AbstractLong-term experiments were undertaken to evaluate the role of polyurethane foam (PUF) on performance and in alleviation of fouling in a ceramic membrane integrated in an anaerobic hybrid membrane bioreactor (An-HMBR), treating high-strength wastewater. A mass balance equation was also developed to assess the mixed liquor suspended solids (MLSS) concentration in PUF effluent by taking into account the “sloughing” of the biofilm layer. Results showed that MLSS concentration was overpredicted by the equation in the final stages and this was attributed to the retention of microbial dead mass in the interstices of PUF. This study revealed that the pore-blocking mechanism was dominant during the initial stages of reactor operation followed by cake layer formation in the final stage of treatment. Reversible fouling (98%) dominated over irreversible fouling (0.9%), which also supported cake layer formation. Increasing hydraulic retention time (HRT) and decreasing sludge retention time (SRT) resulted in higher concentration of soluble microbial products (SMP) and extracellular polymeric substances (EPS) in the suspended sludge, PUF biomass, and cake layer attached to the membrane. This, in turn, resulted in increasing the membrane resistance and fouling.