The role of Fe3O4@biochar as electron shuttle in enhancing the biodegradation of gaseous para-xylene by aerobic surfactant secreted strains

To study the role of electron shuttles in accelerating the biodegradation of volatile organic compounds (VOCs) and provide theoretical support for purification of waste gas containing PX, two self-producing biosurfactant strains were used to improve solubility, and the magnetic Fe3O4@biochar composites were prepared as electron shuttles to accelerate extracellular electron transfer during the process of para-xylene (PX) biodegradation. The composites were characterized by scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The biodegradation time of PX by Enterobacter sp. HN01 and Klebsiella sp. HN02 decreased from 192 h to 12 h and 120 to 12 h, and approximately 93.75% and 90.00% of the removal times were saved after the addition of the composites. Furthermore, the effects of Fe3O4@biochar on the bacterial biosurfactant secretion, self-enzyme activity, and bacterial growth inhibition by PX were explored. The electron transport capacity of Fe3O4@biochar was 4.583 mmol·e-/g detected by mediated electrochemical reduction and mediated electrochemical oxidation, and possible electron transport pathways were revealed. The possible products of PX biodegradation by HN01 and HN02 were determined through gas chromatography-mass spectrometry. The molecular structure of PX was deduced through density functional theory calculation to validate the key product. Results indicated that Fe3O4@biochar can be used as an electronic shuttle to accelerate extracellular electron transfer and significantly improve VOCs removal rate.