Anaerobic digestion of specified risk materials with cattle manure for biogas production

Biogas production from anaerobic digestion (AD) of specified risk materials (SRM) co-digested with cattle manure was assessed in a 3 × 2 factorial design. SRM replaced manure at 0 (control), 10% or 25% (w/w) as the substrate fed to six 2-L biodigesters maintained at 37 °C or 55 °C. Digesters were fed substrate (30 g L−1 total volatile solids) at 6-d intervals for 90 d, with a retention time of 30 d. Keratin (<20 mg) was added to each digester to model the degradation of β-sheet rich proteins. Methane production was measured daily, and effluent was collected at feeding to monitor SRM degradation using real-time PCR analysis of bovine-specific DNA fragments. Compared with control, methane production increased by 83% or 161% (P < 0.05) with 10% or 25% SRM at 37 °C, and by 45% and 87%, respectively, at 55 °C (P < 0.05). Bovine DNA degradation over 6 d was higher (P < 0.05) at 37 °C as compared to 55 °C. Dry matter degradation of keratin at 37 °C decreased with increasing SRM concentration (P < 0.05), whereas at 55 °C no difference between treatments was observed (P > 0.05). Inclusion of SRM increases the production of methane during the anaerobic digestion of manure and may offer a means of deriving economic value from the disposal of SRM.