G. Lehne, J. A. Müller and J. Schwedes


Institute of Mechanical Process Engineering, Technical University of Braunschweig,

Post Box 3329, D-38023 Braunschweig, Germany




The mechanical disintegration can be used for an accelerated and improved anaerobic digestion of excess sludge. Mechanical disintegration can be used to disrupt the cell walls and to cause the release of the organic material from the cells. Particle size analysis describes the size reduction but is not suitable for characterising the release of the organic material and the cell disruption. Two biochemical methods were developed for these phenomena.

An ultrasonic homogenizer, a high pressure homogenizer and stirred ball mills were used for disintegration experiments using various parameters. Investigations had to detect the influence of the solid content on the disintegration results. For sludge with a higher solid content better results in terms of energy consumption could be achieved. An optimum of the bead diameter and the stress intensity in stirred ball mills could be detected. A comparison of the results of different methods of sludge disintegration shows that the investigated ultrasonic homogenizers are inferior to a high pressure homogenizer and a stirred ball mill in terms of energy consumption.

The hydrolysis is the limiting step of excess sludge digestion. For disintegrated excess sludge an improved and accelerated anaerobic digestion could be detected. The digestion process is characterised through higher degrees of degradation with increasing degree of disintegration. For batch and continuous experiments the degree of degradation could be improved. A combination of mechanical disintegration, short hydraulic retention times and an immobilisation of the biomass showed more than doubled degrees of degradation in comparison to untreated sludge.




anaerobic digestion, cell-disruption, disintegration devices, excess sludge, mechanical disintegration






G. Lehne, J. Müller, J. Schwedes (1999). Mechanical Disintegration and Anaerobic Digestion of Excess Sludge, IAWQ Conference on Disposal and Utilisation of Sewage Sludge, October 1999, Athens, Greece, pp. 137-144