Abstract
The effect of pH on chemical conditioning with potassium ferrate (K2FeO4) for improving sludge filtration dewatering performance has been studied. The variation of extracellular polymeric substances (EPS) in conditioning process was investigated in detail to unravel the reaction mechanism. The results indicated that sludge dewaterability was improved by decreasing solution pH in terms of filtration rate and cake solids content. At acid conditions, protonation of EPS resulted in reduction of negative charge and densification of sludge floc. Sludge conditioning efficiency was improved with decrease in pH. Ferrate can solubilize EPS through oxidation process and also remove a portion of soluble EPS (SEPS) by charge neutralization and interfacial adsorption of hydrolyzed ferric ions, consequently compressing EPS and decreasing total extractable EPS content. In addition, when pH and potassium ferrate were 3 and 0.1g/gTSS, the sludge filtration dewatering rate and extent reached the maximum. Deterioration of sludge dewaterability was observed as the ferrate was overdosed (>0.2g/gTSS). This could be attributed to the release of a large amount of bound EPS (BEPS) as a result of ferrate oxidation, consequently increasing the sludge filtration resistance.
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