The term ‘membrane bioreactor’ (MBR) is generally used to define wastewater treatment processes where a perm-selective membrane, eg. microfiltration or ultrafiltration is integrated with a biological process – a suspended growth bioreactor.
MBRs differ from ‘polishing’ processes where the membrane is employed as a discrete tertiary treatment step with no return of the active biomass to the biological process. All commercial MBR processes available today use the membrane as a filter, rejecting the solid materials which are developed by the biological process, resulting in a clarified and disinfected product effluent.
A membrane bio reactor is essentially a version of the conventional activated sludge (CAS) system. While the CAS process uses a secondary clarifier or settlement tank for solid/liquid separation, an MBR uses a membrane for this function. This provides a number of advantages relating to process control and product water quality.