Effects of seasonal and local co-feedstocks on the performance of continuous anaerobic digestion of cattle slurry

The study's aim was to assess the robustness of farm-type anaerobic digestion with cattle slurry as the main feedstock under the change of co-feedstock type and quality. Fish biomass, rainbow trout offal, potato, and reindeer offal were investigated as possible co-feedstocks in a 428-day semi-continuous reactor experiment. Using fish biomass or rainbow trout offal as co-feedstock (19 % of VS of the feed) produced an average of 220 and 305 L CH4/kg VS compared to the 201 L CH4/kg VS for the manure control. For other co-feedstocks, the differences were not statistically significant. Despite recommendations to acclimate biogas process to new feedstocks with caution, no disturbances in the biogas process were observed, even with sudden changes in co-feedstocks. The use of locally available and seasonal co-feedstocks improved the agronomic quality of the digestates and could be important in securing farms' supply of and self-sufficiency in both energy and fertilizers.