0011-9164/08/$– See front matter © 2008 Elsevier B.V. All rights reserved *Corresponding author. Performance characteristics of a hybrid membrane pilot-scale plant for oilfield-produced wastewater Xiangli Qiao*, Zhenjia Zhang, Jialiang Yu, Xiaofeng Ye Environmental Science and Engineering, Shanghai Jiaotong University, Shanghai 200240, China Tel. +86 (21) 54747412; Fax +86 (21) 54747368; email: qiao_xl@sjtu.edu.cn Received 15 May 2006; accepted 8 April 2007 Abstract Oilfield produced wastewater is a complicated system containing high levels of oil, SS (total suspended solid), sulfide, reductive substances and salinity, etc. The current treatment process operating in Daqing oilfield cannot treat the oily wastewater to satisfy the discharging standard to surrounding environment or the water quality for injection into low-osmosis oilfield. In this paper, a pilot-scale plant involving aeration tank, air floatation, sand filter and UF has been designed and performance characteristics of the hybrid process have been studied for treatment of the oily wastewater. Operation results show that this process can largely reduce the oil, SS contents in the oily wastewater to less than 0.5 mg/L, 1.0 mg/L, respectively, and the concentration levels of Fe, reductive substances, sulfate reduction bacteria (SRB), metatrophic bacteriaTGBand iron bacteriaIBcan also meet the required standard for discharging or injection water. Keywords: Oil-field produced wastewater; Hybrid membrane plant; Performance characteristics 1. Introduction Nearly 50 millions tons of oilfield-produced wastewater is generated every year in China. Water quality of the oily wastewater fluctuates very much, depending on the crude oil extraction process, oil/water separation and subsequent pre- liminary treatment [1–3]. It is a complex multi- phase system containing high levels of oil, SS (to- tal suspended solid), reductive substances, salts, and bacteria, etc. which are very difficult to dis- posed of. The current treatment process operat- ing in Daqing comprises settlement tank, air floatation, regulating tank, etc. (Fig. 1). It cannot treat the oily wastewater to meet the discharge standard to surrounding environment. Thus, the discharge not only seriously polluted the environ- ment, but wasted the water resources. With the profound exploitation of crude oil, more and more low-osmosis oilfields appeared where crude oil extractions required large volumes Desalination 225 (2008) 113–122 doi:10.1016/j.desal.2007.04.092