Enhancing Bioremediation of Petroleum-Contaminated Soil Using Rhamnolipids: A Combined Laboratory and Field Study

Abstract

Abstract Hydrocarbon spills can occur at various stages of the oil and gas exploration and production workflow. It would be beneficial to be able to treat these spills on-site to avoid more expensive excavation and incineration processes. This study aims to optimize the use of rhamnolipid biosurfactants for enhancing the bioremediation of hydrocarbon-contaminated soil. The goal of this work was to explore the effects of rhamnolipid application on hydrocarbon degradation rate under both laboratory and field conditions, and to examine the effects of this treatment on the indigenous soil microorganism population. The results have demonstrated the potential for rhamnolipids to enhance the remediation of petroleum hydrocarbons in contaminated soils. The laboratory experiments showed that the application of rhamnolipids at above 0.5g/kg was effective in increasing bacteria activity in the soil. Knowledge from the lab tests was used to design the field experiments, and the respirometry results were combined with biological stoichiometric calculations to determine the appropriate nutrient loading for the field site. Lab tests are a critical prerequisite for understanding bioremediation mechanisms for a particular contaminated site and designing an effective field treatment program. The field results correlated with the laboratory respirometry results, and the field study confirmed that the application of rhamnolipid in combination with ammonium chloride as the nitrogen source was able to improve the overall health of the soil. Bacterial analysis demonstrated that addition of rhamnolipid enriched the soil in Pseudomonas and Serratia bacterial species, which are known hydrocarbon degraders. Additionally, these strains were shown to degrade rhamnolipid, and this affirms the beneficial aspect that applied rhamnolipid won't accumulate and persist in the environment. Overall, this work provides insight into the combination of laboratory and field studies when using rhamnolipids to enhance bioremediation of contaminated soils.