New method for evaluation of dissolved oxygen probe response forKLa determination

Adaptive control of dissolved oxygen concentration in a bioreactor

A new adaptive DO (dissolved oxygen) concentration control algorithm considering DO electrode dynamics with response time delay has been developed. A system model with two time-varying parameters was used to relate the DO concentration with two control variables: air flow rate and agitation speed. Parameters of this model were estimated on-line using a regularized constant trace recursive least-squares method. An extended Kalman filter was used to remove the effect of noises from the DO concentration measurements and thus to improve control performance. A discrete one-step ahead control scheme was adopted to determine control actions based on the parameter estimation results. Experimental results showed that the new adaptive DO concentration control algorithm performed better than other algorithms tested, a PID controller and adaptive algorithms without the DO electrode dynamics.

A New Model for the Reconstruction of Biomass History from Carbon Dioxide Emission during Batch Cultivation of Geotrichum candidum

A non-structured model has been developed to describe the CO2 emission during growth of Geotrichum candidum on a lactate + peptone-based liquid medium. From the nitrogen and carbon mass balances, it was shown that about 50% of the total CO2 released was from the metabolism of the energy supply for biosynthesis, and the remaining from that for maintenance; thus, CO2 production was considered to be partially associated with growth. The model fitted the experimental data as long as a net growth was observed (0-50 h). The coefficients for growth- and non-growth-associated CO2 production were A = 0.646 (dimensionless) and B = 0.017 h(-1), respectively. From the coefficients of the model and the CO2 history data, the biomass kinetics has been reconstructed, and the calculated biomass concentrations agree fairly well with the experimental data. From this, measurement of the CO2 evolved may be used as an indirect and non-intrusive method of monitoring fungal growth during the first 50 h of cultivation.

Evolution of a phase separated gravity independent bioreactor

The evolution of a phase-separated gravity-independent bioreactor is described. The initial prototype, a zero head-space manifold silicone membrane based reactor, maintained large diffusional resistances. Obtaining oxygen transfer rates needed to support carbon-recycling aerobic microbes is impossible if large resistances are maintained. Next generation designs (Mark I and II) mimic heat exchanger design to promote turbulence at the tubing-liquid interface, thereby reducing liquid and gas side diffusional resistances. While oxygen transfer rates increased by a factor of ten, liquid channeling prevented further increases. To overcome these problems, a Mark III reactor was developed which maintains inverted phases, i.e., media flows inside the silicone tubing, oxygen gas is applied external to the tubing. This enhances design through changes in gas side driving force concentration and liquid side turbulence levels. Combining an applied external pressure of four atmospheres with increased Reynolds numbers resulted in oxygen transfer intensities of 232 mmol O2/l/h (1000 times greater than first prototype and comparable to a conventional fermenter). A 1.0 liter Mark III reactor can potentially deliver oxygen supplies necessary to support cell cultures needed to recycle a 10 astronaut carbon load continuously.