Removal of oil hydrocarbons from petroleum produced water by indigenous oil degrading microbial communities

Plugging membrane filters with oil (mostly n-alkanes) constitutes one of the main barriers to treating PW for its integration into industrial and agricultural uses. A previous study shows that the combined supply of protein-rich matter and CO2 stimulates the activity of indigenous oil degrading microbial communities. Here we study the feasibility of using this stimulation method to remove dissolved oil hydrocarbons from petroleum produced water (PW) in storage tanks. The experimental procedure consisted of vial experiments using actual PW collected from the Stillwater and Cushing oilfields of Oklahoma, USA. Experiments aimed to determine the kinetics and degree of oil hydrocarbon degradation, assess the effect of pH and ORP, and elucidate the mechanism of oil degradation by the discovered stimulation method. Our results show that the discovered stimulation method works at mesophilic and thermophilic temperatures, isolated soy protein can be used as a substitute for yeast extract, and HCl can be used as a substitute for Na2S to reduce the ORP of PW to optimum levels for oil hy-drocarbon degradation. Our results support the hypothesis that CO2 supplied as NaHCO3 boosts the stimulating effect of protein-rich matter by removing H2, which constitutes a thermodynamic barrier for the degradation of oil hydrocarbons. Initial oil concentrations (0.8-1.9 mg-oil/L) decreased by 40-90 % within 7-35 days. The specific rate coefficient and half-saturation constant to represent the kinetics of oil hydrocarbon degradation are 0.614 day-1 and 5.7 mg-oil/L, respectively.