Iron material for the remediation of DNAPL-polluted groundwater

Abstract: Tetrachloroethylene and its daughter-products represent a group of contaminations which are frequently found at sites with industrial activities, such as metal processing, electrotechnical and pharmaceutical industries as well as dry cleaning of clothing and the production of colours, paints and laquers. Due to their toxicity and persistence under natural conditions "denser-than-water" non aqueous phase liquids are substantial threats to the subsurface environment as well as the surface ecosystems including human beings. During the last two decades a number of technical solutions has been presented to enhance the situation of contaminated areas. One of the more recently established concepts are permeable reactive barriers. Permeable reactive barriers are passive in situ treatment zones containing a reactive material suitable to remove the contamination from the groundwater. They are installed downgradient from the pollution source perpendicular to the groundwater flow direction to immobilise or degrade the dissolved pollutants in the groundwater as it flows through. This project was organised in two main parts. The first part assessed seven different iron powders in batch experiments to determine the most efficient powder in terms of degradation velocity. The second part of the study employed this powder in a column experiment using different mixing ratios with sand to evaluate its performance under simulated subsurface conditions in a permeable reactive barrier. The aim of this experiment was to obtain a more detailed description of the behaviour and performance of the selected material. In the batch experiment the most promissing iron powder produced a half-life of tetrachloroethylene of 2.36 h. The column study demonstrated that cis-dichloroethylene has the longest half-life compared to tetrachlorethylene and trichloroethylene with 1.65 h. Having the longest half-life of all chloroethylenes included in this investigation the cis-dichloroethylene concentration will determine the dimensioning of a permeable barrier for remediation purposes.