Floating Light Ball Reactor: A Scalable and Flexible Photobioreactor Design for Microalgae Cultivation

Abstract

Bringing microalgae cultivation to industrial large-scale production needs photobioreactor designs suitable for economic scale-up to large volumes. Current designs using sunlight lack around-the-clock cultivation, are location dependent, and, when using artificial lighting, do not possess the ability for economic scale-up due to physical connection of lighting to the photobioreactor or thin structures such as tubes or plates. We present a photobioreactor design where floating light balls are used to bring light into the reactor and therefore allow for a flexible and easy scale-up in three dimensions. The physical separation of light balls and reactor housing allows for the transformation of empty containers into photobioreactors. Using a modular and flexible design with assemblies of light balls, we present the transformation of a metal cylinder and a brewery tank into floating light ball reactors for microalgae cultivation. The diatom Phaeodactylum tricornutum was successfully grown on 22-L and 234-L scale in our reactors up to 0.9 g/L dry biomass. Potential biofilm formation can be flexibly handled by quickly cleaning or replacing the light ball assemblies, while at the same time harvesting the biofilm biomass. Our concept is transferrable to all cultivation and reaction systems where light needs to be brought efficiently into a liquid.

Keywords

Algae technology - Scale-up - Photobioreactor - Floating Light Ball Reactor

Publikationsverlauf

Eingereicht: 02. September 2025

Angenommen nach Revision: 09. Oktober 2025

Artikel online veröffentlicht:
07. November 2025

• References

• 1a Xu P, Shao S, Qian J. et al. Bioresour Technol 2024; 398: 130528
• 1b Posten C, Schaub G. J Biotechnol 2009; 142 (01) 64-69
• 1c Stephens E, Ross IL, King Z. et al. Nat Biotechnol 2010; 28 (02) 126-128
• 1d Guieysse B, Plouviez M. Front Bioeng Biotechnol 2024; 12: 1359755
• 2 “Why are we still so far away from mass market” Round Table Discussion, 1st International Congress on Algae Biotechnology 2025 Lisbon, Portugal https://algaebiotechnology.pt/ (accessed 2025-08-30)
• 3 J Agric Food Chem. 1953; 1 (09) 596-597
• 4 Gilmore K, Seeberger PH. Chem Rec 2014; 14 (03) 410-418
• 5a Cho C, Nam K, Seo YH. et al. Sci Rep 2019; 9 (01) 1723
• 5b Benner P, Meier L, Pfeffer A, Krüger K, Oropeza Vargas JE, Weuster-Botz D. Bioprocess Biosyst Eng 2022; 45 (05) 791-813
• 5c Posten C. Eng Life Sci 2009; 9 (03) 165-177
• 6a de Vree JH, Bosma R, Janssen M, Barbosa MJ, Wijffels RH. Biotechnol Biofuels 2015; 8: 215
• 6b Heining M, Buchholz R. Biotechnol J 2015; 10 (08) 1131-1137
• 6c Legrand J, Artu A, Pruvost J. React Chem Eng 2021; 6 (07) 1134-1151
• 7 Kusuma P, Pattison PM, Bugbee B. Hortic Res 2020; 7: 56
• 8a Yeh Y-C, Syed T, Brinitzer G. et al. Bioresour Technol 2023; 390: 129882
• 8b Syed T, Krujatz F, Ihadjadene Y. et al. Comput Biol Med 2024; 172
• 8c Zhang F, Li Z, Chen C. et al. Adv Mater 2024; 36 (03) 2303714
• 9a Neumann U, Derwenskus F, Flaiz Flister V, Schmid-Staiger U, Hirth T, Bischoff SC. Antioxidants 2019; 8: 6
• 9b Bashan O, Bashan O, Drummey S. US Patent 11,912,966 B2 2024
• 10a Buchholz R, Heining M, Lindenberger C, Manstetten P. European Patent EP2719753B1; 2015
• 10b Murray AM, Fotidis IA, Isenschmid A, Haxthausen KRA, Angelidaki I. Algal Res 2017; 25: 244-251
• 11 Deprá MC, Dias RR, Zepka LQ, Jacob-Lopes E. Processes 2025; 13 (01) 51
• 12 Golan I. US Patent 2023051997A1 2023
• 13a Gehring T, Maurer P. European Patent EP24190886.2 filed 2024
• 13b Gehring T, Maurer P. European Patent EP24182686.6 filed 2024
• 14a Experimental section (Supporting Information (SI) for additional information)
• 14b Microalgae strains: Phaeodactylum tricornutum (SAG-1090a and SAG-1090b) were used in this work. Axenic precultures were maintained in a F/2-type medium (see SI) in 500 mL flasks on an orbital shaker at 22 °C, 100 μmol/m²/s illumination, light/dark cycle 18 h/6 h, Niello QB1000 LED with 3500 K light color. Light balls: PVC-U transparent housing, each light ball contains 6 × 50 W full-spectrum COB LEDs with 3500 K spectrum (model DOB4075 with average efficiency 2.9 J/μmol). For detailed component listing and manufacturing of the light balls, see SI. LED intensity can be varied using a frequency dimmer. Light intensity measurements were conducted using the ITC Parwise Smart Submersible Quantum (PAR) Sensor. Setup and microalgae cultivation in FLBR^®-2 (234 L): Five assemblies with a total of eleven light balls were used and arranged in a spatial arrangement as shown in Fig. 1c. Starting with a microalgal inoculum concentration of 0.2 g/L (OD₇₀₀ = 1.1) after 28 days an algal dry biomass concentration of 0.87 g/L was obtained (experiment MY-028). Light/dark cycle was L/D = 18 h/6 h. Air injection via a sterile filter (Midisart 2000 Sartorius, type 17804) at the bottom with 300 L/h provided gas exchange. A circulation pump with 7 m³/h was used for repumping algal suspension from the bottom valve to the container lid. pH was measured in the recirculation loop using InPro 3253I/SG/120 sensor (Mettler-Toledo) and neat CO₂ injection via a solenoid valve into the airflow inlet stream from a gas cylinder was controlled using Mettler-Toledo M800 PID controller to keep the pH stable at 8.0–8.2. A Huber Unichiller was used to keep the cultivation temperature at 20.0–21.5 °C, and a second minichiller (Huber Olé) was attached to the five light ball assemblies to prevent aluminium cuboid temperatures inside the light ball exceeding 50 °C (where the LEDs are attached). After four weeks of cultivation, the five assemblies were cleaned outside and after centrifugation (5 min, 5000 × g), a pellet of 245 g wet biomass of P. tricornutum was obtained (in addition to the growth in the medium; Fig. 3). Analytics: Optical density was measured at 700 nm (UviLine 9400). 100 mL samples from the cultures were centrifuged, rinsed twice (resuspending in water and centrifugation), and dried (50 °C overnight) to determine microalgal dry biomass concentration. All microalgae concentrations are given as dry biomass. See SI for further details on FLBR^®-1.