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MEMBRANE BIOREACTOR (MBR)
Three generic membrane processes are used in biological wastewater treatment:
- Solid-liquid membrane separation bioreactors employ ultra or micro-filtration modules for the retention of biomass for recycle to the bioreactor.
- Gas permeable membranes provide bubbleless oxygen transfer to the biomass present in the reactor vessel and may additionally act as a support for the biofilm with direct oxygen transfer through the membrane wall in one direction and nutrient diffusion from the bulk liquid to the biofilm in the other.
- An extractive membrane process for the transfer of biodegradable organic pollutants via a nonporous silicone membrane to a nutrient medium for subsequent degradation. This process is normally used for industrial effluents to extract the biodegradable fraction from an aggressive non-biodegradable solution.
The latter of the three operational options noted above is rarely utilised, the most common operational configuration being the first option that is used with separate sub-surface diffusers to provide oxygen for biological oxidation and growth. This method of treatment is often referred to as "outside-in", the membranes acting as a true filter medium producing a very high quality (bathing water standard) effluent. Air scouring caused by the sub-surface air diffusers and occasional 'back-pulsing' using treated effluent prevent fouling of the membrane surface during operation.
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