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. At room pressure and temperature biogas is in gaseous form, not liquid like LPG (propane). Bottling biogas is a very expensive process.
Organic waste is put into a sealed tank called BioCNG plant. 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 feed stocks for digesters as they are difficult to digest.
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.
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. By extracting methane out of waste and using it to produce heat and/or electricity we ensure that the waste will not degrade in an open environment therefore reducing direct methane atmospheric emissions. Moreover, the energy provided by the biogas is likely to displace fossil fuel which is the main contributor to GHG emissions. Biogas energy is considered carbon neutral, since carbon emitted by its combustion comes from carbon fixed by plants (natural carbon cycle).
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.
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.
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.
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.
The formation of biogas is a natural phenomenon that naturally occurs in wetland, manure stack, human and animal intestines. For centuries, humans have harvested the power of bacteriological digestion, by recovering naturally formed biogas to use for lighting, cooking, heating or to power mechanical engines.
In Asia, millions of family digesters were built to provide cooking fuel and lighting in rural areas. During the Second World War, German army trucks were fueled with biogas collected from farmers manure (gas engine).
Over the last 50 years remarkable progress has been made in the development of anaerobic digesters (bioreactors) to increase methane (CH4) yield and improve its process flow technologies.
Nowadays, thousands of projects around the world, from small dairy farms to large municipal waste water treatment plants, are demonstrating that biogas recovery systems are environmentally and economically sound. In Europe, villages are entirely supplied in electricity and heat from their local centralized biogas pant.
Actually, anaerobic digesters alleviate odor problems, especially as suburban growth surrounds farms and introduces neighbors who complain about manure smells. By installing an anaerobic digester, the farmer solves odor issues to everyone's satisfaction. Since the digesters are airtight, the smell stays within, and the liquids and solids coming out of the digester have only a very slight odor compared to raw slurry.
While in unfortunate situations, explosions can occur, biogas itself is not explosive. Under normal operating conditions, low pressure and low temperature, biogas is an uncompressed, wet gas, and tests have shown that it can simply be burned off (or oxidized with a flare) in a controlled setting.
Undesirable materials include those that cannot easily or at all be digested, or those that inhibit gas production. For example, wood has a high lignin content and cannot easily be digested; it would create sedimentation issues and impact digester functioning. Materials containing heavy metals would inhibit the gas-producing bacteria. Inorganic materials (plastics, metals, glass, etc.) would create mechanical issues. Even organic and easily digested feedstocks should be evaluated on their own merit.