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Published: 1977

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A large scale laboratory system was constructed to evaluate the methane yields from various organic materials. The initial substrate for these studies was beef feed lot manure. Methane yields ranged from 0.11 to 0.259 m3 per kg volatile solids fed with a fermentation temperature of 58°C. The gas yield for a given manure was a function of retention time. However, fresh manure produced substantially more gas than manure that had been on the lots for several months. Retention times of 3.7 days and loadings of 8.76 kg per m3 per day resulted in stable operation. The results of a separate study of the effect of reactor type on methane production showed that if a balanced population of organisms can be maintained in the initial stage, a multi-stage fermentation is more efficient than a complete-mix system. However, when the system is stressed, failure of the multi-stage system is more rapid. If the objective is to maximize the conversion of solids to methane, a staged system will produce more methane per unit volume of reactor. If the objective is to maximize methane production per unit volume of reactor, a single stage complete-mix reactor operating at near the critical retention time is required.