Nemecek, J., J. Steinova, R. Spanek, T. Pluhar, P. Pokorny, P. Najmanova, V. Knytl, and M. Cernik.
Science of the Total Environment 622623:743-755(2018)

Thermally enhanced in situ bioremediation was tested in aquifers situated in sandy saprolite and underlying fractured granite. The system comprised pumping, heating, and subsequent injection of contaminated groundwater, aiming at an aquifer temperature of 20-30°C. A fermentable substrate (whey) was injected in separate batches. The test was monitored using hydrochemical and molecular tools (qPCR and NGS). Addition of the substrate and increased temperature promoted a rapid increase in the abundance of reductive dechlorinators (e.g., Dehalococcoides mccartyi, Dehalobacter sp., and functional genes vcrA and bvcA) and a strong increase in CVOC degradation. On day 34, CVOC concentrations decreased by 87-96% in groundwater from the wells most affected by the heating and substrate. On day 103, CVOC concentrations were below the limit of quantitation, resulting in degradation half-lives of 5 to 6 days. Neither an increase in biomarkers nor a distinct decrease in the CVOC concentrations was observed in a deep well affected by the heating but not by the substrate. NGS analysis detected Chloroflexi dechlorinating genera (Dehalogenimonas and GIF9 and MSBL5 clades) and other genera capable of anaerobic metabolic degradation of CVOCs. Of these, bacteria of the genera Acetobacterium, Desulfomonile, Geobacter, Sulfurospirillum, Methanosarcina, and Methanobacterium were stimulated by the substrate and heating. In contrast, groundwater from the deep well (affected by heating only) hosted representatives of aerobic metabolic and aerobic cometabolic CVOC degraders. Results document that heating in the treated aquifer accelerated the treatment process significantly if in the presence of abundant substrate.