With the help of a consulting firm in Guizhou, Kaiyang's methane program has been listed as one of China's CDM programs, and has applied for registration in March as a UN CDM program.

"If all goes well, the program will be registered by the UN CDM Executive Board next October, so we can start the real deal," says He Junyuan, general manager of Guizhou Zhongshui Hengyuan Project Management and Consulting Co. Ltd.

Japan's biggest carbon trading company Eco Asset is willing to buy the reduced emissions by Kaiyang's 15,000 methane pools for 8.2 euros (US$12.3) per tonne, says He.

If the deal is clinched, the county could earn 430,000 euros (US$645,000) a year, with 60 percent distributed to methane farmers.

"The cost of a methane pool is 30 percent construction and 70 percent maintenance," says Ai Xinglong. "If it's not well-maintained, it will not produce biogas, then the preliminary investment will be a total waste.

"In relatively poor regions like Guizhou, many people can't afford the cost of methane pool maintenance."

Ai Guangzeng's four sons are all working away from home, so the elderly hire young people to clear the residue in their methane pool and stir the biogas slurry.

"We have to spend hundreds of yuan on the cleaning, which is very hard," she says.

China has been promoting biogas utilization in rural areas to make use of renewable energy and protect the environment.

Experts estimate that binding the CDM with China's rural methane program will help fund construction and maintenance of methane digesters, ensuring normal operation of big methane projects, and promoting exchanges of technologies and experiences with other countries.

According to the Agriculture Ministry, as of 2008, the number of rural households using biogas in China was 30.5 million.

A total of 12.2 billion cubic meters of methane was produced per year by the household methane pools and 39,500 large biogas projects, which process livestock excrement and other agricultural waste into the gas.

The total methane burnt in the rural areas is equivalent to 18.5 million tonnes of coal, which would produce more than 45 million tonnes of carbon dioxide.