When the dam gates are opened, the water surges through a tunnel to turbines. The water turns the turbines which turn generators to produce electricity. Hydroelectric dams are expensive to build. They also need relatively large areas of water close to civilisation. Organic, biodegradable waste is collected and compacted to a specific density in a repository.
Gas production begins as the waste is broken down by microbes.
The pipes are connected to engines, which are powered by the gas to produce electricity. If the gas is not collected it could be harmful to the atmosphere. Methane is significantly more damaging to the environment than carbon dioxide, the main greenhouse gas. More information on greenhouse gases and climate change, see Platts' feature on the Kyoto Protocol. The British government is particularly keen to stop waste just being buried in landfill sites.