WATER RECLAMATION PRACTICES AT THE PINELLAS COUNTY (FL) RESOURCE RECOVERY FACILITY

Transcription

1 9th Annual North American Waste to Energy Conference ASME 2001 WATER RECLAMATION PRACTICES AT THE PINELLAS COUNTY (FL) RESOURCE RECOVERY FACILITY Joseph K. Robinson, PE, HDR Engineering, Inc. * Pete Stasis, PE, Pinellas County Mark Schwartz, Wheelabrator Pinellas, Inc. *HDR Engineering, Inc. of the Carolinas, 128 S. Tryon Street, Suite 1400, Charlotte, NC ABSTRACT The Pinellas County Resource Recovery Facility (PCRRF) combusts 3,150 tons per day of municipal solid waste from Pinellas County, Florida and produces 75 megawatts (MW) of electrical generation capacity. The facility requires about 1.7 million gallons per day (MGD) of makeup water for the cooling tower and up to 200 thousand gallons per day of high-purity water for boiler makeup. The facility currently uses recovered stolm water for cooling during summer months (rainy season) and treated municipal wastewater ("reclaimed water") during the winter months (dry season). The facility currently uses potable water for boiler makeup and is planning to use reclaimed water in the future. Use of reclaimed water for plant water demands is consistent with the philosophy of resource recovery. Reclaimed water, once considered a waste product, is no\\' a valuable resource in water-short areas such as peninsular Florida. Pinellas County's population of over 1 million people requires water for residential, commercial and industrial purposes. Use of reclaimed water for demands at the PCRRF minimizes the impact on limited freshwater resources and can also build support for the facility among the environmental community. Reclaimed water also has economic benefits. Tampa Bay is experiencing ever-increasing potable water costs. Potable water prices are expected to outpace inflation for the next several years to fund capital improvements associated with the Tampa Bay water program. Reclaimed water is available during the winter season, and the PCRRF has the ability to procure it from two separate sources at competitive rates. During the summer months, the facility depends more on its stolm water source. A lime softening pretreatment system processes the stolm water prior to its use in the cooling towers. Reclaimed water for boiler makeup will require membrane treatment followed by ion exchange. Microfiltration is being evaluated to remove bacteria-size particles and prevent fouling of the reverse osmosis membranes. Potable water will be used as a backup in the event of availability or quality problems with the reclaimed water supply. KEYWORDS Water reuse, resource recovery, microfiltration, reverse osmosis, boiler makeup, cooling water, reclaimed water 103

2 INTRODUCTION Fresh water resources in peninsular Florida serve residential, commercial, agricultural, industrial, recreational and environmental purposes. In many areas, the increased demand for this resource has created availability and economic challenges for users. In many cases, users are looking at alternative sources to meet their water requirements. Reclaimed water is municipal wastewater that has received a high level of treatment. These processes usually include biological treatment, solids separation, and disinfection. Advanced treatment processes include nutrient removal and effluent filtration. Reclaimed water for public access in Florida is required to receive effluent filtration and high-level disinfection. Florida Administrative Code (F AC), Chapter , governs the reuse of reclaimed water and land application in Florida. F AC establishes design and operations and maintenance (O&M) criteria for the beneficial reuse of reclaimed water, as well as for land application disposal of reclaimed water. The Florida Department of Environmental Protection (FDEP) oversees implementation of F AC Public access reuse requirements include total suspended solids of less than 5 mg/l and highlevel disinfection (F AC ). Part VII of F AC addresses the use of reclaimed water from domestic wastewater sources for cooling water, wash water, or process water at industrial facilities. Reclaimed water used for industrial purposes must meet the secondary treatment and disinfection requirements of the supplying domestic WWTP. These requirements are established in F AC FDEP does not regulate treatment that may be required at the industrial facility to meet more stringent water quality requirements for the cooling or process application. Advisory signs are required around the portions of the industrial site where reclaimed water is used and the main entrances to the site. These advisory signs notify employees and the public of the nature of the reclaimed water use; however, access control is not required. Reclaimed water flowing out of industrial processes shall be considered an industrial wastewater and shall be subject to regulation under the chapters of F AC that apply to industrial wastewater discharges. PCRRF OPERATING CHARACTERISTICS The Pinellas County Resource Recovery Facility (PCRRF) began operation in 1983 and consists of three (3) combustion units (boilers) having a combined rated capacity to mass-burn 3,150 tons per day of municipal solid water (MSW) with a heating value (HHV) between 3,800 and 5,000 BTU/lb. Each boiler is rated to produce 261,400 pounds per hour (lbs/hr) of 615 psig, 7500 F steam. This steam is directed to two (2) turbine-generators, which can nominally generate a total of 75 megawatts (MW) of electricity. Condenser cooling is achieved by a circulating water system through a five (5) cell mechanicaldraft cooling tower. Emission control consists of a flue gas scrubber, filter fabrics, a common Selective Non-Catalytic Reduction (SNCR) system and a common Powdered Activated Carbon Injection System (p ACIS) on each of the boiler trains. Energy and available capacity from the PCRRF generating units are contracted for sale to the local utility, after in-plant electrical loads have been served. Original air pollution control equipment for the boilers were electrostatic precipitators. From 1987 through the year 2000, Pinellas County invested $85 million to retrofit the air pollution control equipment in order to meet the USEP A's Clean Air Act. Wheelabrator Pinellas, Inc. (WPJ) is currently contracted by Pinellas County for operations and maintenance of the facility. PLANT WATER DEMANDS The PCRRF requires about 1.7 million gallons per day (MGD) of makeup water for the cooling tower 104

3 and up to 200 thousand gallons per day of highpurity water for boiler makeup. An additional amount of water is required for potable uses such as drinking water, toilet flushing, and hose bibs. and about 3.5 to 4 cycles of concentration when using reclaimed water. WATER QUALITY REQUIREMENTS PLANT WATER SOURCES In August 1998, Tampa Bay Water (TBW), successor to the West Coast Regional Water Supply Authority, was empowered by the Florida legislature to manage the supply of potable water to utilities located in the Tampa Bay region, including Pinellas County. Pinellas County is located in the Southwest Florida Water Management District (SWFWMD). Due to the prolonged drought, groundwater resources have been impacted dramatically in the Tampa Bay region. SWFWMD has directed TBW to reduce pumping from its existing groundwater supply wells and to fmd alternative water supplies for its customers to make up the difference. Reclaimed water is an excellent replacement source for irrigation and industrial users. Sources of water for cooling, boiler makeup and other plant purposes include reclaimed water from the cities of Largo, Florida Wastewater Treatment Plant (WWTP) and St. Petersburg, Florida WWTP, recovered storm water, and potable water from Tampa Bay Water. Table 1 provides a summary of each water demand and its corresponding sources. Table 2 provides water quality data for each of the water sources. For the sake of clarity, the table does not distinguish between the two reclaimed water sources. Reclaimed water is superior in quality to recovered storm water for almost all of the parameters measured. Consequently, the reclaimed water requires less treatment prior to use in the cooling towers. However, because the recovered storm water receives lime-softening treatment, the cooling towers are able to run at slightly higher cycles of concentration when using recovered stolm water. The cooling towers operate at about 4 to 4.5 cycles of concentration when using recovered stolm water Cooling Table 3 presents the water quality limits originally designed for the cooling water system. Boiler Makeup High-purity, demineralized water is required for boiler makeup. Table 4 presents a summary of these water quality requirements. TREATMENT PROCESSES Cooling Water Water from the two reclaimed water sources (Largo and St. Petersburg WWTPs) require very little additional treatment prior to use in the cooling towers. Chlorine is added to the cooling water supply to inhibit biological growth in the cooling tower system. The chlorine gas is stored in one-ton containers. When recovered storm water is used for cooling, the lime softening process precedes disinfection. Lime softening is used to reduce the calcium concentration in the cooling water to prevent scaling. The lime softening system will not remove dissolved solids such as chloride and sulfate. The lime softening system reduces the calcium concentration to less than 100 mgll (as CaC03) and the total hardness to less than 150 mgll (as CaC03). The cold lime softening process uses lime slurry to precipitate hardness from the solution. Soda ash is added for magnesium removal and to impro\"e settling characteristics. Hardness is the measurement of polyvalent cations, usually calcium and magnesium, in a water supply. Lime and soda ash are applied to the water stream at dosages that cause magnesium hydroxide and calcium carbonate to exceed their respective solubilities. The resultant precipitation of magnesium hydroxide and calcium carbonate removes magnesium and calcium from 105

4 the water stream. Silica and phosphorus also will be reduced, coincident with lime softening. Lime also precipitates soluble iron and manganese, and reduces total suspended solids (TSS). The high ph inherent in the process kills biological growth, thus further reducing the potential for slime (i.e. biofouling or algae growth) in the cooling system. Boiler Makeup In order to meet the requirements for boiler water makeup, extensive treatment is required. The proposed treatment system for boiler water makeup includes a 200-gpm micro filtration system, two-pass reverse osmosis (RO), and ion exchange. The micro filtration system and first stage RO is a singletrain configuration with potable water for backup. The complete boiler makeup water system is comprised of the following components: Media Filtration (Existing) - suspended solids in the feedwater. Microfiltration - Removes or reduces Removes bacteria-sized particles in the 0.1 to 10 micron range. Prevents bio-fouling of the downstream reverse osmosis membranes. The proposed system is a single 200-gpm skid mounted unit with PVDF hollow fiber membrane modules. The prefiltration assembly includes a backwashable strainer for large particulate removal, automatic reverse flow and air scrub, and integrated clean-inplace (CIP). Membrane prefiltration was selected for its reduced turbidity, higher recovery, smaller footprint, ease of operation, competitive capital cost, and reduced operation and maintenance (O&M) costs compared to other technologies. In addition, the membranes provide a reliable barrier to particulates 0.1 micron and larger. Cartridge Filtration - from particulate matter. Reverse Osmosis - Reduces Provides a secondary barrier dissolved solids. Upgrading the existing single-pass RO system to a two-pass system removes nearly all dissolved solids, substantially reducing the load on the downstream ion exchange system. Projected savings in resin regeneration costs, when added to the savings from used of reclaimed water, will offset the capital cost of the pretreatment system in a short time. Ion Exchange - Provides final polishing of the boiler feedwater. Reduces mineral and other dissolved solids concentrations to the extremely low levels required for high-purity boiler feed. Cooling water blowdown and membrane system concentrate is blended with sanitary sewage and discharged into the City of Pinellas Park sewer system. BENEFITS OF USING RECLAIMED WATER There are many benefits to using reclaimed water for plant process demands. Among these benefits are environmental, public relations, water quality, and economic savings. Environmental Benefits Use of reclaimed water for plant water demands is consistent with the PCRRF's philosophy of resource recovery. Reclaimed water is a valuable resource in water-short areas such as peninsular Florida. Pinellas County's population of over I million people requires water for residential, commercial and industrial purposes. Use of reclaimed water for demands at the PCRRF minimizes the impact on limited freshwater resources. The beneficial use of reclaimed water also reduces the quantity that must otherwise be reintroduced into the environment (disposed of) by methods such as surface water discharge and deep well injection. Public Relations Benefits Use of reclaimed water can build support for the facility among the environmental and regulatory community. This can be particularly important when siting a resource recovery facility or relicensing an existing one. The improved public perception received by championing water reuse can potentially offset possible objections to the facility. 106

5 Water Quality Benefits Depending upon the degree of treatment received, reclaimed water often has better water quality characteristics than raw surface or groundwater supplies. For example, in areas with hard groundwater, calcium and magnesium ions are by using reclaimed water whenever it is available for boiler makeup. This saving will increase each year as the cost of potable water increases. The PCRRF is currently realizing even greater savings from its cooling water makeup system as it is using reclaimed water and recovered storm water for this purpose. removed as part of the water treatment process. When the water is subsequently introduced into the sewer system, it has the benefits of already being softened. The same concept applies to raw water supplies with high dissolved solids content. Membrane processes at the water treatment plant remove chloride ions thereby reducing the CHALLENGES TO USING RECLAIMED WATER Along with the benefits of using reclaimed water, there are also several challenges inherent with the use of this resource. concentration of total dissolved solids and conductivity. This particular benefit would be voided, however, in coastal areas with aging sewer collection systems that allow saltwater infiltration Availability During the summer months (rainy season), the PCRRF depends more on its storm water as a into their system. primary makeup water source. Competition for Economic Benefits Reclaimed water use also has economic benefits. Tampa Bay is experiencing ever-increasing potable water costs. Potable water prices are expected to reclaimed water increases due to landscape irrigation needs of the residential community and other commercial customers. Reliability outpace inflation for the next several years to fund The potential exists for process upsets at the capital improvements associated with the Tampa Bay Water program. Reclaimed water is available during the winter season, and the PCRRF has the ability to procure it from two separate sources at competitive rates. Based on a nominal demand at the PCRRF of 200 kgal per day for boiler makeup and a potable water cost of $5.41 per kgal, the cost of providing potable water for boiler makeup is about $32,500 per month. Reclaimed water is available to the PCRRF for $0.25 per kgal. Based on an influent demand of 250 kgal per day (some water is lost during the additional treatment required for reclaimed water), the cost of providing reclaimed water for boiler makeup would be about $1,900 per month. Another $12,000 per month is allowed for capital recovery and operational costs of the pretreatment equipment in the boiler feedwater train. Thus, the PCRRF will save about $18,600 per month ($223,000 per year) wastewater treatment plant that provides the reclaimed water. The PCRRF has two sources of reclaimed water (Largo and St. Petersburg) that essentially serve as a backup for each other. Potable water is proposed as a backup for the boiler makeup treatment system. There are also diurnal and seasonal variations. Depending upon the length and the configuration of the sewer collection system, reclaimed water availability peaks lag potable water demand peaks by several hours. Onsite or offsite storage can be used to attenuate diurnal peaks. Seasonal variations must be compensated for with alternative water sources, such as recovered storm water. Water Quality Reclaimed water can cause biofouling of downstream treatment equipment such as reverse osmosis (RO) membranes. Microfiltration will be used to removed bacteria-sized particles in the

6 to 10-micron range and reduce the potential for biofouling. A chlorine residual will be maintained if necessary. The RO membranes will be constructed from cellulose acetate and are not damaged by chlorine. The PVDF micro filtration membranes are resistant to oxidation and can also operate when a chlorine residual is present. Phosphates might exist in the reclaimed water supply as a result of their use as corrosion inhibitors in the public utility's water treatment process and from industrial discharges. Phosphates are often not removed from reclaimed water supplies because it can be beneficial to turf grass customers. If not removed, phosphates can limit the cycles of concentration for the cooling tower system. The RO system will remove phosphates from the boiler makeup water. Depending upon the disposal method of cooling tower blowdown, use of reclaimed water might require additional treatment to meet regulatory requirements. At the PCRRF, blowdown is blended with sanitary sewage and disposed of in the City of Pinellas Park sewer system. No additional treatment is required by the PCRRF. Charlie McAllister, Systems Components Corporation Rick Moro, Pall Corporation REFERENCES Florida Department of Environmental Protection. Chapter , Florida Administrative Code: Drinking Water Standards, Monitoring and Reporting. Florida Department of Environmental Protection. Chapter , Florida Administrative Code: Reuse of Reclaimed Water and Land Application. Pinellas County Resource Recovery Facility Capital Replacement Project. June Wheelabrator Pinellas Cooling Water Treatment Log Sheets (May, June and September 2000). Wheelabrator Pinellas, Inc. Consolidated Management Agreement. Appendix D. Wheelabrator Pinellas, Inc. Monthly LSS Influent and Effluent Water Analyses (2000). CONCLUSIONS Use of reclaimed water for power plant cooling and boiler makeup is consistent with the PCRRF's philosophy of resource recovery. It provides environmental, public relations, water quality, and economic benefits to the facility and the surrounding community. Although there are several challenges to the use of this resource, sound solutions exist for each of them. ACKNOWLEDGEMENTS Steve Reinhart, Wheelabrator Ridge Energy Robert Henson, Wheelabrator Pinellas Daniel Penn, Wheelabrator Pinellas Ron Larson, PE., HDR Engineering 108

7 Table 1 Water Demands and Sources Demand :, : 'PiimarY Source - Secondary Source Cooling Water - Winter Largo Reclaimed S1. Petersburg Reclaimed Cooling Water - Summer Recovered Storm Water Reclaimed Water Boiler Makeup - Current Potable None Boiler Makeup - Proposed Reclaimed Potable Potable Potable (Tampa Bay Water) None Table 2 Water Quality Summary (Based On Monthly LSS Influent Water Analysis) Parameter p. '{ lli:fsj 'r eolaim!wat r ',, tomi_ Water, Potable Water.; ; )';4-,.; _: ;.. ','0:,,"' " f' f ph SU to 8.5 Conductivity Ilmhos 786 1,777 NS Ca1ciwn (as CaC03) mgil NS Hardness (as CaC03) mgll to 200 Total Alkalinity (as mgil NS CaC03) Chloride mgll <250 Sulfate mgil <250 Turbidity NTU to 1.0 Sources: Monthly LSS Influent and Effluent Water Analyses (2000) Wheelabrator Pinellas Cooling Water Treatment Log Sheets (May, June and September 2000) Primary and Secondary Drinking Water Standards, 62 FAC 550: Drinking Water Standards, Monitoring and Reporting. J\otes: NTU - Nephelometric Turbidity Units NS - no standard 109

8 Table 3 Water Quality Requirements for Cooling Parameter ;.,.. "'.... "..! Conductivin.r Calcium Total Chloride Sulfate Source: SU. "D". Consolidated Wheelabrator Pinellas Inc Table 4 Water Quality Requirements/or Boiler Makeup (CRP),..,. Calcium Total Silica as Free Chlorine Conducti as <0.1 <0.1 <0.1 <0.020 <0.1 <10 lacement 'r,,' ect. PCRRF. 110