Rural families can slash their energy costs, improve their health and help preserve local forests by harvesting natural gas from rotting manure, researchers argue.
They say the use of biogas plants, which store the decomposing manure and capture the natural gas it releases, could improve rural farmers' livelihoods, while protecting the environment.
Biogas digesters are used across the Indian subcontinent, Africa, and Latin America, but few rigorous studies have been done of their overall costs and benefits. So Govindasamy Agoramoorthy of Tajen University and Minna Hsu of National Sun Yat-sen University, both in Taiwan, surveyed 125 rural households in India that use biogas plants.
These plants, also called digesters, typically take the form of a sealed brick-lined pit, in which the manure ferments. The biogas that escapes from the manure is half carbon dioxide, but about half methane, the main component of natural gas, and is piped off to be burnt in stoves or gas lamps.
Many families in these rural Indian areas own several cows and buffalo, supplying them with a few dozen kilos of manure a day – enough to keep the digester well supplied.
After investing in biogas plants, families were found to cut back consumption of both firewood and kerosene by about 60%, Agoramoorthy and Hsu found. The savings on fuel mean the plants, which cost about $250 to install, pay for themselves in about 2 years.
Before having a digester, many families scavenged firewood illegally. Afterwards, Agoramoorthy says, "villagers saved more money and also had less negative impact on the forests."
Replacing kerosene and firewood with cleaner-burning biogas also greatly reduces indoor air pollution, a leading cause of death for rural villagers, especially women and children.
After starting to use biogas in the home, the study found, families made about half as many visits to the doctor for smoke-related problems such as respiratory infections.
The farmers also spread the leftover slurry from the biogas plant on their fields, reducing their need for chemical fertilisers, and saving them even more money.
"The usage [of biogas plants] is still low in villages, so governments need to promote biogas in villages of not only India, but also in other countries," Agoramoorthy says. "Even developed countries should promote this."
The study is quite original, says Peter Haas of the Appropriate Infrastructure Development Group, a non-profit organisation that operates in Guatemala and Haiti. "I have not seen a study before that draws a solid link between installation of a biodigester and health improvements."
"People want biodigesters because of the cost-savings benefits and energy production," Haas says. "The health impacts are really just an added bonus."