Plant Growth Promoting Rhizobacteria (PGPR) Enhanced Phytoremediation Systems (PEPS) have been successfully developed through a collaboration between Waterloo Environmental Biotechnology, Earthmaster Environmental Strategies and the University of Waterloo.
These remediation systems are based on multiple complementary techniques that target different aspects of petroleum and salt impacted soil remediation. The result is enhanced systems with improved and accelerated remediation kinetics. This leads to more rapid and more complete removal of hydrocarbons and salt from soil. Importantly, PEPS not only removes hydrocarbons from soil, but results in their metabolism to non-toxic molecules. For salt, PEPS provides plant tolerance to elevated salt levels, allowing better plant growth with commensurate sodium chloride up-take into above-ground plant tissue.
Soil Pre-Treatment: cultivate soil to homogenize, prepare a seed bed, aerate and allow for some photochemical degradation of contaminants.
Phytoremediation (plant growth) with plant growth promoting rhizobacteria (PGPR): The PGPR increase plant tolerance to petroleum and salt stress. This leads to rapid growth of plants, including roots, for effective partitioning of contaminants out of the soil.
The resulting PGPR-induced vigorous plant growth leads to greater proliferation of naturally existing microbes in the soil, leading to a very active rhizosphere. This is typical of soils with normal plant growth. The tremendous biological activity we realize in the rhizosphere results in hydrocarbon degradation. The high biomass is also important for salt partitioning out of the soil into above-ground plant tissue.
The PGPR used in this work are all non-pathogenic, non-genetically modified pseudomonads native to Canadian soils. They are sensitive to common antibiotics, do not grow at 37C, and are all classified as Biosafety Level 1 (the safest possible designation). Thus, they pose no threat to humans, wildlife or the environment. The PGPR are used only via a seed treatment; the seeds are treated in a controlled environment and only the plant roots of the treated seeds are inoculated with the PGPR as they pass through the seed coat. Thus, this is classified as a seed treatment, not bioaugmentation.
The complementary processes build on each other so that remediation is rapidly initiated and is sustained throughout the growing season.
The PGPR mitigate production of deleterious stress ethylene in the plants, and they synthesize auxin, which is transferred to the plant. Together, these processes promote vigorous root and shoot growth under environmental stress conditions.
With PGPR, the large amount of root biomass in the soil allows for effective partitioning of contaminants out of the soil.
The PGPR have the ability to metabolize PHC.
PEPS results in high rates of metabolism of hydrocarbons, and improved up-take of salt.
The PGPR also protect plants against other potentially phytotoxic compounds (e.g., metals) and conditions (e.g., cold, drought) at the site to be remediated.
We have successfully field tested PEPS at several PHC and salt impacted sites across Canada. We remediated F2, F3 and F4 PHC to generic Tier 1 criteria at 4 sites (3 in Alberta and 1 in Manitoba).
We are now using PEPS at 6 second generation PHC impacted sites and are realizing results similar to the 4 first generation sites. Over the past 3 years we have field tested the system for salt remediation at 5 sites in Saskatchewan, Alberta and the Northwest Territories. The results are excellent: for soils with ECe’s in the range of 25 dS/m, we have achieved vigorous plant growth and NaCl uptake. Based on this, we predict that within the rooting zone of sites with Ece’s in the range of 15 dS/m, the sites could be remediated in approximately 5 – 7 years.