Evaluating the efficiency of phytoremediation, a plant aided clean-up technology, for soil contaminated by volatile organic compounds (VOCs) is important since limited information is available on the mechanisms and effects of phytoremediation on VOCs contaminated vadose zone. The objectives of this research are, (i) to investigate the main mechanisms of VOCs dissipation in soil, (ii) to examine the applicability of grasses for remediation of soils contaminated by VOCs, and (iii) to establish practical guidelines for phytoremediation of VOCs contaminated vadose zone.; First, a microcosm study was conducted to quantify the amounts of trichloroethylene (TCE), tetrachloroethylene (PCE) and 1,1,1-trichloroethane (TCA) volatilized, sorbed, and degraded biologically using four different types of treatments. Second, a bioreactor study was performed in a planted system using a glass chamber to clarify the plant contamination by VOCs, and to evaluate the contaminant uptake by roots and/or shoot in the phytoremediation process. Third, a greenhouse study was conducted using multiple Polyvinyl Chloride (PVC) column lysimeters to evaluate the VOCs removal efficiency of gamagrass and ryegrass to remediation VOCs contaminated soil and to establish practical guidelines for phytoremediation of soil contaminated by VOCs.; Keeping the soil moisture content at field capacity was desirable for contaminant dissipation. An additional substrate can also enhance biodegradation, but it needs time for acclimation for chemicals and substrate. The root uptake rate was very low and the possibility of shoot uptake through the gas-phase might be small in the experimental conditions. Volatilization was assumed as the major mechanisms for dissipation of VOCs under the experimental conditions of the bioreactor study. Results of the greenhouse study showed that the main mechanism of the dissipation of the chlorinated hydrocarbons was volatilization. Only small amounts of contaminants were leached, and sorption effect was negligible.
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