Kinetics and mass-transfer phenomena in anaerobic granular sludge

The kinetic properties of acetate-degrading methanogenic granular sludge of different mean diameters were assessed at different up-flow Velocities (V- up). Using this approach, the influence of internal and external mass trans fer could be estimated. First, the apparent Monod constant (K-S) for each d ata set was calculated by means of a curve-fitting procedure. The experimen tal results revealed that variations in the V-up did not affect the apparen t K-S-value, indicating that external mass-transport resistance normally ca n be neglected. With regard to the granule size, a clear increase in K-S wa s found at increasing granule diameters. The experimental data were further used to validate a dynamic mathematical biofilm model. The biofilm model w as able to describe reaction-diffusion kinetics in anaerobic granules, usin g a single value for the effective diffusion coefficient in the granules. T his suggests that biogas formation did not influence the diffusion-rates in the granular biomass. (C) 2001 John Wiley & Sons, Inc.