Frequently Asked Questions

The WTE industry receet the EPA’s New Clean Air Act “Maximum Control Technology” (MACT) standards. In a 2002 letter, U.S.E.P.A. Assistant Administrators Jeffery Holmstead, Office of Air and Radiation, and Marianne Lamont Horinkontly completed a more than $1 billion retrofit to existing facilities to me, Office of Solid Waste and Emergency Response, recognized the “vital role of the nation’s municipal waste-to-energy industry” and concluded that “these plants produce 2800 megawatts of electricity with less environmental impact than almost any other source of electricity.” The Table below shows the dioxin/furan TEQ emissions in the U.S. from various sources that also include WTEs. The following figure compares mercury emissions from WTEs and coal-fired power plants in the U.S.

In the U.S., most of today’s operating WTE plants were built in the period of 1980-1995. Energy prices and landfill disposal costs dropped in the mid-1990’s making WTE plants more difficult to develop. However, new WTE units have been built or are under construction in Florida and Hawaii. Crowded urban areas and locations where groundwater is close to the surface benefit most from WTE facilities. Abroad, there have been over 200 new WTE plants built since 1996 and some are under construction. In all there are over 700 WTE plants in the world located in 37 nations, including Bermuda, Singapore and China. New WTEs are under construction in the U.K., Azerbaijan and other nations.

Generally, WTE residues can be differentiated into two fractions: The term fly ash refers to the fine particles that are removed from the flue gas. However, usually the fly ash includes also residues from other air pollution control devices, such as scrubbers. Fly ash typically amounts to 10-20% by weight of the total ash.

The rest of the WTE ash is called bottom ash (80-90% by weight). The main chemical components of ash are silica (sand, quartz), CaO, Fe2O3, and Al2O3 for a mass burn WTE plant. Usually the ash has a moisture content of 22-62% by dry weight. The chemical composition of the ash depends strongly on the original MSW feedstock and the combustion process.

Dr. Jurgen Vehlow of Karlsruhe Research and an EEC Research Associate has compiled ash composition data from several studies (see figure below). E.g. Hg can vary from 0.1 to 10 ppm in bottom ash and from 1 to 30 ppm in fly ash (before treatment).

WTE ash has been reused in construction since the early 70’s. Common applications are sub-base material, structural fill, and aggregate in asphalt or concrete. However, in the past, contaminant concentrations of fly ash exceeded the allowable threshold values. Ash reuse is therefore restricted to proven processes. Because there are no nationwide standards in the U.S. less than 5% of the WTE ash is beneficially used (compared to bottom ash reuse of ~70% in Germany and ~90% in the Netherlands). The government of Bermuda uses the entire WTE ash in concrete products for artificial reefs or shore abatements. The Waste-to-Energy Research and Technology Council is therefore taking an innovative approach towards our understanding and beneficial use of ash. An interdisciplinary and inter-institutional research group will carry out a comprehensive project on reuse applications such as engineered aggregate, cement blocks, asphalt, remediation of brownfields and abandoned mines, and concrete. One of the main goals is to recommend authoritative, nationwide standard specifications.

Ashes that cannot be reused are landfilled. Usually, combined WTE ashes do not qualify for unrestricted disposal but are placed in monofills while it is easier to place bottom ash alone because it rarely exceeds the maximum permitted concentrations for landfilling. In contrast, fly ash alone may have to be handled as hazardous waste and thus introduces additional problems if not stabilized prior to its disposal.

WTE facilities are primarily regulated under the federal Clean Air Act and the Resource Conservation and Recovery Act. The Clean Air Act requires plants to obtain permits whose provisions are based on plant size and technology. Federal and state regulators enforce emissions limits for sulfur dioxide, hydrogen chloride, nitrogen oxides, carbon monoxide, particulates, cadmium, lead, mercury, and dioxins. Operating conditions, monitoring, reporting, training and safety requirements also apply under the Clean Air Act. The Resource Conservation and Recovery Act requires testing of the plants’ ash residue to determine that the ash is non-hazardous and properly disposed or reused. States often take authority for enforcement of the regulations and require even stricter environmental limits on the facilities’ operation than imposed by the federal rules. State-specific requirements can include more strict emission limits, testing or reporting than federal rules; additional solid waste management, recycling, noise, site selection, transportation and related regulations; and water use or waste water management limits.

The dominant technology is mass burning and the foremost process used is that developed by Martin (Munich, Germany) with installed annual capacity of about 60 million metric tons. AE&E Company (Von Roll technology) mass burn process follows with 35 million tons worldwide. Other mass burning technologies are the roller grate (DB), Westinghouse process, the Keepel-Seghers process, and the Fisia Babcock process. There are several plants in the U.S. based on the Refuse-Derived Fuel (RDF) process that pre-shreds the waste into small pieces and separates some of the non-combustible materials (metals and glass).

As a rule, the communities that invest in WTE plants, because of the energy and environmental benefits described above, also do as much as possible recycling before sending the non-recyclable waste to their WTE. Despite all good intentions and efforts some waste materials are not recyclable economically in the U.S. because of the comparatively low cost of fossil fuels. For example, out of the 25 million tons of plastics generated annually in the U.S., only 1.5 million tons are recycled, 3.5 million are combusted and 20 million tons are landfilled, despite the fact that their heating value is higher than the best U.S. coal. The graph below shows that nations that have practically eliminated landfilling have done so, invariably, by a combination of recycling and WTE.

It is easy to juggle % recycling rates but the real evidence of sound waste management is provided by how many tons of MSW a city landfills. The official SF web page, SFgov.org, reports that SF generates 4,000 tons MSW per day of which 60% is landfilled. Therefore, SF citizens (population 760,000) landfill 0.96 tons per capita which is slightly higher than the California average of 0.9 tons and nearly the same as NYC. Tourist destinations usually generate more MSW per capita.

Dioxin formation and emissions are not related to the MSW feed but to the performance of the Air Pollution Control (APC) system of the facility. Testing the APC once a year (three tests over an eighteen hour period) for dioxins is adequate, similarly to the annual car emissions test required by New York and other states.

Some dioxins are toxic (EPA has determined that 50 grams of measured total dioxins are equivalent to 1 gram of toxic dioxins – 1 gram TEQ). However, dioxins exist in nature as a result of both human (biomass, coal and MSW combustion, metal production, etc.) and natural (forest fires, volcanoes) activities. Fifteen years ago, EPA reported dioxin emissions of 12,000 grams TEQ. As a result of implementation of the Maximum Achievable Control technologies (MACT) of EPA, the US emissions have decreased by now to about 1,200 grams TEQ (12 grams from WTE, 60 grams for coal-fired power plants, 500 from “backyard burning””). It should be noted that even when dioxin emissions were ten times higher than are now, there has not been a single recorded evidence of a person becoming ill or dying from dioxin poisoning in the U.S. Apart form the Seveso (Italy) industrial chemical accident and the allegations regarding the use of Agent Orange in the Vietnam war, the only reported case of dioxin poisoning was recently when an undetermined quantity of dioxins was mixed in the food of Mr. Yushchenko, the current President of Ukraine. He has survived this attack.

Landfilling is cheaper except in cases like New York City where the MSW has to be transferred long distances. For example, in the case of NYC, the landfilling fee is about $30 but the truck transport costs an additional $70. However, when the “external” environmental costs are factored in, WTE is less expensive in all cases. For one thing, the constantly increasing use of land for landfilling is not sustainable. In the case of the Freshkills landfill of New York City, about 3,500 acres of land were lost to landfilling over a period of fifty years. The burden has now been shifted to Pennsylvania and other states but to this has been added the environmental cost of truck transport of MSW from NYC to PA.

Comparing with landfills that do not recover any LFG (i.e., 80% of the world’s landfills), the WTE advantage over landfilling, including GHG reduction and electricity generation is one ton CO2/ton MSW. Comparing with landfills that practice LFG recovery and thus recover 50% of LFG, reduces the WTE advantage to about 0.5 ton CO2/ton MSW.