MSc David Parzych

Seeds differ in their ability to survive the extreme conditions during anaerobic digestion in biogas reactors. Seeds that survive anaerobic digestion can be distributed over arable land when digestate, the left-over of the substrate after anaerobic digestion, is used as a fertilizer. The factors that influence and the mechanisms that are responsible for the inactivation of seeds are poorly understood. In this study, I investigated the extent to which temperature was responsible for inactivation by comparing the survival curves of four plant species in water baths at 35, 42 and 49 °C with the survival curves in experimental, continuous flow-through biogas reactors that were operated at the same temperatures. Seeds belonged to the species Chenopodium album, Lycopersicon esculentum (tomato), Melilotus albus and Malva alcea. The first two species are not hardseeded and frequently used as references in studies on anaerobic digestion; the latter two species and were expected to be better able to survive anaerobic digestion because they are hardseeded (physical dormancy).

In the case of tomato and C. album, temperature could explain only part of the inactivation of the seeds as observed in biogas reactors. Additional factors or mechanisms, such as inactivation due to chemical substances or microbial activity, must have been involved as well. In the case of the hardseeded species, temperature could explain all or a large part of the inactivation as observed in biogas reactors.