Alg-Flex, an Open-Source Raspberry Pi Acquisition System for a Photobioreactor

Microalgae biomanufacturing is a promising technology that converts carbon dioxide into valuable products. However, it faces limitations in scaling, online monitoring, and controlling biological variables. In photobioreactors, light intensity influences growth and operational efficiency. This study presents Alg-flex, a low-cost, open-source monitoring and control platform based on a Raspberry Pi 4. Alg-flex integrates sensors for light intensity regulation and real-time monitoring of pH, temperature, and dissolved oxygen, enabling data visualization and logging, while providing full portability without hardware modifications. These features offer broader applicability than conventional single-variable loggers. The hardware was obtained for under $1834 USD, approximately 4% of the average cost of similar commercial units. Its performance was evaluated during the cultivation of Haematococcus lacustris in a bubble column photobioreactor. The pH and temperature sensors were validated against certified benchtop probes over the operating range used in this study, yielding median errors below 1.5%. Under the tested conditions, bioreactor cultures showed approximately two-fold higher final optical density that was significantly different than flask cultures (p = 0.0333). These results confirm that growth dynamics in small-volume microalgal cultures may differ substantially from controlled photobioreactor systems. The affordability, reliability, and multi-reactor compatibility of Alg-flex support broader biomanufacturing applications beyond microalgae cultivation.