Microalgal cultivations present challenges for monitoring and process control posed by their large scale and the likelihood that they will be composed of multiple species. Cell concentration is a fundamental parameter in any cultivation but is typically performed using off-line methods that may be time-consuming, laborious, or subject to interferences. Here, an in-situ microscope has been adapted to monitoring microalgal cultivations by adding a flowthrough cell and adjusting image-processing algorithms. After installation in the bypass of a photobioreactor, the microscope enabled the continuous, automated acquisition of cell count, cell size, and cell morphology data on-line during cultivation processes over a period of 20 days, without sampling. The flow-through microscope was tested in cultivations of Chlamydomonas reinhardtii and Chlorella vulgaris. Cell concentration measurements were in agreement with off-line optical density measurements for both species. In addition, cell size and morphology distributions were obtained that revealed population shifts during the cultivation of C. vulgaris. This monitoring system thus provides a means to obtain detailed, non-invasive insights of microalgal cultivation processes.

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In the field of biotechnology, the estimation of relevant process parameters is still a challenge. Particularly with regard to efficient control of processes with high product yields, a real‐time and reliable documentation with process analytical sensors is essential. Moreover, stricter regulations of the US Food and Drug Administration for the pharmaceutical industry concerning process documentation, imposed by the Process and Analytical Technology Initiative, have increased the demand for sensors that are able to very accurately monitor and document the production process. For the monitoring and control of bioprocesses, a huge variety of sensors is used. Most systems are based on optical or electrochemical sensors. Furthermore, the market demand for disposable sensor systems increases rapidly as the application of disposable bioreactors represents the biggest technical advance in modern biotechnology. These presterilized plastic bags significantly reduce the cost/income ratio and build a meaningful concept for the design and implementation of standardized peripheral bioproduction. Simple and flexible adaptation of sensors is a bottleneck and high‐production requirements of the sensor components have to be met. This contribution gives an overview on concepts of sensor systems and image‐based techniques that allow the online estimation of relevant process parameters used in single‐use bioreactor systems.

The quality of upstream processes and their products strongly depends on the control of all influencing parameters. However, several relevant parameters are not measured in standard bioreactor systems. Near-infrared spectroscopy (NIRS) is one promising technology capable of becoming the missing link in sensor technology. This review gives an overview of the technological principles and the technological progress. A broad range of possible applications is presented, forming in its entirety a valuable toolbox for process risk mitigation. Recent applications of NIRS in upstream bioprocesses are discussed. Moreover, the review includes regulatory aspects in implementation, calibration and validation of NIRS instrumentation and models. Key termProcess trajectory: Road of process evolution that displays whether an actual batch process runs similar to good historical batches.

In situ Microscopy (ISM) is an optical analysis method that allows non-invasive monitoring of processes in real-time. In this article online monitoring of enzyme carriers and the determination of their mechanical stability are presented as new application areas for ISM. As proof of principle the fragmentation of Lewatit VP OC 1600 particles in a stirred tank reactor is tracked. The image algorithm that was used to analyze the acquired image data is described and the results of the stability study are shown. Additional application possibilities of ISM in the area of two-phase systems are demonstrated.

A new in-line method for the monitoring of enzymatic hydrolysis of cellulose is described. Using a new in situ microscope prototype, the noninvasive determination of particle size distributions was possible. For the automated analysis of the acquired images, a new processing algorithm called CelluloseAnalyzer was developed. It enabled tracking of the number of particles and moreover allowed monitoring of the proportions of particle size fractions during the course of enzymatic hydrolysis reactions. Using this technique, significant differences between hydrolysis with endoglucanases and cellulase mixtures were observed. Furthermore, the in situ microscopy results were compared with results from off-line measurements with laser diffraction spectroscopy and gel permeation chromatography.

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