Reporter 441, 25 October 1999


Dye researchers protecting the world's water from the not so glorious technicolour

The textile industry may produce some of the prettiest looking effluent but it costs tens of millions each year to remove waste and excess dyes from our water. University researchers believe they may have a novel solution using bacteria with a taste for rotting fish heads. The research team has harnessed the bug's robust palate to help clean up when the rivers run red, and yellow, pink, blue...

As those of us who have ever turned white washing pink with a rogue red sock will testify, removing clothing dyes is no easy task. Water companies currently bleach our drinking water to remove stray colours from industry effluents with powerful chemicals like ozone, but costs are rising, and dye manufacturers, textile producers and water companies are all seeking other solutions.

Clothing dyes are relatively benign pollutants. They are not particularly toxic or corrosive, and will not react with other chemicals to cause more complex problems. They can, however, block sunlight penetrating the water, which restricts the growth of aquatic life. Waste dyes are also, of course, extremely visible.

Shot of lab.

Most waste water in the UK travels unseen to water works through the network of sewers. In countries such as India, China and Mauritius, however, discharges from huge numbers of the textile producers go straight into rivers. "I've been in Mauritius and seen people washing in river water which is bright green one day and yellow the next," said civil engineering researcher Nigel Horan.

Dr Horan is working to develop novel technology to treat coloured effluents. The approach is based on the unusual diet of bacteria first identified in colour chemistry. Professor Jim Guthrie and former postgraduate student Nicola Willmott isolated the bugs from sludge around a textile factory outflow pipe. Shewanella putrefaciens has such a liking for the vivid azo-dyes that laboratory flasks of bright blue and red water were rendered colourless inside a few hours.

Areti Kamilaki
Before and after: PhD student Areti Kamilaki prepares to feed another batch of polluted water to the colour-hungry bacteria. In a matter of hours the water will be as clean as the sample on the left. The team is developing commercial technology based on this principle

The bug is more commonly found in dead and decaying fish and this was the first time its decolourising properties had been identified. This allowed the researchers to patent the bacteria. "It may sound a little strange to be able to patent a living organism but we now own the rights to its ability to break up these dyes," said Professor Guthrie.

The identification and isolation of the bug was carried out jointly with Dr Gordon Nelson at textile research company BTTG, through the postgraduate training partnership (PTP) scheme.

A second PTP student, Areti Kamilaki, then began working with Professor Guthrie and Dr Horan on how the bug's unusual tastes could be applied to treating the gallons and gallons of brightly coloured waste produced by industry. "The problem with using bacteria to treat running water is that they are very easily washed away," said Dr Horan. "We needed to keep the bugs around long enough for them to have a beneficial effect, ie, to remove the colour and any by-products."

The researchers solved the problem with plastic beads the size of ping-pong balls, which float about in the dirty water. The patented bacteria grow on the plastic surface and break down the dyes in the water flowing around them. In this way the team's reactor vessels can treat up to 25 litres of coloured water a day. The next stage is scaling up the technology sufficiently to cope with the volume produced by a factory, perhaps up to 500,000 litres a day.

By tagging a second reactor onto the system, the researchers can also remove the remaining (non-coloured) pollution from the water, leaving the textile firms with cleaner discharges, fewer headaches and smaller bills.

The researchers have joined forces with chemical giants Eastman to help develop the technology. Both Professor Guthrie and Dr Horan believe a commercial prototype can be produced within six months. They estimate it would cost a textile company about £300,000 to buy one of the twin-reactor kits. With current treatment costs running at about £1,000 a day for coloured water from a single factory, rivers around the world may soon be running a clearer, if more mundane, colour.

Dyenamic duo
Dyenamic duo: Dr Nigel Horan (left) and Professor Jim Guthrie are leading research to develop a novel method of treating effluents from the dye and clothing industry

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