Sustainable Cultivation of Galdieria phlegrea in an IoT-Integrated Twin-Layer Photobioreactor: System Design, Growth Dynamics, and Isotopic Perspective

This study showcases an attached-biomass system based on twin-layer technology for cultivating Galdieria phlegrea using municipal wastewater, equipped with a smart sensor system for the remote monitoring of operational parameters. From an industrial scale-up perspective, the system offers high scalability, with low impact and operating costs. Mathematical approximation modelling identified the optimal growth conditions across five experiments. The theoretical yield was estimated to reach 1 kgDW/m2 of biomass within two months. Integrated use of isotopic mass spectrometry and spectrophotometric methods allowed us to study the metabolic strategies implemented by the algal community during the best growth condition at different resolutions, showing an increase in the nitrogen concentration over time and a favourable affinity of the organism for nitrogen species that are commonly present in the urban effluent. SEM studies showed a clean algal biofilm (free of foreign organisms), which could guarantee usage in the high economic potential market of biorefineries.