Kinetics and mass‐transfer phenomena in anaerobic granular sludge

Abstract

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 transfer could be estimated. First, the apparent Monod constant (K(S)) for each data set was calculated by means of a curve-fitting procedure. The experimental results revealed that variations in the V(up) did not affect the apparent K(S)-value, indicating that external mass-transport resistance normally can be neglected. With regard to the granule size, a clear increase in K(S) was found at increasing granule diameters. The experimental data were further used to validate a dynamic mathematical biofilm model. The biofilm model was able to describe reaction-diffusion kinetics in anaerobic granules, using a single value for the effective diffusion coefficient in the granules. This suggests that biogas formation did not influence the diffusion-rates in the granular biomass.

Strategies for stable anaerobic digestion of vegetable waste

“…These changes could not be compensated for in the long term by the use of chemical buffer solutions. The use of a trace element solution according to Gonzalez-Gil et al [25] allowed stable digestion at a low loading of 2 g VS L -1 day -1 but the recommended dose may have been insufficient to satisfy trace element requirements when higher loadings were applied. The formulation was also shown to be deficient in tungsten and supplementation with this element was required even at low OLR.…”

“…In the 4-liter trial the TE solution proposed by Gonzalez-Gil et al [25] was added at the start of the experiment to each digester in the proportion of 1 mL L -1 , and then weekly in the same proportion based on the volume of feedstock added. In the 1.…”

“…If the failures were simply due to rapid acidification as suggested, however, the effects should be apparent from an early stage; yet the digesters in the 4-liter trial only started to show stress after relatively stable operation for a fairly long period (approximately 3 HRT). This study used the trace element solution of Gonzalez-Gil et al [25], but it is possible that the concentrations of some of the components were not high enough to satisfy the enzyme demands at the higher OLR applied. It is also likely that there was a washout of tungsten to a critical level and supplementation of this restored the digesters to normal operation at the lower loading.…”

“…This may be because the trace element concentrations in the vegetable wastes are very low, or the availability to microorganisms is limited. The trace element solution of Gonzalez-Gil et al [25] contains EDTA as a chelating agent. This is known to have an adverse effect on metal bioavailability, which may be persistent due to its non-biodegradability under both aerobic and anaerobic conditions [38].…”

A model to describe the performance of the UASB reactor

“…transfer of substrate from the bulb liquid to the particle surface) is of minor relevance for the removal of substrate. Similarly, Gonzalez-Gil et al (2001) studied the influence of internal and external mass transfer in the Monod model and concluded that external mass transfer can normally be neglected. Consequently, Eq.…”