Oxygen transfer rate (OTR) in bioreactors: under otherwise similar conditions, which change is most likely to increase OTR?

Introduction:
OTR depends on the product k_La * (C* − C). The interfacial area a is heavily influenced by bubble size and coalescence behavior. Additives that prevent bubble coalescence generally increase a, thereby improving OTR for a given gas flow and agitation level.

Given Data / Assumptions:

• Surfactant-like (detergent) molecules reduce surface tension and suppress bubble coalescence.
• Antifoams and oils often increase bubble size and reduce a.
• Temperature increases lower oxygen solubility C* in water-like media.

Concept / Approach:
Smaller, more numerous bubbles increase interfacial area and k_La. Detergent-like molecules can stabilize small bubbles, limiting coalescence and raising OTR. In contrast, many antifoams and oils promote coalescence, decreasing the interfacial area and reducing k_La. Temperature effects are mixed but typically reduce OTR due to falling C*.

Step-by-Step Solution:
Identify which additives decrease bubble size/coalescence → detergents.Recognize antifoams/oils commonly enlarge bubbles → reduced a, lower k_La.Consider temperature: C* decreases with T; net OTR may fall.Choose the option that most consistently raises OTR: detergent-like molecules.

Verification / Alternative check:
k_La measurements often rise in the presence of mild surfactants that inhibit coalescence, holding gas flow and power constant.

Why Other Options Are Wrong:

• oil is added / antifoam is added: Typically reduce k_La by promoting coalescence.
• increase in the reactor temperature: Lowers C*, often counteracting any modest k_L increase.
• reduce gas flow rate: Decreases interfacial area and OTR.

Common Pitfalls:
Assuming any additive that changes surface tension improves OTR; many antifoams do the opposite of detergents. Always confirm with k_La testing.

Final Answer:
detergent like molecules are added