Treatment of synthetic hypersaline produced water employing electrocoagulation-membrane bioreactor (EC-MBR) process and halophilic bacteria

Abstract

Treatment of hypersaline oilfield produced water using a combined electrocoagulation-membrane bioreactor (EC-MBR) process was investigated using synthetic produced water. The electrocoagulation (EC) experiments were conducted using two electrodes (steel and aluminum) at different current densities and contact times. The investigation results showed that aluminum electrode had better performance in terms of COD and turbidity removal efficiencies. The combined EC-MBR investigation was performed using aluminum electrodes, an immersed membrane and oil concentrations of 100, 150 and 200 mg/L. Permeate flux of the membrane unit was set at a constant value of 12 L/m2 h. The results of the combined EC-MBR showed that the transmembrane pressure (TMP) did not exceed 4 psi and membrane fouling was not encountered throughout the experimental period, which was mainly attributed to use of the EC process that resulted in forming agglomerated particles. Moreover, at the end of the three stages, MLVSS concentrations were 7255, 7692 and 8255 mg/L, while bacterial counts were 4430, 3880 and 3230 CFU, respectively, which indicated the inconsistency between MLVSS and bacterial growth. Furthermore, chemical oxygen demand (COD) and oil and grease (O&G) removal efficiencies were found to decrease from 97 to 91% and 95 to 80%, respectively, when influent oil concentrations were increased from 100 to 200 mg/L. Particle size distributions showed mean values of 15.63, 15.96 and 22.72 μm for stages 1, 2 and 3, respectively.