CHENGDU — Xiejiahe Wetland Park looks no different from any other waterfront green space, but visitors could be surprised to discover that its most photogenic spot — a stepped waterfall — is a treated sewage outlet.

The treated sewage, discharged from the Xiejiahe Water Reclamation Plant in Neijiang, Sichuan province, is filtered one final time through the wetland park before flowing into the Tuojiang River, a tributary of China's longest river, the Yangtze.

In order to improve the water quality of the Tuojiang, which used to be heavily polluted, Neijiang has embarked on a comprehensive upgrading of the aquatic environment in the river basin. With an investment totaling 6.28 billion yuan ($858 million), it is building sewage treatment facilities, cleaning "black and odorous water bodies", and restoring ecosystems on its banks.

The water reclamation plant, which began operating at the end of June last year, is part of that effort. The Tuojiang was once the most heavily polluted river in Sichuan, and even in the upper reaches of the Yangtze, as it passes through the most densely populated and economically active parts of Sichuan.

"When I was young, I was always astonished to find people swimming in the river, because it was unacceptable to me to swim in that dirty water," said Jiang Min, who grew up in Neijiang and now works for Sichuan Aqua Gathering Eco-environment Management, the operator of the upgrade program. "But now it is perfectly fine to swim here."

The water reclamation plant, in downtown Neijiang, collects residential sewage and was built underground to minimize disturbance to the surrounding neighborhood.

The entrance to the plant is a slope with a solar panel roof. Inside are numerous pools of varying sizes. When urban sewage is channeled to the plant, garbage and floating objects are first intercepted, and the rest proceeds through sedimentation, degradation of organic matter, removal of phosphides and nitrogen, decolorization and disinfection.

The Xiejiahe plant can now treat about 10,000 cubic meters of sewage a day and is expected to reach a daily capacity of 30,000 cubic meters in the future.

The recycled water was used to replenish the nearby Xiejiahe River, flush toilets in public buildings, clean city streets and irrigate parks and greenery, said Wang Guiqiang, the general manager of Sichuan Aqua Gathering Eco-environment Management.

In the plant control room, a huge screen displays the smart operation platform used to monitor sewage treatment facilities at different sites, and to analyze real-time water quality.

Eleven "black and odorous water" sites in Neijiang have now been cleaned up, with 39 green corridors and wetland parks built.

Xinhua