In a demonstration project in Sanxing Township on the island of Chongming in Shanghai, a bio-active filter integrated purification tank developed by CRRC Corporation Limited, China's largest high-speed rail carriage maker, has been installed underground about 10 meters away from two rural houses.

Domestic sewage from the two families is gathered by gravity flow and treated with a microbial anaerobic-aerobic process, then goes through a deep treatment with a bio-active filter in the tank.

After treatment, the sewage has been turned into clear and odorless water, which has been tested as meeting Shanghai's first-class standard of discharged water, suitable for irrigation and supplementing natural water.

The CRRC-developed purification tank wirelessly provides real time data on its operating conditions and decontamination results to a village control room, which means any technical issues or faults can be identified and remotely fixed in a timely fashion.

"The secret of the purification tank is the bio-active micro flora that eat the dirty stuff in sewage," said Ni Xiaohong, 25, a sewage treatment worker in Chongming.

Yang Zhen, vice general manager of Shandong Zhongche Locomotive Co. Ltd. Shanghai Branch, said the biological purification tank is based on the vacuum-drainage and biotechnology integrated treatment devices used in toilets on high-speed trains.

Pilot projects of similar decentralized rural domestic sewage treatment equipment have been launched in over 20 provinces and regions across China since 2015, he said.

A small purification tank can be installed in one day. It can deal with at least one ton of sewage a day, enough for treating daily discharge from two to three families. The treated water can be sluiced directly into streams.

Yang said the tanks address the needs of household sewage treatment for people living in remote areas.

The Chongming District government has set the target to achieve full coverage of rural domestic sewage treatment by 2020. In some villages, drones are used to monitor water pollution.

It plans to introduce the CRRC-developed sewage tanks for isolated households. For densely-populated villages, centralized treatment like Shanghai Electric's container-size sewage treatment station using micro-dynamic high-efficiency biofilm technology can meet the needs of sewage purification for up to 200 households.

Apart from a regular sewage treatment fee, rural residents do not have to pay for the installment and maintenance of the equipment.

The technology can help Chongming to achieve its goal to develop a world-class ecological island, said district official Xu Xiaodong.

The island, 45 kilometers east of downtown Shanghai, is located at the mouth of China's largest river of Yangtze. It is the world's largest estuary alluvial island. A sound water environment is crucial for maintaining the bio-diversity along with rural development on the island.