From: Membrane Bioreactor (MBR) Technology for Wastewater Treatment and Reclamation: Membrane Fouling by Oliver Terna Iorhemen *, Rania Ahmed Hamza and Joo Hwa Tay https://www.mdpi.com/2077-0375/6/2/33/htm
If you operate an activated sluge sytem with secondary clarifiers, you are very familar with problems related to filamentous and non-filamentous bulking. Gravity solids separation requires biological solids to settle and compact within the clarifier's hydraulic residence time. Bulking is related to influent makeup, biological unit environmental conditions, and many factors that can create a biomass that dose not settle and/or compact.
Enter the membrane solids separation systems - the MBR utilizes a membrane that retains solids in the biological unit and allows water to pass through the membrane for effluent discharge. As pressure required to push water through the membrane increases, the system uses backflushing to clean the membrane. If backflushing does not improve pressure requirements, the membrane must be chemically cleaned and eventually will require replacement.
What causes permeability decline?
This brings us back to how filamentous and non-filamentous bulking organisms can impact the membrane. A non-ideal MLSS increases biological fouling potential. EPS in particular can foul the membrane by:
If your biomass drifts to increased EPS (non-filamentous bulking, foaming filaments) and filaments that can stregthen biofilms on the membrane, then the membrane maintenance will include more cleaning cycles and earlier replacement than a system with better conditioned MLSS. Therefore, it is important to monitor EPS and filaments even with an MBR system.
A great short reivew of MBR fouling - https://www.mdpi.com/2077-0375/6/2/33/htm
Enter the membrane solids separation systems - the MBR utilizes a membrane that retains solids in the biological unit and allows water to pass through the membrane for effluent discharge. As pressure required to push water through the membrane increases, the system uses backflushing to clean the membrane. If backflushing does not improve pressure requirements, the membrane must be chemically cleaned and eventually will require replacement.
What causes permeability decline?
- Influent
- Hydrophobic compounds - i.e. Fats, Oils & Grease
- Colloids
- Particulates - both organic & inorganic
- Biological
- Extracellular polymer substances (EPS)
- Soluble mirobial products - some can impact membrane pores
This brings us back to how filamentous and non-filamentous bulking organisms can impact the membrane. A non-ideal MLSS increases biological fouling potential. EPS in particular can foul the membrane by:
- Cake formation - common and cleaned during backflush
- Pore blocking - solids/eps impede water flow through pores
- Biofilm growth - EPS allows for biofilm attachment to membrane thereby blocking pores
If your biomass drifts to increased EPS (non-filamentous bulking, foaming filaments) and filaments that can stregthen biofilms on the membrane, then the membrane maintenance will include more cleaning cycles and earlier replacement than a system with better conditioned MLSS. Therefore, it is important to monitor EPS and filaments even with an MBR system.
A great short reivew of MBR fouling - https://www.mdpi.com/2077-0375/6/2/33/htm
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