Osmotically assisted reverse osmosis: Assessing pretreatment on hypersaline produced water

In a rapidly developing oil and gas industry, sustainable management of produced water (PW) is a key challenge. Due to increasing environmental regulations, the industry is driven towards reducing volumes of PW requiring deep well injection and maximizing beneficial reuse. Among multiple innovative technologies being explored, osmotically assisted reverse osmosis (OARO) has been gaining attention as a possible cost-efficient route for brine concentration. This study addressed key knowledge gaps associated with facilitating the industrial application of OARO for hypersaline PW including a systematic evaluation of pretreatment requirements, membrane organic fouling potential, and product water quality for beneficial reuse applications. A sequence of multiple technologies, including chemical coagulation, softening, microfiltration, stripping, and granular activated carbon (GAC) adsorption, were configured and tested as pretreatment level I, level II, and level III. Approximately 60–70 % of the dissolved organic carbon (DOC) in the PW originated from organic acids, which were proven to exhibit low membrane fouling potential. The remaining DOC (30–40 %), composed of other constituents including the high-fouling potential hydrophobic organic carbon (HOC), were reduced by ~17 %, ~38 %, and ~ 62 % via application of pretreatment level I, level II, and level III, respectively. Membrane fouling tests using level I PW quality resulted in immediate fouling and a flux drop of ~20 %. A flux loss of ~8 % was obtained using level II PW quality which was reduced to ~4 % by application of level III pretreatment. Generated results were used to depict the fouling mechanism for the different DOC fractions in the PW including, organic acids (electrostatic), HOC (adsorption), and uncharged/neutrals (diffusion). The study also shared preliminary insights on the expected product water quality and discussed implications for reuse applications including posttreatment, toxicological evaluations, and regulatory requirements. • Investigated desalination via osmotically assisted reverse osmosis (OARO) • Tested efficacy of multiple pretreatment technologies on saline produced water (PW) • Improved removal of high fouling potential organics by pretreatment, 17 to 62 % • Reduced organic membrane fouling by pretreatment; flux loss dropped from 20 % to 2 % • Generated preliminary product water quality for potential beneficial reuse