Coupled effect of organic fouling and scaling in the treatment of hyper-saline produced water using forward osmosis

Hyper-saline water streams, such as the produced water from the oil industry, cannot be treated via the conventional desalination method, such as reverse osmosis (RO), due to the extreme required pressure to overcome the osmotic pressure. This research investigates the effect of oil fouling and cleaning behaviors when the forward osmosis (FO) process is applied to treat hyper-saline-produced water. Synthetic produced water with total dissolved solids (TDS) concentration of 240 g/l (contained Na, Ca, Mg, Fe, Cl, SO4, and CO3 ions) and oil content of 100 ppm was used as a feed solution. Also, two draw solutions, namely: ammonium bicarbonate (NH4HCO3) and magnesium chloride (MgCl2) of concentrations 6 M and 4.8 M, respectively, were utilized for the FO operation. Results showed that the MgCl2 draw solution provided significantly higher water flux than NH4HCO3 due to MgCl2's high osmotic pressure and low scaling influence. Furthermore, the individual impact of oil was found to be low on the FO's water flux. However, a synergistic effect between the oil and inorganic scaling was noticed. SEM technique was used to comprehend the observation and analyze the fouling content. Although the feed was a highly polluted stream, it was found that osmotic backwashing can recover more than 90% of the initial flux.