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

Abstract

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 (30gL−1 total volatile solids) at 6-d intervals for 90d, with a retention time of 30d. Keratin (<20mg) 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 6d 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.