What is an oxygen transfer rate?

What is an oxygen transfer rate?

Oxygen transfer is often the rate-limiting step in the aerobic bioprocess due to the low solubility of oxygen in the medium. The possible increasing on OTR due to the oxygen consumption by the cells is taken into account through the use of the biological enhancement factor.

What is oxygen mass transfer?

At the liquid surface, there are two types of oxygen transfer: firstly, the direct transfer of oxygen to the liquid surface due to large eddies created by impeller rotation and, secondly, the oxygen transfer by the contact of projected water droplets with air, while the oxygen mass transfer inside the liquid body …

What is OTR and our?

Under conditions of constant dissolved oxygen concentration, the OUR of the microorganism equals the OTR. 4. OUR is calculated by means of an oxygen mass balance around the reactor, and since OUR = OTR, OTR is quantified as a result. An oxygen mass balance around the reactor is conceptually defined in Equation 8.12.

How can I increase my oxygen transfer?

For a successful aerobic cultivation, a good oxygen transfer is vital. It can be increased by: Creating a bigger surface of gas bubbles (kLa) by increasing gas flow and stirrer speed and by adding baffles. Creating a higher O2 concentration gradient by adding O2 to gasmix and increasing the pressure.

What is kLa value?

In biotechnological processes, the kLa coefficient indicates the efficiency of oxygen supply to microorganisms in a bioreactor. The characterization of a bioreactor with regard to its kLa value provides information about its optimization potential and thus paves the way to maximum product yield.

WHAT IS A in kLa?

kLa is a gas transfer coefficient, a measurement of the capacity of the bioreactor to transfer oxygen into the cultures. kLa is influenced by factors such as bioreactor geometry, gas flow, superficial gas velocity, impeller type and speed, and power input for mixing per unit reaction volume.

Is Dissolved oxygen?

Dissolved oxygen (DO) is the amount of oxygen that is present in water. Water bodies receive oxygen from the atmosphere and from aquatic plants. Running water, such as that of a swift moving stream, dissolves more oxygen than the still water of a pond or lake.

How is KLa calculated?

For 860 mL working volume: KLa (h-1) = 1.5803x liquid speed (cm/sec) Knowing the liquid flow rate as well as the bioreactor type (fixed-bed height, compaction rate, working volume), the liquid flow rate can be easily converted in stirring speed (RPM) using the dedicated application note (Characterization of the liquid …

Does temperature affect kLa?

Numerous investigators have performed experiments of Kla determination at different test water temperature, ranging from 0 °C to 55 °C. These data appear to support the hypothesis that Kla is proportional to the 5th power of absolute temperature for a range of temperatures close to 20 °C and higher.

What is oxygen uptake rate?

The Specific Oxygen Uptake Rate (SOUR), also known as the oxygen consumption or respiration rate, is defined as the milligram of oxygen consumed per gram of volatile suspended solids (VSS) per hour.

What is kLa used for?

kLa is a gas transfer coefficient, a measurement of the capacity of the bioreactor to transfer oxygen into the cultures. A common scaling-up strategy for aerobic bioprocess is keeping the kLa constant within the different scales.

What is kLa formula?

Is kLa constant?

Utility of kLa values The conventional scale‑up of bioprocesses is based on physicochemical and geometric similarity. kLa is kept constant for this scenario.

What happens if dissolved oxygen is too high?

Just as low dissolved oxygen can cause problems, so too can high concentrations. Supersaturated water can cause gas bubble disease in fish and invertebrates ¹². Significant death rates occur when dissolved oxygen remains above 115%-120% air saturation for a period of time.

Does pH affect dissolved oxygen?

Does pH affect a body of water’s dissolved oxygen levels? We hypothesize that the dissolved oxygen levels decrease due to increasing levels of pH, thus inhibiting aquatic life that keeps dissolved oxygen levels high.

What is a kLa value?

What does kLa depend on?

The values of kLa are affected by many factors, such as geometrical and operating characteristics of the reactor (type of impeller, the geometry of the bioreactor, the agitation speed and the air flow rate), media composition and properties, concentration and microorganism’s morphology and biocatalyst’s properties [3].

What causes low dissolved oxygen?

Causes of Low Dissolved Oxygen Low dissolved oxygen (DO) primarily results from excessive algae growth caused by phosphorus. Nitrogen is another nutrient that can contribute to algae growth. As the algae die and decompose, the process consumes dissolved oxygen.

Why is oxygen uptake important?

Maximal oxygen uptake is considered the best index of aerobic capacity and maximal cardiorespiratory function. By defining the limits of the cardiopulmonary system, it has been an invaluable measurement clinically for assessing the efficacy of drugs, exercise training, or invasive procedures.

Why is mass transfer of oxygen important?

Oxygen transfer is often the limiting factor in the aerobic bioprocess due to the low solubility of oxygen in the medium; so aeration is a critical factor in industrial aerobic fermentations [5-9].

How do you increase oxygen transfer rate?

How do you calculate oxygen transfer?

The rate of oxygen mass transfer (dC/dt, gO2 •m-3•d-1) is then multiplied by the volume (V, m3) of the aerator to yield the oxygen transfer rate (OTR, gO2•d-1 ), a key input in diffuser design.

What do you mean by NA in mass transfer?

NA is the molar mass transfer of A across the boundary (moles /(area time)), cA∞ is molar concentration of A (moles / volume) in the bulk of the system far away from the boundary (surface), and cAS is the molar concentration of A right at the boundary but still on the same side as the bulk of the system.

What are the factors affecting the oxygen transfer rate?

Key variables that impact kLa values

• Gas bubble size. When gas bubble size decreases, surface area and gas residency time increases, causing bubbles to stay in the culture longer.
• Mixing.
• Air flow rate.
• Properties of the liquid or medium.

  How is oxygen transferred from gas to liquid?

  The rate of oxygen transfer (OTR) from gas to liquid interface is a function of physicochemical properties of the cell culture medium, the geometrical parameters of the bioreactor, and presence of cells. Diagram of a gas bubble in liquid, showing how the bubble is released, solubilized, and transferred to a cell.

  How is OTR related to mass transfer of oxygen?

  As cell density increases during the exponential phase, OUR increases until OTR becomes a limiting rate, as determined by the mass transfer of oxygen into the bulk liquid. The OTR and OUR rates are correlated by the oxygen mass transfer coefficient, kLa.

  How is the transfer rate of oxygen calculated?

  The dissolved oxygen concentration, for all practical purposes, will be zero and the KLa may then be calculated from the equation: where OTR is the oxygen transfer rate.

  What’s the best way to transfer oxygen to cells?

  Several different methods are used. Most commonly the nitrogen stripping (i.e., gassing‑out) method is employed.

  The rate of oxygen transfer (OTR) from gas to liquid interface is a function of physicochemical properties of the cell culture medium, the geometrical parameters of the bioreactor, and presence of cells. Diagram of a gas bubble in liquid, showing how the bubble is released, solubilized, and transferred to a cell.

  As cell density increases during the exponential phase, OUR increases until OTR becomes a limiting rate, as determined by the mass transfer of oxygen into the bulk liquid. The OTR and OUR rates are correlated by the oxygen mass transfer coefficient, kLa.

  The dissolved oxygen concentration, for all practical purposes, will be zero and the KLa may then be calculated from the equation: where OTR is the oxygen transfer rate.

  Several different methods are used. Most commonly the nitrogen stripping (i.e., gassing‑out) method is employed.