Sir, - Dioxins are extremely toxic and carcinogenic compounds are formed in very small quantities when organic material and substances containing chlorine are burned together. They are also formed when household waste is disposed of on a domestic fire or a garden bonfire; even the combustion of coal (and smoking tobacco!) may produce dioxins.
Fear of these deadly chemicals has resulted in legitimate public concern over the incineration of municipal solid wastes so that so-called "thermal treatment plants" seem now unacceptable to the Irish public, even though modern installations would operate at temperatures high enough to reduce dioxin formation and would also be fitted with sophisticated flue-gas purification systems. Consequently, projects such as the Galway and Kildare waste treatment plants have been abandoned.
However, "gasification" is an alternative form of thermal treatment for urban waste. The waste is turned into a combustible gas which is cleaned and then burned in a gas turbine to generate power; additional electricity can be produced by steam raised in a boiler utilising the heat in the gas turbine exhaust.
The emission of dioxins would be negligible and about half the energy in the waste could be recovered. Forestry residues and specially-grown "energy crops" such as coppiced willow could also be used in such plants, alone or together with waste. These energy crops could provide a new source of farm income in certain agriculturally disadvantaged areas. - Yours, etc.,
C Lyndhurst Davies, Gas Engineer and Fuel Technologist, Templeogue Wood, Dublin 12.