Evaluation of FO-RO and PRO-RO designs for power generation and seawater desalination using impaired water feeds

PRO and FO coupling with an RO membrane process is proposed to reduce the cost of seawater desalination and the potential for power generation. Three conceptual design configurations, PRO-RO, FO-RO and RO-PRO were evaluated here using standard seawater concentration and impaired water as the draw and the feed solutions respectively. The PRO-RO and RO-PRO designs were evaluated for power generation and seawater desalination while the FO-RO design was proposed for seawater desalination only. The impact of the draw and feed solutions' flow rate and the impaired water TDS on the performance of each design was estimated using pre-developed software. The simulation results showed that the performance of all designs was more sensitive to the increase in the flow rate of draw solution than to the flow rate of feed solution. Furthermore, all designs showed a decrease in membrane flux and recovery rate with increasing the TDS of feed water from 0.2 g/L to 10 g/L as a result of decreasing the net driving force across the membrane and the concentration polarization phenomenon. The FO-RO design produced the lowest RO permeate concentration followed by the PRO-RO and RO-PRO designs respectively. In terms of power generation, the RO-PRO design was more efficient than the PRO-RO design. The FO-RO design exhibited the lowest desalination power consumption followed by the PRO-RO and RO-PRO designs respectively. At 10 g/L feed concentration, the net power consumption in the FO-RO was 9.4% less than that in the PRO-RO which was in turn 5.3% less than that in the RO-PRO design. The estimated cost of the FO/PRO module in the PRO-RO design was 2.2 and 4.3 times higher than that in the FO-RO and RO-PRO designs respectively.