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16 pages, 2592 KiB

Open AccessArticle

Effects of Nutrient Content and Nitrogen to Phosphorous Ratio on the Growth, Nutrient Removal and Desalination Properties of the Green Alga Coelastrum morus on a Laboratory Scale

by Aida Figler, Kamilla Márton, Viktória B-Béres and István Bácsi

Energies 2021, 14(8), 2112; https://doi.org/10.3390/en14082112 - 09 Apr 2021

Cited by 24 | Viewed by 2693

Abstract

In wastewater, nutrient concentrations and salinity vary substantially, however, the optimal N:P ratio for the treatment using microalgae is not well described. In this study, the effects of higher and lower nitrate and phosphate contents and N:P ratios on growth, nutrient removal ability [...] Read more.

In wastewater, nutrient concentrations and salinity vary substantially, however, the optimal N:P ratio for the treatment using microalgae is not well described. In this study, the effects of higher and lower nitrate and phosphate contents and N:P ratios on growth, nutrient removal ability and halotolerance of the common green alga Coelastrum morus were investigated in model solutions. The results suggest that high nitrate content (above 100 mg L⁻¹) with a similarly high phosphate concentration (resulting low N:P ratio) is not favorable for growth. The studied isolate can be considered as a halotolerant species, showing remarkable growth up to 1000 mg L⁻¹ NaCl and it seems that despite the negative effects on growth, higher nutrient content contributes to higher halotolerance. A significant amount of nitrate removal was observed in media with different nutrient contents and N:P ratios with different salt concentrations. High N:P ratios favor phosphate removal, which is more inhibited by increasing NaCl concentration than nitrate uptake. Overall, with a relatively higher nutrient content and a favorable (5 or higher) N:P ratio, a common green algal species such as C. morus could be a promising candidate next to species from the Chlorellaceae and Scenedesmaceae families. Full article

(This article belongs to the Special Issue Microalgae Cultures: Environmental Tool and Bioenergy Source)

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10 pages, 2593 KiB

Open AccessArticle

An Easily Accessible Microfluidic Chip for High-Throughput Microalgae Screening for Biofuel Production

by Shubhanvit Mishra, Yi-Ju Liu, Chi-Shuo Chen and Da-Jeng Yao

Energies 2021, 14(7), 1817; https://doi.org/10.3390/en14071817 - 24 Mar 2021

Cited by 14 | Viewed by 2761

Abstract

Microalgae are important green energy resources. With high efficiency in fixing carbon dioxide, microalgae are broadly applied for biofuel production. Integrating various cultivation parameters, we applied ultraviolet (UV) mutagenesis, one of the most common approaches, to induce genomic mutation in microalgae and thus [...] Read more.

Microalgae are important green energy resources. With high efficiency in fixing carbon dioxide, microalgae are broadly applied for biofuel production. Integrating various cultivation parameters, we applied ultraviolet (UV) mutagenesis, one of the most common approaches, to induce genomic mutation in microalgae and thus enhance the production of lipid content, but the screening process is convoluted and labor-intensive. In this study, we aimed to develop an accessible microfluidic platform to optimize the biofuel production of microalgae. Instead of traditional lithography, we designed hanging-drop microfluidic chips that were fabricated using a cheap computer numerical control (CNC) micro-milling technique. On each chip, we cultured in parallel Botryococcus braunii, one of the most common freshwater microalgae for biofuel production, in sets of ten separated hanging drops (~30 µL each); we monitored their growth in each individual drop for more than 14 days. To optimize the culturing conditions, using drops of varied diameter, we first identified the influence of cell density on algae growth and lipid production. After introducing UV-induced random mutations, we quantified the lipid content of the microalgae in situ; the optimized UV-C dosage was determined accordingly. In comparison with wild-type B. braunii, the results showed increased biomass growth (137%) and lipid content (149%) of the microalgae mutated with the desired UV process. Moreover, we showed a capacity to modulate the illumination on an addressed chip area. In summary, without using an external pump system, we developed a hanging-drop microfluidic system for long-term microalgae culturing, which can be easily operated using laboratory pipettes. This microfluidic system is expected to facilitate microalgae mutation breeding, and to be applied for algae cultivation optimization. Full article

(This article belongs to the Special Issue Microalgae Cultures: Environmental Tool and Bioenergy Source)

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17 pages, 1095 KiB

Open AccessArticle

Optimizing Docosahexaenoic Acid (DHA) Production by Schizochytrium sp. Grown on Waste Glycerol

by Natalia Kujawska, Szymon Talbierz, Marcin Dębowski, Joanna Kazimierowicz and Marcin Zieliński

Energies 2021, 14(6), 1685; https://doi.org/10.3390/en14061685 - 18 Mar 2021

Cited by 23 | Viewed by 2751

Abstract

The aim of this study was to optimize biomass and docosahexaenoic acid (DHA) production by Schizochytrium sp. grown on waste glycerol as an organic carbon source. Parameters having a significant effect on biomass and DHA yields were screened using the fractional Plackett–Burman design [...] Read more.

The aim of this study was to optimize biomass and docosahexaenoic acid (DHA) production by Schizochytrium sp. grown on waste glycerol as an organic carbon source. Parameters having a significant effect on biomass and DHA yields were screened using the fractional Plackett–Burman design and the response surface methodology (RSM). Schizochytrium sp. growth was most significantly influenced by crude glycerin concentration in the growth medium (150 g/dm³), process temperature (27 °C), oxygen in the bioreactor (49.99% v/v), and the concentration of peptone as a source of nitrogen (9.99 g/dm³). The process parameter values identified as optimal for producing high DHA concentrations in the biomass were as follows: glycerin concentration 149.99 g/dm³, temperature 26 °C, oxygen concentration 30% (v/v), and peptone concentration 2.21 g/dm³. The dry cell weight (DCW) obtained under actual laboratory conditions was 66.69 ± 0.66 g/dm³, i.e., 1.27% lower than the predicted value. The DHA concentration obtained in the actual culture was at 17.25 ± 0.33 g/dm³, which was 3.03% lower than the predicted value. The results obtained suggest that a two-step culture system should be employed, with the first phase focused on high production of Schizochytrium sp. biomass, and the second focused on increasing DHA concentration in the cells. Full article

(This article belongs to the Special Issue Microalgae Cultures: Environmental Tool and Bioenergy Source)

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13 pages, 1359 KiB

Open AccessArticle

Operation Regimes: A Comparison Based on Nannochloropsis oceanica Biomass and Lipid Productivity

by Inês Guerra, Hugo Pereira, Margarida Costa, Joana T. Silva, Tamára Santos, João Varela, Marília Mateus and Joana Silva

Energies 2021, 14(6), 1542; https://doi.org/10.3390/en14061542 - 11 Mar 2021

Cited by 14 | Viewed by 2968

Abstract

Microalgae are currently considered to be a promising feedstock for biodiesel production. However, significant research efforts are crucial to improve the current biomass and lipid productivities under real outdoor production conditions. In this context, batch, continuous and semi-continuous operation regimes were compared during [...] Read more.

Microalgae are currently considered to be a promising feedstock for biodiesel production. However, significant research efforts are crucial to improve the current biomass and lipid productivities under real outdoor production conditions. In this context, batch, continuous and semi-continuous operation regimes were compared during the Spring/Summer seasons in 2.6 m³ tubular photobioreactors to select the most suitable one for the production of the oleaginous microalga Nannochloropsis oceanica. Results obtained revealed that N. oceanica grown using the semi-continuous and continuous operation regimes enabled a 1.5-fold increase in biomass volumetric productivity compared to that cultivated in batch. The lipid productivity was 1.7-fold higher under semi-continuous cultivation than that under a batch operation regime. On the other hand, the semi-continuous and continuous operation regimes spent nearly the double amount of water compared to that of the batch regime. Interestingly, the biochemical profile of produced biomass using the different operation regimes was not affected regarding the contents of proteins, lipids and fatty acids. Overall, these results show that the semi-continuous operation regime is more suitable for the outdoor production of N. oceanica, significantly improving the biomass and lipid productivities at large-scale, which is a crucial factor for biodiesel production. Full article

(This article belongs to the Special Issue Microalgae Cultures: Environmental Tool and Bioenergy Source)

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20 pages, 5247 KiB

Open AccessArticle

Biorefinery-Based Approach to Exploit Mixed Cultures of Lipomyces starkeyi and Chloroidium saccharophilum for Single Cell Oil Production

by Gaetano Zuccaro, Angelo del Mondo, Gabriele Pinto, Antonino Pollio and Antonino De Natale

Energies 2021, 14(5), 1340; https://doi.org/10.3390/en14051340 - 01 Mar 2021

Cited by 9 | Viewed by 1862

Abstract

The mutualistic interactions between the oleaginous yeast Lipomyces starkeyi and the green microalga Chloroidium saccharophilum in mixed cultures were investigated to exploit possible synergistic effects. In fact, microalga could act as an oxygen generator for the yeast, while the yeast could provide carbon [...] Read more.

The mutualistic interactions between the oleaginous yeast Lipomyces starkeyi and the green microalga Chloroidium saccharophilum in mixed cultures were investigated to exploit possible synergistic effects. In fact, microalga could act as an oxygen generator for the yeast, while the yeast could provide carbon dioxide to microalga. The behavior of the two microorganisms alone and in mixed culture was studied in two synthetic media (YEG and BBM + G) before moving on to a real model represented by the hydrolysate of Arundo donax, used as low-cost feedstock, and previously subjected to steam explosion and enzymatic hydrolysis. The overall lipid content and lipid productivity obtained in the mixed culture of YEG, BBM + G and for the hydrolysate of Arundo donax were equal to 0.064, 0.064 and 0.081 g_lipid·g_biomass⁻¹ and 30.14, 35.56 and 37.22 mg_lipid·L⁻¹·day⁻¹, respectively. The mixed cultures, in all cases, proved to be the most performing compared to the individual ones. In addition, this study provided new input for the integration of Single Cell Oil (SCO) production with agro-industrial feedstock, and the fatty acid distribution mainly consisting of stearic (C18:0) and oleic acid (C18:1) allows promising applications in biofuels, cosmetics, food additives and other products of industrial interest. Full article

(This article belongs to the Special Issue Microalgae Cultures: Environmental Tool and Bioenergy Source)

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17 pages, 1635 KiB

Open AccessArticle

Perspective Design of Algae Photobioreactor for Greenhouses—A Comparative Study

by Kateřina Sukačová, Pavel Lošák, Vladimír Brummer, Vítězslav Máša, Daniel Vícha and Tomáš Zavřel

Energies 2021, 14(5), 1338; https://doi.org/10.3390/en14051338 - 01 Mar 2021

Cited by 23 | Viewed by 6375

Abstract

The continued growth and evolving lifestyles of the human population require the urgent development of sustainable production in all its aspects. Microalgae have the potential of the sustainable production of various commodities; however, the energetic requirements of algae cultivation still largely contribute to [...] Read more.

The continued growth and evolving lifestyles of the human population require the urgent development of sustainable production in all its aspects. Microalgae have the potential of the sustainable production of various commodities; however, the energetic requirements of algae cultivation still largely contribute to the overall negative balance of many operation plants. Here, we evaluate energetic efficiency of biomass and lipids production by Chlorella pyrenoidosa in multi-tubular, helical-tubular, and flat-panel airlift pilot scale photobioreactors, placed in an indoor environment of greenhouse laboratory in Central Europe. Our results show that the main energy consumption was related to the maintenance of constant light intensity in the flat-panel photobioreactor and the culture circulation in the helical-tubular photobioreactor. The specific power input ranged between 0.79 W L⁻¹ in the multi-tubular photobioreactor and 6.8 W L⁻¹ in the flat-panel photobioreactor. The construction of multi-tubular photobioreactor allowed for the lowest energy requirements but also predetermined the highest temperature sensitivity and led to a significant reduction of Chlorella productivity in extraordinary warm summers 2018 and 2019. To meet the requirements of sustainable yearlong microalgal production in the context of global change, further development towards hybrid microalgal cultivation systems, combining the advantages of open and closed systems, can be expected. Full article

(This article belongs to the Special Issue Microalgae Cultures: Environmental Tool and Bioenergy Source)

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19 pages, 1997 KiB

Open AccessArticle

Pigments Production, Growth Kinetics, and Bioenergetic Patterns in Dunaliella tertiolecta (Chlorophyta) in Response to Different Culture Media

by Yanara Alessandra Santana Moura, Daniela de Araújo Viana-Marques, Ana Lúcia Figueiredo Porto, Raquel Pedrosa Bezerra and Attilio Converti

Energies 2020, 13(20), 5347; https://doi.org/10.3390/en13205347 - 14 Oct 2020

Cited by 9 | Viewed by 2560

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 (X_max = 1223 mgDM·L⁻¹), specific growth rate (µ_max = 0.535 d⁻¹), cell productivity (P_X = 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 (n_Ph), total Gibbs energy absorbed by the photosynthesis (ΔG_a) 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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14 pages, 2034 KiB

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

by Kenichi Furuhashi, Fumio Hasegawa, Manabu Yamauchi, Yutaka Kaizu and Kenji Imou

Energies 2020, 13(16), 4139; https://doi.org/10.3390/en13164139 - 10 Aug 2020

Cited by 4 | Viewed by 2554

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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14 pages, 2920 KiB

Open AccessArticle

Electro-Fenton Based Technique to Enhance Cell Harvest and Lipid Extraction from Microalgae

by Shuai Zhang, Yuyong Hou, Zhiyong Liu, Xiang Ji, Di Wu, Weijie Wang, Dongyuan Zhang, Wenya Wang, Shulin Chen and Fangjian Chen

Energies 2020, 13(15), 3813; https://doi.org/10.3390/en13153813 - 24 Jul 2020

Cited by 9 | Viewed by 2700

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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15 pages, 2511 KiB

Open AccessArticle

Consortium Growth of Filamentous Fungi and Microalgae: Evaluation of Different Cultivation Strategies to Optimize Cell Harvesting and Lipid Accumulation

by Savienne M. F. E. Zorn, Cristiano E. R. Reis, Messias B. Silva, Bo Hu and Heizir F. De Castro

Energies 2020, 13(14), 3648; https://doi.org/10.3390/en13143648 - 15 Jul 2020

Cited by 13 | Viewed by 2707

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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Review

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18 pages, 3487 KiB

Open AccessReview

Immobilising Microalgae and Cyanobacteria as Biocomposites: New Opportunities to Intensify Algae Biotechnology and Bioprocessing

by Gary S. Caldwell, Pichaya In-na, Rachel Hart, Elliot Sharp, Assia Stefanova, Matthew Pickersgill, Matthew Walker, Matthew Unthank, Justin Perry and Jonathan G. M. Lee

Energies 2021, 14(9), 2566; https://doi.org/10.3390/en14092566 - 29 Apr 2021

Cited by 30 | Viewed by 6176

Abstract

There is a groundswell of interest in applying phototrophic microorganisms, specifically microalgae and cyanobacteria, for biotechnology and ecosystem service applications. However, there are inherent challenges associated with conventional routes to their deployment (using ponds, raceways and photobioreactors) which are synonymous with suspension cultivation [...] Read more.

There is a groundswell of interest in applying phototrophic microorganisms, specifically microalgae and cyanobacteria, for biotechnology and ecosystem service applications. However, there are inherent challenges associated with conventional routes to their deployment (using ponds, raceways and photobioreactors) which are synonymous with suspension cultivation techniques. Cultivation as biofilms partly ameliorates these issues; however, based on the principles of process intensification, by taking a step beyond biofilms and exploiting nature inspired artificial cell immobilisation, new opportunities become available, particularly for applications requiring extensive deployment periods (e.g., carbon capture and wastewater bioremediation). We explore the rationale for, and approaches to immobilised cultivation, in particular the application of latex-based polymer immobilisation as living biocomposites. We discuss how biocomposites can be optimised at the design stage based on mass transfer limitations. Finally, we predict that biocomposites will have a defining role in realising the deployment of metabolically engineered organisms for real world applications that may tip the balance of risk towards their environmental deployment. Full article

(This article belongs to the Special Issue Microalgae Cultures: Environmental Tool and Bioenergy Source)

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