Development and application of dynamic air chambers for measurement of volatilization fluxes of benzene and MTBE from constructed wetlands planted with common reed

Abstract

Phytoremediation of industrially contaminated groundwater has been a proven technique for several decades. However, mass balances of contaminants are often focused in laboratory investigations. The evaluation of the transfer of volatile organic compounds (VOCs) under field conditions from the saturated and vadose soil zone into the atmosphere, directly or via plants, is rarely part of the research scope. This can provoke problems – particularly with regard to legal issues – if large-scale phytoremediation sites are situated near residential areas. In this study volatilization of VOCs was quantified in a horizontal-flow constructed wetland planted with reed grass. For this purpose, a specially designed air chamber was constructed, validated, and routine sampling campaigns were performed over the course of one year. Results indicate that the overall volatilization of the observed contaminants benzene and methyl tert-butyl ether (MTBE) depended on seasonal variations with the highest volatilization fluxes measured in summer, when the detected volatilization fluxes of 846 ± 116 and 252 ± 11 μg m −2 h −1 for MTBE and benzene, respectively, accounted for 2.4% and 5.6% of the respective overall contaminant mass loss in the planted wetland. Furthermore, chamber data give strong evidence for the increased volatilization of VOCs through vegetation by direct comparison of planted and unplanted wetlands.