Heavy metals, particularly mercury have proved another source of concern. Less mercury is used today than in the past. This combined with better filtration systems has reduced mercury emissions from power-from-waste plants in the USA to around 2 tonnes/year. Coal-fired power plants release over 40 tonnes/year.
There are other metals such as cadmium and lead which must be monitored. However in general the emissions of metals from waste incineration plants should fall well below legal emission limits. Today proponents of these plants would argue that they are significantly less polluting than landfills. New technologies may well be able to provide even higheremission performance. Whether this will be sufficient to overcome the reputation which has already attached itself to such plants remains to be seen.
The traditional technology used for waste combustion is robust and extensively tested. Any risk associated with its use is small and well documented. New technologies under development such as gasification and pyrolysis have not yet been proved and the risks associated with their use are higher.
There is also a risk associated with the waste which is to provide the fuel for a power-from-waste plant. It is important to ascertain exactly what type of waste will be available to a particular project and its typical content. This can only be discovered by careful analysis of actual samples. Long-term analysis is necessary since waste content varies seasonally. However waste quality can also vary over a longer time scale, particularly if the supplier changes or where there are demographic changes within the catchment area.
Regulations and legislation also pose a threat. Any planned project will be required to meet current regulations but these may change once the plant has been built, necessitating modifications to meet new requirements. While the legislative situation is stable in areas such as Europe, it may not be everywhere. It would seem prudent when planning a project to choose the best technology available since this is likely to meet both current and future regulations anywhere in the world.
Perhaps the greatest risk with a power-from-waste project relates to its economics. If a plant is to be operated as a public service, then the economic viability will normally be guaranteed by the public sector. If it is to be a wholly private sector project, then the viability will depend on the value to waste collectors of the service offered. The price collectors are prepared to pay will depend on the competition. Under these circumstances, long-term contracts may offer the best security.
The capital cost of equipment to generate electricity from waste is generally much higher than for conventional power generation equipment to burn fossil fuel. Plant design is specialised and must include refinements for emission control that are not necessary in the fossil fuel plant. Grate design is unique too.
Against this must be offset the revenue of the plant, not only from the electricity generated but also from the fuel itself, the waste. Industry and municipalities expect to pay to dispose of their waste. Consequently, the economics of a project should be designed so that the revenue from the waste disposal contracts is adequate to enable the power from the plant to be sold competitively.
The cost of a typical municipal waste combustion plant is $5000-10,000/ kW, at least three times the cost of a coal-fired power plant of the same generating capacity. Smaller plants will be relatively more expensive. The cost of operating a plant is probably three times that of a coal-fired power plant too. According to US government estimates, such plants generate electricity at between $0.02 and $0.14/kWh.
1 Modern plants often recycle any reusable material, burning only the remainder.
2 European Union, Council Directive 1999/31/EC of 26 April 1999 on the landfill of waste, Official Journal of the European Communities, pp. L182/1-19 (July 1999).
3 In the developed world the waste from rural communities is often handled in a similar way.
4 Mining the Urban Waste Stream for Energy: Options, Technological Limitations, and Lessons from the Field, United States Agency for International Development, 1996 (Biomass Energy Systems and Technology Project DHR-5737-A-00-9058-00).
5 US Energy Information Administration, International Energy Outlook, 2004.
6 Refer supra note 4.
7 Refer supra note 4.
8 This figure is from the EU DG of Energy.
9 An overview of the global waste to energy industry, Nickolas J. Themelis, Waste Management World (July-August 2003).
10 The process, called R21, was developed by Mitsui Engineering and Shipbuilding. The first plant was completed in 2000.
12 US Environmental Protection Agency. These figures are quoted in 'An overview of the global waste-to-energy industry' Waste Management World (July-August 2003).
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