On-line monitoring of photosynthetic activity based on pH data to assess microalgae cultivation

[EN] Microalgae performance of outdoor cultivation systems is influenced by environmental and operating dynamics. Monitoring and control systems are needed to maximise biomass productivity and nutrient recovery. The goal of this work was to corroborate that pH data could be used to monitor microalgae performance by means of data from an outdoor membrane photobioreactor (MPBR) plant. In this system, microalgae photosynthetic activity was favoured over other physical and biological processes, so that the pH data dynamics was theoretically related to the microalgae carbon uptake rate (CUR). Shortand long-term continuous operations were tested to corroborate the relationship between the first derivate of pH data dynamics (pH') and microalgae photosynthetic activity. Short-term operations showed a good correlation between gross pH' values and MPBR performance. An indicator of the maximum daily average microalgae activity was assessed by a combination of on-line pH' measurements obtained in the long-term and a microalgae growth kinetic model. Both indicators contributed to the development of advanced real-time monitoring and control systems to optimise microalgae cultivation technology. Authors would like to acknowledge the Ministry of Economy and Competitiveness (Spain) for their support in Projects CTM2014-54980C2-1-R and CTM2014-54980-C2-2-R, together with the European Regional Development Fund. The author J. Gonzalez-Camejo would also like to thank the Ministry of Education, Culture and Sport (Spain) for its support (pre-doctoral fellowship, FPU14/05082).E-supplementary data can be found in on-line version of the manuscript. Gonzalez-Camejo, J.; Robles Martínez, Á.; Seco, A.; Ferrer, J.; Ruano, MV. (2020). On-line monitoring of photosynthetic activity based on pH data to assess microalgae cultivation. Journal of Environmental Management. 276:1-8. https://doi.org/10.1016/j.jenvman.2020.111343 Abu‐Ghosh, S., Dubinsky, Z., & Iluz, D. (2020). Acclimation of thermotolerant algae to light and temperature interaction1. Journal of Phycology, 56(3), 662-670. doi:10.1111/jpy.12964 Arbib, Z., de Godos, I., Ruiz, J., & Perales, J. A. (2017). Optimization of pilot high rate algal ponds for simultaneous nutrient removal and lipids production. Science of The Total Environment, 589, 66-72. doi:10.1016/j.scitotenv.2017.02.206 Barbera, E., Sforza, E., Grandi, A., & Bertucco, A. (2020). Uncoupling solid and hydraulic retention time in photobioreactors for microalgae mass produ