Transformation of typical components in anaerobically digested sludge during its conditioning process by KMnO4

Many efforts have been made to improve the dewaterability during anaerobically digested sludge (ADS) conditioning. However, the conversion of substances in ADS conditioning, as an important process of sludge treatment and application, has received little attention. This study investigated the transformation process of typical components in sludge such as extracellular polymeric substances (EPS), sulfide, Fe and Mn species. The effects of KMnO4 dosage and pH change on the ADS conditioning were investigated in detail. The results showed that the sludge particle size and capillary suction time decreased with the increase of KMnO4 dosage. The water content of sludge cake by vacuum filtration gradually dropped from 84.5% to 78.8% after conditioning with 0-5.0 g KMnO4/L sludge. Based on fluorescence excitation-emission matrix, EPS and dissolved organic carbon measurements, the improvement of sludge dewaterability was due to the disruption of EPS and the release of intracellular substances. Interestingly, 11.5% sulphides (S2-) in ADS were oxidized into SO42- at KMnO4 dosage of 3.0 g/L, which can effectively inhibit the release of hazardous H2S even the sludge pH changed to 2 in conditioning process. Moreover, about 30 mg/L of PO43- in centrifugate can be completely immobilized by the generated iron, manganese and their binary oxides as a result of the interaction between Fe2+ and KMnO4. These findings provided a new insight to explore the sludge conditioning process and the transformation of typical components.