Improving sludge dewaterability via Fe²⁺ chelated citrate activated peroxydisulfate oxidation

Citrate (Ct) was chosen as a typical chelator used in the Fe²⁺-peroxydisulfate (PDS) process to improve sludge dewaterability. The PDS-Fe²⁺-Ct process exhibited better performance in sludge dewatering than PDS-Fe²⁺. Specifically, with a PDS dosage of 1.2 mmol/g VS, the molar ratio of PDS/Fe²⁺ and Ct/Fe²⁺ were 4:5 and 1:4, respectively, the capillary suction time decreased from 155.8 to 24.8sec, and the sludge cake water content decreased from 82.62% to 64.11% (-0.06MPa). The oxidation led to a reduced negative charge and a decrease in particle size. The enhanced sludge dewaterability and changes of sludge properties were attributed to the decomposition of extracellular polymeric substances, and it was explored by protein, polysaccharide, 3D-EEMs, and FT-IR. Additionally, the quenching experiments of radical species demonstrated that SO₄^-• played a more important role than •OH, and its productivity was improved with the addition of Ct. Moreover, the reasons for the improved productivity of radicals with the addition of Ct were discussed. The results of this study could serve as a basis for improving sludge dewatering using the PDS-Fe²⁺-Ct process and suggest that the addition of Ct may improve the productivity of SO₄^-• in the activation of PDS via Fe²⁺.