Adsorption–synergic biodegradation of aryl ethers model compounds constructed from lignite

Abstract

The bioconversion of lignite under ambient conditions is a promising technology for coal processing. However, the bioconversion mechanism of lignite via microorganisms is unclear due to its complex structure. In this work, for the first time, four aryl ether model compounds (AEMCs) of lignite with three aromatic rings were selected based on the unique attack sites of fungi on lignite to explore the bioconversion performance. The results show that the biodegradation rates of 4,4′-(1,3-phenylenebis[oxy]) dianiline (4,4-1,3-POD), formononetin, 9,10-dibutoxyanthracene (9.10-DBO), and 6-methoxy-2-(4-methoxyphenyl) benzo [b] thiophene (6-M-2-B) reached 89.91%, 69.40%, 39.45%, and 83.44%, respectively. During the process, AEMCs serving as inducers increased the production of extracellular enzymes secreted by the WF8 fungus. Through analysis using ultraviolet–visible spectroscopy (UV–Vis), Fourier transform infrared spectroscopy (FTIR) and gas chromatography/mass spectroscopy (GC/MS), it was confirmed that new organic compounds (OCs) were generated after biodegradation of AEMCs, wherein the UV–Vis spectra of the four AEMCs after biodegradation were fitted by 5,5,9 and 8 sub-curves and the numbers of OCs identified in GC/MS spectra were 41, 48, 33 and 35, respectively. Predominantly, these new OCs contained carboxyl, hydroxyl or carbonyl groups, indicating the involvement of hydroxyl radicals and extracellular enzymes in the process. In addition, the adsorption of AEMCs onto the fungi was well-fitted with the Langmuir model, suggesting that the adsorption process was monolayer chemisorption. Finally, it was concluded that the adsorption–synergic biodegradation process can be divided into two stages: AEMCs were adsorbed by the fungi, stimulating the production and release of fungal enzymes, and were subsequently oxidatively attacked and degraded. This study provided a theoretical basis for well understanding the biodegradation of lignite.