A distributed model of anaerobic digestion of solid waste was developed. Waste, volatile fatty acids (VFA), methanogenic biomass and methane concentrations were the model variables. A system of parabolic partial differential equations in the one space variable and time with slab, cylindrical or spherical symmetry of the problem was solved numerically. Diffusion of VFA inhibiting both polymer hydrolysis and acetoclastic methanogenesis was taken into account. The model showed that concentration waves of methanogenic biomass and VFA propagated over reaction space. Diffusion-based “acceleration” of methane production in the reactor was possible when intensity of VFA utilisation in the methanogenic area was sufficient for complete digestion of incoming VFA. Otherwise, methanogenic area propagation would be suppressed. Optimum conditions for the solid waste digestion can be reached at low mass transfer at the beginning and at high mass transfer when methanogenic population increases. If the initial methanogenic biomass was localised at the centre of the reactor, the total reaction time was shorter as compared to the case when the initial biomass was uniformly distributed over the reactor volume. In the last case, there was no concentration wave propagation.

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