Bioethanol production generates large amounts of vinasse, which is suitable for biogas production. In this study, the anaerobic digestion of sugar beet vinasse was optimised using continuous stirred-tank reactors (CSTR) supplemented either with lime fertiliser or with 3% cow manure. In both reactors, the C/N ratio was adjusted by adding straw. The biochemical methane potential (BMP) of vinasse was 267.4 +/- 4.5 L CH4 kg VS-1. Due to the low content of macro-and micronutrients and low C/N ratio of vinasse, biogas production failed when vinasse alone was fed to the reactor. When co-substrate was added, biogas production achieved very close to the BMP of vinasse, being 235.7 +/- 32.2 L CH4 kg VS-1 from the fertiliser supplied reactor and 265.2 +/- 26.8 L CH4 kg VS-1 in manure supplied reactor at steady state. Anaerobic digestion was the most stable when cow manure was supplied to digestion of vinasse. (C) 2015 Elsevier Ltd. All rights reserved.