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The improvement of anaerobic digestion was investigated in an interdisciplinary research group. Using four different methods of mechanical cell disintegration the influence of the degree of disintegration and the digestion parameters on the performance of the anaerobic process was investigated. Analytical methods to describe the degree of cell-disruption had to be developed. The best results were obtained using a stirred ball mill and a high-pressure homogenizer. As a result of disintegration the degradation is accelerated and the digestion time can be reduced, especially when using immobilized micro-organisms. The treatment of digested sludge by ozonization respectively by mechanical disintegration led to an improved biodegradability of residual organic compounds. In a following second anaerobic process the treated sludge reached an even higher degree of degradation. On the other hand the disruption of the particle structure leads to an increase in polymer-demand and no improvement in dewatering results. Sludge water, returned to the aeration tanks, is slightly more polluted, especially the concentration of ammonia increases because of the better anaerobic digestion.