hapensiirto

Hapensiirto, often called oxygen transfer in English, is the process by which molecular oxygen moves from the gas phase into the liquid phase and becomes dissolved oxygen. It is a fundamental concept in aerobic bioprocessing, including fermentation, cell culture, wastewater treatment, and aquaculture, where adequate dissolved oxygen (DO) is essential for the metabolism of air-loving organisms.

The rate at which oxygen becomes available in the liquid is described by the oxygen transfer rate (OTR). In steady state, OTR can be expressed as OTR = kLa (C* − C_L), where kLa is the volumetric mass transfer coefficient, C* is the oxygen saturation concentration in the liquid, and C_L is the actual dissolved oxygen concentration. The term kLa captures how efficiently oxygen is transported from the gas to the liquid and depends on factors such as agitation speed, gas flow or sparging rate, bubble size and distribution, reactor geometry, liquid viscosity, and temperature. Temperature affects both the solubility of oxygen (C*) and the mass transfer properties, typically reducing DO solubility at higher temperatures.

Measurement and control methods include the gassing-out (dynamic) method and the sulfite method to determine kLa, along with dissolved oxygen probes to monitor C_L. In process control, hapensiirto is managed to match the Oxygen Uptake Rate (OUR) of the culture, ensuring DO remains within a desired range. Scale-up and reactor design must account for changes in kLa to maintain sufficient oxygen transfer across different production scales.

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