Synergetic sludge conditioning by US enhanced Fe²⁺ activated sodium persulfate: Physicochemical properties and...

Efficient dewatering of sewage sludge is an energy- and carbon-saving procedure for sludge treatment in wastewater treatment facilities. The ultrasound-coupled divalent iron ion activated persulfate process can effectively promote sludge dewatering and improve organic substance content. Under the action of ultrasound (US 50 w/L), divalent iron ions (Fe²⁺) 200 mg/g (TS), and persulfate (PDS) 200 mg/g (TS) for 60 min, the capillary suction time (CST) was reduced by 79.74%, and the moisture content of the dewatered sludge cake reached 56.51 wt%. The organic carbon content of treated sludge was also four times higher than the original sludge and types were richer in short-chain volatile species in US/Fe²⁺/PDS. Moreover, the correlation analysis found that the relationship of between CST and SV₃₀, Zeta and lactate dehydrogenase (LDH) were positive correlation, and the relationship of SCOD and TC were positively correlated with the PN (SB-EPS). Mechanistic studies showed that the US/Fe²⁺/PDS system could produce oxygen activators by US coupling Fe²⁺ to strengthen the effect of activated PDS strongly, while the sulfate radicals (SO₄·^-) radical was a dominant role. The cracking mechanism is divided into two pathways effectively degraded the macromolecule EPS into a small-molecule acid and further reduced the water-holding interfacial affinity as follow: (1) the radical path dominated by hydroxyl radicals (·OH), SO₄·^-, and superoxide radical (O₂·^-); (2) the non-radicals dominated by monoclinic oxygen (¹O₂). Afterwards, the electrostatic force and interfacial free energy were reduced, resulting in enhanced self-flocculation and mobility to enhanced dewaterability. These findings demonstrated the US/Fe²⁺/PDS system had significant advantages in sludge cracking and provided theoretical support for its practical application.