Development of the polymer-enhanced forward osmosis desalination process

Abstract

Global stress on depleting water resources due to man-made contamination and exhausting freshwater reservoirs has increasingly drawn attention to the desalination of sea water as a renewa-ble source of freshwater. Sea water constitutes 97% of the water resources on earth and if desalinat-ed, can potentially yield an unlimited supply of freshwater. Currently, two major desalination tech-nologies are commercially available: Reverse Osmosis (RO) and thermal distillation. However, economic widespread use of these technologies is largely limited due to their exorbitant cost. On the other hand, Forward Osmosis (FO) is a considerably less energy intensive process in which natural thermodynamic driving force is utilized. Core research topics on FO include development of suita-ble membrane and draw solution. Conventional researches on FO desalination process focus on the use of electrolyte solution to extract fresh water, but high energy input requirement in draw solute recovery process is often neglected. The purpose of this research is to propose the new concept Forward Osmosis(FO) process with water soluble polymer. Therefore, development of a novel draw solute with high osmotic pressure and its economics in recovery process were investigated in this study. Lab-scale FO desalination process and ultra-filtration process for draw solute separation were designed and setup. Polyethyleneimine (PEI) is a hyper branched water-soluble polymer which contains a high density of amine groups in its structure. The presence of labile amine groups in PEI renders it very attractive in many areas of application. For this reason, we have proposed PEI as a potential draw solute for the FO process. Effects of various parameters, such as concentration of draw solution, temperature, viscosity and etc., on water flux performance were studied by using lab-scale FO de-salination process system. Ultrafiltration (UF) was used to reconstitute the PEI draw solute and separate PEI it from the pr...