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Simple depiction of an MBR biological tank with membrane separationCredit: Judd Water & Wastewater Ltd
Installation of a flat sheet module, JellystoneCredit: MMBR Systems
The Woolston WwTW site. Clockwise from the foreground: the sludge processing building, two cylindrical sludge holding tanks, storm tank (beneath canopy), primary clarification building and secondary biological treatment buildingCredit: Southern Water

Introduction to MBRs

A ‘membrane bioreactor’ (MBR) is a type of wastewater treatment process where a perm-selective membrane, e.g. microfiltration or ultrafiltration, is integrated with a suspended growth biological process. It is essentially a version of the conventional activated sludge (CAS) process.

MBR processes predominantly use the membrane as a filter, rejecting the solid materials which are developed by the biological process, resulting in a clarified and largely disinfected effluent product.

MBR JJ i MBR complete scheme

What are MBRs?

A membrane bioreactor is essentially a version of the conventional activated sludge (CAS) process. While CAS uses a settlement tank for retaining the mixed liquor suspended solids, an MBR uses a membrane for near-complete solids retention.

What are membrane bioreactors?

Advantages of MBRs over other technologies

The two most widely-recognised advantages of MBRs are the reduced footprint and the superior treated water quality − particularly with respect to suspended solids, nutrient and microbial content − compared with conventional treatment.

What are the advantages of MBRs?

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What are the components of an MBR?

As with a CAS process, an MBR is a combination of tanks, pipework, pumps and blowers. It requires more rigorous pretreatment than a CAS, as well as various equipment and instrumentation associated with the membrane separation stage.

MBR Components
Image of a Toray MBR wastewater treatment plant
Credit: Toray Membrane

Applications of MBRs in wastewater treatment

MBRs become an attractive treatment option when space is limited and/or a high treated water quality is required, though they are considered more costly and operationally complex than conventional technologies. MBR installations have steadily increased in capacity since their original implementation in the early/mid 1990s.

Applications of membrane bioreactors in wastewater treatment

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M SINAP Cembrane SEM
Credit: Shanghai SINAP | Cembrane

Membrane materials: polymeric/ceramic

MBR membranes are generally in the pore size range between coarse ultrafiltration (UF) and microfiltration (MF). Almost all commercial MBR membranes have rated pore sizes between 0.02 and 0.4 µm. Both polymeric and ceramic membrane materials have been commercialised for MBR use.

Membrane materials used in MBR technology: polymeric and ceramic
Graphic to demonstrate an AnMBR


The implementation of AnMBRs has been limited to a few niche industrial effluent applications where the high organic carbon concentrations make the process energetically favourable. AnMBRs are challenged by the highly fouling nature of the anaerobic biomass.

Anaerobic MBRs
Simple schematic of MABR


In an MABR, the membrane (often a hollow fibre) is used as an alternative aerator, rather than for biomass separation. As such, it does not provide the highly-clarified effluent of a classical MBR. However, membrane aeration provides very efficient oxygen transfer into the biomass leading to efficient biological treatment.

MABRs: Membrane aerated biofilm reactors and oxygenation
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MBR glossary

Having problems with our abbreviations? Keep our MBR glossary to hand for help with definitions and acronyms. Contact us if you find a term you think it would be useful to add.

MBR glossary