Relationship between electron donor-acceptor capacity of organic components and sludge dewatering performance during pre-oxidation

Currently, pre-oxidation has been reported as an effective method for deep sludge dewatering. However, both insufficient and excessive degrees of pre-oxidation lead to poor dewaterability. An evaluation of a proper sludge pre-oxidation degree is crucial for optimization of oxidant dose in sludge dewatering. This study proposed a new evaluation tool, the electron donor-acceptor capacity of organic components in the filtered sludge supernatant (also refers to soluble extracellular polymeric substances (S-EPS)), to correlate with sludge dewatering performance and other hydrophilic organic components affecting sludge dewaterability. Organic components in S-EPS revealed higher specific absorption coefficients, humification degree, and cytochrome c concentrations than those in bound EPS. The electron acceptor capacity (S-EAC) and electron donor capacity (S-EDC) of organic components in soluble extracellular polymeric substances exhibited powerful associations with capillary suction time (S-EAC: correlation coefficient (r) = −0.99, probability (p) < 0.01; S-EDC: r = 0.97, p < 0.01), and specific resistance to filtration (S-EAC: r = −0.88, p < 0.05; S-EDC: r = 0.82, p < 0.05). The structure properties (mainly aromatic groups, carboxyl groups, O₁₀-O₁₂ species distribution within the CHONS compound, tryptophan-like proteins, humic acid-like substances, protein secondary structure of β-sheet, sulfur-containing organic components, and carbon saturation) of organic components significantly affected the electron transfer capacities. Multiple linear regression models were created to better illustrate the linear relationship in the middle of S-EAC and S-EDC values and other parameters influencing sludge dewatering performance. The absolute S-EAC value of more than 25.43 μmol e⁻/g total organic carbon (TOC) or the absolute S-EDC value of less than 1.59 μmol e⁻/g TOC was recommended for sludge pre-oxidation, which was further validated via a laboratory-scale filtration device.