Residue characteristics of sludge from a chemical industrial plant by microwave heating pyrolysis.

Sludge from biological wastewater treatment procedures was treated using microwave heating pyrolysis to reduce the environmental impact of a chemical plant. In this study, major elements, trace elements, PAHs and nitro-PAHs in raw sludge, and pyrolysis residues were investigated. The contents of major element from raw sludge were carbon 46.7 ± 5.9%, hydrogen 5.80 ± 0.58%, nitrogen 6.81 ± 0.59%, and sulfur 1.34 ± 0.27%. Trace elemental concentrations including Zn, Mn, Cr, Cd, As, and Sn were 0.410 ± 0.050, 0.338 ± 0.008, 0.063 ± 0.006, 0.019 ± 0.001, 0.004 ± 0.001, and 0.003 ± 0.002 mg/g, respectively. For various pyrolysis temperatures, Ca, Fe, Sr, Cr, and Sn contents remained at almost the same level as those in raw sludge. Results indicated that these elements did not easily volatilize. The content of 16 PAH species was about 4.78 μg/g in the raw sludge and 23-65 μg/g for pyrolysis residues associated with various temperatures. The content of ten nitro-PAHs was about 58 ng/g for the raw sludge and 141-744 ng/g for pyrolysis residues. The total nitro-PAH content was highest at 600 °C and then decreased when the temperature was over 600 °C. Total nitro-PAH content was about 247 ng/g at 800 °C.