1.   Experts believe the absence of water in the toilet allowed a lethal build-up of methane gas.

2.   Four others are hooked into systems to control the release of methane gas.

3.   It is the biggest single concept, many others being devoted to using methane gas at waste product dumps.

4.   Methane gas from rubbish tips is another potentially valuable source of energy.

5.   Producing methane gas from landfill sites, sewage works and organic wastes is another extremely practical use of resources.

6.   That plant uses methane gas from the landfill to generate electricity.

7.   Then it is combined with hydrogen in a catalytic converter to produce methane gas and water.