Biological treatment of real petrochemical wastewater containing styrene using submerged membrane bioreactor: effects of HRT

In this study, real petrochemical wastewater treatment was investigated at four hydraulic retention times (HRTs) of 30, 18, 12 and 6 h, using membrane bioreactor. Initial evaluation confirmed the presence of styrene and more than 30 different types of compounds in petrochemical wastewater. Laboratory tests and gas chromatography–mass spectrometry (GC–MS) studies indicated that at all HRTs, styrene and chemical oxygen demand (COD) removal efficiencies are higher than 99 and 95%, respectively. Further investigations also revealed that HRT decreasing, not only does not reduce the COD removal efficiency, but also improves the effluent COD by increasing mixed liquor suspended solids. Also GC–MS analysis indicated that styrene as the major pollutant was removed over 99%. Transmembrane pressure was monitored for determining membrane fouling. Data showed severe membrane fouling occurred at HRT of 6 h which was attributed to increase in soluble microbial products.