Practitioner's Tool / Chinese Dome Digester
Background
The Chinese dome digester, or fixed dome digester, has been used since the 19th century in the coastal areas of China. It has become the standard construction design for biodigesters in other countries. The major difference between the Chinese dome digester and other biogas digesters is its fixed dome shape at the top. This shape restricts the amount of gas that can be collected and stored. It is constructed using bricks and mortar and requires experienced laborers to construct the dome in the upper section. It also has to be airtight to prevent the leakage of methane into the environment.
How it Works
Human, livestock or poultry waste is fed through an inlet pipe to the digestive chamber. The temperature in the digester is critical to decomposition and methane production because digestive bacteria typically produce methane at 30 to 60 degrees Celsius. The gas produced in the chamber is mostly methane (50-75%) and carbon dioxide (25-50%) with minute amounts of nitrogen, hydrogen, hydrogen sulfide and oxygen. Digestion time can take a few weeks to a couple of months, depending on the type of waste and temperature within the digester. The slurry produced as a by-product can be removed at the outlet and used as fertilizer. One cubic meter of biogas produce is estimated to feed a family of five for a day. Human waste and livestock manure are big sources of pollution of land, rivers and lakes in many rural communities. The biodigester serves as a clean, effective way to eliminate this source of pollution while utilizing methane as a renewable source of energy. The methane produced is combustible and can be a valuable resource to households in rural developments. It provides a safe alternative to the use of wood as fuel for cooking and reduces environmental degradation, health problems and competition for fuel resources. The slurry derived from the digester is rich in nutrients essential to crops and animals and is thus a valued fertilizer and can be used as organic manure on agricultural land.
For more information on how to design you biodigester, see the Biogas Training Center's Chinese Dome Digester Design Guide.
