Nanofiltration and microfiltration for the removal of chromium, total dissolved solids, and sulfate from water

This study was designed to evaluate the hybrid system performance of nanofiltration (NF) and microfiltration (MF) processes in removing the hexavalent chromium (Cr(VI)) and sulfate from water. To do so, we made a hybrid pilot, including 1 μm and 5 μm filters, sand filter, activated carbon filters, and a nanofilter. We studied the effects of various parameters on the removal of Cr(VI) from polluted water and drinking water such as pH, pressure, concentrations of chromium, concentrations of sulfate, and total dissolved solids (TDS). The selected parameters were as follows: pressure: 0.1-0.4 MPa, pH: 2–10, Cr(VI) concentration: 0.1–0.4 mg/l, and sulfate concentration: 40–500 mg/l. According to the results, the efficiency of chromium removal increased with increasing the pH, while increasing the pressure from 0.1 to 0.4 MPa decreased the removal rate of chromium. In addition, increasing the concentrations of sulfate led to a decreasing trend in the removal efficiency. According to the findings of the study, the hybrid pilot made is able to reduce the chromium and sulfate to the levels under the WHO standard (Cr(VI) = 0.05 mg/l and sulfate = 500 mg/l). • The optimal conditions for removal of Cr(VI) included the initial chromium concentration of 0.1 mg/l, pressure of 0.1 Mpa, pH of 10, and the sulfate concentration of 40 mg/l. • In general, the experimental results revealed that the fabricated hybrid system including MF, NF, sand filter, and carbon filter has the ability to remove chromium and sulfate from drinking water (tap water) at a rate of 99%. • At sulfate concentration of 40 mg/l, the TDS elimination efficiency was 97.75% and increased by 99.87% as the concentration increased to 500 mg/l. The presence of sulfate ions increases the TDS in water.