Growth effectiveness factor

If a chemical reaction is used to generate the insoluble species, the rate of chemical reaction is another possible rate limiting step. To account for the chemical reaction rate, a growth effectiveness factor, j), is defined as [3,4,51]... 

FIGURE 6.12 Ciystal growth effectiveness factor as defined by equation (6.56). Redrawn, with permission from Ciarside [521... 

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)... 

Use of bioflocs rather than supported film particles will maximize the effectiveness factor for a given particle, but uneven growth of floes can cause severe stratification in the bed. If stratification can be overcome by methods such as the use of a tapered bed to control porosity the removal, breaking up, and recycle of biomass at the bottom of the bed or, ideally, the use of microbial strains or species that will stop growing at a desirable floe size, such as a Zymomonas mobilis strain that stops growing at one millimeter in diameter (Scott, 1983), the use of bioflocs rather than support particles can improve reactor productivity. 

At no point should the radial variation in growth rate be greater than 5% in terms of effectiveness factors,... 

The committee recommended a comparison of subtherapeutic with therapeutic use of antibiotics on the prevalence of resistant transfer factors in meat animals. Also recommended was a study comparing the enteric flora of vegetarians and meat-eaters. A third study would involve workers in abattoirs and their contacts. These studies are in progress under the direction of Dr. Edward Kass at Harvard University and investigators at the Loma Linda Medical School. The committee also recommended further research on the mechanisms of the antibiotic growth effect. The report (7) said there is little indication that sale of antibiotics, including penicillin and tetracyclines, for feed and veterinary use, "has decreased as a result of the Swann Report."... 

Lombardi B, Ove P, Reddy TV. 1985. Endogenous hepatic growth-modulating factors and effects of a choline-devoid diet and of phenobarbital on hepatocarcinogensis in the rat. Nutr Cancer 7 145-154. 

Orally administrable nonpeptide oxindole derivatives, (HI), prepared by Tokunago (4) were effective in stimulating the release of growth hormone factor. 

The effectiveness factor, 17, varies from 1.0 to 0.0 as D goes fium 0 to as shown in Figure 6.12 [52]. From this plot we can see the effectiveness factor, rj, is low for large Damkohler number corresponding to laii[e saturation ratio, S, where growth is limited by diffusion not chemical reaction. 

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