Release characteristics of POPs during preheating and sintering processes of ceramsite produced with the contaminated...

The ceramsite sintering using contaminated sediment or sewage sludge is an effective stratagem for resource utilization and the removal of organic pollutants. However, the release of persistent organic pollutants (POPs) during the ceramsite production is generally overlooked, leading to the excessive POPs emission in exhaust gas. This study explored the release characteristics of typical pollutants in both the solid and gas phases during preheating and sintering processes of ceramsite production under the different field conditions, including polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), polycyclic aromatic hydrocarbons (PAHs), and organochlorine pesticides (OCPs). Compared with preheating duration and moisture content in the raw ceramsite, preheating temperature was the main factor influencing the removal of POPs during the preheating process (150-300 ℃). Although the residual POPs in the preheated ceramsite could be effectively eliminated by the high temperature (>700 ℃) in the sintering processes, the POPs level in gas phase was generally elevated to some extent. The removal ratio of PCDD/Fs could reach up to 62.8 % and 99.9 % in the preheated and sintered ceramsite, respectively, which were comparable to those for OCPs (71.2 % and 99.7 %). By contrast, they were 21.4 % and 94.1 % for PAHs, respectively. POPs in the exhaust gas emitted during the preheating process accounted for more than 20 % of the overall emissions, which could not be overlooked during the field production. Concerning the energy consumption and efficiency, preheating temperature of 150-200 ℃ and sintering temperature of 900 ℃ were recommended for sintering ceramsite.