Treatment of oil-field produced wastewater by electron beam technology: Demulsification, disinfection and oil removal

Abstract

The treatment of polymer-containing produced wastewater with high viscosity and emulsification is a challenging issue in the oilfield. In this paper, electron beam (EB) radiation technology was firstly applied to treat the real oilfield produced wastewater. The results showed that the viscosity of the produced wastewater decreased rapidly from initial 3.7 mPa s to 1.5 mPa s after EB radiation at absorbed dose of 1.0 kGy, then it gradually reached the level of pure water at 5.0 kGy. The produced wastewater was negatively charged and the absolute value of zeta potential diminished stepwise during EB radiation process, indicating that the stability of oil/water emulsion decreased. Radiation pretreatment contributed to the oil removal by coagulation. The efficiency of oil removal increased remarkably from 47% by coagulation alone to 85% with EB pretreatment at 1.0 kGy. Radiation is also effective to disinfect the three typical bacteria in oilfield wastewater, saprophytic bacteria (TGB), sulfate-reducing bacteria (SRB) and iron bacteria (IB). More than 99.8% of TGB, SRB and IB were killed at 1.0 kGy, and a complete inactivation was obtained at 2.5 kGy. Oxidation by ·OH radicals formed in water radiolysis is the major pathway to decrease the viscosity and kill the bacteria, while the direct action of EB radiation also plays a role. The members belonging to genera Thauera, Defluviimonas and Comamonadaceae were predominant in the produced wastewater, with a relative abundance of 40%, 19% and 16%. Based on PICRUSt analysis, the function genes related to metabolism exhibit the highest abundance (25%), which increased at 1.0 kGy, and then decreased at 10 kGy, suggesting that EB radiation at low dose might stimulate the bacterial activity.