Surfactant-enhanced anoxic biodegradation of polycyclic aromatic hydrocarbons (PAHs) in aged subsurface soil pretreated with persulfate

The integrated application of chemical oxidation and anoxic biodegradation presents an effective strategy for remediating PAHs-contaminated soils. However, certain PAHs remain in the soil even after the combined treatments, primarily due to the restricted bioavailability of the residual compounds. In this study, the initial concentration of PAHs in the contaminated soil was determined to be 398.47 +/- 36.66 mg center dot kg- 1 . The effects of different surfactant concentrations (800 and 3000 mg center dot L- 1 ) and mass ratios (SDBS/Tween 80=1:0, 0:1, 1:3, 1:2, 1:1, 2:1, and 3:1) on PAHs desorption, indigenous bacteria, and anoxic PAHs removal in aged subsurface soil pre- oxidized with persulfate (PS) were investigated. The results indicated that applying of surfactants at a low dose (800 mg center dot L-1) enhanced PAHs desorption, bolstered the growth of potential degrading bacteria, and subsequently promoted the anoxic biodegradation of PAHs in pre-oxidized soil. Compared with the control group, the degradation rates of 3-ring and 4-ring PAHs increased by 22.79 % and 20.7 %, respectively. In contrast, a high- dose surfactants (3000 mg center dot L- 1 ) inhibited PAH biodegradation by limiting bacterial growth, resulting in decreased degradation rates of 3-ring and 4-ring PAHs by 12.84 % and 13.72 %, respectively. Furthermore, mixed surfactants were found to be more effective than single surfactants in promoting the anoxic degradation of PAHs in pre-oxidized soil. These findings provide valuable insights for further enhancing the biodegradation of PAHs in pre-oxidized soils.