The potential of anaerobic digestion for the treatment of poultry blood has been evaluated in a co‐digestion process. The organic fraction of municipal solid waste (OFMSW) was employed as the co‐substrate to avoid digestion inhibition by dilution of nitrogen content and improvement of biodegradability. A semi‐continuous mesophilic anaerobic digester was studied with a hydraulic retention time (HRT) of 36 days and an organic loading (OLR₁) of 1.5 kg VSS_feed m⁻³ d⁻¹. The normal operational conditions of the reactor were altered with the application of an OLR₂ of 2.0 kg VSS_feed m⁻³ d⁻¹ for a short period causing an imbalance in the process. The reduction of the OLR to initial conditions allowed the recovery of the system. The digestion process reached a final specific gas production (SGP) and a methane yield of 0.33 and 0.20 m³ kg⁻¹ VSS_feed, respectively, maintaining low total and free ammonia concentrations.

Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA) were used to gain an insight into transformations experimented by the organic matter at the end of the stabilization process. Furthermore, these analytical techniques were used for evaluating the transformations undergone by the nitrogen‐rich protein components of blood after digestion. It was proved that a reduction in volatile content and aliphatic structures of biowastes along with an increase in the degree of aromaticity occurred during the digestion process.