Correlation between oxidation-reduction potential values and sludge dewaterability during pre-oxidation

Pre-oxidation is effective in enhancing sludge dewaterability. Different types and doses of oxidants are used to improve sludge dewaterability in pre-oxidation. Rapid evaluation of the sludge dewaterability is vital for optimizing the type and dose of oxidants in pre-oxidation. It normally takes more time to evaluate sludge dewaterability by measuring typical indicators such as specific resistance to filtration (SRF), content of bound water, and composition of EPS. This study presented a rapid parameter, oxidation-reduction potential (ORP), to correlate it with the dewaterability of pre-oxidized sludge samples. An index of Delta ORP (Delta ORP = ORPt=0.5 (min)-ORPt=0 (min)) showed positive correlations with SRF (r = 0.89, p < 0.05), content of total organic carbon in soluble and loosely-bound EPS (r = 0.86 and 0.84, p < 0.05), zeta potential (r = 0.86, p < 0.05), and content of Fe(III) in the sludge cake (r = 0.92, p < 0.01). However, the Delta ORP index showed negative correlations with tryptophan-like proteins, tyrosine-like proteins, microbial byproduct-like materials in tightly-bound EPS (r = -0.85, -0.90 and -0.90, p < 0.05), and sludge particle sizes (p < 0.01). A multiple linear regression model was developed to further reflect the linear correlation between the Delta ORP values and the key factors reflecting sludge dewaterability. An optimal dose of oxone (0.4 mmol/g VS) for sludge pre-oxidation with the Delta ORP value of 387 mV combined with Fe(III) coagulation conditioning system were verified by the results of dewatering experiments using a laboratory-scale diaphragm filter press. This study demonstrated the feasibility of using Delta ORP as a potential rapid evaluation tool for sludge dewaterability. (C) 2019 Elsevier Ltd. All rights reserved.