Behavior of mixed Chlorophyceae cultures under prolonged dark exposure. Respiration rate modeling

[EN] The behavior of three different microalgal cultures, when exposed for a long period (>48 h) to dark conditions, was studied with a methodology based on respirometry. The cultures were transferred to darkness and the oxygen evolution in the reactors was monitored after successive air injections. Several sequential oxygen uptake rates were thus calculated and a respiration constant, assuming a first order decay of a fraction of the biomass, was obtained by calibration. Initial specific oxygen uptake rates were in the range of 0.9 5.1 mg O2 g TSS−1 h−1 and dark respiration constants in the range of 0.005 0.018 h−1.This research work has been supported by the Spanish Ministry of Economy and Competitiveness (MINECO, CTM2011-28595-C02- 01/02) jointly with the European Regional Development Fund (ERDF) which are gratefully acknowledged. This research was also supported by the Spanish Ministry of Science and Innovation via a pre doctoral FPU fellowship to the first author (AP2009-4903). The authors would also like to thank the water management entities of the Generalitat Valenciana (EPSAR).Ruiz Martínez, A.; Serralta Sevilla, J.; Seco Torrecillas, A.; Ferrer, J. (2016). Behavior of mixed Chlorophyceae cultures under prolonged dark exposure. Respiration rate modeling. Ecological Engineering. 91:265-269. https://doi.org/10.1016/j.ecoleng.2016.02.025S2652699

Development of Finite Element Model based on Carrera Unified Formulation for Laminated Composites

Laminated composite structures are increasingly being used in the aerospace, automobile and wind energy sectors due to their superior specific mechanical properties, fatigue life and design tailorability. Accurate stress analysis of composite laminates has become crucial for safe design under realistic loads and boundary conditions. Different approaches based on analytical, experimental and numerical techniques are available for stress analysis. The classical theories like Euler-Bernoulli Beam Theory, Timoshenko Beam Theory, Kirchhoff plate theory and Reissner-Mindlin Plate Theory, respectively for beams and plates/shells are inaccurate for stress analysis of thick laminates as the effects such as transverse shear and normal deformations are neglected. Further, these models are limited by assumptions of material heterogeneity, structural geometry and Saint-Venant’s principle, which limits the accuracy of the stress field solution away from supports, discontinuities and singularities in the structures. For accurate evaluation of 3D stress / strain fields in the composite structures, computationally expensive 3D finite element analyse is usually carried out. New computationally efficient approaches are required for 3D evaluation of stresses in laminated composite structures. Recently, an advanced structural theory, namely Carrera Unified Formulation (CUF), has been proposed to accurately evaluate 3D stress / strain fields in slender beam-like and plate-like composite structures. CUF permits us to develop higher order displacement based beam and plate theories in a generic way. CUF provides a systematic approach for implementing the higher order theories. In this work, 1D and 2D CUF is implemented in a finite element framework to determine the 3D displacement, strain and stress fields of laminated composite structures. In the case of 1D CUF finite element formulation, the Lagrange shape functions of cubic and quadratic orders is used along the beam length and cross-section respectively. In the case of 2D CUF finite element formulation, the Lagrange shape functions are used to define the mid-surface deformation of the laminate and Taylor shape functions are used to define the thickness deformation of the laminate. In 2D CUF finite elements, the MITC plate formulation is followed to avoid the locking problems. The developed CUF finite element framework is validated against benchmark problems available in the literature and also with 3D finite element solutions. The convergence and accuracy of the stress field solution obtained using CUF finite elements are studied by varying the element order, element size and mesh distribution

Energetic Performance of Photobioreactors for Algal Cultivation

Microalgae are currently being investigated as a potential fuel crop. For algae to be an energy-efficient fuel crop, cultivation systems and operating conditions that have been optimized for biomass productivity have to be refocused toward energy production. In this work, data from the literature on a variety of algal photobioreactors (PBRs) were compiled to reassess them in terms of biomass productivity per unit energy input to the cultivation process. This assessment showed that PBRs that have been optimized for biomass productivity without considering the energy input did not necessarily perform well in terms of energy efficiency. This review recommends that selection of algal PBRs for energy production should consider optimal geometry for efficient utilization of incident light, and their operation should be based on the optimal sparging rate for efficient mixing to maximize energy efficiency

Optimal control for micro-algae on a raceway model

© 2017 American Institute of Chemical Engineers We apply numerical optimal control methods to an existing algae growth model with the aim to determine the best performance of the model under known conditions using a variety of decision variables. We transform the system of differential algebraic equations in the existing model to a system of ordinary differential equations which introduces dynamics for average light intensity and chlorophyll. In addition, we allow for variable nitrogen concentration of the inflow as well as variable initial nitrogen concentration of the raceway. Our main focus is on optimizing of the production of lipids. We calculate both open and closed loop optimal controllers and test their robustness. Finally, we also consider raceway depth as a decision variable. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 34:107–119, 2018