Effects of biostimulation and bioaugmentation on diesel removal and bacterial community

Abstract

The evolution of the bacterial community during the bioremediation of diesel-contaminated soil using laboratory scale bioreactors was investigated for 120 days, evaluating the effect of adding individually or together, a mature compost, a bacterial consortium and the biosurfactant (β-cyclodextrin). The dynamics of microbial community was assessed using both a culture-dependent method and denaturing gradient gel electrophoresis (DGGE) analysis of PCR-amplified 16S rDNA gene fragments. Results showed that the addition of compost plus a bacterial consortium caused a progressive increase in both heterotrophic cultivable aerobic bacteria and presumptive Pseudomonas. During the initial stage of the process, biostimulation and bioaugmentation increased species diversity (evaluated by DGGE analysis) and increased biomass-C content. After a transient drop caused by the xenobiotic contaminant, the bacterial community diversity and biomass-C content were restored at the end of the process. The density and activity of the microflora were similar in microcosms with or without β-cyclodextrin, but under the conditions tested, a reduction in total petroleum hydrocarbon (THP) removal was observed in the microcosms containing β-cyclodextrin. The combined use of mature compost and of a selected microbial consortium is a useful strategy for improving TPH removal, achieving a high TPH degradation (96%) at the end of the bioremediation process (120 days).