Anaerobic digestion of residual liquid effluent (brown juice) from a green biorefinery

This work studied the anaerobic digestion of brown juice, a liquid residual stream generated from biomass fractionation in a green biorefinery. Biomethane potential batch tests and inhibition studies of brown juice were performed during continuous processing in an upflow anaerobic sludge blanket reactor. Prolongation of the lag phase in the batch tests with increasing substrate/inoculum ratio suggested initial inhibition, which was, however, overcome by adaptation. This was indicated by high final methane yields, which were close to the theoretical maximum of up to 500 L-CH4 kg-VS−1, achieved after 15 days for most of the set-ups. Reactor operation at the organic loading rate of 13.9 g-COD L−1 day−1 and hydraulic retention time of 3 days revealed methane yields of 202 L-CH4 kg-COD−1 (307 L-CH4 kg-VS−1). Particle size analysis of the granules used in the reactor showed disintegration of the larger granules.