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15 pages, 1741 KiB

Open AccessEditor’s ChoiceArticle

Comprehensive Computational Model for Coupled Fluid Flow, Mass Transfer, and Light Supply in Tubular Photobioreactors Equipped with Glass Sponges

by Albert Mink, Kira Schediwy, Clemens Posten, Hermann Nirschl, Stephan Simonis and Mathias J. Krause

Energies 2022, 15(20), 7671; https://doi.org/10.3390/en15207671 - 18 Oct 2022

Cited by 9 | Viewed by 3285

Abstract

The design and optimization of photobioreactor(s) (PBR) benefit from the development of robust and quantitatively accurate computational fluid dynamics (CFD) models, which incorporate the complex interplay of fundamental phenomena. In the present work, we propose a comprehensive computational model for tubular photobioreactors equipped [...] Read more.

The design and optimization of photobioreactor(s) (PBR) benefit from the development of robust and quantitatively accurate computational fluid dynamics (CFD) models, which incorporate the complex interplay of fundamental phenomena. In the present work, we propose a comprehensive computational model for tubular photobioreactors equipped with glass sponges. The simulation model requires a minimum of at least three submodels for hydrodynamics, light supply, and biomass kinetics, respectively. First, by modeling the hydrodynamics, the light–dark cycles can be detected and the mixing characteristics of the flow (besides the mass transport) can be analyzed. Second, the radiative transport model is deployed to predict the local light intensities according to the wavelength of the light and scattering characteristics of the culture. The third submodel implements the biomass growth kinetic by coupling the local light intensities to hydrodynamic information of the CO₂ concentration, which allows to predict the algal growth. In combination, the novel mesoscopic simulation model is applied to a tubular PBR with transparent walls and an internal sponge structure. We showcase the coupled simulation results and validate specific submodel outcomes by comparing the experiments. The overall flow velocity, light distribution, and light intensities for individual algae trajectories are extracted and discussed. Conclusively, such insights into complex hydrodynamics and homogeneous illumination are very promising for CFD-based optimization of PBR. Full article

(This article belongs to the Special Issue Conception, Modelling, Control, and Intensification of Photobioreactors Applied to the Valorization of Microalgae)

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15 pages, 5410 KiB

Open AccessArticle

Model Based Optimal Control of the Photosynthetic Growth of Microalgae in a Batch Photobioreactor

by George Adrian Ifrim, Mariana Titica, Georgiana Horincar, Alina Antache, Laurențiu Baicu, Marian Barbu and José Luis Guzmán

Energies 2022, 15(18), 6535; https://doi.org/10.3390/en15186535 - 7 Sep 2022

Cited by 6 | Viewed by 2238

Abstract

The present paper investigates the optimal control of the photosynthetic growth process in an artificial light photobioreactor operated in batch mode, the objective being to find an optimal incident light intensity for which the consumption of light energy, for any amount of newly [...] Read more.

The present paper investigates the optimal control of the photosynthetic growth process in an artificial light photobioreactor operated in batch mode, the objective being to find an optimal incident light intensity for which the consumption of light energy, for any amount of newly formed biomass, is minimal. By using a simple and reliable model for the photosynthetic growth of microalgae of microalgae, predictions can be made on the quantity of produced biomass and on the amount of light consumed, whose ratio gives the biomass yield on light energy. This variable is unimodal on the allowed range of incident light intensities and has been used as objective function. An improved objective function is proposed by using the specific growth rate and a weighing factor that allows obtaining the desired amount of biomass while the light energy consumption is optimal. A closed-loop control structure has been designed based on the developed optimization algorithm. The optimal controller has been validated in simulation, comparing different lengths of the optimization horizon and the sampling period. It was found that a bigger sampling period, for the cases where there is no online information on the biomass concentration, does not significantly affect the productivity. The optimization algorithm can be used either online or offline, being useful for various experimental setups. Full article

(This article belongs to the Special Issue Conception, Modelling, Control, and Intensification of Photobioreactors Applied to the Valorization of Microalgae)

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18 pages, 3924 KiB

Open AccessArticle

Outflow from a Biogas Plant as a Medium for Microalgae Biomass Cultivation—Pilot Scale Study and Technical Concept of a Large-Scale Installation

by Marcin Zieliński, Marcin Dębowski and Joanna Kazimierowicz

Energies 2022, 15(8), 2912; https://doi.org/10.3390/en15082912 - 15 Apr 2022

Cited by 16 | Viewed by 2823

Abstract

Microalgae-based technologies have huge potential for application in the environment sector and the bio-energy industry. However, their cost-efficiency has to be improved by drawing on design and operation data for large-scale installations. This paper presents a technical concept of an installation for large-scale [...] Read more.

Microalgae-based technologies have huge potential for application in the environment sector and the bio-energy industry. However, their cost-efficiency has to be improved by drawing on design and operation data for large-scale installations. This paper presents a technical concept of an installation for large-scale microalgae culture on digestate liquor, and the results of a pilot-scale study to test its performance. The quality of non-treated digestate has been shown to be insufficient for direct use as a growth medium due to excess suspended solids, turbidity, and organic matter content, which need to be reduced. To that end, this paper proposes a system based on mechanical separation, flotation, and pre-treatment on a biofilter. The culture medium fed into photobioreactors had the following parameters after the processing: COD—340 mgO₂/dm³, BOD₅—100 mgO₂/dm³, TN—900 mg/dm³, and TP—70 mg/dm³. The installation can produce approx. 720 kg_VS/day of microalgal biomass. A membrane unit and a thickening centrifuge (thickener) were incorporated into the design to separate and dehydrate the microalgal biomass, respectively. The total energy consumption approximated 1870 kWh/day. Full article

(This article belongs to the Special Issue Conception, Modelling, Control, and Intensification of Photobioreactors Applied to the Valorization of Microalgae)

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15 pages, 956 KiB

Open AccessArticle

Producing Energy-Rich Microalgae Biomass for Liquid Biofuels: Influence of Strain Selection and Culture Conditions

by Vladimir Heredia, Olivier Gonçalves, Luc Marchal and Jeremy Pruvost

Energies 2021, 14(5), 1246; https://doi.org/10.3390/en14051246 - 24 Feb 2021

Cited by 10 | Viewed by 2692

Abstract

Energy-storage metabolites such as neutral lipids and carbohydrates are valuable compounds for liquid biofuel production. The aim of this work is to elucidate the main biological responses of two algae species known for their effective energy-rich compound accumulation in nitrogen limitation and day–night [...] Read more.

Energy-storage metabolites such as neutral lipids and carbohydrates are valuable compounds for liquid biofuel production. The aim of this work is to elucidate the main biological responses of two algae species known for their effective energy-rich compound accumulation in nitrogen limitation and day–night cycles: Nannochloropsis gaditana, a seawater species, and Parachlorella kessleri, a freshwater species. Lipid and carbohydrate production are investigated, as well as cell resistance to mechanical disruption for energy-rich compound release. Nitrogen-depleted N. gaditana showed only a low consumption of energy-storage molecules with a non-significant preference for neutral lipids (TAG) and carbohydrates in day–night cycles. However, it did accumulate significantly fewer carbohydrates than P. kessleri. Following this, the highest levels of productivity for N. gaditana in chemostat cultures at four levels of nitrogen limitation were found to be 3.4 and 2.2 ×

10^{- 3}

kg/m²·d for carbohydrates and TAG, respectively, at 56%

_{N O_{3}}

limitation. The cell disruption rate of N. gaditana decreased along with nitrogen limitation, from 75% (at 200%

_{N O_{3}}

) to 17% (at 13%

_{N O_{3}}

). In the context of potentially recoverable energy for biofuels, P. kessleri showed good potential for biodiesel and high potential for bioethanol; by contrast, N. gaditana was found to be more efficient for biodiesel production only. Full article

(This article belongs to the Special Issue Conception, Modelling, Control, and Intensification of Photobioreactors Applied to the Valorization of Microalgae)

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14 pages, 4084 KiB

Open AccessArticle

Modelling and pH Control in Raceway and Thin-Layer Photobioreactors for Wastewater Treatment

by María José Rodríguez-Torres, Ainoa Morillas-España, José Luis Guzmán and Francisco Gabriel Acién

Energies 2021, 14(4), 1099; https://doi.org/10.3390/en14041099 - 19 Feb 2021

Cited by 15 | Viewed by 2701

Abstract

One of the most critical variables in microalgae-related processes is the pH; it directly determines the overall performance of the production system especially when coupling with wastewater treatment. In microalgae-related wastewater treatment processes, the adequacy of pH has a large impact on the [...] Read more.

One of the most critical variables in microalgae-related processes is the pH; it directly determines the overall performance of the production system especially when coupling with wastewater treatment. In microalgae-related wastewater treatment processes, the adequacy of pH has a large impact on the microalgae/bacteria consortium already developing on these systems. For cost-saving reasons, the pH is usually controlled by classical On/Off control algorithms during the daytime period, typically with the dynamics of the system and disturbances not being considered in the design of the control system. This paper presents the modelling and pH control in open photobioreactors, both raceway and thin-layer, using advanced controllers. In both types of photobioreactors, a classic control was implemented and compared with a Proportional–Integral (PI) control, also the operation during only the daylight period and complete daily time was evaluated. Thus, three major variables already studied include (i) the type of reactors (thin-layers and raceways), (ii) the type of control algorithm (On/Off and PI), and (iii) the control period (during the daytime and throughout the daytime and nighttime). Results show that the pH was adequately controlled in both photobioreactors, although each type requires different control algorithms, the pH control being largely improved when using PI controllers, with the controllers allowing us to reduce the total costs of the process with the reduction of CO₂ injections. Moreover, the control during the complete daily cycle (including night) not only not increases the amount of CO₂ to be injected, otherwise reducing it, but also improves the overall performance of the production process. Optimal pH control systems here developed are highly useful to develop robust large-scale microalgae-related wastewater treatment processes. Full article

(This article belongs to the Special Issue Conception, Modelling, Control, and Intensification of Photobioreactors Applied to the Valorization of Microalgae)

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20 pages, 3200 KiB

Open AccessArticle

Continuous Production of Lipids with Microchloropsis salina in Open Thin-Layer Cascade Photobioreactors on a Pilot Scale

by Torben Schädler, Anna-Lena Thurn, Thomas Brück and Dirk Weuster-Botz

Energies 2021, 14(2), 500; https://doi.org/10.3390/en14020500 - 18 Jan 2021

Cited by 14 | Viewed by 3297

Abstract

Studies on microalgal lipid production as a sustainable feedstock for biofuels and chemicals are scarce, particularly those on applying open thin-layer cascade (TLC) photobioreactors under dynamic diurnal conditions. Continuous lipid production with Microchloropsis salina was studied in scalable TLC photobioreactors at 50 m [...] Read more.

Studies on microalgal lipid production as a sustainable feedstock for biofuels and chemicals are scarce, particularly those on applying open thin-layer cascade (TLC) photobioreactors under dynamic diurnal conditions. Continuous lipid production with Microchloropsis salina was studied in scalable TLC photobioreactors at 50 m² pilot scale, applying a physically simulated Mediterranean summer climate. A cascade of two serially connected TLC reactors was applied, promoting biomass growth under nutrient-replete conditions in the first reactor, while inducing the accumulation of lipids via nitrogen limitation in the second reactor. Up to 4.1 g L⁻¹ of lipids were continuously produced at productivities of up to 0.27 g L⁻¹ d⁻¹ (1.8 g m² d⁻¹) at a mean hydraulic residence time of 2.5 d in the first reactor and 20 d in the second reactor. Coupling mass balances with the kinetics of microalgal growth and lipid formation enabled the simulation of phototrophic process performances of M. salina in TLC reactors in batch and continuous operation at the climate conditions studied. This study demonstrates the scalability of continuous microalgal lipid production in TLC reactors with M. salina and provides a TLC reactor model for the realistic simulation of microalgae lipid production processes after re-identification of the model parameters if other microalgae and/or varying climate conditions are applied. Full article

(This article belongs to the Special Issue Conception, Modelling, Control, and Intensification of Photobioreactors Applied to the Valorization of Microalgae)

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23 pages, 4350 KiB

Open AccessArticle

Impact of Dropwise Condensation on the Biomass Production Rate in Covered Raceway Ponds

by Jack Hoeniges, Keyong Zhu, Jeremy Pruvost, Jack Legrand, El-khider Si-Ahmed and Laurent Pilon

Energies 2021, 14(2), 268; https://doi.org/10.3390/en14020268 - 6 Jan 2021

Cited by 6 | Viewed by 2342

Abstract

This study investigates the effect of condensed water droplets on the areal biomass productivity of outdoor culture systems with a free surface, protected by a transparent window or cover to prevent contamination and to control the growth conditions. Under solar radiation, evaporation from [...] Read more.

This study investigates the effect of condensed water droplets on the areal biomass productivity of outdoor culture systems with a free surface, protected by a transparent window or cover to prevent contamination and to control the growth conditions. Under solar radiation, evaporation from the culture causes droplets to condense on the interior surface of the cover. To quantify the effect of droplets on the system’s performance, the bidirectional transmittance of a droplet-covered window was predicted using the Monte Carlo ray-tracing method. It was combined with a growth kinetics model of Chlorella vulgaris to predict the temporal evolution of the biomass concentration on 21 June and 23 September in Los Angeles, CA. A droplet contact angle of 30

^{\circ}

or 90

^{\circ}

and a surface area coverage of 50% or 90% were considered. Light scattering by the condensed droplets changed the direction of the incident sunlight while reducing the amount of light reaching the culture by up to 37%. The combined effect decreased the daily areal biomass productivity with increasing droplet contact angle and surface area coverage by as much as 18%. Furthermore, the areal biomass productivity of the system was found to scale with the ratio

X_{0} / a

of the initial biomass concentration

X_{0}

and the specific illuminated area a, as previously established for different photobioreactor geometries, but even in the presence of droplets. Finally, for a given day of the year, the optical thickness of the culture that yielded the maximum productivity was independent of the window condition. Thus, the design and operation of such a system should focus on maintaining a small droplet contact angle and surface area coverage and an optimum optical thickness to maximize productivity. Full article

(This article belongs to the Special Issue Conception, Modelling, Control, and Intensification of Photobioreactors Applied to the Valorization of Microalgae)

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Review

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63 pages, 5687 KiB

Open AccessReview

Modeling and Simulation of Photobioreactors with Computational Fluid Dynamics—A Comprehensive Review

by Giovanni Luzi and Christopher McHardy

Energies 2022, 15(11), 3966; https://doi.org/10.3390/en15113966 - 27 May 2022

Cited by 23 | Viewed by 5698

Abstract

Computational Fluid Dynamics (CFD) have been frequently applied to model the growth conditions in photobioreactors, which are affected in a complex way by multiple, interacting physical processes. We review common photobioreactor types and discuss the processes occurring therein as well as how these [...] Read more.

Computational Fluid Dynamics (CFD) have been frequently applied to model the growth conditions in photobioreactors, which are affected in a complex way by multiple, interacting physical processes. We review common photobioreactor types and discuss the processes occurring therein as well as how these processes have been considered in previous CFD models. The analysis reveals that CFD models of photobioreactors do often not consider state-of-the-art modeling approaches. As a comprehensive photobioreactor model consists of several sub-models, we review the most relevant models for the simulation of fluid flows, light propagation, heat and mass transfer and growth kinetics as well as state-of-the-art models for turbulence and interphase forces, revealing their strength and deficiencies. In addition, we review the population balance equation, breakage and coalescence models and discretization methods since the predicted bubble size distribution critically depends on them. This comprehensive overview of the available models provides a unique toolbox for generating CFD models of photobioreactors. Directions future research should take are also discussed, mainly consisting of an extensive experimental validation of the single models for specific photobioreactor geometries, as well as more complete and sophisticated integrated models by virtue of the constant increase of the computational capacity. Full article

(This article belongs to the Special Issue Conception, Modelling, Control, and Intensification of Photobioreactors Applied to the Valorization of Microalgae)

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