Phytoremediation removal rates of benzene, toluene, and chlorobenzene

ABSTRACT

Phytoremediation is a sustainable remedial approach, although performance efficacy is rarely reported. In this study, we assessed a phytoremediation plot treating benzene, toluene, and chlorobenzene. A comparison of the calculated phytoremediation removal rate with estimates of onsite contaminant mass was used to forecast cleanup periods. The investigation demonstrated that substantial microbial degradation was occurring in the subsurface. Estimates of transpiration indicated that the trees planted were removing approximately 240,000 L of water per year. This large quantity of water removal implies substantial removal of contaminant due to large amounts of contaminants in the groundwater; however, these contaminants extensively sorb to the soil, resulting in large quantities of contaminant mass in the subsurface. The total estimate of subsurface contaminant mass was also complicated by the presence of non-aqueous phase liquids (NAPL), additional contaminant masses that were difficult to quantify. These uncertainties of initial contaminant mass at the site result in large uncertainty in the cleanup period, although mean estimates are on the order of decades. Collectively, the model indicates contaminant removal rates on the order of 10⁻²–10⁰ kg/tree/year. The benefit of the phytoremediation system is relatively sustainable cleanup over the long periods necessary due to the presence of NAPL.

KEYWORDS:

• rhizodegradation
• hydrocarbon phytoremediation
• site cleanup

Competing interests

The authors declare no competing financial interests

Funding

This work was funded by the Dow Chemical Company. Methods and procedures applied were based upon work supported by the National Science Foundation under Grant #1336877, and Matt Limmer was supported by the National Science Foundation through a graduate research fellowship and by the USDA through a postdoctoral fellowship (Award #2016-67012-24673).