Thesis Abstracts 2003

An Assessment of Hydrocarbon Bioremediation in the Canadian Arctic

By: 2Lt Paul Francis, MSc

Supervisors: Dr. Kenneth Reimer and Dr. John Poland

Abstract

Spilled hydrocarbons are currently the most prevalent chemical contaminant in Arctic soils. The remote and austere nature of Arctic installations has created an impetus for the development of robust, and cost-effective remediation methods. Landfarming and biopile treatment systems have shown promise as two potential treatment methods that reduce soil hydrocarbon concentrations through a combination of volatilization and biodegradation.

The focus of this thesis was to determine the relative contributions of physical and biological processes to hydrocarbon degradation, in both field and laboratory based studies. Two actively heated and aerated biopiles were constructed at the North Warning System radar site at Cape Dyer, Nunavut. The effectiveness of these biopiles over a period of one year was compared to the bio-venting system at Savitok Point which has been operating since the summer of 2000. Laboratory microcosms were used to study the extent of biodegradation and volatilization of fresh and weathered spills at 7?C and 20?C under optimal soil conditions.

Changes in total TPH concentration were used to assess the overall effectiveness of the field treatments. The ratios of the straight-chain alkanes heptadecane, and octadecane, to the branched alkanes, pristane and phytane was used to determine the presence of biodegradation at both sites. Preferential depletion of straight-chain alkanes is indicative of hydrocarbon biodegradation. The effectiveness of biodegradation in the laboratory microcosms was monitored using a combination of hydrocarbon removal, 14C labeled dodecane mineralization, preferential depletion of straight-chain alkanes, and changes in microbial population.

Both field applications demonstrated an ability to decrease the total concentration of hydrocarbons in the soil; however, losses in the Cape Dyer biopiles were restricted to the surface layer of soil. No preferential alkane depletion was observed in either the Cape Dyer or Savitok Point treatments, suggesting that volatile losses may have been dominant in both systems. This result is not conclusive, however, as the low concentrations of pristane and phytane in the fuels used resulted in poor precision when calculating the various ratios.

The laboratory experiments indicated that stimulation of microbes indigenous to Cape Dyer by nutrient addition was minimal. All treatments, regardless of biological activity or spill age demonstrated an ability to lower hydrocarbon concentrations to some extent, with sterile microcosms that were left open to the air producing levels of hydrocarbon removal equal to the most effective live treatments. The relative rates of total hydrocarbon removal were not found to correspond to the rates of dodecane mineralization, suggesting that care must taken when interpreting the results of this method when assessing the potential of a soil for bio-treatability.

In general, the results of this thesis suggest that the relative contribution of volatilization in above-ground landfarms and biopiles may be much greater than the contribution from biodegradation. Effective aeration to encourage volatilization therefore appears to be the most promising method for rapid and effective removal of hydrocarbon contamination from excavated soils.