Plant bacterial inoculants to remediate hydrocarbon contaminated soil
Fernet, Jennifer Lynne
The hypothesis for this study was that phenanthrene degrading bacterial inoculants, in combination with grass species able to tolerate petroleum hydrocarbon contamination, will result in increased degradation, as compared to natural rates of hydrocarbon degradation, or to rates of degradation attributed to bacteria or plants alone. Three experiments were performed to examine this hypothesis: i) assessment of the effect of phenanthrene degrading bacteria (Sphingomonas yanoikuyae, Rahnella aquatilis, and Arthrobacter globiformis) on seed germination, location of attachment on seeds and roots, and inoculant survival on selected grass species, ii) determination of the inoculant survival in contaminated soil in the absence of plants and the ability to degrade target compounds, and iii) degradation potential and survival of selected grass species and bacterial inoculants in soil. In general, all applied inoculants were able to effectively colonize the seeds and had a neutral or positive effect on seed germination and seedling growth. Possible plant and bacteria pairs were chosen based on positive influence of the inoculant and are as follows: perennial ryegrass (Lolium perenne) or creeping red fescue (Festuca rubra) with A. globiformis or S. yanoikuyae, or slender wheatgrass (Elymus trachycaulus) with A. globiformis or R. aquatilis. Soil-based assessment of the survival and degradation of hydrocarbons by the selected inoculants was examined with or without a manure nutrient amendment. The addition of the inoculants had a positive impact on the efficacy of hydrocarbon removal in the soil. The manure-amended soil, or A. globiformis inoculated non-amended soil treatments reduced total petroleum hydrocarbon concentration by ~45%, whereas the non-amended control only resulted in a ~20% reduction. When soils were amended with manure and inoculated with any of the phenanthrene degrading bacteria, contaminant concentration decreased in soil by ~33%. Sphingomonas yanoikuyae survived the longest in soil in the absence of plants. A growth chamber experiment was conducted to determine the efficacy of plant and bacteria pairs for hydrocarbon removal in recalcitrant contamination found in soil from Bruderheim, Alberta. Additional replicates containing this soil were spiked with hexadecane, phenanthrene, and pyrene so the effectiveness of the plant and bacteria pairs at higher levels of fresh contamination could be assessed. In the spiked treatment, inoculation with S. yanoikuyae increased creeping red fescue root biomass. In the non-spiked treatment, S. yanoikuyae application increased creeping red fescue root and shoot biomass. Perennial ryegrass root and shoot biomass did not increase when inoculated with S. yanoikuyae, although root biomass values were observably higher in non-spiked soils. Creeping red fescue inoculated with S. yanoikuyae resulted in the greatest decrease in hydrocarbon concentration as compared to other treatments (~61%). The perennial ryegrass treatment, when inoculated with S. yanoikuyae increased percent hydrocarbon removal (~10%) above that obtained with perennial ryegrass alone. The addition of plants and S. yanoikuyae increased hydrocarbon degradation relative to control soils, although the addition of vegetation alone had a comparable effect. A critical benefit of inoculation was the increase in creeping red fescue root biomass at higher concentrations of contamination. This is important because the larger the root biomass the larger the volume of soil that can be remediated. The results indicate that the use of specific plant-bacterial inoculants can enhance remediation of hydrocarbon contaminated soils.
DegreeMaster of Science (M.Sc.)
SupervisorLawrence, John R.; Germida, James J.
CommitteeKnight, J. Diane; Hynes, Russell K.; Walley, Frances L.
Copyright DateFebruary 2008
creeping red fescue