Effects of in situ bioremediation strategies on the biodegradation and bioavailability of polycyclic aromatic hydrocarbons in weathered manufactured gas plant soil.

摘要

Poor waste management practices at former manufactured gas plant (MGP) sites have left behind a legacy of soil, groundwater, and surface water contamination. MGP waste residues contain a number of hazardous compounds, including polycyclic aromatic hydrocarbons (PAHs), which require effective remediation strategies to mitigate environmental and health impacts. In situ bioremediation is a lower cost alternative for sites where conventional remediation strategies (e.g., excavation and landfill disposal) are either cost-prohibitive or infeasible; biological strategies are sometimes combined with more aggressive treatments such as chemical oxidation, to reduce treatment times. To realize the potential for in situ bioremediation at MGP sites, a series of continuous-flow columns packed with contaminated MGP soil were operated for over two years, representing treatment by persulfate oxidation, treatment by biostimulation, and a control. Changes in PAH distribution and bioavailability, soil- and aqueous-phase PAH concentrations, and the quantity and activity of the indigenous microbial community and known PAH-degrading bacteria were monitored over time.;Persulfate oxidation did adversely impact the overall microbial community and specific PAH-degrading bacteria; however, recovery of PAH degraders occurred well after the general microbial community. These findings suggest that the use of total bacterial quantity as a surrogate for the recovery of contaminant degraders may be inappropriate for evaluating the compatibility of chemical treatment with subsequent bioremediation.;Biostimulation resulted in significant PAH removal (up to 80%). Spatial and temporal variations in soil PAH concentration and PAH-degrader abundance were strongly correlated to dissolved oxygen advancement, suggesting that oxygen was the limiting factor in PAH removal. Bacterial transport was also implicated as a factor in the establishment of PAH-degrading bacteria ahead of the oxygen front.;Density-separation of the MGP soil revealed that a majority of PAH mass was associated with carbonaceous particles. Desorption of PAHs from this soil fraction was substantially reduced after biostimulation, although a small portion remained bioavailable. Fast-desorbing fractions in the original MGP soil, quantified by a two-site desorption model, were found to be poor predictors of PAH bioavailability under long-term biostimulation. Overall, this research highlights the importance of physical and biological assessment tools for the evaluation and implementation of in situ bioremediation at MGP sites.