Wu Boran, Li Hewei, Zhou Kun, Yu Ningrui, Xu Qinqin, Chai Xiaoli, Dai Xiaohu
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.
State Key Laboratory of Pollution Control and Resource Reuse, College of Environmental Science and Engineering, Tongji University, 1239 Siping Road, Shanghai 200092, China.
Water Res. 2023 Oct 1;244:120496. doi: 10.1016/j.watres.2023.120496. Epub 2023 Aug 17.
This study proposed to improve the dewaterability of waste-activated sludge (WAS) through crystallization-driven evolution of water occurrence states. Primarily, the feasibility of clathrate hydrate (i.e., CO hydrate) formation in WAS was examined. The thermodynamic analysis indicated that the CO hydrate formation with the excessive water in WAS followed pseudo-first-order kinetics, and fit of the data yielded a k value of 3.905 × 10 L∙mol∙s for 274.15 K. With the water conversion efficiency of 100%, the crystallization-dissociation process of CO hydrate significantly improved the dewaterability of WAS in term of capillary suction time (CST) decreasing from 251.5 s to 57.4 s. Also, the relief of gas pressure can induce the hydrate dissociation, which creates a novel way to recycle CO gas and save the consumption of chemicals required by sludge dewatering process. Regarding the mechanism of hydrates-based sludge dewatering, the evolution of water occurrence state was investigated. The in-situ synchrotron X-ray computed microtomography visually analyzed the micro-scale porosity and interstitial water of WAS flocs. The model of three-dimensional pore structure was established and the porosity parameters of solid aggregates were determined. It was found that the volume of connected pores and the total pore volume fraction of solid compositions increased. But the mean volume and mean area of isolated pores simultaneously decreased by 14.6% and 12.4%, respectively, which meant that the steric hindrance caused by isolated pores was weakened due to the reduced solid-water contact area. In addition, the crystallization of water caused the reformation of conformation arrangement of vicinal water and solid molecules, which highly organized the water molecules into the crystal structure. Accordingly, an estimation method for vicinal water layer thickness was developed based on atom force microscope. The thickness of vicinal water layer was found to be reduced by 77.4% and the hydration repulsion among solid compositions was correspondingly weakened, which facilitated the aggregation of solid compositions, and the relatively separated hydrate phase and solid phase could be formed. All the above results open up a novel strategy for enhanced water-solid separation of WAS through the crystallization-driven evolution of water occurrence states. As distinguished from the conventional approaches, the hydrates-based sludge dewatering enhances the water-solid separation only with regulating the spatial arrangement of water-solid molecules, but without altering the chemical compositions. Thus, more chances can be created to increase the environmentally friendly attributes related to WAS dewatering.
本研究旨在通过水赋存状态的结晶驱动演化来提高剩余活性污泥（WAS）的脱水性能。首先，研究了WAS中形成笼形水合物（即CO水合物）的可行性。热力学分析表明，WAS中过量水形成CO水合物遵循准一级动力学，在274.15K下对数据拟合得到的k值为3.905×10⁻⁴L∙mol⁻¹∙s⁻¹。在水转化效率为100%时，CO水合物的结晶-解离过程显著提高了WAS的脱水性能，毛细吸水时间（CST）从251.5s降至57.4s。此外，气体压力的释放可诱导水合物解离，这为回收CO气体和节省污泥脱水过程所需的化学药剂消耗创造了一种新方法。关于基于水合物的污泥脱水机理，研究了水赋存状态的演变。原位同步辐射X射线计算机断层扫描直观地分析了WAS絮体的微观孔隙率和间隙水。建立了三维孔隙结构模型并确定了固体聚集体的孔隙率参数。结果发现，连通孔隙体积和固体成分的总孔隙体积分数增加。但孤立孔隙的平均体积和平均面积同时分别减少了14.6%和12.4%，这意味着由于固水接触面积减小，孤立孔隙造成的空间位阻减弱。此外，水的结晶导致邻近水和固体分子的构象排列重新形成，使水分子高度有序地进入晶体结构。因此，基于原子力显微镜开发了一种邻近水层厚度的估算方法。发现邻近水层厚度减少了77.4%，固体成分之间的水化排斥力相应减弱，这促进了固体成分的聚集，并可形成相对分离的水合物相和固相。上述所有结果为通过水赋存状态的结晶驱动演化增强WAS的水-固分离开辟了一种新策略。与传统方法不同，基于水合物的污泥脱水仅通过调节水-固分子的空间排列来增强水-固分离，而不改变化学成分。因此，可为增加与WAS脱水相关的环境友好属性创造更多机会。
