Salinity Gradient Energy Recovery with Batch Reverse Osmosis

Abstract

Integrating desalination with energy requires dispatchable mechanisms to modulate power consumption over time. Related, Blue Energy technologies like pressure retarded osmosis (PRO) have struggled to be viable, but may find a niche where regulations require dilution of desalination brine. In this paper, we study the technological and economic feasibility of coupling double-acting piston Batch Reverse Osmosis (BRO) with PRO. Two different hybrid configurations were developed as a demand-response method to provide electrical energy to the grid and are compared to stand-alone RO and BRO. We considered desalinating seawater with an overall recovery ratio of 50% and PRO operating by mixing BRO brine with wastewater effluent. The hybrid configurations were able to substantially lower the overall energy consumption of desalination by up to 26.6% compared to stand-alone RO and 10.2% compared to a stand-alone BRO. Sensitivity analysis reveals that high water permeability, low salt permeability, and high collapse pressure membranes can favor energy recovery. While the economics are very location-dependent, the levelized cost of water in hybridized systems is still above stand-alone desalination systems due to the extra membrane modules installed. Nonetheless, hybrid configurations are flexible in delivering electricity to the grid or lowering the energy consumption of desalination.

Keywords: Specific energy consumption, Reverse osmosis, Batch reverseosmosis, Pressure retarded osmosis, demand response