Biogas production within the bioethanol production chain: Use of co-substrates for anaerobic digestion of sugar beet vinasse

• Co-substrates addition enhanced the anaerobic digestion of sugar beet vinasse in CSTR.
• Cow manure and lime fertiliser provided trace elements and straw improved C/N ratio.
• Biogas production in the CSTR was close to the BMP of vinasse at steady state.
• Stable CH4 yields and low VFA accumulation were detected at the maximum OLR.
• Modified Gompertz model fitted to the experimental data to describe BMP.

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.