Biogas is produced through Anaerobic Digestion (AD), in a bio-digester, of a wide variety of available organic materials and wastes, including sewage sludge, animal manure, municipal/industrial organic waste, crop residues, and specially grown energy crops.
Bio-digesters are a simple to operate, environmentally friendly alternative energy source with little carbon footprint. The use of bio-digesters in many developing countries is extensive.
Bio-digesters, through AD, take advantage of the energy that is naturally present in animal waste and kitchen waste. As these wastes break down, whether in the ground, a compost heap, landfill, or bio-digester, they release a methane rich biogas. Methane is a dangerous greenhouse gas 21 times more dangerous to the Earth’s atmosphere than CO2. In contrast to the other waste storage and disposal methods mentioned, a bio-digester traps the methane and stores it for heating, cooking, lighting or electrical generation.
In this way, bio-digesters provide a sustainable substitute for propane, kerosene, firewood or grid based polluting electricity. The use of a bio-digester can save hundreds of US dollars every year.
In addition to providing clean energy to the user, a bio-digester is also a source of high quality, organic fertilizer. During the biological process in the bio-digester, the waste is sterilized and odor is eliminated. Many studies have shown that the fertilizer that leaves a bio-digester after being processed has a higher nutritional value than the raw waste that is put in.
The following diagram shows the basic components of a Covered Lagoon Biogas Digester.