Response of extracellular polymeric substances to the toxicity of 2,4-dichlorophenol in aerobic granular sludge system: production and interaction mechanism

Abstract

The objective of this study was to investigate the response of extracellular polymeric substances (EPS) to the toxicity of 2,4-dichlorophenol (2,4-DCP) in an aerobic granular sludge system. Results implied that the presence of 2,4-DCP could cause toxicity in the performance of biological nitrogen removal. Compared with the control experiment, NH₄⁺–N removal efficiency decreased to 37.27 and 20.71% after the exposure of 2,4-DCP of 20 and 50 mg L⁻¹, respectively. The main components of EPS, including polysaccharides and proteins, generally increased from 35.22 ± 0.69 to 38.25 ± 1.46 mg g⁻¹ SS and 76.28 ± 0.34 to 83.30 ± 0.31 mg g⁻¹ SS in the presence of 2,4-DCP. Three-dimensional excitation–emission matrix (3D-EEM) fluorescence spectroscopy as well as synchronous fluorescence spectra was used to evaluate the interaction mechanism between EPS and 2,4-DCP. 3D-EEM showed that the intensities of EPS obviously decreased with the increase of 2,4-DCP concentration. According to synchronous fluorescence spectra, the mechanism of fluorescence quenching involves to static quenching with a formation constant (K_A) of 3.46 × 10³ L mol⁻¹. Fourier transform infrared spectroscopy (FTIR) was used to evaluate the change of functional groups of EPS samples before and after the addition of 2,4-DCP.