In order to reduce energy requirements of wastewater treatment plants, sludge disintegration in form of thermochemical hydrolysis is considered as an alternative method for sludge treat-ment. It is supposed to improve biogas yield by means of improved biodegradation, thus in-creasing energy production. However, accumulation of persistent organic matter has been re-ported as a result of thermochemical hydrolysis. To examine the effects, thermochemical hy-drolysis of excess sludge and thickened excess sludge has been carried out in the laboratory in the temperature range of 50 °C to 90 °C with a base addition of 0,02 gNaOH/gTS to 0,08 gNaOH/gTS. The treated sludge was then analysed in biomethane potential tests regard-ing its biogas yield and in Zahn-Wellens-Tests concerning the accumulation of persistent or-ganic matter. Due to complications in both experiments a methodology which solved these issues had to be developed first. Only the experiments done after the completion of this meth-odology were evaluated. The biomethane potential test resulted in an increase of biogas yield in nearly all tests. Optimal conditions were found at 70 °C and with 0,08 gNaOH/gTS with an increase of 26 % in biogas yield to 272 NmL/g oTR. Only one Zahn-Wellens-Test could be fully evaluated due to foaming problems. The treated sludge showed an increased formation of refractory COD from the initial VS of the samples. The conversion factor rose with an increased base addition. 3,15 % of VS of the untreated sample were converted into refractory COD, whereas it was 5,15 % for the sample treated at 70 °C and with 0,08 gNaOH/gTS. To obtain generalizable statements for wastewater treatment plants, foaming problems should be re-duced and further experiments carried out to verify the found results.