High moisture content of waste-activated sludge (WAS) limits energy-efficient treatment, as conventional dewatering processes struggle to remove micropore-confined water, resulting in elevated conditioning agent consumption. This study proposes enhancing interstitial water removal from fine solid pores of WAS through phase-transfer driving force of CO2 clathrate hydrate crystallization. Hydrate formation was accelerated via templating effects induced by ordering the packing conformation of interfacial water molecules using low-dosage surface-active flocculant. Atomic force microscopy and sum frequency generation spectroscopy revealed reduced vicinal water layer thickness and reconfigured water molecule packing, indicating lowered hydrate nucleation energy barriers. Accordingly, thermodynamic analysis showed 12% reduction in equilibrium pressure, 14.6% decrease in formation enthalpy, 78% shortening of induction time, and 273.7% increase in growth rate. Hydrate-based dewatering process achieved up to 94% reduction in capillary suction time and final cake water content of 47% after non-thermal plate-frame filtration without inorganic coagulants, thereby preserving the calorific value for subsequent energy recovery. In-situ synchrotron X-ray computed microtomography and low-field NMR T1-T2 relaxometry tracked crystallization-driven pore evolution and water mobility. Hydrate crystallization induced water migration from intermolecular spaces of gel-like matrix, resulting in solid densification, elimination of isolated pores, and coalescence of water into conductive channels. Pore network modeling identified a 2.37-fold increase in coordination number, indicating enhanced pore connectivity. Overall, these findings highlight a reagent-efficient and energy-saving route for WAS dewatering by restructuring pore connectivity rather than non-selectively disrupting solid components, and provide new insights into the role of water molecular conformation in solid-water separation of colloidal microbial systems.
Ye et al. (Mon,) studied this question.