Bioremédiation de sols en milieu nordique : des ressources locales pour traiter une variété d’hydrocarbures pétroliers et autres contaminants avec la phytoremédiation, la mycoremédiation et l’aide de matières résiduelles fertilisantes

Petroleum hydrocarbons are shipped and used in virtually all parts of the world and have become one of the most common and widespread contaminants in soils. Trace elements are sometimes associated with them, and they can increase the toxicity of a site, complicate remediation, and increase the costs of traditional treatments. In northern areas where spills occur at multiple sites, the clean-up time and cost of traditional remediation methods can be significantly higher than in temperate regions. Alternative research aimed at faster and cheaper remediation adapted to subarctic climates is needed and the use of native plants and fungi integrated into the local ecosystem are promising approaches. Concurrently, governments in multiple countries aim to reduce greenhouse gas emissions, namely through the reduction of putrescible waste destined for landfills. By using locally-sourced residual fertilizing materials for decontamination processes, an opportunity arises to valorize these materials while restoring soils. This doctoral research aims to develop locally-adapted bioremediation methods, with indigenous plant and fungal inputs, to treat petroleum hydrocarbon contaminated soils in three large-scale field research projects, including one also contaminated with trace elements. Two projects were carried out in a subarctic climate at the 60 ° parallel (Whitehorse, Yukon), using an innovative approach of phytoremediation assisted by mushrooms and municipal compost; we call this integrated technique the "ecological microsystem" approach. Because soil volume has significant impacts on the efficiency of bioremediation methods, considerable volumes of 0.15 m3 and 1 m3 were used (at the first and second sites, respectively) to maximize the relevance of results in the event of a scale-up operation. At the first site, the effectiveness of the various components of the microsystem were evaluated in four different combinations, as well as compared to the usual basic treatment (fertilizer) in soil contaminated by an accidental diesel spill. The plant species chosen was Salix planifolia and Pleurotus ostreatus was selected for the fungus. Results indicate that after one treatment season, the microsystem was the treatment with the fastest diesel removal rates. After three seasons, treatments containing one or more elements of the microsystem were below standards for agricultural soils and were more effective than fertilizer treatment or natural attenuation. The second northern site was a waste oil pit located on top of a mine waste rock pile, at the heart of an old landfill. The microsystem was implanted into ground-level cells with a contaminant-proof leachate liner. The plant species Salix alaxensis and Salix planifolia were used in combination with the fungus Trametes versicolor. This approach in a highly contaminated soil was able to significantly reduce petroleum hydrocarbons (65 to 75%). The potential for metal accumulation in aerial plant tissues was also measured. Both willow species demonstrated distinct trace element accumulation patterns and different rooting strategies. A fungus of the Psathyrellaceae family was observed for the first time at a site so highly contaminated and was recurrent on the cells of the microsystem for 4 years. The first two sites contribute to the development of efficient and passive bioremediation methods applicable in subarctic climates. The third research site focused on the use of two residual fertilizing materials (fragmented rameal wood and brewer’s spent grain) and manure for the degradation of motor oil in a humid continental climate at a medium latitude (Neuville, Quebec). Mesocosms of 0.76 m3 with controlled aeration were used. Innovative aspects of this project include the use of rameal wood and spent grain at this scale, as well as the acquisition of residual materials in a very close radius of the treatment center to explore how a circular economy approach could apply in such a context. Results indicate that the addition of manure is more effective than the usual fertilizer treatment alone. Brewer’s spent grain and fragmented rameal wood were useful for maintaining soil moisture (an important bioremediation parameter) but did not increase degradation. This study, conducted in close collaboration with an industrial partner, falls under the objectives set by Canadian and Quebec policy on greenhouse gas reductions and circular economy approaches by working on the valorization of local residual organic matter. This thesis has demonstrated that combining strategies with local biological components is an effective bioremediation method in a subarctic climate. Two new willow species (Salix planifolia and Salix alaxensis) have been successfully used for the bioremediation of petroleum hydrocarbons and for the accumulation of certain trace elements. In collaboration with an industrial partner, it has been possible to demonstrate the applicability of certain circular economy concepts and the ecosystemic approach to bioremediation.

Keyphrases: Mycoremédiation, Bioremediation, Phytoremediation, Cold climate, Mycoremediation, Petroleum hydrocarbons, Trace elements, Metals and metalloids, Contaminated sites, Circular economy, Ecological microsystem, Soil microbiome, Genomic, Ecosystemic approach