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Moving Bed Biofilm Reactor Retrofit for Ammonia and Nitrate Removal
B&V SACWSD Lela Parsons, P.E Greg Fabisiak Mark Maxwell, P.E Joan Chavez 2002 RMSAWWA / RMWEA ANNUAL CONFERENCE
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Phase 2 Project Components
Wastewater Collection System Master Plan Utility Plan Preliminary Design Report Detailed Plans & Specifications Contract Administration
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Utility Plan Goals Provide information required by DRCOG and for SRF Funding Evaluation of existing facilities Population & flow projections Environmental assessment to support FNSI Alternative analysis and recommendations Implementation and financial plans Public participation Determine necessary wastewater facilities for capacity and regulatory compliance through 2020
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Site Layout
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WM WWTP Existing Unit Processes
East Trickling Filter Final Clarifiers Chlorination P Flow Splitter Discharge to South Platte River Raw Wastewater Mechanical Screenings Primary Clarifiers Rotating Biological Contactors Dechlorination P P West Trickling Filter Final Clarifier Chlorination Combined Primary & MBBR Sludge Accelerated Air Drying of Dewatered Biosolids Prior to Ultimate Disposal of Class A Product Degritting Gravity Thickener Anaerobic Digesters Deskins “Quick-Dry” Filtration SystemTM P
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WM WWTP Existing Unit Process Capacities
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Treatment Issues Regulatory Compliance
Reclassification of the South Platte River requires additional disinfection Updated model of Segment 15 of the South Platte River resulted in imposition of effluent ammonia limit Current and Future Water Quality Concerns Dissolved oxygen Ammonia Nitrates Nutrients
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South Platte Dischargers
Centennial SACWSD Brighton MWRD Central Plant Future Sand Creek Satellite WWTP Littleton- Englewood Bear Creek Clear Creek Sand Creek Burlington Ditch Diversion Glendale Segment 14 Segment 15 Chatfield Reservoir South Platte River Segments 14 & 15 of South Platte River (Not shown are non-point sources, diversion dams, reaeration structures etc.) Cherry Creek
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Treatment Issues (con’t)
WM WWTP Treatment Capacity Surge in residential and commercial activity in the service area Current treatment capacity of 4.4 mgd forecasted to only be sufficient through 2003 Limited room for additional expansion at the existing site
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SACWSD Future Plan Complete Phase 2 expansion at WM WWTP by 2004
Phase 2 will provide capacity until 2008 New WWTP will be needed by could be regional WWTP or SACWSD WWTP Upgrade WM WWTP when appropriate to meet future water quality regulations
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WM WWTP Expansion Increase treatment capacity from 4.4 to 7.0 mgd
Notice to proceed issued September 2002 Short-term - capacity expansion allows growth while new WWTP is designed and constructed Long-term - WM WWTP will continue to serve the southern area of the District
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Phase 2 Improvements Major Expansions Additional Improvements
Secondary Treatment Process Solids Handling Process Additional Improvements Replace Manual Bar Screen Demolish RBCs Upgrade Disinfection Facilities Add Stand-by Power Capacity Expand Administration Building/Garage
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Treatment Alternatives
Alternative A Alternative B Activated Sludge Anoxic/oxic basins WAS Pumping Station and Blower Building New Aerobic Sludge Handling Centrifuge Aerated sludge holding Biological Nutrient Removal (future) Fixed Film MBBR Anoxic/oxic basins Blower Building Additional Anaerobic Solids Processing Convert secondary digester to primary digester New secondary digester Chemical Phosphorous Removal (future) Post Denitrification (future)
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Alternative Evaluation
Alternative A slightly less expensive Alternative A more operationally complex- requires separate solids handling process Alternative B will require chemical addition for future phosphorous removal SACWSD has always utilized and prefers fixed film processes
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Selected Alternative: Moving Bed Biofilm Reactors
Fixed film process manufactured by Kaldnes Employs high-density polyethylene plastic media, coarse bubble aeration, and sieves Biofilm grows on inside of the media Specific gravity of 0.96 150 ft2/ft3 media surface area 0.93 %/ft clean water oxygen transfer rate
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Design Conditions 2 anoxic and 2 oxic reactors in series
100 mg/L influent BOD 2 anoxic and 2 oxic reactors in series 60% fill in each reactor Coarse bubble diffuser system in oxic reactors Submersible propeller mixers in anoxic reactors 4 mg/L summer DO concentration 5 mg/L winter DO concentration 200% internal recycle for nitrate removal
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Treatment Requirements
East Plant Effluent BOD5 reduction <10 mg/L Total ammonia reduction <2 mg-N/L (complete nitrification) Total nitrate reduction <10 mg-NO3/L (partial denitrification) Blended Effluent (East and West Plant) CBOD reduction <25 mg/L Total ammonia reduction <10 mg-N/L
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Selected Alternative Flow Schematic
East Trickling Filter Anoxic MBBR Oxic MBBR Final Clarifiers Chlorination P P Discharge to South Platte River Raw Wastewater Mechanical Screenings Primary Clarifiers Dechlorination P Flow Splitter P West Trickling Filter Final Clarifier Chlorination Combined Primary & MBBR Sludge Accelerated Air Drying of Dewatered Biosolids Prior to Ultimate Disposal of Class A Product Degritting Gravity Thickener Anaerobic Digesters Deskins “Quick-Dry” Filtration SystemTM P Existing Facilities Phase 2 New Phase 2 Modified
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Operational Issues Portion of primary effluent must be bypassed around existing trickling filter Requires construction of a new flow splitter structure Prevents hydraulic surcharging of underdrains Assures sufficient soluble BOD for denitrification Allows ETF pumping station to be taken out of service Trickling filter snail accumulation Installed an automatic, self-cleaning strainer with 1/8- inch openings at the ETF pumping station
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Total Project Costs Engineer’s Construction Cost Opinion Low Bid Price
Difference Between High and Low Bids $13,283,000 $12,774,000 $475,300
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