Thermophilic anaerobic digestion of cattle manure and improving the hydrolysis yield

Due to global warming and the depletion of fossil fuels, there is a trend towards renewable energy sources, such as solar power, bio-ethanol and biogas. Anaerobic digestion is an established technology for the recovery of chemical energy from e.g. wastewater and manure as biogas [1,2]. Although a proven technology, research is required to increase biogas yields and productivity. In the present research, the thermophilic anaerobic digestion of cattle manure, codigested with food waste, is studied. Inoculum and substrate are sampled at a thermophilic anerobic digester of Göteborg Energi AB (Sävsjö, Sweden). At this site, cattle manure and food waste are pretreated at 70 °C (1 h for hygienisation). Hereafter, the substrate is digested at 55 °C in a continuously fed stirred tank reactor. It is expected that hydrolysis of the lignocellulosic material contained in the substrate is a limiting step [3]. This will be verified in laboratory studies, mimicking the conditions at the plant. The substrate will be characterized, focusing on the lignocellulosic material and the changes this material undergoes during anaerobic digestion. Moreover, the responsible organisms and the enzymes they excrete will be characterized, which will indicate how to improve hydrolysis. It is expected this may be done through adjusting micro and macro nutrient availability [4] and selection of process conditions. The effect of the selected parameters on the microbial community and the hydrolysis yield will be established. Moreover, the effect of particle size will be studied. The expected outcome of the study is that by an improved understanding of the microbial community, esp. the organisms responsible for hydrolysis of lignocellulosic material, the biogas yield, biogas productivity and system stability can be increased