Potential of low-temperature anaerobic digestion to address current environmental concerns on swine production.

Environmental issues associated with swine production are becoming a major concern among the general public and are thus an important challenge for the swine industry. There is now a renewed interest in environmental biotechnologies that can minimize the impact of swine production and add value to livestock by-products. An anaerobic biotechnology called psychrophilic anaerobic digestion (PAD) in sequencing batch reactors (SBR) has been developed at Agriculture and Agri-Food Canada. This very stable biotechnology recovers usable energy, stabilizes and deodorizes manure, and increases the availability of plant nutrients. Experimental results indicated that PAD of swine manure slurry at 15 to 25 degrees C in intermittently fed SBR reduces the pollution potential of manure by removing up to 90% of the soluble chemical oxygen demand. The process performs well under intermittent feeding, once to 3 times a week, and without external mixing. Bioreactor feeding activities can thus be easily integrated into the routine manure removal procedures in the barn, with minimal interference with other farm operations and use of existing manure-handling equipment. Process stability was not affected by the presence of antibiotics in manure. The PAD process was efficient in eliminating populations of zoonotic pathogens and parasites present in raw livestock manure slurries. Psychrophilic anaerobic digestion in SBR could also be used for swine mortality disposal. The addition of swine carcasses, at loading rates representing up to 8 times the normal mortality rates on commercial farms, did not affect the stability of SBR. No operational problems were related to the formation of foam and scum. The biotechnology was successfully operated at semi-industrial and full commercial scales. Biogas production rate exceeded 0.20 L of methane per gram of total chemical oxygen demand fed to the SBR. The biogas was of excellent quality, with a methane concentration ranging from 70 to 80%. The recovery of green energy, the production of a value-added odorless fertilizer, the elimination of manure pathogens, and the proper disposal of swine mortalities will substantially reduce the carbon and environmental footprints on products of swine origin.