The main aim of this work was to test various organic wastes, i.e. from a livestock farm, a cattle slaughterhouse and agricultural waste streams, for its ability to produce methane under thermophilic anaerobic digestion (AD) conditions. The stability of the digestion, potential biomethane production and biomethane production rate for each waste were assessed. The highest methane yield (110.83 mL CH 4 /g VS added •day) was found in the AD of crushed animal carcasses on day 4. The experimental results were analyzed using four kinetic models and it was observed that the Cone model described the biomethane yield as well as the methane production rate of each substrate. The results from this study showed the good potential of model organic wastes to produce biomethane.

In this paper, the anaerobic co-digestion of three different organic wastes, including livestock manure, slaughterhouse waste, and agricultural by-products (ABs), was carried out to enhance the efficiency of mono-digestion of livestock manure. The characteristics of co-digestion were evaluated at different mixing ratios. The experiment was performed using the Batch test and was divided into two parts. The first experimental section (EXP. 1) was designed to evaluate the seasonal characteristics of ABs, which are the different ratios of fruits and vegetables, where the mixing ratio of spring (fruits:vegetables = 3:7) showed the highest biogas yield (0.24 m3/kg volatile solids). The second experiment (EXP. 2) was conducted by using ABs in the ratio that gave the highest biogas yield in EXP. 1 in combinations of three wastes livestock manure, slaughterhouse waste, and ABs. The highest CH4 yield was 0.84 m3/kg volatile solids (VS), which was obtained with a mixing ratio that had even amounts of the three feedstocks. In addition, the results of the second biochemical methane potential test, which assessed the digestive efficiency according to the mixing ratio of the three types of organic waste, showed that the CH4 production rate of the merged digestion was approximately 1.03–1.29 times higher than that of the mono-digestion of livestock manure. The results of our experiment were verified using the modified Gompertz model, the results of which were relatively similar to the experimental results.

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