Use of a Forward Osmosis–Membrane Distillation Integrated Process in the Treatment of High-Salinity Oily Wastewater

In this work, the feasibility of using a hybrid forward osmosis (FO)–membrane distillation (MD) process for treating hypersaline produced water was studied. Four draw solutions [i.e., sodium chloride (NaCl), potassium chloride (KCl), lithium chloride (LiCl), and magnesium chloride (MgCl2)] at concentrations near to their saturation limits were considered. LiCl manifested relatively high FO flux due to its high osmotic pressure (about 1600 atm at 10 M). However, the MD water flux for the 10 M LiCl was relatively low due to the low vapor pressure. NaCl and KCl showed a different behavior of a high MD flux and low or negative FO flux. MgCl2 at a concentration of 4.8 M showed comparable fluxes for both FO and MD. This work has demonstrated that the FO–MD process has the ability to treat extremely saline solutions that contain hydrocarbons and to produce high-purity water.