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Information about Biogas

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Biogas-bus in Bern, Switzerland
Biogas typically refers to a (biofuel) gas produced by the anaerobic digestion or fermentation of organic matter including manure, sewage sludge, municipal solid waste, biodegradable waste or any other biodegradable feedstock, under anaerobic conditions. Biogas is comprised primarily of methane and carbon dioxide.

Depending on where it is produced, biogas is also called: Biogas containing methane is a valuable by-product of anaerobic digestion which can be utilised in the production of renewable energy [1].Biogas can be used as a vehicle fuel or for generating electricity. It can also be burned directly for cooking, heating, lighting, process heat and absorption refrigeration.

Biogas and anaerobic digestion

Main article: anaerobic digestion
Biogas production by anaerobic digestion is popular for treating biodegradable waste because valuable fuel can be produced, while destroying disease-causing pathogens and reducing the volume of disposed waste products. It burns more cleanly than coal, and emits less carbon dioxide per unit of energy. The harvesting of biogas is an important part of waste management because methane is a greenhouse gas with a greater global warming potential than carbon dioxide. The carbon in biogas was generally recently extracted from the atmosphere by photosynthetic plants, so releasing it back into the atmosphere adds less total atmospheric carbon than burning fossil fuels.

Recently, developed countries have been making increasing use of biogas generated from both wastewater and landfill sites or produced by mechanical biological treatment systems for municipal waste. High energy prices and increases in subsidies for electricity from renewable sources (such as renewables obligation certificates) and drivers such as the EU Landfill Directive have led to much greater use of biogas sources.

Landfill gas

Electricity from biogas (GWh)[2]
Country 2006 2005
Germany7 3384 708
UK4 9974 690
Italy1 2341 198
Spain675620
Greece579179
France501483
Austria41070
Netherlands286286
Denmark285275
Poland241175
Belgium237240
Czech Republic175161
Ireland108106
Sweden5454
Portugal3335
Luxembourg3327
Slovenia3232
Hungary2225
Finland2222
Estonia77
Slovakia44
Malta00
EU (GWh) 17 27213 397


Biogas in EU 2006 (GWh)[2]
Country Total Landfill Sludge Other
Germany22 3706 6704 30011 400
UK19 72017 6202 1000
Italy4 1103 61010490
Spain3 8902 930660300
France2 6401 72087050
Netherlands1 380450590340
Austria1 370130401 200
Denmark1 100170270660
Poland1 09032077010
Belgium97059029090
Greece8106301800
Finland7405901500
Czech Republic70030036040
Ireland4002906050
Sweden39013025010
Hungary12009040
Portugal11000110
Luxembourg10000100
Slovenia100801010
Slovakia6005010
Estonia101000
Malta0000
EU (GWh) 62 20036 25011 05014 900


Landfill gas is produced from organic waste disposed of in landfill. The waste is covered and compressed mechanically and by the pressure of higher levels. As conditions become anaerobic the organic waste is broken down and landfill gas is produced. This gas builds up and is slowly released into the atmosphere. This is hazardous for three key reasons:

Biogas composition

The composition of biogas varies depending upon the origin of the anaerobic digestion process. Landfill gas typically has methane concentrations around 50%. Advanced waste treatment technologies can produce biogas with 55-75%CH4 [4].

Typical composition of biogas[5]
Matter %
Methane, CH450-75
Carbon dioxide, CO225-50
Nitrogen, N20-10*
Hydrogen, H20-1
Hydrogen sulphide, H2S0-3
Oxygen, O20-2*


*often 5 % of air is introduced for microbiological desulphurisation

Siloxanes and gas engines

In some cases, biogas from landfills and sewage treatment contains siloxanes. During combustion of biogas containing siloxanes, silicon is released and can combine with free oxygen or various other elements in the combustion gas. Deposits are formed containing mostly silica () or silicates () in general, but can also contain calcium, sulphur, zinc, phosphor… as indicated by the analysis piston scrapings from biogas-fired engines. These (mostly white) deposits can ultimately build to a surface thickness of several millimetres and are difficult to remove by chemical or mechanical means.

In internal combustion engines deposits on pistons and cylinder heads are extremely abrasive and even a small amount is sufficient to cause enough damage to the engine to require a complete overhaul at 5,000 h or less of operation. The damage is similar to that caused by carbon build up during light load running of diesel engines. Deposits on the turbine of the turbocharger will eventually reduce the charger’s efficiency.

Luckily, simply cooling the gas to roughly -4 C is sufficient to remove siloxanes due to condensantion.

Stirling engines are more resistant against siloxanes, though deposits on the tubes of the heat exchanger will reduce the efficiency.[6][7]

Biogas to natural gas

If biogas is cleaned up sufficiently, biogas has the same characteristics as natural gas. In this instance the producer of the biogas can utilize the local gas distribution networks. The gas must be very clean to reach pipeline quality. Water (H2O), hydrogen sulfide (H2S) and particulates are removed if present at high levels or if the gas is to be completely cleaned. Carbon dioxide is less frequently removed, but it must also be separated to achieve pipeline quality gas. If the gas is to be used without extensively cleaning, it is sometimes cofired with natural gas to improve combustion. Biogas cleaned up to pipeline quality is called renewable natural gas or biomethane.

Applications of renewable natural gas

In this form the gas can be now used in any application that natural gas is used for. Such applications include distribution via the natural gas grid, electricity production, space heating, water heating and process heating. If compressed, it can replace compressed natural gas for use in vehicles, where it can fuel an internal combustion engine or fuel cells.

Cooking

Gober gas is a biogas generated out of cow dung. In India, gober gas is generated at the countless number of micro plants (an estimated more than 2 million) attached to households. The gober gas plant is basically an airtight circular pit made of concrete with a pipe connection. The manure is directed to the pit (usually directed from the cattle shed). The pit is then filled with a required quantity of water (usually waste water). The gas pipe is connected to the kitchen fire place through control valves. The flammable methane gas generated out of this is practically odorless and smokeless. The residue left after the extraction of the gas is used as biofertiliser. Owing to its simplicity in implementation and use of cheap raw materials in the villages, it is often quoted as one of the most environmentally sound energy source for the rural needs.

Railway transport

A biogas-powered train has been in service in Sweden since 2005 [8].

Landfill gas legislation

United States

In the United States, because landfill gas contains these VOCs, the United States Clean Air Act and Title 40 of the Code of Federal Regulations (CFR) requires landfill owners to estimate the quantity of non-methane organic compounds (NMOCs) emitted. If the estimated NMOC emissions exceeds 50 tonnes per year the landfill owner is required to collect the landfill gas and treat it to remove the entrained NMOCs. Treatment of the landfill gas is usually by combustion. Because of the remoteness of landfill sites it is sometimes not economically feasible to produce electricity from the gas.

See also

External links

References

1. ^ Biogas and Bioenergy
2. ^ Biogas barometer 2007 - EurObserv’ER Systèmes solaires - le journal des énergies renouvelables n° 179, s. 51-61, 5/2007
3. ^ Biogas barometer 2007 - EurObserv’ER Systèmes solaires - le journal des énergies renouvelables n° 179, s. 51-61, 5/2007
4. ^ Juniper Biogas Yield Comparison
5. ^ Basic Information on Biogas
6. ^ Presentation - Siloxanes in landfill gas
7. ^ Paper - Siloxanes in landfill and digester gas
8. ^ Biogas train in Sweden
Renewable energy
  • Biofuels
  • Biomass
  • Geothermal power
  • Hydro power
  • Solar power
  • Tidal power
  • Wave power
  • Wind power
Biofuel (also called agrofuel[1]
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Gas is one of the four major states of matter, consisting of freely moving atoms or molecules without a definite shape. Compared to the solid and liquid states of matter a gas has lower density and a lower viscosity.
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Anaerobic digestion (AD) is the natural process of biological degradation of organic material in the absence of air. An anaerobic digester is a man-made system that harnesses this process to treat waste and produce biogas and anaerobic digestate, a soil-improving material.
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Fermentation is a process of energy production in a cell under anaerobic conditions (with no oxygen required). In common usage fermentation is a type of anaerobic respiration, however a more strict definition exists which defines fermentation as respiration under anaerobic
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Organic matter (or organic material) is matter that has come from a recently living organism; is capable of decay, or the product of decay; or is composed of organic compounds.
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Hypoxia or oxygen depletion is a phenomenon that occurs in aquatic environments as dissolved oxygen (DO
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Methane is a chemical compound with the molecular formula CH4. It is the simplest alkane, and the principal component of natural gas. Methane's bond angles are 109.
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landfill, also known as a dump or tip (and historically as a midden), is a site for the disposal of waste materials by burial and is the oldest form of waste treatment.
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Anaerobic digestion (AD) is the natural process of biological degradation of organic material in the absence of air. An anaerobic digester is a man-made system that harnesses this process to treat waste and produce biogas and anaerobic digestate, a soil-improving material.
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Anaerobic digestion (AD) is the natural process of biological degradation of organic material in the absence of air. An anaerobic digester is a man-made system that harnesses this process to treat waste and produce biogas and anaerobic digestate, a soil-improving material.
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A pathogen or infectious agent is a biological agent that causes disease or illness to its host.[1] The term is most often used for agents that disrupt the normal physiology of a multicellular animal or plant.
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Coal (IPA: /ˈkəʊl/) is a fossil fuel formed in swamp ecosystems where plant remains were saved by water and mud from oxidization and biodegradation.
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Carbon dioxide is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. It is a gas at standard temperature and pressure and exists in Earth's atmosphere in this state.
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