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This article is from the In-Depth Report China, the Olympics, and the Environment

Smoky Home: Cleaning Up Indoor Air with Human Waste

The secret weapon in the fight against indoor air pollution—and deforestation—in China might be decomposing human waste
biogas-burner



David Biello/ © Scientific American

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LIMING, CHINA—Fourteen-year-old Feng Yu's parents used to have to carry as much as 66 pounds (30 kilograms) of wood daily to fuel the cooking stove in their kitchen. Although the old stove was in a separate building from the two-story wooden living quarters where she sleeps, its smoky smell still permeates its corner of the walled compound the family calls home and the walls are still blackened by years of smoke.

View a Slide Show of a Chinese Biogas Home

Now the head of this mountain village in the southwest of China—roughly 1,300 miles (2,100 kilometers) from the capital Beijing—has installed a stove capable of producing the same heat with less wood at the urging of his environmentally-educated daughter, one of the founding members of a club called Earth Helpers at the local middle school. "We save a lot of wood," says Yu. "My parents do not work as hard as before and it is also a benefit for the forest."

Villages not far from this one in the red sandstone mountains of Yunnan Province used to be dark in the middle of the day 30 years ago, according to local residents. Tall forests blocked out the sunlight, while providing the firewood, animal bedding, fertilizer and even food that sustained these farming communities. The local Naxi and Lisu ethnic minorities' religions even forbade cutting certain trees and they took the names of local animals—birds, bees and bears—in effect making them their ancestors.

Now the hillsides are covered in sparse, spindly pines rather than a vibrant mix of foliage. Erosion scars slice down mountainsides, serving as the sluices for timber. In addition to boosting floods, the massive deforestation has killed off the wild forage and animals that sustained area residents when farming failed. Although much of that timber went to feed growing commercial demand for wood for construction or furniture, the primary cause is local: fuel for home fires.

Both local and international environmental and public health groups have tried to address this problem by bringing more efficient stoves into the countryside, which burn only half as much wood and are better at funneling the resulting smoke outside.

The ultimate answer, however, may lie in a more unique technology: so-called biogas, or, as the Chinese call it, marsh gas, made from decomposing waste. Buried concrete tanks store human—and animal—waste that is digested by bacteria and turned into marsh gas, or methane, which can then be burned for cooking. Yu’s father, for example, built such a system in their house last year. "We need to find something that is both a benefit to the locals and to forest conservation," says Li Shiyang of Rare. "The problem is fuel wood collection so we promote efficient stoves and biogas. But if you just give them everything for free then it won't work."

In Liming, local communities used to harvest wood on a rotational basis, assigning mature trees by lottery and strictly policing how much could be cut, even as other cultural practices—such as cooking the fodder for pigs—added more pressure. "We think the meat is more tasty that way," explains Cun "Angela" Yan Fang, who went from guiding Western tourists as a local Naxi to guiding her fellow locals through the biogas technology and environmental conservation promoted by Western environmental groups such as the Nature Conservancy and Rare. But "if we do it for all animals we'll be finished."

A population boom—as well as the cultural changes wrought by Communism—put increasing pressure on local natural resources in recent decades. "As local people, we cannot live without wood," says Cun. "Fuel wood consumption is the big thing we have to face."

Smoky, low stoves see the bulk of that wood; aging hunks of iron that belch much of the residue of their burning—despite chimneys—into the homes themselves. World Health Organization and U.S. Environmental Protection Agency soot "standards are 25 micrograms per cubic meter over 24 hours. These houses have 400 to 1,100 micrograms per cubic meter over 12 hours," says environmental epidemiologist Jill Baumgartner of the University of Wisconsin–Madison, who has researched indoor air pollution in the region. "Air pollution in these households is really, really high."

That has helped to boost rates of cardiovascular disease and other health effects of such air pollution, a problem that combined with the health effects of air pollution from industrial coal burning that costs China roughly $66 billion dollars per year and causes 760,000 premature deaths, according to a World Bank report.

That expense helps to put the costs of marsh gas systems into perspective. Although such systems can cost about 2,000 yuan ($300) per house to install, they have also proved popular—at least with officials such as the village heads in communities from Liming in the west to Shijialing in Shandong Province in the east. "More than 50 households use marsh gas," says Shijialing's leader Shi Tongkang, or more than one-third of homes. "We have developed animal husbandry as well to collect the waste."

The government—and non-governmental groups such as the ones Cun works for—subsidize installation, but they don't pay the full price. "It's just too easy if they don't make a contribution," says Rare's Li. "Then they don't take it seriously."

And that has been amply proven by the more than 30 years of promoting such systems, starting with Mao Zedong's drive to adopt them in the 1970s, which did not prove a lasting success. But such marsh gas can provide for a home's cooking needs and it emits far less pollution than burning wood, charcoal or even coal in a stove. As a result, more than 18 million rural households have adopted the fuel source, according to the Chinese government—a number they would like to boost to 40 million by 2010.

The benefits such marsh gas systems provide seem to be as bright as the blue flame in the biogas burners—at least to the next generation like Yu, who treasures the remaining forest. And it certainly won't hurt her lungs either.

View a Slide Show of a Chinese Biogas Home

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