News related to Science, Technology, Environment, Agriculture and Medicine in India

Removing Toxic Dye from Water

Using Ceiba Pentandra Seeds

Toxic dyes released into water bodies by textile industries are a major environmental concern. One could use chemical precipitation, ion exchange, membrane filtration, coagulation, reverse osmosis, liquid–liquid extraction, ozonation, electrochemical oxidation, and electrodialysis to remove dyes from effluents. But they are expensive. Adsorption, on the other hand, is highly effective and does not require inputs of energy or chemicals.

Senthil Kumar, SSN College of Engineering, and A. Saravanan from the Dr Rangarajan Dr Sakunthala Engineering College, Chennai have been experimenting with methods to remove toxic dyes and metals from effluents. Recently, they collaborated with G. Manikandan, from Adhiparasakthi Engineering College, Kancheepuram, to put to use Ceiba pentandra seeds to create an adsorbent for removing methylene blue from an aqueous solution. Methylene blue is a highly water soluble cationic dye, has low biodegradability and high resistivity.

And Ceiba pentandra seeds is an agricultural waste.

Kapok-Ceiba_pentandra_Philstone

The kapok tree produces cotton for stuffing pillows and cushions.
Image: Philstone via Wikimedia Commons

They collected the seeds, washed and dried the seeds. A part of the seeds was heated to 500 °C, in the absence of oxygen. They wanted to compare this physically activated seeds with chemically activated ones. For chemical activation, they used sulphuric acid.  

The researchers tested the ability of the physically and chemically activated seeds to remove methylene dye. They found that the chemically activated seeds were superior. While  a gramme of the physically activated seeds could adsorb a little more than 300 milligrammes of the dye, the chemically activated seeds could adsorb more than 450 milligrammes per gramme.

To understand the difference, they compared the characteristics of these physically and chemically activated the seeds. “The chemically activated seeds were more carbonaceous, more porous and had more active surface. It also had amino, hydroxyl, alkyl and alcohol groups whereas the physically activated seeds had more aliphatic groups”, explains Senthil Kumar.

Using the adsorption isotherms obtained experimentally they found that the optimum adsorption conditions for an initial dye concentration of 50 mg/L at a temperature of 30oC and pH 7. The seeds adsorb the dye for about an hour before an equilibrium is reached.

“The adsorption process is exothermic – useful in removing the methylene blue from polluted water”, says G. Manikandan.

Ample C. pentandra seeds are locally available and can be collected with minimal effort. They have high adsorption limit. It is now for the industries to take these results for application in textile industries..

Ind. Eng. Chem., 62: 446–461

Prof N Sekar

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Categorised in: Environment, Tamil Nadu, Technology, Water

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