Aeration rate

Various species and many strains oiyAcetobacter are used in vinegar production (48,49). Aeration rates, optimum temperatures and nutrient requirements vary with individual strains. In general, fermentation alcohol substrates require minimal nutrient supplementation whde their addition is necessary for distilled alcohol substrates. 

Submerged culture oxidizers can also be operated on a continuous basis. Continuous monitoring of ethanol and acetic acid concentrations, temperature, and aeration rates permit control of feed and withdrawal streams. Optimum production, however, is achieved by semicontinuous operation because the composition of vinegar desired in the withdrawal stream is so low in ethanol that vigorous bacterial growth is impeded. Bacterial... 

Impeller Reynolds number and equations for mixing power for particle suspensions are in Sec. 5. Dispersion of gasses into liquids is in Sec. 14. Usually, an increase in mechanical agitation is more effective than is an increase in aeration rate for improving mass transfer. 

Fermentation biomass productivities usually range from 2 to 5 g/(l h). This represents an oxygen demand in the range of 1.5 to 4 g 0/(l h). In a 500-m fermenter, this means achievement of a volumetric oxygen transfer coefficient in the range of 250 to 400 h"f Such oxygen-transfer capabihties can be achieved with aeration rates of the order of 0.5 (volume of air at STPA ohime of broth) and... 

Bioprocess Control An industrial fermenter is a fairly sophisticated device with control of temperature, aeration rate, and perhaps pH, concentration of dissolved oxygen, or some nutrient concentration. There has been a strong trend to automated data collection and analysis. Analog control is stiU very common, but when a computer is available for on-line data collec tion, it makes sense to use it for control as well. More elaborate measurements are performed with research bioreactors, but each new electrode or assay adds more work, additional costs, and potential headaches. Most of the functional relationships in biotechnology are nonlinear, but this may not hinder control when bioprocess operate over a narrow range of conditions. Furthermore, process control is far advanced beyond the days when the main tools for designing control systems were intended for linear systems. 

Once the unit is running well, it is often assumed that the aeration system is sized properly, but changes in the catalyst physical properties and/or catalyst circulation rate may require a different purge rate. It should be noted that aeration rate is directly proportional to catalyst circulation rate. Trends of the E-cat properties can indicate changes in the particle size distribution, which may require changes in the aeration rate. Restriction orifices could be oversized, undersized, or plugged with catalyst, resulting in over-aeration, under-aeration, or no aeration. All these phenomena cause low pressure buildup and low slide valve differential. 

Like in dtric acid production relatively modest aeration rates are required. Stopping aeration for literally a minute or so will permanently arrest product formation. 

High aeration rates are required to stimulate glucose oxidase production and activation. 

In biochemical engineering processes, measurement of dissolved oxygen (DO) is essential. The production of SCP may reach a steady-state condition by keeping the DO level constant, while the viable protein is continuously harvested. The concentration of protein is proportional to oxygen uptake rate. Control of DO would lead us to achieve steady SCP production. Variation of DO may affect retention time and other process variables such as substrate and product concentrations, retention time, dilution rate and aeration rate. Microbial activities are monitored by the oxygen uptake rate from the supplied ah or oxygen. 

Table 2.2. Effect of aeration rate on baker s yeast production ...

Dj = Dtank/3 = 0.8 m for three sets of impellers Impeller speed 150 rpm assume broth viscosity is 1 cp and the specific gravity of the broth is 1.2 aeration rate is 1 vvm given ratio of gassed power to un-gassed system is 0.4 specific oxygen uptake is 0.65 mmol 02/kg cell OTR = 6 X 10 3 kg/m3. 

For the agitated and aerated vessel, the ratio of power requirements for aerated versus non-aerated systems is expressed by a dimensionless number known as the aeration rate the value is obtained from Figure 6.7. 

The inoculate was prepared in 250 ml flasks containing 100 ml of growth medium, which is inoculated with 10 ml of spore suspension. The mixture was shaken at 250 rpm and the temperature was controlled at 26 °C for 48 h. Then, 110 ml of resulting mycelia suspension is used to inoculate a 1000 ml broth in the airlift fermenter. The sterilised media are slowly pumped into the bioreactor at a flow rate of about lOOmlh-1 until 2 1 working volume is fully utilised. Aeration rates of 0.5, 1 and 2vvm (1,2 and 4 1 air/min) are used.6,7 Samples were taken at 24 hour intervals and evaluated for biomass, sugars and antibiotic concentrations. 

Dimensionless aeration rate is defined by the following equation ... 

There has to be a relation between kLa with aeration rate and agitation speed, and scale-up factor has to be determined. To eliminate the effect of viscous forces, the rheology of the media and broth for a large vessel have to be similar to that of a bench-scale vessel. For scale-up based on geometric similarity, the constant values a and b are proposed for the mass-transfer correlation in Table 13.1. 

It is well understood that mixing and mass transfer are affected by agitation and aeration rates. Typically, in an agitated vessel, the working volume is about 75% of nominal CSTR volume. 

Calculate mass transfer coefficient in a 60 m3 fermenter with a gas and liquid interfacial area of a = 0.3 m2-m 3, given pbroth = 1200kg m-3. The small reactor has working volume of 0.18m3, 1 vvm aeration rate. Oxygen transfer rate (OTR) is 0.25kmol in 3 h 3. There are two sets of impellers, and flat-blade turbine types of impeller were used, HL= 1.2/),. Find the exact specifications of a large fermenter. 

Number of blades = 8, turbine Aeration rate = 1 Will... 

BalHca and Ryu [158] correlated reductions in cell yield in Datura stramonium suspensions with the increased Reynolds stresses associated with higher aeration rates in a 1.2-1 ALR. A more recent study [159] of C. roseus suspensions cultivated in a 1.5-1 bubble column showed that the increased bubble sizes associated with both larger sparger pores and higher aeration rates caused a reduction in system performance. Here, also, it was postulated that the effects were due to increased Reynolds shear stresses in the flow field. However, it was not possible to rule out gas-stripping effects. 

KLa varies with stirring speed (N) and aeration rate (G) according to... 

Vary stirrer speed N and aeration rate G and observe the response in dissolved oxygen Cq and product concentration Cp. 

Reduce the aeration rate until the reaction becomes oxygen-limited. This can be done interactively. Maintain this and then reduce the catalyst amount by 1/2 (reduce Vm by one-half)- Does the initial rate decrease by 1/2 Is the reaction still oxygen-limited ... 

The results in Figs. 5.19 and 5.20 show the influence of stirrer speed and aeration rate. 

Ahn HK, Richard TL, Choi HL (2007) Mass and thermal balance during composting of a poultry manure - wood shavings mixture at different aeration rates. Process Biochem 42 (2) 215-223... 

Several researchers emphasized that compost is also an excellent material to use to prevent the acidification and the deterioration of soil productivity [8, 51-54]. Several factors including moisture content, temperature, aeration rate, and carbon to nitrogen ratio have direct influence on composting process, which has been reviewed in detail in the past. 

Aeration of the downcomer can also be provided with a conical distributor plate (No. 3 flow) with greatly increased solids circulation rate as shown in Fig. 8. At lower downcomer aeration, the solids circulation rate is essentially similar to that without downcomer aeration at a distributor plate location ofL = 21.7 cm. At higher downcomer aeration, however, a substantial increase in solids circulation rate is realized with the same total gas flow rate. Apparently, a minimum aeration in the downcomer is required in order to increase substantially the solids circulation rate. For polyethylene beads, this critical aeration rate is at a downcomer superficial... 

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 ... 

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