Oxygen Transfer Rate Determination: Chemical, Physical and Biological Methods

Abstract

A proper mechanical design of the bioreactor is aimed at maintaining the environmental and nutritional conditions for optimal growth and/or product formation. Among the various environmental and nutritional factors that influence the aerobic bioprocess, oxygen is a critical parameter since it is the only nutrient that has to be provided continuously, even in batch cultures. The oxygen transfer rate (OTR) determination is essential in order to establish aeration efficiency and to quantify the effects of the operation variables on the requirement of oxygen since dissolved oxygen concentration is dependent on transport processes. Under these conditions OTR (and K L a ) is one of the key parameters involved in the design, operation, and scale‐up of bioreactors There are several approaches to determine OTR. The most common measuring methods applied can be classified depending on whether the determination is realized in the absence of microorganisms or with dead cells (chemical and physical methods), or in the presence of biomass that consumes oxygen at the same time that the measurement is carried out (biological methods). Sometimes when OTR from a physical method is determined, it must take into account the enhancement factor, E . In recent literature predictive methods have been proposed to calculate k L a and E , and thus find the value of OTR. This approach is much more reliable than those based on the use of empirical equations. In this chapter, OTR description is discussed and the main experimental methods for k L a determination are described; recent predictive methods for k L a and E are also presented.

The ejector loop reactor: Application for microbial fermentation and comparison with a stirred‐tank bioreactor

“…For OTR characterisation, values were determined at different volumetric air flow rates and power inputs according to the physical dynamic method . Accordingly, the change in dissolved oxygen (DO) was monitored after switching the feed gas from nitrogen to air.…”

“…These findings were unexpected as the fermentations in both reactors were carried out at analogous k L a conditions. It has previously been reported that the physical dynamic method yields lower k L a values than methods that measure oxygen consumption [28] due to back mixing of bubbles with elevated nitrogen content [20]. This effect may be more prominent in an ELR as fine bubbles with elevated nitrogen content can remain in the reactor longer.…”

The Measurement, Application, and Effect of Oxygen in Microbial Fermentations: Focusing on Methane and Carboxylate Production

“…When sparging is used for aeration, the oxygen transfer rate is defined as the amount of oxygen transferred from the gas into the liquid phase, where it is taken up by the microbes (oxygen uptake rate) [46]. This oxygen transport can be described by several mass transfer resistances, which decrease the final oxygen attained relative to the amount of oxygen supplied.…”

Automated algorithm to determinekLaconsidering system delay

“…Physical methods for k L a estimation are based on dissolved oxygen (DO) concentration changes with time, where dynamic gassing‐in and gassing‐out procedures are still the most commonly used . However, these approaches could become inaccurate if the delay of the measuring system is neglected .…”

“…10 Physical methods for k L a estimation are based on dissolved oxygen (DO) concentration changes with time, 2,10 where dynamic gassing-in and gassing-out procedures are still the most commonly used. 1,11,12 However, these approaches could become inaccurate if the delay of the measuring system is neglected. 2,13 -15 This can mainly be attributed to the response time , e , of the electrode's probe, whose dynamic response can be approximated by the following first-order equation: 2,11,14,16…”