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Treating Wet Weather Flows in a Membrane Bioreactor

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Treating Wet Weather Flows in a Membrane Bioreactor

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    1. Treating Wet Weather Flows in a Membrane Bioreactor Shane Trussell, Ph.D., P.E.

    2. Outline Introduction Review of Important Wet Weather MBR Data Possible Explanations What Do We Know Today Conclusions

    3. Outline Introduction Review of Important Wet Weather MBR Data Possible Explanations What Do We Know Today Conclusions

    4. Introduction An MBR is not a membrane process An MBR is a biological process that uses membranes for solids-liquid separation

    5. Principle Advantages of MBR Process High quality effluent Compact Footprint High MLSS concentrations

    6. Principle Disadvantage of MBR Process Ability to maintain hydraulic capacity All treated wastewater exiting an MBR process must pass through the membrane

    7. Outline Introduction Review of Important Wet Weather MBR Data Possible Explanations What Do We Know Today Conclusions

    9. Two Pilot Studies on Large Combined Sewer Systems SEATTLE WPTP Kubota ES-75s - 1 deck Flat plate MF - 0.4 ?m 9 min cycle - 1 min relax Flux rate = 32 gfd Aeration = 28 to 36 scfm June 2002 to June 2003 Capacity ~ 10,000 gpd Treating primary effluent

    10. San Francisco - 2003 to 2005

    11. SF Year 1 - 5 d SRT

    12. SF Year 3 - 5 d SRT

    13. Summary of Membrane Fouling Rates and Exp. Conditions

    14. Varsseveld MBR 2005

    15. Varsseveld MBR 2005

    16. Varsseveld MBR 2005

    17. What’s happening?

    18. Sludge Deflocculation

    19. Summary of Mixed Liquor Properties for San Francisco

    20. Summary of Findings Sludge filterability decreased after significant storm events A significant decrease in membrane permeability occurred Potentially serious issue - when the peak flux is required - cannot perform due to low permeability Poor sludge filterability resulted from diffuse flocs with an abundance of single cells and disperse filaments Same phenomenon occurred in two independent studies on combined sewers and at one full-scale

    21. Outline Introduction Review of Important Wet Weather MBR Data Possible Explanations What Do We Know Today Conclusions

    22. Possible Causes for Observed Sludge Deflocculation Due to Wet Weather Increase in influent colloidal material Increase in influent toxicants Decrease in influent COD Decrease in divalent cation conc. Issues with pilot reactor design (CSTR)

    23. Possible Causes for Observed Sludge Deflocculation Due to Wet Weather Increase in influent colloidal material Increase in influent toxicants Decrease in influent COD Decrease in divalent cation conc. Issues with pilot reactor design (CSTR)

    24. Outline Introduction Review of Important Wet Weather MBR Data Possible Explanations What Do We Know Today Conclusions

    25. Possible Causes for Observed Sludge Deflocculation Due to Wet Weather Increase in influent colloidal material Increase in influent toxicants Decrease in influent COD Decrease in divalent cation conc. Issues with pilot reactor design (CSTR)

    26. Influent Colloidal Material

    27. Possible Causes for Observed Sludge Deflocculation Due to Wet Weather Increase in influent colloidal material Increase in influent toxicants Decrease in influent COD Decrease in divalent cation conc. Issues with pilot reactor design (CSTR)

    28. Tri-City Service District MBR Pilot Studies Designed Experiments to Test Wet Weather Flow Conditions ZW500D UF - 0.035 ?m/ Area: 680 ft2 Treating primary effluent 4-month operation As membrane flux is increased to simulate peak flows, secondary effluent is fed to the reactor as make up water (dilution of influent COD) Same divalent cation concentrations and ratios

    29. Decrease in Influent COD

    30. Possible Causes for Observed Sludge Deflocculation Due to Wet Weather Increase in influent colloidal material Increase in influent toxicants Decrease in influent COD Decrease in divalent cation conc. Issues with pilot reactor design (CSTR)

    31. Issues with Pilot Reactor Design (CSTR) Increase in sludge colloidal content occurred at the Varsseveld MBR in wet weather season The Varsseveld facility is an oxidation ditch with an effective PFR design Additionally, other large MBR facilities are reporting “more than normal temperature correction” fouling during wet weather flows Although there is no doubt that the reactor design is important, this does not appear unique to pilot MBRs with CSTR designs

    32. Outline Introduction Review of Important Wet Weather MBR Data Possible Explanations What Do We Know Today Conclusions

    33. Conclusion Sludge filterability decreases after significant storm events and decrease in membrane permeability Poor sludge filterability results from deflocculation Exact cause of deflocculation is not known What we do know: Not caused by an increase in influent colloidal content Not caused by the dilution of influent COD Not only an artifact of pilot-scale MBRs (CSTR)

    34. Conclusion Possible causes of sludge deflocculation: Toxicity Dilution of divalent/trivalent cation concentrations In addition, this sludge deflocculation will reduce the efficacy of the coarse bubble air scour: Deflocculation negatively impacts sludge viscosity Temperature will also negatively impact sludge viscosity

    35. Mixed Liquor Viscosity

    37. Mixed Liquor Viscosity

    38. Conclusion Nothings changed for biological design! Need a good biological design that encourages bioflocculation and minimizes the mixed liquor colloidal content

    39. Acknowledgements Dr. Rion Merlo, Professor Slawomir Hermanowicz, Professor Emeritus David Jenkins at UC Berkeley The City and County of SF SEP staff King County Wastewater Treatment Division The Tri-City Service District Staff MWH Americas: Jude Grounds and Dale Richwine GE/Zenon

    40. Thank you! shane@trusselltech.com

    41. Two Pilot Studies San Francisco SEP GE/Zenon’s ZW500C UF - 0.035 ?m Total filtration area: 660 ft2 Treating primary effluent 3-year operation

    42. MBR Colloidal Material

    43. Seattle - 2003

    44. KC Exp 1 - 54 d SRT

    45. KC Exp 2 - > 54 d SRT

    46. KC Exp 3 - 15 d SRT

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