Separation performance in pilot-scale fractional freeze desalination and reverse osmosis for produced water reuse

Produced water (PW) treatment for beneficial reuse has garnered significant interest as a strategy to enhance environmental sustainability of oil and gas industry and augment regional freshwater supplies. Robust treatment systems are required to purify the hypersaline PW to meet water quality requirements for fit-for-purpose applications. This pilot study demonstrated innovative processes to treat PW from the Permian Basin, including pretreatment, multistage fractional freeze desalination (FD), granular activated carbon filtration, and seawater reverse osmosis (SWRO). The feasibility of utilizing the purified PW for agricultural irrigation, land application, and instream-flow augmentation via surface water discharge was explored by comprehensive characterization of the PW quality. In addition to routine water quality monitoring on site, six water sampling events were conducted over a ten-month field demonstration period to evaluate comprehensive water quality and assess the treatment efficiency of both individual unit processes and the overall integrated treatment train. Over 440 analytes were quantified, including metals, anions, volatile organic compounds, semi-volatile organic compounds across various groups, and radionuclides. This paper focuses on the separation performance of bulk, inorganic, and radionuclides. The findings illuminated that integrating the novel FD system into the treatment train effectively removed the majority of ions, enhancing the desalination capacity of the subsequent SWRO system to an overall removal of ~99 %. This study demonstrates that a treatment train incorporating FD with SWRO, and appropriate pre- and post-treatment, can facilitate PW reuse to address the critical challenges of water scarcity and brine management.