Pilot Scale Bioremediation of Creosote-Contaminated Soil—Efficacy of Enhanced Natural Attenuation and Bioaugmentation Strategies

ABSTRACT

In this study, the efficacy of bioremediation strategies (enhanced natural attenuation with nitrate and phosphate addition [ENA] and bioaugmentation) for the remediation of creosote-contaminated soil (7767 ± 1286 mg kg⁻¹ of the 16 EPA priority PAHs) was investigated at pilot scale. Bioaugmentation of creosote-contaminated soil with freshly grown or freeze dried Mycobacterium sp. strain 1B (a PAH degrading microorganism) was applied following bench scale studies that indicated that the indigenous soil microflora had a limited PAH metabolic activity. After 182 days, the total PAH concentration in creosote-contaminated soil was reduced from 7767 ± 1286 mg kg⁻¹ to 5579 ± 321 mg kg⁻¹, 2250 ± 71 mg kg⁻¹, 2050 ± 354 mg kg⁻¹ and 1950 ± 70 mg kg⁻¹ in natural attenuation (no additions) and ENA biopiles and biopiles augmented with freshly grown or freeze dried Mycobacterium sp. strain 1B respectively. In ENA and bioaugmentation biopiles, between 82% and 99% of three-ring compounds (acenaphthene, anthracene, fluorene, phenanthrene) were removed while four-ring PAH removal ranged from 33 to 81%. However, the extent of PAH degradation did not vary significantly between the ENA treatment and biopiles augmented with Mycobacterium sp. strain 1B. Four-ring PAH removal followed the order fluoranthene > pyrene > benz[a]anthracene > chrysene. The high residual concentration of some four-ring PAHs may be attributable to bioavailability issues rather than a lack of microbial catabolic activity. Comparable results between ENA and bioaugmentation at pilot scale were surprising given the limited degradative capacity of the microbial consortia enriched from the creosote-contaminated soil.

KEYWORDS:

• bioaugmentation
• bioremediation
• enhanced natural attenuation
• fluoranthene
• PAHs
• pyrene

ACKNOWLEDGEMENTS

This research was supported by an AusIndustry BioInnovation Fund grant awarded to Flinders Bioremediation by the Commonwealth Government of Australia. We wish to thank Charles Ling for his assistance during the project.

Notes

^a Values represent the mean and standard deviation of three replicate measurements.

^b Concentration after fertiliser addition.

^a Values represent the mean and standard deviation of three replicate measurements.

^a Rates of PAH removal were calculated using PAH concentrations in killed controls at the corresponding time point. PAH removal rates within rows followed by the same symbol are not significantly different from each other (p < 0.05).

^b Not Determined.

^a After 182 days in biopiles augmented with freshly grown Mycobacterium sp. strain 1B.

^b Determined using the bioavailability method of Cuypers et al. (2000).

^c Values represent the mean and standard deviation of three replicate measurements of residual PAH concentrations in soil.

^d Not determined.