Evaluation of ethanol as draw solute for forward osmosis (FO) process of highly saline (waste)water

Abstract

In the study, ethanol was evaluated for its potential as a draw solution in forward osmosis (FO) in terms of performance for treating highly saline (waste)waters and energy requirements for regeneration. When compared to NH4HCO3 (a thermolytic draw solution) ethanol exhibited significantly higher osmotic pressure and significantly easier regeneration. In FO experiments using commercial TFC FO membranes, the ethanol draw solution exhibited a water flux comparable to that of NH4HCO3 at equivalent osmotic pressure albeit a relatively high reverse solute flux (RSF) due to its volatility. The modeling prediction based on membrane transport properties obtained from the FO experiments revealed the critical role of the ethanol permeability of the membrane in the overall FO performance, thereby suggesting the necessity of a higher water-ethanol selective membranes for the extensive application of the ethanol draw solution for the treatment of highly saline wastewater. Easy-regeneration of the ethanol draw solution was also demonstrated based on experimental results obtained using laboratory scale vacuum distillation at room temperature and exergy analysis of the integrated system. The results indicated that the regeneration process required an estimated 8.8 kWh/m3, thereby supporting the feasibility of ethanol as a potent draw solution for FO application of highly saline waters.