Abstract
In the present study, a combined treatment strategy involving the addition of rhamnolipid, rhamnolipid-producing bacteria (Shewanella sp. BS4) and a native soil microbial community for the remediation of hydrocarbon-contaminated soil under pilot-scale conditions was adopted. The isolate BS4 (rhl+), demonstrating the highest emulsification activity and surface tension reduction efficiency, was identified based on 16 S rDNA sequencing as Shewanella sp. strain. Growth conditions for rhamnolipid production were optimized based on Central Composite Design (CCD) as 2.9% crude oil, a 54 × 106 CFU g−1 inoculation load of soil, a temperature of 30.5 °C, and a pH of 6.7. In situ bioremediation experiments, conducted using hydrocarbon-contaminated soil treated with the combination of rhamnolipid and rhamnolipid-producing bacteria, showed that the inoculated Shewanella sp. BS4, along with the indigenous soil microbial community, supported the highest hydrocarbon-degrading bacterial population and soil respiration activity, and this treatment resulted in 75.8% hydrocarbon removal efficiency, which was higher compared to contaminated soil devoid of any treatment.
Highlights
Heavy dependence on petroleum products as a major energy source has led to the contamination of soils by oil-derived hydrocarbons to a great extent [1]
Among a total of 37 morphologically and biochemically distinct isolates that were able to grow on a mineral salt medium supplemented with 2% crude oil, the presence of the RhlAB operon was confirmed for four isolates by PCR analysis (Figure S1)
[52,53,54],and andany anychange changeinin organic matter quantity or quality can be observed as a change in soil respiration and/or inin organic matter quantity or quality can be observed as a change in soil respiration [54,55] and/or ofof the present study clearly showed that the addition ofof rhamnolipids
Summary
Heavy dependence on petroleum products as a major energy source has led to the contamination of soils by oil-derived hydrocarbons to a great extent [1]. Soil contamination by hydrocarbons can be a result of an improper production process (i.e., oil spills from drilling), transport (i.e., oil spills from tankers or pipelines), storage (i.e., leaking storage tanks), or an improper disposal process. Soil hydrocarbon contamination can affect the functional equilibrium that exists between soil biota and their natural environment. Numerous physicochemical remediation techniques can be applied to clean up oil-polluted soils, these techniques are expensive and disruptive [2]. The application of biological remediation techniques, such as biostimulation and bioaugmentation, as well.
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