Remediation trials for hydrocarbon-contaminated soils in arid environments: Evaluation of bioslurry and biopiling techniques

• Biopile and bioslurry remediation methods were compared.
• Bioslurry was the more effective treatment hydrocarbon contaminated soils.
• Shift in microbial community composition observed.
• Alpha-proteobacteria dominated the microbial community in the contaminated soils.
• Bioslurry treatment led to Gamma-proteobacteria dominating the microbial community.

Effective bioremediation requires an extensive understanding of the soil parameters and microbial community diversity. Long term contamination of petroleum hydrocarbon soils in arid areas present unique opportunities to study the response of the impacted microbial community to bioremediation efforts. Two bioremediation treatments viz., biopile and bioslurry, were applied to assess the efficacy of different bioremediation methods in long term petroleum hydrocarbon contaminated soils. The bioslurry treatment was markedly more effective at treating the long term petroleum hydrocarbon contaminated soils in a short period of time. First order rates of hydrocarbon degradation in the bioslurry treatment were between 0.066 and 0.073 d−1 compared with the biopile treatment where the rates ranged from 0.011 to 0.03 d−1, depending on the level and nature of the hydrocarbon fractions present in the soils. Bioslurry treatment of the long term contaminated soils exhibited a shift in the microbial community composition. Alpha-proteobacteria dominated the microbial community present in the hydrocarbon contaminated soils but bioslurry treatment of the contaminated soils led to a clear shift in the microbial community present in the soils, with Gamma-proteobacteria dominating the remediation environment along with microbial sequences associated with the TM7 phylum and a subsequent reduction in hydrocarbon concentration in the soils.