Biogas is a byproduct of the decomposition of organic matter by anaerobic bacteria. Biogas is typically composed of 60% methane and 40% CO2. It is similar to natural gas which is composed of 99% methane. Biogas is a clean and renewable energy that may be substituted to natural gas to cook, to produce vapor, hot water or to generate electricity.

Organic waste is put into a sealed tank called a digester (or bioreactor) where it is heated and agitated. In the absence of oxygen anaerobic bacteria consume the organic matter to multiply and produce biogas.

Any organic waste has the ability to produce biogas: human excreta, manure, animal slurry, fruit and vegetable waste, slaughterhouse waste, meat packing waste, dairy factory waste, brewery and distillery waste, etc. Fiber rich wastes like wood, leaves, etc. make poor feedstocks for digesters as they are difficult to digest. How much biogas can I get out of my waste? The amount of biogas you can extract from your organic waste depends on the waste itself and the design of the digester system. Some digesters can yield 20 m3 of biogas per tonne of waste while others can yield as much as 800 m3 per tonne. It all depends on waste quality, digester design and proper operation of the system.

Biogas is normally produced in nature by the anaerobic degradation of organic waste in soil, marshes, ocean, etc. Biogas is also produced in landfills where organic food waste degrades in anaerobic conditions. Biogas can be produced in anaerobic digesters. These are equipment (tanks) providing full control of the process and ensuring full biogas recovery. Since methane is a potent greenhouse gas, isn’t it stupid to produce biogas? Methane has a greenhouse gas (GHG) heating factor 21 times higher than CO2. Combustion of biogas converts methane into CO2 and reduces the GHG impact by over 20 times.

Each cubic meter (m3) of biogas contains the equivalent of 6 kWh of calorific energy. However, when we convert biogas to electricity, in a biogas powered electric generator, we get about 2 kWh of useable electricity, the rest turns into heat which can also be used for heating applications. 2 kWh is enough energy to power a 100 W light bulb for 20 hours or a 2000W hair dryer for 1 hour.

It always costs money to get rid of waste. If it doesn’t cost you anything, you are probably creating an environmental hazard. By putting a digester in your waste treatment chain you introduce a potential revenue center. For example: On a farm the manure is not considered to be a waste but a fertilizer. By installing a digester the farmer can profit from the biogas by reducing odors and enhancing the fertilizing value of the manure. In an agro-food industry the digester can be used as a primary waste treatment unit where the biogas is used to offset some energy cost in the plant and to reduce the size of the secondary waste treatment.

Despite popular belief, the amount of waste going in the digester is almost equal to the amount coming out. However the quality of the waste is altered for the better (less odor, better fertilizer, organic load reduced, less polluting) Waste coming out of the digester can be separated (solid/liquid):the solid part can be composted and the liquid part can be used as liquid fertilizer or can be treated further and disposed.