Petrochemical wastewater treatment and reuse by MBR: A pilot study for ethylene oxide/ethylene glycol and olefin units

• Employing MBR for treatment of petrochemical wastewater was studied in pilot scale.
• Various MLSS, HRTs and mixed ratio of EO/EG to olefin unit wastewater were studied.
• At best mixed ratio of 2/1 and HRT of 24 h, COD removal of 96% was achieved.
• Membrane fouling in MBR at various MLSS concentrations was analyzed and discussed.

This study aims to investigate the technical feasibility of employing membrane bioreactor (MBR) as a practical approach for ethylene oxide/ethylene glycol (EO/EG) and olefin units wastewater treatment in a petrochemical complex. EO/EG unit wastewater mainly contains ethylene glycol and acetaldehyde and olefin unit wastewater includes benzene and ethyl benzene, with COD concentration of 1900 ± 900 mg/L and 900 ± 300 mg/L, respectively. Experimental studies of MBR pilot plants with volume of 2.5 m3 were carried out during 6 months in different HRTs and various mixed ratios of EO/EG to olefin unit wastewater. Results revealed that using MBR, COD removal efficiency of 97.5% is accomplished in HRT of 13.5 h for EO/EG and 85% in HRT of 18 h for olefin wastewater. For the mixed ratio of 2/1 and in HRT of 18 and 24 h, COD removal efficiency of 93.5% and 96% was achieved, respectively. Membrane fouling was analyzed at different MLSS concentrations. The results at optimum MLSS of 8 g/L revealed that fouling resistance is mainly due to the membrane pore blocking, and cake and gel resistances contribute less to membrane fouling. Results indicated that MBR is a promising technology for treatment of high fluctuation toxic components in petrochemical wastewater.