Mechanism Investigation of Excess Sludge Disintegration by Stirred Ball Mill—Utilized Transmission Electron Microscope Observation and Peptidoglycan Concentration Determination

The stirred ball mill (SBM) method is a common method applied in large-scale sludge disintegration. Many reports focus on the disintegration results of sludge or the influence of parameters on the anaerobic process of treated sludge, but there have been few studies on the mechanism of sludge disintegration by SBM. This study focused on the mechanism of sludge disintegration by the SBM method. The results show that the flocs and bacterial cell wall were well disrupted and that the cytoplasm flowed remarkably out of the cell. Although the size with the largest volume distribution was expected to decrease with increasing treatment time, the volume of particles with a size of 34.56–44.04 μm increased in the sample treated for 60 min. We observed a temperature increase in the reflocculation of the biomacromolecules. The maximal value of DDCOD was 18.6%, and the concentrations of proteins and nucleic acids reached peaks at 691.80 mg/L and 281.05 mg/L, respectively. The peptidoglycan concentration showed that only 25.4% of the cell wall was broken and dissolved into liquid. From the results, we show that SBM can effectively break flocs and bacterial cell walls, but the method has a low efficiency for breaking biomacromolecule fragments into the liquid phase.