Membrane bioreactor (MBR) is defined as a combination of a biological process like activated sludge process with membrane separation using micro/ultrafiltration. It is broadly used for treating municipal and industrial wastewaters. Compared to conventional biological treatment system, it has several advantages, among others high effluent quality, limited space requirements, no secondary clarifier needed, possibilities for phased extension of the treatment plant.

MBR technology can reach treatment performance up to 99.9% removal of most pollutants. For example, treatment for domestic wastewater using this system will produce effluent with non-detectable solids (TSS), low BOD concentration of 2 mg/L, ammonia-nitrogen of 0.5 mg/L, bacteria and germs (fecal coliform count) will be less than 20 per 100 mL and the total nitrogen of less than 5 mg/L. In general, MBR technology restore the wastewater to a hygienic condition hence suitable for use as re-use water like watering the garden or flushing toilets.