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Chemosphere
Vol. 169, 2017, Pages: 124–130

Bioremediation of hydrocarbon degradation in a petroleum-contaminated soil and microbial population and activity determination

Luke Martinkosky, Jaimie Barkley, Gabriel Sabadell, Heidi Gough, Seana Davidson

Department of Civil and Environmental Engineering, University of Washington, Seattle, WA, USA.

Abstract

Crude oil contamination widely impacts soil as a result of release during oil and gas exploration and production activities. The success of bioremediation methods to meet remediation goals often depends on the composition of the crude oil, the soil, and microbial community. Earthworms may enhance bioremediation by mixing and aerating the soil, and exposing soil microorganisms to conditions in the earthworm gut that lead to increased activity. In this study, the common composting earthworm Eisenia fetida was tested for utility to improve remediation of oil-impacted soil. Efetida survival in soil contaminated with two distinct crude oils was tested in an artificial (lab-mixed) sandy loam soil, and survival compared to that in the clean soil. Crude oil with a high fraction of light-weight hydrocarbons was more toxic to earthworms than the crude oil with a high proportion of heavy polyaromatic and aliphatic hydrocarbons. The heavier crude oil was added to soil to create a 30,000 mg/kg crude oil impacted soil, and degradation in the presence of added earthworms and feed, feed alone, or no additions was monitored over time and compared. Earthworm feed was spread on top to test effectiveness of no mixing. TPH degradation rate for the earthworm treatments was ~ 90 mg/day slowing by 200 days to ~ 20 mg/day, producing two phases of degradation. With feed alone, the rate was ~ 40 mg/day, with signs of slowing after 500 days. Both treatments reached the same end point concentrations, and exhibited faster degradation of aliphatic hydrocarbons < C21, but all fractions, including aromatics > C21, decreased. During these experiments, soils were moderately toxic during the first three months, then earthworms survived well, were active and reproduced with petroleum hydrocarbons present. This study demonstrated that earthworms accelerate bioremediation of crude oil in soils, including the degradation of the heaviest polyaromatic fractions.

Graphical abstract

Keywords: Bioremediation; Earthworms; Heavy crude oil; Polycyclic aromatic hydrocarbons.

 
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