Membrane Bioreactors for Wastewater Treatment
Membrane bioreactors (MBRs) combine biological wastewater treatment with membrane filtration, producing high-quality effluent for discharge or reuse. As PFAS wastewater standards tighten for industrial and municipal discharges, MBR performance on PFAS has become an important characterization need.
MBR PFAS Removal Mechanisms
MBRs remove PFAS through two potential mechanisms: biofilm sorption and membrane filtration. Ultrafiltration membranes in standard MBR systems (0.04–0.2 µm pore size) do not provide molecular-level PFAS rejection—PFAS are too small to be filtered by UF membranes. However, PFAS that sorb to mixed liquor solids (biological floc) are removed when solids are wasted from the system.
Performance Data and Limitations
Studies of MBR PFAS removal show highly variable results: long-chain PFAS with higher sorption to biological solids show 30–60% removal, while short-chain PFAS show <20% removal in most MBR studies. This performance is substantially below the regulatory requirements for PFAS in wastewater discharges being established in several states, meaning MBRs alone are insufficient for PFAS compliance in most discharge-to-receiving-water scenarios.
Advanced MBR Configurations
Adding PAC (powdered activated carbon) to MBR mixed liquor significantly improves PFAS removal by providing additional adsorption capacity integrated into the biological treatment system. PAC-MBR systems show 60–80% PFAS removal for long-chain compounds—improved but still insufficient for stringent effluent standards. Coupling MBR with downstream advanced treatment (RO, ion exchange) is required for discharge compliance to waterways with low-PFAS water quality objectives