Co-digestion of pig slaughterhouse waste with sewage sludge

•Meat tissue gave the highest methane yield of 976dm3/kgVS.•The biomethane potential of sewage sludge was 370dm3/kgVS.•The co-digestion of SHW with sewage sludge yielded 600dm3CH4/kgVS.•A slight inhibition of methanogenesis was observed at higher loading rate. Slaughterhouse wastes (SHW) are potentially very attractive substrates for biogas production. However, mono-digestion of these wastes creates great technological problems associated with the inhibitory effects of ammonia and fatty acids on methanogens as well as with the foaming in the digesters. In the following study, the co-digestion of slaughterhouse wastes with sewage sludge (SS) was undertaken. Batch and semi-continuous experiments were performed at 35°C with municipal sewage sludge and pig SHW composed of meat tissue, intestines, bristles and post-flotation sludge. In batch assays, meat tissue and intestinal wastes gave the highest methane productions of 976 and 826dm3/kgVS, respectively, whereas the methane yield from the sludge was only 370dm3/kgVS. The co-digestion of sewage sludge with 50% SHW (weight basis) provided the methane yield exceeding 600dm3/kgVS, which was more than twice as high as the methane production from sewage sludge alone. However, when the loading rate exceeded 4kgVS/m3d, a slight inhibition of methanogenesis was observed, without affecting the digester stability. The experiments showed that the co-digestion of sewage sludge with large amount of slaughterhouse wastes is feasible, and the enhanced methane production does not affect the digester stability.