HOW do you get rid of the stink that comes in the aftermath of a flooded basement? Plaster the floor and walls with some hungry bacteria, says Evguenii Kozliak, who came up with the answer after his own town, Grand Forks in North Dakota, was flooded, causing heating-oil tanks to buckle and burst.
After the deluge, the fetid oily residues had worked their way into the porous concrete floors and wooden walls, making them stink to high heaven.
The householders tried sponging and mopping with detergent. They even tried 鈥渓ocking in鈥� the smell by painting the walls and floors, and when that didn鈥檛 work they turned to activated charcoal and coffee beans.
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But the only thing that actually got rid of the source of the smell鈥攖he volatile hydrocarbons鈥攚as to chip away the contaminated concrete and strip out the wood. That鈥檚 because hydrocarbons can sink several centimetres into the pores in concrete and wood, forming blobs that are hard to reach.
Roger Dunn from the National Environmental Technology Centre, near Oxford, agrees that this is a common problem after floods. 鈥淧eople tend to remove the concrete floors and replace them. It鈥檚 messy and hard work.鈥� He says any non-destructive way to get rid of the smelly compounds would make life easier, especially with load-bearing sections of concrete that can鈥檛 be cut away.
Kozliak, a microbiologist at the University of North Dakota, initially tested two different approaches to the problem. One relied on cleaning products containing surfactants鈥攕ubstances that reduce the surface tension of liquids鈥攖o make the hydrocarbons more soluble. In the other he used a liquid mix of bacteria. But in both cases he found that the water in the solutions simply clogged up the pores, stopping the contaminants from leaching out. He could remove only 0.3 per cent of the contaminants with the surfactant, and 10 per cent with the bacteria.
The breakthrough came when Kozliak and a university colleague David Tilotta replaced the liquid with a thick gel that didn鈥檛 contain so much water. They filled their gel with a mixture of bacteria, including bacteria found in oil-contaminated areas鈥攕uch as those beside railway tracks鈥攁nd the common soil bacterium Pseudomonas aeruginosa.
When applied to a contaminated surface, the bugs in this thick gel ate the hydrocarbons closest to them. This in turn created a concentration gradient in each pore that slowly pulled contaminants from deeper inside the material up to the surface, where they too could be digested.
Although the process was slow, taking weeks in the case of non-volatile chemicals such as hexadecane, it did remove 80 to 90 per cent of the residue. Kozliak and Tilotta will present their results at an environmental biotechnology meeting in Mexico this June.
Kozliak adds that bacteria should be able to pull almost anything out of porous materials. He is now working on ways to use his active slime to remove pesticides and even explosives residues from buildings.