Kinetics of primary sludge digestion at various temperatures

Anaerobic digestion is now commonly used for sludge treatment. Most industrial digesters operate under mesophilic (37°C) or thermophilic (55°C) conditions. These two regimes are considered as optimal for methane production. In this work, continuous sludge digestion has been operated at labscale at 5 different temperatures comprised between 28° and 55°C. The reactors were first inoculated with anaerobic mesophilic sludge and were acclimatized to their new temperature during 4 weeks at a low loading rate. Then, they were fed with the same (primary) sludge during 9 weeks. The 1 st results revealed that the methane production rate is increasing with temperature. In our experiments, the maximal methane production rate is obtained at 49°C. At 55°C, the methane production was slightly lower, probably due to the fact that volatile fatty acids (especially propionate) were formed at relatively large amounts (> 1500 mg/L).