A greenhouse lysimeter experiment was performed to evaluate the use of in-situ bioremediation and phyto-remediation to reduce mineral oil concentrations in a weathered contaminated soil. The hypotheses for the study were (1) a combination of microbial- and phyto-remediation would yield a best remediation strategy, and (2) the addition of low levels (10 mg/L) of a biosurfactant would stimulate and increase the rate of remediation by increasing the bioavailability of the mineral oil in the soil. The results indicate, on average, a higher rate of mineral oil removal occurred in planted lysimeter tanks versus non-planted lysimeter tanks. Specifically, for unplanted treatments an average of 22% of the mineral oil was removed in 24 weeks in comparison to the planted treatments for which an average of 54% of the mineral oil was removed. The effect of application of fertilizer on mineral oil degradation was unclear, but a visual inspection showed that vegetated tanks receiving fertilizer had better growth. No conclusions can be made regarding the addition of biosurfactant. Though a couple of the lysimeter tanks receiving biosurfactant performed relatively well, overall, the results were inconclusive. Enumeration of mineral oil degraders showed that there was a statistical difference between planted tanks and unplanted tanks with planted tanks having higher numbers. These results help support the conclusion that plants enhanced mineral oil degradation. Enumeration of total heterotrophs showed that there was no statistical significant difference between the planted and unplanted treatments. In conclusion, this study demonstrated that a low-cost, low-maintenance approach to facilitate remediation of weathered mineral oil contaminated soil is a combination of microbial- and phyto-remediation.
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