Thermophilic anaerobic digestion of pasteurised food wastes and dairy cattle manure in batch and large volume laboratory digesters: Focussing on mixing ratios

Abstract

The potential of pasteurised food wastes in mixtures with cattle manure as feedstock for anaerobic digesters was assessed in batch and high volume laboratory digesters under thermophilic conditions. While food wastes is an attractive substrate for anaerobic digestion plants, their characteristics, especially the high nitrogen content, renders their treatment problematic. During this study, for the different mixtures of cattle manure and food wastes, methane yields of 281–385 m3CH4/tonVSadded have been achieved in organic loading rates of up to 6.85 kgVS/m3d with the TS levels of the influent reaching as high as 15.7%. However, as the OLR and TS levels of the influent stream increase, the specific methane production is adversely affected. Addition of 25% (w/w) food wastes to thermophilic digesters treating cattle manures can be considered safe and results in an improvement of the specific methane production by 86%, the volumetric methane production by 430% and the VS reduction by 35.2% compared to cattle manure monodigestion.