Sustainable Cultivation of _Galdieria phlegrea_ in an IoT-Integrated Twin-Layer Photobioreactor: System Design, Growth Dynamics, and Isotopic Perspective  
[PERSON]  
1 Dipartimento di Scienze e Tecnologie Ambientali, Biologiche e Farmaceutichte, Universita degli Studi della Campania [PERSON], Via Vivaldi, 43, 81100 Caestra, Italy; [EMAIL_ADDRESS] (S.A.); [EMAIL_ADDRESS] (C.C. ); [EMAIL_ADDRESS] (A.M.); [EMAIL_ADDRESS] (C.V.); [PERSON]] (I.G. ); carmela. environmental remediation and pioneering applications in biomining and urban mining, including the recovery of critical raw materials from electronic waste [5; 6]. The industrial-scale production of microalgae began in the early 1960s and has since gained increasing traction, with an expanding number of algal strains now regulated and commercially cultivated (Novel Food status Catalogue published and available on the website [[https://ec.europa.eu/food/food-feed-portal/screen/novel-food-catalogue/search--accessed](https://ec.europa.eu/food/food-feed-portal/screen/novel-food-catalogue/search--accessed)]([https://ec.europa.eu/food/food-feed-portal/screen/novel-food-catalogue/search--accessed](https://ec.europa.eu/food/food-feed-portal/screen/novel-food-catalogue/search--accessed)) on 28 February 2025). The most commercially widespread phyla and classes are those with the most desirable nutritional or energy profiles, particularly for food-related applications [7]. Currently, the commercial landscape is dominated by green and blue-green algae, particularly _Chorella_ spp. and _Limnospira/Arthospira_ spp. [8]. However, in recent years, the scientific community has increasingly recognised the biotechnological potential and diverse applications of extremophilic strains [9]. Among these, Cyanidiophyceae--and, in particular, the genus _Galdieria_--hold unique biotechnological interest due to their tolerance and metabolic productivity under environmental conditions that are typically inhospitable to most eukaryotes. These conditions include highly acidic pH, elevated temperatures (above 50 \({}^{\circ}\)C), and especially the presence of typically phytotoxic elements in their surroundings [10; 11]. When considered within a biorefinery framework, these extremophilic strains can be efficiently cultivated using municipal effluents as a nutrient source, offering significant advantages. Specifically, their ability to utilise nitrogen- and phosphorus-rich waste compounds reduces cultivation costs by minimising the need for synthetic culture media. At the same time, by assimilating these compounds for growth, microalgae contribute to the phytoremediation of polluted effluents [12]. Furthermore, the use of wastewater as a cultivation medium decreases the reliance on freshwater and marine water resources, which in Europe account for approximately 96% of the total water usage in this sector [8]. Despite these advantages, the cultivation of _Galdieria_ species using municipal effluents remains largely unexplored in the international literature [13]. To date, only two strains have been studied: _G. sulphuraria_ CCMEE 5587.1 and _G. phlegrea_ ACUF 784.3. In the first case, _G. sulphuraria_ was cultivated using municipal wastewater from the Las Cruces wastewater treatment plant (New Mexico, USA) in semi-continuous plastic bag type photo-bioeractors (PBRs), to develop a process suited for hot, arid regions [14]. The second study focused on _G. phlegrea_, which was cultivated in urban wastewater from the province of Salerno (Southern Italy) using laboratory-scale cultivation methods [15]. This strain was specifically selected and studied in comparison with _G. sulphuraria_ to assess its potential for growth in milder climatic conditions compared to New Mexico. Scaling up these suspended cultivation methods to industrial scale poses significant technical challenges, regardless of which microalgae species has been selected. The management of culture conditions, such as temperature, pH, nutrient availability and light exposure, is critical to maximise biomass production [16].