The Stockholm Convention is the global treaty responsible for regulating releases of harmful, persistent organic pollutants (POPs). In April 2019, convention members will vote on whether to expand its current contaminant list by two. If annexed, the proposed POPs will raise the number of restricted compounds to thirty-two total. Nearly a third of these compounds are aromatic organochlorines (AOCs), <i>i.e.</i>, compounds containing at least one aromatic ring and one chlorine constituent. These AOCs are semi-volatile, hydrophobic, and microbial resistant, making them not only environmentally-persistent, but also notoriously difficult to remediate in soils and sediments.  One emerging technology has shown remarkable success in remediating AOC-contaminated soils and sediments. The technology combines thermal conduction heating with soil vapor extraction (TCH-SVE), and works by 1) raising subsurface temperatures &gt;100°C, 2) thermally inducing contaminant desorption/degradation, and 3) extracting volatilized contaminants by sweeping away system soil gases. Until recently, TCH-SVE has largely targeted removal of long-chain or polycyclic, aromatic hydrocarbons. These compounds resist thermal degradation as high as 800°C, so TCH-SVE designs largely ignore the impacts of thermal degradation on removal. However, AOCs are much more susceptible to thermal degradation in temperature ranges typical in TCH-SVE (100-400°C).  Moreover, conditions favoring degradation may also favor dioxin-formation during treatment, making mechanistic behavior a critical concern.<br/>The current research investigates the relative importance of different removal pathways during TCH-SVE treatment of AOCs. We use pentachlorophenol as a probe for AOCs and examine reaction by-products to determine (and ultimately predict) how removal mechanisms shift across treatment conditions.

Pentachlorophenol removal pathways in thermal conduction heating-soil vapor extraction (TCH-SVE)

2019 Spring National Meeting

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