Dear Colleagues,

This Special Issue, entitled ‘Modeling, Optimization, and Control in Algal Biotechnology (Applications of General Principles and Techniques)’, aims to publish a set of articles that present ‘success stories’ of the application of general principles and techniques of mathematical modeling, numerical simulation, optimization, and control theory in the field of algal biotechnology. We intend to showcase the very best insightful and influential examples of the cultivation and utilization of both micro- and macroalgae in a variety of industrial processes.

We would like to include articles that will form a useful benchmark against which other articles are measured. Energies readers and authors are encouraged to send their very best work to be showcased. The key criteria for manuscript acceptance will be novelty and the potential contribution to the field.

Prof. Dr. Štěpán Papáček
Prof. Dr. Francisco Gabriel Acién Fernández
Prof. Dr. José M. Fernández-Sevilla
Guest Editors

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Energies is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2200 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

• algae
• microalgae
• macroalgae
• modeling
• optimization
• numerical simulation
• control theory
• algae biofuels
• CFD simulations

Title: Opportunities for Light Utilization Improvement in Large Scale Reactors

Authors: Marta Barcelo; Cristian Inostroza; Jose Luis Guzman; Jose M. Fernandez-Sevilla; Francisco Gabriel Acién-Fernández
Affiliation: Department of Chemical Engineering, University of Almería, 04120, Almería, Spain.
Abstract: Major factors determining the biomass productivity of microalgae cultures includes nutrients availability, temperature and culture parameters such as dissolved oxygen and pH, but light availability is the most relevant. Thus, the aim is to design reactors able to provide all the requirements of the cells at minimum cost then only light availability limiting the cells growth. At these conditions, to maximize the performance of microalgae cultures it is mandatory to optimize the light utilization efficiency of the cells. To achieve this objective in the laboratory is possible, a large number of papers showing that light/dark cycles in the range of 1-10 Hz allows to maximize the light utilization efficiency. However, at large scale to achieve full integration of light is much more difficult. Due to the low energy usually provided to microalgae cultures the axial liquid velocity is low, in the range of 0.1-1.0 m/s. At this velocity the transversal velocity is much lower, in the range of 0.01-0.10 m/s. Considering the biomass density and water depth in different reactors it is possible to summarize the scenarios on which relevant light integration could take place. It is found than in raceway reactors no opportunities for light integration exist. In tubular photobioreactors only the utilization of tube diameters below 0.05 m and liquid velocities upper than 0.5 m/s allows to approximate to full light integration conditions. However, at these conditions the energy consumption is enormous, up to 400 W/m3 in front of 10 W/m3 usually found in raceway reactors. The only option to improve the light utilization efficiency while keeping a low energy consumption is to reduce the water depth in raceway reactors, then arriving to the concept of thin-layer reactors.

Title: CFD Simulation of both Microalgae Growth and dissolved Oxygen Concentration in a Thin-Layer Cascade Reactor
Authors: Karel Petera; Štěpán Papáček; Cristian Inostroza; Francisco Gabriel Acién-Fernández; Jose M. Fernandez-Sevilla
Affiliation: Czech Technical University in Prague, Faculty of Mechanical Engineering, Department of Process Engineering, Technická 4, Prague 6, Czech Republic The Institute of Information Theory and Automation of the Czech Academy of Sciences, 18200 Prague, Czech Republic Department of Chemical Engineering, University of Almería, 04120, Almería, Spain
Abstract: In this work, the microalgae growth and dissolved oxygen concentration in a thin-layer cascade (TLC) reactor are simulated using computational fluid dynamics (CFD) code ANSYS Fluent. The main achievement resides in successful integration of commercial CFD code with reaction kinetics via user-defined-function (UDF), which makes our approach reliable and simple to implement. To validate the method, the simulation results for both microalgae growth and dissolved oxygen distribution within an open thin-layer cascade reactor were compared against our experimental data. Our modeling framework consisting of the advection-diffusion-reaction PDE system within a phenomenological model of photosynthesis and photoinhibition can be applied to any geometry, thus, it is eventually suitable as a tool for design and operating parameters optimization.

Title: Building Distributed Parameter Model for Further in Silico Optimization of Algal Culture Systems Operating Conditions
Authors: Štěpán Papáček; Volodymyr Lynnyk; Branislav Rehák; Ctirad Matonoha
Affiliation: The Institute of Information Theory and Automation of the Czech Academy of Sciences, 182 00 Prague, Czech Republic Institute of Computer Science, Czech Academy of Sciences,182 08 Prague, Czech Republic
Abstract: Mathematical modeling of algal culture systems, e.g. photobioreactors, open ponds, thin layer cascades, is a challenging task because of the non-linear coupling between biology (photosynthetic organism growth) and physics (mass transport by convection and/or dispersion and radiative transfer properties) involving multiple time and spatial scales. This study describes an attempt to find (or to build) the holy grail, being a reliable computational model serving for further optimization of algal culture systems operating conditions. In view of high complexity of this problem, a relatively simple mechanistic three-state model of photosynthesis and photoinhibition (PSF model) has been chosen as the reaction kinetics model. Nevertheless, the proposed modeling framework is independent of the particular re-action (sub)model; moreover, it is paradigm shift (from Lagrangian to Eulerian) which is thoroughly analyzed. The value of the presented Eulerian modeling framework dwells on the way how the (sub)models, i.e. the state system – mass balance equations in form of advection-diffusion-reaction PDEs, the Navier-Stokes equations and the irradiance profile, are coupled. In order to benchmark our modeling framework,the in silico optimization of the operating conditions of the well known Couette-Taylor device is performed.