Abstract
Polycyclic aromatic hydrocarbons (PAHs) are recalcitrant contaminants which are routinely found in numerous environmental matrices, contributing to ecological degradation. In this study, the removal of LMW and HMW PAHs with 4- and 5-benzene rings, by Bacillus licheniformis STK 01, Bacillus subtilis STK 02 and Pseudomonas aeruginosa STK 03, was evaluated in silty soil for a period of 60 days. Subsequently, a biosurfactant produced from Beta vulgaris agrowaste was used to augment the removal of the aforementioned PAHs in mono- and co-cultures. The isolates proved to be proficient in removing the contaminants, with B. licheniformis STK01 cultures achieving the highest removal rates. Biosurfactant supplementation significantly enhanced the removal of benzo(a)pyrene- a 5-ring benzene HMW PAH. The highest removal rates achieved in biosurfactant-supplemented cultures were: 100% for phenanthrene, 95.32% for pyrene, 82.71% for benz(a)anthracene and 86.17% for benzo(a)pyrene. The kinetic data used to simulate removal rates were suitably described by first-order kinetics, with the rate constants showing that phenanthrene removal was rapid in cultures without biosurfactant (k = 0.0620 day-1) as well as with biosurfactant (k = 0.0664 day-1), while the removal rates for others followed in the order of their increasing molecular weight. The synergy of the bacterial isolates and the biosurfactant produced from B. vulgaris agrowaste could be used in environmental bioremediation of PAHs even in silty soil. Key words: Benz(a)anthracene, benzo(a)pyrene, bioremediation, biosurfactant, Beta vulgaris, polycyclic aromatic hydrocarbons.
Highlights
Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous and recalcitrant contaminants, released into the environment through natural and anthropogenic sources (Sánchez et al, 2015)
The kinetic data used to simulate removal rates were suitably described by first-order kinetics, with the rate constants showing that phenanthrene removal was rapid in cultures without biosurfactant (k = 0.0620 day-1) as well as with biosurfactant (k = 0.0664 day-1), while the removal rates for others followed in the order of their increasing molecular weight
The cultures containing B. licheniformis were supplemented with biosurfactant and with an agrowaste (B. vulgaris) extract in order to investigate the effect of co-metabolic substrate utilization on the bioremediation of PAH contaminated soil
Summary
Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous and recalcitrant contaminants, released into the environment through natural and anthropogenic sources (Sánchez et al, 2015). These sources are mainly biogenic, petrogenic and pyrolitic (Harvey, 1998). Of the sixteen PAHs classified as priority pollutants by the United States Environmental Protection Agency (IRIS: EPA's Integrated Risk Information System, 1997), eight were identified as potential human carcinogens. These eight PAHs belong to the high molecular weight (HMW) class, a group associated with a higher tendency to bioaccumulate in environmental matrices
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