Biogas is naturally produced through the fermentation of many different types of animal- and plant-derived organic matter. New biogas plants and even landfills increasingly tap into this little-known energy from waste, using methanation to provide heat, power or automotive fuel.
A Natural Phenomenon
anaerobic fermentation (methanation)Fermentation in the absence of air or free oxygen. is an anaerobicDescribes an organism or microorganism that requires an environment without air and... fermentation process whereby putrescible (readily biodegradableA substance capable of being decomposed by naturally occurring fungi and microorganisms. ) matter is broken down by bacteriaTiny living organisms that are made up of a single cell that does not have a distinct nucleus, such as a prokaryotic cell... in the absence of oxygen. This process naturally occurs in marshes, where it leads to the production of marsh gas. Methanation produces biogasA product of the methanation (anaerobic digestion) of organic waste... , a mixture of gases consisting mainly of methane (ch4)The main component of natural gas deposits and oil deposit gas caps. Methane is produced naturally by landfills... (CH4), which also accounts for over 90% of the content of the fossil fuelFuel is any solid, liquid or gaseous substance or material that can be combined with an oxidant... natural gas.
Methanation is a process that occurs naturally in marshes and organic waste landfills.
Methanation can be applied to any form of naturally fermenting organic waste. Examples include paper and cardboard, food waste and leftovers, agricultural waste, manure and slurry from livestock, and sludge from wastewater treatment plants. Developed in the 1980s, methanation is a booming waste treatment solution across Europe. In 2013, roughly 7 million tons of municipal waste was processed using methanation.
The composition of biogas obtained through methanation is as follows:
- 55 to 70% methane (CH4);
- 30 to 45% carbon dioxide (CO2See Carbon Dioxid );
- Small quantities of ammonia (NH3) and hydrogenThe simplest and lightest atom, the most abundant element in the universe. sulfide (H2S);
- Solid residue from methanation, or digestateThe solid material remaining after methanation.. , which can be dried and used as fertilizer.
A methanation unit consists of a large, covered tank into which the waste to be treated is deposited. These tanks are called reactors, fermenters or digesters. They operate at a temperature of 35°C, running on some of the biogas produced from the waste. In the newest reactors, methanation takes several days, producing 1 to 10 cubic meters of biogas per cubic meter of waste per day.
The size of biogas production units can vary significantly. A small anaerobic digester on a farm typically has a capacity of about 100 cubic meters. On the other end of the scale, the Penkun plant in Germany can generate up to 20 MW of powerIn physics, power is the amount of energy supplied by a system per unit time. In simpler terms, power can be viewed as energy output... using 40 enormous digesters.
Landfills as Powerful Energy Sources
The other main method of producing biogas is through the recovery of landfill gases. Over long periods of time, landfills spontaneously produce methane through a process of fermentationThe conversion of certain organic compounds by enzymes secreted by microorganisms... .
55 to 70%: the methane content of biogas generated through this process
In these waste disposal facilities, refuse is compacted and placed in trenches known as cells that are sometimes sealed to give better results. The cells are then covered with several meters of soil. A system of horizontal and vertical pipes run through the cells, the former to collect the biogas produced and the latter to bring the biogas to the surface. This underground fermentation process can take 25 years.
Methane, a harmful greenhouse gas (ghg) Gas with physical properties that cause the Earth's atmosphere to warm up. There are a number of naturally occurring greenhouse gases... , must be recovered to prevent its release into the atmosphere. Where waste methane is not recovered, it is burned. The carbon dioxide produced in this way is much less damaging than methane.
Biogas’ Many Applications
Before biogas can be used, all traces of hydrogen sulfide - which corrodes metal - must be removed. Hydrogen sulfide is highly toxic when burned as it releases sulfur dioxide (SO2), which can damage both forests (through acid rain) and our lungs.
Biogas can be burned to produce heatIn the field of statistical thermodynamics today, heat refers to the transfer of the thermal agitation of the particles making up matter... , power or both, through cogenerationThe simultaneous production of both heat (thermal energy) and power... , with 170 kWh of power and 340 kWh of heat generated per ton of methanized waste. After all the impurities have been removed, including carbon dioxide, the gas can be fed into the municipal gas network. It can also be used to fuel natural gas vehicles (NGVs) that run on compressed methane. In addition, several European countries have successfully integrated biogas fuel into their mass transit systems.
Biogas, a Valuable Resource for Farms Extensively developed in Denmark and Germany, biogas digesters can be used on farms to produce energy locally from livestock slurry. In 2010, a total of 5,800 on-farm digesters were already in place in Germany. In March 2013, the French government launched the EMAA plan to improve nitrogen management and develop methanation1. Under the plan, 1,000 digesters should be operating on France’s farms by 2020, compared with just 90 at the end of 2012. Millions of digesters are already up and running in China, India and Nepal.
(1) French Ministry of Agriculture (in French only)