Pilot-scale evaluation of hypersaline produced water treatment and reuse via freeze desalination and seawater reverse osmosis: Organic removal, aquatic and human cell line toxicity studies

Produced water (PW) is the largest waste stream generated during oil and gas extraction, with an estimated global production of ~40 million m 3 per day. Sustainable PW treatment and reuse have gained increasing interest to reduce the economic and environmental challenges of PW management. This pilot study evaluated an innovative multistage treatment system combining pretreatment, fractional freeze desalination (FD) with seawater reverse osmosis (SWRO) to treat hypersaline PW in the Permian Basin for beneficial reuse. A comprehensive chemical analysis of ~450 analytes and toxicity assessment were conducted to examine the ecotoxicity and human health impacts of the treated PW. The potential reuse for irrigation, land application, and applications requiring drinking water quality was evaluated against relevant water quality criteria. This study primarily focused on assessing the separation efficiency in removing organic contaminants, with approximately 360 organic compounds analyzed in water samples collected throughout the treatment train during 10-month pilot testing. Greater than 99% of salts were removed and the detected organic contaminants in raw PW were reduced to below detection limit in the final purified PW. The principal component analysis was conducted to correlate the removal efficiency with the physicochemical properties of organic compounds. Four types of human cell lines were used to assess the impact of PW treatment on human health, including human breast cancer cells (MCF-7), human embryonic kidney cells (HEK293), human liver cancer cells (HepG2), and human lung cancer cells (A549). Both metabolic activity and ATP-based cell viability assays demonstrated that the multistage treatment system effectively mitigated the impact of PW on cell viability. Additionally, the concentrations of residual compounds in the SWRO permeate were below regional screening levels set by the U.S. Environmental Protection Agency, indicating no potential health risks for residential and commercial use. The whole effluent acute and chronic toxicity tests on fathead minnow Pimephales promelas, water flea Ceriodaphnia dubia , and green alga Raphidocelis subcapitata indicated the non-toxicity of the zeolite-treated SWRO permeate on aquatic organisms. The pilot study demonstrated the potential of the integrated multistage FD-SWRO system to enable beneficial reuse of hypersaline PW. The results provide scientific and technical information to advance PW reuse strategies that support both environmental protection and water security.