Synergistic effects of anaerobic co-digestion of whey, manure and fish ensilage

•Co-digestion of fish ensilage (FE), manure (M) and whey (W) was investigated.•Co-digestion resulted in BMP higher than weighted average of individual substrates.•Co-digestion of M+FE gave the highest synergetic effects (84% higher methane yield).•The extent of biodegradation of substrates explain the observed synergetic effects. Biogas production potential of the three feedstocks fish ensilage, manure and whey was evaluated using biochemical methane potential (BMP) tests. Since anaerobic digestion of single substrates may be inefficient due to imbalances in the carbon-nitrogen ratio, degree of biodegradability and/or due to lack of nutrients needed by the microbial community, co-digestion of these substrates was also assessed, revealing synergistic effects and a particularly good effect of combining manure with fish ensilage. In this latter case, methane yields were up to 84% higher than the weighted average of the methane yields obtained with the individual substrates. The type of substrate was the dominating cause of variation in methane production rates and yields.