The effectiveness of phytoremediation as a secondary treatment for aged polycyclic aromatic hydrocarbons (PAHs) in soil

Zakia Denise Parrish, Purdue University

Abstract

Polycyclic aromatic hydrocarbons (PAHs) are potentially carcinogenic compounds found in high concentrations in manufactured gas plant (MGP) residues. However, PAHs in soils contaminated with these residues are often highly resistant to degradation, particularly after the soils have been remediated with conventional techniques such as composting or land treatment. Phytoremediation holds promise as a finishing procedure for traditional approaches when significant PAH concentrations are present. Two greenhouse studies investigated the fate of the 16 EPA priority pollutant PAHs in MGP soil using phytoremediation as a secondary treatment. In the first study, contaminated soil was composted, and then planted with tall fescue (Festuca arundinacea), annual ryegrass ( Lolium multiflorum), and yellow sweet clover (Melilotus officinalis ). Total PAH concentrations decreased after 12 months in treatments with tall fescue, annual ryegrass, and yellow sweet clover by 23.9%, 15.3%, and 9.1%, respectively. Tall fescue and annual ryegrass both had significantly higher root surface area than yellow sweet clover, but were not significantly different from one another. The PAH-degrader populations were not significantly different between treatments. In the second study, contaminated soil was land treated, and then planted in the greenhouse with tall fescue and yellow sweet clover. To evaluate the impact of root decay on contaminant dissipation, plants were killed in some of the vegetated pots to induce root decay. Significant differences were noted between treatments for seven PAHs, with unkilled yellow sweet clover resulting in 60–75% degradation of these compounds. The PAH degrader populations in the vegetated treatments were over 100 times greater than that of the unvegetated control. The PLFA structural group profile shifted over time, indicating a change in the community structure. A final study evaluated the lability of the PAHs in the soil from both greenhouse experiments. Resin-extractable PAHs (assumed to be bioavailable) decreased significantly during the greenhouse experiments. For five PAHs in the compost samples and three PAHs in the land-treated samples, the planted soils had lower available concentrations than unplanted soils; for the remaining PAHs, no differences existed. Phytoremediation is clearly capable of enhancing contaminant dissipation beyond that of conventional biotreatment techniques.

Degree

Ph.D.

Advisors

Banks, Purdue University.

Subject Area

Environmental engineering|Civil engineering|Environmental science

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