On-site sanitation technologies such as septic tanks are widely used in low- and middle-income countries. A comprehensive management of the accumulating faecal sludge (FS) is however missing in most contexts and uncontrolled disposal of FS results in serious public and environmental health risks. Given the high pathogen and organic matter content of FS it is urgent to find an appropriate method to treat FS. One promising, but little investigated technology to treat FS is anaerobic digestion (AD). The goal of the present thesis was to evaluate the influence of temperature, VFA and pH on the inactivation of pathogens in AD of synthetic FS. Ascaris suum eggs and bacteriophages MS2 and T4 were selected as model organisms for parasitic, respectively viral pathogens. At a temperature of 50°C, Ascaris suum eggs were inactivated after 6 h, independent of the pH and the VFA concentration. Bacteriophages MS2 and T4 were however not fully inactivated after 6 h at 50°C, their initial concentration was reduced by almost 99 % for T4 but only by 50 % for MS2. The pH had an effect on bacteriophages T4 but not on MS2. VFA concentration did not have an influence on the bacteriophages inactivation at the tested temperatures. Viruses and not parasites seem to be the critical organisms to consider in thermophilic AD (TAD) at 50°C of FS. Future research could therefore focus on the inactivation of human viruses in TAD as bacteriophages are conservative indicators for inactivation of human viruses.