REDUCTION OF CHEMICAL OXYGEN DEMAND AND POTENTIALLY TOXIC METALS IN LEACHATES GENERATED FROM ISOLO DUMPSITE USING DIFFERENT COAGULANTS

Abstract

Leachate samples were collected from Isolo dumpsite within a seven month period, at eight different times after rainfall. The characterization of the leachate shows that they were sourced from an old landfill. The highest concentration of chemical oxygen demand (COD), biological oxygen demand (BOD) and total organic carbon (TOC) in the most polluted leachate samples were 392 mg/L, 203 mg/L and 5090 mg/L respectively. The levels of Fe, Pb, Cu and Zn were 19.7 mg/L, 2.06 mg/L, 2.18 mg/L and 3.50 mg/L respectively. Three different coagulants: ferric chloride, ferrous sulphate and aluminium sulphate were used to treat the most polluted leachate sample. Different pH and concentrations were investigated to obtain the optimal dosage for the most effective coagulant. The experimental results showed that at a neutral pH, 96% COD, 66.2% Fe, 94.3% Zn reductions were achieved at the lowest concentration of 1000 mg/L of Al₂SO₄.14H₂O while FeCl₃ and FeSO₄ gave <96% reduction at a high concentration of 25,000 mg/L. The pH of 3, 5, 9 and 11 at optimal dosage of Al₂SO₄.14H₂O gave 14%, 78%, 82%, 88% reduction of COD respectively. The result therefore indicates that Al₂SO₄.14H₂O is the most effective of the three coagulants with optimal pH and dosage of 7 and 1000 mg/L respectively.