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New Insight in Microalgae Cultivation and Downstream Processes: Route toward Sustainable and Cost-Effective Production

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

Deadline for manuscript submissions: closed (30 June 2021) | Viewed by 41877

Special Issue Editor

Special Issue Information

Dear Colleagues,

Microalgae and cyanobacteria represent high taxonomic diversity, making them very attractive to produce valuable and diverse biomolecules (such as pigments, proteins, enzymes, biofuels, polyunsaturated fatty acids, and hydrocolloids). Research on microalgae has been abundantly published and patented in recent years, but the development and commercialization of these metabolites is still new and only niche markets are currently available for microalgae products. Their low usage may be easily explained by the costs involved in microalgae production, linked to photoproduction, the harvest of microalgae in diluted media, the recycling of culture media, and the difficulty in refining this biomass. Much effort has been made by research groups and companies to improve these processes, which currently limit microalgae compound applications to the field of high value products. Some studies have been focused on the increase of biomass and bioproducts productivities (new culture system designs, culture strategies, selection of strains, etc.), the use of wastewater to reduce medium costs, and downstream processes (harvesting, fractionation, biorefinery, etc.), in order to achieve more sustainable and cost-effective production of biomass and bioproducts. The aim of this Special Issue, therefore, is to provide recent reviews and original research articles highlighting the innovations and dynamism of the research in the field of microalgae cultivation and downstream processes.

I look forward to receiving your submissions for this Special Issue.

Prof. Dr. Céline Laroche
Guest Editor

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Keywords

  • microalgae
  • photobioreactors
  • culture systems
  • downstream processes
  • biorefinery
  • bioproducts

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Published Papers (6 papers)

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Research

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11 pages, 830 KiB  
Article
Static Magnetic Fields Effects on Polysaccharides Production by Different Microalgae Strains
by Kricelle M. Deamici, Michele G. de Morais, Lucielen O. Santos, Koenraad Muylaert, Christine Gardarin, Jorge Alberto V. Costa and Céline Laroche
Appl. Sci. 2021, 11(11), 5299; https://doi.org/10.3390/app11115299 - 7 Jun 2021
Cited by 22 | Viewed by 3275
Abstract
Microalgae are able to produce many valuable biomolecules, such as polysaccharides, that presents a large diversity of biochemical structures and functions as antioxidant, antifungal, anticancer, among others. Static magnetic fields (SMF) influence the metabolism of microorganisms and has been shown as an alternative [...] Read more.
Microalgae are able to produce many valuable biomolecules, such as polysaccharides, that presents a large diversity of biochemical structures and functions as antioxidant, antifungal, anticancer, among others. Static magnetic fields (SMF) influence the metabolism of microorganisms and has been shown as an alternative to increase microalgae biomass, yield and compounds production. Especially, some studies have highlighted that SMF application could enhance carbohydrate content. This study aimed to evaluate different conditions of SMF on Spirulina and Chlorella in indoor and outdoor conditions, in order to confirm the influence of SMF on polysaccharides production, evaluating which polysaccharidic fraction could be enhanced by SMF and highlighting a possible modification in EPS composition. Starch from Chlorella and exopolysaccharides (EPS) from Spirulina were quantified and characterized. SMF increased the starch content in Chorella fusca biomass. EPS productions from A. platensis and Spirulina sp. were not significantly increased, and global composition appeared similar to the controls (constituted basically of 80–86% neutral sugars and 13–19% uronic acids). However, the monosaccharide composition analysis revealed a significant modification of composition, i.e., the amount of fucose, arabinose, rhamnose, galactose and glucuronic acid was increased, while the glucose content was decreased. SMF application led to significant modification of polysaccharides production and this study demonstrate that combining the outdoor conditions with SMF, the starch content and EPS composition was positively affected. Full article
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Review

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15 pages, 600 KiB  
Review
Arthrospira platensis as a Feasible Feedstock for Bioethanol Production
by Enrique Gonzalez Bautista and Céline Laroche
Appl. Sci. 2021, 11(15), 6756; https://doi.org/10.3390/app11156756 - 22 Jul 2021
Cited by 13 | Viewed by 3073
Abstract
In recent decades and to deal with the scarcity of fossil fuels, many studies have been developed in order to set up a sustainable biofuel production sector. This new sector must be efficient (high productivity), economically profitable (low production costs and therefore acceptable [...] Read more.
In recent decades and to deal with the scarcity of fossil fuels, many studies have been developed in order to set up a sustainable biofuel production sector. This new sector must be efficient (high productivity), economically profitable (low production costs and therefore acceptable fuel prices), and ethical (low carbon balance, no competition with food resources). The production of bioethanol is based on the fermentation of reserve sugars, accumulated in the form of starch in microalgae and glycogen in cyanobacteria. The advantage of this bioenergy production route lies in the fact that the post-crop fermentation process is at the industrial stage since it has already been tested for many years for the production of bioethanol from agricultural resources. One of the most cultivated cyanobacteria is Arthrospira (“Spirulina”) and its production is also already at industrial scale. Depending on the cultivation conditions, this cyanobacteria is able to accumulate up to 65% DW (dry weight) of glycogen, making it a feasible feedstock for bioethanol production. The aim of this review is to provide a clear overview of these operating conditions for glycogen accumulation. Full article
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20 pages, 1711 KiB  
Review
Extraction of Pigments from Microalgae and Cyanobacteria—A Review on Current Methodologies
by Fernando Pagels, Ricardo N. Pereira, António A. Vicente and A. Catarina Guedes
Appl. Sci. 2021, 11(11), 5187; https://doi.org/10.3390/app11115187 - 3 Jun 2021
Cited by 51 | Viewed by 13769
Abstract
Pigments from microalgae and cyanobacteria have attracted great interest for industrial applications due to their bioactive potential and their natural product attributes. These pigments are usually sold as extracts, to overcome purification costs. The extraction of these compounds is based on cell disruption [...] Read more.
Pigments from microalgae and cyanobacteria have attracted great interest for industrial applications due to their bioactive potential and their natural product attributes. These pigments are usually sold as extracts, to overcome purification costs. The extraction of these compounds is based on cell disruption methodologies and chemical solubility of compounds. Different cell disruption methodologies have been used for pigment extraction, such as sonication, homogenization, high-pressure, CO2 supercritical fluid extraction, enzymatic extraction, and some other promising extraction methodologies such as ohmic heating and electric pulse technologies. The biggest constrain on pigment bioprocessing comes from the installation and operation costs; thus, fundamental and applied research are still needed to overcome such constrains and give the microalgae and cyanobacteria industry an opportunity in the world market. In this review, the main extraction methodologies will be discussed, taking into account the advantages and disadvantages for each kind of pigment, type of organism, cost, and final market. Full article
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21 pages, 1485 KiB  
Review
Digestate as Sustainable Nutrient Source for Microalgae—Challenges and Prospects
by Lisa Bauer, Karolína Ranglová, Jiří Masojídek, Bernhard Drosg and Katharina Meixner
Appl. Sci. 2021, 11(3), 1056; https://doi.org/10.3390/app11031056 - 25 Jan 2021
Cited by 46 | Viewed by 5276
Abstract
The interest in microalgae products has been increasing, and therefore the cultivation industry is growing steadily. To reduce the environmental impact and production costs arising from nutrients, research needs to find alternatives to the currently used artificial nutrients. Microalgae cultivation in anaerobic effluents [...] Read more.
The interest in microalgae products has been increasing, and therefore the cultivation industry is growing steadily. To reduce the environmental impact and production costs arising from nutrients, research needs to find alternatives to the currently used artificial nutrients. Microalgae cultivation in anaerobic effluents (more specifically, digestate) represents a promising strategy for increasing sustainability and obtaining valuable products. However, digestate must be processed prior to its use as nutrient source. Depending on its composition, different methods are suitable for removing solids (e.g., centrifugation) and adjusting nutrient concentrations and ratios (e.g., dilution, ammonia stripping). Moreover, the resulting cultivation medium must be light-permeable. Various studies show that growth rates comparable to those in artificial media can be achieved when proper digestate treatment is used. The necessary steps for obtaining a suitable cultivation medium also depend on the microalgae species to be cultivated. Concerning the application of the biomass, legal aspects and impurities originating from digestate must be considered. Furthermore, microalgae species and their application fields are essential criteria when selecting downstream processing methods (harvest, disintegration, dehydration, product purification). Microalgae grown on digestate can be used to produce various products (e.g., bioenergy, animal feed, bioplastics, and biofertilizers). This review gives insight into the origin and composition of digestate, processing options to meet requirements for microalgae cultivation and challenges regarding downstream processing and products. Full article
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21 pages, 646 KiB  
Review
The Use of Microalgae and Cyanobacteria in the Improvement of Agricultural Practices: A Review on Their Biofertilising, Biostimulating and Biopesticide Roles
by Ana L. Gonçalves
Appl. Sci. 2021, 11(2), 871; https://doi.org/10.3390/app11020871 - 19 Jan 2021
Cited by 145 | Viewed by 11290
Abstract
The increase in worldwide population observed in the last decades has contributed to an increased demand for food supplies, which can only be attained through an improvement in agricultural productivities. Moreover, agricultural practices should become more sustainable, as the use of chemically-based fertilisers, [...] Read more.
The increase in worldwide population observed in the last decades has contributed to an increased demand for food supplies, which can only be attained through an improvement in agricultural productivities. Moreover, agricultural practices should become more sustainable, as the use of chemically-based fertilisers, pesticides and growth stimulants can pose serious environmental problems and lead to the scarcity of finite resources, such as phosphorus and potassium, thus increasing the fertilisers’ costs. One possible alternative for the development of a more sustainable and highly effective agriculture is the use of biologically-based compounds with known activity in crops’ nutrition, protection and growth stimulation. Among these products, microalgal and cyanobacterial biomass (or their extracts) are gaining particular attention, due to their undeniable potential as a source of essential nutrients and metabolites with different bioactivities, which can significantly improve crops’ yields. This manuscript highlights the potential of microalgae and cyanobacteria in the improvement of agricultural practices, presenting: (i) how these photosynthetic microorganisms interact with higher plants; (ii) the main bioactive compounds that can be isolated from microalgae and cyanobacteria; and (iii) how microalgae and cyanobacteria can influence plants’ growth at different levels (nutrition, protection and growth stimulation). Full article
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24 pages, 1093 KiB  
Review
Microalgal Biomass Generation via Electroflotation: A Cost-Effective Dewatering Technology
by Jaison Jeevanandam, Mohd Razif Harun, Sie Yon Lau, Divine D. Sewu and Michael K. Danquah
Appl. Sci. 2020, 10(24), 9053; https://doi.org/10.3390/app10249053 - 18 Dec 2020
Cited by 13 | Viewed by 4082
Abstract
Microalgae are an excellent source of bioactive compounds for the production of a wide range of vital consumer products in the biofuel, pharmaceutical, food, cosmetics, and agricultural industries, in addition to huge upstream benefits relating to carbon dioxide biosequestration and wastewater treatment. However, [...] Read more.
Microalgae are an excellent source of bioactive compounds for the production of a wide range of vital consumer products in the biofuel, pharmaceutical, food, cosmetics, and agricultural industries, in addition to huge upstream benefits relating to carbon dioxide biosequestration and wastewater treatment. However, energy-efficient, cost-effective, and scalable microalgal technologies for commercial-scale applications are limited, and this has significantly impacted the full-scale implementation of microalgal biosystems for bioproduct development, phycoremediation, and biorefinery applications. Microalgae culture dewatering continues to be a major challenge to large-scale biomass generation, and this is primarily due to the low cell densities of microalgal cultures and the small hydrodynamic size of microalgal cells. With such biophysical characteristics, energy-intensive solid–liquid separation processes such as centrifugation and filtration are generally used for continuous generation of biomass in large-scale settings, making dewatering a major contributor to the microalgae bioprocess economics. This article analyzes the potential of electroflotation as a cost-effective dewatering process that can be integrated into microalgae bioprocesses for continuous biomass production. Electroflotation hinges on the generation of fine bubbles at the surface of an electrode system to entrain microalgal particulates to the surface. A modification of electroflotation, which combines electrocoagulation to catalyze the coalescence of microalgae cells before gaseous entrainment, is also discussed. A technoeconomic appraisal of the prospects of electroflotation compared with other dewatering technologies is presented. Full article
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