What are the Fundamentals of Anaerobic Sludge Digestion?
Under anaerobic circumstances, organic materials from a mixture of primary settled sludge and biological sludge from the secondary clarifier is transformed to CH4 and CO2. This is done in an oxygen-free environment in an airtight reactor. Sludge is delivered constantly or intermittently into the reactor and held there for varying amounts of time.
Liquefaction and gasification are two fundamental processes in anaerobic digestion.
The non-putrescible stabilized sludge that is removed constantly or intermittently from the process has a considerably reduced pathogen content.
The biological oxidation of degradable organic sludge by bacteria in anaerobic conditions is known as anaerobic digestion. It occurs when there is a lack of oxygen and organic matter serves as a source of food for microbes. The majority of the bacteria involved in this digestion are either obligatory anaerobes or facultative anaerobes. For the treatment of organic sludge, this method is used.
When organic matter is oxidised anaerobically, the following reactions happen-
Organic matter CO2 + CH4+ new cell + energy for cells + other products (Anaerobic bacteria) (H2S, H2, N2, etc.)
Anaerobic bacteria's microbial action is divided into three stages:
1) Solids liquefaction,
2) Digestion of soluble solids,
3) Production of natural gas.
Organic acid-forming heterotrophs synthesise organic acids from complex organic substrates such as carbohydrates, proteins, lipids, oils, and their degradation products.
The following is a breakdown of three primary organic matters:
- Carbohydrates Simple sugars Alcohols,
- Aldehydes Organic acids
- Proteins Amino acids Organic acids + NH3
- Fats and oils organic acids
Most of these bacteria that produce organic acids are facultative anaerobes that can be found in soil and work in a wide pH range. To manufacture CO2 and CH4, methane-producing heterotrophs, which are obligately anaerobes, utilise organic acids with a pH range of 6.7 to 7.4.
Organic acids CO2 + CH4 (55-75%) (35-45%) + H2S, H2, N2
Hydrolytic bacteria are the first group of microorganisms that hydrolyse complicated organic compounds into soluble end products.
Acidogenic bacteria, the second group of microorganisms, turn the previous group's product into simple end products, principally VFA and alcohols.
Methanogenic bacteria, the third group, transforms the acid produced by the second group into methane and carbon dioxide. The reactor's contents should be oxygen-free. The alkalinity in the reactor should be sufficient for the digester to function properly and keep the pH between 6.5 and 8.0. Temperature has a significant impact on how well a digester works.
Biodegradation is caused by two types of bacteria: mesophilic (20 to 40 degrees Celsius) and thermophilic (45 to 65 degrees Celsius). As a result, the digester can work in a mesophilic or thermophilic temperature range. The digesters must be heated outside to get the temperature to the mesophilic range in places where the temperature is less than 20o C.
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