A sequential batch reactor - Forward osmosis system for water reuse

Forward osmosis (FO) is a rapidly-growing membrane technology that can be used as an energy-saving alternative to standard membrane water treatment systems such as reverse osmosis (RO). FO in combination with low pressure RO can be applied to water reuse. The present study investigates a combination of a sequential batch reactor with FO (SBR-FO) to treat wastewater as well as to dilute a draw solution (DS). Pre-filtered (0.45μm) seawater from the Red Sea was used as the draw solution. Real wastewater after primary treatment was used to start-up the SBR, then a standard influent (synthetic municipal wastewater) was fed to the SBR. The processes were conducted with two modes. Mode 1 was operated in three steps including aeration, sedimentation and FO filtration (decantation) while aeration followed by FO filtration with air scouring was implemented in mode 2. The FO filtration was performed in cycles of 15 hours, with daily changes of fresh draw solution. The removal rate of the SBR for total organic carbon was 94.9%. The average FO flux reached in mode 1 was 2.95 L/m².h. Filtration with air scouring could reduce the fouling on the membrane surface, consequently increasing the FO average flux to 3.10 L/m ².h in mode 2. Organic fouling and biofouling occurred on both the AL and SL of the FO membrane. Biopolymers such as polysaccharides, proteins and amino sugars were the main constituents of the fouling layer. FO membrane did not allow passage of humics and building blocks. However passage of low molecular weight neutrals from the feed side (wastewater being treated) to the draw solution side (seawater) was inevitable. The SBR-FO in mode 2 achieved 96%, 88%, 58%, and 100% removals of nitrite, ammonium, nitrate, and phosphate, respectively.