Abstract
Heavy metals in sewage sludge can be classified as difficult solid waste with potential hazards for environment. This report examined how an aqueous solution of EDTA (ethylenediaminetetraacetic acid) washing changes selected heavy metals’ (Zn, Cu, Cd, Ni, Pb) fractionation in sewage sludge. The analyzed sludge was dried and homogenized sewage sludge was obtained from a municipal treatment plant. The samples of sewage sludge were extracted with 0.1M EDTA solution for 24 h. Primary as well as extracted sewage sludge was examined for the total content of heavy metals and speciation of mentioned heavy metals using BCR sequential extraction procedure. Analyzed sewage sludge samples were quite significantly contaminated with heavy metals. The total content of zinc, copper, cadmium, nickel, and lead in initial sewage sludge was equal to: 2306.5, 263.7, 9.0, 118.0, and 117.0 mg kg−1 dM, respectively. After EDTA extraction: 1514.5, 253.5, 7.5, 83.0, and 58.0 mg kg−1 dM, respectively. In sewage sludge before extraction, the percentage of metals in fractions I (exchangeable and carbonates), II (Fe and Mn oxides), III (organic matter and sulfides), and IV (residual) was: for Zn 21, 47, 31, 1%, for Cu 0, 0, 99, 1%, Cd 0, 32, 68,0%, Ni 28, 22, 42, 8%, and Pb 6, 3, 34, 57%, respectively. In sludge after extraction, the percentage of metals in fractions was for Zn 17, 47, 33, 2%, Cu 0, 0, 98, 2%, Cd 0, 30, 70, 0%, Ni 13, 20, 46, 21%, and Pb 4, 5, 24, 67%, respectively. EDTA washing resulted in decreasing of nickel and lead percentage in mobile fractions and an increase in fractions strongly bounded to sludge matrix. The effect was most evident for Ni. Efficiency of EDTA solution for zinc, copper, and cadmium fractionation changes was practically negligible. EDTA extraction influenced the content of metals in municipal sewage sludge fractions. The process caused a decrease in each fraction; however, a strong chelating agent removed metals mostly from a dominant fraction.
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