Thermally enhanced anoxic biodegradation of polycyclic aromatic hydrocarbons (PAHs) in a highly contaminated aged soil

During the application of in situ thermal desorption technology (ISTD), heat in some areas often can not be effectively utilized. Nevertheless, the heat in these areas might promote the biodegradation of polycyclic aromatic hydrocarbons (PAHs). However, few studies have concentrated on the effect of temperature on biodegradation of PAHs, especially under anoxic conditions. The effects of temperature on the abundance and community characteristics of indigenous bacteria in soil are also unclear. Consequently, thermally enhanced anoxic biodegradation of PAHs in subsurface soil was investigated in this study. After 150 days of anoxic incubation, both the bacterial abundance and the removal rates of PAHs in soil were positively affected by temperature. The total number of potential PAH-degrading bacteria (Proteobacteria and Firmicutes) was increased by 0.11-0.72 orders of magnitude compared to the untreated soil in different temperature treatment groups (20 degrees C, 30 degrees C, 40 degrees C, and 50 degrees C). Firmicutes was more adaptable to higher temperatures than Proteobacteria. The removal rates of total PAHs increased from 28.85% to 50.44% with increasing temperature. The degradation rates of three- and four-ring PAHs were significantly higher than those of five- and six-ring PAHs. These findings provide a more applicable and economical way to treat with PAHs contaminated subsurface soil where the temperature is lower than the target temperature needed for the desorption of PAHs from the soil when ISTD is used.