Project Overview
Approved for funding through ERA’s Biological GHG Management Program in 2014, this project explored the use of native plants and biochar to clean contaminated soil while reducing greenhouse gas (GHG) emissions in the process. By its completion in 2015, the project trials demonstrated significant reduction of contamination using phytotechnologies, leading to a recommendation for a follow-up field trial.
Sustainable Soil Remediation Using Plant Technologies
Petroleum hydrocarbons (PHCs), found in oil, coal, and bitumen, are one of the most widespread soil contaminants, found frequently in abandoned and orphan wells across Alberta. Soil can become contaminated with PHCs from accidental spills and improper waste disposal. Polycyclic aromatic hydrocarbons (PAHs) are a particularly toxic group of PHCs, and cleaning contaminated soil is energy-intensive, time-consuming and expensive. In addition to GHG emissions directly related to the contamination, traditional clean-up strategies generate emissions from disturbing the soil and transporting it long distances to appropriate hazardous landfill facilities for disposal.
This project tested an improved solution for remediating contaminated soils. Phytoremediation, the process of planting native trees and plants in contaminated soil, encourages the growth of petroleum-eating bacteria while also naturally removing carbon from the atmosphere. For this project, two phytotechnologies were selected to address contamination: (1) Rhizodegradation, the breakdown of organic contaminants through microbial activity in the plant root zone (rhizosphere), and (2) Biochar amendment, mixing biochar into the soil to promote plant growth and reduce GHG emissions from organic decay. Combining phytoremediation with biochar amendment offers a sustainable, green solution to lower carbon emissions of contaminated sites.
This project aimed to remediate and characterize PHC contaminated soils from a selected PHC-contaminated site in Alberta while assessing potential GHG reductions for a follow-on demonstration. Greenhouse experiments used native plant species, such as alfalfa and yellow clover, as well as biomass to determine how phytotechnologies and biochar can best interact to lower carbon emissions and optimize contaminated site remediation. The techniques explored in this project could support PHC cleanup across the province —from light products like gasoline, to heavy lubricating oils.
Trials Demonstrated Significant Reduction in Soil Contamination
The project conducted one greenhouse experiment to determine if plant species could remediate the hydrocarbons with and without biochar. Results indicated that biochar enhanced plant growth. During the trials, both alfalfa and yellow clover showed promising results, with significant remediation of PAHs demonstrated in alfalfa planted soils. One experiment involved “spiking” soil with diesel to determine how well the combination of rhizodegradation and biochar would work on different concentrations and types of PHC contamination. This experiment resulted in significant remediation when planting these soils with clover. The researchers found that biochar did not enhance the rhizodegradation of PHCs in the short-term, however, over the long-term, adding biochar has the potential for improved degradation. Assessment of the microbial activity in the soils indicated biochar may improve soil quality, and showed promise in reducing immediate toxicity of recent hydrocarbon spills. Overall, the project greenhouse treatability trials demonstrated significant reductions of PHC and PAH levels in the Alberta soils using rhizodegradation and biochar amendment.
What’s next?
A follow-up field trial using alfalfa and yellow clover is highly recommended . The success of the trials during the study indicated that significant reductions in petroleum hydrocarbons can occur within a single growing season, therefore, a field trial would allow a full assessment of the potential GHG reductions. The GHG reductions from biochar production and increased plant growth depend on the production and source material of the biochar and plant species used. It is recommended the follow-up field trial should incorporate at least two plant species and the use of locally produced biochar to enhance GHG reductions. The plant species reported on in this study would provide the most promising remediation for soils contaminated with PHCs in the top 30 cm. Although phytoremediation is still considered an emerging technology, it has been researched for decades and remains a current practice for remediating PHC contaminated soils. Biochar continues to be explored in the ecosystem and shows promise, however, it is very challenging due to the environmental factors involved.