Peng Sainan, Wang Zhiyue, Yu Pingfeng, Liao Guiying, Liu Rui, Wang Dongsheng, Zhang Weijun
Faculty Materials Science and Chemistry, China University of Geosciences, Wuhan 430074, Hubei, China.
Department of Civil and Environmental Engineering, University of Hawai'i at Mānoa, USA, Honolulu, HI, USA 96822-2217; Water Resources Research Center, University of Hawai'i at Mānoa, USA, Honolulu, HI, USA 96822-2217.
Water Res. 2023 Apr 1;232:119675. doi: 10.1016/j.watres.2023.119675. Epub 2023 Jan 28.
Interactions between cations and extracellular polymeric substances (EPS) play an important role in the formation of microbial aggregates and have key effects on the physical properties of activated sludge across wastewater and sludge treatment process. Here, a molecular model of EPS cluster in activated sludge was constructed and simulated by molecular dynamics (MD) to probe the structural properties of EPS and the interaction between EPS and prevalent multivalent cations (Ca, Mg, Al). Then the predicted changes in physical properties were validated against the dynamic light scattering, XAD resin fractionation and rheology test. The binding dynamics and interactions mechanisms between multivalent cations and EPS functional groups were further investigated using MD in combination with spectroscopic analysis. Results suggest that biopolymers are originally aggregated by electrostatic and intermolecular interactions forming dynamic clusters with negatively charged surface functional groups, which induced electrostatic repulsion preventing further agglomeration of biopolymer clusters. In the presence of multivalent cations, surface polar functional groups in biopolymers are connected, causing the rearrangement of EPS molecular conformation that forms larger and denser agglomerates. Reduced solvent accessible surface area, enhanced hydrophobicity, and increased binding free energy lead to a strong gel-like network of EPS. Ca and Al predominantly interact with functional groups in polysaccharides, promoting agglomeration of macromolecules. In contrast, Mg and Al disrupted the secondary structure of proteins, exposing hydrophobic interaction sites. Al can better agglomerate biopolymers with its higher positive charge and shorter coordination distance as compared to Ca and Mg, but compromised by the effect of hydration. This work offers a novel approach to explore the construction and molecular aggregation of EPS, enriching the theoretical basis for optimization of wastewater and sludge treatment.
阳离子与胞外聚合物（EPS）之间的相互作用在微生物聚集体的形成中起着重要作用，并且在整个废水和污泥处理过程中对活性污泥的物理性质具有关键影响。在此，通过分子动力学（MD）构建并模拟了活性污泥中EPS簇的分子模型，以探究EPS的结构特性以及EPS与常见多价阳离子（Ca、Mg、Al）之间的相互作用。然后，通过动态光散射、XAD树脂分级分离和流变学测试验证了预测的物理性质变化。使用MD结合光谱分析进一步研究了多价阳离子与EPS官能团之间的结合动力学和相互作用机制。结果表明，生物聚合物最初通过静电和分子间相互作用聚集形成具有带负电表面官能团的动态簇，这会引发静电排斥，阻止生物聚合物簇进一步团聚。在多价阳离子存在的情况下，生物聚合物中的表面极性官能团相互连接，导致EPS分子构象重排，形成更大、更致密的团聚体。溶剂可及表面积减小、疏水性增强以及结合自由能增加导致EPS形成强凝胶状网络。Ca和Al主要与多糖中的官能团相互作用，促进大分子团聚。相比之下，Mg和Al破坏了蛋白质的二级结构，暴露出疏水相互作用位点。与Ca和Mg相比，Al具有更高的正电荷和更短的配位距离，能够更好地使生物聚合物团聚，但会受到水合作用的影响。这项工作提供了一种探索EPS构建和分子聚集的新方法，丰富了优化废水和污泥处理的理论基础。
