Co-digestion of waste from the salmon aquaculture sector with regional sewage sludge: effects on methane yield and digestate nutrient content

In Western Norway, the availability of aquaculture waste resources is relevant for both biogas production and nutrients recovery. In this study, fish sludge from the farming of salmon was tested as co-digestion substrate in the anaerobic digestion of municipal sewage sludge from different regional treatment plants. Additions of 5, 10, 25 and 30% of fish sludge in volume were evaluated. Fish sludge did not improve the methane yield of Grødaland sewage sludge. In contrast, Bergen plant’s sewage sludge yield increased up to 40% with additions of 25% fish sludge. Co-digestion mixtures are being further tested in semi-continuous reactors for its long-term process stability, methane yield, and the effects that fish sludge may have on the final digestate’s nutrient content.