Study on the Effect of Applied Pressure on Iron and Manganese Rejection by Polyamide and Polypiperazine Amide Nanofiltration Membranes
The aim of this research is to investigate the removal behavior of iron and manganese that naturally exist as divalent ions in groundwater by using nanofiltration membranes. The main focus of this study is to better understand the effect of applied pressures during the rejection of these metallic ions from synthetic groundwater in order to achieve drinking water standard. Polyamide and polypiperazine amide nanofiltration membranes denoted as PA-NF and PPA-NF were selected to investigate the iron and manganese rejection at low applied pressures (1-5 bar). In single solute solution with feed concentration at 10 mg/L and initial pH of 6.8 ± 0.5, the rejection of iron was ≥96% by PA-NF membrane at applied pressure of 2 bar. However, the rejection percentage by PPA-NF was 86.6% whereby this membrane unable to remove iron to the allowable drinking water standard. The rejection of manganese with single solute at concentration of 1 mg/L with initial pH of 6.8 ± 0.5 by using the PA-NF membrane was ≥98% and almost all of dissolved manganese were rejected at 5 bar. However, manganese removal by PPA-NF membrane was found less than 70% for all of the applied pressures. Findings from this work showed that the removal of iron and manganese were dependent on the applied pressures. PA-NF membrane able to remove both metallic ions that comply with the drinking water standard. The increased of applied pressure contributed to concentration polarization effect on the membrane surfaces leading to a decrease in solute rejection by decreasing the charge effect mainly for the iron removal from synthetic groundwater.