A large-scale pig farm on the outskirts of Shanghai is proving that industrial agriculture doesn't have to be a burden on the environment. The Songlin Ecological Agricultural Zone operates a "closed-loop" system that transforms animal waste into high-value fertilizer and green energy.

Located in Jinshan district, the facility raises approximately 80,000 hogs a year. While traditional farms of this size often struggle with the environmental impact of manure, Songlin has managed a 100-percent conversion rate of waste into resources.

Through a comprehensive recycling process, the system processes approximately 100,000 metric tons of pig waste annually, producing 3.65 million cubic meters of biogas. The resulting biogas slurry is used to fertilize farmland spanning 867 hectares nearby, saving 2 million yuan ($290,000) in fertilizer costs.

Industry experts have praised this approach as a replicable and scalable model for zero-waste city development.

Fu Juanlin, general manager of the agricultural zone, said that what was once a troublesome pollutant has become a valuable resource through this system.

"The animal excrement and urine from the pigsties flow through pipes directly to anaerobic tanks, maintaining a closed-loop system that prevents any ground or atmospheric pollution, achieving zero emission of the pollutants," he said.

In the vegetable area of the agricultural zone, diluted biogas slurry, which comes from the anaerobic fermentation of the pig waste, is sprayed on tomatoes and lettuce.

"We've created this complete 'pig waste-biogas-vegetable' cycle. The biogas slurry serves as high-quality organic fertilizers, and the carbon dioxide produced during biogas purification acts as an additional gaseous fertilizer, enhancing vegetable yield while thoroughly solving the waste pollution problem," said Fu, adding that the gaseous fertilizer can increase vegetable yields by around 20 percent.

The surplus biogas from this agricultural park is purified into biomethane gas, and is the first project in Shanghai where biomethane gas is integrated into the city's urban gas pipeline network.

"We have revolutionized the traditional use of biogas, truly converting agricultural waste into green energy," said Lu Qiang, deputy general manager of Shanghai Shenji Energy and Environmental Technology Co, partner of the agricultural zone for the biomethane gas project.