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Attached Growth Biological WW treatment Systems

Attached Growth Biological WW treatment Systems. Biofilm Systems. Biofilm a biological slime layer bacteria in biofilm degrade organics biofilm will develop on almost anything. Types of Biofilm Systems. Trickling filters Rotating biological contactors Fluidized bed reactors

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Attached Growth Biological WW treatment Systems

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  1. Attached Growth Biological WW treatment Systems

  2. Biofilm Systems • Biofilm • a biological slime layer • bacteria in biofilm degrade organics • biofilm will develop on almost anything

  3. Types of Biofilm Systems • Trickling filters • Rotating biological contactors • Fluidized bed reactors • Biofilters • Wetlands systems • Sequencing batch biofilm reactors (many of these can be aerobic or anaerobic)

  4. TricklingFilters

  5. Flow Diagram for Trickling Filters

  6. Trickling Filters • Not a true filtering or sieving process • Material only provides surface on which bacteria to grow • Can use plastic media • lighter - can get deeper beds (up to 12 m) • reduced space requirement • larger surface area for growth • greater void ratios (better air flow) • less prone to plugging by accumulating slime

  7. Trickling Filters Filter Material

  8. Typical Trickling Filter

  9. Typical Modular and Random Packed Plastic Media Schematic diagrams of modular and random packed media used in fixed-film treatment systems (Source: Bordacs and Young, 1998)

  10. Random Packing Leonard W. Casson, Ph.D., P.E., DEE

  11. Structured Media Leonard W. Casson, Ph.D., P.E., DEE

  12. Bio-towers

  13. Trickling Filter • Tank is filled with solid media • Rocks • Plastic • Bacteria grow on surface of media • Wastewater is trickled over media, at top of tank • As water trickles through media, bacteria degrade BOD • Bacteria eventually die, fall off of media surface • Filter is open to atmosphere, air flows naturally through media • Treated water leaves bottom of tank, flows into secondary clarifier • Bacterial cells settle, removed from clarifier as sludge • Some water is recycled to the filter, to maintain moist conditions

  14. Trickling Filter System

  15. Trickling Filter Process

  16. Bacteria Removal

  17. Types of Trickling Filters • Standard or low rate • single stage rock media units • loading rates of 1-4 m3 wastewater/m2 filter cross-sectional area-day • large area required

  18. Types of Trickling Filters • High rate • single stage or two-stage rock media units • loading rates of 10-40 m3 wastewater/m2 filter cross-sectional area-day • re-circulation ratio 1-3

  19. Types of Trickling Filters • Super rate • synthetic plastic media units • modules or random packed • specific surface areas 2-5 times greater than rock • much lighter than rocks • can be stacked higher than rocks • loading rates of 40-200 m3 wastewater/m2 filter cross-sectional area-day • plastic media depths of 5-10 m

  20. Design Criteria for Trickling Filters

  21. Single stage E1 = fraction of BOD5 removal for first stage at 20 oC, including recirculation and sedimentation Q = wastewater flow rate, m3/s Cin = influent BOD5, mg/L V = volume of filter media, m3 R = Qr/Q F = recirculation ratio Qr = recirculation flow rate, m3/s Design Equation (NRC)

  22. Design Equation (NRC) Second stage E2 = fraction of BOD5 removal for second stage filter at 20 oC, including recirculation and sedimentation Ce = effluent BOD5 concentration from first stage,mg/L

  23. Study examples 9-2,9-3 and 9-4 Ex. 5-5 Given: Single-stage, low rate trickling filter Volume of filter = 1,443 m3 Hydraulic loading = 1,900 m3/d F = 2.78; Cin = 150 mg/L Question: BOD5 of the effluent Solutions: 1. Hydraulic loading: Q = (1,900 m3/d) (1d /86400 s) = 0.022 m3/s 2. Efficiency: 3. Concentration of BOD5: Ce = (1-0.8943)(150) = 15.8 mg/L

  24. Rotating Biological Contactor Rotating Biological Contactors, commonly called RBC’s, are used in wastewater treatment plants (WWTPs). The primary function of these bio-reactors at WWTPs is the reduction organic matter.

  25. RBC Schematic Film of Microorganisms Rotation Leonard W. Casson, Ph.D., P.E., DEE Wastewater

  26. Rotating Biological Contactors

  27. Rotating Biological Contactors • RBCs constructed of plastic media on a long shaft • Media is submerged in a tank • Shaft rotates media through water • Bacteria grow on media, degrade BOD in water • Bacteria get air by exposure to atmosphere • Bacteria eventually die, fall off media surface • Dead bacteria and other solids are removed in the secondary clarifier • Media up 12 feet in diameter • Shafts as long as 25 feet • Media areas up to 180,000 square feet per shaft

  28. Primary Settling Secondary Settling Sludge Treatment Sludge Treatment Rotating Biological Contactors

  29. Flow Diagram for RBCs

  30. Rotating Biological Contactor (RBC) Single RBC

  31. Rotating Biological Contactor (RBC) Defective RBC’s at the Easton Wastewater Treatment Plant

  32. Package RBC System Leonard W. Casson, Ph.D., P.E., DEE

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