High recovery and fouling resistant double stage seawater reverse osmosis: An inter-stage ERD configuration optimized with internally-stage design (ISD)

Fouling in seawater reverse osmosis (SWRO) is a crucial parameter for a long-term operation. This study investigated a standard configuration wherein energy recovery device (ERD) being placed in the front of the first stage, an inter-stage ERD (ISERD) configuration wherein the ERD booster being placed in-between the two stages, and ISERDISD configuration wherein internally-staged design (ISD) being optimized by ISERD. The fouled ISERD-based configurations have been proven to sustain optimum permeate recovery to 55%-60%, produce permeate TDS of 397 mg/L (ISERD), and lower 378 mg/L (ISERDISD), better compared to 40-45% and TDS of 436 mg/L (standard one). Thanks to an improved flux distribution, the foulant deposition was halved to 11.7 in ISERD from 20.4 g/m2 and reduced further to the level of 10.3 g/m2 in ISERDISD. The ISERD exhibited almost the same apparent SEC as that of standard one (3.34 vs 3.26 kWh/m3), while ISERDISD exhibited reduced level to 2.75 kWh/m3. The incorporation of the fouling into the unit water cost (UWC) showed ISERDISD being the least costly with $0.45/m3 compared to $0.47 and $0.59/m3 for the ISERD and standard configurations respectively. An ultra-high-pressure membrane, osmotic dilution, and antiscalants for the loaded second stage might be recommended for ISERDISD implementation.