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TECHNOLOGY DETAIL FACT SHEET: Biological Aerated Filter (BAF) DESCRIPTION In the BAF process, wastewater flows upwards through tanks (called cells) that are filled with media. The media within the filter cells is tightly packed and provides a surface for microorganisms to attach to and grow on. The microorganisms consume organic material. The upward flow of wastewater through the tightly packed media also provides filtering, eliminating the need for a separate clarification ste
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  TECHNOLOGY DETAIL FACT SHEET: Biological Aerated Filter (BAF) DESCRIPTION In the BAF process, wastewater flows upwards through tanks (called cells) that are filled with media. The media within thefilter cells is tightly packed and provides a surface for microorganisms to attach to and grow on. The microorganismsconsume organic material. The upward flow of wastewater through the tightly packed media also provides filtering,eliminating the need for a separate clarification step in the treatment process. Air is added to the bottom of the cell toprovide oxygen for the microorganisms. The BAF system typically employs multiple filter cells that are rotated in and outof service as needed to accommodate varying wastewater flow rates and concentrations of organic materials in the flow.During operation, the filter cells are periodically washed (called backwashing) to remove excess biological growth andflush out captured suspended solids to ensure they operate well. This is accomplished by increasing the flow rate throughthe filter, and agitating the filter media using an air scour system to loosen the media bed. The waste stream frombackwashing is returned to the treatment plant for subsequent treatment.There are two types of media used in the BAF system depending on the vendor selected. The system being tested in thepilot plant uses lightweight, buoyant polystyrene beads as the media. The beads are retained within the filter cell by aconcrete deck with holes provided with screens located above the media near the top of the cell. The BAF can beconfigured to provide secondary treatment as well as nitrogen removal. To provide high levels of nitrogen removal,additional filter cells and addition of a supplemental carbon source such as methanol is required.More information on the BAF process can be found on the City of Portsmouth’s website atwww.cityofportsmouth.com/publicworks/wwmp.htm. Schematic of BAF Using Polystyrene MediaTop View of Full Scale BAF Cell View of Full Scale BAF Piping Gallery REPORTED ADVANTAGES OVER CONVENTIONAL SECONDARY TREATMENT TECHNOLOGY   Elimination of secondary clarifiers reduces the associated costs and operational problems that can accompanytraditional treatment processes   Reduced space requirements due to small footprint   Fully automated operation; minimum operator attention required   Treatment of cold and dilute wastewaters   Capable of handling wide flow and temperature variations POTENTIAL DISADVANTAGES / CONCERNS   Plant personnel should receive sufficient training on the use of the automated control system   Extensive use of automated valves and on-line instrumentation may increase level of preventative maintenancerequired  PILOT UNITS:  First Stage BAFTop of First Stage BAF First Stage BAF Media PILOT UNIT DATA: Pilot Unit flow Rate: 5-20 gallons per minuteFirst Stage BAF Column Diameter: 36 inchesFirst Stage BAF Media Depth: 11.5 feetSecond Stage BAF Column Diameter: 26 inchesSecond Stage BAF Media Depth: 5.0 feetDenitrification Carbon Source: Micro-CPilot System Vendor: Kruger, Cary NC  TECHNOLOGY DETAIL FACT SHEET: Conventional Activated Sludge (CAS) with BioMag DESCRIPTION The BioMag process works with the conventional activated sludge (suspended growth) system consisting of aerationtanks and secondary clarifiers. In the first step of the process, biological microorganisms are combined with the incomingwastewater and mixed with air to provide oxygen in the aeration tanks. The microorganisms consume organic material.The second step entails separating the microorganisms and other suspended materials from the treated water in theclarifiers. BioMag adds powdered magnetite (an inert iron ore) in the aeration tank and clarifiers. The microorganismsattach to the magnetite, which adds weight, and helps the mixture of microorganisms and suspended solids settle to thebottom of the clarifiers more quickly. The settled material creates sludge on the bottom of the clarifier. The sludge iscontinuously pumped out, and some of it is returned to the aeration tank to keep the right amount of microorganisms inthe aeration tank. Magnetite is recovered from the excess sludge before the excess sludge is further processed for disposal. Some magnetite is lost in the recovery process and is replaced with new magnetite that is added to the aerationtank to begin the process again. The BioMag process allows treatment plants to operate with a higher concentration of microorganisms, which reduces the footprint of the aeration tanks.BioMag uses conventional rectangular or circular secondary clarifiers for clarification. Since the magnetite allows thesludge to settle more quickly than with conventional secondary clarifiers, the clarifiers can also be smaller. The BioMagprocess can be configured to provide secondary treatment as well as nitrogen removal. For nitrogen removal, theaeration tank is partitioned into different zones with different levels of oxygen, which allows the microorganisms to removenitrogen. To provide high levels of nitrogen removal, addition of a supplemental carbon source such as methanol isrequired.More information on the Conventional Activated Sludge with BioMag process can be found on the City of Portsmouth’swebsite at www.cityofportsmouth.com/publicworks/wwmp.htm. Schematic of the Conventional Activated Sludge with BioMag Process Full Scale Aeration Tank Using the CAS with BioMag Process  REPORTED ADVANTAGES OVER CONVENTIONAL SECONDARY TREATMENT TECHNOLOGY   Increased settling rates and control over sludge results in increased reliability   Reduced space requirements due to the ability to operate at higher concentrations of suspended solids   Increased efficiency in nitrogen removal resulting from higher suspended solids concentrations and increasedsludge age   Capable of handling wide flow and temperature variations   Increased waste sludge concentrations may avoid need for downstream sludge thickening POTENTIAL DISADVANTAGES / CONCERNS   Concern over long term wear on mechanical equipment due to continuous pumping of abrasive magnetite slurry   Mechanically intensive process requiring increased operator attention PILOT UNITS: CAS With BioMag Aeration TankCAS With BioMag Clarifier Magnetite Make-up and Feed Tanks PILOT DATA: Pilot Unit flow Rate: 5-20 gallons per minute Aeration Tank Dimensions: 26 feet long, 4 feet wide, 8 feet deep Aeration Tank Volume: 5,000 GallonsClarifier Dimensions: 4 feet wide, 4 feet long, 6.5 feet deep (2 clarifiers)Denitrification Carbon Source: Micro-CPilot System Vendor: Siemens (Formerly Cambridge Water Technology), Cambridge MA
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