Beijing has a 200,000-strong army of recyclers and garbage collectors, who dispose of 20 million residents' waste.

Sun Youzhi is one of them. The 29-year-old from central Henan province's Gushi county has a small recycling business in a residential area near the Bird's Nest - the 2008 Beijing Olympics' main stadium.

"There are a lot of tourists around here," Sun says. "I collect a lot of empty water bottles."

Sun has spent ten hours a day collecting waste at his residential area for the past four years.

"People sell water bottles, but few know where they end up," Sun says.

He buys waste from local residents and garbage collectors. In his eyes, waste materials like empty bottles will start a new journey from his recycling station.

Sun transports his waste every evening to a scrap market six kilometers away, in suburban Dongxiaokou town.

Dongxiaokou is Beijing's largest waste trading center. Scores of collectors deal in waste paper, scrap metal, plastic and foam.

Waste is sorted and processed in the town. Waste paper dealers pick out old books and sell them to flea markets. Old newspapers are sorted and sent to paper mills, while paper cartons end up in packing stations.

Dealers compress and shred water bottles after removing their caps and labels. They sell the plastic shreds to chemical plants in neighboring Hebei province, where it's turned into polyester threads used to make clothes.

"The polyester in our T-shirts is very likely from water bottles," says Sun, who once worked in a plastic-shredding plant.

New China's first recycling stations were established shortly after the country was founded in 1949. Goods were scarce then.

The stations were state-owned and run. But most have shut down amid national economic reforms and urbanization.

Garbage collectors and recyclers in cities today are mostly migrant workers. About 98 percent of the capital's 120,000 registered recyclers come from three provinces -- Henan, Anhui and Hebei, the Beijing Resource Recycling Association reports.

"The actual figure is more like 200,000 if the unregistered recyclers are counted," says Beijing University of Technology researcher Cheng Huiqiang, who specializes in the economics of recycling.

Some recyclers pick up trash from the city's streets, while others go door-to-door. Some, like Sun, run their own businesses. They are ubiquitous in Beijing, gathering, sorting and processing wastes to feed the manufacturing machine.

China Resource Recycling Association Vice-Secretary-General Fu Hongjun says: "The recyclers are efficient. They work very hard transforming trash into treasure for themselves and the country."

Sun's family of nine depends entirely on recycling. His parents work for a water bottle dealer, who pays them to remove caps and labels from bottles before they are recycled. His brother-in-law works with him. Both have children and their wives look at kids at home.

Sun and his brother-in-law collect an average of 3,000 empty water bottles, a tonne of waste paper, 100 kg of iron scrap and nearly 200 kg of plastic waste a day.

Sun says they each earn about 150 yuan (25 U.S. dollars) a day.

"We've made less money this year because the economy is gloomy," Sun says. "But it's still better than returning to our hometown."

About 4.67 million tonnes of recyclable waste was collected in Beijing in 2010. In the same year, 6.35 million tonnes of trash ended up in the city's landfills, municipal government figures show.

Cheng views recycling as saving. Recycling a tonne of waste paper can save three cubic meters of timber. One tonne of scrap metal can be processed into 0.8 tonnes of new metal.

Cheng says three million tonnes of empty water bottles are thrown away in China a year. If all these were recycled, 18 million tonnes of crude oil could be saved, he says.

"In that sense, there are invisible oil fields, forests and mines in the cities," Cheng says.