Measurement of atmospheric PCDD/F and PCB distributions in the vicinity area of Waelz plant during different operating stages

A comprehensive sampling program was conducted at four sampling sites in the vicinity area of a Waelz plant prior to and after the retrofitting of this plant for reducing PCDD/F (polychlorinated dibenzo-p-dioxin and polychlorinated dibenzofuran) and polychlorinated biphenyl (PCB) emission to evaluate its effects on atmospheric PCDD/F and PCB concentrations. During the shutdown stage of the Waelz plant investigated, the atmospheric PCDD/F and PCB concentrations measured in the vicinity area (sites A, B and C) range from 24 to 170 fg-I-TEQ/m3 and 5.0 to 8.2 fg-TEQWHO/m3, respectively. As the facility restarted to operate, the atmospheric PCDD/F and PCB concentrations measured increased to 570–1460 fg-I-TEQ/m3 and 23–59 fg-TEQWHO/m3, respectively. When activated carbon injection (ACI) was adopted in the facility in early 2006, the PCDD/F concentrations measured in stack gas decreased dramatically from 190 to 3.4 ng-I-TEQ/Nm3, while the PCB concentrations decreased from 4.9 to 0.08 ng-TEQWHO/Nm3. In the meantime, the atmospheric PCDD/F and PCB concentrations measured at sites A, B and C decreased to 150–340 fg-I-TEQ/m3 and 13–19 fg-TEQWHO/m3, respectively. However, relatively high PCDD/F (180–1460 fg-I-TEQ/m3) and PCB (9.3–59 fg-TEQWHO/m3) concentrations were measured at site D during all sampling stages. Overall, atmospheric sampling results indicate that over 50% of PCDD/Fs distributed in solid phase, while over 90% of PCBs distributed in vapor phase during all sampling stages.