Disintegration of excess activated sludge with potassium permanganate: Feasibility, mechanisms and parameter optimization

• Excess sludge was effectively disintegrated with KMnO4 oxidation.
• Supernatant proteins and polysaccharides increased by 490% and 141% respectively.
• Loosely bound EPS increased by 498% due to efficient release.
• KMnO4/TS mass ratio was the most important factor for sludge disintegration.

Sludge disintegration destroys the sludge floc structure and releases the extracellular polymeric substances (EPS) and cell contents into the liquid phase, to enhance the sludge anaerobic digestion. Potential benefits of potassium permanganate (KMnO4) disintegrating excess sludge were investigated in this paper. Sludge disintegration feasibility was analyzed with soluble chemical oxygen demand (SCOD) increase in supernatant. Sludge disintegration mechanisms were explored with analyzing the change of particle size, EPS, oxidation reduction potential (ORP) and Mn state. Sludge disintegration process was optimized through analyzing disintegration degree (DDCOD). Results showed that KMnO4 effectively disintegrated the excess sludge with a SCOD increase of 3473% and more than 97% of Mn transferred into the solid phase. A slow decrease in particle size was observed. EPS was efficiently released into supernatant, and supernatant proteins and polysaccharides increased by 490% and 141%, respectively. Loosely bound EPS increased by 498%, which was much higher than slime EPS and tightly bound EPS. The main mechanism of sludge disintegration was KMnO4 oxidation. After sludge oxidation, KMnO4 mainly transferred to the sludge solids with the states of MnO2 and Mn3O4, and a state of KxMnO4 also existed in the solids. Optimization experiments showed that suitable reaction time was 30 min, and KMnO4/sludge solid mass ratio was the most important factor and its optimal value was 0.1 with a stable DDCOD of about 34%.