As(V) rejection by NF membranes using high temperature sources for drinking water production

In Nicaragua, a Central American country, geothermally influenced waters are frequently found to be contaminated with arsenic (as As(V)). This study investigated the effect of high-temperatures (25–50 °C), as found in geothermally influenced source waters, on the rejection of monovalent H2AsO4 - and divalent HAsO4 2- species (at pH 6,7 and 8) during NF membrane filtration of a multi-component solution containing Cl- and HCO3 -. In this multi-component solution, As(V) rejection was found to be enhanced at higher temperatures, which was in contrast to the previous assumption that temperature increase would have a negative effect on As(V) rejection. Previous studies were conducted with deionized waters, where pore size expansion and decreased viscosity drove As(V) rejection; however, in the presence of other anions such as those utilized in this study, As(V) rejection was promoted at higher temperatures. The enhancement of As(V) rejection at high temperature was associated with the presence of HCO3 - and Cl-, which are considerably more permeable than both As(V) species. An additional advantage of the higher temperature was the lower feed pressure (down to 1.5 bar) needed to operate these NF membranes, compared to colder waters. The lower energy consumption in combination with the improvement in As(V) rejection at higher temperatures shows the potential application of this technology for efficient treatment of As(V) contaminated, geothermally influenced waters for decentralised, rural drinking water production, in As-affected countries such Nicaragua.