Measurement of the biological oxygen uptake rate (OUR) is a key feature for bioprocess monitoring and characterization. Relatively recently, microscale bioreactor systems have been developed, with working volumes from the microliter to milliliter range. These microreactors generally include dissolved oxygen (DO) sensors, making them a convenient tool for process characterization of several simultaneous microbial cultures. To the best of our knowledge and despite its potential, DO monitoring in microreactors has only received partial attention and deserves a more exhaustive assessment.
In the present work, the potential of microreactors systems for OUR measurement was assessed with a Pall Micro-24 system, one of the most widespread equipment used in bioprocess laboratories. We focused on DO measurements and volumetric oxygen transfer coefficient (KLa) under an exhaustive set of varying conditions including cassette design, agitation speed, gas flow rate, liquid volume, temperature and ionic strength, within others. From a total of over 2,000 experiments it was observed that, after proper calibration, DO and KLa measurements in microreactors are similar in accuracy, precision, signal to noise ratio and response time to typical DO electrodes operated in standard fermenters. The microreactor system was also tested in a variety of microbial processes, including mixed and axenic cultures of autotrophic and heterotrophic bacteria. The results obtained confirm the potential of DO monitoring in microreactors, for simple monitoring to complex kinetic and stoichiometric characterization. It is concluded that, compared to standard fermenters, microreactor systems allow for similar OUR analysis with significant experimental time savings.