Effect of operating variables in ionic solutes removal from groundwater by nanofiltration membranes

The presence of heavy metals in groundwater is a persistent problem in many parts of the world. Membrane technology
could be considered as an alternative technology for heavy metals removal from water. Iron and manganese naturally occur in groundwater. These metallic ions at excessive amount, contribute to rusty taste with reddish color that is unsuitable for drinking or daily usage. In this study, rejection of heavy metals (iron (Fe) and manganese (Mn)) by two commercially available nanofiltration membranes, TS-40 and TFC-SR3 were investigated. Low applied pressure and adjustment on feed pH have influenced the metallic ions rejection mechanism. Experimental results showed that rejection of both metals by using TFC-SR3 was much higher than TS-40 membrane. An increase of applied pressure has decreased Fe rejection for TFC-SR3 (99-94%) and TS-40 (86-69%) due to solvent permeability. A similar decreasing trend was also observed for Mn rejection by TFC-SR3 (92-75%) and TS-40 (75-65%). In the aim to achieve drinking water standard, feed pH was adjusted in the range of 3 to 9. Rejection of both metals was improved. At pH 9, permeate concentration (Cp) has reached the drinking water standard for TFC-SR3 (0.07 mg Fe/L and 0.04 mg Mn/L) and TS-40 (0.14 mg Fe/L and 0.18 mg Mn/L). The pH adjustment has significantly influenced membrane performance due to solute-membrane interaction. As for conclusion, all findings proved that nanofiltration is a promising method for groundwater treatment in drinking water production.