Biogas Digesters

Biogas Digesters

This article relates to The Big Necessity

In The Big Necessity Rose George introduces readers to biogas digesters in rural China. Biogas digesters (often shortened to biodigesters) are permanent structures, usually constructed of cement, in which waste (human, animal and agricultural leftovers) decompose in the lower section causing the micro-organisms to release methane that is collected in the upper section.

There’s evidence that biogas was used to heat bath water in Assyria around 10 BC. The first modern-day biodigester was built in a leper colony in Bombay India in 1859. China began using biogas technology back in the late nineteenth century. By the end of 2005 there were about 17 million digesters, predominantly in rural areas, with about 50 million Chinese reaping the benefits. By 2020 biogas could potentially supply energy to one quarter of Chinese rural households. The reactors are commonly built in tandem with new pigsties, with toilets draining directly into them. In China, a biodigester can be built in about a week for about $80.



The benefits and uses for biogas technology are numerous. It can be tapped into immediately for cooking, as well as for the generation of heat and electricity. An efficient digester can supply 60% of a rural family's energy requirements. Biogas methane can even be harnessed as vehicle fuel. Further, it can be used to heat greenhouses, boosting photosynthesis as well as increasing silkworm egg hatching. The liquids and solids remaining in the digester act as extremely rich crop fertilizer. Finally, the digestion process greatly reduces disease transmission, since waste is no longer stored in open festering pits.

In addition to the many practical benefits to farmers, harnessing biogas is environmentally responsible. Methane is a key 'greenhouse' gas, second only to carbon dioxide in its effect on global warming.

Reports from the Institute of Science in Society and Canada's Office of Urban Agriculture offer further details on Chinese biogas digesters, as well as some interesting photographs and diagrams.

Biodigesters are becoming commonplace in virtually every developing country from India to Guatamala; and the developed world is slowly picking up speed, led by Sweden which is said to be 20 years ahead of countries such as the USA and UK.

Filed under Medicine, Science and Tech

This "beyond the book article" relates to The Big Necessity. It originally ran in November 2008 and has been updated for the July 2009 paperback edition. Go to magazine.