Hazardous emission from thermal drying of municipal sludge and industrial sludge as well as associated odor pollution

Disposal of sewage sludge, a by-product of wastewater treatment, is one of the most intractable problems for environmental protection industry. The odorous gases discharged from sludge drying has seriously affected the life quality of residents, causing growing public concern of its odor pollution. The previous studies mainly focused on municipal sludge. In this research, samples of distillery sludge, municipal sludge and pharmaceutical sludge were collected and dried under identical conditions to compare the pollutant release characteristics of municipal sludge and industrial sludge. Throughout the drying process, the amounts of emitted ammonia, hydrogen sulfide and benzene series were detected every 10 min, and the odor pollution of different drying exhaust was quantitatively evaluated using odor threshold. The results of the drying experiments showed that the odor problem of municipal sludge was significantly worse compared to industrial sludge. The maximum odor index during thermal drying of municipal sludge was 15,332, which was 3 times that of distillery sludge and 24 times that of pharmaceutical sludge. The odor pollution caused by benzene series was negligible for any type of sludge, but drying process should be ceased before the moisture content falls to 10% to reduce their carcinogenic risk to exposed individuals.