Methane is a type of biomass energy. Some examples of biomass energy are wood, straw and manure. The foundation of this is based on the bacteria that live in the intestines of many animals. When this bacterium breaks down cellulose (the main ingredient in plant fibres) it produces biogas. The bio-digester works by utilizing the same process. For this reason methane is found in many other places as well, such as bogs, swamps and landfills.It can be used as an alternative opposed to natural gas for heating and cooking. Biogas is considered renewable because it mainly depends on the supply of grass which grows back but natural gas comes from the fossilized remains of plants and animals from thousands of years ago so it is not considered “renewable”.

Biogas is also produced in bogs and wetlands due to the rotting of vegetation, it mainly consists of methane. Biogas generators can be used to produce biogas as well. To start the process shredded plant and animal wastes are mixed and put into a tank with some water. Than it is sealed so it is air tight. Soon a special kind of bacteria called “methanogenic” bacteria will begin to produce gas. After the material has been used and production slows down it can be dried up and used as fertilizer.

Burning one molecule of methane, in the presence of oxygen, releases one molecule of CO2, (carbon dioxide) and two molecules of H2O (water). The burning of methane is a lot cleaner than the burning of coal because there is less emissions of carbon dioxide and produces more energy than coal as well.

Biogas vs. Natural gas

If purified biogas is not very different than natural gas. Biogas can be filtered so it contains higher amounts of methane compared to other gases in the substance. The applications for it are the same ones of natural gas, from heating to electricity production and can even be compressed to be used in fuel cells of internal combustion engines.
But what makes biogas better than natural gas? The way they are obtained is what makes the difference. When you obtain natural gas you are taking substances from underground which took millions of years to form and you are burning them and putting them into the atmosphere. When you keep burning these gasses, the CO2 levels just rise faster than the rate which trees can use the carbon dioxide.

When you use a generator you make the gas in less time. Also you generate it from above ground from above the ground so basically your taking stuff from the air and putting it back in the air (does not cause a rise in levels of CO2 in the atmosphere). What this means is that when we burn the methane the carbon dioxide that is put in the air will be used by the plants, then the animals will eat the plants (grass etc.) and using the manure of animals it will produce methane again and once the manure runs out of the ability to produce more methane it can be used as fertilizer for the plants.

(fig 3-1) This picture shows that the production of biogas is like a cycle. The manure from the cow goes into the digester. Afterwards the gas that is burned produces carbon dioxide but the plants that are being fed by the fertilizer simply use it in photosynthesis. This helps the plants grow which in turn feed the cow.

Landfill Biogas

Landfill biogas is produced from organic waste in the landfill. When the organic waste has more waste on top the upper layers cause pressure on the lower layers. As the pressure increases on the lower layer conditions become anaerobic and the organic waste begins producing biogas. When this gas builds up it begins to escape, this is dangerous because of the effects it can cause. Methane is a more pollutant green house gas than carbon dioxide also; it could cause risk of explosion. Since methane is a green house gas it is essential to collect it as an important function of waste management. Landfill gas generally has lower concentrations of methane than some other types of biogas. The methane concentrations are only about 50% but with waste treatment technologies it can be filtered to have higher concentrations.

(fig 3-2) Picutre shows how landfill biogas is formed.

Purification and Filtration

When you first make the biogas it is not very pure. It contains about 50-75% methane, 25-50% carbon dioxide, 0-10% nitrogen, 0-1% hydrogen, 0-3% hydrogen sulphide and 0-2% oxygen. These percentages vary depending on the different sources the gas is obtained. Generally in a digester the methane percentages are greater than the biogas from other sources. The quality of gas is also affected by the conditions the generator is in. Some ways to purify this gas is to filter it through limewater to remove the carbon dioxide, pass it through iron filings to absorb corrosive hydrogen sulphide and through calcium chloride to extract water vapor.