Concentrations, congener patterns, and correlations of unintentional persistent organic pollutants in cement kilns co-processing hazardous waste

Emissions from two typical cement kilns co-processing different kind of hazardous waste were analyzed for 143 congeners of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), polychlorinated biphenyls, polychlorinated naphthalenes, polybrominated dibenzo-p-dioxins and dibenzofurans, and polybrominated diphenyl ethers. The congener distributions in different process stages were investigated. One of the plants co-processed waste chemical reagents from laboratories. The emission factor (TEQ basis) for the plant was 2.09 ng WHO₂₀₀₅ TEQ/t, with the kiln head and the kiln back end contributing 1.18, 0.91 ng WHO₂₀₀₅ TEQ/t, respectively. The other plant co-processed municipal waste incineration fly ash. The emission factor for the plant was 0.12 ng WHO₂₀₀₅ TEQ/t, with the kiln head and the kiln back end contributing 0.022, and 0.10 ng WHO₂₀₀₅ TEQ/t. These results indicate that co-processing of waste containing reagents from laboratories may lead to higher emission levels than co-processing of other types of waste. The congener patterns of persistent organic pollutants (POPs) in ash samples from the humidifier tower were similar to those in samples from the bag filter at the kiln back end. The correlation coefficients of five pollutants between the humidifier and bag filters samples were generally high, which indicated that conditions in those two stages similarly favored the formation of these POPs. Comparison of the concentrations for different process stages suggested that the main stage for formation of unintentional POPs was the humidifier tower. These results improve our understanding of emission characteristics and could be used for simultaneous control of multiple POPs.