Municipal incinerators
Municipal waste incineration is still the first cause of dioxin pollution, according to a 1999 United Nations Environment Programme study *[is this still true?]*. Over the past few years *[when was "past few years?]*, many countries have updated their old incinerators or built new ones. In doing so, they have taken advantage of improved technologies for air pollution control. This has resulted in a substantial reduction in toxic emissions.
Although this is an improvement, toxic waste production is still a serious global issue. In fact, the problem has now shifted, and more dioxins and other toxic substances are appearing in the ashes, therefore creating new disposal and pollution problems.
Medical waste - useful waste into hazardous waste
Only 10 percent or less of a typical hospital's waste stream is potentially infectious. It is possible to sterilise this waste with heat, microwaves and other non-burn disinfection technologies.
The remaining waste is not infectious and often includes paper, plastic and food waste. This is similar to the waste coming from hotels, offices and restaurants, as hospitals serve all of these functions.
Incineration of medical waste has become a formidable chemical pollution problem, that is costly to manage and difficult to contain. Fortunately, there are alternative technologies available to ensure the appropriate sterilisation of medical waste.
Waste-to-energy schemes
The generation of energy from waste has increased. It is now used extensively by governments and industry to "green" incineration, with the desire to make it more acceptable to the public. However, all the negative impacts of incineration also apply to "waste-to-energy" facilities.
Waste-to-energy schemes include:
- Direct combustion in "waste-to-energy" incinerators
- Waste turned into refuse-derived fuel (RDF), before incineration (or combustion in power plants)
- Waste is gasified using pyrolysis or thermal gasification techniques
Landfill gas recovery is another "waste-to-electricity" technology that permits electricity production from existing landfills. This is possible via the natural degradation of municipal waste by anaerobic fermentation (digestion) into landfill gas. Anaerobic digestion can also be used on municipal sewage sludge.
The energy used to produce the product is lost and only a fraction of the intrinsic energy content of the materials can be recovered. Reuse and recycling, even from an energy perspective, are the preferred options.
Refuse-derived fuel (RDF)
Refuse-derived fuel (RDF) typically consists of pelletized or fluff waste that remains after the removal of non-combustible materials such as ferrous materials, glass and grit. The remaining material is then sold as RDF and used in dedicated RDF boilers or co-incinerated with coal or oil in a multi-fuel boiler. The environmental concerns of incineration also apply to RDF combustion facilities.
Pyrolysis and thermal gasification
Pyrolysis and thermal gasification are related technologies. Pyrolysis is the thermal decomposition of organic material at elevated temperatures, in the absence of gases such as air or oxygen. The process, which requires heat, produces a mixture of combustible gases (primarily methane, complex hydrocarbons, hydrogen and carbon monoxide), liquids and solid residues.
Thermal gasification of waste is different from pyrolysis in that the thermal decomposition takes place in the presence of a limited amount of oxygen or air. The generated gas can then be used in either boilers or cleaned up and used in combustion turbine generators.
Both of these technologies are at the development stage *[are they still at development stage?]*, with a limited number of units in operation. Most of the environmental concerns for incineration also apply to pyrolysis and thermal gasification facilities.
Cement kilns
Throughout the world some 60 cement kilns *[any advance on 60?]* have been modified so that various wastes can be burned along with conventional fuels.
However, cement kilns are designed to make cement and not to dispose of waste. A study by the US Centre for the Biology of Natural Systems, found that emissions of dioxins are eight times higher from cement kilns that burn hazardous waste than those that do not burn it.