Bio Gas

Biogas typically refers to a (biofuel) gas produced by the anaerobic digestion or fermentation of organic matter including manure, sewage sludge, municipal solid waste, biodegradable waste or any other biodegradable feedstock, under anaerobic conditions. Biogas is comprised primarily of methane and carbon dioxide.
Depending on where it is produced, biogas is also called:
• swamp gas
• marsh gas
• landfill gas
• digester gas
Biogas containing methane is a valuable by-product of anaerobic digestion which can be utilised in the production of renewable energy.Biogas can be used as a vehicle fuel or for generating electricity. It can also be burned directly for cooking, heating, lighting, process heat and absorption refrigeration.
Benefits of Biogas in Nepal
 Bio gas can be use in place of Lp gas and other petrolium products.
 It helps to utilize the waste materials.
 Organic substances will be used for biogas .
 Unimployment problem of nation will reduce.
 Fertilizer of cattles and other animals as well as human will be utilized .
 It may help in peoples income rate.
 Government and nongovernment companies are helping us so it is cheaper to install and maintain.

Biogas and anaerobic digestion
Main article: anaerobic digestion


Biogas holder and flare
Biogas production by anaerobic digestion is popular for treating biodegradable waste because valuable fuel can be produced, while destroying disease-causing pathogens and reducing the volume of disposed waste products. It burns more cleanly than coal, and emits less carbon dioxide per unit of energy. The harvesting of biogas is an important part of waste management because methane is a greenhouse gas with a greater global warming potential than carbon dioxide. The carbon in biogas was generally recently extracted from the atmosphere by photosynthetic plants, so releasing it back into the atmosphere adds less total atmospheric carbon than burning fossil fuels.
Recently, developed countries have been making increasing use of biogas generated from both wastewater and landfill sites or produced by mechanical biological treatment systems for municipal waste. High energy prices and increases in subsidies for electricity from renewable sources (such as renewables obligation certificates) and drivers such as the EU Landfill Directive have led to much greater use of biogas sources
Landfill gas
Landfill gas is produced from organic waste disposed of in landfill. The waste is covered and compressed mechanically and by the pressure of higher levels. As conditions become anaerobic the organic waste is broken down and landfill gas is produced. This gas builds up and is slowly released into the atmosphere. This is hazardous for three key reasons:
• Risk of explosion
• Global warming through methane as a greenhouse gas
• Volatile organic compounds (VOCs) as precursor to photochemical smog
Biogas composition
The composition of biogas varies depending upon the origin of the anaerobic digestion process. Landfill gas typically has methane concentrations around 50%. Advanced waste treatment technologies can produce biogas with 55-75%CH4
Typical composition of biogas
Matter %
Methane, CH4 50-75
Carbon dioxide, CO2 25-50
Nitrogen, N2 0-10
Hydrogen, H2 0-1
Hydrogen sulphide, H2S 0-3
Oxygen, O2 0-2
*often 5 % of air is introduced for microbiological desulphurisation
Safety
The methane in biogas forms explosive mixtures in air. The lower explosive limit is 5% methane and the upper explosive limit is 15% methane.
Applications of renewable natural gas in Nepal
In this form the gas can be now used in any application that natural gas is used for. Such applications include distribution via the natural gas grid, electricity production, space heating, water heating and process heating. If compressed, it can replace compressed natural gas for use in vehicles, where it can fuel an internal combustion engine or fuel cells.
Cooking
Gober gas is a biogas generated out of cow dung. In Nepal, gober gas is generated at the countless number of micro plants (an estimated more than 2 million) attached to households. The gober gas plant is basically an airtight circular pit made of concrete with a pipe connection. The manure is directed to the pit (usually directed from the cattle shed). The pit is then filled with a required quantity of water (usually waste water). The gas pipe is connected to the kitchen fire place through control valves. The flammable methane gas generated out of this is practically odorless and smokeless. The residue left after the extraction of the gas is used as biofertiliser. Owing to its simplicity in implementation and use of cheap raw materials in the villages, it is often quoted as one of the most environmentally sound energy source for the rural needs.