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Wednesday, September 29, 1999 Published at 11:25 GMT 12:25 UK


Sci/Tech

'Curtain' of bacteria to purify pollution



Australian scientists are aiming to clean up groundwater pollution by creating a "curtain" of bacteria that eat toxic chemicals.

They discovered the useful soil bugs earlier this year and are now about to put them to work, clearing up a plume of the weedkiller atrazine which lurks below a suburb of Perth in Western Australia.

Team leader Dr Greg Davis, of CSIRO Land & Water, told BBC News Online that the idea is to create a permeable underground barrier of the bacteria and then let the natural groundwater flow carry the pollution through it.

A bug's life

The key to the technique is getting a colony of the Pseudomonas microbes to thrive. Laboratory tests have shown that this can be done by pumping oxygen-rich air into the ground.

The pollution under Perth results from a chemical spill and is a 400-metre-long plume, 40m wide and five metres deep. The groundwater forms part of the city's water supply and must therefore be kept as pure as possible.

"In this initial test, our plan is to create a series of 18cm-diameter, 15m-deep boreholes, each containing a barrier of permeable matting," said Dr Davis.

A slurry of the bacteria is pumped down the holes first and then another pump, which could be solar powered, delivers oxygen to the microbes.

"This creates an environment in which these particular microbes thrive," added Dr Davis.

Fast food

It takes just a few hours for the bugs to consume the atrazine, leaving only water and carbon dioxide. And over a few years, the whole plume should flow through the bacteria.


[ image: Greg Davis:
Greg Davis: "System could become a lifesaver for inumerable polluted sites"
For well-defined plumes like this one, Dr Davis believes his team's approach will be cheaper than alternative extract-and-treat methods, partly because once installed the system is very low maintenance.

"They can probably obtain all the nutrient they need from carbon in the groundwater itself, as well as from the chemical," said Dr Davis.

Sensors and mini-samplers are being buried both upstream and downstream of the barrier to measure oxygen and atrazine levels. This will allow the team to check the bugs' efficiency at removing atrazine.

Dr Davis said: "We also want to determine whether we really have to add microbes to degrade the atrazine. The atrazine-eating microbes will be injected in some boreholes, but in other boreholes, natural low-levels of the microbes will be encouraged to grow and attack the atrazine."

Groundwater pollution is a worldwide problem. There are thousands of sites in cities and industrial centres where underground water has been contaminated by leaks, spills and discharges of toxic industrial solvents, pesticides, oils and industrial chemicals.





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