Maximum biofilm thicknesses

FIGURE 12.16. Maximum biofilm thickness versus velocity for temperatures 37 and 42°C... 

The concentration of inhibitors will be a function of the active cells present in the system. At the end of the dynamic or exponential growth phase a plateau or maximum biofilm thickness will have been produced (i.e. and (see Fig. 

What are the theoretical maximum biofilm thicknesses for different biofilm conductivities ... 

What Are the Theoretical Maximum Biofilm Thicknesses for Different Conductivities While biofilms may grow thick enough to restrict cells at their base from receiving nutrients, for practical applications, it is often desirable to have a biofilm that is entirely active across its thickness. To determine the maximum theoretical biofilm thickness, the model is restricted to cases where the biofilm is not substrate limited and the entire biofilm is active. We define the limiting biofilm thickness to be the distance at which the Nernst-Monod term drops to below 0.01 (the point in the biofilm where the biofilm activity is restricted to just 1 % of by potential drop lim-... 

Figure 9.11 Maximum biofilm thickness as a function of conductivity, for conduction-based EET biofilms only. (Black) standard case, (gray) high-activity case.

Intraparticle Mass Transfer. One way biofilm growth alters bioreactor performance is by changing the effectiveness factor, defined as the actual substrate conversion divided by the maximum possible conversion in the volume occupied by the particle without mass transfer limitation. An optimal biofilm thickness exists for a given particle, above or below which the particle effectiveness factor and reactor productivity decrease. As the particle size increases, the maximum effectiveness factor possible decreases (Andrews and Przezdziecki, 1986). If sufficient kinetic and physical data are available, the optimal biofilm thickness for optimal effectiveness can be determined through various models for a given particle size (Andrews, 1988 Ruggeri et al., 1994), and biofilm erosion can be controlled to maintain this thickness. The determination of the effectiveness factor for various sized particles with changing biofilm thickness is well-described in the literature (Fan, 1989 Andrews, 1988)... 

Fig. 12.15 shows a remarkable increase in biofilm thickness for only 5°C temperature change. These data were obtained for Escherichia coli in an experimental apparatus with flow Reynolds number of 6.3 x 10, i.e. turbulent [Bott and Pinheiro 1977]. The optimum temperature for maximum growth for this species is around 35 - 40°C. Work by Harty [1980] using the same species (Escherichia coli) demonstrated similar effects. Fig. 12.16 also shows that as velocity is increased (i.e. increased shear at the surface) in the particular system studied, the effect of temperature becomes less. It would be expected that the effects of shear are likely to be more pronounced than the effects of temperature on growth. 

The most critical parameters for the total current from an S. oneidensis biofilm are biofilm thickness, fraction of electrons recoverable for current, biofilm density, maximum specific lactate utilization rate, and electron equivalence of lactate ... 

While the flux predicted for the deep biofilm may be larger, we have the condition that substrate would not reach the electrode. While it may be possible that cells distant from the electrode could conduct electrons to it using nanowires or mediators, we shall restrict our calculations here for the first case of a shallow biofilm where the biofilm thickness is the maximum possible based on Bq. For this case, we have the current and power densities for zero order kinetics of... 

Poulsen (1997) investigated the anoxic transformations of wastewater in biofilms originating from a biofilter and found maximum NUR values of 0.025-0.055 gN03-N nr2 h-1 at 20°C. The change from 0-order to 1/2-order kinetics was found to be about 3 gN03-N m-3. Aesoey et al. (1997) found an NUR from a 1-2 mm thick sewer biofilm to be 0.15-0.18 gN03-N m-2 h-1 at... 

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