Zapping microbes with electricity could replace tonnes of chemicals used in cleaning up mining wastewater, thanks to scientists who have developed a new water treatment system.

Microbes are already used in conventional wastewater treatments to mop up contaminants by adding or removing electrons. But to work effectively, they need to be 'fed' using vast amounts of nutrients and chemicals.

The researchers from the University of Utah say that their electrobiochemical reactor (EBR) system bypasses the addition of excess chemicals by feeding electrons directly to the microbes. This boosts how quickly they can clean up pollutants, such as arsenic, mercury, selenium, nitrates and sulphates.

''We've seen that microbes with the EBR system work between 2 and 10 times faster than the same process without the added voltage,'' says Jack Adams, the research professor at Utah's Department of Metallurgical Engineering who pioneered the system. ''Because the microbes are at least twice as efficient, we can reduce the amount of chemicals by over 50% and still effectively remove the contaminants.''

He adds, ''The metal contaminants are removed and collected in a form that can be recycled. Similarly, the concept behind the EBR may make it possible to recover more of the valuable product itself and with similar environmental benefits.''

The low voltage used by the EBR can also easily be generated using a small solar power grid, helping to minimise the overall environmental impact.

Following their successful trial in treating wastewater at an inactive gold mine, Adams and his colleagues are now embarking on a second pilot-scale study at a mine for silver and other metals in Canada's Yukon Territory.

''This research will help us to gain insight into how we can improve the system even further, and we anticipate that the pilot-scale tests will lead to full-scale treatment systems,'' he says.

Although the research team are focusing on removing metals from mining wastewater, Adams points out that EBR has great potential for other applications.

''Essentially, all biological and chemical reactions involve electrons being added and removed, which the EBR delivers in a controlled way,'' he explains. ''This makes it possible for many other microbial and chemical systems to be better controlled and more efficient as well as better for the environment.''