Effect of Oil Concentration in Treatment of Saline Oily Wastewater Using Forward Osmosis Process

Treatment of the produced water, as a major wastewater in oil and gas industry, is concerned with reduction of the wastewater volume or providing water for some applications such as agriculture. Since membrane technologies play an important role in the separation of dissolved and emulsified oil droplets, forward osmosis (FO) was used in this research as a novel process to reduce the volume of such wastewater. A cellulose commercial flat membrane was applied in a FO laboratory system. The results showed that by increasing the concentrations of the most important inorganic solutes in produced water from 0 to 20 g/L, water flux decreased from 11 to 6.6 L/m2.h due to an increase in feed osmotic pressure. In the presence of 1000 and 3000 mg/L oil in deionized feed water, 12 and 15 percent reduction of the water flux was observed, respectively. This was due to the increased viscosity of feed and the precipitation and adsorption of emulsified oil particles on the membrane surface. On the other hand, adding oil to the solution with different salt concentrations, led to a further reduction in the water flux. This was a result of the increase in feed osmotic pressure and changes in the condition of oil-water emulsion in the presence of salts. The salts increased the surface tension of the solution, which caused coagulation of oil droplets and higher fouling in the membrane surface.