III. Strict anaerobic environment The core bacteria of the biogas microorganisms - methanogens are anaerobic bacteria that are particularly sensitive to oxygen. They do not require air, air in the growth, development, reproduction, metabolism, and other life activities. Oxygen in the air will inhibit its life activities and even cause death. Methanogens can only grow in a strictly anaerobic environment. Therefore, the construction of biogas digesters must be tightly sealed, watertight, and non-leakable. This is not only the need to collect biogas and the raw materials for biogas fermentation, but also to ensure that the biogas microorganisms can live well under the anaerobic ecological conditions, so that the biogas digesters can function normally. Gas production needs. This is why the leaking and leaking biogas digesters are called "pathological pools."
Fourth, the appropriate temperature fermentation temperature is an important external factor for biogas fermentation, the temperature is suitable for the vigorous growth of bacteria, strong vitality, anaerobic decomposition and methane production speed is fast, more gas production. In this sense, temperature is the key to good gas production.
The study found that biogas can normally produce gas in the range of 10 to 60°C. Less than 10°C or higher than 60°C severely inhibits the survival and reproduction of microorganisms and affects gas production. In this temperature range, the higher the general temperature, the more active microbial activity and the higher the gas production. Microorganisms are very sensitive to temperature changes, sudden rise or sudden drop in temperature can affect the life activities of microorganisms and deteriorate the gas production.
Usually the different fermentation temperatures are divided into three ranges, namely, 46 to 60°C as high-temperature fermentation, 28 to 38°C as medium-temperature fermentation, and 10 to 26°C as normal-temperature fermentation. The rural biogas digester is fermented by natural temperature and belongs to room temperature fermentation. At room temperature fermentation, although the temperature range is wide, in the range of 10-26°C, the higher the temperature, the better the gas production. This is why the biogas digesters in summer, especially the highest temperature in July, produce a large amount of gas, while in the coldest January in winter, there is little gas production, and even the reason for not producing gas is that the management of rural digesters emphasizes that winter must be taken. Wintering measures to ensure normal gas production.
5. Appropriate acidity and alkalinity The growth and reproduction of biogas microorganisms require that the pH of the fermentation raw materials be kept neutral or slightly alkaline, and that overacidity and alkalinity will affect gas production. Measurements showed that pH can be produced between pH=6~8, gas production can be achieved with pH=6.5~7.5, and no gas can be produced when pH value is lower than 6 or higher than 9.
In the early stages of fermentation in rural household biogas digesters, a large amount of organic acids were produced in the pool due to the activity of acid-producing bacteria, resulting in a decrease in pH. As the fermentation continues, ammonia produced by ammoniation neutralizes a portion of the organic acids. At the same time, the activity of the methanogenic bacteria causes a large amount of volatile acids to be converted into methane (CH4) and carbon dioxide (CO2), gradually returning the pH to normal values. Therefore, in the normal fermentation process, the acidity and alkalinity changes in the biogas digesters can be naturally mediated, first from high to low, then increased again, and finally reach a constant natural balance (ie, a suitable pH value), and generally do not need to be artificially adjusted. . Only in the case of improper ingredients and improper management, the normal fermentation process will be destroyed, it will be possible that there will be a large accumulation of organic acids, and the fermentation liquor will be too acidic. At this point, you can remove some of the liquid, add the same amount of inoculum, the accumulation of organic acids into methane, or add the appropriate amount of plant ash or lime clarifier, neutralize organic acids, so that the pH to return to normal.
6. Moderate Fermentation Concentration The load of a rural biogas digester is usually expressed in terms of organic load, ie the amount of organic matter per unit volume of biogas digester, usually in kilograms of COD per cubic meter per day. Volumetric loading is an important parameter for the design and operation of biogas digesters, and its size is mainly determined by the quantity and activity of anaerobic activated sludge.
The load of rural biogas digesters is usually represented by the concentration of fermentation raw materials, and the appropriate dry matter concentration is 4% to 10%, that is, the moisture content of the fermentation raw materials is 90% to 96%. Fermentation concentration changes with temperature, generally about 6% in summer and 8% to 10% in winter. High or low concentrations are not conducive to biogas fermentation. If the concentration is too high, the water content is too small, the fermentation raw materials are not easily decomposed, and a large amount of acidic substances are easily accumulated, which is not conducive to the growth and reproduction of the methane bacteria and affects the normal gas production. If the concentration is too low, the water content is too high, the content of organic matter in the unit volume is relatively reduced, and the amount of gas production is also reduced, which is not conducive to the full utilization of the biogas digester.
VII. Continuously Stirring Static Fermentation The biogas digester raw materials are mixed with water and inoculated into the biogas digester. According to their specific gravity and natural sedimentation laws, they are gradually divided into the scum layer, the clear liquid layer, and the active layer from top to bottom. Slag layer. This layered distribution is very detrimental to microbes and gas production. The raw materials and micro-organisms are unevenly distributed. A large number of micro-organisms accumulate in the bottom layer because there are many inoculated sludges and good anaerobic conditions, but the raw materials are lacking, especially when carbon-rich straw is used as a raw material, it is easy to float to the surface layer of the feed liquid. It is not easy to be absorbed and decomposed by microorganisms. At the same time, the dense crust formed is not conducive to the release of biogas. In order to change this unfavorable situation, it is necessary to take stirring measures and change from static fermentation to dynamic fermentation.
Practice has proved that proper stirring methods and strength can make the raw materials of fermentation evenly distributed, enhance the contact between microorganisms and raw materials, increase the chance of obtaining nutrients, increase the activity, grow vigorously, and thus increase the amount of gas. Stirring can also crush the crusts, improve the utilization of raw materials and energy conversion efficiency, and is conducive to the release of bubbles.
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