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61-422: In 2009 a biogas plant was built to provide electric power to the city. Lünen is the first city in the world to receive electricity via public utility companies that is generated on the base of animal waste. The plant produces up to 6.6 MW, supplying 26,000 homes with heat and electricity. Structure Museum Theatre The current mayor of Lünen is independent politician Jürgen Kleine-Frauns since 2015; he

122-405: A benefit to using thermophilic temperatures instead of mesophilic. Additional pre-treatment can be used to reduce the necessary retention time to produce biogas. For example, certain processes shred the substrates to increase the surface area or use a thermal pretreatment stage (such as pasteurisation) to significantly enhance the biogas output. The pasteurisation process can also be used to reduce

183-490: A biogas with a elevated methane content. The produced carbon dioxide in biogas dissolves more into the water phase under pressure then methane does. Hence the produced biogas is richer in methane. Research at the University of Groningen demonstrated that the bacterial community changes in composition under the influence of pressure. Individual bacteria species have their optimum circumstances in which they grow and replicate

244-410: A chain length greater than that of acetate must first be catabolised into compounds that can be directly used by methanogens. The biological process of acidogenesis results in 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 byproducts. The process of acidogenesis

305-407: A domino effect of inhibition. Total ammonia nitrogen is the combination of free ammonia and ionized ammonia. TAN is produced through degrading material high in nitrogen, typically proteins and will naturally build in anaerobic digestion. This is depending on the organic feed stock fed to the system. In typical wastewater treatment practices, TAN reduction is done with via nitrification . Nitrification

366-611: A farm-based digester that uses dairy manure as the primary feedstock, the gas production may be significantly increased by adding a second feedstock, e.g., grass and corn (typical on-farm feedstock), or various organic byproducts, such as slaughterhouse waste, fats, oils and grease from restaurants, organic household waste, etc. (typical off-site feedstock). Digesters processing dedicated energy crops can achieve high levels of degradation and biogas production. Slurry-only systems are generally cheaper, but generate far less energy than those using crops, such as maize and grass silage; by using

427-527: A frozen lake in Alaska" has produced 200–300 litres of methane per day, about 20 to 30% of the output from digesters in warmer climates. Mesophilic species outnumber thermophiles, and they are also more tolerant to changes in environmental conditions than thermophiles. Mesophilic systems are, therefore, considered to be more stable than thermophilic digestion systems. In contrast, while thermophilic digestion systems are considered less stable, their energy input

488-439: A gas-tight door. Neither approach has mixing inside the digester. The amount of pretreatment, such as contaminant removal, depends both upon the nature of the waste streams being processed and the desired quality of the digestate. Size reduction (grinding) is beneficial in continuous vertical systems, as it accelerates digestion, while batch systems avoid grinding and instead require structure (e.g. yard waste) to reduce compaction of

549-439: A high percentage of solids (40-60%) in gas-tight chambers called fermenter boxes. It is with this understanding that mechanical biological treatment plants are designed. The higher the level of pretreatment a feedstock requires, the more processing machinery will be required, and, hence, the project will have higher capital costs. National Non-Food Crops Centre . After sorting or screening to remove any physical contaminants from

610-472: A larger volume of the digesters (spread across several batches) to handle the same amount of waste as a continuous process digester. Higher heat energy is required in a thermophilic system compared to a mesophilic system, but the thermophilic system requires much less time and has a larger gas output capacity and higher methane gas content, so one has to consider that trade-off carefully. For solids content, low will handle up to 15% solid content. Above this level

671-428: 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 on which they are feeding, and increases the rate of gas production. Digestion systems can be configured with different levels of complexity. In a single-stage digestion system (one-stage), all of the biological reactions occur within

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732-480: A modest amount of crop material (30%), an anaerobic digestion plant can increase energy output tenfold for only three times the capital cost, relative to a slurry-only system. A second consideration related to the feedstock is moisture content. Drier, stackable substrates, such as food and yard waste, are suitable for digestion in tunnel-like chambers. Tunnel-style systems typically have near-zero wastewater discharge, as well, so this style of system has advantages where

793-402: A number of chemical processes in converting the biomass to biogas . Gaseous oxygen is excluded from the reactions by physical containment. Anaerobes utilize electron acceptors from sources other than oxygen gas. These acceptors can be the organic material itself or may be supplied by inorganic oxides from within the input material. When the oxygen source in an anaerobic system is derived from

854-399: A number of different configurations and can be categorized into batch vs. continuous process mode, mesophilic vs. thermophilic temperature conditions, high vs. low portion of solids, and single stage vs. multistage processes. Continuous process requires more complex design, but still, it may be more economical than batch process, because batch process requires more initial building money and

915-496: A single, sealed reactor or holding tank. Using a single stage reduces construction costs, but results in less control of the reactions occurring within the system. Acidogenic bacteria, through the production of acids, reduce the pH of the tank. Methanogenic archaea, as outlined earlier, operate in a strictly defined pH range. 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

976-532: Is twinned with: Anaerobic digestion Anaerobic digestion is a sequence of processes by which microorganisms break down biodegradable material in the absence of oxygen . The process is used for industrial or domestic purposes to manage waste or to produce fuels. Much of the fermentation used industrially to produce food and drink products, as well as home fermentation, uses anaerobic digestion. Anaerobic digestion occurs naturally in some soils and in lake and oceanic basin sediments , where it

1037-451: Is a major factor in determining the methane yield and methane production rates from the digestion of biomass. Techniques to determine the compositional characteristics of the feedstock are available, while parameters such as solids, elemental, and organic analyses are important for digester design and operation. Methane yield can be estimated from the elemental composition of substrate along with an estimate of its degradability (the fraction of

1098-685: Is an anaerobic lagoon . These lagoons are pond-like, earthen basins used for the treatment and long-term storage of manures. Here the anaerobic reactions are contained within the natural anaerobic sludge contained in the pool. In a two-stage digestion system (multistage), 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 archaea. Methanogenic archaea require stable pH and temperature to optimise their performance. Under typical circumstances, hydrolysis, acetogenesis, and acidogenesis occur within

1159-479: Is an aerobic process where TAN is consumed by aerobic heterotrophic bacteria. These bacteria release nitrate and nitrite which are later converted to nitrogen gas through the denitrification process. Hydrolysis and acidogenesis can also be impacted by TAN concentration. In mesophilic conditions, inhibition for hydrolysis was found to occur at 5500 mg/L TAN, while acidogenesis inhibition occurs at 6500 mg/L TAN. The most important initial issue when considering

1220-459: Is applied to its treatment. To use a high-solids anaerobic digester for dilute feedstocks, bulking agents, such as compost, should be applied to increase the solids content of the input material. Another key consideration is the carbon:nitrogen ratio of the input material. This ratio is the balance of food a microbe requires to grow; the optimal C:N ratio is 20–30:1. Excess N can lead to ammonia inhibition of digestion. The level of contamination of

1281-413: Is considered high solids content and can also be known as dry digestion. In a single stage process, one reactor houses the four anaerobic digestion steps. A multistage process utilizes two or more reactors for digestion to separate the methanogenesis and hydrolysis phases. Anaerobic digestion can be performed as a batch process or a continuous process. In a batch system, biomass is added to the reactor at

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1342-597: Is higher, with more biogas being removed from the organic matter in an equal amount of time. The increased temperatures facilitate faster reaction rates, and thus faster gas yields. Operation at higher temperatures facilitates greater pathogen reduction of the digestate. In countries where legislation, such as the Animal By-Products Regulations in the European Union, requires digestate to meet certain levels of pathogen reduction there may be

1403-573: Is released by methanogenic archaea as methane. Populations of anaerobic microorganisms typically take a significant period of time to establish themselves to be fully effective. Therefore, common practice is to introduce anaerobic microorganisms from materials with existing populations, a process known as "seeding" the digesters, typically accomplished with the addition of sewage sludge or cattle slurry. The four key stages of anaerobic digestion involve hydrolysis , acidogenesis , acetogenesis and methanogenesis . The overall process can be described by

1464-406: Is similar to the way milk sours . The third stage of 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. The terminal stage of anaerobic digestion is the biological process of methanogenesis . Here, methanogens use the intermediate products of

1525-476: Is typically an agricultural anaerobic digester that accepts two or more input materials for simultaneous digestion. The length of time required for anaerobic digestion depends on the chemical complexity of the material. Material rich in easily digestible sugars breaks down quickly, whereas intact lignocellulosic material rich in cellulose and hemicellulose polymers can take much longer to break down. Anaerobic microorganisms are generally unable to break down lignin,

1586-698: Is used as part of the process to treat biodegradable waste and sewage sludge . As part of an integrated waste management system, anaerobic digestion reduces the emission of landfill gas into the atmosphere. Anaerobic digesters can also be fed with purpose-grown energy crops, such as maize . Anaerobic digestion is widely used as a source of renewable energy . The process produces a biogas , consisting of methane , carbon dioxide , and traces of other 'contaminant' gases. This biogas can be used directly as fuel, in combined heat and power gas engines or upgraded to natural gas-quality biomethane . The nutrient-rich digestate also produced can be used as fertilizer . With

1647-439: Is usually referred to as "anaerobic activity". This is the source of marsh gas methane as discovered by Alessandro Volta in 1776. Anaerobic digestion comprises four stages: The digestion process begins with bacterial hydrolysis of the input materials. Insoluble organic polymers , such as carbohydrates , are broken down to soluble derivatives that become available for other bacteria. Acidogenic bacteria then convert

1708-467: The sugars and amino acids into carbon dioxide, hydrogen , ammonia , and organic acids . In acetogenesis, bacteria convert these resulting organic acids into acetic acid , along with additional ammonia, hydrogen, and carbon dioxide amongst other compounds. Finally, methanogens convert these products to methane and carbon dioxide. The methanogenic archaea populations play an indispensable role in anaerobic wastewater treatments. Anaerobic digestion

1769-399: The addition of water. The primary styles of dry digesters are continuous vertical plug flow and batch tunnel horizontal digesters. Continuous vertical plug flow digesters are upright, cylindrical tanks where feedstock is continuously fed into the top of the digester, and flows downward by gravity during digestion. In batch tunnel digesters, the feedstock is deposited in tunnel-like chambers with

1830-432: The application of anaerobic digestion as a process for reducing waste volumes and generating useful byproducts. It 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. Biogas Too Many Requests If you report this error to

1891-527: The application of anaerobic digestion systems is the feedstock to the process. Almost any organic material can be processed with anaerobic digestion; however, if biogas production is the aim, the level of putrescibility is the key factor in its successful application. The more putrescible (digestible) the material, the higher the gas yields possible from the system. Feedstocks can include biodegradable waste materials, such as waste paper, grass clippings, leftover food, sewage, and animal waste. Woody wastes are

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1952-513: The bacterial groups responsible for the different organic matter degradation steps. The degree of the inhibition depends, among other factors, on the concentration of the inhibitor in the digester. Potential inhibitors are ammonia, sulfide, light metal ions (Na, K, Mg, Ca, Al), heavy metals, some organics (chlorophenols, halogenated aliphatics, N-substituted aromatics, long chain fatty acids), etc. Total ammonia nitrogen (TAN) has been shown to inhibit production of methane. Furthermore, it destabilises

2013-450: The biomass is kept in the reactor which is then used for in-vessel composting before it is opened As the batch digestion is simple and requires less equipment and lower levels of design work, it is typically a cheaper form of digestion. Using more than one batch reactor at a plant can ensure constant production of biogas. In continuous digestion processes, organic matter is constantly added (continuous complete mixed) or added in stages to

2074-591: The chemical reaction, where organic material such as glucose is biochemically digested into carbon dioxide (CO 2 ) and methane (CH 4 ) by the anaerobic microorganisms. C 6 H 12 O 6 → 3CO 2 + 3CH 4 In most cases, biomass is made up of large organic polymers. 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 to other bacteria. The process of breaking these chains and dissolving

2135-405: The digestion system. In a typical two-stage mesophilic digestion, residence time varies between 15 and 40 days, while for a single-stage thermophilic digestion, residence times is normally faster and takes around 14 days. The plug-flow nature of some of these systems will mean the full degradation of the material may not have been realised in this timescale. In this event, digestate exiting

2196-401: The discharge of digester liquids are a liability. 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 produced. The moisture content of the target feedstock will also affect what type of system

2257-538: The emission of greenhouse gases in a number of key ways: Anaerobic digestion is particularly suited to organic material, and is commonly used for industrial effluent , wastewater and sewage sludge treatment . Anaerobic digestion, a simple process, can greatly reduce the amount of organic matter which might otherwise be destined to be dumped at sea, dumped in landfills , or burnt in incinerators . Pressure from environmentally related legislation on solid waste disposal methods in developed countries has increased

2318-494: The exception, because they are largely unaffected by digestion, as most anaerobes are unable to degrade lignin . Xylophagous anaerobes (lignin consumers) or high temperature pretreatment, such as pyrolysis, can be used to break lignin down. 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 codigestion or cofermentation plant

2379-449: The fastest. Commonly known are pH, temperature, salinity etc. but pressure is also one of them. Some species have adapted to life in the deep oceans where pressure is much higher than at sea level. This makes it possible in similar vein as other process parameters such as Temperature, Retention Time, pH to influence the anaerobic digestion process. The anaerobic digestion process can be inhibited by several compounds, affecting one or more of

2440-418: The feedstock mass are potentially convertible to biogas. Low solids (wet) 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 increased volumes associated with the increased liquid-to-feedstock ratio of the digesters. There are benefits associated with operation in

2501-551: The feedstock material is a key consideration when using wet digestion or plug-flow digestion. If the feedstock to the digesters has significant levels of physical contaminants, such as plastic, glass, or metals, then processing to remove the contaminants will be required for the material to be used. If it is not removed, then the digesters can be blocked and will not function efficiently. This contamination issue does not occur with dry digestion or solid-state anaerobic digestion (SSAD) plants, since SSAD handles dry, stackable biomass with

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2562-401: 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 maceration of solids can be achieved by using a chopper pump to transfer the feedstock material into the airtight digester, where anaerobic treatment takes place. Substrate composition

2623-445: 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. High solids digesters also require correction of conventional performance calculations (e.g. gas production, retention time, kinetics, etc.) originally based on very dilute sewage digestion concepts, since larger fractions of

2684-426: 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 to kill harmful bacteria in

2745-414: The input waste. In this instance, there may be a pasteurisation or sterilisation stage prior to digestion or between the two digestion tanks. Notably, it is not possible to completely isolate the different reaction phases, and often some biogas is produced in the hydrolysis or acidogenesis tanks. The residence time in a digester varies with the amount and type of feed material, and with the configuration of

2806-428: 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. A recent development in anaerobic reactor design is High-pressure anaerobic digestion (HPAD) also referred to a Autogenerative High Pressure Digestion (AHPD). This technique produces

2867-415: The microbial community, impacting the synthesis of acetic acid. Acetic acid is one of the driving forces in methane production. At an excess of 5000 mg/L TAN, pH adjustment is needed to keep the reaction stable. A TAN concentration above 1700– 1800 mg/L inhibits methane production and yield decreases at greater TAN concentrations. High TAN concentrations cause the reaction to turn acidic and lead to

2928-411: The organic material itself, 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, and trace levels of hydrogen sulfide . In an anaerobic system, the majority of the chemical energy contained within the starting material

2989-413: The organic matter has completed. There can be severe odour issues if a batch reactor is opened and emptied before the process is well completed. A more advanced type of batch approach has limited the odour issues by integrating anaerobic digestion with in-vessel composting . In this approach inoculation takes place through the use of recirculated degasified percolate. After anaerobic digestion has completed,

3050-565: The pathogenic concentration in the digestate, leaving the anaerobic digester. Pasteurisation may be achieved by heat treatment combined with maceration of the solids. In a typical scenario, three different operational parameters are associated with the solids content of the feedstock to the digesters: High solids (dry) digesters are designed to process materials with a solids content between 25 and 40%. Unlike wet digesters that process pumpable slurries, high solids (dry – stackable substrate) digesters are designed to process solid substrates without

3111-437: The preceding stages and convert them into methane, carbon dioxide, and water. These components make 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. The remaining, indigestible material the microbes cannot use and any dead bacterial remains constitute the digestate. Anaerobic digesters can be designed and engineered to operate using

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3172-608: The re-use of waste as a resource and new technological approaches that have lowered capital costs , anaerobic digestion has in recent years received increased attention among governments in a number of countries, among these the United Kingdom (2011), Germany, Denmark (2011), and the United States. Many microorganisms affect anaerobic digestion, including acetic acid-forming bacteria ( acetogens ) and methane-forming archaea ( methanogens ). These organisms promote

3233-507: The reactor (continuous plug flow ; first in – first out). Here, the end products are constantly or periodically removed, resulting in constant production of biogas. A single or multiple digesters in sequence may be used. Examples of this form of anaerobic digestion include continuous stirred-tank reactors , upflow anaerobic sludge blankets , expanded granular sludge beds , and internal circulation reactors . The two conventional operational temperature levels for anaerobic digesters determine

3294-458: The recalcitrant aromatic component of biomass. 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 much of the energy content taken out by the animals that produced it. Therefore, many digesters operate with codigestion of two or more types of feedstock. For example, in

3355-452: 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. Through hydrolysis the complex organic molecules are broken down into simple sugars , amino acids, and fatty acids . Acetate and hydrogen produced in the first stages can be used directly by methanogens. Other molecules, such as volatile fatty acids (VFAs) with

3416-459: The species of methanogens in the digesters: A limit case has been reached in Bolivia , with anaerobic digestion in temperature working conditions of less than 10 °C. The anaerobic process is very slow, taking more than three times the normal mesophilic time process. In experimental work at University of Alaska Fairbanks , a 1,000-litre digester using psychrophiles harvested from "mud from

3477-439: The stacked pile. Continuous vertical dry digesters have a smaller footprint due to the shorter effective retention time and vertical design. Wet digesters can be designed to operate in either a high-solids content, with a total suspended solids (TSS) concentration greater than ~20%, or a low-solids concentration less than ~15%. High solids (wet) digesters process a thick slurry that requires more energy input to move and process

3538-400: The start of the process. The reactor is then sealed for the duration of the process. In its simplest form batch processing needs inoculation with already processed material to start the anaerobic digestion. In a typical scenario, biogas production will be formed with a normal distribution pattern over time. Operators can use this fact to determine when they believe the process of digestion of

3599-552: The substrate that is converted to biogas in a reactor). In order to predict biogas composition (the relative fractions of methane and carbon dioxide) it is necessary to estimate carbon dioxide partitioning between the aqueous and gas phases, which requires additional information (reactor temperature, pH , and substrate composition) and a chemical speciation model. Direct measurements of biomethanation potential are also made using gas evolution or more recent gravimetric assays. Using anaerobic digestion technologies can help to reduce

3660-448: The system will be darker in colour and will typically have more odour. In the case of an upflow anaerobic sludge blanket digestion (UASB), hydraulic residence times can be as short as 1 hour to 1 day, and solid retention times can be up to 90 days. In this manner, a UASB system is able to separate solids and hydraulic retention times with the use of a sludge blanket. Continuous digesters have mechanical or hydraulic devices, depending on

3721-477: Was originally elected as a member of Together for Lünen (German: Gemeinsam für Lünen = GFL), but later left the party. The most recent mayoral election was held on 13 September 2020, with a runoff held on 27 September, and the results were as follows: The Lünen city council governs the city alongside the Mayor. The most recent city council election was held on 13 September 2020, and the results were as follows: Lünen

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