Water-energy nexus for estuarine systems with seasonal salinity variations: A thermodynamic feasibility analysis of reverse osmosis (RO)-pressure retarded osmosis (PRO) combinations

Abstract

The underlying philosophy of pressure retarded osmosis (PRO)-reverse osmosis (RO) hybrid technology is the assumption of the availability of 'fresh' water for the purpose, which gets severely affected once the fresh-water streams undergo seasonal salinity variations. In the present article, the authors have tried to understand the overall feasibility of PRO-RO combination in such estuarine systems with appreciable variation of seasonal salinity. The article first discusses the feasibility of pretreating the feed of PRO using RO and later understanding the feasibility of PRO as supplemental technology to existing RO units. It was found that pretreating the PRO feed in such estuarine systems was energetically infeasible. However, PRO as supporting technology was found to produce energy of around 0.0994 kWh for 50% recovery. It was also concluded that with a fraction of RO permeate used for PRO, energy savings increase for estuarine systems with seasonal salinity variations.