Evaluation in microcosm of biostimulation and bioaugmentation efficacy on diesel-contaminated soil

Abstract

Bioremediation is a promising technology for the treatment of hydrocarbon (HC) contaminated soils that is based on the biodegradation capacities of native or introduced microbial populations. Biotractability tests are essential for choosing the optimal bioremediation treatment. For this purpose, multiple microcosm tests, based on biostimulation by landfarming or bioventing and addition of nutrients, were conducted for 120 days on a soil contaminated by diesel, after assessing its intrinsic catabolic potential. An additional bioaugmentation treatment was performed for further 60 days by inoculating selected HC degrading bacteria. HC (C10-C40) concentration was monitored by GC-FID analysis and the bacterial community evolution was analyzed by Illumina-MiSeq sequencing. The contaminated soil was dominated by Acidobacteria, Actinobacteria, Alphaproteobacteria and contained high diversity of potential HC degrading genera. The bacterial communities in microcosms after 120 days of biostimulation respond to bioremediation treatment with a shift on the composition. The main changes observed were an increase of Actinobacteria, Betaproteobacteria and Alphaproteobacteria in bioventing microcosms, while TM7 and Gammaproteobacteria increased in landfarming treatment. Higher abundance of HC degrading genera was detected in both microcosm types in respect to the untreated soil, mainly in landfarming. Approximately 40% of HC was removed after 180 days of sequential bioremediation applications. Longer incubation and finer tuning of nutrients could bring to a more effective reduction of pollutants, encouraging the HC degrading bacteria and increasing the biodegradation efficiency.