Biogas is a kind of biomass energy, which utilizes feces, crop straw and other organic substances to produce CH4 and CO 2 through microbial physiological metabolism under anaerobic conditions. It also has a small amount of combustible gases such as H2S, CO and so on. The research on biogas fermentation is of great significance and function. In this paper, the influencing factors of biogas fermentation are discussed by the manufacturer of biogas desulfurization equipment.
Biogas fermentation can be divided into three temperature ranges: high-temperature fermentation at 50-65 degrees C, medium-temperature fermentation at 20-45 degrees C and low-temperature fermentation at 20 degrees C. In addition, the fermentation mode that changes with natural temperature is called normal temperature fermentation.
Biogas fermentation is affected by temperature and temperature fluctuation. Under the same temperature type, because the metabolic activity of biogas fermentation microorganisms increases with the increase of temperature, in a certain temperature range, the higher the temperature, the faster the fermentation gas production rate; if the temperature fluctuation is too large in a short time, it may lead to the cessation of gas production.
2. Acidity and alkalinity (PH value)
Usually, the suitable PH value of methanogens in biogas digesters ranges from 6.5 to 7.8. The change of PH value will directly affect the survival and metabolism of methanogens. In general, the PH value of biogas digester should be maintained between 6.8 and 7.5, preferably around 7.2.
When the pH value is below 5.5, the activity of methanogens is completely inhibited, while when the pH value rises to 8 or even 8.5, a certain gas production rate is maintained. The pH value of acid-producing bacteria ranges from 4.0 to 7.0. Acidification may occur in the reactor when acidic fermentation exceeds the optimum pH value of methanogens.
The main factors affecting the change of pH value are as follows: firstly, the pH value of fermentation raw materials; secondly, when anaerobic fermentation is started, excessive feed concentration, insufficient number of methanogens in inoculate, and sudden increase of load in digestion stage will cause the accumulation of volatile acid due to the imbalance of the speed of acid production and methanogenesis, resulting in the decrease of pH value, which often results in anaerobic fermentation. The main reasons for failure or termination of startup.
3. Oxygen content
The oxygen brought in during the start-up and feeding of biogas fermentation is not harmful to the biogas fermentation and will not destroy the normal process of biogas fermentation. This is because there are some aerobic bacteria and facultative bacteria in the biogas digester. The oxygen brought in will soon be consumed by the aerobic bacteria or facultative bacteria in the methane-free bacteria, so that the anaerobic environment will be maintained in the digester. At the same time, this part of oxygen also keeps a dynamic balance between the aerobic bacteria, facultative bacteria and anaerobic bacteria. But in order to maintain a good anaerobic environment, no leakage must be found in the fermentation process.
4. C/N Ratio of Biogas Fermentation Materials
The C/N ratio of fermentation raw materials refers to the ratio of organic carbon content to nitrogen content in raw materials. Biogas fermentation microorganisms need certain nutrients such as carbon, nitrogen and phosphorus to grow normally and carry out life activities. Carbon provides energy for microbial life activities and is an important material for methane formation. Nitrogen is also the main element for microbial cells. The ratio of nitrogen to phosphorus, whether aerobic fermentation or biogas fermentation, is determined to be 5:1. The ratio of carbon to nitrogen is relatively wide. Previous practice considered that C/N of fermentation raw materials should be (13-30:1). The effect of more than 30:1 is not good. Fermentation can be normal if the ratio is less than 13:1. However, in fact, biogas digesters with human excrement as the main raw material (C/N=3.9:1) can also operate well. Therefore, normal biogas fermentation requires appropriate carbon-nitrogen ratio, but not strict. We should pay attention to the start-up of biogas digester and cultivate suitable strains to improve the adaptability of biogas fermentation bacteria.
5. Biogas fermentation inoculum
The quantity and quality of biogas fermentation bacteria directly affect biogas fermentation, gas production rate and biogas quality. The rapid start-up of biogas fermentation is related to high quality and a large number of inoculants.
If the inoculum is not enough at the start of biogas fermentation, the start-up may be slow, and after a long time, the gas production rate is still low; the inoculum quality is poor, the number of methanogenic bacteria is small, and the activity is low. At this time, hydrolytic bacteria and hydrogen-producing acidogenic bacteria multiply quickly, while methanogenic bacteria multiply slowly, resulting in a faster non-methanogenic effect, and methanogenic and non-methanogenic effects. The imbalance of methane process may result in the slow accumulation of organic acids, the decrease of pH value of fermentation broth, the acidification of biogas digester, the slow production of gas and the low content and poor quality of methane in biogas.
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