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Difference between revisions of "Anaerobic digestion"
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Anaerobic digestion is a process through which micro-organisms break down organic matter, such as animal manure, wastewater biosolids, and food wastes, in the absence of oxygen. Anaerobic digestion intended for biogas production takes place in a sealed tank (called an anaerobic digester), which is designed and constructed in various shapes and sizes specific to the site and feedstock conditions. These sealed vessels contain complex microbial communities that break down the waste and produce biogas and digestate (i.e., the solid and liquid material end-products of the process). | <onlyinclude>'''Anaerobic digestion''' is a process through which micro-organisms break down organic matter, such as animal manure, wastewater biosolids, and food wastes, in the absence of oxygen. Anaerobic digestion intended for biogas production takes place in a sealed tank (called an anaerobic digester), which is designed and constructed in various shapes and sizes specific to the site and feedstock conditions. These sealed vessels contain complex microbial communities that break down the waste and produce biogas and digestate (i.e., the solid and liquid material end-products of the process).</onlyinclude> | ||
== Feedstock == | == Feedstock == | ||
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== Process and technologies == | == Process and technologies == | ||
=== Process === | === Process === | ||
There are three basic anaerobic digestion processes, namely psychrophilic, mesophilic, and thermophilic, which take place over different temperature ranges. Psychrophilic digestion is a low temperature (<20°C) process. Mesophilic digestion takes place between 20 and 45°C, which can take a month or two to complete, and thermophilic digestion between 45 and 65°C, which is faster, but its micro-organisms are more sensitive. The majority of the agricultural biogas plants are operated at mesophilic temperatures. Thermophilic temperatures are applied mainly in large-scale centralised biogas plants with co-digestion<ref>{{Cite web|year=2021|title=Anaerobic digestion|e-pub date=2021|date accessed=6/9/2021|url=https://www.eubia.org/cms/wiki-biomass/anaerobic-digestion/}}</ref>. The process of anaerobic digestion takes place through four successive stages: hdyrolysis, fermentation, acetogenesis, and methanogenesis.<ref>{{Cite journal|author=Junye Wang|year=2014|title=Decentralized biogas technology of anaerobic digestion and farm ecosystem: opportunities and challenges|journal=Fronties in Energy Research|volume=2|page=|doi=10.3389/fenrg.2014.00010}}</ref> In the hydrolysis step, the feedstock is broken down into soluble substrates (e.g., sugar and amino acids) by enzymes. Fermentation involves the conversion of sugar, amino acids, and fatty acids into ammonia, organic acids, hydrogen (H<sub>2</sub>) and CO<sub>2</sub>. In the acetogenesis step, volatile fatty acids are broken down into acetic acids, CO<sub>2</sub> and H<sub>2</sub>. Finally, methanogenesis step converts acetate, formaldeyde, and H<sub>2</sub> to CH<sub>4</sub> and water<ref>{{Cite journal|author=Jay N. Meegoda, Brian Li, Kush Patel, Lily B. Wang|year=2018|title=A review of the Processes, Parameters, and Optimization of Anaerobic Digestion|journal=International Journal of Environmental Research and Public Health|volume=15|page=|doi=10.3390/ijerph15102224}}</ref>. | There are three basic anaerobic digestion processes, namely psychrophilic, mesophilic, and thermophilic, which take place over different temperature ranges. Psychrophilic digestion is a low temperature (<20°C) process. Mesophilic digestion takes place between 20 and 45°C, which can take a month or two to complete, and thermophilic digestion between 45 and 65°C, which is faster, but its micro-organisms are more sensitive. The majority of the agricultural biogas plants are operated at mesophilic temperatures. Thermophilic temperatures are applied mainly in large-scale centralised biogas plants with co-digestion<ref>{{Cite web|year=2021|title=Anaerobic digestion|e-pub date=2021|date accessed=6/9/2021|url=https://www.eubia.org/cms/wiki-biomass/anaerobic-digestion/}}</ref>. The process of anaerobic digestion takes place through four successive stages: hdyrolysis, fermentation, acetogenesis, and methanogenesis.<ref>{{Cite journal|author=Junye Wang|year=2014|title=Decentralized biogas technology of anaerobic digestion and farm ecosystem: opportunities and challenges|journal=Fronties in Energy Research|volume=2|page=|doi=10.3389/fenrg.2014.00010}}</ref> In the hydrolysis step, the feedstock is broken down into soluble substrates (e.g., sugar and amino acids) by enzymes. Fermentation involves the conversion of sugar, amino acids, and fatty acids into ammonia, organic acids, hydrogen (H<sub>2</sub>) and CO<sub>2</sub>. In the acetogenesis step, volatile fatty acids are broken down into acetic acids, CO<sub>2</sub> and H<sub>2</sub>. Finally, methanogenesis step converts acetate, formaldeyde, and H<sub>2</sub> to CH<sub>4</sub> and water<ref>{{Cite journal|author=Jay N. Meegoda, Brian Li, Kush Patel, Lily B. Wang|year=2018|title=A review of the Processes, Parameters, and Optimization of Anaerobic Digestion|journal=International Journal of Environmental Research and Public Health|volume=15|page=|doi=10.3390/ijerph15102224}}</ref>. | ||
[[File:Anaerobic stages.png|thumb|Simplified scheme of pathways in anaerobic digestion (not own work)]] | [[File:Anaerobic stages.png|thumb|Simplified scheme of pathways in anaerobic digestion (not own work)]] | ||