Release of Electron Donors during Thermal Treatment of Soils

Abstract

Thermal treatment of soil and groundwater may provide an in situ source of soluble organic compounds and hydrogen (H) that could stimulate microbial reductive dechlorination (MRD) at sites impacted by chlorinated solvents. The objectives of this study were to identify and quantify the release of electron donors and fermentable precursors during soil heating and to estimate availability of these compounds following thermal treatment. Fourteen solid materials containing <0.01 to 63.81 wt % organic carbon (OC) were incubated at 30, 60, or 90 °C for up to 180 d, leading to the release of direct electron donors (i.e., H and acetate) and fermentable volatile fatty acids (VFAs). Total VFA release ranged from 5 ± 0 × 10 carbon per gram solid (mol C/g) during 30 °C incubation of quartz sand to 820 ± 50 × 10 mol C/g during 90 °C incubation of humic acid, and was positively impacted by incubation time, temperature, and solid-phase OC content. H gas was detected at a maximum of 180 ± 50 × 10 mol H/g, accounting for less than 0.3% of reducing equivalents associated with VFAs released under the same conditions. These findings will allow for more reliable prediction of substrate release during thermal treatment, supporting the implementation of coupled thermal and biological remediation strategies.

Thermally Enhanced Biodegradation of TCE in Groundwater

“…The specific response of the microbiome on location to temperature must be investigated; however, most commonly reported temperatures are 20-30 • C with deterioration of the process above 35-40 • C [27][28][29][30][31][32]; thus, thermally enhanced anaerobic dechlorination could be costly, but effective [30]. The highest efficiency of the remediation method will be reflected in the shortening of the time required to reach the target remediation limits through improved biological parameters, e.g., cell growth and (bio)reaction rates [33][34][35] and physical-chemical, e.g., pollutant desorption, their volatilization and (bio)availability [36] and releasing of direct electron donors [35] and thus in lower remediation costs. However, costs could be reduced by replacing conventional heating with some modern and sustainable approach, e.g., geothermal heat pumps and solar heating [37] or synergistic coupling dechlorination remediation with underground thermal energy storage [36,38].…”