Every year Americans throw away 250 million tons of rubbish. New York alone generates almost 10 million tons a year. It has been estimated that America’s garbage could provide as much energy as 100 million tons of coal. However, most of it is buried, and never used.
About half of the world’s domestic waste is paper, while kitchen waste makes up a quarter and plastics less than a tenth. Only a fifth will not burn and most of that can be recycled.
Western Europe has more than 200 plants which burn rubbish to produce electricity. A large plant at Edmonton in London, which opened in 1974, burns about 400,000 tons of refuse a year. The burning refuse heats water to create steam which powers the electric generators. Within ten years the plant has saved a million tons of coal.
In Dusseldorf, West Germany, six similar plants supply steam to generate electricity for district heating schemes.
In Peekskill, New York, a plant has been built to handle 2250 tons of refuse a day, generating 60 megawatts of electricity – enough to supply 70,000 people.
Rubbish can also be burned by factories instead of coal or oil, but it must be treated first. The rubbish is separated by feeding it though a vibrating screen which sifts out the fine organic particles to be turned into compost for treating land. In Sweden a quarter of all solid waste is turned into compost and recycled.
Next the heavy part of the rubbish, mainly metals, must be sorted out and removed, leaving mainly paper and textile waste. These are pressed into cylindrical pellets and sold as fuel.
Even rubbish dumped in the ground can be used as a source of fuel. As it begins to rot, it produces methane gas – identical to the natural gas found in pockets under the Earth’s crust. Each ton of refuse can produce over 8000 cubic feet (227 cubic metres) of methane. Left alone, the gas will find its way to the surface and escape, sometimes causing explosions. But it can be tapped very cheaply and used to generate heat or electricity. There are more than 140 such schemes in operation in 15 countries, saving a total of at least 825,000 tons of coal a year. In England, for example, a large tip has been drilled with wells to extract the gas, which is piped to a brickworks where it replaces coal.
Other plants use the gas on site to generate electricity by burning it in simple gas engines. This allows all the gas to be used, rather than trying to match output to the fluctuating demands of a factory.
In the future, production of gas in rubbish tips may be improved by ‘seeding’ the tips with bacteria. Some strains of bacteria break down refuse faster than others. By introducing the best mix of bacteria for the particular waste in a tip, the maximum amount could be produced.
Picture Credit : Google