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What is an MBR?

An MBR (Membrane Bioreactor) consists of an aerobic or combined aerobic/anoxic biological treatment system where the biological sludge is contained in the system by membrane filtration that only lets clean water out of the system. Mixed Liquor is circulated back through the system depending on the process design. The process below is a simplified system that includes Equalization, a Process Zone and the Membrane Filtration Module. Within the process zone, several processes can take place.

Nitrification is the biological conversion of ammonium (toxic to fish) to nitrate nitrogen, and is a two-step process. In the first step, aerobic bacteria known as Nitrosomonas convert ammonium to nitrite. Another group of aerobic bacteria called Nitrobacter finish the conversion of nitrite to nitrate. The reactions are generally coupled and proceed rapidly to the nitrate form, therefore nitrite levels at any given time are usually low.

If total Nitrogen levels are a concern, Denitrification incorporated into the process design. Denitrification is an anaerobic respiration process in which dissolved oxygen levels are depleted and nitrate becomes the primary oxygen source for the microorganisms. These bacteria obtain their carbon and energy from the same source – by biodegrading influent wastewater containing carbon. When bacteria break apart nitrate to gain the oxygen, the nitrate is reduced nitrogen gas, which bubbles out into the atmosphere.

Membrane Bioreactor Process
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