Study On Disintegration Of Excess Activated Sludge With KMnO₄/K₂FeO₄

Treatment and disposal of excess activated sludge is a difficult problem in urban wastewater biological treatment plants. Cost for treatment and disposal of excess sludge accounted for25%to40%of the total cost of the sewage treatment plant, sometimes even up to60%. Nowadays, anaerobic digestion is the mostly used method in sludge treatment. However, anaerobic digestion shows several problems such as too slow reaction, long sludge retention time, and low gas production. Upgrading of activated sludge treatment might be required in order to increase sludge biodegradability of and maximize biogas production.In this study, potassium permanganate and potassium ferrate were used as oxidants to disintegrate the sludge. The change of solid phase and liquid phase of sludge after the disintegration were discussed. The main mechanism of sludge floc disintegration was also studied. This paper also investigated sludge biogas production after disintegrated with KMnO4/K2FeO4. The main conclusions of this study are as follows:KMnO4treatment was effective for sludge disintegration and the suitable reaction time was30min. The mechanism of sludge disintegration was that the proteins and polysaccharides release into the liquid phase with KMnO4oxidation. The oxidation of KMnO4on protein was better than that on polysaccharide. More loosely bound EPS was stripped by KMnO4Oxidation than the slime EPS and tightly bound EPS. The sludge disintegration was attributed to the high oxidation potential of KMnO4. The optimal KMnO4dosage for sludge disintegration was500mg/L, DDCOD under optimal conditions can be34.4%. Sludge disintegration effectiveness declined along with the increase of sludge total solids (TS). Mass ratio between KMnO4and sludge TS was the most important factor for sludge disintegration and when KMnO4/TS mass ratio was0.1, the disintegration effectiveness was the highest with a DDCOD between33.8%to35.2%. The settlability and dewaterability of sludge became worse after disintegrated with KMnO4. The cumulative gas production of sludge anaerobic digestion after disintegration was higher than the raw sludge. When the KMnO4dosage was500mg/L, the cumulative gas production reached the maximum.K2FeO4treatment was also effective for sludge disintegration. The same K2FeO4dosage showed better sludge disintegration effectiveness than that of KMnO4while the reaction time is shorter. The mechanism of sludge disintegration was that K2FeO4oxidized proteins and polysaccharides into the liquid phase, especially the polysaccharide in slime and protein in tightly bound EPS. When the K.2FeO4dosage was500mg/L, the DDcod reached68.7%, which was the maximum. Treatment effectiveness declined along with the increase of sludge TS. The settlability and dewaterability of sludge were worse after disintegrated with K2FeO4The cumulative gas production of sludge anaerobic digestion after oxidation was higher than the raw sludge. The optimal K2FeO4dosage for sludge anaerobic digestion was500mg/L.