Space & Innovation

A Man-Made Wetland Will Help Treat Shanghai's Foul Industrial Wastewater

The treated water will be reused by factories within the industrial park.

A French company has secured a $19.7 million contract to build a wetland to clean the water at one of the largest petrochemical industrial parks in Asia.

Suez will build what it calls a Dragonfly Zone - a type of constructed wetland - to treat wastewater produced at the Shanghai Chemical Industry Park (SCIP). The industrial park sits on the coast about an hour south of China's largest city, and claims to be among the largest industrial zones dedicated to petrochemical production in Asia. The treated water will be used by factories within the industrial park, which sits on a spit of land surrounded by a hodgepodge of factory and apartment buildings, golf courses and farm fields near the mouth of Hangzhou Bay.

In recent years, Chinese water quality has worsened while access to clean water has grown more difficult. Studies show 60 percent of the country's groundwater to be substandard, and water shortages have left whole cities dry. Exacerbating this is the fact that China is home to 20 percent of the world's population but only 7 percent of the world's freshwater resources.

"Dragonfly Zone" is the term the Suez company has trademarked for its engineered wetland systems, which are artificial wetlands designed to treat and purify industrial or municipal wastewater. The SCIP project will use native plants to filter water in the 88-acre project.

"Several dozen plant species will be chosen locally based on their treatment capabilities," a spokesperson for Suez told Seeker. Those include cattails, reeds and other aquatic plant life, which will capture and break down pollutants in the water as it passes through the wetland.

The advantage of constructed wetlands is that they treat wastewater naturally, Bruce Thomson, professor emeritus in civil engineering at the Water Resources Program at the University of New Mexico, told Seeker. "You're not adding chemicals, you're not treating it mechanically," he said. "You require just a little bit of energy to pump it."

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Plus, constructed wetlands provide "a very pleasant environment for aquatic organisms - rushes and birds and vegetation and wildlife," he said. "So there is a lot of appeal there."

Constructed wetlands have been used in wastewater treatment in the United States and Europe for decades. According to Suez, the Dragonfly Zone systems are guaranteed to reduce the amounts of specific pollutants to comply with Chinese government surface water standards. The Dragonfly Zone is based on a Suez design first implemented in Hérault, France in 2009.

However, the aquatic plants cannot break down complex and highly toxic effluent from a petrochemical plant. As Thomson explained, wetlands cannot degrade heavy metals and oils, which will collect in sediments and eventually kill plant and animal life if not previously removed.

That job is tackled by a primary industrial waste treatment facility, which Suez currently operates at the SCIP. The new Dragonfly Zone will offer an additional cleaning, known as a "polishing treatment," to reduce remaining contaminants such as total nitrogen, total phosphorous and micropollutants.

And it might just turn out to be a pretty place to hang out.

"The wetland is designed and planned to be open to the public," said the Suez representative. Thomson said this is the case for many of the constructed wetlands in the US, which often include public viewing areas.

He noted, for example, the Houston Ship Channel in Texas, which suffers from decades of petrochemical contamination from the surrounding oil refineries and processing plants. Yet, "some of the best places to fish are the outfalls from the wastewater treatment lagoons," Thomson said. "Wastewater treatment lagoons are not too different from wetlands."

He explains: "There's a lot algae, and the fish feed on the algae, and the water quality will support game fish." (Nonetheless, the Texas Park and Wildlife Department doesn't necessarily recommend eating the fish you do catch there.)

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