1. Dissolved Oxygen Objective 1 The fermentation broth is thoroughly mixed to form a uniform microbial suspension, which promotes the transfer of the substrate from the fermentation broth to the bacterium and metabolites from the bacterium to the fermentation broth. 2. Relationship between growth rate and oxygen concentration: 3. Factors affecting microbial oxygen demand (BOD): 4. The effect of dissolved oxygen on fermentation: In order to properly control the dissolved oxygen concentration, it is necessary to examine the (critical dissolved oxygen concentration) and (optimum dissolved oxygen concentration) of each fermentation product and maintain the fermentation process at the optimum dissolved oxygen concentration. The optimum dissolved oxygen concentration is related to (strain characteristics) and (the route of product synthesis). Aerobic fermentation is not the higher the dissolved oxygen, the better. Properly high levels of dissolved oxygen favor bacterial growth and product synthesis; however, too high dissolved oxygen sometimes inhibits product formation. 5. The abnormal cause of the dissolved oxygen in the fermentation process may be caused by the following reasons: 6. The abnormal increase in dissolved oxygen during the fermentation process may have the following reasons: 7. Factors affecting the rate of oxygen transmission: Applicator,Medical Dressing,Waterproof Wound Dressing,Wound Care Dressings Henan Maidingkang Medical Technology Co.,Ltd , https://www.mdkmedical.com
2 Supply oxygen required for microbial growth and metabolism.
Critical oxygen concentration: The oxygen consumption rate of microorganisms is affected by the concentration of fermentation broth. Various microorganisms have a minimum requirement for dissolved oxygen concentration in the fermentation broth. This dissolved oxygen concentration is called "critical oxygen concentration".
u=um*c/(K02+c)
Physiological characteristics, medium composition, dissolved oxygen concentration and fermentation conditions of the strain
1 polluting aerobic bacteria, a large amount of dissolved oxygen is consumed, so that dissolved oxygen drops to near zero in a short time, if the bacteria itself is not strong in oxygen consumption, the dissolved oxygen change may not be obvious;
2 abnormal phenomenon of bacterial metabolism, increased aerobic requirements, so that dissolved oxygen decreased;
3 Some equipment or process control failure or change can also cause dissolved oxygen to fall, such as the stirring power consumption becomes smaller or the stirring speed becomes slower, which affects the oxygen supply capacity and reduces the dissolved oxygen. Another example is that the defoaming oil will cause a rapid decrease in dissolved oxygen due to the failure of the automatic oiler or excessive artificial addition. Other process operations that affect oxygen supply, such as stopping the stirring, stuffing the tank (closing the exhaust valve), etc. Will cause abnormal changes in dissolved oxygen.
In the absence of changes in oxygen supply conditions, a significant reduction in oxygen consumption will result in an abnormal increase in dissolved oxygen. Such as:
1. Abnormal metabolism of bacteria, decreased oxygen consumption, and increased dissolved oxygen.
2, the pollution of strong phage, the most obvious impact, before the bacteria have not been lysed, the breathing has been inhibited, dissolved oxygen is obviously increased, the bacteria completely lost breathing capacity after rupture, dissolved oxygen will rise straight.
(1) Stirring:
Stirring can make large air bubbles into tiny bubbles, increasing the contact area, and the rate of rise of small bubbles is slower than that of large bubbles, so the contact time also increases. Stirring causes the liquid to vortex, so that the bubble does not rise straight but the spiral motion rises, prolonging the movement path of the bubble, that is, increasing the contact time of the gas and liquid. Stirring causes the fermentation broth to move in a turbulent flow, thereby reducing the thickness of the liquid film around the bubble and reducing the resistance of the liquid film, thereby increasing kLa.
4 Stirring to disperse the bacteria to avoid agglomeration, which is beneficial to increase the contact area during solid-liquid transfer and make the driving force uniform.
Type and flow pattern of the agitator: straight blade agitating paddle (secondary), inclined blade paddle stage, mechanical compression type defoaming paddle (level 1), four block board
(2) Air flow rate:
Only when the Q is increased, the rotation speed N is increased correspondingly, so that the Pg is not excessively lowered, and the Kla can be most effectively improved.
(3) Air distribution tube: single tube, porous ring tube and porous branch ring tube. Most of the fermentation industry adopts single tube air distributor. The smaller the diameter of the nozzle, the smaller the diameter of the bubble, the larger the dissolved oxygen coefficient.
(4) Oxygen partial pressure:
Increasing the air pressure means increasing the tank pressure or using oxygen-containing air or pure oxygen to increase the partial pressure of oxygen.
(5) The height of the liquid column in the tank:
Ventilation efficiency increases with the increase of the height-to-diameter ratio H/D of the fermenter, and H/D=2~3 is appropriate.
(6) Tank capacity
(7) sputum properties
(8) Temperature
(9) Organic substances and surfactants
(10) Ionic strength:
The oxygen transfer coefficient K Lα of the electrolyte solution is larger than that of water, and as the electrolyte concentration increases, K Lα also increases.
How does the rate of dissolved oxygen affect the fermentation?