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Water Science and Technology Vol 41 No 3 pp 43–50 © IWA Publishing 2000

Two-particle model of anaerobic solid state fermentation

S. Kalyuzhnyi*, A. Veeken** and B. Hamelers***

*Department of Chemical Enzymology, Chemistry Faculty, Moscow State University, 119899 Moscow, Russia
**Department of Environmental Technology, Wageningen Agriculture University, 6700 EV Wageningen, The Netherlands
***Department of Environmental Technology, Wageningen Agriculture University, 6700 EV Wageningen, The Netherlands


ABSTRACT
A structured mathematical model of anaerobic solid state fermentation (ASSF) has been developed. Since a stable ASSF requires addition of significant quantities of methanogenic seed sludge and mass-transfer limitation becomes important, the model postulates the existence of two different types of particles inside the fermenting solid mass - so-called "seed" particles with low biodegradability and high methanogenic activity and so-called "waste" particles with high biodegradability and low methanogenic activity. Any particle is assumed to be a completely mixed reactor and mass transfer of solutes between the particles is brought about by diffusion. The model includes multiple-reaction stoichiometry, microbial growth kinetics, material balances, liquid-gas interactions and liquid phase equilibrium chemistry. The theoretical model agrees on the qualitative level with existing experimental studies of ASSF. Hypothetical computer simulations are presented to illustrate the influence of biodegradabilityand mass transfer intensity on the stability of ASSF. On this basis, possible measures are proposed to prevent accumulation of volatile fatty acids inside the "seed" particles beyond their assimilative methanogenic capacity.

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