Enhanced anoxic biodegradation of polycyclic aromatic hydrocarbons (PAHs) in aged soil pretreated by hydrogen peroxide

Abstract

Although integrated chemical-biological treatment of PAHs contaminated soil has received significant attention over the past decades, information is scarce regarding integrated chemical oxidation and anoxic biodegradation of PAHs in contaminated subsurface soil in unsaturated zones. In this study, anoxic biodegradation of PAHs in an aged soil pretreated with hydrogen peroxide (H2O2) was investigated. Anoxic incubation experiment was performed in 50-mL serum bottles containing 30 g of soil and 7 mL of solution, then the soils (moisture, 29.3%; pH, 7.18) were incubated at 30 °C in the dark for 180 days. Apparent removal was observed for 16 USEPA priority PAHs in soil treated with H2O2. The removal percentage of 16 PAHs was 33.2%–95.9%, whereas the application of H2O2 resulted in 3.5 orders of magnitude decrease in the log gene copy number of the bacteria in soil. However, the bacterial numbers rebounded after 180 days of anoxic incubation under favorable conditions (inoculation or/and additional nutrients). The use of either nutrients (CY) or electron acceptor (nitrate, CN) did not enhance the anoxic degradation of PAHs, whereas coupling of both nutrients and electron acceptor led to anoxic biodegradation of PAHs (YN). Moreover, higher anoxic biodegradation efficiency was observed for 3-rings and partial 4-rings PAHs (fluoranthene and pyrene) in inoculated soil than that of non-inoculated soil in treatment YN where both nutrients and electron acceptor were added. The results of this study provide an attractive approach to the removal of PAHs from subsurface soils.