Landfill sites are potentially a huge source for biogas. Rubbish of one form or another, much of it biological in nature has been deposited there in layers over a period of years. The conditions lower down in the heap are essentially anaerobic, and generally reasonably damp – ideal for the growth of anaerobic bacteria!
A landfill is generally covered with earth for land reclamation when it is full, creating perfect anaerobic conditions and allowing the gas produced to be collected in pipes sunk into the landfill site. It is generally necessary to check the quality and quantity of the landfill gas produced. A borehole will in time produce less gas and the methane content will reduce as well as the carbon products are consumed. It is generally also worthwhile to check the level of oxygen in the gas. This is important for two reasons: the presence of oxygen will cause the aerobic bacteria to flourish, producing carbon dioxide instead of methane and methane mixed with oxygen can form a potentially explosive mixture over a very broad range of concentrations. There have been a number of accidents in the history of landfill sites, mostly due to a build up of methane under uncontrolled circumstances.For this reason, regular checks with a landfill gas analyser are essential. Simply monitoring the total gas from all the boreholes together is not enough to catch dangerous situations or boreholes producing mostly carbon dioxide.