Comparison of fouling characteristics between reverse electrodialysis (RED) and pressure retarded osmosis (PRO)

Abstract

The generation of salinity gradient power (SGP) is a promising technique to extract energy from either seawater or reverse osmosis (RO) brine. There are two methods for harvesting SGP, including reverse electrodialysis (RED) and pressure retarded osmosis (PRO). Although they have been individually investigated, few works have been done to compare their fouling behaviors under similar conditions. Accordingly, this study intended to compare RED and PRO processes using various low salinity (LS) solutions and high salinity (HS) solutions in terms of power density and fouling potential. Experiments were carried out in bench-scale RED and PRO systems. Three types of LS solutions including deionized water (DW), wastewater (WW), and wastewater reverse osmosis brine (WB) and two types of HS solutions including seawater (SW) and seawater reverse osmosis brine (SB) were considered. The power density was measured under non-fouling (initial) and fouling conditions. Results indicated that the power density for the PRO was higher (1.09– 3.24 W/m2) than that for the RED (0– 1.66 W/m2) under the non-fouling condition. However, the loss of power density due to fouling was smaller in RED (0– 11.2%) than in PRO (14.2– 58.7%). The use of WB as the LS solution resulted in low power density in both RED process (<0.1 W/m2) and PRO process (0.45– 0.9 W/m2). This was attributed to the severe fouling of ion exchange membranes in RED process and deposition of foulant on the support side of the membrane in PRO process.