For thousands of years, crop stubble, stems, stalks, and branches have been the main fuel for cooking and for livestock feed in China's rural areas, but now, with greater economic growth and better living conditions this residue is less valuable and some farmers just burn it off, causing air pollution across many provinces.

Now, thanks to technology for turning it into activated carbon, with many applications, thousands farmers in Anhui and Henan provinces have discovered a new source of income, as carbon-bearing materials are changed into activated carbon using hot kiln gas.

Local farmers can use the slack season to work in teams to fire up the kilns that produce charcoal, which can bring in 170-180 yuan ($27-29) per day on average, which adds a lot to merely tilling the soil.

Most of the farmers are in their 40s or 50s who already have grandchildren at school. The company that oversees the business arranges for regular physical exams.

Workers filling up kilns with straw, on April 5. [Photo by Liu Yuan/Asianewsphoto]