Enhanced biodegradation of PAHs in historically contaminated soil by biochar immobilized with M. gilvum cells

Rice straw biochar inoculated with PAH-degrading actinobacteria (Mycobacterium gilvum) (1.27x1011±1.24×1010cell g-1) was tested (18d) for its ability to biodegrade soil associated PAHs, using a coke plant soil. Biochar alone... [ view full abstract ]

Rice straw biochar inoculated with PAH-degrading actinobacteria (Mycobacterium gilvum) (1.27x1011±1.24×1010cell g-1) was tested (18d) for its ability to biodegrade soil associated PAHs, using a coke plant soil. Biochar alone had limited potential for PAH degradation; with no significant (P>0.05) reductions in phenanthrene and fluoranthene and a small reduction in pyrene (13.46±2.82%) being observed. Free M. gilvum cells inoculated directly into the soil showed no significant reduction in fluoranthene, little reduction in pyrene (19.73±6.52%,), and some reduction in phenanthrene (47.30±4.09%). In contrast, inoculated biochar treatments indicated significant (P<0.05) reductions of 62.6±3.2, 52.1±2.3and 62.1±0.9%, in phenanthrene, fluoranthene, and pyrene concentrations, respectively. It is hypothesized that this enhanced remediation performance was underpinned by i) biochar enhanced mass transfer of PAHs from soil to thecarbonaceous biochar “sink”, and ii) the subsequent degradation of the fluxed PAHs by the immobilized M. gilvum. To test this mechanisms a surfactant (Brij 30; 2 mg g-1 soil), was added to impede PAH mass transfer to the biochar. The surfactant increased solution phase PAH concentrations and significantly (P<0.05) reduce PAH degradation in the biochar immobilized M. gilvum treatments. These results support the potential application of inoculated biochars for the low cost remediation of PAH contaminated soils.