Efficacy of Nanofiltration and Reverse Osmosis for the Treatment of Oil-Field Produced Water Intended for Beneficial Reuse

Treatment and reuse of unconventional oil and gas (UOG) produced water are important strategies that address the dual challenges of water scarcity and pollution posed by UOG production. Considering the high salinity and complex chemistry of UOG produced water, it is important to comprehensively analyze the water quality and potential ecological risk of treated produced water for reuse applications. In this study, we evaluated and compared the efficacy of pretreatment followed by nanofiltration (NF) and reverse osmosis (RO) using membranes of varied permselectivity in treating produced water from the Niobrara Shale play in Colorado. We determined the efficacy of each technology in removing inorganic and organic constituents as well as reducing toxicity on Daphnia magna. Our results show that the pretreatment step resulted in a minor reduction of chemical constituents and toxicity and that the NF permeates did not meet the water quality criteria for irrigation and livestock drinking water. Despite high removal rates for most contaminants in the produced water by RO, the concentrations of chloride and boron as well as the sodium adsorption rate (SAR) in the RO permeates exceeded irrigation guidelines. We observed the passage of surfactants with molecular weights much higher than the molecular weight cutoff of NF and RO membranes, suggesting that membranes are not an absolute barrier to organic contaminants. Our results demonstrate that thorough chemical and toxicological analyses are needed to understand the feasibility and potential risk of treating UOG produced water for beneficial reuse