Biodegradability of Cellulose in a Continuous Reactor with Increasing Feeding Rates

Cellulose is significantly present during the anaerobic digestion of energy crops and agricultural waste for biogas production. Nevertheless, its degradation poses some challenges due to its structure and resulting slow hydrolysis. The purpose of the current research was to analyse the response of a continuous anaerobic system digesting cellulose to increasing loading rates, in terms of the impact on the specific methane yield and biogas composition as well as on the process dynamics. To this end, a continuously stirred tank reactor with a working volume of 10 litres was operated under mesophilic conditions for over 60 days. Cellulose was added in the reactor daily as the sole carbon source at different organic loading rates (1gVS/l/d and 1.5 gVS/l/d). An increase in the OLR up to 1.5gVS/l/d resulted in an important decrease of the degree of solubilisation, thus creating an accumulation of the cellulose in the reactor and fluctuating methane production, below potential values. In particular, the results suggest that an acetate concentration of 1.3g/l in the medium, which was reached after increasing the loading, could have an effect on the enzymatic cellulose hydrolysis. This work contributes to the limited knowledge of cellulose solubilisation in continuous systems under anaerobic conditions.