Comprehensive analysis of a hybrid FO-NF-RO process for seawater desalination: With an NF-like FO membrane

Abstract

Process optimization is a popular strategy to improve efficiency, reduce the energy consumption and total cost of the seawater reverse osmosis (SWRO). Forward osmosis (FO) process with a nanofiltration (NF)-like membrane has emerged as a cost-effective technology for seawater desalination pretreatment, due to its high water permeability and low energy consumption compared to RO-like FO membrane. The present work comprehensively evaluated the potential of using an NF-like FO membrane for SWRO pretreatment and analyzed the feasibility of the NF-like membrane-based FO-NF-RO process for seawater desalination. The performance of the FO-NF-RO integrated process was investigated with MgSO4, Na2SO4, and Mg(CH3COO)2 as draw solute, respectively. Besides, the energy consumption and total cost of the hybrid process were also estimated on the laboratory and large scale. The NF-like membrane-based FO process could effectively remove organic molecules and divalent ions effectively. The hybrid process product water could reach the drinking water standard in China (TDS ≤ 1000 mg/L). When water recovery was 42.0%, the hybrid process could produce freshwater with specific energy consumption of 2.99 kWh/m3 and specific water cost of 0.92 $/m3, which were comparable with the conventional SWRO process. Overall, our study revealed the feasibility of the FO-NF-RO process for seawater desalination.