Pilot Scale Osmotic Concentration Process for Reducing Wastewater Volumes from Gas Processing Facilities in Qatar

Abstract

Over the past 10-15 years, there has been increasing attention in the development of forward osmosis (FO) technology as a low-energy technical solution to wastewater treatment through the exploitation of the natural osmosis phenomenon across semi-permeable membrane. The significant energy benefit arises in applications where direct recovery of the permeate product from the draw solution (DS) is obviated such as in osmotic concentration (OC) process. In the current research, an OC FO-based pilot-scale unit was applied for wastewater volume reduction from oil and gas processing facilities in Qatar. The pilot unit uses seawater of 40 g/L salinity as a DS and wastewater generated during oil and gas operations as a feed. This feed water is of comparatively low conductivity (2 g/L salinity), making it unusually suited to treatment by OC. Based on FO technology principles, the feed gets concentrated at lower volume with the water permeation through the membrane, meanwhile the water transfer to DS side dilutes it. The diluted DS could be directly discharged into the ocean; so the energy intensive step of DS recovery is entirely eliminated. Two FO membranes (Toyobo and NTU) of hollow fiber configuration were tested to assess their performance and fouling propensity on both synthetic and real wastewaters. Results demonstrated that the membrane-based process can achieve feed water recoveries up to 90% without any scaling issues. Achieved water flux ranges between 1.5 to 12 LMH for feed recoveries between 60 and 90% using a constant dilution rate of the draw solution. Above all, the pilot unit maintained stable water flux of 1.62 and 6 LMH using at 75% feed recovery for over 48 hours of continuous operation Toyobo and NTU membranes respectively.