MicrOLED-photobioreactor: Design and characterization of a milliliter-scale Flat-Panel-Airlift-photobioreactor with optical process monitoring

Small-scale cultivation systems with real-time-monitoring of suspension parameters are important for high-throughput bioprocess development. This manuscript describes the design and characterization of a new photobioreactor (PBR) approach using 3D-printing and organic light emitting diodes (OLEDs) in the design step.

The structurally complex miniaturized PBR periphery was manufactured from polyamide using the selective laser sintering technology. The MicrOLED-PBR - the first Flat-Panel-Airlift photobioreactor (FPA-PBR) with a working volume below 20mL - was equipped and validated with non-invasive optical sensors for cell- (microalgal dry weight concentration and chlorophyll fluorescence) and suspension parameters (pH, dO2 and dCO2) allowing multiparametric high-resolution physiological studies of microalgae growth at low photon flux densities.

The OLED modules used in the MicrOLED-PBR were characterized with respect to their spectral photosynthetically active radiation efficiency (35.31%), maximum photon flux density (83μmolm−2s−1) and resulting photon flux density profiles across the layer thickness of the FPA-cultivation chamber (10mm) according to Lambert-Beers law (150μmolm−2s−1 for dual-plane external illumination).

The hydrodynamic properties of the FPA-cultivation chamber, i.e. its volumetric oxygen transfer coefficient kLa (1.5–57h−1), superficial gas velocity (0.8–42mh−1), mixing time (1.5–34.5s) and gas hold-up (0.016–0.2) were comparable to those for lab- and production-scale FPA-PBRs at volumetric aeration rates of 0.5–5.0Lh−1.

The application of the MicrOLED-PBR was demonstrated for optimizing the CO2 conditions during batch-mode growth of Chlamydomonas reinhardtii 11-32b. By analyzing the suspension dynamics in real-time limitations of dissolved carbon dioxide were identified at a CO2 amount of 0.1vol% whereas 2.0vol% CO2 was identified as optimum conditions for growing C. reinhardtii 11-32b in the MicrOLED-PBR..