Currently used KLA determination methods are direct method, dynamic method and sodium sulfite oxidation method. This article focuses on the use of sodium sulfite to simulate cell oxygen consumption, combined with the steady state of continuous culture, the KLA value was determined quickly and easily.
In the presence of the catalyst cobalt or copper ion ions, sodium sulfite can be rapidly oxidized to sodium sulfate. Using this feature, sodium sulfite can be continuously injected into the reactor at a constant rate under continuous aeration and agitation of the reactor. At this time, the oxygen consumption rate can be calculated by injecting sodium sulfite.
With the continuous addition of oxygen-consuming agents, the dissolved oxygen in the reactor is consumed, and the dissolved oxygen value is lowered, thereby forming an oxygen transporting force of the liquid phase in the reactor. At the steady state of continuous culture, the dissolved oxygen concentration in the reaction solution is constant, that is, dc/dt is zero, so oxygen supply and oxygen consumption are equal at this time. Thus, after the formula is transformed, the calculation formula of KLa is obtained:
Experimental condition
Testing equipment and equipment: Bailun Biological 10L glass fermenter, dissolved oxygen electrode, peristaltic pump, overflow device, temperature control system and recording system are assembled into an experimental system. Different oxygen supply conditions are provided by adjusting the agitation speed and aeration. The 0.05 mol/l sodium sulfite solution prepared by using distilled water was separately added as an oxygen-consuming agent, and the dissolved oxygen concentration was monitored by the dissolved oxygen electrode to maintain a constant volume of the reaction liquid. Since the temperature affects the test results, the temperature is guaranteed to be uniform throughout the process.
Method of operation
In the experiment, a certain amount of 7L distilled water was added to the reactor, and then 5 ml of a 1 mol/l CuSO4 solution was added to the reactor for continuous ventilation for 15 minutes to bring the dissolved oxygen in the reaction solution to a saturated state. The corrected dissolved oxygen electrode output is 100% and is automatically recorded. The newly prepared sodium sulfite solution was added to the reactor through a peristaltic pump, and the aeration amount was adjusted by a flow meter valve, and the stirring speed was adjusted between 100 and 800 rpm. According to the difference of oxygen supply capacity, the rotation speed of the peristaltic pump is changed accordingly, so that the steady state can be achieved under each operating condition. After the dissolved oxygen concentration was constant, the C/C* value was recorded.
Method for dynamically calculating KLa
OTR is the ability or state of oxygen supply in a facility, and OUR is the level or state of oxygen uptake by cells. Therefore, OTR is equivalent to the product of KLa and C*-C. So when DO rises, it means OTR is greater than OUR, and the reaction is also true.
When the oxygen content of the exhaust gas can be detected, the mass can be saved by the air flow rate, the air oxygen content and the exhaust gas oxygen content, and the OUR can be calculated. Dc/dt can be calculated by the change in dissolved oxygen. For example, if DO is reduced from 70% to 60% within 1 hour, it can be calculated by calculating the change in oxygen concentration corresponding to 10% DO. C*-C can also be obtained by changing the oxygen concentration corresponding to 35% DO (average of 60% and 70%, 65%, and 100% difference). In this way, KLa can be calculated dynamically, then OTR can be obtained through KLa and C*-C.
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