Removal of iron and manganese from groundwater by nanohybrid silver decorated graphene oxide (Ag-GO) polysulfone nanofiltration membrane

Iron (Fe) and manganese (Mn) are common metallic elements that naturally coexist in groundwater. Elevated levels of these metallic ions will result in an undesirable rusty taste and reddish hue, rendering the water unsuitable for consumption. Polymer-based membrane technology can play a significant role in removing Fe and Mn from groundwater. However, polymer-based such polysulfone (PSf) membrane possessed a hydrophobic characteristic. Thus, the objective of this study was to fabricate and characterize PSf nanofiltration membrane impregnated with silver decorated graphene oxide (Ag-GO) via wet phase inversion technique. Based on results obtained, PSf/Ag-GO exhibit enhanced properties, such as good water flux (32.47 L/m2.h) and improved hydrophilicity (89% of porosity). The performance of fabricated membranes was studied using a bench-scale dead-end stirred cell by investigating salt (1000 mg/L) rejection and Fe & Mn removal at feed concentration of 10-100 mg/L and 1 mg/L, respectively. Results showed that the rejection of Na2SO4 was higher compared to NaCl. Good rejection of Fe and Mn was also achieved higher than 85%. The most substantial impact on removal efficiency was caused by adjusting the pH of feed solution (pH 3-12). The removal of Fe and Mn was found significantly higher at basic pH (between 9 and 12) compared to acidic pH. This was due to the transformation of soluble divalent Fe2+ and Mn2+ ions to insoluble Fe3+ and Mn4+. At this condition, it is expected that the rejection mechanism by sieving effect has contributed to the improvement of Fe and Mn removal in basic pH. In conclusion, embedding Ag-GO has successfully improved the hydrophilicity of PSf membranes due to the additional of hydroxyl group and more importantly, able to achieve high removal of Fe and Mn at 10 – 100 mg/L. Above all, the rejection mechanism of Fe and Mn was found have been impacted by the adjustment of feed solution pH whereby the sieving effect and Donnan effect are resulted by the solute-membranes interaction.