Comparison between different bio-treatments of a hydrocarbon contaminated soil from a landfill site

Abstract

We investigated the bio-remediation of a hydrocarbon contaminated soil pile that was slated for landfill disposal, by utilising laboratory based-soil microcosms. The objective was to accelerate the reduction of soil total petroleum hydrocarbon (TPH) to levels that could potentially allow the soil to be used outside a landfill site. Soil TPH content reduced by 57% over a 2 year period from 15,800 to ~6,800 mg kg^-1 in the untreated pile, making the soil eligible for landfill disposal under current Australian legislation. Subsequent bio-remediation (natural attenuation, biostimulation, bioaugmentation and biostimulation-bioaugmentation) resulted in over 74% reduction (~1,800 mg kg^-1) in soil TPH content over 56 days with most of the reduction occurring in the first 21 days (~60%). Nutrient and microbial amendments did not confer any long-term benefit on the rate of soil TPH reduction with natural attenuation being equally efficient as other bioremediation strategies at day 56. TPH bioavailability assay showed a linear decrease from an initial 84 to 35% by day 56 and could explain the reduced TPH reduction rates observed after day 21. Denaturing gradient gel electrophoresis (DGGE) analyses of 16S rDNA and internal transcribed spacer regions genes revealed diverse and stable (unaffected by amendments) bacterial and fungal communities. Microbial analysis also showed substantial populations of alkane (alkB) degrading bacteria in the soils. This study therefore showed that soils slated for landfill disposal possess substantial hydrocarbon degrading capacity, which can be exploited for greater TPH removal through natural attenuation. The soil TPH can be potentially reduced lower than the 1,800 mg kg^-1 obtained in this study provided the contaminant is made more bio-available. This would potentially allow the use of such soils for more productive purposes outside the landfill sites extending the lifespan of these sites.

Key words: Bioremediation, denaturing gradient gel electrophoresis (DGGE), 16S rDNA, ITS, alkB