Investigating the effect of different NaCl concentrations as draw solution used to concentrate synthetic municipal wastewater in a Forward Osmosis system

The main bottleneck towards resource and energy valorization of municipal wastewater is the low strength of sewage; characterized by low organic matter and nutrient concentrations. In this study, a bench scale Forward Osmosis (FO) system with a cellulose triacetate membrane (CTA) was used as a pre-treatment system in order to concentrate synthetic municipal wastewater. Increasing concentrations of sodium chloride (NaCl) (0.6, 1.2, 1.7, 2.7 and 3 M) were tested as draw solution (DS), achieving a concentration factor ranging from 1.4 to 4.4. Afterwards, the different concentrated effluents of the FO were anaerobically treated. Based on the results, the most concentrated sewage with the higher water recovery rates yielded higher methane production. The concentration of 1.2 M NaCl (similar concentration to the brine produced in seawater desalination) proves to be the most attractive solution. Ηigh water flux (Jw) can be achieved by utilizing the by-product of the reverse osmosis (RO) system as draw solution and closing the loop on the management of two non-conventional water sources.