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 96822-2217, USA; Water Resources Research Center, University of Hawai'i at Mānoa, USA, Honolulu, HI 96822-2217, USA.
Sci Total Environ. 2024 Jan 1;906:167719. doi: 10.1016/j.scitotenv.2023.167719. Epub 2023 Oct 13.
Extracellular polymeric substances (EPS) are the key components determining the dewatering behavior of wastewater sludge. However, current technical optimization of sludge conditioning for dewatering is limited by the poor understanding of the conditioner-EPS interactions at molecular levels. Herein, a combination of molecular dynamic (MD) simulations, dewaterability assessment and EPS characterization was used to reveal the sludge dewatering mechanisms using dual conditioning processes (prevalent inorganic (poly aluminum chloride (PAC)) and organic (poly dimethyl diallyl ammonium chloride (PDDA)). Results suggested that PAC and PDDA bridged the biopolymers mainly through electrostatic interactions, promoting the agglomeration of biopolymers and reducing their contact probability with water molecules. Water molecules were tightly bound to EPS mainly through hydrogen bonding with polar oxygen-containing functional groups. The adsorption of PAC and PDDA on hydrophilic components reduced the molecular polarity of biopolymers and altered the conformation of water molecules in the hydration shell, resulting in a decreased hydration capacity of EPS and the release of bound water, and sludge dewaterability was improved. PAC was found to be more effective than PDDA in disrupting the hydrogen bonding between water molecules and EPS, especially the protein β-sheet structure inside the molecular clusters with its high charge strength and diffusivity. Sludge bound water decreased by 73.16 % after PAC conditioning. In addition, PDDA exhibited superior agglomeration ability to biopolymers and promoted the electrostatic interaction between PAC and polar groups during dual conditioning. The strength and hydrophobicity of EPS molecular clusters were thus enhanced, and the conditioning efficiency was improved. This study offers molecular-level insights into the coagulation treatment process of sludge and provides theoretical references for process optimization and new conditioner development.
胞外聚合物（EPS）是决定废水污泥脱水性能的关键成分。然而，目前污泥调理脱水的技术优化受到对分子水平上调理剂-EPS 相互作用理解不足的限制。在此，通过分子动力学（MD）模拟、脱水性能评估和 EPS 特性分析相结合的方法，揭示了使用双重调理过程（普遍存在的无机（聚合氯化铝（PAC））和有机（聚二甲基二烯丙基氯化铵（PDDA））调理污泥的脱水机制。结果表明，PAC 和 PDDA 主要通过静电相互作用桥联生物聚合物，促进生物聚合物的聚集，降低其与水分子的接触概率。水分子主要通过与带极性含氧官能团的氢键紧密结合到 EPS 上。PAC 和 PDDA 在亲水组分上的吸附降低了生物聚合物的分子极性，并改变了水合壳中水分子的构象，导致 EPS 的水合能力降低和结合水的释放，从而提高了污泥的脱水性能。与 PDDA 相比，PAC 更有效地破坏水分子和 EPS 之间的氢键，特别是在分子簇内破坏蛋白质β-折叠结构，这与其高电荷强度和扩散性有关。经过 PAC 调理后，污泥结合水减少了 73.16%。此外，PDDA 对生物聚合物具有优异的聚集能力，并在双重调理过程中促进 PAC 和极性基团之间的静电相互作用。因此，EPS 分子簇的强度和疏水性增强，调理效率提高。本研究为污泥混凝处理过程提供了分子水平的见解，为工艺优化和新型调理剂的开发提供了理论参考。
