Anaerobic co-digestion of waste yeast biomass from citric acid production and waste frying fat.

Abstract

The application of spent yeast for biogas production has been studied only in the context of breweries so far. This study is focused on the anaerobic digestion of concentrated yeast biomass (CYB), being a by-product of citric acid biosynthesis. Two experimental set-ups were used in order to test CYB as a mono-substrate and co-substrate for closing the loop in accordance with the 'bioeconomy' approach. The results show that CYB allows for obtaining a high biogas yield, with a maximum of 1.45m3 N/kgVS produced when CYB was used as a mono-substrate. The average methane concentration was 66±4%. However, anaerobic digestion of CYB alone was difficult to perform because of a tendency for over-acidification, meaning that the maximum possible organic loading rate was 1kg/(m3*d). Repeated clogging of tubes with coagulated biomass also disturbed continuous feeding. In contrast, the co-digestion of CYB with waste frying fat at a ratio of 1:20 showed stable operation during a 70-day fermentation period. The biogas yield using the substrate mixture was 1.42m3/kgVS at an organic loading rate of 2kg/(m3*d). The methane concentration reached 67±4% and the acetate concentration did not exceed 30mg/L during the entire fermentation.