An effective automated glucose sensor for fermentation monitoring and control

Phenol degradation by Ralstonia eutropha: colorimetric determination of 2-hydroxymuconate semialdehyde accumulation to control feed strategy in fed-batch fermentations

Phenol biodegradation by Ralstonia eutropha was modeled in different culture modes to assess phenol feeding in biotechnological depollution processes. The substrate-inhibited growth of R. eutropha was described by the Haldane equation with a Ks of 2 mg/L, a Ki of 350 mg/L and a mumax of 0.41 h(-1). Furthermore, growth in several culture modes was characterized by the appearance of a yellow color, due to production of a metabolic intermediate of the phenol catabolic pathway, 2-hydroxymuconic semialdehyde (2-hms) which was directly correlated to the growth rate and/or the phenol-degradation rate, because these two parameters are coupled (as seen by the constant growth yield of 0.68 g biomass/g phenol whatever the phenol concentration). This correlation between color appearance and metabolic activity was used to develop a control procedure for optimal phenol degradation. A mass-balance equation modeling approach combined with a filtering step using an extended Kalman filter enabled state variables of the biological system to be simulated. A PI controller, using the estimation of the phenol concentration provided by the modeling step, was then built to maintain the phenol concentration at a constant set-point of 0.1 g/L which corresponded to a constant specific growth rate of 0.3 h(-1), close to the maximal specific growth value of the strain. This monitoring strategy, validated for two fed-batch cultures, could lead, in self-cycling fermentation systems, to a productivity of more than 19 kg of phenol consumed/m(3)/d which is the highest value reported to date in the literature. This system of monitoring metabolic activity also protected the bacterial culture against toxicity problems due to the transient accumulation of phenol.

Principles and applications of biosensors for bioprocess monitoring and control

Biosensors are useful analytical devices that can be integrated with on-line process monitoring schemes. In this article, the principles and applications of these devices for bioprocess monitoring are considered. Several different types of biosensors are described, and the applications and limitations of flow injection analysis (FIA) for these applications are discussed. It is hoped that the background provided here can be useful to researchers in this area.

Development of a process-FIA system using mediator-modified enzyme electrodes

A computer-controlled process-FIA system for monitoring industrial bioprocesses was developed using mediator-modified enzyme electrodes. The single-line FIA system was modified by replacing the mixing coil with a flexible operating sample dilution unit. By this way, the analyzer offers automatic procedures for self-calibration 'real-time' dilution and recalibration based on the current analyte concentration. In regard to the dynamic range of the sensors, the FIA system is able to self-adapting to any analyte concentration of the bioprocess. The technique was tested for control of glucose during microbial fed-batch processes of gluconic acid production.