The use of a submerged membrane bioreactor for the treatment of a styrene containing synthetic wastewater

In this study, the potential of a membrane bioreactor for treating styrene contaminated synthetic wastewater, with COD that simulated a petrochemical wastewater, was evaluated and compared with previous studies. At hydraulic retention times of 18 and 24 hours, the removal efficiency of COD and styrene was consistently higher than 99%. More significantly no styrene was detected in the exhaust air, which meant that, at both hydraulic retention times, the mechanism of styrene removal in the membrane bioreactor was exclusively through biodegradation. The lower contribution of stripping to overall styrene removal obtained in the present work compared to that previously reported for traditional activated sludge processes was attributed to the higher Mixed Liquor Suspended Solids (MLSS) that can be achieved in a membrane bioreactor. Decrease of hydraulic retention time from 24 h to 18 h also resulted in significant increase in the rate of membrane fouling as quantified by transmembrane pressure gradiant. This was attributed to decrease in extracellular polymeric substance concentration which resulted in sludge deflocculation. As a consequence, the particle size distribution of the activated sludge shifted to lower mean particle sizes and the increase in the percentage of smaller particles resulted in increase in the rate of membrane fouling.

Keywords
Activated sludge, Biodegradation, Immersed membrane bioreactor, Styrene, Volatile organic compound