Oxidation-flocculation conditioning to improve the performance and mechanism of municipal sludge dewatering

In this study, ferrous iron (Fe²⁺)-catalyzed sodium percarbonate (2Na₂CO₃·3H₂O₂) was used for conditioning (referred to as F-N conditioning) municipal sludge. On this basis, Fe²⁺-catalyzed 2Na₂CO₃·3H₂O₂ was coupled with polymerized ferrous sulfate (PFS) conditioning (referred to as F-N-P conditioning) as well as coupled with the compounding of PFS and cationic polyacrylamide (CPAM) conditioning were explored (referred to as F-N-P-C conditioning) for municipal sludge. The results showed that the optimal dosages of Fe²⁺, 2Na₂CO₃·3H₂O₂, PFS and CPAM were 15, 40, 200 and 0.3 mg/g of absolutely dry sludge (DS), respectively, in which the specific resistance of the sludge (SRF) and the water content of the filtered sludge cake (WC) dropped from 2.1 × 10¹³ m/kg and 90.5 % to 2.9 × 10¹¹ m/kg and 75.3 %, respectively. The mechanism study showed that the hydroxyl radicals (•OH) generated by F-N-P-C effectively cleaved the extracellular polymer (EPS) and remodeled the protein secondary structure by affecting the ratio of α-sheet and β-helix in the proteins secondary structure. PFS and CPAM neutralized the negative charge on the surface of municipal sludge flocs, and adsorbed-bridged with sludge flocs to improve the settling performance of sludge. Finally, the results of the plate and frame filter press dewatering tests verified that the F-N-P-C conditioning mode was the best formulation of sludge conditioning and determined the optimal working conditions: sludge feeding time, pressing time and pressing pressure were 5400 s, 5400 s and 1.2 MPa, respectively. The chemical cost of F-N-P-C conditioning was preliminarily estimated as 58.55 USD$/ton DS. Therefore, The F-N-P-C process had certain practical value and promotion significance.