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A special issue of Applied Sciences (ISSN 2076-3417). This special issue belongs to the section "Environmental Sciences".

Deadline for manuscript submissions: closed (30 April 2020) | Viewed by 34221

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Dr. Giorgos Markou

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Guest Editor

Institute of Technology of Agricultural Products, Hellenic Agricultural Organization – Demeter (ELGO-Demeter), Leof, SofokliVenizelou 1, 141 23 Lykovrysi, Greece
Interests: cultivation of algae; biomass production; biotechnology for food, feed and biofuels; valorization of waste-streams; recovery and reuse of nutrients
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Special Issue Information

Dear Colleagues,

Algae (including microalgae, macroalgae and cyanobacteria) have become important players in the bio-based industry as a result of their huge potential to produce many different bioproducts, such as food, feed and nutraceuticals, pharmaceuticals and cosmetics, biofuels and biochemicals. Economic growth has put pressure on natural resources, necessitating the development of production schemes that follow the paradigm of Circular Economy and hence lead to the recovery and reuse of resources on the entire production chain. Algal biotechnology shows that it is possible to couple the production of bioproducts with the utilization of resources contained in various waste-streams, such as those of the industrial, municipal and agro-industrial sectors.

This Special Issue aims to gather original research works on recent advances in algal biotechnology focusing on the production of bioproducts by utilizing various waste-streams in the Circular Economy framework, i.e., works dealing with cultivation, safety, feasibility and sustainability aspects of the utilization of waste-streams as nutrient sources for growing algal biomass and the production of bio-based goods.

Dr. Giorgos Markou
Guest Editor

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Keywords

algal biotechnology
Circular Economy
bioproducts
food
feed
biofuels
biochemicals
valorization of waste-streams
nutrient recovery and reuse

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Published Papers (7 papers)

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Research

19 pages, 2304 KiB

Open AccessArticle

Production of Microalgal Slow-Release Fertilizer by Valorizing Liquid Agricultural Digestate: Growth Experiments with Tomatoes

by Raquel Jimenez, Giorgos Markou, Saida Tayibi, Abdellatif Barakat, Camille Chapsal and Florian Monlau

Appl. Sci. 2020, 10(11), 3890; https://doi.org/10.3390/app10113890 - 3 Jun 2020

Cited by 28 | Viewed by 8068

Abstract

Anaerobic Digestion (AD) is a process that is well-known and fast-developing in Europe. AD generates large amounts of digestate, especially in livestock-intensive areas. Digestate has potential environmental issues due to nutrients (such as nitrogen) lixiviation or volatilization. Using liquid digestate as a nutrient source for microalgae growth is considered beneficial because digestate could be valorized and upgraded by the production of an added value product. In this work, microalgal biomass produced using liquid digestate from an agricultural biogas plant was investigated as a slow-release fertilizer in tomatoes. Monoraphidium sp. was first cultivated at different dilutions (1:20, 1:30, 1:50), in indoor laboratory-scale trials. The optimum dilution factor was determined to be 1:50, with a specific growth rate of 0.13 d⁻¹ and a complete nitrogen removal capacity in 25 days of culture. Then, outdoor experiments were conducted in a 110 dm³ vertical, closed photobioreactors (PBRs) in batch and semi-continuous mode with 1:50 diluted liquid digestate. During the batch mode, the microalgae were able to remove almost all NH₄⁺ and 65 (±13) % of PO₄³⁻, while the microalgal growth rate reached 0.25 d⁻¹. After the batch mode, the cultures were switched to operate under semi-continuously conditions. The cell densities were maintained at 1.3 × 10⁷ cells mL⁻¹ and a biomass productivity around 38.3 mg TSS L⁻¹ d⁻¹ during three weeks was achieved, where after that it started to decline due to unfavorable weather conditions. Microalgae biomass was further tested as a fertilizer for tomatoes growth, enhancing by 32% plant growth in terms of dry biomass compared with the control trials (without fertilization). Similar performances were achieved in tomato growth using synthetic fertilizer or digestate. Finally, the leaching effect in soils columns without plant was tested and after 25 days, only 7% of N was leached when microalgae were used, against 50% in the case of synthetic fertilizer. Full article

(This article belongs to the Special Issue New Trends on Algal Biotechnology for a Circular Economy)

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15 pages, 3831 KiB

Open AccessArticle

Evaluation of Microbial Load, Formation of Odorous Metabolites and Lipid Stability during Wet Preservation of Nannochloropsis gaditana Concentrates

by Joran Verspreet, Sabine Kreps and Leen Bastiaens

Appl. Sci. 2020, 10(10), 3419; https://doi.org/10.3390/app10103419 - 15 May 2020

Cited by 9 | Viewed by 3033

Abstract

Wet preservation of algae allows us to bridge the time period between algae harvest and processing while avoiding the costs and nutritional losses associated with algae drying. This study aimed to identify suitable storage conditions for the wet preservation of Nannochloropsis gaditana concentrates. The impact of storage temperature, time and the way of closing the storage recipient was evaluated using a full factorial design. The effect of acetic acid addition was tested for one storage condition. Storage temperature was the main factor determining the microbial count and had a vast impact on the formation of odorous metabolites. Storage at 20 °C in closed recipients led to rapid O₂ consumption, accumulation of malodorous short-chain fatty acids above their odor thresholds, and the production of H₂S and methanethiol. These odorous metabolites were not formed or to a much lower extent during 4 °C and 8 °C storage in closed recipients. Acetic acid supplementation (50 mM) suppressed the formation of short-chain fatty acids during 8 °C storage in unsealed recipients and reduced the aerobic microbial count and the number of yeasts and molds by approximately one log unit after 14 days. Yet, acetic acid addition also induced lipid hydrolysis and decreased chlorophyll levels when algae were stored for more than one week. This study demonstrated that temperature control is needed and that acetic acid addition is a promising approach when N. gaditana concentrates are stored for less than one week. Full article

(This article belongs to the Special Issue New Trends on Algal Biotechnology for a Circular Economy)

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18 pages, 2601 KiB

Open AccessArticle

Red Light Variation an Effective Alternative to Regulate Biomass and Lipid Profiles in Phaeodactylum tricornutum

by Nikunj Sharma, Gabriel Fleurent, Fatima Awwad, Michael Cheng, Fatma Meddeb-Mouelhi, Suzanne M. Budge, Hugo Germain and Isabel Desgagné-Penix

Appl. Sci. 2020, 10(7), 2531; https://doi.org/10.3390/app10072531 - 7 Apr 2020

Cited by 29 | Viewed by 4887

Abstract

Marine water diatom Phaeodactylum tricornutum is a photosynthetic organism that is known to respond to the changing light environment and adapt to different temperatures to prevent photoinhibition and maintain its metabolic functions. The objective of the present study was to test whether light shift variations in different growth phases impact the growth and lipid metabolism of P. tricornutum. Thus, we investigated R exposure in different growth phases to find the most effective light shift condition. The results showed that substituting white light (W) by red light (R) under autotrophic conditions, a condition called red shift (RS), increased biomass and lipid content compared to levels found under continuous W or R exposure alone. We observed an increase by 2-fold biomass and 2.3-fold lipid content in RS as compared to W. No significant change was observed in the morphology of lipid droplets, but the fatty acid (FA) composition was altered. Specifically, polyunsaturated FAs were increased, whereas monounsaturated FAs decreased in P. tricornutum grown in RS compared to W control. Therefore, we propose that a light shift during the beginning of the stationary phase is a low-cost cultivation strategy to boost the total biomass and lipids in P. tricornutum. Full article

(This article belongs to the Special Issue New Trends on Algal Biotechnology for a Circular Economy)

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15 pages, 7392 KiB

Open AccessArticle

Complete Evaluation of Cell Mixing and Hydrodynamic Performance of Thin-Layer Cascade Reactor

by Shehnaz Akhtar, Haider Ali and Cheol Woo Park

Appl. Sci. 2020, 10(3), 746; https://doi.org/10.3390/app10030746 - 21 Jan 2020

Cited by 6 | Viewed by 2463

Abstract

Microalgae are a great source of food and supplements as well as a potential source for the production of biofuels. However, the operational cost must be reduced to allow viable productions of bulk chemicals such as biofuels from microalgae. One approach to minimize the cost is to increase the efficiency of the photobioreactor. Photobioreactor efficiency is correlated to hydrodynamic mixing, which promotes single cell exposure to sunlight, keeps algae cells in suspension, and homogenizes the distribution of nutrients. Thus, a possible route to enhance the efficiency of the photobioreactor can be identified through an improved understanding of the mixing phenomenon. Therefore, for the current thin-layer cascade reactor, two aspects of its performance—namely, cell mixing and hydrodynamic characteristics—are evaluated under varying mass flow rates, slope angles, water depths, and aspect ratios of the channel by using computational fluid dynamics. The resulting model is validated with experimental data. Results reveal that limited cell mixing is achieved in the thin-layer cascade reactor with increased water depth and large aspect ratios. However, cell mixing is significantly increased at high mass flow rates. The increase in the mass flow rate and slope angle results in increased flow velocity and power consumption. Full article

(This article belongs to the Special Issue New Trends on Algal Biotechnology for a Circular Economy)

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14 pages, 1338 KiB

Open AccessArticle

Carbon Mass Balance in Arthrospira platensis Culture with Medium Recycle and High CO₂ Supply

by Masatoshi Kishi, Yukina Yamada, Tomoyo Katayama, Tatsushi Matsuyama and Tatsuki Toda

Appl. Sci. 2020, 10(1), 228; https://doi.org/10.3390/app10010228 - 27 Dec 2019

Cited by 16 | Viewed by 5008

Abstract

Medium recycling combined with CO₂ recovery helps sustainable use of the alkaline medium in Arthrospira culture. However, high CO₂ supply may cause inorganic carbon accumulation and pH reduction, which could result in low CO₂ recovery and reduced algal growth. This study aimed to elucidate the effect of medium recycling and high CO₂ supply through carbon mass balance analysis in Arthrospira culture. In all CO₂ supply conditions, carbon supply was higher than Arthrospira carbon assimilation, which accounted for 30–58% of supply. However, CO₂ recovery of nearly 100% and 63% for lower (0.20 and 0.39 gC L⁻¹ d⁻¹) and higher (0.59 gC L⁻¹ d⁻¹) CO₂ supply rates were achieved, respectively, because of the high concentration of the alkaline agent. The excess carbon accumulated in the medium and ultimately escaped from the system in a form of dissolved inorganic carbon (DIC). Dissolved organic carbon (DOC) contributed to 16–24% of the total photosynthetically assimilated carbon, and the final concentration reached 260–367 mgC L⁻¹, but there was no significant growth reduction caused by DIC and DOC accumulation. This study demonstrated the stability of the medium-recycling process even at high CO₂ supply rates although a balanced supply is recommended for longer operations. Full article

(This article belongs to the Special Issue New Trends on Algal Biotechnology for a Circular Economy)

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10 pages, 774 KiB

Open AccessFeature PaperArticle

Effect of Glycerol Concentration and Light Intensity on Growth and Biochemical Composition of Arthrospira (Spirulina) Platensis: A Study in Semi-Continuous Mode with Non-Aseptic Conditions

by Giorgos Markou, Eleni Kougia, Io Kefalogianni, Vasiliki Tsagou, Dimitrios Arapoglou and Iordanis Chatzipavlidis

Appl. Sci. 2019, 9(21), 4703; https://doi.org/10.3390/app9214703 - 4 Nov 2019

Cited by 14 | Viewed by 4871

Abstract

In this study, Arthrospira platensis was grown in the presence of different glycerol concentrations (0.5–9 g/L) under three light intensities (5, 10 and 15 Klux) in semi-continuous mode and under non-axenic conditions. The aim of this study was to investigate the growth performance, the biomass biochemical composition and any interactions between A. platensis and bacteria that would potentially grow as well on glycerol. The results here show that glycerol did not have any positive effect on biomass production of A. platensis. In contrast, it was observed that by increasing glycerol concentration the growth performance of A. platensis was restricted, while a gradual increase of bacteria population was observed, which apparently outcompeted and repressed A. platensis growth. Chlorophyll fluorescence measurements (Quantum Yields) revealed that glycerol was not an inhibiting factor per se of photosynthesis. On the other hand, cyanobacterial biomass grown on glycerol displayed a higher content in proteins and lipids. Especially, protein productivity was enhanced around 15–35% with the addition of glycerol compared to the control. In distinction, carbohydrate and photosynthetic pigments (phycocyanin and chlorophyll-α) content decreased with the increase of glycerol concentration. The results here suggest that A. platensis did not utilize glycerol for biomass production but most probably as metabolic energy carrier towards synthesis of proteins and lipids, which are more energy consuming metabolites compared to carbohydrates. The study revealed that the addition of glycerol at amounts of 0.5–1.5 g/L could be a strategy to improve protein productivity by A. platensis. Full article

(This article belongs to the Special Issue New Trends on Algal Biotechnology for a Circular Economy)

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14 pages, 1635 KiB

Open AccessArticle

Solving Nuisance Cyanobacteria Eutrophication Through Biotechnology

by S. Orfanidis, N. Stamatis, A. Parasyri, M. S. Mente, S. Zerveas, P. Pigada, A. Papadimitriou, M. Paschou, O. Nisiforou, A. Papazi, M. Moustaka-Gouni and K. Kotzabasis

Appl. Sci. 2019, 9(12), 2566; https://doi.org/10.3390/app9122566 - 24 Jun 2019

Cited by 1 | Viewed by 4658

Abstract

Management of nutrient inputs and usage of nuisance biomass as feedstock for bioenergy may be the solution of coastal lagoons eutrophication. We studied the species composition, photosynthetic pigments (Chl-a and Chl-c) and performance (OJIP-kinetics and JIP-test parameters), biochemistry (lipids and carbohydrates composition), and hydrogen production potential of Limnoraphis (Lyngbya) nuisance biomass collected from Lafri lagoon (1.24 km²) in Greece. The results showed that the removal of algal biomass from Lafri lagoon before its sedimentation, characterized by low Fν/Fm (0.42) and PItotal (2.67) values, and transfer of this in a simple, closed bioreactor, has the potential to produce hydrogen (H₂), a renewable CO₂-neutral energy that can directly be converted into electricity. The free carbohydrates of the lagoon water and that from the algal cells (42g glucose analogs per m³) could be also transferred to alcohols (biofuels), while the rest of the biomass could be used as organic fertilizer. The total lipid content (2.51%) of dry biomass composed primarily by palmitic acid was low. However, the presence of eicosapentaenoic (3.5%), and docosahexaenoic (1.7%), polyunsaturated fatty acids is worth mentioning. By harvesting and conversion of this coastal lagoon nuisance algal biomass to energy or other products, one could improve its water quality and, therefore, biodiversity and fish production; that is a sustainable solution of eutrophication necessary for the ongoing climatic change. Full article

(This article belongs to the Special Issue New Trends on Algal Biotechnology for a Circular Economy)

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