Synergistic TA/(NH)SO conditioning for sludge dewatering: Mechanisms of EPS redistribution and hydrophobic enhancement.

With the rapid development of wastewater treatment plants during China's urbanization, efficient dewatering of waste activated sludge (WAS) has become a critical challenge for sludge reduction and resource recovery. In this study, tannic acid (TA) coupled with ammonium sulfate ((NH)SO) conditioning methods were employed to improve WAS dewatering, and the intrinsic mechanism was explored. The experimental results demonstrated that the combined application of 26.20 mmol/g VSS (NH)SO and 0.40 mmol/g VSS TA synergistically optimized dewatering efficiency, while reducing reagent consumption compared to individual treatment. TA facilitated the redistribution of tightly bound EPS proteins into soluble EPS and loosely bound EPS, improving dewaterability. Concurrently, (NH)SO compressed the hydration layer of proteins, destabilizing colloidal structures and inducing precipitation. Three-dimensional fluorescence spectroscopy showed that the combined treatment decreased fluorescence intensities of tryptophan-like and aromatic protein components in S-EPS, while also increased the proportion of hydrophobic humic acid-like substances. Additionally, the synergistic system significantly lowered the zeta potential of sludge particles, reducing electrostatic repulsion and promoting flocculation. Morphological analysis indicated the presence of surface cracks in treated sludge after vacuum filtration, while the enhanced dewaterability was further validated by the improved rheological properties. The TA/(NH)SO combined system also released inorganic phosphorus from the solid phase into the liquid phase, suggesting potential for phosphorus recovery. This synergistic approach not only optimizes WAS dewatering performance, but also expands pathways for sludge resource utilization, providing theoretical support for sustainable sludge management.