Zoom in on microorganisms

Microorganisms that restore soil

 Pseudomonas aeruginosa ZoomZoom
© Richard Villemur, INRS- Institut Armand-Frappier

In recent decades, industrial spillages of various chemical products such as petroleum hydrocarbons or polychlorinated biphenyls (PCBs) have created an environmental pollution problem. Furthermore, some of these products may cause health problems.

The enzymes of some organisms found in the environment, bacteria and fungi, are capable of breaking the chemical structure of these substances and reducing them to harmless compounds. These microorganisms may be used as a biological alternative to conventional methods of decontamination (incineration, for example) or burial, offering a promising approach to the treatment of contaminated sites.

It is possible to optimize the use of microorganisms for the biodegradation of hydrocarbons and other contaminants.

The big petroleum companies such as Shell Canada hire experts to characterize and biologically treat contaminated industrial soils in order to restore them. According to the guidelines established by the Soil Protection Policy of the Ministry of Environment (criteria: A 100 ppm, B 700 ppm, C 3500 ppm), biotreated soils containing a maximum of 15 000 ppm (parts per million) of petroleum hydrocarbons can be classified as biotreated soils instead of contaminated soils. However, these soils must be used as industrial soils, for the burial of domestic waste, for example.

At the Shell Canada treatment platform in Montreal, the contaminated soils are aerated in order to facilitate the development of the microorganisms (bacteria and fungi). Naturally present in the soil, these microorganisms then feed on hydrocarbons. The bacteria Pseudomonas aeruginosa is one of these useful indigenous bacteria. If necessary, the soil can be inoculated with other bacteria or fungi to accelerate the process. In these cases, the fungi Phanerochaete chryssosporium, a microscopic fungus of white rot, may be added. This fungus naturally degrades lignin (a molecule present in bark of trees) due to the presence of a non-specific enzyme. It can also rapidly degrade recalcitrant hydrocarbons.