Optimization of Integrated Forward – Reverse Osmosis Desalination Processes for Brackish Water

Abstract

Reverse Osmosis (RO) is a membrane desalination process which considered to be an efficient technology for desalination. However, the performance of RO process is facing some challenges; the most important of them are the energy consumption and fouling problem due to external concentration polarization (ECP). Forward osmosis (FO) is an osmotic-driven membrane desalination process, it exhibits lower energy consumption than pressure driven process like RO. It has been suggested to be coupled with RO in order to reduce salinity and the energy consumption. For this objective, a mathematical model has been designed to optimize the operational conditions for FO, RO and FO-RO hybrid system. Firstly, an individual FO experiment has been conducted using urea and sodium chloride as draw solutions to evaluate the FO performance in both agriculture waste treatment and desalination. Then, a modeling approach of an individual FO process has been investigated with considering water flux, solute flux and concentration polarization. In addition, the performance of FO-RO integrated system was compared with conventional RO process in terms of energy consumption, permeate quantity, quality and solute flux. The results of modeling calculations showed that the feed solution concentration, draw solution concentration and concentration polarization are very important factors that affect the overall performance. In addition, it indicated a good performance of individual FO process. Moreover, it revealed increase in both water productivity and permeate quality and a significant decline in energy consumption upon using the efficient FO-RO hybrid system to about 0.9 kWh/m3. Consequently, it offered high energy saving ranged between 87.57% and 87.81%, which confirmed that FO/RO integrated system is more energy efficient than the RO process only.