Scrap the waste

By Ragini Letitia Singh
Published: Tuesday 31 March 2009

Junk iron from scrap yards to clean polluted water

IN 1983 the entire Mianus river bridge in Connecticut, US, collapsed when the bearings rusted internally. Rusting thus proved to be a bane. But a bane can be turned into a boon. A group of researchers from China used scrap iron to treat industrial wastewater.

Pollutants of industrial wastewater include toxic materials like nitrogen, phosphorus and organic dyes. Commonly used technologies like biotreatment are unable to remove them. The new technology uses scrap iron that is in its stable, unoxidized form. In the wastewater it develops a strong tendency to react with these pollutants and makes them more biodegradable. In other words while the iron oxidizes (rusts) it helps clean up the polluted water.

In a series of experiments carried out since 2001, Luming Ma from Tongji University, China and Wei-xian Zhang from Lehigh University, UK, successfully used scrap iron to treat wastewater from petrochemical, textile and pharmaceutical industries.

During the full-scale application of the process in 2006, the iron-based reactor was connected to the biological treatment plant at the Taopu industrial district, Shanghai, to be used as a treatment preceding the biological clean-up. The researchers found that nitrogen removal had gone up from 13 to 85 per cent. Phosphorus removal increased from 55.6 to 63.3 per cent and up to 80.4 per cent of the colour was reduced. This partial degradation of polluted water using scrap iron helped it turn completely biodegradable.

"Conventional technologies like biotreatment and chemical precipitation are either ineffective or expensive," said Zhang. In chemical precipitation, chemicals are added to wastewater. They react with the contaminants and settle down. The wastewater is then decanted. "But this requires continuous addition of chemicals and produces large amounts of sludge which is expensive to be disposed off," added Zhang. Biotreatment proves ineffective due to the highly toxic nature of the pollutants.

The scrap iron technology is cheaper since iron scraps are readily available from scrap yards. While the scrap too needs to be disposed, Zhang explained that its estimated lifetime is three to five years. The spent iron can be recycled to make new iron and steel products.

The method is being used to treat wastewater from industries like textile, printing, iron and steel production and petrochemical refining. It would be environmentally beneficial in providing iron scraps with a better role than simply dumping them in the junkyard.

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