A fermentation system designed to independently evaluate mixing and/or oxygen tension effects in microbial processes: development, application and performance.

In order to evaluate the independent effects of hydrodynamic conditions and/or oxygen tension on culture physiology and productivity, a fermentation system designed to control dissolved oxygen at constant power drawn (P/V) was developed. The system included a fully instrumented 14 l bioreactor coupled to a PC for data acquisition and control. Power drawn was measured (using a commercial torquemeter coupled to the shaft) and maintained constant by varying the agitation speed; while gas blending was used to control dissolved oxygen concentration. To validate the system, rheological-complex fermentations involving xanthan gum production and filamentous fungal cultivation (using Xanthomonas campestris and Trichoderma harzianum) were developed. In both cases, and despite the changing environmental conditions (due to increased broth viscosities and microbial respiration), both variables were controlled at the desired set points. Through such a system, a rigorous evaluation of the hydrodynamic conditions and/or oxygen tension on culture physiology and productivity is now feasible.