Evaluation of a natural polymer-based cationic polyelectrolyte as a draw solute in forward osmosis

We synthesized cationic starch by grafting 2,3-epoxyproplytrimethylammonium chloride onto the backbone of corn starch, and investigated its potential as a draw solute in forward osmosis (FO). The experimental results have shown that the as-prepared cationic starch easily dissolved in water; at 30 wt% cationic starch solution, the osmotic pressure was 11.91 atm. Increasing the solution temperature decreased the viscosity of the draw solution and resulted in a higher flux of water from the feed solution. For the 30 wt% cationic starch at 45 °C, the maximum flux of water from deionized water was 4.10, and that from a 2 g L− 1 NaCl feed solution was 2.20 L m− 2 h− 1 (pressure retarded osmosis mode). In addition, the cationic starch was satisfactory for protein concentration without protein denaturation. The diluted draw solute was also recovered, and the results indicated that ultrafiltration was effective to reconcentrate the diluted draw solution with a rejection rate > 99% at a concentration < 6 wt% cationic starch. To improve the water flux during the regeneration process, membrane crossflow filtration or other recycling membrane processes, such as membrane distillation, were recommended. Cationic starch was demonstrated to be feasible as a draw solute in FO processes.