Forward Osmosis (FO) for Water Reclamation from Emulsified Oil/Water Solutions: Effects of Membrane and Emulsion Characteristics

The effects of membrane and oil/water emulsion characteristics as well as their interactions on the performance and fouling behaviors of forward osmosis (FO) processes for emulsified oily water have not been studied in depth. By constructing thin-film composite (TFC) membranes with tailored surface chemistry and employing petroleum-in-water emulsion solutions with variable physicochemical properties, we have systematically investigated these effects for water reclamation from the emulsified oily water under FO operations. It is found that the surfactant not only plays an important role in determining the emulsion droplet size but also its distribution and surface charge properties, which would significantly affect the fouling propensity and reversibility of the FO membrane. FO shows a relatively high water flux and feed recovery as well as great rejection to oil/water emulsions (>99.9%) under both pressure retarded osmosis (PRO) and FO modes. However, the FO mode is superior to the PRO mode in terms of performance stability, antifouling behaviors and fouling reversibility despite of its lower initial water flux induced by internal concentration polarization. In FO mode, the water fluxes of the fouled TFC membranes could be recovered back up to 92-97% of the original values via water flushing on the fouled surfaces because the fouling primarily occurs on the polyamide skin instead of within the porous substrate. The polyethylenimine (PEI) modification to reduce membrane surface pore size and/or lower the charge-charge interactions with the emulsion particles could effectively ameliorate fouling and enhance fouling reversibility. The current work would provide insightful guidelines for the development of effective FO membranes and processes for oily wastewater treatment.