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. 

Abbreviation

PAHs, Polycyclic aromatic hydrocarbons; BaP, 5-benzene ring PAH; LMW, low molecular weight; HMW, high molecular weight; rDNA, ribosomal deoxyribonucleic acid; SPE, solid phase extraction;  HEX,  hexane;  DCM, dichloromethane; GC-FID, gas chromatography-flame ionisation detector; NCBI, National Center for Biotechnology Information.