A model of anaerobic bacterial degradation of solid substrates in a batch digester

Abstract Batch digestion of piggery slurry shows a number of peaks in gas production rate occurring at different times during the digestion. These peaks have been equated with the degradation of free acids in the slurry and degradation of fibrous solids of different compositions and particle sizes. A computer model has been made which considers bacterial growth on acids and on fibre particles which are heterogeneous in structure but composed of cellulose, hemicellulose and lignin, and the degradation of these substrates to give biogas. The model reproduces the gas production rates and solids and acids degradations in the batch digestion and bacterial growth is within the possible limits of bacterial numbers in a digester.