Plug flow bioreactor

Industrial hazardous wastewater can be treated aerobically in suspended biomass stirred-tank bioreactors, plug-flow bioreactors, rotating-disc contactors, packed-bed fixed-biofilm reactors (or biofilters), fluidized bed reactors, diffused aeration tanks, airlift bioreactors, jet bioreactors, membrane bioreactors, and upflow bed reactors [28,30]. 

Fig. 3.4. Substrate, product and cell concentration versus length of plug flow bioreactor.

At unsteady-state conditions, the change of concentration with respect to time is detectable, ASIAt + 0 but for steady-state conditions the leaving substrate may be constant. For a plug flow bioreactor we can treat it like a batch system. 

We wish to compare the performance of two reactor types plug flow versus CSTR with a substrate concentration of Csf = 60g-m 3 and a biomass yield of Y = 0.1. In a plug flow bioreactor with volume of 1 m3 and volumetric flow rate of 2.5 m -li what would be the recycle ratio for maximum qx compared with corresponding results and rate models proposed for the chemostat ... 

A tubular bioreactor design with operational may lead to a CSTR, having sufficient recycle ratio for plug flow that behave like chemostat. The recirculation plug flow reactor is better than a chemostat, with maximum productivity at C, 3 g-m 3. Combination of plug flow with CSTR which behave like chemostat was obtained from the illustration minimised curve with maximum rate at CSf = 3 g-m-3. 

The bioreactor has been introduced in general terms in the previous section. In this section the basic bioreactor concepts, i.e., the batch, the fed-batch, the continuous-flow stirred-tank reactor (CSTR), the cascade of CSTRs and the plug-flow reactor, will be described. 

In the ideal plug-flow reactor (Figure 11.16) the continuous phase flows as a plug through the reactor i.e., there is no mixing or, in other words, no axial dispersion. Consequently, if a compound is consumed or produced, a concentration gradient will exist in the direction of flow. The mass balance is therefore first set up over an infinite small slice perpendicular to the direction of the flow with volume dV of the bioreactor. Assuming steady state and F =Fq=F, Equation (11.5) then is reduced to ... 

While the batch process is the dominant one in current use, researchers and companies have attempted to create continuous bioreactor systems. Lopez et al. immobilized Candida rugosa in polymethacrylamide hydrazide beads and polyurethane foam 3 with the intent to achieve the continuous production of lipase enzymes. Despite flow problems with the polyurethane foam, it showed high lipolytic activity. Biomass buildup was problematic. Feijoo et al. immobilized Phanerochaete chry-sosporium on polyurethane foam in packed bed bioreactors under near-plug flow conditions. Continuous lignin peroxidase production was accomplished, the rate of which was studied as a function of recycle ratio. 

The treatment of PAH-contaminated soil in a reactor environment is basically limited to the use of soil slurry reactors. Conversely, many different bioreactor designs exist for the treatment of water contaminated with PAHs. As reviewed by Grady (1989) and Grady Lim (1980), these include fixed film reactors, plug flow reactors, and a variety of gas-phase systems, to name a few. Given the depth and magnitude of such a topic, for the purposes of this review discussions will be limited to a generic overview of reactor applications for PAH bioremediation. 

Kaplan, L. A., and J. D. Newbold. 1995. Measurement of streamwater biodegradable dissolved organic carbon with a plug-flow bioreactor. Water Research 29 2696-2706. 

Fig. 32. Examples of plug-flow bioreactor processing, (a) Staged vessels (b) tubes with moving compartments (c) annulus around rotating cylinder. (After Moo-Young, 1986.)...

For large-scale bioreactors (21), especially those of the air lift type (22), the gas phase is best considered as being in plug flow, so that a log mean value of driving force is obtained ... 

Biodegradation complete debromination under anaerobic microbial degradation in a fixed-film plug-flow bioreactor (Rayne et al. 2003)... 

Figure 8.5 Schematic of bioreactor and two extremes used for modeling the contacting pattern, (a) Complete backmix. (b) Plug flow. [Reproduced from AnaKsis of a Continuous, Aerobic Fixed-Film Bioreactor. I. Steady-State Behavior. b Y. Park. M. E. Davis, and D. A. Wallis, Biotech. Bioeng., 26 (1984) 457, copyright 1984 Wiley-Liss, Inc., a subsidiary of John Wiley and Sons, Inc ]...

Figure 8.5.4 Corr aii-i i jvnomtaii-.e. n. . inpletely back -, xe.i, uid plug flow contacting pattenis. [Reproduced from Anal>"sis of a Continuou.s.. Aerobic Fixe Eilm Bioreactor. I. Steiidy-State Bclia ior, by P. Park. M. E. Davis, aiul D. A. Wallis, Biotet / Bioi. j. 2(t 984i 45 . c. pv 1984. Wi Liss. Inc., a. sf.- - di. -v of John Wiley...

An ideal stirred bioreactor is assumed to be well mixed so that the contents are uniform in composition at all times. The plug-flow bioreactor (PFB) is an ideal tubular-flow bioreactor without radial concentration variations. The nutrient concentration of an ideal batch bioreactor after time t will be the same as that of a steady-state PFB at the longitudinal location of the residence time. Therefore, the following analysis applies for both the ideal batch bioreactor and the steady-state PFB. 

A continuous bioreactor type plug flow reactor (PFR) with immobilized cell of Saccharomyces cerevisiae in spherical particle was used in the work to take into account the variations of concentrations at the reactor length and inside spherical particle. 

Continuous SSF processes are usually operated in plug flow mode. Such processes will require pasteurization or sterilization of the substrate as it enters the bioreactor, mixing with an inoculum, and at the outlet end of the bioreactor, continuous removal of spent substrate. Such a process was operated on a pilot scale for the production of ethanol from fodder beets by Saccharomyces cerevisiae [81,82]. The bioreactor had a screw within a 4.7 m long and 15.25 cm diameter tube. The screw was rotated intermittently to mix the substrate and move it along the tube. At the front end was a hammer-mill and a pasteurization chamber for substrate preparation and a port for inoculation. New substrate was added, inoculated, and the screw rotated at 12-h intervals, resulting in a residence time of 72 h. 

The functional equivalent of a PFBR (plug flow bioreactor) when selectivity, inhibition by product species, or other considerations dictate the desirability of striving to avoid mixing of volume elements that are characterized by different degrees of conversion. 

The various types of plug flow bioreactors were recently surveyed by Moser (1985a). They utilize surface aeration by means of a variety of rotating brushes, rotors, cone aerators, or gas or fluid jets such as are found in biological waste water treatment plants. Beyond all mechanically driven systems, reactors can also be both aerated and mixed pneumatically, or one pump can serve for both mixing and hydrodynamic stirring. 

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