School of Environmental Studies, China University of Geosciences, Wuhan 430074, Hubei, China.
School of Environmental Studies, China University of Geosciences, Wuhan 430074, Hubei, China.
Sci Total Environ. 2021 May 15;769:144798. doi: 10.1016/j.scitotenv.2020.144798. Epub 2021 Jan 13.
In this study, the molecular transformation of sludge biopolymers during hydrothermal treatment with the temperature ranging from 25 °C to 200 °C was examined and was seen to significantly affect the macrophysical properties (dewaterability and rheological property) of sludge. The results showed that the sludge dewaterability and flow ability under high shear stress deteriorated by a hydrothermal process at 25 °C to 120 °C, but the deterioration alleviated above the temperature threshold of 120 °C. The consistence of changes in sludge dewaterability and rheological property in HT process was mainly attributed to the variation in gel properties of soluble biopolymer. Two-stage changes in biopolymer transformation were identified, beginning with a solubilization stage from 25 °C to 120 °C in which a biopolymer with a gel-like network structure was released into liquid phase, creating flow resistance under high shear stress such that sludge dewaterability deteriorated. The second stage was identified as a conversion stage (120 °C-200 °C) in which proteins and polysaccharides hydrolyzed and experienced a Maillard reaction, leading to the degradation of the biopolymer network structure. The newly formed recalcitrant Maillard products showed weak flow response to high shear stress, allowing for an improvement in sludge dewaterability. The pathways of a Maillard reaction were identified via gas chromatography-mass spectrometer (GC-MS), H nuclear magnetic resonance spectroscopy (H NMR) and two-dimensional correlation spectral analysis (2D-COS) of Fourier-transform infrared spectrometer (FTIR), etc. Three-dimensional excitation-emission matrix (3D-EEM) proved to be an applicable method for tracking Maillard reaction in sludge hydrothermal process due to the distinctive fluorescence characteristics of Maillard products. This study further clarifies the obscure process of sludge hydrothermal treatment and will help improve the accuracy of subsequent research.
在这项研究中，考察了温度范围在 25°C 至 200°C 的热水处理过程中污泥生物聚合物的分子转化，发现其显著影响了污泥的宏观物理性质（脱水性能和流变性能）。结果表明，在 25°C 至 120°C 的热水处理过程中，污泥的脱水性能和高剪切应力下的流动能力恶化，但在高于 120°C 的温度阈值以上，这种恶化得到缓解。HT 过程中污泥脱水性能和流变性能变化的一致性主要归因于可溶性生物聚合物凝胶性质的变化。确定了生物聚合物转化的两阶段变化，从 25°C 至 120°C 的溶解阶段开始，其中具有凝胶状网络结构的生物聚合物被释放到液相中，在高剪切应力下产生流动阻力，从而使污泥脱水性能恶化。第二阶段被确定为转化阶段（120°C-200°C），其中蛋白质和多糖水解并发生美拉德反应，导致生物聚合物网络结构降解。新形成的难降解美拉德产物对高剪切应力表现出较弱的流动响应，从而改善了污泥的脱水性能。通过气相色谱-质谱联用仪（GC-MS）、H 核磁共振波谱（H NMR）和傅里叶变换红外光谱仪（FTIR）的二维相关光谱分析（2D-COS）等方法鉴定了美拉德反应的途径。三维激发-发射矩阵（3D-EEM）被证明是一种适用于跟踪污泥热水处理中美拉德反应的方法，因为美拉德产物具有独特的荧光特性。本研究进一步阐明了污泥热水处理过程中的模糊过程，并将有助于提高后续研究的准确性。
