Field and greenhouse phytoremediation of soils impacted by manufactured gas plant (MGP) activities
Abstract
The presence of vegetation contributes to the degradation of polycyclic aromatic hydrocarbons (PAHs) found in contaminated soils of manufactured gas plants (MGPs). Soils contaminated with PAHs at MGP sites frequently extend several feet in depth depending upon the time since deposition. This study focuses on the reduction of 16 EPA priority PAHs found at depths exceeding 4 feet from a wetland impacted by MGP activities more than a century ago. Two greenhouse studies were conducted using intact, 6-foot soil cores recovered from the wetland. Three tree species, Fraxinus pennsylvanica (green ash), Populus deltoides x P. nigra DN 34 (hybrid poplar), and Salix nigra (black willow), were planted as saplings in the soil cores. After eighteen months, soils were removed and PAHs extracted. Concentrations of all PAHs were lower in all treatments especially in vegetated treatments. Five PAHs were significantly lower in the ash and poplar treatments than in the controls. Total PAH-degraders were significantly higher in vegetated treatments than in non-vegetated treatments. A field study conducted at a former MGP site in Bedford, Indiana identified significant regions of soil contaminated by PAHs. Nine replicate plots were randomly placed over these contaminated zones. Hybrid poplar was selected for its rapid growth and ability to withdraw large volumes of water from soils. Each plot contained 60 hybrid poplar trees planted in 3-foot spacing in rows that were also spaced 3 feet apart. The evaluation of PAH-degrader populations after 18 months confirmed the hypothesis that hybrid poplar trees stimulate PAH-degrader microbial growth. Bacterial counts for vegetated treatments were higher than counts for unvegetated treatments (vegetated: log10 6.740 cfu g−1 versus unvegetated: log10 5.827 cfu g−1). Most contaminant concentrations declined over the 18-month period by nearly one log unit. This study showed that vegetation in the form of deep-rooting trees has the potential to enhance the growth of select PAH-degrading bacteria to degrade a number of the 16 EPA priority PAHs. Evidence of improvements within the rhizosphere by improving soil texture, lowering soil moisture, increasing oxygen diffusion, or by a combination of all three appears to have improved growth of these microorganisms.
Degree
Ph.D.
Advisors
Banks, Purdue University.
Subject Area
Environmental engineering|Environmental science
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