Landfill gas is made up of a collection of different gases and is classed as a biogas. It typically consists of the following:
| Gas | % |
|---|---|
| Methane | 30-50% |
| Carbon dioxide | 30-60% |
| Nitrogen | 0-10% |
| Hydrogen | Less than 1% |
| Hydrogen sulphide | Less than 3% |
| Oxygen | Less than 2% |
| Trace gases | Less than 1% |
It is difficult to make the cap on the landfill airtight. Often, especially during dry conditions when the uppermost clay barrier may dry and split, air is drawn in by the vacuum pumps diluting the Methane content.
Certain other volatile organic compounds may be contained in the trace gases depending on the composition of the waste, and when the gas first emerges it is 100 per cent saturated.
Also, the mixture often contains siloxanes (a compound of hydrocarbons and silicon) which form abrasive deposits on the generator pistons and cylinders during combustion.
This aspect, combined with other corrosive gases such as hydrogen sulphide, forces a strict engine maintenance regime and a periodic complete overhaul.
Source: [1]