Electric blight orchestra
7 Apr 2000
A combination of electrochemistry and specific microorganisms could help reduce levels of nitrates in contaminated water, according to researchers at EA Technology. Although the technique is still in its early stages, the researchers believe it could be more effective than ion exchange, reverse osmosis and biological reduction.
The system uses autotrophic organisms, which are microorganisms that feed off simple inorganic molecules, to degrade the nitrates. This in itself is nothing new, but the researchers have added a twist - the organisms are stimulated by an electrochemical reaction which produces hydrogen.
The organisms grow in a thin biofilm on the surfaces of a pair of electrodes, immersed in the contaminated water stream. As a current is passed through the electrodes, the water decomposes into hydrogen and oxygen. The hydrogen then donates electrons to the organisms, which break the dissolved nitrates into nitrogen gas and other harmless by-products.
Research leader Luke O'Brien, on a postgraduate training programme at EA Technology through UMIST, explains that the system could offer several advantages. Reverse osmosis and ion exchange are unselective, removing ions other than nitrates and generating large volumes of waste reagent. Other biological methods avoid this problem, but generally rely on carbon sources, such as methanol, to act as electron donors. The process becomes more expensive to run and the carbon source itself can become a pollutant. The researchers are determining whether the process is commercially viable.
The research was carried out in partnership with Thames Water, which is seeking ways to decontaminate water in boreholes. However, it has since attracted a great deal of interest, says O'Brien. `We are assessing its potential for other applications, such as treating contaminated waste streams and the removal of heavy metals.'
