The microalga Scenedesmus sp. (Chlorophyceae) was cultured in a raceway pond (RWP) placed in a greenhouse. The objective of this case study was to monitor the photosynthesis performance and selected physicochemical variables (irradiance, temperature, dissolved oxygen concentration) of microalgae cultures in situ at various depths of RWP. The data of actual photochemical yield Y(II), the electron transport rate monitored by in vivo chlorophyll fluorescence and photosynthetic oxygen production both in situ and ex situ revealed that (i) even in diluted cultures (0.6 g DW L⁻¹), the active photic layer in the culture was only about 1 cm, indicating that most of the culture was “photosynthetically” inactive; (ii) the mechanism of non-photochemical quenching may not be fast enough to respond once the cells move from the surface to the deeper layers; and (iii) even when cells were exposed to a high dissolved oxygen concentration of about 200% sat and higher, the cultures retained a relatively high Y(II) > 0.35 when monitored in situ. The presented work can be used as exemplary data to optimize the growth regime of microalgae cultures in large-scale RWPs by understanding the interplay between photosynthetic activity, culture depth and cell concentration.

En este trabajo se evaluó el efecto bioestimulante de siete extractos de microalgas aplicados en plantas de pepino a nivel de maceta pequeña. Los ensayos se realizaron en la Estación Experimental Cajamar “Las Palmerillas” con aplicaciones a nivel radicular de los diferentes extractos de microalgas proporcionados por la empresa Biorizon Biotech y dentro de las actividades del proyecto Alceres. Las microalgas se han perfilado como una alternativa sostenible a los agroquímicos tradicionales, contienen nutrientes esenciales y fitohormonas que promueven el crecimiento vegetal y mejoran la fertilidad del suelo. Los extractos se obtuvieron a partir de 3 cepas de microalgas mediante métodos mecánicos-enzimáticos y solventes biocompatibles. Los resultados mostraron que los extractos correspondientes a los tratamientos ALC1 y ALC3 aplicados en la zona radicular en plantas de pepino, tuvieron un efecto significativo en el crecimiento y desarrollo de las plantas, destacando por un mayor incremento en altura (21,7 y 22,5 cm), numero de hojas (5,4 y 5,3 hojas) y contenido de clorofila (SPAD) (22 ddt, ALC1 42,9 μmoles m-² y ALC3 37,6 μmoles m-²), en comparación con el control y el resto de los tratamientos. La materia seca vegetativa, área foliar y materia seca de raíces también fue significativamente mayor en estos tratamientos (ALC1 y ALC3), con valores superiores al resto de tratamientos.

Microalgae dewatering is a major bottleneck for the industrial deployment of microalgal biorefineries due to its high energy and water requirements. This study investigates the optimization and modeling of an industrial-scale aerated submerged ultrafiltration (UF) system for microalgae pre-concentration under real operating conditions. A submerged hollow-fibre Koch LE8 UF module (348 m², 0.03 µm) was operated directly on Chlorella sp. cultures produced in an 800 m² outdoor photobioreactor. Filtration–backwash cycles were experimentally optimized, identifying an optimal sequence of 8.33 min filtration and 1 min backwash, enabling up to 80% net water removal per cycle while maintaining fouling largely reversible under the tested conditions. Long-term trials (6–7 h) achieved stable concentration factors of 3.6–4.3 with complete biomass retention and sustained permeate flux despite increasing solids concentration. Reuse of permeate for backwashing eliminated freshwater consumption without compromising membrane performance. A dynamic resistance-in-series (RIS) model, incorporating mass balances and an empirically derived concentration-polarisation resistance, accurately reproduced permeate flux and biomass concentration dynamics (R² > 0.83) using a single fitted parameter. The validated model was further applied as a digital twin to simulate operation up to the theoretical concentration factor of 10, quantifying the associated energy and water demands. The system exhibited a low estimated specific energy consumption of 1.25 kWh·kg⁻¹ biomass and a water demand of 0.30 m³·kg⁻¹, demonstrating that aerated submerged UF is a robust, scalable, and energy-efficient solution for industrial microalgae harvesting.