Enhancing energy efficiency and water recovery in two-stage seawater reverse osmosis through advanced brine treatment technologies

Two-stage reverse osmosis (2SRO) has demonstrated superior energy efficiency and higher clean water productivity compared to single-stage reverse osmosis. However, 2SRO energy consumption is still relatively high. Recently, advanced technologies for brine treatment using RO membranes have been developed such as Osmotically Assisted Reverse Osmosis (OARO), Low-Salt Rejection Reverse Osmosis (LSRRO), and Cascading Osmotically Mediated Reverse Osmosis (COMRO). These technologies help to overcome the limitation of maximum applied pressure of conventional RO. In this study, we use the concept of OARO, COMRO, and LSRRO to enhance the performance of 2SRO. We first suggested possible integration of OARO, COMRO, and LSRRO in 2SRO, then determined the specific energy consumption, the energy efficiency, and the maximum achievable water recovery of each configuration. The results demonstrated superior performance of the proposed configurations compared to 2SRO, with higher water recovery and better overall energy efficiency. Specifically, LSRRO achieved 70 % water recovery and 46 % energy efficiency, while OARO and COMRO delivered 72 % water recovery with energy efficiency of 46 % and 66 %, respectively. To decide on the feasibility of the suggested integrations, we performed a techno-economic analysis using the levelized cost of water, payback period, and return in investment as financial performance metrics. The analysis revealed a very promising result where the levelized cost of water is reduced from $1.1/m 3 to $0.79/m 3 in a payback period of 4.2 years, instead of 5.7 years for 2SRO, indicating that the proposed configurations can have a significant impact on improving the performance of existing RO desalination plants. • The integration of brine treatment technologies in two-stage RO has been investigated. • The energy consumption and energy efficiency have been assessed. • Water recovery of 72 % is achievable with only ∼3 kWh/m 3 of energy consumption. • Levelized cost of water can be reduced by ∼25 % using the proposed configurations.