Benzene is difficult to break down in deeper soil layers were no oxygen is available. PhD student ir. Sander Weelink of Wageningen University found a solution to this problem. He isolated a strain of bacteria that can break down benzene aerobically in soil without oxygen.
This sounds paradoxical. How can you break down benzene with oxygen if there isn't any oxygen? ‘By using a clever method to produce oxygen on the spot’, explains Weelink. He isolated a strain of bacteria that breaks down benzene by using chlorate. The chlorate is reduced to chloride, which produces oxygen. The bacteria then use this oxygen to break down benzene and related compounds aerobically. The bacterium itself is therefore the oxygen factory.
According to Weelink, this principle itself is not new. However, he saw an opportunity to isolate a new strain of bacteria from contaminated soil and sludge that could use this trick to tackle the benzene problem. This turned out to be the Alicycliphilus denitrificans bacterium, BC strain. Weelink says that the TNO research institute has meanwhile conducted a successful trial under practical conditions with this breakdown route for benzene.
However, there is one disadvantage: in order for the bacteria to break down benzene, chlorate must be added to the soil. ‘And chlorate is itself a contaminant.’ Therefore the TNO trial used an experimental design where the groundwater was pumped away after the conclusion of the experiment.
According to Weelink, the use of chlorate should not have to be a problem. ‘You're simply adding sodium chloride to the soil. After that breaks down, all that remains is carbon dioxide and table salt. At the very worst, the soil becomes slightly more saline.’
Before the method can be used, it must of course be clear if the specific bacteria are present in sufficient numbers. Moreover, you must use the correct quantity of chlorate. At the Laboratory of Microbiology, two PhD students are now conducting a follow-up study.
For that matter, Weelink's method is not limited to breaking down benzene. The trick with chlorate can be used for many kinds of contamination that are difficult to remove anaerobically.
Sander Weelink defended his doctoral thesis on 18 November; his PhD supervisor was Prof. Fons Stams, who holds a personal chair at the Laboratory of Microbiology of Wageningen University. / Roelof Kleis
The above article was written by the editorial staff of Resource, the weekly newspaper for Wageningen University and Research Centre. For more information, contact the press and science information officer of Wageningen UR, e-mail: pers.communicatie@wur or the editorial staff of Resource, e-mail: resource@wur.nl. See the archived articles at http://www.resource-online.nl