Sterile feed

For a single vessel with sterile feed, this reduces to ... 

If there are no eells in the ineoming medium (e.g., a sterile feed), Equation 11-44 beeomes... 

The bioreactor involves sterile feed (C = 0) and constant volume steady state conditions imply that... 

A continuous fermenter is operated at a series of dilution rates though at constant, sterile, feed concentration, pH, aeration rate and temperature. The following data were obtained when the limiting substrate concentration was 1200 mg/1 and the working volume of the fermenter was 9.8 1. Estimate the kinetic constants Km, //, and kd as used in the modified Monod equation ... 

The term chemostat refers to a tank fermentation which is operated continuously. This bioreactor mode of operation normally involves sterile feed (Xo=0), constant volume and steady state conditions, meaning that dV/dt=0, d(VSd/ dt=0, d VX1)/dt=0. 

A continuous fermenter with sterile feed is referred to as a chemostat. For constant volume operation, the inlet volumetric flow rate is equal to that at the output. With this model chemostat start-up, resultant steady state behaviour and cell washout phenomena are easily investigated by simulation. 

Then, substituting for S using equation 5.133 so that for a CSTF at steady state utilising sterile feed, the biomass concentration is ... 

Calculate the steady-state substrate and biomass concentrations in a continuous fermenter which has an operating volume of 25 1 when the sterile feed stream contains limiting substrate at 2000 mg/1 and enters the vessel at 8 1/h. The values of Ks and ftm are 10.5 mg/l and 0.45 h " respectively, and the yield coefficient may be taken to be 0.48. 

There are certain circumstances when it may be desirable to operate a series of stirred-tanks in cascade, with the effluent of one forming the feed to the next in the chain. In the case of two such fermenters the first will behave in the manner of a simple chemostat and the performance equations of the chemostat will apply. The second tank, however, will not have a sterile feed so that some of the simplifications which led to those relationships will not be valid. 

Note that this expression does not involve the feed to the first fermenter, which may well operate under sterile feed conditions. In that case, and provided that the tanks are of equal size, the washout condition is analogous to the case of the single stirred-tank fermenter, that is ... 

In contrast to the batch fermentation based methods of determining kinetic constants, the use of a continuous fermenter (Fig. 3.71) requires more experiments to be performed, but the analysis tends to be more straightforward. In essence, the experimental method involves setting up a continuous stirred-tank fermenter to grow the micro-organisms on a sterile feed of the required substrate. The feed flowrate is adjusted to the desired value which, of course, must produce a dilution rate below the critical value for washout, and the system is allowed to reach steady state. Careful measurements of the microbial density X, the substrate concentration S, and the flowrate F are made when a steady state has been achieved, and the operation is then repeated at a series of suitable dilution rates. 

The modelling of real food webs can be an exceedingly complicated task but, to illustrate the basic technique, a situation may be defined where a continuous stirred-tank biological reactor contains two species, one the predator, the other the prey. The food for the prey is assumed to enter as the sterile feed stream to the reactor, so that the predator may only consume the prey which grows in the reactor. Material balances can be drawn up for the process in much the same way as has... 

It would be interesting to derive the equations for the cell concentration and residence time at this maximum cell productivity. The cell productivity for a steady-state CSTF with sterile feed is... 

It should be noted that actual flow rates of the streams going in and out of the filter unit do not matter as far as overall material balance is concerned. For a steady-state CSTF with cell recycling and a sterile feed,... 

The balance on total cells for a sterile feed is given by ... 

Inoculum from seed fermenters and sterile feeds are transferred to the fermenter by air pressure. Centrifugal pumps (316 S/S) are used to pump non-sterile raw materials, slurries, harvested broth, etc. The centrifugal pumps and piping should be cleaned immediately after a transfer has been completed. Occasionally a specialty pump may be required. 

Inspect closely and critically the inoculum and sterile feed transfer lines and procedures. Make sure when they are sterilized that no steam condensate accumulates in the line, but is bled off and all parts of the lines are up to sterilizing temperature. 

For the common case of sterile feed, Cq = 0, these equations give DK,... 

A material balance for the microorganism around the CSTBR in Figure 13.8 indicates that for a sterile feed (Xq = 0) the rates of various terms obey the relation... 

Consider the cascade of two chemostats shown in Eigure 113.5. This physical configuration differs from that analyzed in equations (13.2.71) to (13.2.80) in that the feed to the second chemostat consists of two streams the effluent from the first chemostat and a supplementary sterile feed stream that is characterized by a volumetric flow rate V and a concentration of the limiting substrate equal to s. Derive the equations for the concentrations of biomass and the limiting substrate in the effluent from the second reactor for the situation in which the limiting substrate is the same in both chemostats. 

Note that we cannot run the PFR with a sterile feed (i.e., with [C]o = 0) because plug flow would prevent the fluid from being inoculated by cells. Whatever cells were initially introduced into the reactor get washed out without recycle. This phenomenon of cell washout is considered next. It can be circumvented by introducing a recycle so that the input stream is inoculated before entering the reactor. 

FIGURE 33.19 Aseptic open spray drying system (1, drying chamber 2, air dispenser 3, atomizer 4, prefilter 5, filter 6, heater 7, HEPA filter 8, sterile feed filter 9, feed pump 10, cyclone collector 11, packing room). (Courtesy of A/S Niro Atomizer, Soeborg, Denmark.)... 

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