Membrane fouling mechanisms in the membrane-coupled anaerobic bioreactor

This study focused on the membrane fouling mechanisms during the longtime operation of a membrane-coupled anaerobic bioreactor (MCAB) system designed for the treatment of alcohol-distillery wastewater. This system provided interesting information on anaerobic digestion and membrane performance associated with the fouling mechanisms in the membrane bioreactor. Enhanced COD removal was achieved with the complete retention of biomass either inside the anaerobic reactor or on the membrane surface. Membrane fouling was many attributed to external fouling, which was closely related to the movement of cell population to the membrane surface and inorganic precipitation at the membrane surface. The major composition of the inorganic foulant was identified as MgNH₄PO₄·6H₂O (struvite), whose deposition together with the microbial cells attached at the membrane surface played a significant role in the formation of the strongly attached cake layer limiting membrane permeability. The struvite precipitation/deposition mechanisms were examined thoroughly in relation to the chemical composition of the influent wastewater and the subsequent anaerobic decomposition in the membrane bioreactor. The conceptual resistance-in-series model was applied to assess the fouling characteristics.