Advancing produced water quality via integrated mechanical vapor recompression: Chemical and toxicological characterization, hazard identification and mitigation

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This study evaluated Permian Basin produced water (PW) treatment through an advanced treatment train comprising mechanical vapor recompression (MVR) distillation, granular activated carbon (GAC), and zeolite adsorption. More than 400 analytes, including volatile and semivolatile organics (VOCs and SVOCs), inorganic ions, heavy metals, radionuclides, pesticides, dioxins, furans, and per- and polyfluoroalkyl substances (PFAS) - were quantified. Whole effluent toxicity (WET) tests were conducted across four trophic levels using Vibrio fischeri, Raphidocelis subcapitata, Ceriodaphnia dubia, and zebrafish (Danio rerio). In zebrafish, developmental endpoints and transcriptional responses of genes were assessed to detect sub-lethal effects. MVR distillation reduced total dissolved solids by 99.95%, total organic carbon by 89%, and total petroleum hydrocarbons by 92%. However, reductions in bulk organic parameters did not consistently reflect decreases in individual VOCs and SVOCs. Several hydrophilic VOCs (e.g., acetone, 2-propanol, 2-butanone) exhibited limited removal or even net increases during distillation. Caproic, propionic, and valeric acids (86.5, 123 and 198 mg/L) exceeded several toxicity thresholds for aquatic species. Untreated and distilled PW induced acute and chronic toxicity across all test species, with untreated PW causing 100% mortality in zebrafish embryos and the distillate resulting in 58-67% developmental abnormalities (edema, scoliosis, and impaired posture). In contrast, post-treatment with GAC and zeolite reduced most constituents to below detection limits and eliminated observable toxic effects. Zebrafish developmental and gene expression analyses confirmed the absence of significant perturbations following final treatment. This integrated chemical and biological assessment demonstrates that advanced multi-barrier treatment can effectively mitigate PW toxicity, supporting its potential reintegration into the hydrological cycle.