The solid pore characteristics are commonly considered as the important influential factors on waste-activated sludge (WAS) dewaterability, and should be related to the cohesive force of bio-flocs dominated by cation-organic interactions at solid-water interface. This study aimed to establish an approach for regulating the solid pore structure of WAS by cationic regulation. The influential mechanism of WAS dewaterability was accordingly explored from the perspective of the pore characteristics dominated by cation-organic interactions. Primarily, with the gradient removal or addition of bivalent cations, the varying pore structure of WAS flocs was tracked by in-situ synchrotron X-ray computed microtomography imaging technique (CMT). The three-dimensional visual model was established to quantify the pore structure parameters of WAS flocs. Following the visualization analysis, the artificial intelligence means, the gradient-weighted class activation mapping (Grad CAM) of three-dimensional convolutional neural network (3D-CNN), was applied for the first time to explore the linkages among solid surface properties, solid pore structure, water occurrence states and sludge dewaterability. It was found that the number and volume of isolated pores jointly determined the mobility and the fractions of vicinal water and interstitial water (p-value ≤ 0.02); also, the decreasing polar or acid-based interfacial free energy with the cationic addition was accompanied with the decreasing isolated pore mean-volume (Pearson coefficient=-0.77, p-value < 0.01). These results indicated that the pore structure characteristics determined the water occurrence states, but the solid porosity strongly depended on the interfacial properties. Accordingly, the molecular docking was applied to explore the interfacial reaction mechanism between Ca2+/Mg2+ and solid compositions in terms of complexation sites, molecular dynamics and free energy calculations. As a result, how the cation-organic interactions affected the pore characteristics through solid surface modification could be clarified, which is expected to serve as theoretical foundation for the development of novel sludge conditioning technologies, i.e., more efforts should be devoted to increasing the dense degree of sludge particles through weakening the hydration repulsion of solid surface.

中文翻译：

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废弃物活性污泥水发生状态的影响机制：特别关注阳离子-有机物相互作用主导的孔隙特性


固体孔隙特性通常被认为是影响废液活性污泥 （WAS） 脱水性的重要因素，应与固水界面处阳离子-有机相互作用主导的生物絮凝体的内聚力有关。本研究旨在建立一种通过阳离子调控调控 WAS 固体孔结构的方法。因此，从阳离子-有机相互作用主导的孔隙特性的角度探讨了 WAS 脱水的影响机制。首先，通过梯度去除或添加二价阳离子，通过原位同步加速器 X 射线计算机显微断层扫描成像技术 （CMT） 跟踪 WAS 絮凝体的变化孔结构。建立三维可视化模型来量化 WAS 絮凝体的孔结构参数。在可视化分析之后，首次应用人工智能手段，即三维卷积神经网络 （3D-CNN） 的梯度加权类激活映射 （Grad CAM） 来探索固体表面特性、固体孔隙结构、水的赋存状态和污泥脱水性之间的联系。研究发现，孤立孔的数量和体积共同决定了流动性以及附近水和间质水的分数 （p 值≤ 0.02）;此外，随着阳离子添加而极性或酸基界面自由能的降低伴随着孤立孔平均体积的降低 （Pearson 系数 =-0.77，p 值 < 0.01）。这些结果表明，孔隙结构特征决定了水的出现状态，但固体孔隙率在很大程度上取决于界面性质。 因此，应用分子对接技术，从络合位点、分子动力学和自由能计算等方面探讨了 Ca2+/Mg2+ 与固体成分之间的界面反应机理。因此，可以阐明阳离子-有机相互作用如何通过固体表面改性影响孔隙特性，这有望为新型污泥处理技术的发展提供理论基础，即应投入更多精力通过减弱固体表面的水化排斥来提高污泥颗粒的致密度。