Treatment of refinery effluents by pilot membrane bioreactors: pollutants removal and fouling mechanism investigation

The main purpose of this study is to evaluate the performance of a pilot-scale membrane bioreactor (MBR) in the treatment of effluent from a petroleum refinery plant focusing on the efficiency of organic matter and nutrient removal, and assessment and minimization of fouling. Two MBRs were assessed, one with flat sheet microfiltration membranes installed in the biological tank (8m(3)) (inside configuration) and another one with hollow fiber ultrafiltration membrane installed in the membrane tank (0.72m(3)) (outside configuration). Both MBRs share the same biological tank with HRT of 5.6h and sludge age of 40d. Performance of the MBRs was evaluated in terms of efficiency of organic matter (total organic carbon (TOC)) and nitrogen removal and membrane permeability. In order to assess fouling, resistance tests were performed, and soluble microbial products and extracellular polymeric substances concentrations were monitored, as was sludge filterability. As a fouling control strategy, MBR operation with operational flux lower than critical flux as assessed, and a permeability improver was used. Results showed that both MBRs had an average TOC and ammonia removal efficiency of 80 and 90%, respectively. The main contributor to fouling was the formation of cake on the surface of the membrane; the operation with operational flux lower than critical flux and the use of the permeability improver were shown to be good fouling control strategies.