Influencing factors of bioaugmentation treatment of PAH-contaminated soils in slurry bioreactors

Abstract

Polycyclic aromatic hydrocarbons (PAHs) are a group of contaminants with low bioavailability and biodegradability. As a result, removing PAHs from contaminated soils is often inefficient. In this study, soils spiked with fluoranthene and pyrene were inoculated with Aeromonas sp. BCP-3, a newly isolated strain from coke-plant sludge, and treated in slurry bioreactors. The removal of PAHs was significantly affected by aeration rate, slurry water-soil mass ratio, stirring rate, temperature, and the concentration of Tween-80. Such effects were attributed to changes in BCP-3 growth, PAHs solid-liquid mass transfer, and slurry particle size. Notably, under optimal conditions (i.e., aeration rate of 1.5 L/min, temperature of 30 °C, stirring rate of 200 rpm, water-soil mass ratio of 1.5:1, and Tween-80 concentration of 1.3 %), 96.3 % and 97.2 % of initially spiked fluoranthene and pyrene were removed within 12 days, respectively. A PAH-contaminated soil was collected from a local coking plant and treated under the same conditions, except for the Tween-80 concentration. For the real soil, the Tween-80 concentration was 4 % to ensure a significant proportion of PAHs released into the liquid phase. Twenty-one days after inoculation of BCP-3, the removal efficiencies of low molecular weight PAHs and high molecular weight PAHs were 82.2 % and 51.8 %, respectively. The removal efficiencies of PAHs were significantly higher than the slurry without BCP-3 or HgCl2-sterilized slurry. BCP-3 improved the bioavailability and biodegradability of PAHs, resulting in effective PAH removal in slurry bioreactors. Overall, successful bioaugmentation was achieved with the addition of Tween-80 and the optimization of operating conditions.