Long term performance of pilot methanogenic digester filled with seashell wastes treating slaughterhouse wastes: biogas production and environmental impact

High ammonia and organic acids contents of decomposed slaughterhouse waste (SHW) often result in the severe inhibition or even failure of the anaerobic digestion (AD). The two-stage AD system can alleviate the ammonia inhibition; however, addition of alkali is often needed to maintain the neutral condition. In this study, seashell wastes containing high percentage of calcium carbonate (CaCO3) were for the first time added in a pilot scale methanogenic digester treating chicken blood waste to retain the microorganisms and provide pH buffers for the substrate. A long-duration performance of this digester was conducted for 400 days under different organic loading rates (OLRs). The results show that methane yields of the digester were 244.8 and 224.9 mL g-1 CODadded at OLR of 0.4 and 0.6 g COD L-1 d-1, respectively, higher than the results of previous studies treating the similar feedstock. An AD system treating blood wastes of a typical poultry slaughterhouse was also proposed for which energy balance and carbon footprint analyses were conducted. The energy production of 0.35 MJ kg- 1 blood and carbon emissions reduction of 0.05 kg CO2-eq kg- 1 blood can be achieved from treating blood waste of the broiler chicken. This study reveals that using seashell wastes in an AD treating SHW can facilitate the reuse of aquaculture wastes and improve the sustainability of meat industry.