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Turning Waste Into Energy in Denmark
Bears frolic and celebrate clean water in a happy scene. It's the logo on a municipal waste truck in Aalborg, which goes beyond the energy efficiency of even other cities in Denmark with a plant that turns waste into fuel and helps the environment.
Eight miles from town in an old gravel pit is the municipal plant, known as a methane digester. It is surrounded by a high berm that successfully disguises its presence in the rolling countryside. Trucks arrive with inputs for the plant: municipal food waste from restaurants and a small number of households. To that is added a large amount of industrial waste (fish processing and slaughterhouse waste) and manure from farms.
The plant was the last stop in the three-week Green Bike Tour of sustainable sites in Northern Europe by a team of bicyclists from Iowa.
Torstein Nord, the head of the Aalborg municipal solid waste department, took the team to the plant.
The plant's systems are complex. Just the right mixture of wastes and the correct temperature must be maintained for the bacteria to efficiently convert waste to methane gas. The gas is sent by pipeline to a nearby village where it is used as fuel for an electric plant that also provides hot-water heat.
The same trucks that arrive at the plant with hog and cattle manure are reloaded with previously digested material. The waste from the waste plant will be stored on farms for a number of months and then applied to farmland as a fertilizer and soil amendment. This is a closed loop process.
The process of digesting waste has just reached the stage where a report is to be written by several universities. The outcome of the environmental and economic evaluation will help set policy for all Denmark. Kyeld Johansen, the designer of the plant, is cautiously optimistic that the government will require many more plants be sited around the country. His company is already incorporating what it has learned from the Aalborg plant into one being constructed in Spain that will process waste from olive production.
This is another example of the Danish government encouraging new environmental technology that will become a source of export earnings. First with wind-to-electricity technology, then straw-burning methods and now methane digesters, Denmark continues to develop "green" production methods that can only find more markets as the world begins to confront the reality of global warming.
While the new methane plant was built at the edge of the city, Aalborg is tearing down a district heating plant in the town center. That plant only produced hot water for heating the city and did not generate electricity. It is being replaced by a new private electric plant that will tie its heat waste into the city hot-water pipes.
Denmark has no plants that just produce electricity or produce only district heating. A 10-year-old law demands that energy be converted from fuel efficiently. This means getting both electricity and useful heat from power plants, be they powered by fossil fuel, straw or methane.
It's a marked difference from Iowa. The new coal plant MidAmerican Energy is planning in Council Bluffs could not be built in Denmark. It is too inefficient because it will waste nearly two-thirds of its fuel in waste heat that will only serve to warm the Missouri River.
-- David Osterberg
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