A new approach for excess sludge reduction by manganese dioxide oxidation: performance, kinetics, and mechanism studies.

A considerable amount of excess sludge, a kind of hazardous waste, is produced from the conventional wastewater treatment systems such as activated sludge process, and efficient sludge reduction processes are needed. A new chemical method for sludge reduction was proposed by using manganese dioxide as oxidant in this study. A favorable condition for sludge reduction is determined as manganese dioxide dosage of 0.165 g g-1 wet sludge, sulfuric acid concentration of 3 mol L-1, and reduction temperature of 90 °C for 90 min, where the sludge reduction efficiency can reach 73.30%. Reaction kinetic study revealed that the sludge reduction rate was controlled by the surface chemical reaction and the reaction followed a shrinking core kinetic model with apparent activation energy of 37.76 kJ mol-1. Furthermore, reaction process analysis indicated that the sludge hydrolysis included two steps, i.e., floc destruction and microbial cell disruption. Considering the high efficiency and short treatment time, manganese dioxide oxidation is suggested to be a feasible method for disintegration of excess activated sludge.