Establishment of a simple method to evaluate mixing times in a plastic bag photobioreactor using image processing based on freeware tools

Abstract

Objective Accurate determination of the mixing time in bioreactors is essential for the optimization of the productivity of bioprocesses. The aim of this work was to develop a simple optical method to determine the mixing time in a photobioreactor. The image processing method should be based on freeware tools, should not require programming skills, and thus could be used in education within high schools and in early stages of undergraduate programs. Results An optical method has been established to analyze images from recorded videos of mixing experiments. The steps are: 1. Extraction of a sequence of images from the video file; 2. Cropping of the pictures; 3. Background removal; and 4. Image analysis and mixing time evaluation based on quantification of pixel-to-pixel heterogeneity within a given area of interest. The novel method was generally able to track the dependency between aeration rate and mixing time within the investigated photobioreactor. In direct comparison, a pearson correlation coefficient of rho = 0.99 was obtained. Gas flow rates between 10 L h−1, and 300 L h−1 resulted from mixing times of between 48 and 14 s, respectively. This technique is applicable without programming skills and can be used in education with inexperienced user groups.

Integration of Arthrospira platensis (spirulina) into the brewing process to develop new beers with unique sensory properties

“…There is still a lack of knowledge about how to transfer the high growth rates known from lab experiments to large-scale production photobioreactors (PBR) (Khan et al, 2018). For this reason, intense research efforts have been made to improve either the understanding of the complex interaction of cells within the PBR or to improve the PBR performance itself (Enfors et al, 2001;Huang et al, 2017;Wurm and Sandmann, 2021;Sandmann et al, 2022).…”

The Colourimetric Method for Mixing Time Measurement in Single-Use and Multi-Use Bioreactors—Methodology Overview and Practical Recommendations

“…Some papers contained results from experiments involving orbitally shaken devices, i.e., shake flasks [6], orbitally-shaken single-use bioreactors [37,38,40,41] and wave-mixed single-use bioreactors agitated on an orbitally shaken [39] or a rocking platform [39,42]. A few publications contained results and observations of mixing performance inside other devices, such as a bubble column [43], a soft elastic reactor [44] and a plastic bag photobioreactor [45].…”

“…The choice of filming equipment depends primarily on its availability, cost, the desired size in relation to the experimental setup and existing inventory and expertise inside a research facility. The literature contains reports of the use of industrial solutions [6,30,33,36,40,44] or consumer-grade devices such as digital SLRs [27,28,31,57], mirrorless [45] or compact digital cameras [26,29,32,37,38] or webcams [18]. Other consumer equipment could be suitable for a colourimetric method setup, including action cameras or widely available smartphone cameras.…”

“…Additionally, the lighting should be bright enough and uniform to eliminate noise in darker areas, independent of external interference and light sources near the observed device. The literature mentions using white panels behind the vessel to uniformly diffuse [3,22] or reflect [6,10,20,23,32,45] the light emitted from sources placed next to or behind the observed vessel. Different authors also mention using LED lighting panels with a diffuser built into the enclosure [27,28,30,31,36,40,44].…”

“…The dye does not change its chemical structure during mixing. Examples of dyes that have been used in studies with the colourimetric method are methylene blue [26], Cochineal Red [32], Purple Drimarene R 2 RL [43] and Patent Blue V E131 [45].…”