Forward osmosis for water recovery using polyelectrolyte PolyDADMAC and DADMAC draw solutions as a low pressure energy saving process

20 Feb 2019

Polydiallyldimethylammonium Chloride (PolyDADMAC) is a cationic polyelectrolyte utilised widely in drinking water industry. This study has evaluated the performance of cationic organic polyelectrolyte PolyDADMAC and its monomer DADMAC as osmotic agents in Forward Osmosis (FO) process. The properties of PolyDADMAC and DADMAC draw solutions were initially studied. Thereafter, a series of experiments were conducted to examine the efficiency of these solutions for water recovery using CTA and Aquaporin flatsheet membranes under FO mode. The results show a high electrical conductivity of both draw solutions due to the presence of strong cation electrolyte (C8H6N+) in solutions. The obtained water flux and reverse solute diffusion of DADMAC were higher than PolyDADMAC at same concentrations. Factors contributing to the change of water flux and reverse solutes diffusion through membranes were addressed. CTA membranes accomplished higher water flux than the aquaporin membranes, however; the latter was more selective and provided better results of reverse solutes diffusion. Diluted draw solutions were reconcentrated via Nanofiltration-system. High ion rejection of DADMAC (96%) and poor ion rejection of PolyDADMAC (85%) were observed. Lastly, this article introduced a valuable comparison between cationic polyelectrolyte and its electrolyte based on their behaviours as draw solutes in FO process.