Effect of operating parameters on Pb2+ separation from wastewater using electrodialysis

Lead is a highly toxic heavy metal, found in water and air, which should be treated. Lead removal from wastewater is an important problem in battery industries. The separation process by means of electrodialysis (ED) shows several advantages such as highly selective desalination, high water recovery, only a partial addition of chemicals and the possibility of a stop-and-go operation. The performance of an ED plant is determined by a set of fixed and variable process parameters such as stack construction, feed and product concentrations, membrane permselectivity, flow velocities, current density, recovery rates, etc. For an efficient operation of ED, the process has to be optimized in terms of overall costs considering component design and properties as well as all operating parameters. Effects of flow rate, temperature and voltage at different concentrations using two types of commercial membranes on lead removal were studied. Experiments were carried out on three levels of concentration: 100, 500 and 1000 ppm; temperature: 25, 40 and 60°C; voltage: 10, 20 and 30 V; flow rate: 0.07, 0.7 and 1.2 mL/s using a laboratory ED cell. The results show that increasing voltage and temperature improved cell performance; however, the separation percentage decreased with an increasing flow rate. At concentrations of more than 500 ppm, dependence of separation percentage on concentration diminished. Using membranes with higher ion-exchange capacity resulted in better cell performance.

The performance of ED in practical applications depends on membrane properties, feed solution composition and equipment design parameters such as feed flow rate, operation mode and cell geometry. In this paper a full factorial experimental design was employed to determine effects of different operating parameters such as voltage, flow rate, temperature, feed concentration and membrane properties on lead removal from wastewater in a laboratory study. ANOVA was applied to evaluate the relative effectiveness of various factors. It was observed that factor flow rate had the largest contribution to the total sum of squares, and correspondingly had a significant effect on separation percentage. Also, all other factors had almost similar effects on the response. The results confirm that higher IEC of membranes cause higher separation percentage.