Biogas digester
A biogas digester is a technology designed to capture and utilize gas produced from the anaerobic decomposition of organic waste, providing a renewable energy source. This process often makes use of manure, human excreta, food scraps, and other vegetative materials, adapting to various local contexts and needs. Biogas digesters can be found in diverse settings, ranging from large industrial farms to small household units, and even at waste treatment facilities and landfills. The biogas produced is primarily composed of methane and carbon dioxide and can be used for cooking, lighting, electricity generation, or sold on the national grid.
The design and scale of biogas digesters vary widely, with large facilities processing waste from thousands of animals and small-scale systems catering to individual households. These digesters not only provide a sustainable energy alternative but also contribute to environmental benefits by reducing greenhouse gas emissions. Additionally, they improve sanitation and provide organic fertilizer, enhancing the quality of life in communities that may lack reliable energy sources. Successful biogas programs, like those seen in Nepal, demonstrate the potential for biogas technology to transform energy access, environmental sustainability, and public health, while serving as a model for implementation in other regions.
Subject Terms
Biogas digester
Summary: Biogas digesters capture gas released by the decomposition of waste and utilize that gas as a local energy source.
Producing biogas through anaerobic digestion of waste is a technology that has been adapted globally to fit local needs, geography, and input materials. Biogas is often produced from manure, but human excreta, garbage, and vegetative scraps are also used. Biogas digesters are found on large industrial farms, on small subsistence farms, at waste treatment plants, at communal pit toilets, and at landfills. Biogas can be sold into a national electric grid, compressed for use as fuel, or simply piped directly indoors for cooking and lighting. All animals produce waste; biogas digesters of all sizes allow households, towns, and regions to capture and utilize locally produced energy while reducing greenhouse gases.
Biogas from decomposing organic waste produces gas that is roughly 60 percent methane and 40 percent carbon dioxide but may contain traces of other gases. Digesters are typically fueled by cattle, swine, or poultry manure. Other organic waste, such as food scraps or human excreta, are also viable. Biogas digesters vary in design, depending on input material, volume, location, and the gas’s end use. They typically include a manure collection system, anaerobic digester, biogas handling system, gas use device, and storage for effluent. Biogas digesters also range in size and application, from those used by subsistence farmers with two cows in developing countries to those used in massive operations involving thousands of cattle in the United States. China boasted more than 30 million biogas digesters as of 2020, and India more than 3.8 million. Regardless of size, the purpose is to use the gas produced from decomposing manure. A side benefit is that the use of biogas helps to stem greenhouse gas emissions.
Industrial Biogas
Biogas digesters in the United States are often large, processing manure from hundreds or thousands of animals. They involve either lagoons with flexible covers or tanks that can be partially underground with either flexible or fixed dome covers. Such large systems usually have automated systems for delivery and mixing of the manure. The gas produced is often treated on-site to remove impurities before the gas is used. Biogas can be used to generate electricity generation for farm use or for sale to electric companies, to generate heat, and to convert to compressed natural gas. The effluent is separated into liquid and solid, with the liquid becoming fertilizer and the solid used for animal bedding or landscape products. Engineers continue to envision new uses of locally produced renewable biogas, even for fueling large data centers for companies like Google or Hewlett Packard.
Household Biogas
Developing countries are home to both large industrial biogas digesters and small-scale domestic biogas digesters. Domestic biogas digesters can operate on manure from just one cow. Families are encouraged to attach a toilet to their biogas digester both to improve sanitation and to increase biogas generation. Domestic biogas is promoted to farmers as an alternative cooking fuel to replace firewood or fossil fuels purchased in the market. Domestic biogas systems are simpler in design than their large-scale counterparts, but the principle remains the same. Manure is collected and mixed with water manually and released into an underground dome tank. As the gas rises, the pressure pushes the solid effluent out into a holding area; this will be used later as fertilizer. The gas collecting in the dome is piped directly indoors for use in the kitchen to fuel biogas burners or for lighting.
Benefits of Biogas
Biogas has environmental, economic, and social benefits. Large industrial biogas digesters help control odor and potential pollution from large-scale animal enterprises. Biogas digesters reduce greenhouse gas emissions by burning and utilizing methane, which if emitted into the atmosphere would act as a greenhouse gas; as a result, a potential environmental danger is repurposed as a renewable source of energy. The use of biogas contributes further to environmental protection when replacing traditional biomass, such as firewood, which releases carbon dioxide when burned and contributes to deforestation when trees are cut down to collect it. Digesters of all sizes reduce greenhouse gas emissions, which has earned for biogas the status of a clean development mechanism whose emission reductions can be traded on global carbon markets.
Domestic biogas digesters directly impact quality of life by providing clean, renewable energy to places that may lack modern energy services, particularly when replacing firewood, which is time-consuming to collect and may cause respiratory illnesses when burned. Nepal’s biogas program is a success story in the transformative power of biogas for rural farmers. Biogas helps conserve forests by reducing reliance on firewood, improves health by removing smoke from kitchens, improves sanitation through attached toilets, provides organic fertilizer from the effluent, and lightens the burden of securing daily energy needs. As of the 2020s, millions of domestic biogas digesters have been built through the fostering of a strong private-public partnership to create a biogas sector with competitive contractors, quality control, access to microfinance, and government subsidies to farmers. Nepal’s biogas program has proven so successful that the model has been exported to other countries.
Bibliography
Bajgain, Sundar, and Indira Shakya. Nepal Biogas Support Program. Kathmandu: SNV Netherlands Development Corporation, 2005.
"Biogas Digester Explained." Renergon, 2024, www.renergon-biogas.com/en/biogas-digester-explained/. Accessed 30 July 2024.
“AgSTAR: Biogas Recovery in the Agriculture Sector.” Environmental Protection Agency, 22 May 2024, www.epa.gov/agstar. Accessed 30 July 2024.
Vance, Ashlee. “One Moos and One Hums, but They Could Help Power Google.” CNBC, May 19, 2010, www.cnbc.com/2010/05/19/one-moos-and-one-hums-but-they-could-help-power-google.html. Accessed 30 July 2024.