Special Issue "Microalgae Cultures: Environmental Tool and Bioenergy Source"

A special issue of Energies (ISSN 1996-1073). This special issue belongs to the section "Energy and Environment".

Deadline for manuscript submissions: 28 February 2021.

Special Issue Editors

Dr. José Carlos Magalhães Pires
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Guest Editor
LEPABE - Laboratory for Process Engineering, Environment, Biotechnology and Energy, Faculty of Engineering, University of Porto, 4200-465 Porto, Portugal
Interests: air pollution; CO2 capture; microalgal cultures; process integration; process modelling; statistical analysis
Special Issues and Collections in MDPI journals
Dr. Ana Luísa Gonçalves
Website
Guest Editor
LEPABE—Laboratory for Process Engineering, Environment, Biotechnology and Energy, Faculty of Engineering, University of Porto, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal
Interests: biotechnological applications of microalgae; CO2 capture; wastewater treatment; bioenergy production; circular economy; process sustainability; process integration; photobioreactor design; microalgal biomass production; high-valued compounds production
Special Issues and Collections in MDPI journals

Special Issue Information

Dear colleagues,

Microalgae have been intensively studied for CO2 capture, nutrient removal from wastewater, and biofuels production. These photosynthetic microorganisms use solar energy with efficiency ten times greater than terrestrial plants and are responsible for about 50% of the world’s oxygen production. Therefore, microalgae have been considered a sustainable solution for CO2 capture. Besides carbon, their growth also requires other macronutrients: nitrogen and phosphorus. To avoid the addition of fertilizers (increasing the production costs), these nutrients can be supplied if wastewater is used as the culture medium. The integration of biomass production with wastewater treatment enables the reduction of operational costs and the environmental impact. Microalgae are also known for their high lipid contents and high growth rates, and are a promising oil source for biodiesel production.

This Special Issue will present the recent research activities concerning the environmental applications of microalgae and their potential for biofuels production, focusing on the main challenges for their large-scale application. Since microalgal culturing can address different environmental and non-environmental issues, the achievements from the integration of multiple microalgal applications will also be considered in this Special Issue.

Prof. Dr. José Carlos Magalhães Pires
Dr. Ana Luísa Gonçalves
Guest Editors

Manuscript Submission Information

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Keywords

  • biofuels
  • biomass
  • biorefinery
  • CO2 capture
  • microalgae
  • photobioreactor
  • wastewater treatment

Published Papers (4 papers)

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Research

Open AccessArticle
Pigments Production, Growth Kinetics, and Bioenergetic Patterns in Dunaliella tertiolecta (Chlorophyta) in Response to Different Culture Media
Energies 2020, 13(20), 5347; https://doi.org/10.3390/en13205347 - 14 Oct 2020
Abstract
This work dealt with the study of growth parameters, pigments production, and bioenergetic aspects of the microalga Dunaliella tertiolecta in different culture media. For this purpose, cultures were carried out in Erlenmeyer flasks containing F/2 medium, Bold’s Basal medium, or an alternative medium [...] Read more.
This work dealt with the study of growth parameters, pigments production, and bioenergetic aspects of the microalga Dunaliella tertiolecta in different culture media. For this purpose, cultures were carried out in Erlenmeyer flasks containing F/2 medium, Bold’s Basal medium, or an alternative medium made up of the same constituents of the Bold’s Basal medium dissolved in natural seawater instead of distilled water. D. tertiolecta reached the highest dry cell concentration (Xmax = 1223 mgDM·L−1), specific growth rate (µmax = 0.535 d−1), cell productivity (PX = 102 mgDM·L−1·d−1), and photosynthetic efficiency (PE = 14.54%) in the alternative medium, while the highest contents of carotenoids (52.0 mg·g−1) and chlorophyll (108.0 mg·g−1) in the biomass were obtained in Bold’s Basal medium. As for the bioenergetic parameters, the biomass yield on Gibbs energy dissipation was higher and comparable in both seawater-based media. However, the F/2 medium led to the highest values of moles of photons absorbed to produce 1 C-mol of biomass (nPh), total Gibbs energy absorbed by the photosynthesis (ΔGa) and released heat (Q), as well as the lowest cell concentration, thus proving to be the least suitable medium for D. tertiolecta growth. On the other hand, the highest values of molar development of O2 and consumption of H+ and H2O were obtained in the alternative medium, which also ensured the best kinetic parameters, thereby allowing for the best energy exploitation for cell growth. These results demonstrate that composition of culture medium for microalgae cultivation has different effects on pigments production, growth kinetics, and bioenergetics parameters, which should be taken into consideration for any use of biomass, including as raw material for biofuels production. Full article
(This article belongs to the Special Issue Microalgae Cultures: Environmental Tool and Bioenergy Source)
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Open AccessArticle
Improving the Energy Balance of Hydrocarbon Production Using an Inclined Solid–Liquid Separator with a Wedge-Wire Screen and Easy Hydrocarbon Recovery from Botryococcus braunii
Energies 2020, 13(16), 4139; https://doi.org/10.3390/en13164139 - 10 Aug 2020
Abstract
The green colonial microalga Botryococcus braunii produces large amounts of hydrocarbons and has attracted attention as a potential source of biofuel. When this freshwater microalga is cultured in a brackish medium, the hydrocarbon recovery rate increases; furthermore, the colony size becomes large. In [...] Read more.
The green colonial microalga Botryococcus braunii produces large amounts of hydrocarbons and has attracted attention as a potential source of biofuel. When this freshwater microalga is cultured in a brackish medium, the hydrocarbon recovery rate increases; furthermore, the colony size becomes large. In this study, the effects of such changes on the energy balance of harvesting and hydrocarbon recovery were studied via filtrate experiments on an inclined separator and extraction from a concentrated slurry. The inclined separator was effective for harvesting large-colony-forming algae. The water content on the wire screen of slit sizes larger than 150 µm was <80% and a separation rate of >85% could be achieved. The input energy of the harvesting using the brackish medium with this separator was ≈44% of that using the freshwater medium with vacuum filtration, while the input energy of the hydrocarbon recovery using the brackish medium was ≈88% of that using the freshwater medium with pre-heating before n-hexane extraction. Furthermore, the energy profit ratio of the process in the brackish medium was 2.92, which was ≈1.2 times higher than that in the freshwater medium. This study demonstrated that filtration techniques and hydrocarbon recovery from B. braunii with a low energy input through culture in a brackish medium are viable. Full article
(This article belongs to the Special Issue Microalgae Cultures: Environmental Tool and Bioenergy Source)
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Open AccessArticle
Electro-Fenton Based Technique to Enhance Cell Harvest and Lipid Extraction from Microalgae
Energies 2020, 13(15), 3813; https://doi.org/10.3390/en13153813 - 24 Jul 2020
Cited by 1
Abstract
Currently, lipid extraction remains a major bottleneck in microalgae technology for biofuel production. In this study, an effective and easily controlled cell wall disruption method based on electro-Fenton reaction was used to enhance lipid extraction from the wet biomass of Nannochloropsis oceanica IMET1. [...] Read more.
Currently, lipid extraction remains a major bottleneck in microalgae technology for biofuel production. In this study, an effective and easily controlled cell wall disruption method based on electro-Fenton reaction was used to enhance lipid extraction from the wet biomass of Nannochloropsis oceanica IMET1. The results showed that 1.27 mM of hydroxide radical (HO•) was generated under the optimal conditions with 9.1 mM FeSO4 in a 16.4 mA·cm−2 current density for 37.0 min. After the electro-Fenton treatment, the neutral lipid extraction yield of microalgae (~155 mg) increased from 40% to 87.5%, equal to from 12.2% to 26.7% dry cell weight (DCW). In particular, the fatty acid composition remained stable. The cell wall disruption and lipid extraction processes were displayed by the transmission electron microscope (TEM) and fluorescence microscopy (FM) observations, respectively. Meanwhile, the removal efficiency of algal cells reached 85.2% within 2 h after the reaction was terminated. Furthermore, the biomass of the microalgae cultured in the electrolysis wastewater treated with fresh nutrients reached 3 g/L, which is 12-fold higher than that of the initial after 24 days. These finds provided an economic and efficient method for lipid extraction from wet microalgae, which could be easily controlled by current magnitude regulation. Full article
(This article belongs to the Special Issue Microalgae Cultures: Environmental Tool and Bioenergy Source)
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Open AccessArticle
Consortium Growth of Filamentous Fungi and Microalgae: Evaluation of Different Cultivation Strategies to Optimize Cell Harvesting and Lipid Accumulation
Energies 2020, 13(14), 3648; https://doi.org/10.3390/en13143648 - 15 Jul 2020
Abstract
This study aims to evaluate the potential of consortium biomass formation between Mucor circinelloides, an oleaginous filamentous fungal species, and Chlorella vulgaris, in order to promote a straightforward approach to harvest microalgal cells and to evaluate the lipid production in the [...] Read more.
This study aims to evaluate the potential of consortium biomass formation between Mucor circinelloides, an oleaginous filamentous fungal species, and Chlorella vulgaris, in order to promote a straightforward approach to harvest microalgal cells and to evaluate the lipid production in the consortium system. A synthetic medium with glucose (2 g·L−1) and mineral nutrients essential for both fungi and algae was selected. Four different inoculation strategies were assessed, considering the effect of simultaneous vs. separate development of fungal spores and algae cells, and the presence of a supporting matrix aiming at the higher recovery of algae cell rates. The results were evaluated in terms of consortium biomass composition, demonstrating that the strategy using a mature fungal mycelium with a higher algae count may provide biomass samples with up to 79% of their dry weight as algae, still promoting recovery rates greater than 97%. The findings demonstrate a synergistic effect on the lipid accumulation by the fungal strain, at around a fourfold increase when compared to the axenic control, with values in the range of 23% of dry biomass weight. Furthermore, the fatty acid profile from the samples presents a balance between saturated and unsaturated fatty acids that is likely to present an adequate balance for applications such as biodiesel production. Full article
(This article belongs to the Special Issue Microalgae Cultures: Environmental Tool and Bioenergy Source)
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