To produce biogas properly, good conditions must be created for the microorganisms to survive and reproduce. Biogas digesters must meet a variety of conditions. First, the digester must be airtight. The fermentation of organic material into biogas is the result of the activities of many kinds of anaerobic bacteria, so it is necessary to create an anoxic environment for the activities of anaerobic bacteria. When constructing the digester, care should be taken to insulate it from air, so that it is airtight and watertight. Secondly, 20 to 40°C should be maintained in the digester because gas production is usually highest at this temperature. Third, the digester should have sufficient nutrients. For microorganisms to survive and reproduce, they must draw nutrients from the fermented material. In the fermentation raw materials of the digester, human and animal manure can provide nitrogen, and cellulose such as straw from crops can provide carbon. Fourthly, the fermentation material should contain the right amount of water, generally the fermentation material of the digester is required to contain about 80% of water, too much or too little is unfavorable to gas production. Fifth, the pH value of the digester is generally controlled at 7 to 8.5.
Biogas is a mixture of gases, the main components are methane (CH4) and carbon dioxide (C02). Methane accounts for 60% to 70%, carbon dioxide accounts for 30% to 40%, and a small amount of hydrogen, carbon monoxide, hydrogen sulfide, oxygen and nitrogen and other gases. Because of the combustible gas methane, biogas can be used as fuel. Biogas is a product of decomposition of organic matter by bacteria under anaerobic conditions. Municipal organic waste, sludge from sewage treatment plants, animal and human waste from rural areas, crop stalks, etc., can all be used as raw materials for generating biogas. The process of decomposition of organic matter by bacteria is roughly divided into two stages: the first stage, the complex high molecular organic matter into low molecular organic matter, such as acetic acid, propionic acid, butyric acid, etc.; the second stage, the first stage of the product is converted into methane and carbon dioxide.
In the above process, the role of fermentation and decomposition is the result of a variety of bacteria **** the same action. In order for biogas fermentation to continue, the living conditions required by the various microorganisms in biogas fermentation must be provided and maintained. Methane-producing bacteria are anaerobic, and small amounts of oxygen can seriously impair their growth and reproduction. This requires an airtight digester that can be insulated from oxygen. Temperature is an important factor in the anaerobic digestion process, methane bacteria can survive in the temperature range of 0 a 80 ℃, there are respectively adapted to the low temperature (20 ℃), medium temperature (30 ℃), high temperature (50 ℃) of various types of bacteria, the most suitable reproduction temperature of 15 ℃, 35 ℃, 53 ℃ or so. Methane bacteria growth and reproduction of the most suitable pH value of about 7.0 a 7.5, beyond this range, the efficiency of anaerobic digestion will be reduced. Bacteria responsible for waste fermentation in the anaerobic digestion process also need nitrogen, phosphorus and other nutrients. The ratio of raw materials put into the digester, generally in accordance with the carbon and nitrogen ratio equal to 20:1 a 25:1. In addition, it should also control the concentration of harmful substances affecting the fermentation of biogas.
The Attractive Prospects of Biogas Energy
In the world of living creatures, there exists a kind of microorganisms that we can't see or touch with our naked eyes, which can provide energy for human beings. The mention of microorganisms often reminds people that they can make food spoil and infect people with various diseases. As a result, they are feared and hated. However, in the family of microorganisms, because of the different species, their role is not the same, some will bring disaster to mankind, some will bring happiness to mankind. Among the microorganisms, methane bacteria and yeast that can provide energy for human beings, they can produce methane gas and alcohol to contribute to human beings.
When it comes to biogas, as the name suggests, it is the gas from swamps. People often see, in the swamp, sewage ditch or cesspool, there are bubbles come out, if we scratch the match, can be lit, this is the natural occurrence of natural methane gas. Biogas is a combustible gas produced by the fermentation of microorganisms in a variety of organic substances, in isolation from the air (reducing conditions), and must be suitable temperature and humidity. The main component of biogas is methane, which accounts for about 60% to 80% of the gas produced. Methane is an ideal gas fuel, which is colorless and odorless, and burns when mixed with the right amount of air. Each cubic meter of pure methane generates the most 34,000 joules of heat, and each cubic meter of biogas generates about 20,800-23,600 joules of heat. That is, 1 cubic meter of biogas after complete combustion, can produce the equivalent of 0.7 kg of anthracite coal to provide heat.
The basic principles of biogas generation are still being explored. The process of biogas formation can be roughly divided into two stages, first of all, a variety of complex organic matter into low-grade fatty acids, such as butyric acid, propionic acid, acetic acid; and then the above types of products continue to be converted into methane and carbon dioxide and so on.
At present, countries around the world have begun to use biogas as fuel and for lighting. Using biogas instead of gasoline and diesel to start machines is also very effective. Using it as an energy source in rural areas has many advantages. For example, the construction of an average person l-1.5 square meters of fermentation tank, you can basically solve the problem of firewood and lighting throughout the year; human, animal feces, as well as a variety of crop stalks, weeds, etc., through the fermentation, not only produces biogas, but also can be used as fertilizers, and due to the high degree of decomposition so that the fertilizer efficiency is higher, feces and other raw materials for biogas after fermentation, the vast majority of the parasite eggs are killed, which can improve the health of rural areas, and can be used to improve the health of the community, and to improve the environment. After the fermentation of manure and other biogas raw materials, most of the parasite eggs are killed, which can improve the rural sanitation and reduce the transmission of diseases. Now, the application of biogas is being promoted in the majority of rural areas in various countries, the popularization of the development and utilization of biogas energy, has achieved better results.
Some developed countries in the world, is also being carried out using microbial anaerobic digestion of farm wastes, the production of methane on a larger scale test. The United Kingdom has established an automated plant for methane. There are three basic processes in anaerobic digesters:
The first stage of hydrolysis converts insoluble organic compounds and polymers, enzymatically, into soluble organic matter.
The second stage then ferments the products converted in the previous step, such as carbohydrates, proteins, lipids, and alcohols, into organic acids.
The third stage produces methane from the fermentation of organic acids.
It is estimated that in the UK, the methane produced by microbial anaerobic digestion using a wide range of organic wastes from humans and animals could replace 25% of the gas consumed in the whole of the UK. A small methane engine has been designed in Scotland for use in villages, farms or homes.
A ranch in the United States built a plant, the main body is a 30-meter-wide, 213-meter-long sealed pool composed of medium-alkane fermentation structure, its mission is to pasture stable manure and other organic waste, by microbes into methane, carbon dioxide, and dry fertilizer. The plant can process 1,650 tons of stable manure per day, providing 113,000 cubic meters of methane per day to pastures, enough for 10,000 homes. The United States now has 24 energy conversion projects that utilize microbial fermentation. From the world, the use of a variety of microorganisms synergistic effect of methane production research and application, is in the ascendant stage.
In recent years, China's biogas business has gained rapid development, the total number of biogas digesters has reached more than 10 million. In Sichuan, Zhejiang, Jiangsu, Guangdong, Shanghai and other provinces and cities in rural areas, some places in addition to biogas cooking, lighting, but also set up a small biogas power station, the use of biogas energy as a driving force for threshing, processing of food, fodder, and tea, etc., to break out of the "earth" to solve the problem of rural power of the new way.
Experts believe that in the 21st century, biogas in rural areas can become one of the main sources of energy, because it has incomparable characteristics, especially in China's vast rural areas, these features are more significant.
First of all, biogas energy in China's rural areas are widely distributed, with great potential, wherever there are living creatures are possible to obtain raw materials for biogas production, so biogas is an inexhaustible renewable energy. Secondly, it can be used locally to save money. Biogas power station is built in the countryside, the fermentation raw materials generally do not have to seek outside. Build a small biogas power station and power station, equipment and technology are relatively simple, management and maintenance is also very convenient, most of the rural areas can do. According to the survey and comparison, the investment of a small biogas power station is only about 400 yuan per kilowatt, which is only 1/2-1/3 of that of a small hydroelectric power station, and much lower than that of wind, tidal and solar power generation. The construction period of small-scale biogas power station is short, as long as a few months time can be put into use, basically not affected by the change of natural conditions. The use of biogas mixed with diesel combustion can also save 17% of the diesel.
China is a vast country with abundant bioenergy resources. Research shows that in the 21st century, whether in rural areas or towns, according to local conditions, local use of manure, orange rods, weeds, slag, waste and other production of biogas to generate electricity.