Revisiting Fenton process for enhanced dewatering of waste activated sludge: Transformation in spatial distribution and chemical speciation of phosphorus

The effect of enhanced dewatering processes on changing the spatial distribution and chemical speciation of phosphorus (P) in waste activated sludge (WAS) remains to be revealed, which is critical for the selection and efficiency of P recovery processes. This study explored the effect mechanism of Fenton process on P release, spatial distribution, and chemical speciation in simultaneously enhancing WAS dewatering process. The results showed that the total P (TP) content in supernatant increased from 43.08 ± 1.21 mg/L to 106.07 ± 1.46 mg/L after Fenton conditioning. Meanwhile, P was changed from mainly distributed in the precipitate (42.75 % ± 0.21 %) and cells (41.60 % ± 0.12 %) in the raw WAS, to mainly distributed in the supernatant (18.80 % ± 0.26 %) and precipitates (75.19 % ± 0.16 %). Inorganic P in solid phase (IP_S)/TP in solid phase (TP_S) was enhanced from 74.03 % ± 0.36 % to 95.59 % ± 0.09 %, and bioavailable P was enhanced from 65.70 % ± 2.03 % to 91.48 % ± 2.12 %. Mechanistic insights indicated that the Fenton-based enhanced WAS dewatering process achieved WAS floc disintegration, extracellular polymeric substances dissolution, and cell rupture through the interactions of Fe³⁺ and the hydroxyl radical with WAS components, which in turn led to the inorganization of organic P, release of IP_S, and conversion of apatite P to non-apatite inorganic P. This study provided data support and theoretical basis for subsequent resource utilization of WAS and selection of P recovery technologies.