Evaluation of pretreatment and membrane configuration for pressure-retarded osmosis application to produced water from the petroleum industry

Abstract

Pressure-retarded osmosis (PRO) is a promising membrane technology for harnessing the osmotic energy of saline solutions. PRO is typically considered with seawater/river water pairings however greater energy can be recovered from hypersaline solutions including produced water (PW) from the petroleum industry. One of the major challenges facing the utilization of hypersaline PW is its high fouling propensity on membranes. In this unique experimental evaluation, real PW from different sites was pretreated to varying degrees: i) minimal, ii) intermediate, and iii) extensive. The treated effluent was subsequently used for PRO testing and fouling rates were assessed for different membrane configurations over multiple cycles. Commercial grade flat sheet (FLS) coupons and novel hollow fiber (HF) modules were compared to validate the lower fouling propensity of HF membranes in PRO application. When minimally pretreated PW (10-micron cartridge filtration (CF)) was tested in FLS mode, severe membrane fouling occurred and the PRO flux decreased by 60%. In contrast, HF modules showed <1% flux decrease under both minimal and intermediate pretreatment schemes. Extensive pretreatment (1-micron CF, dissolved air flotation (DAF), powdered activated carbon, and microfiltration) reduced FLS PRO flux decline to <1%. These results confirm that PW can be treated to suitable levels for PRO application to avoid membrane fouling. Further validation of these pretreatment methods requires long term pilot testing and techno-economic assessment.