Emission, dispersion, and potential risk of volatile organic and odorous compounds in the exhaust gas from two sludge thermal drying processes.

Emissions of odorous and volatile organic compounds (VOCs) were investigated between two sludge drying methods. A total of 37 chemical compounds were identified and quantified from the off-gases from sludge drying by indirect drying method. The total number of VOCs detected ranged from 3.45 × 10-3 to 4.53 mg/m3, which includes benzene series, volatile organic sulfur, and nitrogenous organic compounds. High emissions were found in the exhaust gas released from drying workshop that used direct drying method. Sulfur dioxide, aromatics, and chlorinated compounds were dominant. Based on the olfactory effect analysis and cancer risk assessment, the main odor-causing gaseous pollutants were methyl mercaptan and methyl sulfide (for indirect sludge drying process) and SO2 (for direct sludge drying process), while the dominant carcinogens were benzene, carbon tetrachloride, chloroform, and methylene. This study provides new insights into the emission characteristics, olfactory effects, and cancer risks of VOCs and odorous compounds in the exhaust gas from thermal sludge drying processes.