Thin film nanocomposite forward osmosis membrane incorporated with bimetallic oxide for heavy metal removal

Abstract

Heavy metal contamination which has threatened human health is a critical environmental issue that caused by the uncontrolled discharge of heavy metal. Membrane technology has been justified as one of the favourable options in wastewater treatment for contaminants removal due to its high rejection to produce high quality of treated water. Recently, forward osmosis (FO) has emerged as an attractive alternative of conventional approaches such as adsorption and reverse osmosis (RO) for heavy metal removal. The advantages of FO process include lower energy consumption and less fouling tendency. During the separation processes, FO membrane ensures the water pass through the membrane while all the dissolved metal ions could be separated and filtered by the TFN FO membrane. Despite the advantages of FO, the major issue of FO membrane is to confront with interfacial concentration polarization (ICP) which causes the deterioration of flux over time. The reduction of critical ICP issue and increased water flux through the modification of TFC membrane by incorporating functional nanomaterials into the substrate layer of the FO TFC membrane has been proven as a feasible strategy to heighten the performance of FO membrane. In this study, thin film nanocomposite (TFN) FO membranes incorporated with titania nanotubes and magnetite oxide (TNT–Fe3O4) hybrid has been successfully fabricated. The TNT–Fe3O4 hybrid nanoparticles was synthesized through hydrothermal and coprecipitation method. In the first stage of this study, different types of nanoparticles i.e. TNT, Fe3O4, TNT–Fe3O4 were embedded into polysulfone (PSf) substrate. The performance of the TFN FO membranes were evaluated for heavy metal removal using the FO system at active layer facing feed solution (AL–FS) mode. Using the membrane incorporated 0.5 wt% of TNT–Fe3O4 hybrid nanoparticles, the FO water flux of 2.84 L/m2.h and 2.54 L/m2.h and the rejection of 98.06% and 88.37% were achieved for Cd2+ and Pb2+ removal, respectively. In the second stage, the effect of different loading of TNT–Fe3O4 embedded into PSf substrate was investigated. The loading of TNT–Fe3O4 hybrid plays a role in improving the FO water flux and rejection, particularly with the increasing loading of the nanofiller. The TFN 0.5 membrane exhibited good water permeability (A) with 3.60 L/m2.h.bar, salt permeability (B) with 2.33 x10-8 m/s and 95.94% of salt rejection. TFN 0.5 achieved the small structural parameters with 1.45 mm and 1.60 mm in Cd2+ and Pb2+ removal, respectively. In addition, the optimized membrane exhibited high flux recovery and rejection which indicated a good quality of the TFN FO membrane. As a conclusion, modification of TFN FO membrane by incorporating TNT–Fe3O4 hybrid as nanofillers in the substrate layer is a promising approach to improve membrane permeability and selectivity.