Home > AIDA, bacteria, Biodigester, dung, methane, sanitation > a look at Biodigesters

a look at Biodigesters

Sun, 06Sep2009

source: The Appropriate Infrastructure Development Group (AIDG)

Summary: Biodigesters convert organic wastes into a nutrient rich liquid fertilizer and biogas, a renewable source of electrical and heat energy. Their use is widespread in developing countries, particularly India, Nepal, China and Vietnam. Biodigesters help families by providing a cheap source of fuel, preventing environmental pollution from runoff from animal pens, and reducing diseases caused by the use of untreated manure as fertilizer.

Biodigesters produce biogas, an alternative fuel source

As organic wastes break down, whether in the ground, a compost heap or landfill, they release methane (a potent greenhouse gas that traps heat at 23 times the rate of carbon dioxide). A biodigester or biogas system is a waste-management solution that traps methane as it is produced, making it available for heating or cooking or even electricity generation. By preventing methane from venting freely into the atmosphere, these systems can help reduce emissions that contribute to climate change.

Biogas is a sustainable substitute for the propane, kerosene, and firewood that many rural families in developing countries use for their domestic energy needs.  For those families that buy their fuel, a biodigester can save them hundreds of U.S. dollars every year. For those that gather their own firewood, it can reduce a family’s workload (particularly women and girls) and help prevent the deforestation prevalent in many of these areas.

Biodigesters also create high quality fertilizer


In addition to providing fuel, these systems offer an environmentally friendly way of treating waste. As waste is processed in a biodigester, it is sterilized by methane-producing bacteria and the high-methane environment; over 90% of protozoa, cysts and disease-causing bacteria, such as E. Coli, are killed. The effluent that remains after gas production is a high quality organic fertilizer that can be safely used on food crops. Some studies have shown that this liquid fertilizer has a higher nutritional value than the feedstock initially put in. Families, for whom AIDG has installed biodigesters, have reported seeing the quality of their crops improve dramatically after only one year of using biodigester fertilizer.

The Good:


  • Provide clean and renewable energy. Families use less firewood, decreasing deforestation, save money and have accessible fuel.
  • Reduce greenhouse gas emissions. The combustion of biogas produces lower greenhouse gas emissions than typical methane emissions from a waste lagoon or septic system.
  • Reduce contamination of surface water, groundwater and other resources.
  • Reduce odors and pathogens. Biodigesting sewage can reduce the parasitic and pathogenic bacterial counts by over 90%.
  • Convert waste into high quality organic fertilizer. Families can obtain improved crop yields and save money.
  • Can accommodate a wide variety of organic wastes including animal manure, night soil, crop stalks, straw, slaughterhouse wastes, biodegradable garbage and wastewater.

While waste needs to be added and effluent removed on a daily basis, biodigesters are typically very reliable systems that require little maintenance.

The Bad:

Biodigesters function poorly in colder climates unless an external heat source is applied. The methanogenic bacteria responsible for generating biogas require temperatures well above freezing (optimal temperature ranges – mesophilic: 30-40°C; thermophilic: 50-60°C), so biodigesters are not ideal in cooler areas.

In order to keep the anaerobic digestion process going continually, biodigesters require a daily amount of work and a consistent source of organic materials:

  • Each day, the waste to be added needs to be mixed with water and/or ground to a liquid state. Manure is naturally manure is water-soluble, but kitchen scraps, such as banana and orange peels need to be ground into smaller which can be time consuming.
  • Each day, the biodigester effluent needs to be removed from the effluent tank.

Biogas provides 20% more energy than if dung/wastes were burned directly, but much less compared to fuels such as propane and natural gas.

The Bottom Line:

Biodigesters are an excellent technological solution for families and farmers that want a combined sanitation and energy solution, who can manage the daily feeding required to produce adequate biogas, and who have use for lots of fertilizer.  more…

  1. Virra Padernal
    Sat, 30Jul2011 at 12:08 pm

    Can you please tell me who is the author of this article? THanks

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