In Situ Bioremediation of Toluene-Polluted Vadose Zone: Integrated Column and Wetland Study

A vertical soil column setup integrated with wetlands is developed to study the biodegradation and transport of toluene, a light non-aqueous phase liquid (LNAPL), in the subsurface environment. LNAPL-contaminated water is applied to infiltrate from the top of the soil column. The observed and simulated breakthrough curves show high equilibrium concentration at top ports rather than at lower ports, indicating effective toluene biodegradation with soil depth. The observed equilibrium concentration of toluene is higher in the case of unplanted wetland, asserting an accelerated biodegradation rate in the planted case. A difference in the relative concentration of toluene between input and output fluxes at 100 h is found as 13.34% and 30.86% for planted and unplanted wetland setups, respectively. Estimated biodegradation rates show that toluene degradation is 2.5 times faster in the planted wetland setup. In addition, the difference in the observed bacterial count and dissolved oxygen prove that toluene degraded aerobically at a faster rate in the planted setup. Simulations show that as time reached 80-100 h, there is no significant change in concentration profile, thereby confirming the equilibrium condition. The results of this study will be useful to frame plant-assisted bioremediation techniques for LNAPL-contaminated soil-water resources in the field.