Sludge-to-energy systems are a well-established technology, but their potential in China was little understood. WRI research demonstrated that such systems in China could reduce solid waste, greenhouse gases and water pollution, and produce organic compost and compressed natural gas – all while saving money. WRI’s work with Chinese officials helped them to plan or install plants in four Chinese cities that can eliminate 700,000 tons of carbon dioxide equivalent emissions per year.

The Challenge

Wastewater and sewage sludge produced in the wastewater treatment process can pollute waterways if not safely treated. Sewage sludge is typically incinerated, releasing carbon dioxide and the potent greenhouse gas nitrous oxide into the atmosphere, or disposed of in landfills, releasing the potent greenhouse gas methane. Both contribute to global climate change. Conventional wastewater treatment is also an energy-intensive process.

WRI's Role

WRI studied a pilot project in the city of Xiangyang to convert sludge to energy. The study evaluated the nutrient recovery, energy consumption, greenhouse gas emissions, reclaimed methane and cost of sludge disposal systems and concluded that a sludge-to-energy system reduced solid wastes, greenhouse gases and water pollution, all while saving money. At the same time, the residue from the sludge treatment can be used as an organic compost, and the methane produced can be used to power the sludge disposal systems and compressed natural gas vehicles, further limiting greenhouse gas emissions.

Based on these findings, WRI worked with the Ministry of Housing and Urban-Rural Development, the agency that sets wastewater and sludge policy for China, to promote sludge-to-energy systems to other cities. WRI organized a study tour to several U.S. sludge-to-energy systems to help city leaders understand the benefits of the process.

The Impact

These efforts helped lead four large cities in China – Beijing, Changsha, Chengdu and Hefei – to install or plan sludge-to-energy systems. Based on WRI estimates, these plants can help reduce 700,000 tons of carbon dioxide equivalent emissions per year, comparable to one-third of the emissions produced each day by all the cars on U.S. roads. The plants are also expected to produce nearly 40 million cubic meters of compressed natural gas for taxis and city buses – enough to fill the tanks of 2 million taxis – while also powering the sludge disposal systems themselves. Further uptake of sludge-to-energy systems will reduce water pollution and help China to reach its greenhouse gas emission reduction targets. WRI is now working with the World Bank and the U.S. Environmental Protection Agency to promote sludge-to-energy systems globally.