This study has been carried out to investigate the effect of microwave, alkalization andfreezing on surplus activated sludge disintegration (release oforganic/inorganic substances into the supernatant) and mesophilic fermentation. After applying pre-treatments, chemical oxygen demand increased by 7 - 35 times, disintegration degree was 35 - 47 %, proteins by 5 - 25, carbohydrates by 2 - 3, phosphates 7 - 22 and ammonium by 3 - 16 times. Disintegration by microwave, alkalization and freezing has a positive effect on the rate of sludge anaerobic digestion. Biogas production increased by: 62; 49 and 58 %, for microwave radiation, alkalization and freezing, respectively. The conducted research shows that the application of disintegration as a pre-treatment of surplus activated sludge is an effective method, allowing for practical using sewage sludge.