Psychrophilic anaerobic digestion biotechnology for swine mortality disposal

The objective of this study was to investigate the feasibility of using psychrophilic anaerobic digestion in sequencing batch reactors (PADSBRs) to co-digest grinded swine carcasses and swine manure slurry at 20 degrees C and 25 degrees C. The PADSBRs were operated on two-week and four-week treatment cycle lengths, which included the fill, react, and draw phases. Two carcass loading rates (CLRs) were tested, that is 20 and 40 g of carcass per litre of manure, which were equivalent to 4 and 8 times, respectively, the normal mortality rate on commercial farms. The PADSBR performance was compared to that of PADSBRs operated at 25 degrees C and fed manure only. The addition of swine carcass to PADSBR feed did not affect the stability of the bioreactors at both CLRs. The performance of the PADSBRs co-digesting swine carcasses was not statistically different from the control in terms of biogas production and quality. There was no accumulation of volatile fatty acids in the bioreactors at the end of the treatment cycle. The mixed-liquor pH and alkalinity remained within acceptable ranges for the anaerobic microflora. Also, there wits no operational problem caused by the formation of foam and scum in the system. (C) 2008 Elsevier Ltd. All rights reserved.