Any waste containing chlorine, including wood and food residues has the potential to produce dioxins when incinerated. As soon as the amount of chlorine in the waste exceeds a threshold of a few fractions of %, the actual amount is not a significant factor. The main factor is the operating conditions of the incinerator. The overwhelming importance of combustion conditions on dioxin formation has been established by numerous researchers. The single most important factor in forming dioxin-like compounds is the temperature of the combustion gases. Oxygen concentration also plays a major role on dioxin formation, but not the chlorine content
The design of modern incinerators minimises PCDD/F formation by optimising the stability of the thermal process. To comply with the EU emission limit of 0.1 ng I-TEQ/m3 modern incinerators operate in conditions minimising dioxin formation and are equipped with pollution control devices which catch the low amounts produced. Recent information is showing for example that dioxin levels in populations near incinerators in Lisbon and Madeira have not risen since the plants began operating in 1999 and 2002 respectively.
PVC is not the main source of chlorine in MSW. For instance, a study commissioned by the E.U. authorities showed that the putrescible fraction contributes 35% of the total chlorine whereas the plastics only contribute 25 %.
Several studies have also shown that removing PVC from waste would not significantly reduce the quantity of dioxins emitted. The European Union Commission published in July 2000 a Green Paper on the Environmental Issues of PVC. The Commission states that: “It has been suggested that the reduction of the chlorine content in the waste can contribute to the reduction of dioxin formation, even though the actual mechanism is not fully understood. The influence on the reduction is also expected to be a second or third order relationship. It is most likely that the main incineration parameters, such as the temperature and the oxygen concentration, have a major influence on the dioxin formation”. The Green Paper states further that “at the current levels of chlorine in municipal waste, there does not seem to be a direct quantitative relationship between chlorine content and dioxin formation”.
