For the process of anaerobic decomposition of organic matter in the biogas plant, what must be the minimum temperature required for the bacteria to breed? If installed at extreme cold places, what may be the best option?
The two conventional operational temperature levels for anaerobic digesters determine the species of methanogens in the digesters: Mesophilic digestion takes place optimally around 30 to 38 °C, or at ambient temperatures between 20 and 45 °C, where mesophiles are the primary microorganism present. Thermophilic digestion takes place optimally around 49 to 57 °C, or at elevated temperatures up to 70 °C, where thermophiles are the primary microorganisms present.
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 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 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 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 the pathogenic concentration in the digesate leaving the anaerobic digester. Pasteurisation may be achieved by heat treatment combined with maceration of the solids.
If installed at extreme cold places, use of Phase change material around the digester to store the heat at sunshine hours and maintain the required temperature may be the best option.
A biogas production is not depending on the external temperature.
In fact, we can have three level of temperatures inside the anaerobic digester (we are talking here on a digester build with concrete), so :
1. Psychrophilic (Ambient temperature with more than one month in retention duration)
2. Mesophilic ( Around 37 °C and up to 25 days of retention duration)
3. Thermophilic ( Around 55 °C and up to 12 days of retention duration)
These levels of temperatures is subject of the kind of wastes and with a good insulation of your tank you can get biogas with the cited durations.
Dear Pavithra,
Biogas production is temperature dependent. Biogas production is low due to the cold climate conditions in winter.But studies show that storing slurry in the mixing tank until its temperature peak at around 14:00 h will increase the temperature in the digester and thus increase potential biogas production.Refer the link for further clarifications.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4093558/
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