Leachate Treatment of Isfahan Composting Plant by Coagulation-Flocculation Process

The main concern in composting plant is leachate generation that is known to be highly polluted wastewater. Migrations of untreated leachates are potential sources of hazardous contaminants in soil, groundwater and surface water. This study was aimed to investigate the heavy metals removal efficiency from Isfahan composting leachate using the following coagulantsferrous sulfate, ferric chloride, poly ferric sulfate, alum and poly aluminum chloride. This is an experimental study. Leachate samples were collected from the Isfahan composting leachate´s collection ponds. At first, leachate characteristics including COD, BOD, TSS and pH as well as the following heavy metals Zn,Cu,Ni, Cr, Cd 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 (4-12) on heavy metal removal. As a result, the effective dosage, optimum pH and the most convenient coagulant were identified. investigating the average of mentioned heavy metal's concentration, Zn had the highest concentration in leachate (6.2mg/l). The optimum pH for precipitation of the metals using alum, polyaluminiumchloride, ferricchloride, ferrous sulfate and poly ferric sulfate was 6.5,7,10,10 and 11 respectively. Optimum concentration of the mentioned coagulants was obtained 2, 1.5, 1.5, 2 and 2g/l respectively. Poly ferric sulfate with70% to 87% of heavy metals removal and 50% of COD removal had the highest efficiency. Poly aluminiumchloride with 65% to 85%, Ferric chloride with 75% to 80%, ferrous sulfate with70% to 80% and finally alum with 70% to75% were the following priorities at heavy metals removal.Discussion & Poly ferric sulfate is the most effective coagulant to remove heavy metals from the leachate and comparing the results with the Iranian guidelinefor effluent discharge shows that the concentration of heavy metals in leachate did not exceed the maximum allowed values.