Evaluation of EDTA salts for potential application to draw solute of a forward osmosis process

The selection of novel draw solution is one of the critical research fields in a forward osmosis (FO) process. Among various materials, ethylenediaminetetraacetic acid (EDTA) was suggested as a good candidate for draw solution due to its high solubility and easy recovery. However, it is important to find the optimum pH of EDTA in the FO process since EDTA form can be changed according to pH values. This study was initiated to find the optimal pH value of the EDTA salt used as a draw solution, as well as to explore the possibility to recover it by using the nanofiltration (NF) process. From the results of this study, the pH value that has the lowest amount of reverse salt flux (RSF) of EDTA and Na+ ions was found to be 7. In case of the rejection rate test of the NF process, two different membranes, each made with different materials, were used (cellulose acetate [CA] membrane and polyamide [PA] membrane). Both of the membranes have high rejection rate, which is over 99.15% at low pressure (5 bar). From the result of water flux, the performance of PA membrane was about twice as good as the CA membrane under all pressures (5, 10, 15 bar). It could be concluded that the EDTA salt has high water flux with low RSF in the FO process as well as the high salt rejection rate in the NF process. In addition, use of the PA membrane is much preferred than the CA membrane for EDTA salt recovery in the NF process.