Energy requirements in the separation-regeneration step in forward osmosis using TMA–CO2–H2O as the draw solution

Abstract

Abstract Forward osmosis (FO) is a low-energy footprint membrane process that utilizes the spontaneous osmotic pressure difference between a dilute effluent and a more concentrated engineered draw solution (DS) to recover water into it. We report results from both laboratory and pilot-scale operation on the separation and regeneration of the DS: the two processes in FO where the operating cost arises from. We estimated the total energy requirement of an FO process using TMA–CO2–H2O as the DS with an experimentally verified thermodynamic model and a mass and energy balance software. The total operating energy consumption of the process was proven to not vary significantly with % carbonation of the DS. However, a strong relationship was identified between the total energy and the DS concentration. The total thermal energy requirements (heat duties) account for 175 to 440 kWh/m3 of fresh water produced and depend on the concentration of the DS fed to the process (8–25 wt.%). The specific equivalent work of our integrated FO process ranges from 6.8 to 16.7 kWh/m3 of fresh water produced, which indicates that FO is more energy efficient than evaporative processes in the recovery of water from high salinity effluents.