High amounts of organic matter and protein in slaughterhouse wastes make them a viable choice for anaerobic digestion and biogas production. The purpose of this study was to investigate potentials of biogas production from poultry slaughterhouse residues -waste and sludge- in a batch-fed anaerobic co-digestion process. In the fi rst phase of the study, laboratory-scale experiments were conducted using 1-liter reactors at 34 °C with a retention time of 50 days in order to optimize digestion parameters; i.e. inoculum-substrate ratio -ISR- and total solids -TS-. Based on these experiments, the ISR of 4 and the TS of 5% were determined as optimal settings for digestion over a retention time of 50 days. The highest biogas and methane yields in these experiments were respectively reported by 0.631 and 0.462 m 3 /kg -VSadded , achieved with 66% removal of volatile solids -VS-. The optimized parameters obtained from thefirst phase were also used for veri fi cation at a larger scale -20 liters-, wherein biogas and methane yields were found to be 0.574 and 0.402 m 3 /kg -VSadded ; respectively. Moreover, results showed that optimal anaerobic digestion of slaughterhouse wastes in 20-liter digester could lead to 63% removal of VS and 88% reduction of chemical oxygen demand -COD- over a retention period of 42 days. The fi ndings also indicated that decreasing ISR and increasing TS could bring about reduced pH as well as accu-mulation of fatty acids and ammonia, which could severely undermine yields of methanogenesis process.

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