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Investigation the Role and Mechanism of Extracellular Polymeric Substances in Biosorption of Various Types of Dyes onto Aerobic Granular Sludge

Kai Li, Dong Wei, Tao Yan1, Bin Du*, Qin Wei

Extracellular polymeric substances (EPS), as a series of metabolic products secreted by microorganisms, have important effect on the formation and stability of sludge. This study evaluated the role of EPS in biosorption of three dyes by using aerobic granular sludge (AGS) as a biosorbent. Meanwhile, the mechanism between EPS and three types of dyes was investigated by using three-dimensional excitationemission matrix (3D-EEM), synchronous fluorescence spectra, twodimensional correlation spectroscopy (2D-COS) and Fourier transform infrared spectroscopy (FTIR). The experimental data revealed that methylene blue (MB), methyl orange (MO) and congo red (CR) sorption onto AGS were favorable for Langmuir and Freundlich isotherms. It was demonstrated that EPS made a different contribution for three types of dyes removal and EPS might play a greater role in the cationic dyes removal. 3D-EEM implied that two protein-like substances in EPS were identified and quenched in the presence of dyes. According to synchronous fluorescence spectra, it was found that dynamic and static quenching might be involved in the fluorescence quenching of EPS by three types of dyes. Moreover, a higher binding ability between MB and EPS was observed than other two dyes. 2D-COS indicated that the spectral changes proceeded in the same direction as the variation of MB, MO and CR concentrations. The results obtained in present study could facilitate a better understanding towards the role and mechanism of EPS during biosorption process.