1 Anaerobic Digestion at Mesophilic and Thermophilic Temperature With Emphasis on Degradation of Phenols and Structures of Microbial Communities

During anaerobic digestion of organic wastes, nutrient-rich digestate is produced. This digestate has great potential as a fertiliser on farmland. However, one concern is the content of organic pollutants in the digestate, as these may influence the soil fertility in the long-term perspective. Different organic pollutants have been found in various organic wastes and types of digestate. This thesis describes the effect of temperature on the anaerobic degradation of different organic pollutant, i.e. aromatic compounds, and on the structure of microbial communities. To isolate the impact of temperature on the degradation, investigations were carried out in two laboratory-scale bioreactors that were stable and equivalent in performance apart from process temperature and hydraulic retention time. These reactors have treated the same type of organic municipal household waste for many years. The aromatic compounds were chosen to represent important anaerobic reaction steps and key intermediates. Several of the selected compounds were efficiently degraded at the mesophilic temperature (37 ºC). In contrast, phenols and phthalic acid were not degraded at the thermophilic temperature (55 ºC). This limited degradation at the higher temperature is contrary to the genera