Heavy-duty battery

need to sponge out heavy metals from industrial wastewater? Try seaweeds. Two researchers at the Kochi-based Central Marine Fisheries Research Institute has found that certain sea plants found along the Gulf of Mannar coast may not only help remove heavy metals such as cadmium and lead but also allow their recovery.

Sargassum wightii, a brown algae, is as effective or better than activated carbon and natural zeolites that are conventionally used to remove heavy metals from industrial effluents, say P Kaladharan and V Vinoj Kumar in a paper published in Current Science (Vol 90, No 9, May 10, 2006). Besides, as the seaweeds wash ashore, they can be easily collected for use, he adds.

The scientists found the seaweeds produce two acids -- mannuronic acid and guluronic acid -- that help adsorb metal compounds from a solution. To exploit this property, the scientists designed a biobattery -- a perforated box packed with dried and pulverised S wightii. They found that for solutions containing over 200 parts per million of the metals, the biobattery adsorbed 70 per cent of lead and 80 per cent of cadmium within 30 minutes, when treated individually. For a multimetal solution, the removal of the metals ranged from 57 to 97 per cent after three hours.

For optimum results, the effluent solution should be moderately acidic (ph between 4 and 5), says Kaladharan. The metals adsorbed can be retrieved by putting the plant biomass into an alkaline solution. The adsorbent column designed as a biobattery can be reused after taking out the metal or by packing in a fresh lot of pulverised Sargassum.