Effect of applied pressure on iron and manganese rejection by polyamide and polypiperazine amide 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 and ultrafiltration 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 membranes denoted as PA-NF, PPA-NF and PA-UF were selected to investigate the iron and manganese rejection at low applied pressure range (1-5 bar). In single solute solution with feed concentration at 10 ppm 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 and PA-UF were 86.6% and 81.1%, respectively whereby both membranes were unable to remove iron to the allowable drinking water standard. The rejection of manganese with single solute at concentration of 1 ppm with initial pH of 6.8 ± 0.5 by using the PA-NF membrane was >98% and almost all of manganese were rejected at 5 bar. Nevertheless, manganese removal by PPA-NF and PA-UF membranes were found less than 70% and 40%, respectively. Findings from this work showed that the applied pressure was significantly influenced the water flux however the removal of iron and manganese were independent. 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 iron removal from synthetic groundwater.