WHEN Xu Guifang sees a pile of filth, she thinks of one thing - power. Mrs. Xu is one of 30 million Chinese peasants who can't stand to waste perfectly good waste. Instead, she turns it into energy to cook food, drive engines, and illumine her thatched home.
``As far as I'm concerned, there's no such thing as waste,'' she says, firing up a clay burner beneath a wok.
The Xu family and the 30 other households at Shunfeng (favorable wind) village ferment a mixture of chaff, barnyard manure, night soil, and water in underground tanks. The resulting methane gas meets 80 percent of their energy needs.
Peasants like the Xus make China the world's largest biogas user. They show farmers in other developing countries how to exploit an energy source that saves money and manpower and reduces rural pollution, United Nations officials say.
Tapping its twin biogas tanks since 1981, the Xu family no longer forages for firewood or buys large amounts of coal or kerosene. Chaff once heated their wok. Now they sell the chaff to a paper company or add it to pig fodder as roughage.
The Xus save about $50 a year in energy costs with their homemade methane, a significant financial fillip when the average annual income for a peasant is $140.
``I use gas from my tank all the time - I don't know why everyone doesn't install one,'' Xu says, lighting a gas-powered lamp she claims is as bright as a 60-watt electric light bulb. Some of her neighbors use methane generated in large tanks to power milling and threshing machines, water pumps, electric generators, and other internal-combustion engines.
Use of biogas tanks has helped reduce pollution and soil erosion in Shunfeng and in the thousands of other Chinese villages that make the most of waste, says Yang Kejun, a senior engineer at the biogas research institute in nearby Chengdu. Peasants who produce biogas no longer strip forests for firewood or dump untreated sewage in fields, ponds, or streams, Mr. Yang says.
Yet not every peasant is able or willing to make gas from gunk. Climates cooler than that in southwestern Sichuan Province inhibit fermentation, and many Chinese and foreign peasants prefer to do nothing more with waste than dispose of it, Yang says.
Most peasants in China's richer, eastern provinces spurn biogas digesters as symbols of impoverishment. Instead, they buy conventional fuels, saysGeorge Lai Chan, an environmental engineer at the Guangzhou Institute of Geography.
The institute has not yet persuaded leaders of Chinese cities to exploit biogas on a large scale. Consequently, home-grown methane, while meeting 40 percent of the energy needs of many Chinese peasants, accounts for less than 1 percent of the country's total power output.
Nevertheless, the prospect of getting a spark from sewage has attracted engineers from 60 countries to the Biogas Institute in Chengdu. With the help of a $4 million grant from the UN Development Program, the institute since 1981 has trained 200 technicians from both industrialized and third-world countries to construct fermentation tanks of various sizes.
``With the world facing finite energy resources and a growing pollution problem, many factories and households would do well to use digesters to treat sewage and other wastes and generate energy,'' Yang says.