Forward osmosis desalination of oil and gas wastewater: Impacts of membrane selection and operating conditions on process performance

Abstract

Water treatment technologies that employ sustainable driving forces for treatment of high ionic strength, complex feed streams and have the capacity to separate a broad range of contaminants are needed for economical treatment of flowback and produced waters in the oil and gas industry. This is especially true given the surging interest in treatment of oil and gas wastewaters for reuse in hydraulic fracturing or discharge to the environment in lieu of deep well injection. Forward osmosis is a robust membrane separation technology that can provide superior rejection of a broad range of feed stream contaminants and dissolved ions, thus providing a brine stream suitable for reuse in hydraulic fracturing or excellent pretreatment for downstream desalination processes. In this work, the impacts of membrane selection (asymmetric cellulose triacetate versus polyamide thin-film composite) and system operating conditions on the performance of FO membranes for desalination of produced water for the Niobrara shale formation are investigated. Specifically, water flux, contaminant rejection, membrane fouling, and chemical cleaning were evaluated using a combination of standard methodology and operating conditions analogous to those employed when operating industrial spiral wound FO membrane modules. Membrane autopsy was conducted to determine what effect(s) membrane physiochemical properties might have on system performance and to interpret the potential molecular level interactions occurring near the membrane-feed stream interface. Results from this study indicate that FO can achieve high rejection of organic and inorganic contaminants, membrane fouling can be mitigated with chemical cleaning, and long-term FO system performance might be better controlled with optimized hydrodynamic conditions near the membrane surface (i.e., feed flow velocity, module design, membrane packing) and not by membrane selection.