Air Injected Phytoremediation of Diesel Contaminated Soils: Modeling and Column Studies

摘要

Phytoremediation is a plant-based technique with potential for enhancing the remediation of land contaminated by various pollutants. The use of deep-rooted plants for phytoremediation of contaminated soils has attracted a great deal of interest as an innovative technology as an alternative other methodologies. As a more innovative technique than conventional phytoremediation methods, air injected phytoremediation technique is introduced to enhance the remediation efficiency or to apply to the former soil vapor extraction or air sparging sites. A mathematical model that can be applied to phytoremediation, especially to air injected phytoremediation, for simulating the fate and the transport of a diesel contaminant in the vadose zone is presented. The approach includes a two-phase model of water flow in vegetated and unplanted vadose zone soil, as well as a two-region soil model of contaminant reactions under varying environmental conditions for vegetated soils. A time-specific root distribution model was combined with a vertical, unsaturated soil water flow equation as well as with a contaminant transport equation. To select the plant species, plant-screening test was conducted by comparing growth rates that were affected by five levels of diesel addition. Alfalfa showed the strongest resistance against the contaminant and its growth rate was not inhibited by diesel additions as corn and barnyard grasses were. Effects of air injection, alfalfa treatment, and air injection with alfalfa treatments on the removal of hydrocarbon were investigated by column studies to simulate the field situation. Polyvinylchloride (PVC) columns, 0.3m in diameter x 1.0m in height, were packed with diesel contaminated soils. Both the removal efficiency of usesel and the microbial activity were highest in air-injected and alfalfa-planted column soils. It was suggested that increased microorganisms activity stimulated by plant root exudates enhanced biodegradation of hydrocarbon compounds. Air injection provided sufficient opportunity for promoting the microbial activity. Air injected phytoremediation may be useful as a further approach to remediate diesel contaminated sites.