Lowly scrap iron can detoxify pollutants in wastewater

November 4th, 2008 - 5:10 pm ICT by IANS  

London, Nov 4 (IANS) A Chinese researcher has used scrap iron to do the unthinkable - clean up and detoxity pollutants in industrial wastewater. Wei-xian Zhang, professor of civil and environmental engineering at Tongji Univesity, Shanghai, concluded a five-year research project with the help of colleagues to detoxify pollutants.

The project, carried out in Shanghai, used iron, called zero valent iron (ZVI) because it is not oxidized. They obtained it in the form of shavings or turnings from local metal-processing shops for about 30 cents a kg.

The ZVI project began with small, “benchtop” lab experiments that used 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 pre-treat wastewater at a treatment plant in the Taopu Industrial District in Shanghai.

Effluents 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, according to an Eurekalert report.

Following the pilot test, the Shanghai city government funded a full-scale treatment reactor in Taopu 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 colours and dyes (52 to 80 percent).

“Before this project,” says Ma, “few people believed scrap iron could work in a wastewater treatment plant. We have developed a copper-activated iron and used a systematic approach to achieve dramatic improvements over biological processes used by themselves.”

ZVI scrap iron is chemically similar to iron-based nanoparticles invented by Zhang that are now widely used in North America to clean decontaminated soil and groundwater. The nanoparticles contain 99.9 percent iron and about 0.1 percent palladium or other noble elements.

These findings were featured in Environmental Science and Technology, published fortnightly by the American Chemical Society.

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