Feed-batch fermenter

The mass balances for a constant volume zero feed batch fermentation are as follows ... 

Activities associated with bioreactors include gas/hquid contacting, on-hne sensing of concentrations, mixing, heat transfer, foam control, and feed of nutrients or reagents such as those for pH control. The workhorse of the fermentation industry is the conventional batch fermenter shown in Fig. 24-3. Not shown are ladder rungs inside the vessel, antifoam probe, antifoam system, and sensors (pH, dissolved oxygen, temperature, and the like). Note that coils may lie between baffles and the tank wall or connect to the top to minimize openings... 

Batch fermentation means the cultivation of microorganisms, where the sterile growth medium in desired volume is inoculated with the microorganisms into the bioreactor and no additional growth medium is added during the fermentation. The product will be harvested at the end of the process. Typically, PHA s production is performed using batch fermentation because of low cost for investment and no special control. In addition, sterilization of the feed stock is easier than other fermentation processes, and operation is flexible. 

Fed-batch fermentation process is a production technique between batch and continuous fermentation. A proper medium feed rate is required to add sequentially into the fermentor during the process and the product is harvested at the end of fermentation just like a batch type. 

Fig. 6 shows a fed batch fermentation of sweet sorghum juice (SSJ) by Bacillus aryabhattai in 3 L fermentor under cultivating condition with agitation rate at 200 rpm, air rate of 1.5 1/min, at 30° C and feeding time at 18 and 24 hr during log phase of the culture. It was found that the cell could continuously produce both biomass and PHAs. Maximum cells were obtained at about 14.20 g/1 at 54 hr when PHAs content reached 4.84 g/1 after 66 hr (Tanamool et al., 2011). In addition, in Table 2, fed batch fermentation by A, latus was used for the production of PHAs (Yamane et al, 1996 Wang Lee, 1997). It could yield high productivity with the use of cheap carbon sources. 

The process developed on lab scale was transferred to pilot plant scale. The process is a fed-batch fermentation with a growth-phase (24h) on complex sugars and a production phase (48h). During production phase a linear feed is added containing various carbohydrates. 

Fermentation follows for several days subsequent to inoculation with the production-scale starter culture (Figure 5.7). During this process, biomass (i.e. cell mass) accumulates. In most cases, product accumulates intracellularly and cells are harvested when maximum biomass yields are achieved. This feed batch approach is the one normally taken during biopharmaceutical manufacture, although reactors can also be operated on a continuous basis, where fresh nutrient media is continually added and a fraction of the media/biomass continually removed and processed. During... 

Starting from an inoculum (X at t=0) and an initial quantity of limiting substrate, S at t=0, the biomass will grow, perhaps after a short lag phase, and will consume substrate. As the substrate becomes exhausted, the growth rate will slow and become zero when substrate is completely depleted. The above general balances can be applied to describe the particular case of a batch fermentation (constant volume and zero feed). Thus,... 

For fed-batch fermentation, the model equations need to include the continuous feeding of sterile substrate to the fermenter, but zero outflow. The increase in volume (total accumulation of mass) that occurs in the fermenter due to the feeding is represented by a total mass balance relationship. 

Fig. 14. Time course of baker s yeast fermentation without (curves 1) and with (E = 2.9) dispersed organic phase (curves 2) simulation of fed-batch fermenter with constant liquid feed rate using data of Table 2...

If a CSTF is considered (Fig. 5.56), which has a volume V, volumetric feed flow rate F, with influent substrate and biomass concentrations S0 and X0 respectively, then suppose that the substrate and biomass concentrations in the fermenter are 5 and X. A material balance can be established over the fermenter in the same manner as for the batch fermenter. This is ... 

As with the batch fermenter, the growth has to be initiated by the addition of an inoculum in this case it is represented by the stream at a volumetric flowrate of F, with biomass concentration X, and substrate concentration S,. This is mixed with the fresh-feed stream which has a volumetric flowrate of F0, biomass concentration X0 and substrate concentration 50 to produce the entry stream of flowrate FA, biomass concentration XA and substrate concentration SA. 

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. 

This article presents the design and implementation of a software sensor for the continuous determination of substrate concentration based on a simple model of a fed-batch fermentation process and the available signals of two other sensors—one for on-line biomass determination (7) and the other for on-line ethanol determination (8)—developed in previous works. The software sensor proposed provides a continuous signal that can be used in a control loop to manipulate the substrate feed flow in order to maintain almost constant substrate concentration and obtain an excellent level of productivity and yield during all of the process, as shown in experimental control strategy studies in previous works (9). 

Index Entries Pilot development unit scale dilute-acid hydrolysate fed-batch fermentation feed rate carbon dioxide evolution rate. 

Fig. 1. CER and feed rate during fed-batch fermentations in PDU-scale. After 2 h the CBS 8066 culture was severely inhibited and the increase in feed rate was stopped. Dilute-acid hydrolysate B was used. (A) TMB 3000 (B) CBS 8066.

Martinez et al. (1963) reported that L. brevis fermented lmol fructose to 0.67 mol mannitol and 0.33 mol lactate and 0.33 mol acetate. Soetaert et al. (1995) reported a fed batch fermentation method with automatic feeding strategy for very fast and rapid production of mannitol and D-lactic acid from fructose or glucose/fructose mixture (1 2) by using Leu. pseudomesenteroides. The maximal volumetric productivity of mannitol was 11.1 g/L-h with a final concentration of 150 g/L in 24 h and a conversion efficiency of 94%. By using a special mutant strain, quantitative conversion and a further concentration increase up to 185 g mannitol per L could be obtained. Grobben et al. (2001)... 

The composition of the fermentation medium is important to the yields of protease. Proteins of many different sources are used in commercial media. Carbohydrates are used as an energy source. The C/N ratio is important to the success of the process. Protein should be present in high concentration, and carbohydrate must not be in excess. A convenient way of obtaining this is to conduct fed-batch fermentation, feeding carbohydrate during the run and maintaining the carbohydrate concentration below 1 percent. Continuous fermentation of protease on a commercial scale is not yet known. 

M Kapadi and R Gudi. 2004. Optimal Control of Fed-batch Fermentation Involving Multiple Feeds using Differential Evolution. Process Biochemistry 39, 1709-1721. 

The functions of these laboratories usually are sterility testing of production samples, and chemical assays of raw materials for approval to use in the processes, blends or batches of raw materials before sterilization, scheduled samples of production batches, fermenter feeds, waste streams and miscellaneous sources. In many instances the analytical work for the culture laboratories will also be performed. 

A constant final concentration in the retentate loop can be maintained by bleeding out a small fraction, either out of the system or to some other location in the process. This operation is described as a batch feed and bleed and is commonly used in the processing of many high value biotechnology products such as batch fermentations to recover vitamins, enzymes and common antibiotics.The CFF system will require larger surface area since the system must be designed at the flux obtained at the final concentration factor (e.g., 20 for 95% recovery). 

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