Biogas is a type of bio-fuel that is naturally produced from the decomposition of organic waste. When organic matter, such as food scraps and animal waste, break down in an anaerobic environment (an environment absent of oxygen) they release a blend of gases, primarily methane and carbon dioxide.  Because this decomposition happens in an anaerobic environment, the process of producing biogas is also known as anaerobic digestion.

Anaerobic digestion is a natural form of waste-to-energy that uses the process of fermentation to breakdown organic matter. Animal manure, food scraps, wastewater, and sewage are all examples of organic matter that can produce biogas by anaerobic digestion. Due to the high content of methane in biogas (typically 50-75%) biogas is flammable, and therefore produces a deep blue flame, and can be used as an energy source such as house hold cooking gas.

The Ecology of Biogas

Biogas is known as an environmentally-friendly energy source because it alleviates two major environmental problems simultaneously:

1. The global waste epidemic that releases dangerous levels of methane gas every day
2. The reliance on fossil fuel energy to meet global energy demand

By converting organic waste using animal waste or other biodegradable from plants; into energy, biogas is utilizing nature’s elegant tendency to recycle substances into productive resources. Biogas generation recovers waste materials that would otherwise pollute homes, villages and larger landfills; prevents the use of toxic chemicals in sewage treatment plants, and saves money, energy, and material by treating waste on-site. Moreover, biogas usage does not require fossil fuel extraction to produce energy. 

Instead, biogas takes a problematic gas, and converts it into a much safer form.

Biogas Plants

As opposed to letting methane gas release to the atmosphere, biogas digesters are the systems that process waste into biogas, and then channel that biogas so that the energy can be productively used.  There are several types of biogas systems and plants that have been designed to make efficient use of biogas. While each model differs depending on input, output, size, and type, the biological process that converts organic waste into biogas is uniform.

Types of Plant

So far, there are mainly two types of plant that can be built and disseminated in Nepal.

• Floating-Drum Plant: The floating-drum plantbased on the Indian type (with an overflow at the top rim of the cylindrical digester instead of an outlet pipe) and 
• Fixed-Dome Plant: The fixed-dome plantswith a flat floor, cylindrical digester and a dome made of concrete. The market-oriented procedure soon led (and earlier than in India) to fixed-dome plants becoming the standard model: since 1980 fixed-dome plants have primarily been disseminated mainly for reasons of cost. These are offered in digester sizes of between 4 m³ and 50 m³.

The Nepali fixed-dome plant is a development peculiar to Nepal which has been modified in various ways over the years.