Waste Incineration

Historically, and even today in some developing countries, the easiest way of disposing of waste has been to burn it in open air. Incineration of raw waste has been practiced throughout the history of humanity in the most crude form of incineration: Indiscriminate burning. The indiscriminate open burning of waste on a large scale, however, causes air, water, and soil pollution. Current incineration technology has come a long way from open burning to sophisticated incinerators. The purpose of burning has also changed from simply getting rid of waste to reducing waste volume and recovering energy. Nevertheless, adverse environmental impacts like air pollution and water pollution have made this process unpopular.

As solid waste constitutes a low-grade fuel, it has become a tradition in recent years, wherever possible, to recover part of the energy content of waste. The energy recovered can be used for energy requirements of the waste facility itself or for heating or residential, industrial, or commercial power generation. Incinerators and waste-to-energy facilities are more common in urban industrialized areas, largely because of the nature of the urban waste stream; rural waste does not normally have sufficient calorific value to make energy recovery efficient.

Incinerators can be classified by the type and form and waste input, by throughput capacity, by rate of production of heat, by the state in which residue emerges from the combustion chamber, and by the shape and number of furnaces. The key systems involved in incineration are the tipping area, storage pit, equipment for charging the incinerator, combustion chamber, bottom ash removal system, and gas cleaning equipment and boiler, if energy has to be recovered.

The process that takes place inside an incinerator is called pyrolysis, the thermal decomposition of waste at high temperatures in the absence or near absence of oxygen. The products of incineration are in all three forms—solid, liquid, and gaseous. It is important to regulate the temperatures of the furnace depending on the quality of waste so that more hazardous products are not produced upon decomposition and released into the environment.

The impact of emissions from waste incinerators on human health is of great public concern, especially the release of toxins like dioxin. Research has identified numerous toxic compounds emitted in gases and in ashes (e.g., organic pollutants such as chlorinated and brominated dioxins, PCBs and PCNs, heavy metals, sulphur dioxide, and nitrogen dioxide), as well as many unidentified substances of unknown toxicity. This leads to contamination of [Page 1911]the environment and to potential exposure of humans to hazardous pollutants that may cause health problems such as cancers.

Besides polluting air, incinerators emit wastes to water from cleaning equipment. While published data on air pollution through emissions from burning waste, fly ash, and bottom ash is available, emissions to water from incineration remain largely understudied. Wastewater from wet exhaust gas cleaning, however, is known to contain heavy metals, the most significant being lead, cadmium, copper, mercury, zinc, and antimony. Wastewater from wet slag removal equipment contains high levels of neutral salts and also contains unburned organic material from the residue. Based on some of this evidence, it can be argued that use of incinerators ignores the adoption of the precautionary principle.

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