(ULPROM) for separating heavy metal: effects of interference parameters

An experimental investigation was conducted to study the performance of an aromatic polyamide (ES 20) ultra-lowpressure reverse osmosis membrane (ULPROM) for separating divalent (Cu2+, Ni2+) and hexavalent (Cr6+) heavy metals from bulk solution. The influence of operating pressure, feed concentration, pH, and effect of other ions (Ca2+ and Mg2+) on the ULPROM performance was studied. The investigation was conducted for synthetic wastewater and wastewater from the heavy metal industry. Experimental results show that the rejection increases with increasing feed pressure, it is dependent on feed pH and is higher at higher pH. Increasing concentration of other ions slightly decreased the rejection of heavy metals. Generally, rejection of heavy metal is found to be greater than 95% for the ULPROM tested, which suggests the suitability of such membranes for industrial application for recovery of heavy metal and reclaiming wastewater.

Table 2 Performance comparison of Ni, Cu and Cr rejection from synthetic wastewater and industrial wastewater using the ES20 ULRPO membrane Wastewater Cu Cr 98.88 99.23 98.83 99.71 99.01 99.91 98.12 99.03 98.03 98.75 95.02 99.37 450 kPa. A flux of 18.63 L/m2.h and rejections, 99.03% of Ni, 98.75% of Cu, and 99.37% of Cr, lower than the flux and the rejections with single metal ion solution, were found. It is well acknowledged that hexavalent Cr is rejected better than the divalents Ni and Cu. The decrease in the rejection of heavy metal in the industrial In general, it can be concluded that the ES20 membrane (ULPROM) has a high rejection capacity of heavy metals under very low pressure and produces good water flux compared to conventional RO membranes. Being a pressuredriven membrane, the higher the transmembrane pressure, the higher the flux and rejection observed. Feed concentration affects the rejection and the flux. The higher the feed concentration, the higher the rejection, but there is a slight reduction in the flux. The pH is found to influence the rejection and flux of heavy metals since the charge property of surface material of polyamide ULPROM membranes changes with pH. At around the isoelectric point (zero potential charge), the rejection is lowest. The optimum range of pH for higher rejection is 7–9. The presence of co-ions decreases the rejection which is significantly observed with industrial wastewater. From the results obtained with the industrial wastewater, ES20 not only satisfies the requirements for wastewater disposal in heavy metal industries but also provides a basis for its application in metal recovery and wastewater reclamation.