Burning waste in cement kilns is another form of incineration, and it wastes resources and results in emissions that are harmful to people's health.
In order to make cement, high temperature kilns (reaching temperatures of up to 1500°C) are needed to produce the clinker that is ultimately ground up and made into cement. Traditionally, coal is used in these kilns, but in the past two decades many "alternative fuels" have been used. The term "alternative fuel" has often been used to disguise the fact that this "fuel" is actually waste.
Cement kilns are neither properly designed for this
purpose, nor are they held to the same regulatory standard as other incinerators.
The types of waste that cement companies try to burn include used solvents, spent tires, waste oil, paint residue, biomass such as wood chips, treated wood and paper, municipal solid waste, medical waste, and sewage sludge. These are added, along with coal, to the kilns. The cement industry uses these materials because they are generally cheaper than coal, and in some instances the kilns are actually paid for using them or can claim carbon credits because they are not using fossil fuels.
While it is claimed that the very high temperatures and long residency times within cement kilns result in high incineration efficiency and low emissions, cement kilns are simply not designed for burning waste. And because they are not regarded as incinerators, they generally avoid having to meet incinerator emissions regulations.
One of the biggest problems with using cement kilns as makeshift incinerators is periodic operating upsets, where the temperature can be reduced and emissions of dioxins dramatically increase. Studies have shown that emissions of some substances are reduced but that others increase substantially. It should also be noted that the residue of the fuel is incorporated into the cement, along with any heavy metals and other contaminants.
GAIA member groundWork has designed a web-based clearinghouse of information on the environmental and public health impacts of cement kilns burning waste. This site provides a meeting point for communities around the world facing similar challenges to exchange information and ideas, and provides a database of sustainable alternatives for waste streams currently being incinerated.