Anaerobic Digestion Of Equine Stall Waste

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The goal of this project is to establish technical parameters for anaerobic digestion of equine stall waste either alone or co-mingled with other biomass with application to on-farm or regional facilities. Anaerobic digesters operated in semi-continuous flow and batch mode were established with horse manure or horse manure plus softwood (pine chip) stall bedding as a feedstock. Initial results indicated that switching the digester feedstock from horse manure alone to horse manure mixed with softwood bedding resulted in inhibition of methane production in semi-continuous laboratory-scale digesters that had been pre-acclimated on horse manure alone. We examined batch methane production potential of horse manure alone and horse manure combined with fresh softwood bedding to examine further the potential for inhibition of methanogenesis by the presence of the bedding. Batch reactor experiments were run at softwood bedding to manure ratios of 0.05 to 4 g softwood volatile solids to horse manure volatile solids. Methane production was monitored following inoculation with a methanogenic community and incubation for up to 60 days at 35°C. Batch reactors amended with fresh (unused) softwood bedding plus horse manure showed no inhibition of methanogenesis relative to controls receiving horse manure alone at any loading. On-going work is examining the effect of aged bedding and comparing microbial community profiles between batch reactors exposed to wood and those not exposed to wood to determine whether acclimation is important in digestion of horse waste mixed with soft wood.