What are membrane bioreactors (MBRs) and what are their advantages over conventional treatment?

Membrane bioreactors combine activated sludge treatment with membrane filtration for solid-liquid separation. Configurations: Submerged MBRs - membranes immersed in aeration tank; air scouring controls fouling; lower energy. Sidestream MBRs - biomass pumped to external membrane modules; higher crossflow but more energy intensive. Membrane types: microfiltration (0.1-0.4 micron) or ultrafiltration (0.01-0.1 micron); hollow fiber or flat sheet. Advantages over conventional: Superior effluent quality - complete solids removal, disinfection (>5 log pathogen reduction), suitable for reuse. Smaller footprint - eliminates secondary clarifiers; higher MLSS (10,000-15,000 mg/L) allows smaller tanks. Consistent operation - decoupled HRT and SRT; resilient to shock loads. Challenges: membrane fouling requires cleaning protocols (air scouring, backwash, chemical cleaning); higher capital and operating costs; energy for aeration and permeation. Applications include water reuse, space-constrained sites, and high-quality effluent requirements.