Abstract

Pressure-Retarded Osmosis (PRO) is an osmotic process that is used to harvest energy from salinity gradients using a semi permeable membrane. The driving force in this system is the difference in produced osmotic pressure between feed and draw solutions. Water flows across the membrane from the feed side and mixes with the draw solution. The draw solution is pressurized at pressure less than the net driving force and depressurizes in a turbine to generate electricity. A thorough comparison between open-loop PRO (OLPRO) and closed-loop PRO (CLPRO) was made regarding their performance and costs. In this study, gold mining wastewater was investigated to be used as the feed solution in PRO and its potential was evaluated. Prior to the main process, this solution was pretreated using ultrafiltration (UF) and nanofiltration (NF) to separate large molecules, colloids, multivalent ions, heavy metals, etc. In each step the fouling components and mechanism were explained. NF permeate characterization showed high removal efficiency of the present ions and heavy metals separation. In PRO, a solution of NH_3-CO_2 with concentration of 3M were used as the draw solution. The proposed system could generate power density of 15.0 ± 0.4 W⁄m^2 . In the last section, Thermal efficiency was calculated and improving this efficiency were discussed. Overall, the utilization of the mining wastewater as the feed solution in PRO showed good potential, though, foulant elements may still have a major impact on pre-treatment steps and harnessing the full potential of the PRO process.