There are different types of digesters for different types of material, but all generally convert organics into biogas and digestate. Biogas is composed mostly of methane and carbon dioxide, with trace amounts of hydrogen sulfide, nitrogen, and other particulates. It is most often used to generate electricity for on-site use or to sell to local utilities. To generate electricity, biogas is used to fuel a gas engine which drives a generator to produce electricity.
It is also commonly used to produce heat by burning the biogas in boilers. With a combined heat and power plant system CHP power is generated and the heat produced can be used to heat the digester. Biogas can also be upgraded to pure methane, also known as bio methane or renewable natural gas, by removing carbon dioxide, hydrogen sulfide, and other trace elements.
Pure methane can be used as a substitute to natural gas in pipe lines and can also be used for vehicle fuel. Biogas is used manly for generating electricity and heating houses and greenhouses. Increasing emissions of greenhouse gases, increase in water consumption and pollution, decrease in soil fertility, ineffective waste utilization and growing problems with deforestation are a part of unsustainable resources utilization all over the world.
Biogas technology is an important component in the chain of measures for fighting the abovementioned problems. In developing countries small biogas plants are used for production of energy and heat. Around 16 million households around the world use biogas energy for lighting, heating and cooking.
This number includes 12 million households in China, 3,7 million households in India and thousand households in Nepal [25]. The history of modern wide dissemination of biogas plants in China has started more than 50 years ago. First biogas plants have been built in the s by wealthy families.
From the beginning of the 70s research work and biogas technologies have seriously supported by Chinese government. In rural areas of China at the moment more than 50 million people are using biogas as a fuel.
Most of the plants are very simple and after some training farmers built and use them independently. From Chinese government provides around million US dollars yearly for supporting construction of biogas plants. In this way, the government has achieved growth of biogas plant number up to 1 million per year [24]. There are also several thousand industrial biogas plants in China and there are plans to increase their number. Figure 5. In India the development of simple biogas plants for rural households has begun in the 50s, although already in in Bombay the first biogas plant was built on the base of leper colony for digestion of solid and liquid waste.
There was a big increase of number of biogas plants supported by the government in s and today there are around 3,7 million of them operating in India. Ministry of untraditional energy sources has supported dissemination of biogas plants from the and has provided subsidies and financing for construction and operation of biogas plants, farmer training, opening and work of service centers. In Nepal the biogas technology support program provides technical expertise, financing and construction services for household biogas plants with digester volumes of m3.
Especially popular are plants with digester volume of 6 m3. Apart from energy and fertilizer production it has been noted that woman labor load in Nepal was decreased through decrease in time of gathering firewood and that increase of yearly savings from substituting 25 liters of kerosene and using biogas for heating instead of buying around 3 tons of firewood and coal.
During realization of biogas implementation program in Nepal around 60 private enterprises that manufacture biogas plants have been established and around micro financing organizations have provided financing for their construction. Quality standards for biogas plants have been developed and special organizations responsible for developing of biogas plant market have been established [24].
Gas and heat production in biogas plants is a growing market in many developing countries. In Philippines biogas plants produce gas for motors that grid rice and irrigate lands from the s. The investment in biogas plants by small private enterprises in India, Indonesia, Sri Lanka for example in textile industry, for drying up spices, bricks, rubber has been compensated within less that 1 season.
Usage of biogas technologies for utilization of sewage waste is widely used in Asia especially in India , and Latin America. Agricultural biogas plants have been widely implemented in developing countries and are used for energy, heat and fertilizer production and solution of water pollution problems.
Figure 6. Photo: Vedenev A. There during the first USSR laboratory and bioenergy production plant have been developed and manufactured. Industrial version of the plant has been calculated to digest the manure of 10 cows. To produce biogas, organic matter ferments with the help of bacterial communities. Four stages of fermentation move the organic material from their initial composition into their biogas state.
The first stage of the digestion process is the hydrolysis stage. In the hydrolysis stage insoluble organic polymers such as carbohydrates are broken down, making it accessible to the next stage of bacteria called acidogenic bacteria. The acideogenic bacteria convert sugars and amino acids into carbon dioxide, hydrogen, ammonia, and organic acids.
At the third stage the acetogenic bacteria convert the organic acids into acetic acid, hydrogen, ammonia, and carbon dioxide, allowing for the final stage- the methanogens. The methanogens convert these final components into methane and carbon dioxide- which can then be used as a flammable, green energy. This anaerobic process of decomposition or fermentation of organic matter happens all around us in nature, and has been happening for a very long time. In fact, the bacteria that break down organic material into biogas are some of the oldest multi-celled organisms on the planet.
More recently, the 20th century has brought about a renaissance of both industrial and small-scale biogas systems. In the 18th century it became clear to Flemish chemist Jan Baptise van Helmont that decomposing organic matter produced a combustible gas.
Soon after, John Dalton and Humphrey Davy clarified that this flammable gas was methane. The first major anaerobic digestion plant dates back to in Bombay. Not long after, in , the UK used anaerobic digestion to convert sewage into biogas, which was then used to light street lamps. For the next century, anaerobic digestion was primarily used as a means to treat municipal wastewater.
The goal was to decrease energy poverty in rural areas, and make cleaner cooking fuels more accessible in remote areas. Close to one third of the global population still uses firewood and other biomass for energy, causing devastating health and environmental problems. Link to blog post on developing countries.
Since then, family-sized biogas units are gaining more attention and popularity as both a means of reducing household waste and as a means of providing clean renewable energy to families throughout the world. In the past 15 years, countries around the globe are adopting biogas programs to make both household biogas systems and larger anaerobic digestion plants accessible, efficient, and convenient.
As landfills get illegally overloaded, and as the release of methane poses more worrying problems, the benefits of using biogas systems to convert waste into energy are increasingly more relevant and important. Many Uses of Biogas:Biogas can be produced with various types of organic matter, and therefore there are several types of models for biogas digesters. Some industrial systems are designed to treat: municipal wastewater, industrial wastewater, municipal solid waste, and agricultural waste.
Small-scale systems are typically used for digesting animal waste. And newer family-size systems are designed to digest food waste. The resulting biogas can be used in several ways including: gas, electricity, heat, and transportation fuels. For example, in Sweden hundreds of cars and buses run on refined biogas. The biogas in Sweden is produced primarily from sewage treatment plants and landfills. Another example of the diversified uses of biogas is the First Milk plant.
New anaerobic digestion plants like these with fascinating stories keep popping up every day!
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