Optimization of energy extraction from salinity gradient using full-scale pressure retarded osmosis systems with hollow fiber membrane modules

Abstract

Pressure-retarded osmosis (PRO) involves a high concentration solution that is circulated through a semipermeable membrane and used to draw water permeate from a lower concentration solution by osmosis. PRO is a membrane-driven process in which the chosen membrane module plays a significant role in energy harvesting. This study aims to evaluate the effect of flow rate, pressure and concentration of draw solutions (30–180 g L−1) on the performance of a full-scale PRO process and by incorporating the characteristics of a 10-inch hollow fiber membrane module from Toyobo Company Ltd. A single-stage PRO system with up to 3 membranes in series in a pressure vessel was considered, and the consumption of the pumps and energy recovery devices were taken into consideration. The results show the optimal operating conditions that maximize net power while varying the draw solution concentration and pressure and both water stream flow rates. A net power density of 2.56 W m−2 was achieved for the concentration gradient of 179.5 g L−1. The present work concludes that single-stage full-scale PRO systems would be energetically feasible, although the results obtained need to be compared with an experimental plant taking into account membrane tear and fouling.