FACTOID # 5: Minnesota and Connecticut are both in the top 5 in saving money and total tax burden per capita.
 
 Home   Encyclopedia   Statistics   States A-Z   Flags   Maps   FAQ   About 
   
 
WHAT'S NEW
 

SEARCH ALL

FACTS & STATISTICS    Advanced view

Search encyclopedia, statistics and forums:

 

 

(* = Graphable)

 

 


Encyclopedia > Anaerobic digestion
Anaerobic digestion & regenerative thermal oxidiser component of Lübeck mechanical biological treatment plant in Germany, 2007
Anaerobic digestion & regenerative thermal oxidiser component of Lübeck mechanical biological treatment plant in Germany, 2007
Renewable energy
Wind Turbine
Biofuels
Biomass
Geothermal
Hydro power
Solar power
Tidal power
Wave power
Wind power

Anaerobic digestion is a series of processes in which microorganisms break down biodegradable material in the absence of oxygen. It is widely used to treat wastewater sludges and organic wastes because it provides volume and mass reduction of the input material.[1] As part of an integrated waste management system, anaerobic digestion reduces the emission of landfill gas into the atmosphere. Anaerobic digestion is a renewable energy source because the process produces a methane and carbon dioxide rich biogas suitable for energy production helping replace fossil fuels. Also, the nutrient-rich solids left after digestion can be used as fertiliser. Image File history File links Metadata Size of this preview: 800 × 402 pixelsFull resolution (1898 × 954 pixel, file size: 322 KB, MIME type: image/jpeg) Photograph of anaerobic digesters at the Lubeck Waste Treatment Facility a mechanical biological treatment plant. ... Image File history File links Metadata Size of this preview: 800 × 402 pixelsFull resolution (1898 × 954 pixel, file size: 322 KB, MIME type: image/jpeg) Photograph of anaerobic digesters at the Lubeck Waste Treatment Facility a mechanical biological treatment plant. ... Anaerobic digestion and air filtration components of the plant The Lübeck Waste Treatment Facility is a mechanical biological treatment plant located near the city of Lübeck in Germany. ... Anaerobic digestion and air processing components of Lübeck mechanical biological treatment plant in Germany A mechanical biological treatment system is a form of waste processing facility that combines a sorting facility with a form of biological treatment such as composting or anaerobic digestion. ... Renewable energy effectively utilizes natural resources such as sunlight, wind, tides and geothermal heat, which are naturally replenished. ... Image File history File links Wind-turbine-icon. ... Bio-energy redirects here. ... Simple use of biomass fuel (Combustion of wood for heat). ... The Nesjavellir Geothermal Power Plant in Iceland Geothermal power (from the Greek words geo, meaning earth, and thermal, meaning heat) is energy generated by heat stored beneath the Earths surface or the collection of absorbed heat in the atmosphere and oceans. ... Hydroelectricity is electricity produced by hydropower. ... Heat and light from the Sun fuels life on Earth. ... Tidal power, sometimes called tidal energy, is a form of hydropower that converts the energy of tides into electricity or other useful forms of power. ... Wave power refers to the energy of ocean surface waves and the capture of that energy to do useful work - including electricity generation, desalination, and the pumping of water (into reservoirs). ... An example of a wind turbine. ... A microorganism or microbe is an organism that is so small that it is microscopic (invisible to the naked eye). ... Biodegradation is the decomposition of material by microorganisms. ... This article is about the chemical element and its most stable form, or dioxygen. ... Wastewater is any water that has been adversely affected in quality by anthropogenic influence. ... Biodegradable waste is a type of waste, typically originating from plant or animal sources, which may be broken down by other living organisms. ... For the company, see Waste Management, Inc. ... Natural gas rig Natural gas (commonly refered to as gas in many countries) is a gaseous fossil fuel consisting primarily of methane. ... Renewable energy effectively utilizes natural resources such as sunlight, wind, tides and geothermal heat, which are naturally replenished. ... Methane is a chemical compound with the molecular formula . ... Carbon dioxide (chemical formula: CO2) is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. ... 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. ... Fossil fuels or mineral fuels are fossil source fuels, that is, hydrocarbons found within the top layer of the earth’s crust. ... Fertilizers are chemicals given to plants with the intention of promoting growth; they are usually applied either via the soil or by foliar spraying. ...


The digestion process begins with bacterial hydrolysis of the input materials in order to break down insoluble organic polymers such as carbohydrates and make them available for other bacteria. Acidogenic bacteria then convert the sugars and amino acids into carbon dioxide, hydrogen, ammonia, and organic acids. Acetogenic bacteria then convert these resulting organic acids into acetic acid, along with additional ammonia, hydrogen, and carbon dioxide. Methanogenic bacteria finally are able to convert these products to methane and carbon dioxide.[2] Phyla Actinobacteria Aquificae Chlamydiae Bacteroidetes/Chlorobi Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Deinococcus-Thermus Dictyoglomi Fibrobacteres/Acidobacteria Firmicutes Fusobacteria Gemmatimonadetes Lentisphaerae Nitrospirae Planctomycetes Proteobacteria Spirochaetes Thermodesulfobacteria Thermomicrobia Thermotogae Verrucomicrobia Bacteria (singular: bacterium) are unicellular microorganisms. ... Polymer is a generic term used to describe a very long molecule consisting of structural units and repeating units connected by covalent chemical bonds. ... Lactose is a disaccharide found in milk. ... The term acetogen refers to a bacterium that generates acetate as a product of anaerobic respiration. ... This article is about sugar as food and as an important and widely-traded commodity. ... This article is about the class of chemicals. ... This article is about the chemistry of hydrogen. ... For other uses, see Ammonia (disambiguation). ... An organic acid is an organic compound that is an acid. ... R-phrases , S-phrases , , , Flash point 43 °C Related Compounds Related carboxylic; acids Formic acid; Propionic acid; Butyric acid Related compounds acetamide; ethyl acetate; acetyl chloride; acetic anhydride; acetonitrile; acetaldehyde; ethanol; thioacetic acid; acetylcholine; acetylcholinesterase Supplementary data page Structure and properties n, εr, etc. ... Methanogens are archaea that produce methane as a metabolic byproduct in anoxic conditions. ...


The technical expertise required to maintain anaerobic digesters coupled with high capital costs and lower process efficiencies have so far limited the level of its industrial application as a waste treatment technology.[3] Anaerobic digestion facilities have, however, been recognised by the United Nations Development Programme as one of the most useful decentralised sources of energy supply, as they are less capital intensive than large powerplants.[4] This is the amount on which you first claim CCA. The capital cost of a depreciable property is usually the total of the purchase price, not including the cost of land (which is not depreciable);the part of your legal, accounting, engineering, installation, and other fees that relates to the... The United Nations Development Programe (UNDP), the United Nations global development network, is the largest multilateral source of development assistance in the world. ...


Careful control of the digestion temperature, pH, and loading rates is crucial to obtaining efficient breakdown of the material, and disturbances to a digest can lead to process failure. Ensuring that the quality of input materials to the digesters is maintained and that the process effectively monitored is essential for ensuring that a digester's performance is reliable. For other uses, see Temperature (disambiguation). ... For other uses, see PH (disambiguation). ...

Contents

History

Gas street lamp
Gas street lamp

Scientific interest in the gases produced by the natural decomposition of organic matter, was first reported in the sixteenth century by Robert Boyle and Stephen Hale, who noted that inflammable gas was released by disturbing the sediment of streams and lakes.[5] In 1808, Sir Humphry Davy determined that methane was present in the gases produced by cattle manure.[6][7] The first anaerobic digester was built by a leper colony in Bombay, India in 1859. In 1895 the technology was developed in Exeter, England, where a septic tank was used to generate gas for street lighting. Also in England, in 1904, the first dual purpose tank for both sedimentation and sludge treatment was installed in Hampton. In 1907, in Germany, a patent was issued for the Imhoff tank, an early form of digester. Image File history File links Size of this preview: 225 × 598 pixelsFull resolution‎ (236 × 627 pixels, file size: 53 KB, MIME type: image/jpeg) I created this file. ... Image File history File links Size of this preview: 225 × 598 pixelsFull resolution‎ (236 × 627 pixels, file size: 53 KB, MIME type: image/jpeg) I created this file. ... For the American art director and production designer, see Robert F. Boyle Robert Boyle (25 January 1627 – 30 December 1691) was a natural philosopher, chemist, physicist, inventor, and early gentleman scientist, noted for his work in physics and chemistry. ... This article or section cites very few or no references or sources. ... Sir Humphry Davy, 1st Baronet FRS (17 December 1778 – 29 May 1829) was a British chemist and physicist. ... For general information about the genus, including other species of cattle, see Bos. ... Animal manure is often a mixture of animals feces and bedding straw, as in this example from a stable. ... A leper colony is a place to quarantine people with leprosy from the rest of the population. ... This article or section should be merged with Mumbai Mumbai (previously known as Bombay) is the worlds most populous conurbation, and is the sixth most populous agglomeration in the world. ... For other uses, see Exeter (disambiguation). ... For other uses, see England (disambiguation). ... example of a JE Webb type lamp // Gasses forming in sewers can be a potentially smelly and explosive hazard (chiefly due to methane). ... Sedimentation describes the motion of particles in solutions or suspensions in response to an external force such as gravity, centrifugal force or electric force. ... Hampton can mean: // Place names United States of America Hampton, Connecticut Hampton, Georgia Hampton, Iowa Hampton, Minnesota Hampton, Nebraska Hampton, New Hampshire Hampton, New Jersey Hampton, New York Hampton, South Carolina Hampton, Tennessee Hampton, Virginia Hampton Cove, Alabama Hampton Falls, New Hampshire New Hampton, New Hampshire Canada Hampton, New Brunswick... The Imhoff tank is a chamber suitable for the reception and processing of sewage. ...


Through scientific research anaerobic digestion gained academic recognition in the 1930s. This research led to the discovery of anaerobic bacteria, the microorganisms that facilitate the process. Further research was carried out to investigate the conditions under which methanogenic bacteria were able to grow and reproduce.[8] This work was developed during World War II where in both Germany and France there was an increase in the application of anaerobic digestion for the treatment of manure. Plato is credited with the inception of academia: the body of knowledge, its development and transmission across generations. ... Combatants Allied powers: China France Great Britain Soviet Union United States and others Axis powers: Germany Italy Japan and others Commanders Chiang Kai-shek Charles de Gaulle Winston Churchill Joseph Stalin Franklin Roosevelt Adolf Hitler Benito Mussolini Hideki Tōjō Casualties Military dead: 17,000,000 Civilian dead: 33,000...


Applications

Anaerobic digestion is particularly suited to wet organic material and is commonly used for effluent and sewage treatment.[9] Anaerobic digestion is a simple process that can greatly reduce the amount of organic matter which might otherwise be destined to be landfilled or burnt in an incinerator. Sewage is the mainly liquid waste containing some solids produced by humans which typically consists of washing water, faeces, urine, laundry waste and other material which goes down drains and toilets from households and industry. ... Look up Dump in Wiktionary, the free dictionary. ... This article needs cleanup. ...


Almost any organic material can be processed with anaerobic digestion.[10] This includes biodegradable waste materials such as waste paper, grass clippings, leftover food, sewage and animal waste. The exception to this is woody wastes that are largely unaffected by digestion as anaerobes are unable to degrade lignin. Anaerobic digesters can also be fed with specially grown energy crops such as silage for dedicated biogas production. In Germany and continental Europe these facilities are referred to as biogas plants. A co-digestion or co-fermentation plant is typically an agricultural anaerobic digester that accepts two or more input materials for simultaneous digestion.[11] For other uses, see Wood (disambiguation). ... Lignin (sometimes lignen) is a chemical compound (complex, highly cross-linked aromatic polymer) that is most commonly derived from wood and is an integral part of the cell walls of plants, especially in tracheids, xylem fibres and sclereids. ... An energy crop is a plant domesticated for use in agriculture and is produced as a low cost and low maintenance harvest (generally, non food crops) to be used to make biofuels or directly exploited for its energy content. ... Silage (hay) somewhere in Allschwil or Schönenbuch, near Basel, Switzerland. ...


In developing countries simple home and farm-based anaerobic digestion systems offer the potential for cheap, low-cost energy for cooking and lighting.[12][13][14][15] Anaerobic digestion facilities have been recognised by the United Nations Development Programme as one of the most useful decentralised sources of energy supply.[16] From 1975, China and India have both had large government-backed schemes for adaptation of small biogas plants for use in the household for cooking and lighting.[17] Presently, projects for anaerobic digestion in the developing world can gain financial support through the United Nations Clean Development Mechanism if they are able to show the provide reduced carbon emissions.[18] UN redirects here. ... CDM directs here. ...


Pressure from environmentally-related legislation on solid waste disposal methods in developed countries has increased the application of anaerobic digestion as a process for reducing waste volumes and generating useful by-products. Anaerobic digestion may either be used to process the source separated fraction of municipal waste, or alternatively combined with mechanical sorting systems, to process residual mixed municipal waste. These facilities are called mechanical biological treatment plants.[19][20][21] Legislation (or statutory law) is law which has been promulgated (or enacted) by a legislature or other governing body. ... For other uses, see Waste (disambiguation). ... World map indicating Human Development Index (as of 2004). ...


Utilising anaerobic digestion technologies can help to reduce the emission of greenhouse gases in a number of key ways:

  • Replacement of fossil fuels
  • Reducing methane emission from landfills
  • Displacing industrially-produced chemical fertilisers
  • Reducing vehicle movements
  • Reducing electrical grid transportation losses

Methane and power produced in anaerobic digestion facilities can be utilised to replace energy derived from fossil fuels, and hence reduce emissions of greenhouse gases.[22] This is due to the fact that the carbon in biodegradable material is part of a carbon cycle. The carbon released into the atmosphere from the combustion of biogas has been removed by plants in order for them to grow in the recent past. This can have occurred within the last decade, but more typically within the last growing season. If the plants are re-grown, taking the carbon out of the atmosphere once more, the system will be carbon neutral.[23][24] This contrasts to carbon in fossil fuels that has been sequestered in the earth for many millions of years, the combustion of which increases the overall levels of carbon dioxide in the atmosphere. Car redirects here. ... A database query syntax error has occurred. ... For the thermonuclear reaction involving carbon that helps power stars, see CNO cycle. ...


If the putrescible waste processed in anaerobic digesters was disposed of in a landfill, it would break down naturally and often anaerobically. In this case the gas will eventually escape into the atmosphere. As methane is about twenty times more potent as a greenhouse gas as carbon dioxide this has significant negative environmental effects.[25] Top: Increasing atmospheric levels as measured in the atmosphere and ice cores. ...


Digestate liquor can be used as a fertiliser supplying vital nutrients to soils. The solid, fibrous component of digestate can be used as a soil conditioner. The liquor can be used as a substitute for chemical fertilisers which require large amounts of energy to produce. The use of manufactured fertilisers is therefore more carbon intensive than the use of anaerobic digestate fertiliser. This solid digestate can be used to boost the organic content of soils. There are some countries, such as in Spain where there are many organically depleted soils, and here the markets for the digestate can be just as important as the biogas.[26]


In countries that collect household waste, the utilisation of local anaerobic digestion facilities can help to reduce the amount of waste that requires transportation to centralised landfill sites or incineration facilities. This reduced burden on transportation has an will reduce carbon emissions from the collection vehicles. If localised anaerobic digestion facilities are embedded within an electrical distribution network, they can help reduce the electrical losses that is associated with transporting electricity over a national grid.[27]


The process

Main article: Anaerobic respiration

There are a number of bacteria that are involved in the process of anaerobic digestion including acetic acid-forming bacteria (acetogens) and methane-forming bacteria (methanogens). These bacteria feed upon the initial feedstock, which undergoes a number of different processes converting it to intermediate molecules including sugars, hydrogen & acetic acid before finally being converted to biogas. Anaerobic respiration refers to the oxidation of molecules in the absence of oxygen to produce energy, in opposition to Aerobic respiration which does use oxygen. ... The term acetogen refers to a bacterium that generates acetate as a product of anaerobic respiration. ... Methanogens are archaea that produce methane as a metabolic byproduct in anoxic conditions. ...


Different species of bacteria are able to survive at different temperature ranges. Ones living optimally at temperatures between 35-40°C are called mesophiles or mesophilic bacteria. Some of the bacteria can survive at the hotter and more hostile conditions of 55-60°C, these are called thermophiles or thermophilic bacteria.[28] Methanogens come from the primitive group of archaea. This family includes species that can grow in the hostile conditions of hydrothermal vents. These species are more resistant to heat and can therefore operate at thermophilic temperatures, a property that is unique to bacterial families.[29] A mesophile is an organism that grows best in moderate temperature, neither too hot nor too cold, typically between 25 and 40 °C (68 and 113 °F). ... This article is about a type of organism. ...


As with aerobic systems the bacteria in anaerobic systems the growing and reproducing microorganisms within them require a source of elemental oxygen to survive.[30]


In an anaerobic system there is an absence of gaseous oxygen. In an anaerobic digester, gaseous oxygen is prevented from entering the system through physical containment in sealed tanks. Anaerobes access oxygen from sources other than the surrounding air. The oxygen source for these microorganisms can be the organic material itself or alternatively may be supplied by inorganic oxides from within the input material. When the oxygen source in an anaerobic system is derived from the organic material itself, then the 'intermediate' end products are primarily alcohols, aldehydes, and organic acids plus carbon dioxide. In the presence of specialised methanogens, the intermediates are converted to the 'final' end products of methane, carbon dioxide with trace levels of hydrogen sulfide.[31][32] In an anaerobic system the majority of the chemical energy contained within the starting material is released by methanogenic bacteria as methane.[33] An oxide is a chemical compound containing at least one oxygen atom and other elements. ... This article does not cite any references or sources. ... An aldehyde. ...


Populations of anaerobic bacteria typically take a significant period of time to establish themselves to be fully effective. It is therefore common practice to introduce anaerobic microorganisms from materials with existing populations. This process is called 'seeding' the digesters and typically takes place with the addition of sewage sludge or cattle slurry.[34]


Stages

The key process stages of anaerobic digestion
The key process stages of anaerobic digestion

There are four key biological and chemical stages of anaerobic digestion:[35][36] Image File history File links Size of this preview: 800 × 201 pixelsFull resolution‎ (921 × 231 pixels, file size: 48 KB, MIME type: image/jpeg) Author: Alex Marshall, Clarke Energy File historyClick on a date/time to view the file as it appeared at that time. ... Image File history File links Size of this preview: 800 × 201 pixelsFull resolution‎ (921 × 231 pixels, file size: 48 KB, MIME type: image/jpeg) Author: Alex Marshall, Clarke Energy File historyClick on a date/time to view the file as it appeared at that time. ...

  1. Hydrolysis
  2. Acidogenesis
  3. Acetogenesis
  4. Methanogenesis

In most cases biomass is made up of large organic polymers. In order for the bacteria in anaerobic digesters to access the energy potential of the material, these chains must first be broken down into their smaller constituent parts. These constituent parts or monomers such as sugars are readily available by other bacteria. The process of breaking these chains and dissolving the smaller molecules into solution is called hydrolysis. Therefore hydrolysis of these high molecular weight polymeric components is the necessary first step in anaerobic digestion.[37] Through hydrolysis the complex organic molecules are broken down into simple sugars, amino acids, and fatty acids.[38] Hydrolysis is a chemical reaction or process in which a chemical compound is broken down by reaction with water. ... Acidogenesis represents the second stage in the four stages of anaerobic digestion: Hydrolysis: Particulates are solubilized and large polymers, converted into simpler monomers; Acidogenesis: Simple monomers are converted into volatile fatty acids; Acetogenesis: Volatile fatty acids are converted into acetic acid, carbon dioxide, and hydrogen; and Methanogenesis: Acetate are converted... Acetogenesis is a process through which acetate is produced by anaerobic bacteria from a variety of energy (for example, hydrogen) and carbon (for example, carbon dioxide) sources. ... Methanogenesis is the formation of methane by microbes. ... Hydrolysis is a chemical reaction or process in which a chemical compound is broken down by reaction with water. ... Monosaccharides are carbohydrates in the form of simple sugars. ... Not to be confused with fats. ...


Acetate and hydrogen produced in the first stages can be used directly by methanogens. Other molecules such as volatile fatty acids (VFA’s) with a chain length that is greater than acetate must first be catabolised into compounds that can be directly utilised by methanogens.[39] Catabolism is the set of metabolic pathways that break down molecules into smaller units and release energy. ...


The biological process of acidogenesis is where there is further breakdown of the remaining components by acidogenic (fermentative) bacteria. Here VFAs are created along with ammonia, carbon dioxide and hydrogen sulfide as well as other by-products.[40] The process of acidogenesis is similar to the way that milk sours. Acidogenesis represents the second stage in the four stages of anaerobic digestion: Hydrolysis: Particulates are solubilized and large polymers, converted into simpler monomers; Acidogenesis: Simple monomers are converted into volatile fatty acids; Acetogenesis: Volatile fatty acids are converted into acetic acid, carbon dioxide, and hydrogen; and Methanogenesis: Acetate are converted... Hydrogen sulfide (or hydrogen sulphide) is the chemical compound with the formula H2S. This colorless, toxic and flammable gas is responsible for the foul odour of rotten eggs and flatulence. ... Wikipedia does not have an article with this exact name. ...


The third stage anaerobic digestion is acetogenesis. Here simple molecules created through the acidogenesis phase are further digested by acetogens to produce largely acetic acid as well as carbon dioxide and hydrogen.[41] Acetogenesis is a process through which acetate is produced by anaerobic bacteria from a variety of energy (for example, hydrogen) and carbon (for example, carbon dioxide) sources. ...


The terminal stage of anaerobic digestion is the biological process of methanogenesis. Here methanogens utilise the intermediate products of the preceding stages and convert them into methane, carbon dioxide and water. It is these components that makes up the majority of the biogas emitted from the system. Methanogenesis is sensitive to both high and low pHs and occurs between pH 6.5 and pH 8.[42] The remaining, non-digestable material which the microbes cannot feed upon, along with any dead bacterial remains constitutes the digestate. Methanogenesis is the formation of methane by microbes. ...


A simplified generic chemical equation for the overall processes outlined above is as follows:

C6H12O6 → 3CO2 + 3CH4

Feedstock

Anaerobic lagoon & generators at the Cal Poly Dairy, United States 2003
Anaerobic lagoon & generators at the Cal Poly Dairy, United States 2003

The most important initial issue when considering the application of anaerobic digestion systems is the feedstock to the process. Digesters typically can accept any biodegradable material, however if biogas production is the aim, the level of putrescibility is the key factor in its successful application.[43] The more putrescible the material the higher the gas yields possible from the system. Image File history File links Metadata Size of this preview: 800 × 600 pixelsFull resolution‎ (2,048 × 1,536 pixels, file size: 1. ... Image File history File links Metadata Size of this preview: 800 × 600 pixelsFull resolution‎ (2,048 × 1,536 pixels, file size: 1. ...


Substrate composition is a major factor in determining the methane yield and methane production rates from the digestion of biomass. Techniques are available to determine the compositional characteristics of the feedstock, whilst parameters such as solids, elemental and organic analyses are important for digester design and operation.[44]


Anaerobes can breakdown material to varying degrees of success from readily in the case of short chain hydrocarbons such as sugars, to over longer periods of time in the case of cellulose and hemicellulose.[45] Anaerobic microorganisms are unable to break down long chain woody molecules such as lignin.[46] Anaerobic digesters were originally designed for operation using sewage sludge and manures. Sewage and manure are not, however, the material with the most potential for anaerobic digestion as the biodegradable material has already had the energy content taken out by the animal that produced it.


A second consideration related to the feedstock will be moisture content. The wetter the material the more suitable it will be to handling with standard pumps instead of energy intensive concrete pumps and physical means of movement. Also the wetter the material, the more volume and area it takes up relative to the levels of gas that are produced. The moisture content of the target feedstock will also affect what type of system is applied to its treatment. In order to use a high solids anaerobic digester for dilute feedstocks, bulking agents such as compost should be applied to increase the solid content of the input material.[47] Another key consideration is the carbon:nitrogen ratio of the input material. This ratio is the balance of food a microbe requires in order to grown. The optimal C:N ratio for the 'food' a microbe is 20–30.[48]


The level of contamination of the feedstock material is a key consideration. If the feedstock to the digesters has significant levels of physical contaminants such as plastic, glass or metals then pre-processing will be required in order for the material to be used.[49] If it is not removed then the digesters can be blocked and will not function efficiently. It is with this logic in mind that mechanical biological treatment plants are designed. The higher the level of pre-treatment a feedstock requires, the more processing machinery will be required and hence the project will have higher capital costs.


After sorting or screening to remove any physical contaminants, such as metals and plastics, from the feedstock the material is often shredded, minced and mechanically or hydraulically pulped to increase the surface area available to microbes in the digesters and hence increase the speed of digestion. The feedstock material is then fed into the airtight digester where anaerobic treatment takes place.


Configuration

Farm-based maize silage digester located near Neumünster in Germany, 2007. Green inflatable biogas holder is shown on top of the digester
Farm-based maize silage digester located near Neumünster in Germany, 2007. Green inflatable biogas holder is shown on top of the digester

Anaerobic digesters can be designed and engineered to operate using a number of different process configurations: Image File history File links Metadata Size of this preview: 800 × 565 pixelsFull resolution‎ (1,909 × 1,349 pixels, file size: 488 KB, MIME type: image/jpeg) Haase maize anaerobic digester Author: Alex Marshall, Clarke Energy Ltd, October 2007 File historyClick on a date/time to view the file as... Image File history File links Metadata Size of this preview: 800 × 565 pixelsFull resolution‎ (1,909 × 1,349 pixels, file size: 488 KB, MIME type: image/jpeg) Haase maize anaerobic digester Author: Alex Marshall, Clarke Energy Ltd, October 2007 File historyClick on a date/time to view the file as... This article is about the maize plant. ... Neumünster is one of four independent towns in Schleswig-Holstein, Germany. ...

  • Batch or continuous
  • Temperature: Mesophilic or thermophilic
  • Solids content: High solids or low solids
  • Complexity: Single stage or multistage

Batch or continuous

A batch system is the simplest form of digestion. Biomass is added to the reactor at the start of the process in a batch and is sealed for the duration of the process. Batch reactors suffer from odour issues that can be a severe problem when they are emptied. Typically biogas production will be formed with a normal distribution pattern over time. The operator can use this fact to determine when they believe the process of digestion of the organic matter has completed. As the batch digestion is simple and requires less equipment and lower levels of design work it is typically a cheaper form of digestion.[50] The normal distribution, also called the Gaussian distribution, is an important family of continuous probability distributions, applicable in many fields. ...


In continuous digestion processes organic matter is constantly or added in stages to the reactor. Here the end products are constantly or periodically removed, resulting in constant production of biogas. Examples of this form of anaerobic digestion include, continuous stirred-tank reactors (CSTRs), Upflow anaerobic sludge blanket (UASB), Expanded granular sludge bed (EGSB) and Internal circulation reactors (IC).[51][52] The continuous stirred-tank reactor or CSTR model is used to estimate, predict, or design the key unit operation variables for a continuous agitated tank reator. ... UASB reactor shown is the larger tank. ... An expanded granular sludge bed (EGSB) reactor is a variant of the UASB concept [1] . The distinguishing feature is that a faster rate of upward-flow velocity is designed for the wastewater passing through the sludge bed. ... The internal circulation reactor (IC reactor) is a form of anaerobic digester. ...


Temperature

There are two conventional operational temperature levels for anaerobic digesters, which are determined by the species of methanogens in the digesters:[53]

  • Mesophilic which takes place optimally around 37°-41°C or at ambient temperatures between 20°-45°C where mesophiles are the primary microorganism present
  • Thermophilic which takes place optimally around 50°-52° at elevated temperatures up to 70°C where thermophiles are the primary microorganisms present

There are a greater number of species of mesophiles than thermophiles. These bacteria are also more tolerant to changes environmental conditions than thermophiles. Mesophilic systems are therefore considered to be more stable than thermophilic digestion systems. A mesophile is an organism that grows best in moderate temperature, neither too hot nor too cold, typically between 20 and 45 °C with an optimal temperature near 37 °C, which is the normal temperature of the human body. ... Thermophiles produce some of the bright colors of Grand Prismatic Spring, Yellowstone National Park A thermophile is an organism – a type of extremophile – which thrives at relatively high temperatures, up to about 60 °C. Many thermophiles are archaea. ...


As mentioned above, thermophilic digestion systems are considered to be less stable, however the increased temperatures facilitate faster reaction rates and hence faster gas yields. Operation at higher temperatures facilitates greater sterilisation of the end digestate. In countries where legislation, such as the Animal By-Products Regulations in the European Union, requires end products to meet certain levels of reduction in the amount of bacteria in the output material, this may be a benefit.[54] The EU Animal By-Products Regulations (No 1774/2002) (SI 1482/2003) allows for the treatment of some animal by-products in composting and biogas plants (anaerobic digesters). ...


A drawback of operating at thermophilic temperatures is that more heat energy input is required to achieve the correct operational temperatures. This increase in energy is not be outweighed by the increase in the outputs of biogas from the systems. It is therefore important to consider an energy balance for these systems.


Solids

Typically there are two different operational parameters associated with the solids content of the feedstock to the digesters:

  • High-solids
  • Low-solids

Digesters can either be designed to operate in a high solids content, with a total suspended solids (TSS) concentration greater than ~20%, or a low solids concentration less than ~15%.[55] Total suspended solids is a water quality measurement usually abbreviated TSS. This parameter was at one time called non-filterable residue (NFR), a term that refers to the identical measurement: the dry-weight of particles trapped by a filter, typically of a specified pore size. ...


High-solids digesters process a thick slurry that requires more energy input to move and process the feedstock. The thickness of the material may also lead to associated problems with abrasion. High-solids digesters will typically have a lower land requirement due to the lower volumes associated with the moisture.


Low-solids digesters can transport material through the system using standard pumps that require significantly lower energy input. Low-solids digesters require a larger amount of land than high-solids due to the increase volumes associated with the increased liquid: feedstock ratio of the digesters. There are benefits associated with operation in a liquid environment as it enables more thorough circulation of materials and contact between the bacteria and their food. This enables the bacteria to more readily access the substances they are feeding off and increases the speed of gas yields.


Number of stages

Two-stage, low-solids, UASB digestion component of a mechanical biological treatment system near Tel Aviv, process water is seen in balance tank and sequencing batch reactor, 2005
Two-stage, low-solids, UASB digestion component of a mechanical biological treatment system near Tel Aviv, process water is seen in balance tank and sequencing batch reactor, 2005

Digestion systems can be configured with different levels of complexity:[56] Image File history File links Metadata Size of this preview: 800 × 600 pixelsFull resolution (2048 × 1536 pixel, file size: 681 KB, MIME type: image/jpeg) Photograph of anaerobic digesters, Tel-Aviv 2005. ... Image File history File links Metadata Size of this preview: 800 × 600 pixelsFull resolution (2048 × 1536 pixel, file size: 681 KB, MIME type: image/jpeg) Photograph of anaerobic digesters, Tel-Aviv 2005. ... UASB - Upflow Anaerobic Sludge Blanket technology normally referred to as UASB Reactor is used in the treatment of wastewater. ... Tel-Aviv was founded on empty dunes north of the existing city of Jaffa. ... Sequencing batch reactors (SBR) or sequential batch reactors are industrial processing tanks for the treatment of waste water. ...

  • One-stage or single-stage
  • Two-stage or multistage

A single-stage digestion system is one in which all of the biological reactions occur within a single sealed reactor or holding tank. Utilising a single stage reduces construction costs, however facilitates less control of the reactions occurring within the system. Acidogenic bacteria, through the production of acids, reduce the pH of the tank. Methanogenic bacteria, as outlined earlier, operate in a strictly defined pH range.[57] Therefore the biological reactions of the different species in a single stage reactor can be in direct competition with each other. Another one-stage reaction system is an anaerobic lagoon. These lagoons are pond-like earthen basins used for the treatment and long-term storage of manures.[58] Here the anaerobic reactions are contained within the natural anaerobic sludge contained in the pool. A photo of the anaerobic lagoon at the Cal Poly Dairy taken in 2003. ...


In a two-stage or multi-stage digestion system different digestion vessels are optimised to bring maximum control over the bacterial communities living within the digesters. Acidogenic bacteria produce organic acids and more quickly grow and reproduce than methanogenic bacteria. Methanogenic bacteria require stable pH and temperature in order to optimise their performance.[59]


Typically hydrolysis, acetogenesis and acidogenesis occur within the first reaction vessel. The organic material is then heated to the required operational temperature (either mesophilic or thermophilic) prior to being pumped into a methanogenic reactor. The initial hydrolysis or acidogenesis tanks prior to the methanogenic reactor can provide a buffer to the rate at which feedstock is added. Some European countries require a degree of elevated heat treatment in order to kill harmful bacteria in the input waste.[60] In this instance their may be a pasteurisation or sterilisation stage prior to digestion or between the two digestion tanks. It should be noted that it is not possible to completely isolate the different reaction phases and often there is some biogas that is produced in the hydrolysis or acidogenesis tanks.


Residence

The residence time in a digester varies with the amount and type of feed material, the configuration of the digestion system and whether it be one-stage or two-stage.


In the case of single-stage thermophilic digestion residence times may be in the region of 14 days, which comparatively to mesophilic digestion is relatively fast. The plug-flow nature of some of these systems will mean that the full degradation of the material may not have been realised in this timescale. In this event digestate exiting the system will be darker in colour and will typically have more odour.


In two-stage mesophilic digestion, residence time may vary between 15 and 40 days.[61]


In the case of mesophilic UASB digestion hydraulic residence times can be (1hour-1day) and solid retention times can be up to 90 days. In this manner the UASB system is able to separate solid an hydraulic retention times with the utilisation of a sludge blanket.[62]


Continuous digesters have mechanical or hydraulic devices, depending on the level of solids in the material, to mix the contents enabling the bacteria and the food to be in contact. They also allow excess material to be continuously extracted to maintain a reasonably constant volume within the digestion tanks.


Products

There are three principal products of anaerobic digestion: biogas, digestate and water.[63][64][65]


Biogas

Main article: Biogas
Biogas holder with lightning protection rods and back-up gas flare
Biogas holder with lightning protection rods and back-up gas flare
Typical composition of biogas[66]
Matter  %
Methane, CH4 50-75
Carbon dioxide, CO2 25-50
Nitrogen, N2 0-10
Hydrogen, H2 0-1
Hydrogen sulfide, H2S 0-3
Oxygen, O2 0-2
Biogas carrying pipes
Biogas carrying pipes

Biogas is the ultimate waste product of the bacteria feeding off the input biodegradable feedstock, and is mostly methane and carbon dioxide,[67][68] with a small amount hydrogen and trace hydrogen sulfide. Most of the biogas is produced during the middle of the digestion, after the bacterial population has grown, and tapers off as the putrescible material is exhausted.[69] The gas is normally stored on top of the digester in an inflatable gas bubble or extracted and stored next to the facility in a gas holder. 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. ... Image File history File links Metadata Size of this preview: 800 × 549 pixelsFull resolution‎ (1,492 × 1,023 pixels, file size: 144 KB, MIME type: image/jpeg) Author: Alex Marshall File historyClick on a date/time to view the file as it appeared at that time. ... Image File history File links Metadata Size of this preview: 800 × 549 pixelsFull resolution‎ (1,492 × 1,023 pixels, file size: 144 KB, MIME type: image/jpeg) Author: Alex Marshall File historyClick on a date/time to view the file as it appeared at that time. ... A gas flare at an oil refinery. ... Image File history File links Metadata Size of this preview: 450 × 600 pixelsFull resolution‎ (1,200 × 1,600 pixels, file size: 212 KB, MIME type: image/jpeg) Author: Alex Marshall, Clarke Energy File historyClick on a date/time to view the file as it appeared at that time. ... Image File history File links Metadata Size of this preview: 450 × 600 pixelsFull resolution‎ (1,200 × 1,600 pixels, file size: 212 KB, MIME type: image/jpeg) Author: Alex Marshall, Clarke Energy File historyClick on a date/time to view the file as it appeared at that time. ...


The methane in biogas can be burned to produce both heat and electricity, usually with a reciprocating engine or microturbine[70] often in a cogeneration arrangement where the electricity and waste heat generated are used to warm the digesters or to heat buildings. Excess electricity can be sold to suppliers or put into the local grid. Electricity produced by anaerobic digesters is considered to be renewable energy and may attract subsidies.[71] Biogas does not contribute to increasing atmospheric carbon dioxide concentrations because the gas is not released directly into the atmosphere and the carbon dioxide comes from an organic source with a short carbon cycle. Internal combustion piston engine Components of a typical, four stroke cycle, internal combustion piston engine. ... This machine has a single-stage radial compressor and turbine, a recuperator, and foil bearings. ... For other uses, see CHP. Cogeneration (also combined heat and power, CHP) is the use of a heat engine or a power station to simultaneously generate both electricity and useful heat. ...


Biogas may require treatment or 'scrubbing' to refine it for use as a fuel.[72] Hydrogen sulfide is a toxic product formed from sulfates in the feedstock and is released as a trace component of the biogas. National environmental enforcement agencies such as the US EPA or the English and Welsh Environment Agency put strict limits on the levels of gases containing hydrogen sulfide, and if the levels of hydrogen sulfide in the gas are high, gas scrubbing and cleaning equipment (such as amine gas treating) will be needed to process the biogas to within regionally accepted levels.[73] An alternative method to this is by the addition of ferric chloride FeCl3 to the digestion tanks in order to inhibit hydrogen sulfide production.[74] Hydrogen sulfide (or hydrogen sulphide) is the chemical compound with the formula H2S. This colorless, toxic and flammable gas is responsible for the foul odour of rotten eggs and flatulence. ... “EPA” redirects here. ... (see also the List of environmental organizations) The Environment Agency (Welsh: Asiantaeth yr Amgylchedd) of England and Wales was created by the Environment Act 1995, along with the Scottish Environment Protection Agency. ... Amine gas treating is a means to remove organosulfur and other undesirable compounds from acid gas by contacting the gas with amine. ...


Volatile siloxanes can also contaminate the biogas; such compounds are frequently found in household waste and wastewater. In digestion facilities accepting these materials as a component of the feedstock, low molecular weight siloxanes volatilise into biogas. When this gas is combusted in a gas engine, turbine or boiler, siloxanes are converted into silicon dioxide (Si02) which deposits internally in the machine, increasing wear and tear.[75][76] Volatility most frequently refers to the standard deviation of the change in value of a financial instrument with a specific time horizon. ... Siloxanes are a class of both organic and inorganic chemical compounds which consist entirely of silicon, oxygen, and an alkyl group. ...


In countries such as Switzerland, Germany and Sweden the methane in the biogas may be concentrated in order for it to be used as a vehicle transportation fuel or alternatively input directly into the gas mains.[77] In countries where the driver for the utilisation of anaerobic digestion are renewable electricity subsidies, this route of treatment is less likely as energy is required in this processing stage and reduces the over all levels available to sell.[78]


Digestate

Main article: digestate

Digestate is the solid remnants of the original input material to the digesters that the microbes cannot use. It also consists of the mineralised remains of the dead bacteria from within the digesters. Digestate can come in three forms; fibrous, liquor or a sludge-based combination of the two fractions. In two-stage systems the different forms of digestate come from different digestion tanks. In single stage digestion systems the two fractions will be combined and if desired separated by further processing.[79][80] Acidogenic digestate produced from mixed municipal waste Digestate is solid material remaining after the anaerobic digestion of a biodegradable feedstock. ...

Acidogenic anaerobic digestate
Acidogenic anaerobic digestate

The second by-product (acidogenic digestate) is a stable organic material comprised largely of lignin and cellulose, but also of a variety of mineral components in a matrix of dead bacterial cells; some plastic may be present. The material resembles domestic compost and can be used as compost or to make low grade building products such as fibreboard.[81][82] Image File history File links Size of this preview: 800 × 513 pixelsFull resolution (1058 × 678 pixel, file size: 166 KB, MIME type: image/jpeg) Acidogenic anaerobic digestate produced by the anaerobic digesters ArrowBio facility in at Hiriya near Tel Aviv. ... Image File history File links Size of this preview: 800 × 513 pixelsFull resolution (1058 × 678 pixel, file size: 166 KB, MIME type: image/jpeg) Acidogenic anaerobic digestate produced by the anaerobic digesters ArrowBio facility in at Hiriya near Tel Aviv. ... Acidogenic digestate produced from mixed municipal waste Digestate is solid material remaining after the anaerobic digestion of a biodegradable feedstock. ...


The third by-product is a liquid (methanogenic digestate) that is rich in nutrients and can be used as a fertiliser dependent on the quality of the material being digested.[83] Levels of potentially toxic elements (PTEs) should be chemically assessed. This will be dependent upon the quality of the original feedstock. In the case of most clean and source-separated biodegradable waste streams the levels of PTEs will be low. In the case of wastes originating from industry the levels of PTEs may be higher and will need to be taken into consideration when determining a suitable end use for the material.


Digestate typically contains elements such as lignin that cannot be broken down by the anaerobic microorganisms. Also the digestate may contain ammonia that is phytotoxic and will hamper the growth of plants if it is used as a soil improving material. For these two reasons a maturation or composting stage may be employed after digestion. Lignin and other materials are available for degradation by aerobic microorganisms such as fungi helping reduce the overall volume of the material for transport. During this maturation the ammonia will be broken down into nitrates, improving the fertility of the material and making it more suitable as a soil improver. Large composting stages are typically used by dry anaerobic digestion technologies.[84][85]


Wastewater

The final output from anaerobic digestion systems is water. This water originates both from the moisture content of the original waste that was treated but also includes water produced during the microbial reactions in the digestion systems. This water may be released from the dewatering of the digestate or may be implicitly separate from the digestate.


The wastewater exiting the anaerobic digestion facility will typically have elevated levels of biochemical oxygen demand (BOD) and chemical oxygen demand (COD), these are measures of the reactivity of the effluent and show an ability to pollute. Some of this material is termed 'hard COD' meaning it cannot be accessed by the anaerobic bacteria for conversion into biogas. If this effluent was put directly into watercourses it would negatively affect them by causing eutrophication. As such further treatment of the wastewater is often required. This treatment will typically be an oxidation stage where air is passed through the water in a sequencing batch reactors or reverse osmosis unit.[86][87][88] This article or section does not cite any references or sources. ... In environmental chemistry, the chemical oxygen demand (COD) test is commonly used to indirectly measure the amount of organic compounds in water. ... Eutrophication, strictly speaking, means an increase in chemical nutrients -- typically compounds containing nitrogen or phosphorus -- in an ecosystem. ... Reverse osmosis (RO) is a separation process that uses pressure to force a solution through a membrane that retains the solute on one side and allows the pure solvent to pass to the other side. ...


See also

Energy portal
Environment portal
Sustainable development portal

Image File history File links Crystal_128_energy. ... Image File history File links Portal. ... Image File history File links Sustainable_development. ... The following is a partial list of different types of anaerobic digesters. ... The bioconversion of biomass to mixed alcohol fuels can be accomplished using the MixAlco process. ... A mass balance (also called a material balance) is an accounting of material entering and leaving a system. ... Sewage treatment, or domestic wastewater treatment, is the process of removing contaminants from wastewater, both runoff and domestic. ...

References

  1. ^ Anaerobic digestion http://www.monsal.com, retrieved 18.09.07
  2. ^ waste.nl Anaerobic digestion reference sheet, www.waste.nl, retrieved 25.10.07
  3. ^ waste.nl Anaerobic digestion reference sheet, www.waste.nl, retrieved 26.10.07
  4. ^ Biogas Bonanza for Third World Development, www.i-sis.org.uk, retrieved 4.11.07, cites United Nations Development Programme (UNDP) 1997 Report, Energy After Rio: Prospects and Challenges
  5. ^ Fergusen, T. & Mah, R. (2006) Methanogenic bacteria in Anaerobic digestion of biomass, p49
  6. ^ Cruazon, B. (2007) History of anaerobic digestion, web.pdx.edu, retrieved 17.08.07
  7. ^ Anaerobic digestion, www.waste.nl, retrieved 19.08.07
  8. ^ Humanik, F. et al (2007) Anaerobic digestion of animal manure, www.epa.gov, retrieved 17.08.07
  9. ^ Anaerobic Digestion, www.wasteresearch.co.uk, retrieved 24.10.07
  10. ^ An introduction to anaerobic digestion, www.anaerobic-digestion.com, retrieved 17.08.07
  11. ^ Lemmer, A. & Oeschsner, H. Co-fermentation of grass and forage maize, Energy, Landtechnik, 5/11, p 56
  12. ^ Anaerobic Digestion Page, www.remade.org.uk, retrieved 17.08.07
  13. ^ Friends of the Earth (2004) Anaerobic digestion Briefing Paper, www.foe.co.uk, retrieved 17.08.07
  14. ^ Cardiff University (2005) Anaerobic Digestion Page, www.wasteresearch.co.uk, retrieved 17.08.07
  15. ^ Doelle, H. W. (2001)Biotechnology and Human Development in Developing Countries, www.ejbiotechnology.info, retrieved 19.08.07
  16. ^ Biogas Bonanza for Third World Development, www.i-sis.org.uk, retrieved 4.11.07, cites United Nations Development Programme (UNDP) 1997 Report, Energy After Rio: Prospects and Challenges
  17. ^ Biogas Bonanza for Third World Development, www.i-sis.org.uk, retrieved 4.11.07
  18. ^ The Clean Development Mechanism in Nepal in The Tiempo Climate Newswatch, www.tiempocyberclimate.org
  19. ^ Juniper (2005) MBT: A Guide for Decision Makers – Processes, Policies & Markets, www.juniper.co.uk, (Project funding supplied by Sita Environmental Trust), Accessed 22.11.06
  20. ^ Svoboda, I (2003) Anaerobic digestion, storage, olygolysis, lime, heat and aerobic treatment of livestock manures, www.scotland.gov.uk, retrieved 17.08.07
  21. ^ Haase Mechanical Biological Treatment and Wet Anaerobic Digestion, www.haase-energietechnik.de, retrieved 23.10.07
  22. ^ Digestion systems website, www.anaerobic-digestion.com, retrieved 19.08.07
  23. ^ Benefits of anaerobic digestion, www.afbini.gov.uk, retrieved 17.08.07
  24. ^ Questions about biomass energy, www.dti.gov.uk, retrieved 17.08.07
  25. ^ Global warming methane could be far more potent than carbon dioxide www.newmediaexplorer.org, retrieved 17.08.07
  26. ^ Introduction and Spanish organic waste situation, www.compostnetwork.info, retrieved 19.08.07
  27. ^ Renewable Energy Framework, www.esru.strath.ac.uk, retrieved 8.11.07
  28. ^ Discovering Anaerobic Digestion and Biogas, www.face-online.org.uk, retrieve 8.11.07
  29. ^ Methanogens, microbewiki.kenyon.edu, retrieved 24.10.07
  30. ^ Aerobic and anaerobic respiration, www.sp.uconn.edu, retrieved 24.10.07
  31. ^ Adapted from Beychok, M. (1967) Aqueous Wastes from Petroleum and Petrochemical Plants, First edition, John Wiley & Sons, LCCN 67019834
  32. ^ What is the anaerobic digestion process?, www.anaerobic-digestion.com, retrieved 17.08.07
  33. ^ Fergusen, T. & Mah, R. (2006) Methanogenic bacteria in Anaerobic digestion of biomass, p49
  34. ^ The biogas plant, www.unu.edu, retrieved 5.11.07
  35. ^ Anaerobic digestion, www.waste.nl, retrieved 19.08.07
  36. ^ Ciborowski, P (2004)Anaerobic Digestion in the Dairy Industry, Minnesota Pollution Control Agency Air Innovations Conference, www.epa.gov, retrieved 19.08.07
  37. ^ Sleat, R. & Mah, R. (2006) Hydrolytic Bacteria in Anaerobic digestion of biomass, p15
  38. ^ Anaerobic digestion of maize for energy generation, www.cropgen.soton.ac.uk, retrieved 24.10.07
  39. ^ Boone, D. & Mah, R. (2006) Transitional bacteria in anaerobic digestion of biomass, p35
  40. ^ What is anaerobic digestion, www-sop.inria.fr, retrieved 24.10.07
  41. ^ Anaerobic digestion, www.biotank.co.uk, retrieved 24.10.07
  42. ^ Martin, A.D. (2007) Understanding Anaerobic Digestion, Presentation to the Environmental Services Association, 16.10.07, www.esauk.org, retrieved 22.10.07
  43. ^ Anaerobic digestion feedstock classification, www.wisbiorefine.org, retrieved 24.10.07
  44. ^ Jerger, D. & Tsao, G. (2006) Feed composition in Anaerobic digestion of biomass, p65
  45. ^ Money for old rope?, www.waste-management-world.com, retrieved 24.10.07
  46. ^ Book Review: Biology of anaerobic microorganisms, www.aslo.org, retrieved 24.10.07
  47. ^ Management of Urban Biodegradable Waste, books.google.com, retrieved 24.10.07
  48. ^ Anaerobic co-digestion of sewage sludge and rice straw, www.bvsde.ops-oms.org, retrieved 24.10.07
  49. ^ Anaerobic digestion of classified municipal solid wastes, www.seas.ucla.edu, retrieved 24.10.07
  50. ^ Anaerobic digestion, www.energy.ca.gov, retrieved 24.10.07
  51. ^ BIOPAQ IC, www.paques.nl, retrieved 19.08.07
  52. ^ Biological processes with Biomar technology, www.envirochemie.com, retrieved 19.08.07
  53. ^ Song, Y.C., Kwon, S.J., Woo, J.H. (2004) Mesophilic and thermophilic temperature co-phase anaerobic digestion compared with single-stage mesophilic- and thermophilic digestion of sewage sludge, Water Res. 2004 Apr;38(7):1653–62
  54. ^ Animal by-products introduction, ec.europa.eu, retrieved 24.10.07
  55. ^ Feasibility study concerning anaerobic digestion in Northern Ireland, www.eunomia.co.uk, retrieved 19.08.07
  56. ^ Feasibility study concerning anaerobic digestion in Northern Ireland, www.eunomia.co.uk, retrieved 19.08.07
  57. ^ Biomethanation in advances in biochemical engineering and biotechnology, books.google.com, retrieved 24.10.07
  58. ^ Anaerobic Lagoons for Storage/Treatment of Livestock Manure, www.missouri.edu, retrieved 8.11.07
  59. ^ Abstract:Methanogenic population dynamics during start-up of anaerobic digesters treating municipal solid waste and biosolids, www3.interscience.wiley.com, retrieved 24.10.07
  60. ^ Animal By-Products Regulations, www.defra.gov.uk, retrieved 24.10.07
  61. ^ HIMET—A Two-Stage Anaerobic Digestion Process for Converting Waste to Energy, www.gastechnology.org, retrieved 19.08.07
  62. ^ Finstein, M. S. (2006) ArrowBio process integrates preprocessing and advanced anaerobic digestion to recover recyclables and generate electricity, www.oaktech-environmental.com, retrieved 19.08.07
  63. ^ Abstract from Operation of Municipal Wastewater Treatment Plants Manual of Practice-MOP 11 Fifth Edition, www.e-wef.org, retrieved 19.08.07
  64. ^ Feasibility study concerning anaerobic digestion in Northern Ireland, www.eunomia.co.uk, retrieved 19.08.07
  65. ^ Anaerobic digestion
  66. ^ Basic Information on Biogas, www.kolumbus.fi, retrieved 2.11.07
  67. ^ guide to biogas, www.adelaide.edu.au, retrieved 19.08.07
  68. ^ [http://www.eere.energy.gov/consumer/your_workplace/farms_ranches/index.cfm/mytopic=30003 How Anaerobic Digestion (Methane Recovery) Works], www.eere.energy.gov, retrieved 19.08.07
  69. ^ Anaerobic digestion briefing sheet, www.foe.co.uk, retrieved 24.10.07
  70. ^ GE Energy - Jenbacher Gas Engines for Power Generation, www.power-technology.com, retrieved 19.08.07
  71. ^ [http://www.defra.gov.uk/environment/climatechange/uk/energy/renewablefuel/pdf/ukbio0507- work3.pdf UK Biomass Strategy 2007], www.defra.gov.uk, retrieved 19.08.07
  72. ^ [http://www.afbini.gov.uk/index/services/specialist-advice/renewable-energy/re-anaerobic- digestion-intro/re-anaerobic-digestion-what-is.htm What is anaerobic digestion?], www.afbini.gov.uk, retrieved 24.10.07
  73. ^ Removal of hydrogen sulfide from anaerobic digester gas, U.S. Patent, www.patentstorm.us, retrieved 17.08.07
  74. ^ Abstract from Online Measurement of Dissolved and Gaseous-Hydrogen Sulfide in Anaerobic Biogas Reactors, www.cheric.org, retrieved 24.10.07
  75. ^ Wheles, E. & Pierece, E. (2004) [http://www.scsengineers.com/Papers/Pierce_2004Siloxanes_Update_Paper.pdf Siloxanes in landfill and digester gas], www.scsengineers.com, retrieved 17.08.07
  76. ^ Biogas Upgrading and Utilisation, EEA Bioenergy, www.iea-biogas.net, retrieved 25.10.07
  77. ^ Biogas as a road transport fuel, www.nfuonline.com, retrieved 24.10.07
  78. ^ Haase biogas energy centre, www.haase-energietechnik.de, retrieved 19.08.07
  79. ^ Fact sheet on anaerobic digestion, www.waste.nl, retrieved 19.08.07
  80. ^ Biomass and biogas, www.globalwarming101.com, retrieved 19.08.07
  81. ^ Oaktech Consultation Response to UK Source Segregation Requirement, www.alexmarshall.me.uk, retrieved 19.08.07
  82. ^ UK Strategy for centralised anaerobic digestion, www.ingentaconnect.com, retrieved 24.10.07
  83. ^ Biomass and biogas, www.globalwarming101.com, retrieved 24.10.07
  84. ^ Vitoria Plant Information, www.ows.be, retrieved 24.10.07
  85. ^ Kompogas Homepage, www.kompogas.ch, retrieved 24.10.07
  86. ^ Abstract: Modelling a sequencing batch reactor to treat the supernatant from anaerobic digestion of the organic fraction of municipal solid waste, www.ingentaconnect.com, retrieved 24.10.07
  87. ^ Clarke Energy Reverse Osmosis Unit, www.clarke-energy.co.uk, retrieved 24.10.07
  88. ^ BOD Effluent Treatment, www.virtualviz.com, retrieved 24.10.07

Aqueous Wastes from Petroleum and Petrochemical Plants is a book about the composition and treatment of the various wastewater streams produced in the hydrocarbon processing industries (i. ... The Library of Congress Control Number or LCCN is a serially based system of numbering books in the Library of Congress in the United States. ...

External links

  • International Energy Association Biogas Forum
  • Anaerobic digestion forum
  • Anaerobic digestion website
  • US Government Information Sheet: Methane from anaerobic digesters
  • Anaerobic biodigester design for small tropical producers
  • Low cost biodigester, Vietnam
  • Appropedia article on home biogas systems
  • Biogas Community on WikiSpaces
  • Online Anaerobic Digester Output Estimator
For the company, see Waste Management, Inc. ... Composting is the aerobic decomposition of biodegradable organic matter, producing compost. ... An eco-industrial park is a type of industrial park in which businesses cooperate with each other and with the local community in an attempt to reduce waste, efficiently share resources (such as information, materials, water, energy, infrastructure, and natural resources), and produce sustainable development, with the intention of increasing... For other forms of waste plant that produce energy, see waste-to-energy. ... Look up Dump in Wiktionary, the free dictionary. ... Anaerobic digestion and air processing components of Lübeck mechanical biological treatment plant in Germany A mechanical biological treatment system is a form of waste processing facility that combines a sorting facility with a form of biological treatment such as composting or anaerobic digestion. ... Radioactive wastes are waste types containing radioactive chemical elements that do not have a practical purpose. ... Reuse is using an item more than once. ... The international recycling symbol. ... It has been suggested that this article or section be merged into Reuse. ... The word sewerage means the provision of pipes etc to collect and dispose of sewage. ... For other uses, see Waste (disambiguation). ... For the corporation, see Waste Management Incorporated Waste management is the collection, transport, processing or disposal of waste materials, usually ones produced by human activity, in an effort to reduce their effect on human health or local amenity. ... Waste sorting is the process by which waste is separated into different elements. ... The waste hierarchy The waste hierarchy refers to the 3 Rs reduce, reuse and recycle, which classify waste management strategies according to their desirability. ... The following page contains a list of different waste management related concepts and acronyms: BANANA Build Absolutely Nothing Anywhere Near Anything Best practicable environmental option (BPEO) Extended producer responsibility Linguistic detoxification NIMBY Not in my back yard Pay as you throw Polluter pays principle Proximity principle Waste strategy Waste hierarchy... Depending upon the country different legislation governs the way waste is managed and disposed of. ... Waste treatment refers to the activities required to ensure that waste has the least practicable impact on the environment. ...

  Results from FactBites:
 
Anaerobic digestion - Wikipedia, the free encyclopedia (1204 words)
Anaerobic digestion is the breakdown of organic matter by bacteria in the absence of oxygen.
Anaerobic digesters have been around for a long time, and they are commonly used for sewage treatment and for managing animal waste.
If the digested materials include low levels of toxic heavy metals or synthetic organic materials such as pesticides or PCBs, the effect of digestion is to significantly concentrate such materials in the digester liquor in order to dispose of this liquid properly.
Anaerobic Digestion of Animal Wastes: Factors to Consider (3554 words)
The key by-products of anaerobic digestion include digested solids (useful as a soil amendment) and methane, the primary component of "bio-gas," which can be used to fuel a variety of cooking, heating, cooling, and lighting applications, as well as to generate electricity.
Thermophilic digestion yields higher levels of gas and kills more pathogenic bacteria, but it has certain disadvantages as well, the greatest of which is the added cost of maintaining higher temperatures and keeping the digester stirred to maximize contact between the bacteria and the organic matter.
Anaerobic digesters are installed for various reasons-as a means of resolving environmental problems, as a means of economically re-using an otherwise wasted resource, as a source of additional revenue.
  More results at FactBites »

 
 

COMMENTARY     


Share your thoughts, questions and commentary here
Your name
Your comments

Want to know more?
Search encyclopedia, statistics and forums:

 


Press Releases |  Feeds | Contact
The Wikipedia article included on this page is licensed under the GFDL.
Images may be subject to relevant owners' copyright.
All other elements are (c) copyright NationMaster.com 2003-5. All Rights Reserved.
Usage implies agreement with terms, 1022, m