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Influence of transmembrane pressure and feed concentration on the retention of arsenic, chromium and cadmium from water by nanofiltration.

One of the main toxic pollutants in drinking water is heavy metals which must be reduced to standard levels. Removal of trace amounts of heavy metals can be achieved by means of membrane processes such as nanofiltration. The removal efficiency of a nanofiltration membrane is strongly affected by operating conditions. The present study focused on the effect of two key parameters, i.e., transmembrane pressure and feed concentration on the removal of heavy metals (arsenic, chromium and cadmium) from water by a polymeric nanofiltration membrane UTC-70UB charged negatively. The rejection experiments included variation of heavy metals feed concentrations in the range of 100 to 400 microg/L for arsenic and chromium and 20 to 80 microg/L for cadmium, and different transmembrane pressures in the range of 5 to 14 bar. The results indicated that under most conditions tested in this research, the rejection of heavy metals was found to increase when the transmembrane pressure was increased. The results also showed the high rejection percentage of the heavy metals, with the maximum retention values of arsenic, cadmium and chromium, 97%, 100% and 95% respectively. The percent reduction of arsenic and chromium was found to enhance as their concentration in the feed increased. However, in the case of cadmium, the rejection was reduced with increase in the concentration.