More than 27 million metric tons of waste are used to produce energy for heating and lighting in Eu-rope. Realizing the ecological, technical and economic limits to ma- terial recycling, European waste managers and decision-makers are attracted to integrated solutions that include energy recovery.
Several countries recover energy from waste, according to the Asso-ciation of Plastics Manufacturers in Europe. For example, Switzerland requires all incinerators to be e-quipped for energy output and is adding 10 new plants. Environ-mentally conscious Denmark has a long-standing policy of energy from waste and Sweden now processes almost 1.5 million metric tons of municipal solid waste (MSW) each year. The Netherlands currently targets 40 percent energy recovery from waste and in Brussels, Bel-gium, thermal recovery processes supply 5 percent of electricity.
In France, 25 percent of the total MSW is incinerated with energy production. By 2002, only "ultimate wastes," or those that cannot be treated further, will be allowed in landfills.
In Germany, new laws have redefined the role of combustion as a way of managing the nation's waste. The 1993 Technical Reg-ulation for Municipal Waste prohibits the landfilling of domestic waste with more than 5 percent organic content. Therefore, thermal treatment is necessary to render non-recycled or non-composted wastes sufficiently inert prior to landfilling. Full compliance will be required by 2005.
In addition, the 1994 Cycle Economy and Waste Law, which will replace the German Waste Law of 1986 by the end of next year, ac-cepts energy recovery as well as re-cycling for unavoidable wastes. Environmental factors such as e-missions, energy, raw materials and hazardous wastes are to be considered on a case-by-case basis to determine whether material or energy recovery is preferable.
Over the past decade, changes in the composition of Germany's re-sidual waste (after removal of recyclables and biodegradable materials) have increased the heating value and decreased the pollutant content. Hubert Vogg of Kern-forschungszentrum Karlsruhe GmbH attributes this to several causes. For example, Duales Sys-tem Deutschland's green dot program removes large quantities of plastics from the household waste stream. In addition, widespread composting has reduced the waste stream's moisture content. Mean-while, metals recovery and construction and demolition debris recycling have reduced the inert fraction and socio-economic developments have increased the bulky waste volumes.
Today, about 30 percent of Ger-many's household, bulky and residential-like commercial waste is in-cinerated, almost exclusively in grate-fired facilities. A federal emissions law sets standards for the combustion process and the flue gas quality.
Two relatively new thermal treatment technologies are capturing the Europeans' attention: the Sie-mens thermal waste recycling technology and the Thermoselect process.
In the following six steps, Sie-mens' process (see figure) treats residual refuse, residential-like commercial waste, bulky waste and sewage sludge:
* Waste receiving and treatment, including size reduction and feeding;
* Conversion, or carbonization, in an oxygen-depleted atmosphere;
* Screening of the solid residue to increase the carbon concentration in the fine fraction;
* Combustion of the resulting gas and fine residues at 1,300 to 1,400 degrees Celsius, with vitrification of the slag;
* Power generation; and
* Flue gas scrubbing.
The process meets German emission limits, according to results at a demonstration plant in Ulm-Wib-lingen. Tests of the leaching characteristics of the coarse residue fraction and the granulated slag reportedly confirm that the stringent German landfilling standards can be met. The materials also are suitable for road construction.
The Thermoselect process transforms waste into synthesis clean gas and minerals by combining re-fuse compression, de-gasification in the absence of ox-ygen, high-temperature gasification and smelting of all inorganic, non-gasifiable components. The synthesis gas is converted into electrical energy and process heat. The operation reportedly produces no waste-water.
In 1994, the first full-scale Thermose-lect plant in Fondo-toce, Italy, was permitted in accor- dance with procedures for EU member states. Experi-ence shows that op- erations can be a-dapted to suit varying feedstock cal-orific values.
To date, thermal waste treatment's greatest obstacle appears to be public opinion. Despite today's advanced pollution controls, past environmental scandals involving incinerators still affect present perceptions. The merits of combustion may be harder to grasp than alar-mist messages but have the advantage of being true, said Karl Tho-me-Kozmiensky of the Technical University Berlin.