Investigating efficiency of coagulants in removing heavy metals from composting plant leachate

Leachate, including various pollutants such as heavy metals, is generated during collection, trasportation and disposal of solid waste as well as composting process. Lack of control, disregarding the leachate treatment and heavy metals removal cause environmental pollution. This study was aimed to investigate the efficiency of heavy metals removal from Isfahan composting leachate, using the following coagulants ferric chloride, poly ferric sulfate and poly aluminium chloride. In this experimental study, leachate samples were collected from the Isfahan composting leachate´s collection ponds. At first, leachate characteristics including TSS, BOD, COD and pH as well as the following heavy metals: Cd, Cr, Zn, Cu and Ni were measured according to the standard methods. Jar-test experiments were carried out to examine the effects of changing coagulant's dosage (0.5, 1, 1.5, 2, 2.5 and 3 g/L) and pH values (4, 5, 6, 7, 8, 9, 11 and 12) on the removal of heavy metals. As a result, the effective dosage, optimum pH and the most convenient coagulant were identified. Investigating the average concentration of mentioned heavy metals, Zn had the highest concentration in leachate (6.2 mg/L) followed by Ni, Cu, Cr and Cd with the concentrations of 2.15, 0.62, 0.48 and 0.21 mg/L, respectively. The optimum pH for precipitation of the metals using poly aluminium chloride, Ferric chloride and poly ferric sulfate was 7, 10 and 11, respectively. Optimum concentration of the three mentioned coagulants was 1.5, 1.5 and 2 g/L, respectively. Poly ferric sulfate with 70% to 87% of heavy metals and 50% of COD removal has the highest efficiency, followed by poly aluminium chloride with 65% to 85% and Ferric chloride with 75% to 80% of heavy metals removal. Among the three mentioned coagulants, poly ferric sulfate is the most effective followed by poly aluminium chloride and ferric chloride, respectively. Since poly ferric sulfate and poly aluminium chloride are more expensive compared to other coagulants, economic estimations need to be done according to their efficiency to choose the best coagulant.