Bioremediation by bacteria in biofilms can target a number of pollutants.
Examples of pollutants that can be degraded by biofilms:
- BTEX (Benzene, Toluene, Ethylbenzene, Xylene)
- PAH (Polycyclic aromatic hydrocarbon)
- Nitroaromatic compounds
- PCB (Polychlorinated biphenyls)
- Chlorinated aliphatic compounds
- Heavy metals (Cd, Cu, Pb…)
- Nuclear wastes
- Agricultural chemical wastes (Triazine, DDT)
Biofilms are used in treating wastewater, heavy metal contaminants such as chromate, explosives such as TNT and radioactive substances such as uranium. Biofilms can either degrade them, or change their mobility or their toxic state and therefore make them less harmful to the environment and to humans.
Nitrification using biofilms is one form of wastewater treatment. During nitrification, ammonia is converted to nitrites and nitrates through oxidation. This can be done by autotrophic bacteria, which grow as biofilms on plastic surfaces, according to a 2013 article published in the journal Water Research. These plastic surfaces are just a few centimeters in size and distributed all through the water.
The explosive TNT (2,4,6-Trinitrotoluene) is considered a soil, surface water and groundwater pollutant. The chemical structure of TNT consists of benzene (a hexagonal aromatic ring made of six carbon atoms) attached to three nitro groups (NO2) and one methyl group (CH3). Microorganisms degrade TNT by reduction, according to a 2007 article published in the journal Applied and Environmental Microbiology. Most microorganisms reduce the three nitro groups, while some attack the aromatic ring. The researchers — Ayrat Ziganshin, Robin Gerlach and colleagues — found that the yeast strain Yarrowia lipolytica was able to degrade TNT by both methods, though primarily by attacking the aromatic ring.
One of the less obvious beneficial applications of biofilms is in cleaning up oil and gasoline spills. That’s right, certain bacteria will eat oil and gasoline. Remember that oil was produced over many years by decaying vegetation, so it is an organic compound. We wouldn’t recommend that you suck up any spilled oil or gasoline, but the fact that some of the naturally occurring bacteria in soil love the stuff leads to a new idea: bioremediation. This is a term that refers to the engineering of a biofilm that can be introduced into the area of an oil or gasoline spill to help clean up the mess, and all with natural, non-harmful means.
Indeed, bioremediation using biofilms has emerged as a technology of choice for cleaning up groundwater and soil at many sites contaminated with hazardous wastes. Bioremediation results in
- the reduction of both contaminant concentration and mass for many subsurface contaminants (e.g., petroleum hydrocarbons and chlorinated organics) and/or
- a beneficial speciation change in the bacteria in the biofilm that allow them to tackle other contaminants, such as heavy metals (e.g., mercury)
In other words, bioremediation is a great idea!
How to actually make it work requires an understanding of biofilm processes and engineering systems for introducing a biofilm into the contaminated ground and providing the necessary environment below the surface of the ground to encourage the biofilm to do its job.
Further reading on biofilms and bioremediation
Khan MM, Chapman T, Cochran K, Schuler AJ. Attachment surface energy effects on nitrification and estrogen removal rates by biofilms for improved wastewater treatment. Water Res. 2013 May 1;47(7):2190-8. DOI: 1016/j.watres.2013.01.036
Ayrat M. Ziganshin, Robin Gerlach, Thomas Borch, Anatoly V. Naumov, and Rimma P. Naumova. Production of Eight Different Hydride Complexes and Nitrite Release from 2,4,6-Trinitrotoluene by Yarrowia lipolytica. Applied and environmental microbiology, 2020. DOI: https://doi.org/10.1128/AEM.01296-07
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