Rapid remediation of soil heavily contaminated with hydrocarbons: a comparison of different approaches

Abstract

To improve our understanding of the dissipation kinetics of total petroleum hydrocarbons (TPH), we tested two bioremediation strategies in soil heavily contaminated with hydrocarbons. In one strategy, different fertilizers and composted winery products were used to stimulate a local microbial community capable of dissipating petroleum hydrocarbons. In the second approach, polluted soil was used for the enrichment and isolation of potential hydrocarbon-degrading bacteria that were subsequently used for implementing a bioaugmentation strategy. The efficacy of both strategies was evaluated using the Hockey-Stick and first-order kinetics models. Two Pseudomonas isolates designated as el20 and el15 were able to readily degrade TPH and n-alkanes both in vitro and in a microcosm study. Phylogenetic analysis based on 16sRNA gene sequencing revealed that both strains showed a high similarity with Pseudomonas otitidis and P. stutzeri. Enrichment with both compost and nitrogen fertilizer enhanced the dissipation of TPH. Overall, compost-treated soils exhibited the highest degradation rates, with half-life (T_½) values ranging from 13 to 37 days. Urea-treated soils exhibited the lowest TPH T_½ values among the soils treated with inorganic fertilizers. The addition of glucose to soils treated with inorganic nitrogen fertilizers retarded the degradation rate of TPH, with estimated T_½values measurements ranging from 70 to 140 days. Different dissipation patterns were noted among the different n-alkane fractions, with short chain molecules (up to 14 carbon atoms) being rapidly reduced within the first 21 days, whereas long chain molecules were more recalcitrant. In summary, we demonstrated that Pseudomonas-like strains and in situ soil incorporation of compost derived from winery byproducts can be effectively used for the rapid bioremediation of soil heavily polluted with hydrocarbons.