Thin film composite membrane based forward osmosis with complex inorganic draw solution for copper removal

Abstract

In order to efficiently remove heavy metal ions from wastewater using forward osmosis (FO), selection of preferable membrane and draw solution (DS) is essential. Thus, the purpose of this study is to investigate the synergistic effect of thin-film composite membranes (TFCs) with complex MgCl2 draw solution for the removal of copper (II) from its aqueous solution using FO. A total of five TFCs with different concentration ratio of polyethyleneimine (PEI) over piperazine (PIP) annotated as 1.0- PIP, 0.3-PEI, 0.5-PEI, 0.7-PEI and 1.0-PEI were fabricated and the physicochemical properties of these membranes were characterized using Fourier transform infrared spectroscopy, scanning electron microscopy, atomic force microscopy, zeta potential and contact angle analysis. Preliminary performance study was done using nanofiltration system on their water fluxes and Cu (II) rejection. The used TFCs were then autopsied under energy dispersive X-ray (EDX) to examine copper attachments on it. Meanwhile, MgCl2 undergoes complexation with complexing agent poly(sodium 4-styrenesulfonate) (PSS). The affinity of MgCl2 with PSS with fixed loading was first studied at different pH (3.0, 5.0, 7.0 and 9.0) using dead-end filtration system. Study of PSS loadings (0.0, 0.1, 0.5, 1.0, 2.5 and 5.0 w/w%) was done later using FO system at 1.0 M MgCl2 DS and reverse solute flux (RSF) was determined. From all of the aforementioned experiments, removal of Cu (II) using FO was carried out at different feed concentrations (1000, 2000 and 5000 ppm) and the performances in term of water flux and rejection were discussed. Physicochemical analysis confirmed the formation of polyamide layer for all TFC membranes. Zeta potential revealed that the positivity of the TFCs’ surface charge increased in an order of 1.0-PIP < 0.3-PEI < 0.5-PEI < 0.7-PEI < 1.0-PEI. Consequently, 1.0-PEI exhibited higher flux compared to 1.0-PIP owing to its higher hydrophilicity. Interestingly, excellent selectivity of 1.0-PEI resulted in Cu (II) ion rejection of more than 95% and 99% in NF and FO operation respectively outperforming the other produced TFCs. EDX result further explained that the copper rejection was also facilitated by the electrostatic interaction with the surface charge of the TFCs. Based on the performance evaluation, 1.0-PIP was selected for complexation study since it portrayed good capability of Cu (II) retention and better FO water flux. Complexation of MgCl2 with PSS was able to lower the effect of RSF up to 60% reduction while maintaining satisfactory water fluxes compared to the control MgCl2 DS. Final Cu (II) rejection by FO using 1.0-PIP and the 1.0 w/w% PSS-MgCl2 complex DS revealed that the water flux slightly decreased with average Cu (II) retention of 95% with increasing Cu (II) feed concentration. This study promotes FO as a promising option for heavy metals removal application using innovative DS with lowered RSF.