Influential mechanism of water occurrence states of waste-activated sludge: specifically focusing on the roles of EPS micro-spatial distribution and cation-dominated interfacial properties.
Influential mechanism of water occurrence states of waste-activated sludge: specifically focusing on the roles of EPS micro-spatial distribution and cation-dominated interfacial properties.
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DOI：
10.1016/j.watres.2021.117461
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发表时间：
2021-07
期刊：
影响因子：
12.8
通讯作者：
Boran Wu;Hao Wang;Xiaohu Dai;Xiaoli Chai
中科院分区：
文献类型：
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作者：
Boran Wu;Hao Wang;Xiaohu Dai;Xiaoli Chai
活性污泥的高水化胶体结构是实现污泥体积最小化的主要障碍。胞外聚合物（EPS）由于与二价阳离子（即，Ca 2+和Mg 2+）和疏水相互作用。然而，很少有研究专门集中在EPS的空间分布，微生物絮体的微观结构和结合水（如邻水和间隙水）的分数之间的定量关系。因此，对于污泥絮体的溶解或絮凝是否以及在何种程度上是最佳的脱水性改善，可能仍然存在一些争论。本研究采用梯度加入阳离子交换树脂（CER）的方法去除EPS中的阳离子，使EPS的空间分布变得松散。因此，EPS层的空间扩展与救济的复杂阳离子的影响的颗粒尺寸分布，分形维数，界面自由能和水的存在状态的WAS进行了系统研究。采用石英晶体微天平（QCM-D）分析了Ca 2+和Mg 2+存在下水与EPS的相互作用。研究结果表明，EPS颗粒的分散附着层导致了生物絮体的分形维数较高，但空间填充度较低。此外，极性/酸为基础的界面自由能的4倍的减少，可以通过从EPS基质中去除阳离子，这表明在疏水性的显着增加诱导。可预测地，邻近水和间隙水的级分分别由微生物聚集体的极性/酸基界面自由能和孔结构主导，这通过强皮尔逊相关性（Rp>0.80，p值<0.04）证实。这些研究结果有望提供更好的机理洞察水的出现状态和WAS的胶体结构之间的关系，并可以作为各种污泥调理方法的优化组合，以调节生物絮体的聚集状态的基础。
The highly hydrated colloidal structure of waste-activated sludge (WAS) is the main obstacle of enhanced dewatering for sludge volume minimization. Extracellular polymeric substances (EPS) maintain the colloidal stability of bio-flocs in a three-dimensional matrix due to bindings with bivalent cations (i.e., Ca2+and Mg2+) and hydrophobic interactions. However, few studies specifically focused on the quantitative relationships among spatial distribution of EPS, microstructure of bio-flocs and fractions of bound water (e.g. vicinal water and interstitial water). Thus, there may be still some debates on whether and what extent of the lysis or flocculation of sludge flocs is optimal for the dewaterability improvement. This study applied the gradient addition of cation exchange resin (CER) to remove EPS-complexed cations and loosen the spatial distribution of EPS. Consequently, how the spatial extension of EPS layers with relief of complex cations influenced the particle size distribution, fractal dimension, interfacial free energy and water occurrence states of WAS was systematically investigated. The quartz crystal microbalance with dissipation (QCM-D) was also applied to analyze the water-EPS interactions with and without the presence of Ca2+and Mg2+. All the results confirmed that the dispersed EPS adhering layers led to the higher fractal dimension (Df) but the lower space filling degree of bio-flocs. Also, the 4-fold reduction in the polar/acid-based interfacial free energy could be induced by the removal of cations from EPS matrix, which indicated the significant increase in hydrophobicity. Predictably, the fractions of vicinal water and interstitial water were dominated by the polar/acid-based interfacial free energy and pore structure of microbial aggregates, respectively, which were confirmed by the strong Pearson correlation (Rp>0.80, p-value<0.04). These findings are expected to provide the improved mechanistic insights into the relationship between water occurrence states and colloidal structure of WAS, and can serve as the basis for the optimal combination of various sludge conditioning approaches towards regulating aggregation states of bio-flocs.