Using backwashed microfiltration as a pretreatment for ultrafiltration of oily wastewater

Application of cross-flow microfiltration (MF) process as a pre-treatment step and, partly in combination, with cross-flow ultrafiltration (UF) system as final-treatment techniques for efficient treatment of oilfield waste water is issued here. It is concluded that by pre-treating the oily wastewater with a large pore MF membrane operated with backwashing, the oils are partially coalesced in the pores of the membrane. This suggests that membrane flux decline is due to the coalescing of oil particles in the membrane pores. In this research, investigations were carried out for treatment of oily wastewater by using hybrid system of MF/UF. A ceramic (α-Al2O3) MF membrane with area of 0.24 m2 in microfiltration process and a hollow fiber Polyvinylchloride (PVC) UF membrane with area of 0.7 m2 in ultrafiltration process were employed for treatment of a typical oily wastewater comes from API effluent of Tehran refinery. The oily wastewater effluent was entered to the MF module and a long term operation was carried out at the optimum condition. The MF output was collected to be used as the UF feed. TSS, Oil and grease, TOC, COD and BOD removal efficiencies are gained in sequence 100%, 98.21%, 86.6%, 85.02%, and 83.9%. This effluent meets the National Discharge Standards. Based on the results, MF-UF hybrid system as a new method proposed can be replaced with the conventional wastewater treatment method