Peel filter

GRAPEFRUIT or chakotra is widely used in bodywashes and gels. But its peel finds limited use. Now, Indian researchers have shown the peel can be effectively used to filter methylene blue, a dye which is used to colour silk and cotton and is the main ingredient of the textile industry effluent. If ingested, water contaminated with the chemical can cause nausea, vomiting and diarrhoea.

Till now, activated carbon was used to filter such impurities. Activated carbon is usually produced by processing charcoal to make it extremely porous and have a large surface area available for adsorption. But the process is costly.

Earlier studies had shown that citron and other varieties of lemon can be used to prepare activated carbon to adsorb effluents like dyes from the textile industry. Now, researchers from National Institute of Technology in Durgapur and Heritage Institute of Technology in Kolkata have shown how the waste of grapefruit can be a good low-cost adsorbent.

To make it, they collected fresh grapefruit peels, washed and sundried for two days. They are then ground and mixed with orthophosphoric acid, an activating agent, and heated. The charred material thus obtained is cooled and washed with dilute ammonia and distilled water to remove the remaining acid. The material was left for drying overnight. Later it was crushed into different sized fractions and used as filter.

To test the efficacy of the peel filter, researchers used an electron microscope and compared its surface area, before and after adsorbing methylene blue, with that of the regular activated carbon. They found the surface area in both are similar. The surface of peel filter turned smoother after adsorbing methylene blue. Its ability to filter methylene blue was 99.08 per cent, the researchers noted in the April issue of Desalination.

“Through this process we convert fruit peel to a value added product. It can help reduce environmental pollution,” says Susmita Dutta, lead author of the study. India produced 193,822 tonnes of grapefruit in 2009.

The team plans to test the efficacy of the peel infiltering effluent arising from industries making artificial flowers, involved in decolourisation of sugar, drinking water treatment, gold recovery, and pharmaceutical production.

The research is worth applause, says Satyanarayana A, senior scientist at the Central Food Technological Research Institute, Hyderabad. “But it is equally important to understand the cost involved in making this adsorbent.”

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