Biogas production from spent rose hips (Rosa canina L.): Fraction separation, organic loading and co-digestion with N-rich microbial biomass

• Fraction separation improved the methane yield of spent rose hip for up to 49%.
• Digestion of yeast resulted in 92% methane yield and complete biodegradation.
• At low reactor loadings the activated sludge supplement initiated denitrification.
• Endogenous microbial activity was suppressed in co-digestion at 20C/1N ratio.

Complex waste streams originating from extraction processes containing residual organic solvents and increased C/N ratios have not yet been considered as feedstock for biogas production to a great extent. In this study, spent rosehip (Rosa canina L.) solid residue (64% VS, 22 MJ/kg HHV, 30C/1N) was obtained from an industrial ethanol aided extraction process, and extensively examined in an automated batch bioreactor system for biogas production. Fraction separation of the compact lignocellulosic seeds increased the available sugar and ethanol content, resulting in high biogas potential of the sieved residue (516 NL/kg VS’). In co-digestion of spent rosehip substrate with non-deactivated nitrogen rich microbial co-substrates, methanogenesis was favored (Ym>68%CH4Ym>68%CH4). In individual digestion of microbial co-substrates, this was not the case, as biogas with 28 vol.% N2 was produced from activated sludge supplement. Therefore, effective inhibition of exogenous microbiota was achieved in the presence of carbonaceous spent rose hip.