Abstract

Oil (or petroleum), consisting of a mixture of hydrocarbons, can leak from oil exploration, production, and use. Due to their complex mixture and interaction with the subsurface soil and water, they are hard to treat and can become a significant environmental concern. Rhamnolipid and sophorolipid biosurfactants, biologically produced surfactants, can be used to remove petroleum hydrocarbons. Nanoparticles have gained attention as promising materials for soil remediation. In many studies, nanoparticles have shown their effective degradation of oil pollutants in the soil, both at bench and field scales. However, the combination of biosurfactants and nanoparticles to treat oil-contaminated soil has not been thoroughly researched. In this study, suspension of iron/copper (Fe/Cu) nanoparticle and biosurfactant and mixture of biosurfactant foam and Fe/Cu nanoparticle were investigated for remediation of oil-contaminated soil. The results showed that Fe/Cu bimetallic nanoparticles were successfully produced with an average diameter of less than 20 nm, while Fe content was higher than Cu. The appearance of iron oxide and copper oxide was confirmed by X-ray diffraction (XRD) analysis.
The biosurfactant/nanoparticle suspension displayed a high oil removal rate from contaminated soil, followed the first-order reaction. For batch experiments, the oil remediation efficiency was up to 84%, based on the experimental conditions. Optimum conditions to achieve the highest oil remediation performance included a rhamnolipid biosurfactant: nanoparticle ratio of 10:1 (wt%: wt%), pH 7, room temperature, and shaking speed of 60 rpm for 60 minutes. The remediation rate was improved by higher temperature and lower ionic strength. In the presence and absence of nanoparticles, rhamnolipid biosurfactant demonstrated a higher remediation efficiency than sophorolipid biosurfactant and ultraplex surfactant. The presence of other surfactants decreased the treatment productivity by 9-14% compared to using only rhamnolipid biosurfactant. After three cycles, nanoparticles were reused with a remediation efficiency of 59% by rhamnolipid biosurfactant.
In column experiments, biosurfactant foam/nanoparticle and biosurfactant/nanoparticle mixtures were effectively used to remediate the actual oil-contaminated soil (fine sandy soil with the original oil content of 3722 mg/kg), whereas the highest treatment efficiency was 67%, 59%, and 52% for rhamnolipid biosurfactant foam/nanoparticle, rhamnolipid biosurfactant/nanoparticle, and only rhamnolipid biosurfactant, respectively. The oil removal productivity decreased with the increase of flowrate due to the shorter contact time between the foam mixture and oil droplets. The breakthrough curves of oil pollutants in the soil column also suggested that the foam mixture's maximum oil treatment efficiency was higher than biosurfactant/nanoparticle suspension and only biosurfactant.
These results suggested that biosurfactant/nanoparticle and biosurfactant foam/nanoparticle suspension can be effectively used to remediate oil from contaminated soil. This work will significantly benefit the soil remediation field by providing an environmentally friendly and economical method for the remediation of oil-contaminated soil. Future studies will evaluate the effect of other factors, such as biosurfactant concentration, nanoparticle dosage, pH, on column experiments. In addition, oil remediation effectiveness by suspension of biosurfactant or biosurfactant foam with other nanoparticles, such as Fe/Ni or Fe/Pd, in batch and column experiments should be evaluated.