Fluidized-Bed Bioreactor

The fluidized-bed bioreactor (FBBT) (26) increases the capacity of existing plants. Primary effluent is passed upward through the columnar reactor filled with sand or carbon with sufficient velocity to fluidize the bed. An attached biomass develops on the bed particles. Intimate contact between the biomass and waste is provided and improved removals are reported. Oxygen is provided by a deep U-tube reactor. No biomass recirculation is required and a secondary clarifier is not necessary. 

Koran, K.M., Suidan, M.T., Khodadoust, A.R, Sorial, G.A., and Brenner, R.C. Effectiveness of an anaerobic granular activated carbon fluidized-bed bioreactor to treat soil wash fluids a proposed strategy for remediating PCP/PAH contaminated soils, Water Res., 35, 2363-2370, 2001. 

Since 1995, the sparks solvent/fuel site located in Sparks, Nevada, a remediation system consisting of MPE, air sparging, and SVE, has been operational. The treatment system consists of 29 MPE wells, an oil-water separator, and a fluidized bed bioreactor, with an influent flow rate of 23.3 L/s (370 gpm) and a retention time of 8 min. Vapors are sent through a condenser, followed by a thermal oxidizer, before its release to the atmosphere. Condensate is sent back through the oil-water separator. Performance data, available for the first 650 days of site operation, showed a reduction in MTBE concentration across the bioreactor from 2400 to 55 pg/L. No data were provided for reduction of MTBE concentrations in the aquifer.51... 

Erlenmeyer flask shaked at 135 rpm and 25°C Continuous degradation in an air-pulsed fluidized bed bioreactor... 

The 1980 s and the early 1990 s have seen the blossoming development of the biotechnology field. Three-phase fluidized bed bioreactors have become an essential element in the commercialization of processes to yield products and treat wastewater via biological mechanisms. Fluidized bed bioreactors have been applied in the areas of wastewater treatment, discussed previously, fermentation, and cell culture. The large scale application of three-phase fluidized bed or slurry bubble column fermen-tors are represented by ethanol production in a 10,000 liter fermentor (Samejima et al., 1984), penicillin production in a 200 liter fermentor (Endo et al., 1986), and the production of monoclonal antibodies in a 1,000 liter slurry bubble column bioreactor (Birch et al., 1985). Fan (1989) provides a complete review of biological applications of three-phase fluidized beds up to 1989. Part II of this chapter covers the recent developments in three-phase fluidized bed bioreactor technology. 

Table 11. Advantages and Positive Features of Three-Phase Fluidized Bed Bioreactors...

Figure 8. The relationship between biological, hydrodynamic, mixing, and transport phenomena in three-phase fluidized bed bioreactors.

There are a wide variety of three-phase fluidized bioreactor designs possible. The conventional reactor, shown in Fig. 9, is fluidized by both gas and liquid entering at the bottom of the reactor and leaving at the top and is the most common type of three-phase fluidized bed bioreactor. This reactor may be configured to operate with little axial liquid mixing or in a well-mixed mode by adding a recycle stream. The airlift reactor or draft tube fluidized bed reactor, Fig. 10, is also frequently used. In this reactor, gas is injected at the bottom of a draft tube placed in the center of the... 

Figure 9. Conventional three-phase fluidized bed bioreactor.

Table 13. System and Biological Parameters that Affect Three-Phase Fluidized Bed Bioreactor Performance...

During start-up, the microbial population distribution in the biofilm varies with time. Initial colonization of the particle may be by one or more species that alter the surface favorably for colonization by other species. For instance, in the operation of a butyrate-degrading fluidized bed bioreactor, methanogens attached to the sand particles early in the start-up process and produced a primary matrix of heteropolysaccharides that allowed attachment of other bacterial species (Sreekrishnan et al., 1991 Zellner et al., 1991 Yongming et al., 1993). This is contrary to findings in an acetate-propionate-butyrate degrading reactor, in which facultative anaerobes were found to be the initial colonizers (Lauwers et al., 1990). 

Several areas are receiving much of the research attention. Approaches that integrate product recovery with the fermentation in a three-phase fluidized bed bioreactor reflect general research trends in biochemical engineering (Yabannavar and Wang, 1991 Davison and Thompson, 1992). The successful use of three-phase biofluidization has also been demonstrated for recombinant protein systems, where it may have some benefit in improving plasmid stability (Shu and Yang, 1996). 

Gas-Liquid Mass Transfer. Gas-liquid mass transfer within the three-phase fluidized bed bioreactor is dependent on the interfacial area available for mass transfer, a the gas-liquid mass transfer coefficient, kx, and the driving force that results from the concentration difference between the bulk liquid and the bulk gas. The latter can be easily controlled by varying the inlet gas concentration. Because estimations of the interfacial area available for mass transfer depends on somewhat challenging measurements of bubble size and bubble size distribution, much of the research on increasing mass transfer rates has concentrated on increasing the overall mass transfer coefficient, kxa, though several studies look at the influence of various process conditions on the individual parameters. Typical values of kxa reported in the literature are listed in Table 19. 

Understanding the effect of reactor diameter on the volumetric mass transfer coefficient is critical to successful scale up. In studies of a three-phase fluidized bed bioreactor using soft polyurethane particles, Karamanev et al. (1992) found that for a classical fluidized bed bioreactor, kxa could either increase or decrease with a change in reactor diameter, depending on solids holdup, but for a draft tube fluidized bed bioreactor, kxa always increased with increased reactor diameter. 

The complexity of the three-phase fluidized bed bioreactor is gradually coming under control as more sophisticated models become available. The chief need is for a model that integrates the microbial kinetics with the... 

An example of the application of a unified model to the design of a three-phase, fluidized bed bioreactor is the scale down, scale up procedure. A model of the full scale reactor is developed, then is used to design... 

If substrate inhibition exists, a well-mixed bioreactor is desirable. Mixing in three-phase fluidized bed bioreactors can be increased by adding an external recycle loop, by inserting a draft tube in the reactor, or by decreasing the height to diameter ratio. 

Effluent is drawn off from a side port. Under conditions in which a conventional three-phase fluidized bed bioreactor operated in an unstable manner because of gas logging, the new bioreactor converted glucose to ethanol at a 27% higher rate. Saccharomyces cerevisiae was grown in alginate beads for this reaction. 

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