Evaluation of forward osmosis as a pretreatment process for multi stage flash seawater desalination

Abstract

The present study evaluates the feasibility of applying forward osmosis (FO) process for the pretreatment of feed solution to a Multi Stage Flash (MSF) desalination plant. For the first time, real brine reject and real seawater were used as the draw solution and the feed solution, respectively in the FO process. The FO pretreatment is expected to dilute the brine reject and reduce the concentration of divalent ions, which are responsible for scale formation on the surface of heat exchanger in the MSF evaporator unit. The FO experiments were performed at different draw solution temperatures ranging between 25 -40 o C, different draw and feed solutions flowrates and different membrane orientations. A maximum average membrane flux of 22.3 L/m 2 .h was reported at a draw solution temperature of 40 o C and 0.8 and 2.0 LPM flow rate of draw and feed solutions, respectively. The experimental results also revealed the process sensitivity to the feed solution temperature. It was found that the average membrane flux in the FO process operating at 0.8 and 2 LPM draw and feed solution flow rates, respectively was 16.9 L/m 2 .h at 25 o C brine temperature but increased to 22.3 L/m 2 .h at 40 o C brine temperature. These membrane fluxes resulted in 3% and 8.5% dilution of the draw solution at 25 o C and 40 o C temperatures, respectively. The average membrane flux in the FO mode was equal to that in the PRO mode at low flow rates but it was lower than that in the PRO mode at high flow rates of the feed and draw solutions. The outcomes of the study are very promising with regard to membrane flux and dilution of draw solution.

Novel Thermal Desalination Brine Reject-Sewage Effluent Salinity Gradient for Power Generation and Dilution of Brine Reject

“…MSF technology has been in operation since the sixties and gained great credit for the capability to handle the harsh environmental conditions of seawater in the Middle East. Due to the salinity of seawater in the Middle East, the total dissolved solids (TDS) of the expelled brine from the MSF plant usually is about 80 g/L, 1.37M NaCl [15]. The salinity of seawater brine reject is higher than the salinity of seawater (35 g/L), around 2.3 times higher, which provides tremendous osmotic power for the PRO process when coupled with a low salinity feed solution such as TSE, TDS 0.026M NaCl (1.5 g/L) [7].…”

“…The salinity of seawater brine reject is higher than the salinity of seawater (35 g/L), around 2.3 times higher, which provides tremendous osmotic power for the PRO process when coupled with a low salinity feed solution such as TSE, TDS 0.026M NaCl (1.5 g/L) [7]. In addition to its high osmotic pressure, the temperature of brine reject's is always from 10 • C to 15 • C higher than seawater, which provides an additional advantage since both permeation flow and osmotic pressure of the membrane incline to increase when a higher feed solution's temperature occurs [15]. Coupling the brine reject with the TSE as a source of salinity gradient has a high prospect for generating power in the PRO as a result of its high osmotic energy.…”

“…Seawater desalination by the MSF technology is one of the conventional methods for freshwater supply in the regions of high seawater salinities. The MSF technology can handle high seawater salinities and produce freshwater of high quality [15]. Brine reject and TSE are paired in the PRO process to generate energy and dilutes the feed solution to the MSF plant ( Figure 1).…”

Chitosan‐modified graphene oxide as a modifier for improving the structure and performance of forward osmosis membranes

“…In various membrane processes, forward osmosis (FO) utilizes the osmotic pressure difference between the feed (FS) and draw solutions (DS) to induce spontaneous water diffusion across a semipermeable membrane, which is different from pressure‐driven membrane processes, such as reverse osmosis (RO), nanofiltration, and ultrafiltration (UF). FO technology has recently attracted great interest in industrial application and academic research due to its low hydraulic pressure, fouling tendency, and energy requirement …”

“…FO technology has recently attracted great interest in industrial application and academic research due to its low hydraulic pressure, fouling tendency, and energy requirement. [1][2][3] During FO process, FO membrane is crucial and determines FO application and separation efficiency. However, existing FO membranes often exhibit low water permeability due to internal concentration polarization (ICP).…”