Dual stage PRO process for power generation from different feed resources

A dual stage PRO process is proposed here for power generation using osmotic energy. The process is able to handle a wide range of feed water salinities with different pretreatment requirements in order to reduce the membrane fouling problems. In the current study, the salinity gradient resource consisted of seawater at standard TDS, 35 g/L, while the first stage feed water was brackish water or fresh water and the second stage feed water was wastewater effluent. The diluted seawater from the first stage of PRO process was the draw solution in the second stage of PRO process. The performance of dual stage PRO process was evaluated for a number of brackish water salinities ranged from 1 g/L to 5 g/L. The TDS of wastewater and freshwater was assumed 0.2 g/L. The results showed that a better PRO performance was achieved when the brackish water and the wastewater were introduced in the first stage and the second stage respectively. In case when wastewater and brackish water were introduced in the first and second stage respectively there was about 28% decrease in the second stage permeate flow. The results also showed a decrease in the first stage permeate flow with increasing the feed salinity but the second stage permeate flow increased with increasing the feed salinity. Furthermore the results showed that the first stage maximum power density was achieved at Delta P = Delta pi/2 while the second stage maximum power density was achieved at Delta P = Delta pi/1.5. Unlike the conventional PRO process, it has been found that the impact of feed salinity increase on the performance of dual stage PRO process was insignificant. Finally, the power generation in the dual stage PRO process was higher than that in the conventional PRO process. The difference was equal to the entire amount of power generated in the second stage of PRO process. Crown Copyright (C) 2014 Published by Elsevier B.V. All rights reserved.