Decoupling EPS-bound and intracellular phosphorus in waste activated sludge: A low-disturbance strategy for controlled recovery.

Phosphorus (P) in waste activated sludge (WAS) exists in both intracellular stores and fractions associated with extracellular polymeric substances (EPS). These EPS-bound phosphorus species are often stabilized through metal - phosphate - EPS linkages, which complicate their selective recovery. In this study, five single extraction methods (acidification, alkalization, heating, ultrasound, and EDTA chelation) and one combined approach (ultrasound-EDTA) were comparatively evaluated to elucidate their mechanisms of EPS disruption and P mobilization. Phosphorus speciation behavior under single treatments was characterized using 31P nuclear magnetic resonance with phytic acid and sodium hexametaphosphate as model compounds, revealing that strong alkaline extraction caused extensive Poly-P depolymerization and OP hydrolysis, whereas EDTA and low-intensity ultrasound preserved P speciation but showed limited extraction efficiency. The ultrasound-EDTA combination achieved a synergistic effect, yielding 62.63 mg·g-1 TSS of EPS and 9.6 mg·g-1 TSS of phosphorus with only 13.2% cell apoptosis, comparable to alkaline extraction yet with minimal biological disruption. Confocal microscopic analysis confirmed that the released phosphorus predominantly originated from the EPS matrix, indicating that the hybrid treatment effectively targeted EPS-P while preventing intracellular release. These findings establish a non-destructive extraction pathway based on the coupling of physical cavitation and selective chelation, providing mechanistic insight into EPS-mediated P binding and offering a new strategy for controlled, high-efficiency phosphorus recovery from sludge.