Fabrication and modification of forward osmosis membranes by using graphene oxide for dye rejection and sludge concentration

In this study, the preparation procedures for the polysulfone (PSf) substrate and polyamide (PA) selective layers were systematically investigated to determine their effects on the separation performance of thin-film composite (TFC) forward osmosis (FO) membranes in terms of the permeate flux (J(w)) and reverse solute flux (J(s)). Furthermore, the PA active layer was modified by adding different proportions of an emerging material, graphene oxide (GO), to increase J(w) and decrease J(s) . The experimental results indicated that special attention should be paid to the preparation of the PSf casting solution, which required thorough degassing, sealing, and humidity and temperature control. The optimum casting height was discovered to be 175 mu m. For PA layer formation, the same amount of polymer solutions (resulting thickness of 78.5 mu m) on the top surface of the PSf substrate (on the side facing the water during phase inversion) resulted in the highest FO performance. GO modification of the PA layer at the dosage of 0.0175 wt% considerably enhanced J(w) to 14 L m(-2) h(-1 )and reduced J(s) to 0.23 mol m(-2) h(-1). However, higher GO dosage (0.02 wt%) led to lower membrane performance due to aggregation of GO nanoparticles, as confirmed using scanning electron microscopy. Next, the prepared membranes were applied to dye rejection and sludge concentration for water recovery. The virgin and modified FO membranes both exhibited high rejection efficiency (>= 96.0 %) for dyes commonly used in the textile industry. The 0.0175 %-GO-modified FO membrane exhibited a higher concentration factor (1.67) and greater water recovery (40.0 %) than the virgin membrane (1.45 and 31.2 %, respectively). Therefore, the application of FO for water recovery is economic and environmentally friendly in terms of saving the transportation cost of sludge disposal while recovering water for reuse in wastewater treatment plants. (C) 2020 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.