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1 WEFTEC 2012 Technical Session Proposal Form IMPORTANT NOTE: Please complete all items. This outline is formatted to complete on a computer and does not leave adequate room for hand-written responses. Submitted by: Name and Organizing WEF Committee (or Other Group): Supporting WEFTEC Program Committee Symposium: SESSION DESCRIPTION Proposed Session Title: Session Format: (check one): Platform Panel Discussion Combination of Both Brief session description (to be used to judge the session and in publicity if selected; a paragraph or two is adequate, but more can be provided if needed): Is this session on a hot topic? YES NO Why? How is the information in this session different or unique from what may come from the call for abstracts? Session keywords: (List or select from attached list) AUDIENCE INFORMATION Who is the target audience for this session? (List or select from attached list) Does this session apply to professionals in water, wastewater, or stormwater? (circle all that apply) WATER WASTEWATER STORMWATER Estimated Attendance: SESSION DETAILS Will this session require different set up (standard is theater seating, podium, head table seating for 2 people, 1 LCD projector/screen)? YES NO If yes, why and what is needed? Is this a full session or half session? FULL HALF A full session consists of 3 hours of presentations with a ½ hour break in the middle; half sessions are 1 ½ hours with no break.

2 Will all speakers provide a manuscript for the proceedings? YES NO If no, please justify. Will any speaker require any assistance (registration for the session, etc.)? YES NO If yes, please justify. Proposed Moderator: Please note that we will send all future correspondence regarding this session to the moderator unless you specifically request here that someone else be included on all communication. Name: Proposed Assistant Moderator 1: Name: Proposed Assistant Moderator 2: Name: Proposed Speakers and Topics: Please list each speaker, and include a one to three page abstract in this proposal for each topic or speaker in the session. If this is a panel, please include the list of speakers and any more detail needed for their topics. Speaker 1: Name Affiliation Title of Presentation Speaker 2: Name Affiliation Title of Presentation Etc. as needed ACKNOWLEDGEMENTS By submitting this, I agree that I have informed the proposed speakers that all are required to prepare a paper for the proceedings, meet all deadlines associated with the presentation, and are responsible for associated registration, transportation, and housing fees, unless an exception is specifically requested above and granted by WEF before final acceptance of this proposal. Moderators and Assistant Moderators have also been informed that they are responsible for their own registration, transportation, and housing fees. Submitter sign here:

3 SESSION KEYWORDS (CIRCLE ALL APPLICABLE) Collection Systems Infiltration/Inflow Potable Water Industrial Water/Wastewater/Process Water Hazardous Materials/Wastes Toxic Substances Groundwater Odor/Air Emissions Legislation (Policy, Legislation, Regulation) TMDLs Public Education/Information/Communication Biosolids/Residuals/Sludge Utility Management Asset Management Environmental Management Systems Alternative Delivery Systems (Design-Build- Operate-Transfer) Workforce Issues / Professional Development Water Reuse Water Recycling Water Reclamation Watershed Management Surface Water Laboratory Methods and Analysis Health and Safety Issues Operations and Maintenance Nutrient Removal Phosphorus Nitrogen Innovative Technology Wet Weather CSOs/SSOs Stormwater Green Infrastructure Decentralized/Distributed Systems Sustainability Energy Conservation/Management Climate Change Greenhouse Gases Infrastructure Process Design Modeling Information Technology Automation SCADA GIS Disinfection Pathogens Membranes Security Research Natural Treatment Systems Microconstituents EDCs PPCPs Nanoparticles Global/International Issues Developing Countries Other (please specify):

4 DEMOGRAPHICS (please use both lists to select target audience) Organization: 1. Municipal/District Water and Wastewater Systems and/or Plants 2. Municipal/District Wastewater Only Systems and/or Plants 3. Municipal/District Water Only Systems and/or Plants 4. Industrial Systems/Plants (Manufacturing, Processing, Extraction) 5. Consulting or Contracting Firm (e.g., Engineering, Contracting and Environmental) 6. Government Agency (e.g., US EPA, State Agency, etc.) 7. Research or Analytical Laboratories 8. Educational Institution (Colleges and Universities, Libraries and other related organizations) 9. Manufacturer or Water/Wastewater Equipment or Products 10. Water/Wastewater Product Distributor or Manufacturer s Rep 11. Other (please specify): 12. Public Official (e.g., Commissioners, Board Members, etc.) Job Function: 1. Upper or Senior Management (e.g., President, Vice President, Owner, Director, Executive Director, General Manager, Mayor, Commissioner, Board Member, etc.) 2. Engineering, Laboratory and Operations Management (e.g., Superintendent, Manager, Section Head, Department Head, Chief Engineer, Division Head, etc.) 3. Engineering and Design Staff (e.g., Consulting Engineer, Civil Engineer, Mechanical Engineer, Chemical Engineer, Planning Engineer, etc.) 4. Scientific and Research Staff (e.g., Chemist, Biologist, Analyst, Lab Technician, etc.) 5. Operations (e.g., Shift Supervisory, Foreman, Plant Operator, Service Representative, Collection Systems Operator, etc.) 6. Purchasing/Marketing/Sales (e.g., Purchasing, Sales Person, Market Representative, Market Analyst, etc.) 7. Educator (e.g., Professor, Teacher, etc.) 8. Student 9. Other (please specify):

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6 You ve Got Grit Slurry. Now What? Three case studies of successful grit slurry pumping systems serving large combined sewer systems Mike Gerbitz, PE Donohue and Associates, Sheboygan, Wisconsin, USA INTRODUCTION The purpose of preliminary treatment systems is to remove debris and grit from raw wastewater and protect downstream processes from those materials. Screening devices remove debris. Grit removal basins remove grit. Grit that accumulates and concentrates at the bottom of the grit removal basin is referred to as grit slurry. Removing, conveying, and processing grit slurry has been problematic at many treatment facilities, particularly those serving combined sewer collection systems. Ironically, a unit process that is intended to prevent or reduce downstream maintenance is often plagued with maintenance issues. Frequent problems include plugged grit slurry collection sumps, plugged grit slurry piping, failed grit slurry pumps, and plugged grit slurry concentrators. Nevertheless, adherence to some sound design and operating strategies can avoid or minimize the occurrence and/or severity of these problems. STRATEGIES FOR EFFECTIVE GRIT SLURRY EXTRACTION AND PUMPING Grit slurry pumping strategies that have proven effective at minimizing the occurrence and/or severity of grit slurry plugging issues are outlined below. Provide fine screening upstream of grit removal Fine screening upstream of grit slurry pumping is the most effective strategy to reduce a grit slurry system s vulnerability to plugging. Systems that are not preceded by effective screening must be designed to be tolerant of large debris. The adherence to the other strategies that follow is particularly important for grit slurry pumping systems that are preceded by either coarse screens or fine screens that offers the potential for long narrow material to pass downstream. Gerbitz, You ve Got Grit Slurry. Now What?, Page 1 of 4

7 Select grit slurry processing equipment consistent with the upstream the screening system Some grit concentrating equipment have relatively small-diameter openings and are more prone to catching debris that cause subsequent plugging. Select a grit slurry pumping rate that provides a peak grit slurry concentration of 1% Experience has shown this strategy yields grit slurry pumping rates considerably larger than those proposed by some prominent grit system manufacturers. Continuously pump the grit slurry Some grit removal system manufacturers recommend intermittent grit slurry pumping. Pumping intermittently increases the concentration of the grit slurry as well as the problematic debris accumulated in the grit sump and grit slurry piping. Select a grit slurry pipe diameter that provides a line velocity of 5 fps This velocity prevents accumulation of grit and debris in the grit slurry piping. Provide redundant grit slurry pumps and pipes Grit slurry pumps are susceptible to plugging. Redundant pumping is always warranted at critical unit processes. Provide redundant grit slurry pipes Grit slurry piping at any facility is susceptible to plugging. Redundant piping is as important as redundant pumping, particularly if the grit slurry piping is long and includes multiple bends. Use flooded suction grit slurry pumps Flooded suction pumping benefits from the advantage of the hydrostatic head above the grit slurry pump centerline to push the grit slurry into the pump. Provide a high capacity source of fluidizing water in the vicinity of the grit slurry pump suction This fluidizing water may prove necessary when extreme wet weather grit loadings inundate the pump suction, most likely because of a power outage or pump malfunction. Provide a flushing water connection that provides a flushing velocity of 5 fps This velocity is necessary to push grit from the piping when a grit pump is removed from service. In addition, the high pressure and capacity water can be effective at clearing a plug. Use smooth-lined pipe A smooth interior is less prone to plugging. Gerbitz, You ve Got Grit Slurry. Now What?, Page 2 of 4

8 Do not connect two or more grit slurry pipes Connective valves and fittings have proven to be catch points for debris. Locate grit slurry pumps as close to the grit sump as possible Use full-port valves Do not use check valves Minimize pipe bends Use long-radius bends Use grooved pipe couplings Provide adequate slope to promote drainage between cycles CASE STUDIES The three large ( mgd) Midwest grit removal systems outlined in the table below were designed and commissioned in the early 2000s. Each serves a combined sewer collection system. The grit slurry conveyance and processing systems were designed in accordance with all or most of the previously outlined strategies. The successful long-term operating experience of these systems reveals that these strategies can eliminate or minimize the occurrence and/or severity of problems that have plagued many systems. The presentation will review design parameters, flow schematics, physical layouts, and historical performance. Facility South Shore Milwaukee, WI Collection System Peak Flow (mgd) Combined 300 Removal System Horizontal Flow Decatur, IL Combined 125 Detritus Fort Wayne, IN Combined 100 Vortex Dewatering System Year Commissioned TeaCup 2003 Conical Washer Hydrocyclone and Classifier Gerbitz, You ve Got Grit Slurry. Now What?, Page 3 of 4

9 CONCLUSIONS Industry-wide experience has found grit slurry extraction, conveyance, and processing systems are frequently plagued with plugging issues. Adherence to some well conceived design and operating strategies can minimize the occurrence and/or severity of problems. Gerbitz, You ve Got Grit Slurry. Now What?, Page 4 of 4

10 Characterisation of Grit to Develop an Integrated Plant Solution Susan Kitching, MWH Global Introduction Grit entering a plant is dependent on the catchment and sewer system, the geology of the area and infiltration however traditional design practice revolves around a single particle size and density. Understanding the true nature of the grit in different conditions led to an integrated plant solution at North Head WWTP in Sydney, Australia. North Head is Sydney Water s second largest treatment plant, treating an average dry weather flow of 350Ml/d. The plant has a large, flat sewer system and a separate wet weather network. This can lead to problems with grit deposition in the network and flushing of these deposits during wet weather events. During the commissioning of an upgrade and extension of the aerated grit facility it became clear that a greater understanding the characterisation of the influent grit was key to developing an overall solution for the site. The Problem Grit is commonly specified as inorganic material with a particle size of 0.2mm and a specific gravity of Whilst this has been based on research of a variety of different systems it may not reflect the true nature of the grit in the influent to a specific plant, which will consist of different size and weight particles. The geology of Sydney is predominantly sandstone and therefore as well as typical grit particles entering the network and sand from the coastal regions, sandstone also forms part of the grit coming into the plant. Kitching, Characterisation of Grit to Form an Integrated Plant Solution, 1

11 The Project The Process, Reliability and Renewals Upgrade at North Head WWTP included the upgrade and extension of the existing aerated grit tanks to process large grit loads in wet weather due to the configuration of the sewer network. In commissioning phase of the project, the grit removed varied significantly between tanks, although operating parameters and hydraulic balancing was equal across the system. In addition, grit was still entering the sludge stream in wet weather, leading to fears that the capacity and performance of the anaerobic digesters would be compromised over time by grit deposition. A sampling program was set up to establish the characterisation of grit being captured by each of the four tanks and that being collected within the primary sludge stream to characterise the grit within the system overall. The results were analysed for particle size distribution and density of the particles. Results The results showed the system was complex, with a number of different factors causing the particles to move in different directions: Heavier particles followed the path of least resistance; Lighter particles would pass through in different directions; Movement of grit particles was influenced by influent pump operation, channel mixing and geometry of the tanks; A significant proportion of the grit in wet weather were small, light particles which were passing through to the sludge stream. Kitching, Characterisation of Grit to Form an Integrated Plant Solution, 2

12 The combination of the profiling and the computation fluid dynamic modelling was then used to form a solution for the plant, with a combination of operational changes, grit tank optimisation and wet weather sludge degritting. This philosophy has now been carried forward to a current study at Sydney Water s largest treatment facility to ensure that the best overall plant solution is found based on the true nature of the grit for protection of the digestion stream. Kitching, Characterisation of Grit to Form an Integrated Plant Solution, 3

13 Critical Grit Removal Design Considerations for Retrofits and Additions at Existing Facilities Robert J. Kulchawik P.E. AECOM Senior Associate, BS Civil Engineering 1979, Illinois Institute of Technology Background and Objective Many wastewater treatment facilities have aging or inefficient grit removal systems with excess solids build-up occurring in downstream sedimentation tanks, channels, aeration tanks and digesters with resulting abrasive wear on solids handling pumps and additional maintenance for cleaning. Inefficient grit systems also lead to a grit product that contains excess organics with odors in the materials handling areas. Retrofits and additions can often include limited space for construction of new processes, difficulty in maintaining existing grit removal during construction, phasing of tie-ins, and hydraulic limitations. The objective of this paper is to review critical grit removal design considerations including grit characterization, grit removal technologies, hydraulic considerations, grit pumping and conveyance, grit washing, and grit storage. Examples at a wide range of facilities will be presented to illustrate the issues. Grit Characterization Traditional grit removal design has commonly been based on settling velocities of clean sand particles of the same size. Actual grit settling velocities vary widely because the particles are irregular in shape and are coated with grease or organic matter that impacts the settling velocity. Sizing and performance requirements for grit removal systems can be properly specified by sampling of incoming grit to obtain a Sand Equivalent Size (SES). Figure 1 shows grit samples taken at four locations at the 22.5 MGD Naperville, Illinois Springbrook WWTP. Figure 2 shows the SES particle size distribution by cumulative percent greater by micron size fraction. The SES a particle size distribution at the Naperville facility were used to evaluate alternative grit removal processes for retrofitting the existing aerated grit system. Kulchawik, Critical Grit Removal Considerations for Retrofits and Additions at Existing Facilities, Page 1 of 4

14 Other factors that should be considered include seasonal variations, wet weather first flush events, and estimated grit volumes. Grit Removal Technologies A range of existing facilities will be reviewed to present design features and lessons learned including proportional weir tanks, detritor tanks, aerated grit tanks, and vortex grit tanks. Hydraulic Considerations Control of flow to grit tanks is critical for efficient grit removal. Features to consider include: Tangential laminar flow into vortex grit tanks Baffles at aerated grit tanks to prevent grit carry over Equal flow distribution to multiple tanks CFD modeling for simulations Grit Pumping and Conveyance Grit loads for conveyance can vary widely. Design criteria must be established for sizing and redundancy. Alternative methods of pumping and conveyance will be presented including: Dry pit pumps with flooded suction condition Vertical cantilever dry pit submersible pumps Submersible pumps Self Priming dry pit pumps with suction lift Air Lifts Screw Conveyors Sluice troughs Based on performance experience, dry pit pumps with flooded suction have been shown to be most reliable with direct discharge to washer classifiers. Piping systems should include the following features: Minimize bends at pump suction. Provide long radius bends with provisions for cleanouts. Include provisions for flushing discharge lines by use of quick-connect fittings for connection of hoses for flushing. Consider grooved type joints for easy disassembly for maintenance. Kulchawik, Critical Grit Removal Considerations for Retrofits and Additions at Existing Facilities, Page 2 of 4

15 Pump Hydraulics should consider: Adequate velocities in the range of 4 to 5 fps Friction factors can vary widely. System curves should evaluate the full range of conditions. Grit pumps commonly include relatively flat pump curves. Consider variable sheaves or variable speed drives to allow for field adjustment. Consider use of grit pumps for drainage of tanks. Evaluation should consider varying suction head conditions. Grit Washing Grit will contain organic material that can be a major source of plant odors when stored unless proper washing and classifying are provided. Aerated grit tanks can provide some initial washing as a result of the rolling pattern within the grit tank. Advantages of grit washer classifiers will be presented including: Cyclone or tea cup devices for washing and dewatering with discharge to screw classifier. Screw classifier with baffles and shaftless screw conveyor Conical tanks with mixers and water or air scour with screw conveyors for discharge. Grit Storage Properly sized washer classifiers should provide a dry washed product containing minimal organic material. To avoid disposal as a special waste, the grit material should pass a paint filter test that limits the amount of moisture that is acceptable. The size and type of disposal containers should be determined by local disposal methods and quantities of grit. Note that grit is not a flowable material and will mound in a conical shape. Thus provisions are required for operators to periodically manually rake the grit pile, or space should be provided to move the container back and forth to equalize the grit loading piles. Closing Inefficient grit removal has been found to be have a major impact on plant reliability and operating costs. Sampling of grit prior to commencing grit system upgrades is an important step in sizing and evaluating the requirements of a grit removal system. Although grit removal is one of the oldest and most basic liquid treatment processes, recent advances and practices have been able to optimize the efficiency of grit removal to reduce operating costs and improve the efficiency of downstream processes. Kulchawik, Critical Grit Removal Considerations for Retrofits and Additions at Existing Facilities, Page 3 of 4

16 Figure 1 Sand Equivalent Size Figure 2 Grit Distribution by Particle Size Kulchawik, Critical Grit Removal Considerations for Retrofits and Additions at Existing Facilities, Page 4 of 4

17 How to Baffle a Vortex By Brian F. McNamara The Problem An ineffective grit removal system can exacerbate operations for down stream unit processes in a wastewater treatment plant, but the economical impacts may not justify the expense of capital dollars for replacement with an alternative technology. In response to this conundrum a municipality desired to improve the performance of two identical grit vortex systems at two separate wastewater treatment plants (WWTP). The owner desired to identify the root inefficiencies of the vortex systems and implement improvements to the unit processes. Goals & Objectives The Hampton Roads Sanitation District (HRSD) owns and operates thirteen (13) WWTPs in southeastern Virginia. Two of these WWTPs have subpar grit removal performance with forced vortex units. Both WWTPs use identical design 360 degree vortex units. HRSD embarked upon a vortex grit removal improvement study with the following five goals: 1. Use computational fluid dynamics (CFD) to model the existing forced vortex system. 2. Use field data to verify the CFD model results and calibrate accordingly. 3. Identify the inefficiencies of the vortex operation. 4. Develop a series of baffle arrangements for model simulation and assess impact for desired improvement. 5. Implement most probably baffle arrangements for full scale testing and evaluation. McNamara et al. How to Baffle a Vortex 1 of 6

18 Methods & Tactics ANSYS Fluent release 13 CFD software was employed for this project. The software was modeled on a cluster network of five high speed desktop computers. The computer cluster arrangement made it possible to expeditiously model a dense mesh computer grid of over 1,000,000 simultaneous calculation points. Hydraulic simulations were modeled in the steadystate condition while batch loads of over 100,000 grit particles were introduced. A range of grit particle characteristics were developed with respect to size (100 to 800 µm), sphericity factor, Stokes shape factor, and density range (1.5 to 2.65) to simulate reality. CFD model results were field verified by: rhodamine dye testing for hydraulics, grit sampling analysis performance evaluation using the vertical sampler and wet sieve method, and acoustic Doppler profiling of internal and effluent hydraulic velocities. Vortex inefficiencies were revealed by examining model runs of various hydraulic scenarios. Baffle ideas were generated based on vortex manufacturer literature and observations of the base vortex simulation results. Results & Conclusions The three dimensional graphic of the 360 degree forced vortex is shown as Figure 1. Field test validated that the model could be used for simulations. The base case simulation model was verified by dye testing and grit sampling. Figure 2 shows the cumulative collection efficiency of the vortex model based on the simulation at three hydraulic flow rates. The hydraulic rate of 25 MGD was calculated to achieve a removal efficiency of 40% which was comparable to a field verified efficiency of 48% at 22 MGD. The dye performance of the computer simulation and the field dye test are shown together as Figure 3. The simulation and the field test corroborated and revealed that there existed a substantial amount of hydraulic short circuiting through the vortex. The effect of specific gravity upon collection efficiency is graphically displayed on Figure 4. McNamara et al. How to Baffle a Vortex 2 of 6

19 Higher density particles exhibit higher collection efficiency while lower density particles exhibit lower collection efficiency. Baffle configurations were designed to address the hydraulic short circuiting and thereby redirect the grit into the vortex chamber to improve performance. Two of the baffle designs for simulation are shown as Figures 5 and 6 respectively. At this writing baffle simulations are still under evaluations and final results are expected this December 2011 for publication. McNamara et al. How to Baffle a Vortex 3 of 6

20 Figure 1 Figure 2 McNamara et al. How to Baffle a Vortex 4 of 6

21 Figure 3 Figure 4 McNamara et al. How to Baffle a Vortex 5 of 6

22 Figure 5 Figure 6 McNamara et al. How to Baffle a Vortex 6 of 6

23 The Last of the Neglected Treatment Processes - Rewriting the Manual of Practice No. 8 Grit Removal Sections Joel C. Rife, P.E., CDM Background and Objectives As the science and art of wastewater treatment evolves, the degree of understanding and innovation associated with each unit process increases the further the unit process is downstream of where the raw wastewater enters the plant. This trend was evidenced in the latest rewrite of the WEF Manual of Practice (MOP) No. 8, Chapter 12 Preliminary Treatment Section. This section in what many regard as the most important manual for establishing good design practice for the profession required extensive revisions in nearly all aspects of the previous version to bring the section up to date. The obvious reason for this was that proper understanding and innovation has only in recent years started to occur in this area of the plant. The purpose of this paper is to discuss the MOP 8 revisions and the basis for them. In several ways, design practice in Europe, where strict regulations on headworks residuals have been in place for longer than the U.S., are the justification for the revisions. Summary of MOP 8 Revisions Benefits of Grit Removal: In addition to well known effects of poor grit removal, abrasive damage to downstream equipment and taking up valuable treatment space in aeration basins and digesters, MOP 8 now lists one of the most aggravating effects of poor grit removal to operators: the inability to pump sludge from primary clarifiers due to excessive thickness of the primary sludge. The greater the diameter of primary clarifier, the worse this problem becomes. WEFTEC-12 Rife, The Last of the Neglected Treatment Processes - Rewriting the Manual of Practice No. 8 Grit Removal Sections Page 1 of 3

24 What do we call the pumped grit flow stream? MOP 8 establishes an official term for the grit/water mixture pumped from the primary grit removal tanks for further processing as grit slurry. This is necessary to differentiate this flow stream from the dewatered grit final product. Grit Quantities and Characteristics: Based on modern (2008) survey data, MOP 8 establishes a range of grit quantities from 0.5 to 20 ft 3 MGD, with an average of 5 ft 3 /MGD, and a revised standard for well washed grit (90-percent solids with minimal organics). Aerated Grit Basins: These are no longer referred to as chambers, an outdated term. Screw augers for grit collection was established as the preferred practice to less successful methods, such as chain and bucket elevators. The use of air lifts is discouraged. The most significant change was related to dimensioning of the basins, with recommendations for longer (L:W of 3-8:1) and narrower (W:D of 0.8 1) aerated grit basins with steeper floor slopes (30 ). Poor dimensioning is the most common cause of aerated grit tank failure. CFD modeling for baffling placement to improve existing aerated grit tank operation is also encouraged. Vortex Grit Systems: Better explanation of the functioning of these systems is provided with clearer differentiation between mechanical and induced vortex systems. Multi-tray Vortex Systems: Completely absent from the previous MOP 8, this proprietary technology, rapidly becoming a standard for the industry, is now included. Primary Sludge Degritting: Previously included in the primary clarifier section, the discussion of this practice is now more appropriately included in the grit removal section. Grit Slurry Processing: Formerly referred to as grit washing, this section was significantly expanded to include all currently available technologies other than the standard cyclone/classifier, including oversized clarifier classifiers and the conical grit washers that are commonly used in Europe and increasing in popularity in the US. WEFTEC-12 Rife, The Last of the Neglected Treatment Processes - Rewriting the Manual of Practice No. 8 Grit Removal Sections Page 2 of 3

25 Performance Testing: A new section describes modern methods of measuring grit removal performance, including using primary sludge sieve analyses for determining grit pass-through. Impact of MOP 8 Revisions on Standard Practice The most significant of the MOP 8 revisions is the redefinition of proper design criteria for aerated grit basins. Aerated grit basins were once the industry standard but poor performance resulted in replacement with mechanical vortex processes. Yet the mechanical vortex processes have also experienced problems, with the most common being the inability to respond to heavy surges in grit loading, resulting in poor performance and plugging of the sumps. As more and more properly designed aerated grit basins are installed, the ability of this process to better respond to erratic grit loading patterns could result in a resurgence of this technology. Inclusion of modern grit removal and grit slurry processing methods, such as the conical tray vortex separator and conical grit washers, should also have a impact on industry trends. With the conical tray separator combining the high grit removal efficiencies of conservatively sized aerated grit basins with the small footprint of a vortex grit system, the market share of this technology is expected to continue to grow. The conical grit washers should also see rapidly increasing popularity as the demand for cleaner grit disposal increases and decreased maintenance needs of this technology are realized. Grit removal is one of the few wastewater treatment processes without established methods of measuring performance. There are still widely varying philosophies on how best to measure grit quantities upstream and downstream of the grit removal processes and there is a great need for standardization. Inclusion of performance measuring methods in MOP 8 should help bring greater attention to this issue, enhancing the ongoing improvements to currently available performance testing methods with an eventual goal of establishing a standardized method. WEFTEC-12 Rife, The Last of the Neglected Treatment Processes - Rewriting the Manual of Practice No. 8 Grit Removal Sections Page 3 of 3

26 A Side by Side Comparison of Grit Removal Technologies: Mechanically Induced Vortex vs. Stacked Tray Jeff Sober 1, Steve Kramer 2, Jeff Ray 2, Bruce Cole 2, Dolan McKnight 2 1 Carollo Engineers, Dallas, TX 2 North Texas Municipal Water District, Wylie, TX *To whom correspondence should be addressed. jsober@carollo.com. The Problem The North Texas Municipal Water District (NTMWD) operates the Panther Creek Regional WWTP (PCRWWTP) in Frisco, Texas. PCRWWTP is a conventional activated sludge process plant which was recently expanded from 5 MGD Annual Average Day Flow (AADF) to 10 MGD AADF. The recent expansion at the facility included the doubling of almost all existing process units, including the grit removal system. In lieu of installing an identical grit system, NTMWD made the choice to install a Stacked Tray (Hydro International Headcell) style grit removal system adjacent to the existing mechanically induced vortex system to achieve optimum grit removal. The existing grit removal system has a 2 HP paddle mixer to maintain a mechanically induced vortex. The unit has a stated capacity of 30 MGD, which is equivalent to PCRWWTPs Peak Daily Flow (PDF). The grit basin lower chamber is fluidized on a timer every hour and pumped to a hydro-cyclone for washing and is then dewatered in a screw conveyor which discharges into a dumpster. Goals and Objectives NTMWD wanted to achieve greater grit removal efficiency to protect downstream equipment. To optimize the system, and improve grit removal efficiency, the design team chose to automate the grit system and install a stacked tray grit removal unit. The stacked tray system was sized to handle a 15 MGD flow, rather than the plant peak of 30 MGD. This decision was made in an effort to lower capital cost, because the existing vortex system is rated for the 30 MGD peak. The system was completely automated to be capable of treating the 30 MGD peak while Sober, A Side by Side Comparison of Grit Removal Technologies: Mechanically Induced Vortex vs. Stacked Tray Page 1 of 5

27 efficiently utilizing the stacked tray. The system was arranged so that the first 15 MGD, as measured by the influent flow meter, would be directed through the stacked tray grit system, which is claimed to achieve grit removal down to 100 microns. When the flow increases above 15 MGD, the system opens the gate to the vortex unit, and then closes the gate to the stacked tray for flows between 15 to 30 MGD. The stacked tray grit system is constantly fluidized and pumped to a cyclone-style washing unit, separate from the existing hydro-cyclone, and then discharged onto a belt for gravity dewatering, before being discharged into the dumpster. The two systems operate independently from each other, allowing a side by side comparison of actual grit removal efficiency to take place. Testing Protocols A battery of tests where completed to provide a sound data set to compare and contrast removal efficiencies of each system. Two testing protocols were used. One test was completed by a third party contractor to verify the removal efficiencies of the grit basins themselves. This first test focused on the quantity (volume) and quality (size of grit) being removed in just the grit basin. A second and third test was completed by NTMWD to look at the actual amount of material removed through not only the grit basin, but the organic washing and dewatering units as well. This testing protocol also included measure the volume of grit disposed of in the dumpster, and sampling for Total Solids and Volatile Solids to compare and contrast the dewatering and organic washing capabilities of the two systems. Results The third party testing was conducted by Grit Solutions. The focus of this test was the removal efficiency of the two grit basins only. The grit basins were isolated and run with a seed sand. Samples were taken before and after the basin to compare the removal efficiency. The stacked Sober, A Side by Side Comparison of Grit Removal Technologies: Mechanically Induced Vortex vs. Stacked Tray Page 2 of 5

28 tray basin showed a removal efficiency of 97%, while the vortex averaged 88% removal of grit, meaning the stacked tray effluent contained 10% less grit. These results are depicted in Figure 1. The two other tests were completed by NTMWD and evaluated the volume of material being removed into the dumpster. This testing regime follows the removal process from the grit basins, through the grit pumps, into the organics washing unit, and finally from the dewatering unit into the dumpster, as shown in Figure 2. The first test showed that the vortex unit was removing more material and thus more grit. After optimizing the controls and adjusting the organics washing unit, the test was conducted again. Figure 3 represents test 2 results, which depict the systems removed approximately the same mass of grit, but that the stacked tray system was more efficient at washing and dewatering, and thus had 50% of the overall mass to dispose of. Conclusion Testing is still ongoing for this system. The initial results show that each system removes approximately the same mass of grit. The stacked tray grit basin appears to remove more grit, but the subsequent washing step may return some of the grit removed in the basin. The stacked tray system did achieve lower water and organic content in the washed grit, as shown in Figure 4, which can help mitigate odors and reduce hauling costs. 1.The stacked tray grit basin unit allowed 10% less solids to pass through to the effluent. 2.The cyclone style grit washer appears to return much of the grit back to the influent, resulting in lower overall grit removal for the stacked tray system. 3.The cyclone style grit washer achieves a grit product that has 21% lower water content and a 23% lower organic content. This reduces the disposal cost and odor potential. 4.After fine tuning, the stacked tray system was removing as much grit as the vortex system. Sober, A Side by Side Comparison of Grit Removal Technologies: Mechanically Induced Vortex vs. Stacked Tray Page 3 of 5

29 5. Figure 1- Removal Efficiencies of Stacked Tray and Vortex Units 6,000 5,000 4,000 97% Removal 88% Removal Total Pounds 3,000 2,000 1,000 0 Headcell Influent Headcell Effluent Vortex Influent Vortex Effluent Figure 2 Grit Removed by Each System (Test 1) 7,000 6,000 5,000 Total Pounds Removed Total Solids Removed Grit Removed (Inorganics) Pounds Removed Per Week 4,000 3,000 2,000 1,000 0 Week 1 (Headcell) Week 2 (Vortex) Week 3 (Headcell) Week 4 (Vortex) Sober, A Side by Side Comparison of Grit Removal Technologies: Mechanically Induced Vortex vs. Stacked Tray Page 4 of 5

30 Figure 3 Grit Removed by Each System (Test 2, After Optimization) 1,200 1,000 Pounds Removed Pounds Removed Solids Removed Grit Removed (Inorganics) Headcell Average Vortex Average Headcell Test 2 Average Figure 4 Summary of Total Solids and Volatile Solids of Each System Vortex Average Headcell Average 74% 80% 45% 30% Percent Solids Percent Inorganics Sober, A Side by Side Comparison of Grit Removal Technologies: Mechanically Induced Vortex vs. Stacked Tray Page 5 of 5