In bioreactor characterization, which standard method(s) can be used to determine the oxygen absorption (transfer) rate in a liquid culture system?
-
ASodium sulfite oxidation method
-
BDynamic gassing-out technique
-
CDirect dissolved-oxygen measurement under steady state
-
DAll of these
-
ENone of these
Answer
Correct Answer: All of these
Explanation
Introduction / Context:Measuring oxygen transfer is central to aerobic fermentation design and scale-up. Engineers routinely estimate volumetric mass transfer coefficients and oxygen absorption rates using chemical and biological methods. This question reviews the common laboratory/plant techniques you should recognize.
Given Data / Assumptions:
- Well-mixed vessel; dissolved oxygen (DO) probe is available when needed.
- Air or oxygen-enriched gas is sparged; temperature and salinity controlled.
- Biological oxygen uptake may be present or purposely eliminated (chemical method).
Concept / Approach:The sodium sulfite oxidation test chemically removes oxygen with a well-known stoichiometry, letting you back-calculate transfer rate. The dynamic gassing-out method strips DO to low levels and then tracks the DO rise after re-aeration to estimate kLa and absorption rate. Under steady state with known oxygen uptake rate, direct DO balance can also yield oxygen absorption/transfer rates.
Step-by-Step Solution:
Sulfite method: dose Na2SO3 plus catalyst; measure oxygen uptake; compute transfer.Dynamic gassing-out: deoxygenate, then fit DO(t) to 1 − exp(−kLa t) to obtain kLa and rate.Direct measurement: at steady state, set transfer rate = biological uptake rate by mass balance.Verification / Alternative check:Cross-compare estimates from chemical vs. biological methods under identical hydrodynamics; values should agree within experimental error if probe response is accounted for.
Why Other Options Are Wrong:
- Saying only one method works ignores standard practice.
- “None”: contradicts decades of reactor testing methodology.
Common Pitfalls:Neglecting probe lag, temperature correction, or catalyst presence in sulfite tests; misfitting DO transients.
Final Answer:All of these.