Effects of Sphingomonas sp. GY2B on the structure and physicochemical properties of stearic acid-modified montmorillonite in the biodegradation of phenanthrene

The objective of this study was to investigate the interaction between stearic acid-modified montmorillonite (SA-Mt) and Sphingomonas sp. GY2B and its effect on the physical and chemical properties of montmorillonite in the 2 days' biodegradation of phenanthrene. Due to bacterial activities, surface and colloidal properties of the bacteria-treated sample evidently changed in comparison with the untreated SA-Mt. Changes in surface morphology and the agglomerate state of SA-Mt were clearly observed by scanning electron microscopy (SEM) after interaction with GY2B for 2 days. Although the interlayer space of SA-Mt structure remained basically unchanged, the decrease of the structural order and the appearance and shift of several absorbance bands in the Fourier transform infrared (FTIR) spectra verified the structural changes of SA-Mt after bacterial treatment. Besides, the second derivative infrared spectra indicated that bacterial growth and metabolism largely affected the microstructure in SA-Mt. Dissolution rates of major elements were obtained by inductively coupled plasma optical emission spectroscopy (ICP-OES) in the solution, which revealed that bacterial activities enhanced the release of major elements and brought about a significant higher dissolution of Si preferentially from the tetrahedral sheet edges of SA-Mt than Al. The improvement of elemental dissolution in the biotic experiment was attributed to the combined action of pH effect and ligand-promoted process. These results substantiated that microorganisms have a considerable influence on the physicochemical properties and structure in the clay-modulated biodegradation of organic compounds. This study has profound impacts on the clay-modulated biodegradation of hydrophobic organic contaminants in the environment.