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BHAVNAGAR – Indian scientists have developed a nano-material from seaweed which can be used for the effective treatment of contaminated textile wastewater – without using any chemicals. The researchers tested a nano-composite by depositing it on a commercial filter paper before using it in a customised flow cell in continuous filtration mode. The scientists claim it took only five minutes of treatment to transform a highly toxic black dye solution into colourless water. Most notably, the researchers claim the solution can be used in conjunction with other membrane-based processes such as reverse osmosis and nano-filtration to treat textile wastewater.

Traditional wastewater treatment techniques are not very efficient or environment-friendly. Membrane-based filtration processes are generally used to treat industrial wastewater but they can’t fully filter out heavy metal contaminants. To address this, processes that use activated carbon, graphene or carbon nano tubes are being developed as carbon-based processes can help remove dyes and heavy metals through adsorption.

Researchers at the Central Salt and Marine Chemicals Research Institute, Bhavnagar, have now gone a step further to make carbon-based cleaning process cleaner by using seaweed as starting material. The researchers synthesised graphene-iron sulphide nano-composite from abundantly found seaweed – Ulva fasciata – through direct pyrolysis technique.

Seaweeds are known as carbon sinks. In some earlier studies, biomass of Ulva fasciata has been directly employed for adsorbing copper and zinc ions from water but the uptake capacities were relatively low. This problem has been overcome by deriving thin carbon sheets from seaweed at very high temperature. These graphene sheets are doped with iron. The nanocomposite obtained from seaweed has shown very high adsorption capacity for various cationic and anionic dyes as well as lead and chromium.

The nanocomposite can be used in up to eight cleaning cycles, with only nominal loss of its adsorption capacity, and even mixed dyes could also be adsorbed. A maximum adsorption capacity of 645 mg per gram for lead was achieved at neutral pH – the highest ever reported for any biomass derived carbon material, according to the scientists, whise study is published in the Journal of Hazardous Materials. It could also remove highly toxic hexavalent chromium from wastewater.

“[The] presence of high concentration of salts had negligible effect on the adsorption properties of the nanocomposite, making it a suitable candidate for the pre-treatment of highly contaminated wastewaters,” explained Dr. Ramavatar Meena, who led the team.

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