 24 hours. The recommended design for Hamilton is a 16 FT by 76 FT long bed, with an insulated building enclosure and a support equipment building that houses the vacuum pumps and controls. A schematic of the drying bed layout is shown in Figure Following removal of the dewatered sludge, the vacuum underdrain plates require washing prior to placing the system back into service. A new drying bed would need to be installed as the existing drying beds could not be retrofitted. The existing drying beds would be used for sludge storage, system redundancy and composting operations. Vacuum drying beds can produce cake dryness up to 20%+ solids. The vacuum drying bed technology offers advantages of easy, versatile operation, familiar technology, low energy costs and ease of operation. Figure 4-10 Vacuum Dewatering Bed System Install Rotary Screw Press (DW7) The screw press is a mechanical device used for liquid/solid separation. A cross section of the press is shown in Figure Liquid/solid separation is accomplished by gradually reducing the volume available for the solids as they are conveyed from the inlet to the outlet end of the screw press. The reduction in volume is achieved by using a tapered shaft that is larger in diameter at the discharge end than the inlet end, as shown in Figure The shaft is surrounded by a screen system that contains small (less than 1/8-inch diameter) holes. A typical screen is shown in Figure The screen support housing includes adjustment nuts to adjust the screen to achieve the proper clearance from the screw flights.

86 4-86 City of Hamilton Wastewater Facilities Plan The leading screw press manufacturer in the US can provide screw presses from 4 inch to 53 inch in diameter, with wetted lengths up to 30 ft. The machines are manufactured from stainless steel and are all welded. The base is typically manufactured from carbon steel, but is available in stainless steel by request. There are several drive systems available, but the most typical is a VFD driven motor, a cyclogear to reduce speed, and a chain drive. This combination provides for a final rotational speed in the range of 0.05 to 1.5 rpm. A typical rotational speed for digested solids is about 0.07 rpm. Figure Cross-Section of Screw Press Figure Typical Screw Press Screen The inlet to the screw press can be piped directly into the press or introduced through the inlet box. In either case, the inlet box is required to allow waste solids to back up into the box which places a hydraulic head on the material to force it into the screw area.