Lobsters, crayfish, crabs, prawns, oysters – they are all served as exquisite dishes. People know how to eat them, but they do not know what to do with the left chitin shells. Today the shells are still considered as waste, but... chitosan – a polysaccharide derived from chitin – is increasingly useful, for instance, for agriculture as a pesticide, fertilizer, or fruit preservative. It is also applied in medicine as a vehicle for pharmaceutical drugs or dressing component, as well as in the production of clothes, and in waste water purification. But is it actually possible that waste water could be purified by...waste?
Tomasz Jóźwiak, a 28-year-old doctoral candidate from the Chair of Environment Protection Engineering at the Faculty of Environmental Sciences and Fisheries UWM, proves that there is such a possibility.
– I found chitosan interesting, because of its high sorption capacity. Activated carbon, which is now most commonly used in substance absorption, has significantly lower sorption capacity – the doctoral candidate explains.
Each year, 700.000 tons of colorants are used up by the world industries. From 10-50% of them get to sewage treatment. However, conventional waste water treatment plants are not able to purify the water of colorants, because customers worldwide require that textiles, furniture, cars, or toys do not fade due to sunlight, rain or low temperatures. Such demands result in the production of more and more durable colorants.
A method for purifying waters of the colorants must be cheap and effective. In order to achieve that, our scientist decided to use chitosan, a derivative of chitin. Chitosan has a lot of advantages: high sorption capacity and low price, but it also has one drawback: chitosan is very sensitive to acidic solutions (with a pH greater than 5), in which it gets dissolved and loses its sorption capacity. And that is the exact problem – sewage are acidic.
– I started to look for a substance that would immunize chitosan to acid, and maintain its sorption capacity – Tomasz Jóźwiak adds.
The research took him over two years. What was the result?
– After modification, the sorption capacity of chitosan is much higher, and its range of application is now utterly wide – Tomasz Jóźwiak says.
What is even more important, chitosan is still a very cheap and capacious absorbent.
– Recycling 1 kilogram of colorant requires 4 kilos of activated carbon, whereas 1 kilo of my modified chitosan is able to absorb 3 kilos of colorant. 1 ton of a good-quality activated carbon costs over 10.000 zlotys. The production of my sorbent will cost roughly 3-4 thousand zlotys – the doctoral candidate says.
Accoridng to Tomasz Jóźwiak, everything tells him that the industry is going to buy his product.
Transl. by AP