Different mixtures of animal byproducts, other slaughterhouse waste (i.e., rumen, stomach and intestinal content), food waste, and liquid manure were codigested at mesophilic conditions (37°C) at laboratory and pilot scale. Animal byproducts, including blood, represent 70–80% of the total biogas potential from waste generated during slaughter of animals. The total biogas potential from waste generated during slaughter is about 1300 MJ/cattle and about 140 MI/pig. Fed-batch digestion of pasteurized (70°C, 1h) animal byproducts resulted in a fourfold increase in biogas yield (1.14L/g of volatile solids [VS]) compared with nonpasteurized animal bypproducts (0.31L/g of VS). Mixtures with animal byproducts representing 19–38% of the total dry matter were digested in continuous-flow stirred tank reactors at laboratory and pilot scale. Stable processes at organic loading rates (OLRs) exceeding 2.5g of VS/(L·d) and hydraulic retention times (HRTs) less than 40 d could be obtained with total ammonia nitrogen concentrations (NH4−N+NH3−N) in the range of 4.0–5.0 g/L. After operating one process for more than 1.5 yr at total ammonia nitrogen concentrations >4 g/L, an increase in OLR to 5 g of VS/(L·d) and a decrease in HRT to 22 d was possible without accumulation of volatile fatty acids.
