| Vacuum-enhanced direct contact membrane distillation (VEDCMD) and forward osmosis (FO) were investigated as potential membrane separation processes for water recovery enhancement in desalination of brackish water. Past studies have demonstrated that both VEDCMD and FO can be effectively utilized in the treatment of a wide range of highly concentrated feed solutions, including saline water. In the current study, two brine streams with average total dissolved solids concentrations of 7,500 and 17,500 mg/L were further desalinated by VEDCMD and by FO. In both processes high water recoveries were achieved; however, recoveries were limited by inorganic scale deposition on the membrane surface. Various cleaning techniques were able to remove the scale layer from the membrane and restore water flux to almost initial levels. FO achieved water recoveries up to 90 percent from the brines and VEDCMD achieved water recoveries up to 81 percent from the brines. Addition of a scale inhibitor during both processes was effective at maintaining high water flux for extended time and further enhancing water recovery. When considering the combined water recovery of EMWD and the investigated processes, close to 97 percent total recoveries were achieved for both the VEDCMD and FO systems.; Keywords. desalination, forward osmosis, membrane distillation, brackish water, zero liquid discharge, brine disposal... |
