Performance analysis of serially-connected membrane element for pressure-assisted forward osmosis: Wastewater reuse and seawater desalination

Abstract

Forward osmosis-reverse osmosis (FO-RO) hybrid process has gained much research attention as a promising alternative to reduce energy consumption and overall plant cost of conventional stand-alone seawater reverse osmosis. Furthermore, pressure-assisted forward osmosis-reverse osmosis (PAFO-RO) hybrid has been suggested to further improve FO water flux and enhance draw stream dilution. Several pilot-based performance analyses and economic assessments using commercial FO modules have been reported to validate the feasibility of this hybrid process in recent years. However, FO/PAFO performance evaluated using real seawater and wastewater has been hardly reported, especially regarding the effect of hydraulic operating conditions. The current study was dedicated to provide a performance analysis of serially-connected FO 8040 spiral-wound element under a broad range of feed, draw flowrate and hydraulic pressure. The results revealed that there was no significant improvement in water flux above 20 LPM of feed flowrate and 5 LPM of draw flowrate regardless of hydraulic pressure and number of elements in a serial configuration. In addi-tion, a significant discrepancy of PAFO performance between artificial and field water conditions was observed. Overall water flux under field water condition was almost half of that under artificial water condition. Diluted concentration showed a relatively smaller discrepancy between the condi-tions, yet, this performance difference can potentially alter the economic feasibility of the FO-RO or PAFO-RO hybrid process. The result and discussion in this study imply that economic assessment based on artificial water conditions can misrepresent the actual economic feasibility of the hybrid process.