Energy Balance for Anaerobic Digestion

Steven I. Ojalvo
John D. Keenan

DOI: 10.2190/4HJV-0BNX-Y6RQ-LJ4R


A model is developed which describes the energy balance of an anaerobic digestion system for energy recovery from organic wastes. The model is used to evaluate the energy efficiency of the process which consists of pre-treatment including primary shredding, magnetic separation, trommel screening, secondary shredding and air classification of the organic fraction; anaerobic digestion yielding methane fuel gas; gas scrubbing for removal of carbon dioxide and hydrogen sulfide; and dewatering of the waste solids. The results indicate that energy efficiencies for the entire process, excluding transportation of input and output materials, of 48 to 65 per cent are possible; and, 20 to 30 per cent are achievable with present technology. The system is relatively insensitive to front-end and back-end power requirements and to the energy needed for digester operation and maintenance. The most significant factor influencing energy conversion efficiency is the rate and degree of completion of the digestion process.

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