Abstract : Biogas, a source of non-conventional energy is produced by fermentation of sludges. The sewage have collected through sewage pumping stations and treated in the primary and secondary treatment steps in sewage treatment plant at Jagjitpur, Hardwar. The Sewage Treatment Plant receives approximately 40 mld sewage from different pumping stations and 18
mld sewage is used for treatment at sewage treatment plant. Raw sewage consists of organic and inorganic solids in dissolved and suspended form with 90-99.9% of water. After treatment, huge amount of solid waste remains as sludge left with the treated water. Around 96X10 5 liters liquid sludge is being collected per day. In this process, the organic fraction of the waste is segregated and fed into a closed container, called biogas digester. Segregated waste undergoes biodegradation in the presence of methanogenic bacteria produce methane-rich biogas known as Biomethanation. Sludge from the anaerobic digestion can be used as a soil conditioner or composting. The present study was focused on biogas production from 1kg of sludge received 0.6 m 3 volume on calculating value. The maximum biogas production was observed in volume 84952.34 m
3 during summer and minimum volume of gas production was observed during winter as 76252.81 m 3 in 2008.The biogas is used as energy source for running the all devices of treatment plant and others as lighting, laboratory works etc.
Key words : Biomethanation, Biocomposting, Biogas, Sewage, Sludge
The success of the plant depends upon the construction. In this paper the construction process of the fixed dome design biogas plant developed by Gobar Gas Company in Nepal is presented.
Biogas production has several advantages in terms of economically as well as environmentally. Therefore, it has to be very important to know about production and utilization of this environmentally friendly technology. This manual explains the most of important aspects of biogas production and utilization.
1.1?????? What is biogas?
Biogas is a mixture of gases produced by microorganisms under anaerobic degradation (digestion) of organic water.? Major component of biogas is methane. Methane is a combustible gas and it can be used for energy generation.
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Methane (CH4)???????????????????????????????? ?????????????????????????????????????????????? 50% - 70%
Carbon dioxide (CO2)????????????????????????????????????????????????????????????????????? 25% - 40%
Various other gases (H2S, NH3, H2O vapour)???????????????????????????? 0%?? - 5%
In addition to above gases N2, CO, O2, and H2 slight concentrations occasionally present in biogas.
Biogas is often named according to its origin.? Biogas is named as landfill gas when they originate from landfill sites and named as sewage gas when they originate from sewage sludge.
The calorific value of biogas varies according to its percentage of methane since methane is the major component of biogas that can produce energy. Other constituents do not produce energy and they absorb energy, which are produced by the combustion of biogas.?
The calorific value of pure methane is 36000kJ/m3. Each 10% of methane can change the calorific value by 3600kJ/m3. For example, calorific value of biogas containing of 70% of methane is 25200kJ/m3. The actual calorific value of biogas is a function of its methane percentage, pressure and temperature. The actual values are very important parameter for the performance of the engines, which are running on biogas.
It can easily be used as an energy source especially for cooking, lighting, generating electricity and motive power. In addition, digested material, which comes out from the digesters, can be used as organic manure and there are various beneficial effects to environment in biogas production.
Production of biogas is a process of generation of renewable energy and a process of waste management as well.
Energy is very important for the development of a country. With the development, the demand for energy is also increasing. And also increase of population makes high demand on energy. Therefore, we have to spend lot of money for importing the petroleum since Sri Lanka do not have fossil fuel. Although we use biomass for major energy source, lots of petroleum fuels are needed for industries and to generate electricity. The energy sources and their contribution and the sectors of energy usage and their percentages are given below.
Almost all the biomass energy is used for household purposes, especially cooking. The limited amount of biomass is used for industries such as bricks & tile, tea, rubber, coconut, etc. Use of biomass as an energy source is compelled to increase deforestation.? Therefore, use of biogas as an energy source for household purposes reduce the deforestation of the country.
In year 2000, cost of petroleum imports was Rs 67187 million and it is considerably high when compared with national income. Considerable amount of petroleum (basically LP gas) is also used for cooking and it can be replaced by biogas. As such the use of biogas save the national income, which is needed to import petroleum fuels.
Uses of firewoods in unventilated kitchens create health problems in housewives due to inhalation of unidentified substances in smokes that are produced by burning of biomass. But biogas burners do not produce other gases than carbon dioxide. Therefore, use of biogas improves the health of the housewives.
Methane is a green house gas by which increase the global temperature 25 times more than carbon dioxides does.? As such production of methane is not environmentally friendly and it can cause to increase global temperature. The estimated anthropogenic green house effect is 15% from methane and 60% from carbon dioxide. The atmospheric methane concentration is increasing at a rate of 0.8-1.0 % per year. The almost all methane emissions are from low land paddy fields, ruminant excreta and landfill sites. Ruminant excreta naturally produce methane and it increases the methane concentration in the atmosphere. But if we can produce methane from animal excreta in control condition and it can be used for energy purposes. Then methane emission to atmosphere is reduced and decreases the global worming. Lowland paddy cultivation is also one reason to increase methane emission to atmosphere. It has been found that emission of methane from paddy cultivation varies from 20-150Tg per year. And also researches showed that methane emission from paddy fields is higher after harvesting due to degrading of straw at the field. Therefore, if we can use straw for biogas production methane emission can be reduced and useful energy could be generated. In the same way, the organic wastes, which are a large part of land filling, can be used for biogas production and it will also reduce the emission of methane to the atmosphere.
Conventional energies such as petroleum, coal and LP gases are not unlimited. The estimated recovable years for petroleum, coal and gases are 43, 232 & 65 years respectively. Therefore, it is beneficial to find out good sources of renewable energies for our requirements. In considering Sri Lanka almost all hydropower capabilities has already been used and wind and biomass energy sources, as renewable energy is a good option.
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