Process capability: for which types of bioprocesses can a stirred-tank fermenter (STF) be appropriately employed under standard configurations?

Introduction / Context:
Stirred-tank fermenters are the workhorse of bioprocessing due to flexible control of mixing, mass transfer, and temperature. Properly configured, they support both oxidative and fermentative metabolisms across diverse organisms.

Given Data / Assumptions:

• Availability of impellers, baffles, spargers, and headspace control.
• Gas handling systems can deliver air/oxygen for aerobic runs or nitrogen/CO2 purges for anaerobic runs.
• Appropriate shear management for sensitive mammalian or plant cells via low-shear impellers.

Concept / Approach:
By adjusting aeration rate, oxygen transfer coefficient (kLa), agitation, and gas composition, the STF can operate in fully aerobic regimes or strictly anaerobic conditions. For shear-sensitive cultures, low-shear impellers and microcarriers enable animal/plant cell processes, while high-kLa setups suit fast-growing microbes.

Step-by-Step Solution:
1) Aerobic mode: supply air or O2-enriched gas; control DO via PID loops and agitation to meet OUR.2) Anaerobic mode: strip O2 with N2/CO2, ensure seals and feeds are O2-free, and monitor redox potential.3) Tailor impeller and baffle design to balance mixing and shear for the specific cell type.4) Therefore, STFs can be used for both aerobic and anaerobic fermentations with proper configuration.

Verification / Alternative check:
Industrial practice spans aerobic antibiotic production (e.g., Streptomyces) to anaerobic ethanol fermentations (e.g., Saccharomyces), all in stirred tanks scaled from liters to hundreds of cubic meters.

Why Other Options Are Wrong:
Option A or B alone understate the versatility of STFs.Option D is overly narrow and excludes widely successful applications.

Common Pitfalls:
Assuming a single impeller type suffices for all cells; neglecting oxygen ingress during anaerobic operations; overlooking foam control and CO2 stripping in aerobic runs.

Final Answer:
Both (a) and (b)