Synergistic Effects of Ultrasound-Assisted Conditioning with Modified Corn-Core Powder and Sludge-Based Biochar on Municipal Sludge Dewaterability: Performance Evaluation and Mechanistic Insights

Effective sludge dewatering remains a critical challenge in wastewater treatment due to the complex structure of extracellular polymeric substances that encapsulate bound water. This study investigated the synergistic effects of ultrasound combined with modified corn-core powder and sludge-based biochar on municipal sludge dewaterability. Orthogonal and single-factor experiments were designed to optimize conditioning parameters, and the underlying mechanisms were elucidated through comprehensive analyses of extracellular polymeric substance composition, three-dimensional excitation-emission matrix fluorescence spectroscopy, fluorescence regional integration, fractal dimension, particle-size distribution, and statistical correlation. The results demonstrated that optimal dewatering performance was achieved at an ultrasonic specific energy of 4000 kJ/kg dry solids for the modified corn-core powder and sludge-based biochar with ultrasound system, where net sludge solids yield increased by 124%, while specific resistance of filtration and moisture content decreased by 78% and 19%, respectively. Mechanistic analysis revealed that low-intensity ultrasound disrupted sludge flocs, released extracellular polymeric substance-bound organic matter, and promoted the shift of organic components from soluble extracellular polymeric substances to tightly bound extracellular polymeric substances, facilitated by the long-chain adsorption of modified corn-core powder and the skeleton-building effect of sludge-based biochar. Excessive ultrasound (specific energy > 8000 kJ/kg dry solids) caused particle fragmentation, increased system viscosity, and deteriorated dewaterability. Pearson correlation and principal component analysis confirmed that ultrasonic specific energy and organic components in soluble extracellular polymeric substances were the dominant factors governing dewatering performance. This study provides a promising strategy for reducing chemical conditioner consumption while enhancing sludge dewaterability through controlled ultrasound assistance.