Dried pellet of exhausted sugar beet cossettes were digested alone and combined with cow manure as cosubstrate in a mesophilic semi-continuous anaerobic system. In single digestion assay, the stable biogas production and stable reactor operation was observed at the hydraulic retention time (HRT) of 20 days (OLR: 3.26 g VS/L-reactor d) which was the minimum HRT tolerated by the system. However, co-digestion with cow manure allowed to decrease the HRT until 15 days (OLR: 4.97 g VS/L-reactor d) with 32% higher biogas generation and efficient reactor operation. Propionic acid was the predominant VFA observed during single digestion assay failure, while acetic acid accumulation was observed in the co-digestion assay. In both single and co-digestion assays, the recovery of digesters was possible by ceasing the feeding and re-inoculation with a well-adapted inoculum. (C) 2015 Elsevier Ltd. All rights reserved.