State Key Laboratory of Pollution Control and Resource Reuse, College of Environmental Science and Engineering, Tongji University, 1239 Siping Road, Shanghai 200092, China; Shanghai Institute of Pollution Control and Ecological Security, Shanghai 200092, China.
College of Electronic and Information Engineering, Tongji University, 4800 Cao'an Highway, Shanghai 201804, China.
Water Res. 2024 Nov 15;266:122386. doi: 10.1016/j.watres.2024.122386. Epub 2024 Sep 3.
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 Ca/Mg 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.
固孔特征通常被认为是影响废活性污泥 (WAS) 脱水性能的重要因素，并且应该与固-水界面上由阳离子-有机相互作用主导的生物絮体的内聚力有关。本研究旨在通过阳离子调节建立一种调节 WAS 固孔结构的方法。相应地，从由阳离子-有机相互作用主导的孔隙特征的角度探讨了 WAS 脱水性能的影响机制。首先，通过梯度去除或添加二价阳离子，利用同步辐射 X 射线计算微断层摄影术 (CMT) 原位跟踪 WAS 絮体的变化孔结构。建立三维可视化模型来量化 WAS 絮体的孔结构参数。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、固体孔结构、水存在状态和污泥脱水性能之间的联系。结果发现，孤立孔的数量和体积共同决定了水的流动性以及毗邻水和间隙水的分数（p 值≤0.02）；此外，随着阳离子的添加，极性或酸性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<0.01）。这些结果表明，孔结构特征决定了水的存在状态，但固体孔隙率强烈依赖于界面特性。因此，应用分子对接来探索 Ca/Mg 与固体成分之间的界面反应机制，从配位位置、分子动力学和自由能计算方面进行探讨。结果表明，阳离子-有机相互作用如何通过固体表面改性影响孔特征，这有望为新型污泥调理技术的发展提供理论基础，即应该更加努力地通过削弱固体表面的水化排斥来增加污泥颗粒的致密程度。
