PCDD/F and dioxin-like PCB minimization: A 13-year experimental study along the flue gas cleaning system of a secondary aluminium refining plant.

A 13-years study shows that a careful design of the flue gas cleaning system of a full scale secondary aluminium refining plant results in a minimized and very stable emission of Polychlorinated Dibenzo-p-Dioxins (PCDD), Polychlorinated Dibenzo Furans (PCDF) and dioxin-like Polychlorinated Biphenyls (PCB). The value of equivalent toxicity of PCDD/F in the emission was definitely of an order of magnitude less than the regulation limit. In the initial flue gas cleaning system, the PCB mean fingerprint after the slow cooling of the flue gas was typical of de novo synthesis. Instead, in the presence of quenching, there was evidence that the fast cooling of flue gas prevented the PCB de novo synthesis. In fact, the PCB profile was similar to that in the air collected from the aspiration hoods for the quenching. The gas-phase and solid-phase partitioning of PCBs, before and after the fabric filters, highlights the predominant role of the vapor phase with respect to the total removal efficiency. The polycyclic aromatic hydrocarbons breakdown could be an additional de novo formation pathway even in industrial plants.