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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.
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.
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.
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.
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.
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.
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.
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.
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.