Washington, Nov 4 : Researchers have used two million pounds of scrap iron to detoxify pollutants in industrial wastewater in Shanghai, China.
The research was led by Wei-xian Zhang, a professor of civil and environmental engineering from Tongji University in Shanghai.
The project, carried out in Shanghai, was the largest in history to use iron in an environmental application.
The iron, called zero valent iron (ZVI) because it is not oxidized, was obtained in the form of shavings or turnings from local metal-processing shops for less than 15 cents a pound.
The ZVI project began with small, "benchtop" experiments in the laboratory that used a total of 90 pounds of iron to treat toxins in solution. It graduated in 2005-06 to a pilot test using 2,000 pounds of iron to pretreat wastewater at a treatment plant in the Taopu Industrial District in Shanghai.
Wastewater at the Taopu plant, which is generated by small chemical, materials and pharmaceutical companies, had previously been treated with microorganisms alone.
ZVI augmented and improved this remediation method.
Following the pilot test, the Shanghai city government approved a grant to construct a full-scale treatment reactor in the Taopu district capable of processing almost 16 million gallons a day of wastewater.
This ZVI reactor was connected to the biological treatment plant two years ago and has been in continuous use since.
The addition of ZVI to the traditional biological methods of wastewater treatment resulted in a significant improvement in pollutant levels, according to Ma, who directs the National Engineering Research Center for Urban Pollution Control in Tongji's College of Environmental Science and Engineering.
The removal of biological oxygen demand (BOD) rose from 76 to 87 percent. Improvements were also recorded with the removals of nitrogen (13 to 85 percent), phosphorus (44 to 64 percent), and colors and dyes (52 to 80 percent).
"Before this project, few people believed scrap iron could work in a wastewater treatment plant," said Ma.
"We have developed a copper-activated iron and used a systematic approach - from benchtop to pilot to full-scale tests - to show that ZVI-enhanced treatment can achieve dramatic improvements over biological processes used by themselves," he added.
The ZVI, which undergoes oxidation during this exchange, has a useful lifetime of about two years in the treatment process.