Benzene series in sewage sludge from China and its release characteristics during drying process

The effective control of the odor pollutants of benzene series (BTEX) is critical for cleaner production in the sewage sludge drying process. Based on the determination of BTEX emission and its contents in four types of sludge (dyeing, leather-tanning, paper mill and municipal), its release characteristics are investigated under drying conditions in the lab and their potential effects on exposed individuals are also evaluated. Results show that in the range of 50–300°C, the total BTEX release from the four types of sludge varies from 4.20 to 161.90 μg m⁻³, suggesting that the emission rate of BTEX is in control of the drying temperature. The emission rate accelerates significantly after drying temperature exceeds 150°C, whereas only 5.09% of the total emission is collected below 100°C. A significant positive correlation between BTEX emission and its total contents in sludge at different drying temperatures is observed. Therefore, BTEX content of sludge also determines its release. The sludge drying process under 150–300°C conditions would pose a benzene-related carcinogenic risk to exposed individuals, especially to females. Application of low-temperature drying techniques in sludge disposal is necessary to control BTEX emission and thereby reduces the carcinogenic risks.