Journal
WATER RESEARCH
Volume 201, Issue -, Pages -Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.watres.2021.117316
Keywords
Extracellular polymeric substances; Waste activated sludge; Macro-physical properties; Variable-temperature infrared spectroscopy; Freezing treatment; Hydrothermal treatment
Funding
- National Natural Science Foundation of China [41630318]
- Major Science and Technology Pro-gram for Water Pollution Control and Treatment [2018 ZX 07110004]
- Fundamental Research Funds for the Central Universities of the China University of Geosciences (Wuhan) [CUGCJ1702]
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In this study, the response of EPS in sludge to temperature was systematically investigated, showing an improvement in sludge dewaterability during freezing treatment through enhancement of EPS hydrophobicity, and a deterioration in sludge dewaterability during hydrothermal treatment due to increased EPS hydrophilicity.
Extracellular polymeric substances (EPS) are important components of activated sludge, whose content and composition have important effects on the macro-physical properties of sludge. In this study, the response of EPS in sludge to temperature (-40-200 degrees C) was systematically investigated using XAD resin fractionation, variable-temperature infrared spectra (VTIS) and two-dimensional correlation spectroscopy (2D-COS). The relationships between the molecular structure of EPS and the macro-physical properties (rheological property and dewatering performance) of waste activated sludge (WAS) at varying temperature were also established. During the freezing treatment, the solubilization of biopolymers and destruction of the hydrophilic functional groups (hydroxy, amino and carboxyl) resulted in the production of small organic matters, which enhanced EPS hydrophobicity and reduced electrostatic repulsion of sludge, and subsequent dewaterability improvement. For the hydrothermal treatment, the EPS transformation showed a two-stages reaction including stage I (70-120 degrees C) and stage II (>120 degrees C). Stage I (70-120 degrees C), a plenty of hydrophilic functional groups (hydroxy, amino and carboxyl) in EPS were exposed via the solubilization of biopolymers, which enhanced electrostatic repulsion of sludge and EPS hydrophilicity, and subsequence in deterioration of sludge dewaterability and fluidity. However, at stage II (>120 degrees C), the high temperature caused hydrolyzation of macromolecular organic matters in completely, in which the secondary structure of the protein was destroyed, causing the peptide chain to unfold. In addition, the reduction of alpha-helix and beta-sheet content and intensified Maillard reaction decreased electrostatic repulsion of sludge, thus resulted in the improvement of sludge dewaterability and fluidity. This study enriched the theoretical basis of the optimal control of sludge treatment based on temperature regulation.
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