PRODIGIO Scientific Articles

Scientific Articles about microalgae production processes:

The power of unicellular primary producers

Cermeño, Pedro ; García-Comas, Carmen; Giner, Caterina R.;  Logares, Ramiro; Marrasé, Cèlia; Massana, Ramon; Pedrós-Alió, Carlos; Sala, M. Montserrat; Simó, Rafel; Tamames, Javier; Vallina, Sergio M.


[EN] Marine phytoplankton, including cyanobacteria and microalgae, dominates primary production across two thirds of the earth’s surface, sustaining virtually all marine life and exerting a fundamental control over global climate through carbon sequestration into the deep ocean. These unicellular photoautotrophs are responsible for roughly 50% of global net primary production, which is equivalent to producing 50 gigatons of organic carbon (C) per year (about 140 million t per day). […]
[ES] El fitoplancton marino, que incluye tanto a las cianobacterias como a las microalgas, domina la producción primaria en dos tercios de la superficie de la Tierra, sustentando prácticamente toda la vida marina y ejerciendo un control fundamental sobre el clima global mediante el secuestro de carbono en las profundidades del océano. Estos productores primarios unicelulares son responsables de aproximadamente el 50% de la producción primaria neta mundial, lo que equivale a producir 50 gigatoneladas de carbono orgánico (C) al año (alrededor de 140 millones de toneladas al día). […]
[CAT] El fitoplàncton marí, que inclou tant als cianobacteris com a les microalgues, domina la producció primària en dos terços de la superfície de la Terra, sustentant pràcticament tota la vida marina i exercint un control fonamental sobre el clima global mitjançant el segrest de carboni en les profunditats de l’oceà. Aquests productors primaris unicel·lulars són responsables d’aproximadament el 50% de la producció primària neta mundial, la qual cosa equival a produir 50 gigatones de carboni orgànic (C) l’any (al voltant de 140 milions de tones al dia). […]

Use of airfoils for enhancement of photosynthesis rate of microalgae in raceways

Cristian Inostroza, Javier Dávila, Sergio Román, José M. Fernández‑Sevilla and F. Gabriel Acién.


The lack of adequate vertical mixing is one of the factors limiting the productivity of open raceway microalgae reactors. The existence of large gradients of light involves the cells being mainly adapted to local irradiance instead of average irradiance, which would allow for maximizing the light utilization efficiency, thus maximizing the biomass productivity of microalgae cultures. To overcome this problem, different alternatives have been proposed, one of the more suitable being the utilization of airfoils to improve vertical mixing. In this work, numerical and experimental studies were performed to analyse the effect of the aerodynamic airfoils patented by the University of Seville (WO2020120818A1). The goal is to improve the photosynthetic efficiency, but also a better understanding of the light regime to which the microalgae cells are exposed in these systems and how to improve it. Computational Fluid Dynamics (CFD) was used to optimize the flow generated by the airfoils. A dynamic photosynthesis model of Rubio Camacho et al. (Biotechnol Bioeng 81:459–473, 2003) was used to estimate the photosynthesis rate as a function of the light regime to which the cells are exposed, including photo-adaptation and photo-inhibition phenomena, the results confirm that the use of airfoils improves the vertical mixing and the photosynthesis rate. The photosynthetic benefits were observed 10 m downstream of the airfoils, resulting in an increase in photosynthesis rate and productivity by up to 30%. These results confirm the benefits of an increase in mixing in microalgae cultures, especially when focusing on the movement of the cells between the different illuminated zones while maintaining low energy consumption and capital expenses.

Influence of pH and dissolved oxygen control strategies on the performance of pilot-scale microalgae raceways using fertilizer or wastewater as the nutrient source

Rebecca Nordio, Emanuele Viviano, Ana Sánchez-Zurano, José González Hernández, Enrique Rodríguez-Miranda, José Luis Guzmán and Gabriel Acién.


Dissolved oxygen concentration and pH are controllable and cost-effective variables that determine the success of microalgae-related processes. The present study compares different control strategies for pH and dissolved oxygen in pilot-scale microalgae production systems. Two 80 m2 raceway reactors were used, one operated with freshwater plus fertilizer and the other with wastewater as the nutrient source. Both were in semi-continuous mode at a fixed dilution rate of 0.2 day􀀀 1. A comparison between the classical On-Off and more advanced pH control strategies, such as PI and Event-based control, was performed, focusing on biomass productivity and the influence of all the process parameters on microalgae growth; “No control” of pH was also assayed. The results show that Event-based control was the best algorithm when using freshwater plus fertilizer. In contrast, no significant differences were observed using the different control strategies when wastewater was the nutrient source. These experiments were performed through selective control strategy, prioritizing pH over dissolved oxygen; however, it was demonstrated that they did not allow to achieve satisfactory dissolved oxygen removal results, especially for the fertilizer system. After modifying the gas diffuser configuration and improving the mass transfer, independent on-off strategies have been developed, permitting effective control of both variables and increasing productivity by up to 20% in both systems. Concluding, a detailed analysis of the energy demand for each strategy implemented in terms of gas consumption and gas flow to biomass ratio is provided.

Scientific articles about anaerobic digestion processes:

Long-term assessment of the nutrient recovery capacity and biomass productivity of Scenedesmus almeriensis in raceway reactors using unprocessed urban wastewater

Rebecca Nordio, Francisco Javier Delgado, Ana Sánchez-Zurano, Jose Gonzalez Hernandez, Enrique Rodríguez-Miranda, José Luis Guzmán, Tomás Lafarga and Gabriel Acién. 


The present work aims to assess the treatment of unprocessed urban wastewater using the microalga Scenedesmus almeriensis. Two 12 m3 raceway reactors, one supplemented by wastewater and the second by chemical fertilizer, operating outdoors in a semi-continuous mode, were used for eight months. Results suggested that S. almeriensis can be produced in wastewater without affecting the photosynthetic apparatus reaching a productivity of 13 g·m−2·day−1 on average in both the systems. Furthermore, the nutrient content in terms of nitrogen, phosphorous and chemical oxygen demand of the wastewater was reduced under the European limitations during most of the period, with an average removal rate of 2.2, 0.2 and 3.0 g·m−2·day−1 respectively. Therefore, raceways demonstrated a high potential for microalgal production and successful biotreatment, proving robust and reliable. Finally, the effect of environmental conditions on biomass productivity of the clean system was evaluated in a model with high accuracy (R2 = 0.9, p = 0.0002).

Respirometric assessment of bacterial kinetics in algae-bacteria and activated sludge processes

A. Sánchez-Zurano, S. Rossi, J.M. Fernández-Sevilla, G. Acién-Fernández, E. Molina-Grima and E. Ficara. 


Algae-bacteria (AB) consortia can be exploited for effective wastewater treatment, based on photosynthetic oxygenation to reduce energy requirements for aeration. While algal kinetics have been extensively evaluated, bacterial kinetics in AB systems are still based on parameters taken from the activated sludge models, lacking an experimental validation for AB consortia. A respirometric procedure was therefore proposed, to estimate bacterial kinetics in both activated sludge and AB, under different conditions of temperature, pH, dissolved oxygen, and substrate availability. Bacterial activities were differently influenced by operational/environmental conditions, suggesting that the adoption of typical activated sludge parameters could be inadequate for AB modelling. Indeed, respirometric results show that bacteria in AB consortia were adapted to a wider range of conditions, compared to activated sludge, confirming that a dedicated calibration of bacterial kinetics is essential for effectively modelling AB systems, and respirometry was proven to be a powerful and reliable tool to this purpose.

Profiling microalgal cultures growing on municipal wastewater and fertilizer media in raceway photobioreactors

Elisa Clagnan, Giuliana D’Imporzano, Marta Dell’Orto, Ana Sanchez-Zurano, Francisco Gabriel Acién-Fernandez, Biancamaria Pietrangeli and Fabrizio Adani. 


Microalgae cultivation is proposed as an effective system for pathogens reduction and wastewater depuration, however, a full characterisation of the risks is still needed. Two raceways were inoculated with Scenedesmus, one using wastewater and the other using a fertilizer medium. Microbial community and pathogen presence were explored by next generation sequencing (NGS), commercial qPCR array and plate counts. These methods proved to be complementary for a full characterization of community structure and potential risks.

Media and sampling locations contributed to shape communities and pathogenic loads. The main pathogenic genera detected were Arcobacter and Elizabethkingia (mainly in wastewater) with an important presence of Aeromonas (all samples). A lower presence of pathogens was detected in fertilizer samples, while wastewater showed a reduction from inlet to outlet. Raceways showed potential as an effective biotreatment, with most of the retained pathogens released in the outlet and only a minor part settled in the biomass.

Rheology of microalgae concentrates and its influence on the power consumption of enzymatic hydrolysis processing

Solaima Belachqer-El Attar, Ainoa Morillas-España, José Luis Casas López, María Guadalupe Pinna-Hernández and Gabriel Acién. 


The optimization of downstream processing is a critical step in any microalgae-related process. The microalgal biomass is separated from the initial diluted cultures to form a concentrated slurry, the properties of which greatly influence the design and performance of further processing steps, such as enzymatic hydrolysis. In this work, the rheological behaviour of two microalgal concentrates produced both in freshwater (Scenedesmus almeriensis) and seawater (Nannochloropsis gaditana) were studied. Measurements were performed on the entire range of biomass concentrations, from 0.5 g/L to 264 g/L. Non-Newtonian behaviour was observed whatever the water type and biomass concentration used, especially at high biomass concentrations above 10 g/L. The rheological data were adjusted to the Power Law model, and the consistency and flow behaviour indexes were correlated with the biomass concentration. The results show that the freshwater and seawater biomasses exhibited different behaviours, with freshwater slurries being more viscous than seawater ones. The high viscosity of freshwater slurries requires increased energy consumption for mixing, with an estimated cost increase of 60% when using them under the non-Newtonian conditions considered. These findings highlight the considerable effect of algal biomass rheology on the mixing power required during microalgal biomass processing.

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