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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废活性污泥水赋存状态的影响机制：重点关注阳离子-有机相互作用主导的孔隙特征


固体孔隙特征通常被认为是废物活性污泥（WAS）脱水性的重要影响因素，并且应该与固-水界面上以阳离子-有机相互作用为主的生物絮体的内聚力有关。本研究旨在建立一种通过阳离子调节来调节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征角度探讨了WAS脱水能力的影响机制。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 絮凝物的不同孔隙结构。建立三维视觉模型来量化WAS絮体的孔隙结构参数。继可视化分析之后，首次应用人工智能手段——三维卷积神经网络（3D-CNN）的梯度加权类激活映射（Grad CAM）来探索固体表面性质、固体孔隙结构、水赋存状态和污泥脱水能力。研究发现，孤立孔隙的数量和体积共同决定了邻近水和间隙水的流动性和比例（p值≤0.02）；此外，随着阳离子添加，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（皮尔逊系数=-0.77，p值％3C 0.01）。这些结果表明，孔隙结构特征决定了水的赋存状态，但固体孔隙率强烈依赖于界面性质。 因此，应用分子对接从络合位点、分子动力学和自由能计算方面探讨了Ca2+/Mg2+与固体组合物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，这有望为新型污泥调理技术的发展提供理论基础，即应在增加密度方面做出更多努力。通过减弱固体表面的水化斥力来降低污泥颗粒的程度。