Converting Garbage into Clean Energy

by Elizabeth Rosenthal

Thanks to a new, cleaner type of incinerator, residents of Horsholm, Denmark, have few complaints about a nearby plant. It also provides heat and electricity.

Johan Spanner for the New York Times

HORSHOLM, Denmark – The lawyers and engineers who dwell in an elegant enclave here are at peace with the hulking neighbor just over the back fence: a vast energy plant that burns thousands of metric tons of household garbage and industrial waste, round the clock.

Far cleaner than conventional incinerators, this new type of plant converts local trash into heat and electricity. In the process, dozens of filters catch pollutants, from mercury to dioxin, that would have emerged from its smokestack only a decade ago.

In that time, such plants have become both the mainstay of garbage disposal and a crucial fuel source across Denmark, from wealthy exurbs like Horsholm to Copenhagen’s downtown area.

Their use has not only reduced the country’s energy costs and reliance on oil and gas, but also benefited the environment, diminishing the use of landfills and cutting carbon dioxide emissions. The plants run so cleanly that many times more dioxin is now released from home fireplaces and backyard barbecues than from incineration.

With all these innovations, Denmark now regards garbage as a clean alternative fuel rather than a smelly, unsightly problem. And the incinerators, known as waste-to-energy plants, have acquired considerable cachet as communities like Horsholm vie to have them built.

Denmark now has 29 such plants, serving 98 municipalities in a country of 5.5 million people, and 10 more are planned or under construction. Across Europe, there are about 400 plants, with Denmark, Germany and the Netherlands leading the pack in expanding them and building new ones.

In Denmark, plants are placed in the communities they serve, no matter how affluent, so that the heat of burning garbage can be efficiently piped into homes.

Planners take pains to separate residential traffic from trucks delivering garbage, and some of the newest plants are encased in elaborate outer shellsthat resemble sculptures.

“New buyers are usually OK with the plant,” said Hans Rast, president of the homeowners’ association in Horsholm.

“What they like is that they look out and see the forest,” he said. (The living rooms in this enclave of town houses face fields and trees, while the plant is some 365 meters over a back fence that borders the homes’ carports). The lower heating costs don’t hurt, either. Eighty percent of Horsholm’s heat and 20 percent of its electricity come from burning trash.

Many countries that are expanding waste-to-energy capacity, like Denmark and Germany, typically also have the highest recycling rates; only the material that cannot be recycled is burned.

In Europe, environmental laws have hastened the development of waste-to-energy programs. The European Union severely restricts the creation of new landfill sites, and its nations already have binding commitments to reduce their carbon dioxide emissions by 2012 under the international pact known as the Kyoto Protocol.

In Horsholm only 4 percent of waste now goes to landfills, and 1 percent (chemicals, paints and some electronic equipment) is consigned to “special disposal” in places like secure storage vaults in an abandoned salt mine in Germany. Sixty-one percent of the town’s waste is recycled and 34 percent is incinerated at waste-to-energy plants.

Emissions from the plants in all categories have been reduced to just 10 to 20 percent of levels allowed under the European Union’s strict environmental standards for air and water discharges.

At the end of the incineration process, the extracted acids, heavy metals and gypsum are sold for use in manufacturing or construction. Small amounts of highly concentrated toxic substances, forming a paste, are shipped to one of two warehouses for highly hazardous materials, in the Norwegian fjords and in a used salt mine in Germany.

“The hazardous elements are concentrated and handled with care rather than dispersed as they would be in a landfill,” said Ivar Green-Paulsen, general manager of the Vestforbraending plant in Copenhagen, the country’s largest.

In Denmark, local governments run trash collection as well as the incinerators and recycling centers, and laws and financial incentives ensure that recyclable materials are not burned.

The Horsholm plant, owned by five adjacent communities, has even proved popular in a conservative region with Denmark’s highest per-capita income. Morten Slotved, 40, Horsholm’s mayor, is trying to expand it. “Constituents like it because it decreases heating costs and raises home values,” he said with a smile. “I’d like another furnace.”


Landfills that collect gas
Part of the waste decomposes, creating landfill gas. The gases are collected through underground wells, usually in areas that are not in active use anymore.
Plants that burn waste to create energy
Waste is burned to heat a boiler that generates steam for a turbine. The turbine runs a generator to create electricity. Excess heat can sometimes be used for heating.
65 kWh of electricity 590 kWh of electricity

3.35 tonnes of CO2 equivalent 600 grams of sulphur dioxide 2,300 grams of nitrogen oxides 0.56 tonnes of CO2 equivalent 220 grams of sulphur dioxide 1,450 grams of nitrogen oxides
Sources: PO Kaplan, J DeCarolis, S Thorneloe “Is it Better to Burn or Bury Waste for Clean Energy Generation?” Environmental Science & Technology 2009, E.P.A.; Energy Information Administration, D.O.E.


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