Phase distribution, migration and relationship of polychlorinated dibenzo-p-dioxins and dibenzofurans and heavy metals in a large-scale hazardous waste incinerator

Abstract

Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F) and heavy metals emitted from hazardous waste incinerators have aroused public concern due to the risks to the environment and human health. In the study, phase distribution, migration, and relationship of PCDD/F and heavy metals (arsenic, cadmium, chromium, copper, mercury, nickel, plumbum, zinc) are investigated in a typical hazardous waste incinerator. The PCDD/F mass concentrations and toxic equivalent quantity are reduced to 3.26 ng/Nm3 and 0.0484 ng/Nm3 by air control pollution devices, with 93.1% remove efficiency. High sulfur content in hazardous waste results in low PCDD/F and heavy metals emissions. Moreover, migration analysis of PCDD/F mass concentrations indicates that vast PCDD/F migrates to the mixtures with sodium bicarbonate and activated carbon (52.4%), followed by fly ash (21.8%), sodium hydroxide solution (19.3%), and atmosphere (6.49%). Furthermore, TCDF isomers (37%) dominate among the PCDD/F congeners, while 1,2,3,4,6,7,8-HpCDF (20%) dominates among 2,3,7,8-substituted congeners. Deduced by the ratio of PCDF/PCDD, the dominant mechanism of PCDD/F is de novo synthesis and chlorobenzene route synthesis. Based on the relative enrichment index, heavy metals are classified into three types: volatile heavy metals (plumbum, zinc, cadmium, mercury), medium volatile heavy metals (copper, chromium, arsenic), involatile heavy metals (nickel). Additionally, copper is inclined to deposit into the bottom slag as CuSO4 rather than the volatile substance due to high levels of sulfur dioxide (3000 parts per million). The migration behavior of heavy metals is dependent on the volatility properties of these metals. Statistically, PCDD/F emissions have the highest correlation coefficient with plumbum (r = 0.815), followed by nickel (r = −0.798). Besides, the PCDD/F formation is promoted by the volatile heavy metal, prevented by medium volatile heavy metals. The study not only provides a comprehensive understanding of PCDD/F and heavy metals characteristics but also effective and feasible strategies to reduce the toxic pollutants emissions in large-scale hazardous waste incinerators.