Biogas is a sustainable and eco-friendly form of renewable energy that is produced from organic waste. It is a versatile energy source that can be used for thermal and electrical purposes, and the slurry produced as a byproduct can be used as organic fertilizer. Biogas technology has been instrumental in generating green jobs in Nepal, with over 2800 villages out of a total of 3915 having biogas systems installed. This technology has also helped to improve health and sanitation while curbing deforestation caused by the use of firewood.
History
Waste to Energy (W2E) is a large energy project that has been recently adopted in Nepal. It aims to utilize the large amounts of organic waste produced by private and public organizations, business complexes, and other sources for thermal and electrical purposes.
Biogas is produced through anaerobic digestion or fermentation of organic waste by methanogenic bacteria. It is composed of 50-70% methane, 30-45% carbon dioxide, and trace amounts of other gases. About 25-30% of the dry matter of waste is converted into a combustible gas, and the remaining 70-75% of the total solids content becomes slurry.
The energy content of biogas is around 6-6.5 KWh/m3, and it has an ignition temperature of 650-750 o C. Biogas can be used as a fuel for any heating purpose, including cooking, or in a gas engine to generate electricity. It can also be compressed and used to power motor vehicles. Biogas is lighter than air, odorless, and burns with a clear blue flame, similar to Liquefied Petroleum Gas (LPG).
Domestic Biogas
The domestic biogas system is a widely implemented technology in rural areas of Nepal. It utilizes manure from domestic animals such as cows, oxen, buffaloes, and human waste/excreta as its primary source of feed. The by-product of this system, slurry, is an effective organic fertilizer that has replaced the use of chemical fertilizers, ultimately saving money and contributing to a clean and green environment in Nepal.
The Government of Nepal (GoN), in partnership with development partners and agencies, has been promoting the installation of biogas plants of varying capacities under this system, ranging from 2cu m to 8cu m. Two designs, GGC 2047 and a modified version of GGC 2047, are commonly used for these plants.
To date, approximately 0.3 million biogas plants have been installed throughout Nepal with the support of GoN and its partners. Biogas companies have played a crucial role in the development of the sector, with around 100 companies currently engaged in construction and promotional activities, identified with Pre-Qualification (PQ) identity.
Urban Domestic Bio-Gas
The Sahari Gharelu Biogas Plant (SGBP) is a new technological concept in Nepal for managing organic kitchen waste in urban and semi-urban households. It is based on the principles of a floating drum biogas plant and was introduced by the GoN after extensive research and experimentation. Currently, plants of 1 cubic meter capacity are available, but the system is designed to accommodate plants up to 4 cubic meters. Subsidies are available accordingly. The SGBP uses daily household organic waste, such as food leftovers and clippings, to produce biogas for cooking purposes. This system is more convenient for maintaining household cleanliness and mitigating indoor and outdoor pollution.
The system was introduced in the fiscal year (FY) 2069/70 B.S. (2012/13 A.D.) with subsidies for piloting in the Kathmandu Valley. Encouraging results in the initial phase have prompted the Alternative Energy Promotion Center (AEPC) to introduce the SGBP in feasible urban areas outside Kathmandu.
Large Bio-Gas
The Large Biogas System in Nepal is a result of long-term practices and international technological learning, specifically on the modified GGC 2047 model. This system encompasses plants with a capacity greater than 12 cubic meters and is categorized into Community, Commercial, and Institutional types.
- Governmental Institutions
- Vegetable Markets
- Commercial Farms
- Different Communities
- Co-operatives
- Hospitals
- Police and Army Offices
- Private Institutions
- Religious Institutions
- Schools and Colleges
- Social Organizations
- Prison Offices
Click the link below to see large bio-gas examples and designs.
Large Biogas Design and Description
For the Construction Manual of Biogas, please go through the link :
Construction Manual for Bio-Gas
Designing a biogas system with a 4 cubic meter capacity would involve the following brief steps:
- Site selection: Choose a location that is easily accessible and has adequate sunlight for the system to function optimally.
- Digging the pit: Excavate a pit with a depth of 2 meters and a width of 2 meters. The length of the pit should be at least 3 times the width.
- Building the inlet and outlet: Install a PVC inlet pipe and outlet pipe on opposite sides of the pit. The inlet pipe should be at least 50mm in diameter, while the outlet pipe should be at least 100mm in diameter.
- Constructing the dome: Build a dome-shaped cover for the pit using bricks and cement. The dome should be at least 1.5 meters high and should have a small opening at the top to allow for the release of excess gas.
- Installing the gas collection system: Install a gas collection system that connects the outlet pipe to a gas storage tank. The storage tank should be made of durable material, such as steel or high-density polyethylene.
- Adding organic material: Add organic material such as cow dung, vegetable waste, and kitchen waste to the pit. The pit should be filled to a depth of about 1.5 meters.
- Starting the biogas production: Fill the pit with water until it covers the organic material. Seal the pit with the dome cover and allow the biogas production to start. The gas can be used for cooking, heating, and lighting.
It's important to note that the design of a biogas system should be done by a qualified professional who can ensure that the system is safe and functional. Additionally, maintenance of the system is important to ensure its longevity and efficient operation.
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