Thermally enhanced biodegradation of benzo[a]pyrene and benzene co-contaminated soil: Bioavailability and generation of ROS

In this study, a set of comprehensive experiments were conducted to explore the effects of temperature on the biodegradation, bioavailability , and generation of reactive oxygen species (ROS) by thermally enhanced biodegradation (TEB) under benzene and BaP co-contaminated conditions. The biodegradation rates of benzene increased from 57.4% to 88.7% and 84.9%, and the biodegradation efficiency of BaP was enhanced from 15.8% to 34.6% and 28.6%, when the temperature was raised from the ambient temperature of 15 °C to 45 °C and 30 °C, respectively. In addition, the bioavailability analysis results demonstrated that the water- and butanol-extractable BaP increased with elevated temperatures. High enzymatic activities and PAH-RHD α gene in gram-positive bacteria favored the long-term elevated temperatures (30 and 45 °C) compared to gram-negative bacteria. Moreover, ROS species (O 2 •− and •OH) generation was detected which were scavenged by the increased superoxide dismutase and catalase activities at elevated temperatures. Soil properties (pH, TOC , moisture, total iron, Fe 3+ , and Fe 2+ ) were affected by the temperature treatments, revealing that metal-organic-associated reactions occurred during the TEB of benzene–BaP co-contamination. The results concluded that biodegradation of benzene–BaP co-contamination was greatly improved at 45 °C and that microbial activities enhanced the biodegradation under TEB via the increased bioavailability and generation and degradation of ROS.