Optimal design of scalable photo-bioreactor for phototropic culturing of Haematococcus pluvialis

Development of a limitless scale-up photobioreactor for highly efficient photosynthesis-based polyhydroxybutyrate (PHB)-producing cyanobacteria

Photosynthetic polyhydroxybutyrate (PHB) production is an attractive technology for realizing a sustainable society by simultaneously producing useful biodegradable plastics and mitigating CO2. It is necessary to establish an economical large-scale photobioreactor (PBR) capable of effectively cultivating photosynthetic microorganisms such as cyanobacteria. A roll-to-roll winding machine/heat-sealer hybrid system for fabricating an easy-to-scale-up PBR was developed in the present study. The baffle design was optimized to facilitate mass transfer within the PBR, and the operating conditions of the gas sparger were investigated to maximize the CO2 transfer efficiency. The newly developed PBR was able to produce biomass of PHB content 10.7 w/w% at a rate of 6.861 g m-2 d-1, 21 % improved biomass productivity compared with the existing PBR. It was confirmed that biomass productivity was maintained even when PBR was scaled up to 2 tons. Consequently, the newly developed PBR is expected to improve the feasibility of photosynthetic PHB production.

Bioenergy, Biofuels, Lipids and Pigments—Research Trends in the Use of Microalgae Grown in Photobioreactors

This scientometric review and bibliometric analysis aimed to characterize trends in scientific research related to algae, photobioreactors and astaxanthin. Scientific articles published between 1995 and 2020 in the Web of Science and Scopus bibliographic databases were analyzed. The article presents the number of scientific articles in particular years and according to the publication type (e.g., articles, reviews and books). The most productive authors were selected in terms of the number of publications, the number of citations, the impact factor, affiliated research units and individual countries. Based on the number of keyword occurrences and a content analysis of 367 publications, seven leading areas of scientific interest (clusters) were identified: (1) techno-economic profitability of biofuels, bioenergy and pigment production in microalgae biorefineries, (2) the impact of the construction of photobioreactors and process parameters on the efficiency of microalgae cultivation, (3) strategies for increasing the amount of obtained lipids and obtaining biodiesel in Chlorella microalgae cultivation, (4) the production of astaxanthin on an industrial scale using Haematococcus microalgae, (5) the productivity of biomass and the use of alternative carbon sources in microalgae culture, (6) the effect of light and carbon dioxide conversion on biomass yield and (7) heterotrophy. Analysis revealed that topics closely related to bioenergy production and biofuels played a dominant role in scientific research. This publication indicates the directions and topics for future scientific research that should be carried out to successfully implement economically viable technology based on microalgae on an industrial scale.

Multifaceted strategies for economic production of microalgae Haematococcus pluvialis-derived astaxanthin via direct conversion of CO2

Owing to its strong antioxidant properties, astaxanthin has a high market price in the nutraceutical and pharmaceutical fields, and its demand is increasing. Furthermore, with an increase in the demand for green technology, astaxanthin production through direct CO₂ conversion using the autotrophic green microalga Haematococcus pluvialis as a bio-platform has received much attention. Large-scale outdoor cultivation of H. pluvialis using waste CO₂ sources and sunlight can secure sustainability and improve economic efficiency. However, low strain performance, reduced light utilization because of increased cell density, and inefficient transfer of gaseous CO₂ into liquid culture broth hinder its large-scale commercialization of astaxanthin. Herein, we presented a multifaceted strategy, including the development of high-efficiency strains, a culture system for astaxanthin accumulation, and astaxanthin extraction from biomass, for economically producing astaxanthin from H. pluvialis through direct CO₂ conversion. Future perspectives were presented by comparing and analyzing various previous studies conducted using the latest technology.

Effective contamination control strategies facilitating axenic cultivation of Haematococcus pluvialis: Risks and challenges

With industrialization, anthropogenic mishandlings have resulted in the discharge of abundant amount of CO₂ into the atmosphere. This has triggered an unnatural warming that has dramatically increased the Earth's temperature in a short duration. This problem can be addressed by the biological conversion of CO₂; several studies have been conducted using H. pluvialis culture that produces high value-added materials, such as astaxanthin and omega-3 fatty acids. However, although H. pluvialis has a high market value, the market size is quite small. Because H. pluvialis cells are susceptible to contamination due to its slow growth rate, hence large-scale culture of H. pluvialis without reliable contamination control strategies poses significant risks. This review comprehensively discusses the contamination that occurs during the culturing of H. pluvialis in various culture systems under different culture conditions. The review also discusses the strategies in controlling the biotic contaminants, such as bacteria and fungi.

Using green alga Haematococcus pluvialis for astaxanthin and lipid co-production: Advances and outlook

Astaxanthin is one of the secondary carotenoids involved in mediating abiotic stress of microalgae. As an important antioxidant and nutraceutical compound, astaxanthin is widely applied in dietary supplements and cosmetic ingredients. However, most astaxanthin in the market is chemically synthesized, which are structurally heterogeneous and inefficient for biological uptake. Astaxanthin refinery from Haematococcus pluvialis is now a growing industrial sector. H. pluvialis can accumulate astaxanthin to ∼5% of dry weight. As productivity is a key metric to evaluate the production feasibility, understanding the biological mechanisms of astaxanthin accumulation is beneficial for further production optimization. In this review, the biosynthesis mechanism of astaxanthin and production strategies are summarized. The current research on enhancing astaxanthin accumulation and the potential joint-production of astaxanthin with lipids was also discussed. It is conceivable that with further improvement on the productivity of astaxanthin and by-products, the algal-derived astaxanthin would be more accessible to low-profit applications.

Improved CO2-derived polyhydroxybutyrate (PHB) production by engineering fast-growing cyanobacterium Synechococcus elongatus UTEX 2973 for potential utilization of flue gas

Industrial application of cyanobacterial poly-β-hydroxybutyrate (PHB) production from CO₂ is currently challenged by slow growth rate and low photoautotrophic PHB productivity of existing cyanobacteria species. Herein, a novel PHB-producing cyanobacterial strain was developed by harnessing fast-growing cyanobacteria Synechococcus elongatus UTEX 2973 with introduction of heterologous phaCAB genes. Under photoautotrophic condition, the engineered strain produced 420 mg L^-1 (16.7% of dry cell weight) with the highest specific productivity of 75.2 mg L^-1 d^-1. When compared with a native PHB producer Synechocystis PCC 6803 under nitrogen deprivation, the engineered strain exhibited 2.4-fold higher PHB productivity. The performance of the engineered strain was further demonstrated in large scale cultivation using photobioreactor and outdoor cultivation employing industrial flue gas as the sole carbon source. This study can provide a promising solution to address petroleum-based plastic waste and contribute to CO₂ mitigation.

Recent advancements in mixotrophic bioprocessing for production of high value microalgal products

Recently, microalgal biomass has become an attractive and sustainable feedstock for renewable production of various biochemicals and biofuels. However, attaining required productivity remains a key challenge to develop industrial applications. Fortunately, mixotrophic cultivation strategy (MCS) is leading to higher productivity due to the metabolic ability of some microalgal strain to utilise both photosynthesis and organic carbon compared to phototrophic or heterotrophic processes. The potential of MCS is being explored by researchers for maximized biochemicals and biofuels production however it requires further development yet to reach commercialization stage. In this review, recent developments in the MCS bioprocess for selective value-added (carotenoids) products have been reviewed; synergistic mechanism of carbon and energy was conferred. Moreover, the metabolic regulation of microalgae under MCS for utilized carbon forms and carbon recycling was demonstrated; Additionally, the opportunities and challenges of large-scale MCS have been discussed.

Incorporation of Magnetic Nanoparticles into Protoplasts of Microalgae Haematococcus pluvialis: A Tool for Biotechnological Applications

Intensive research on the use of magnetic nanoparticles for biotechnological applications of microalgae biomass guided the development of proper treatment to successfully incorporate them into these single-cell microorganisms. Protoplasts, as cells lacking a cell wall, are extensively used in plant/microalgae genetic manipulation as well as various biotechnological applications. In this work, a detailed study on the formation of protoplasts from Haematococcus pluvialis with the use of enzymatic and mechanical procedures was performed. The optimization of several parameters affecting the formation of protoplasmic cells and cell recovery was investigated. In the enzymatic treatment, a solution of cellulase was studied at different time points of incubation, whereas in the mechanical treatment, glass beads vortexing was used. Mechanical treatment gave better results in comparison to the enzymatic one. Concerning the cell recovery, after the protoplast formation, it was found to be similar in both methods used; cell viability was not investigated. To enhance the protoplast cell wall reconstruction, different “recovery media” with an organic source of carbon or nitrogen were used. Cell morphology during all treatments was evaluated by electron microscopy. The optimal conditions found for protoplast formation and cell reconstruction were successfully used to produce Haematococcus pluvialis cells with magnetic properties.

Novel Insights into the Biotechnological Production of Haematococcus pluvialis-Derived Astaxanthin: Advances and Key Challenges to Allow Its Industrial Use as Novel Food Ingredient

Astaxanthin shows many biological activities. It has acquired a high economic potential and its current market is dominated by its synthetic form. However, due to the increase of the health and environmental concerns from consumers, natural forms are now preferred for human consumption. Haematococcus pluvialis is artificially cultured at an industrial scale to produce astaxanthin used as a dietary supplement. However, due to the high cost of its cultivation and its relatively low biomass and pigment productivities, the astaxanthin extracted from this microalga remains expensive and this has probably the consequence of slowing down its economic development in the lower added-value market such as food ingredient. In this review, we first aim to provide an overview of the chemical and biochemical properties of astaxanthin, as well as of its natural sources. We discuss its bioavailability, metabolism, and biological activities. We present a state-of-the-art of the biology and physiology of H. pluvialis, and highlight novel insights into the biotechnological processes which allow optimizing the biomass and astaxanthin productivities. We are trying to identify some lines of research that would improve the industrial sustainability and economic viability of this bio-production and to broaden the commercial potential of astaxanthin produced from H. pluvialis.

Distinctive nutrient designs using statistical approach coupled with light feeding strategy to improve the Haematococcus pluvialis growth performance and astaxanthin accumulation

The optimization of the BG-11 culture medium nutrients using complex statistical design followed by incremental illumination was planned to stimulate the Haematococcus pluvialis growth and astaxanthin accumulation. Based on the Plackett-Burman design results, MgSO₄·7H₂O, H₃BO₃, and Na₂CO₃ were identified as critical components to improve the biomass and astaxanthin productivity. Using central composite design, their initial critical concentrations in the green stage were found as 57.5, 6.2 and 53.0 mg/L, while for the red stage, the 138.3, 8.5 and 41.0 mg/L, recorded as optimum respectively. Using the optimum media, growth and astaxanthin accumulation at the end of the phototrophic and photoinduction stages were boosted by 17 and 54% respectively. The results of scale-up coupled with incremental illumination in phototrophic stage revealed the biomass and astaxanthin concentration improved 50% and 60% over the BG-11 media under constant light intensity. Also, different optimum culture medium formula for green and red stages was proposed.

Rapid selection of astaxanthin-hyperproducing Haematococcus mutant via azide-based colorimetric assay combined with oil-based astaxanthin extraction

The aim of this work was to develop a new approach for simple and high-throughput selection of astaxanthin-hyperproducing Haematococcus mutants through a sequential combination method of azide-based colorimetric assessment and oil-based astaxanthin quantification. Randomly mutagenized cells were spotted on solid culture medium containing 50 µM of sodium azide to accelerate the biosynthesis of astaxanthin. After 3 days, highly-induced mutants were preliminarily isolated by visual inspection and their astaxanthin accumulations were rapidly quantified by soybean oil-based extraction method. On the whole, the selected mutants showed reduced vegetative growth rates but eventually exhibited higher astaxanthin productions than the parental strain owing to their improved inductive growths. Among them, M13 showed 174.7 ± 5.69 mg L^-1 of the highest astaxanthin production, which is 1.59-times higher than that of wild-type. This wide-scope screening method expedites both upstream and downstream astaxanthin quantification, making it a useful tool for isolating microalgae with high astaxanthin production.

Improvement in modular scalability of polymeric thin-film photobioreactor for autotrophic culturing of Haematococcus pluvialis using industrial flue gas

The aim of this study is investigate the effect of column diameter (D), height/diameter (H/D) ratio, and gas flow rate on microalgae cultivation, Haematococcus pluvialis. Bubble column reactors with various D and H/D ratio were tested to assess the hydrodynamic properties and biomass production performance. Then, H. pluvialis was cultured under outdoor autotrophic conditions using industrial flue gas. By optimizing the reactor module, reactor volume increased to 354% with minimized biomass loss. Compared to the control, developed module showed biomass and astaxanthin productivity of 0.052 versus 0.053 g/L/day, and 1.48 versus 1.47 mg/L/day, respectively. Consequently, biomass productivity was maintained with increased reactor scale, and the result is applicable to the scale up of overall microalgae cultivation process.

Development of an X-Shape airlift photobioreactor for increasing algal biomass and biodiesel production

The aim of this work was to develop a high efficient photobioreactor for increasing biomass and lipid production in microalgae by assessment of the hydrodynamic properties and k_La which are important parameters for improving the algal cultivation efficiency. We designed three different photobioreactors (H-Shape, X-Shape and serial-column). Among them, X-Shape showed the highest hydrodynamic properties and k_La for algal cultivation. Thus, we evaluated the biomass and the lipid production in a 20L scale-up X-Shape photobioreactor. The biomass and lipid production from X-Shape photobioreactor are 1.359±0.007gL^-1 and 117.624±3.522mgL^-1, respectively; which are 30.05% and 23.49% higher than those from the control photobioreactor. Finally, we observed the lipid from X-Shape had high MUFAs, CN and low IV, which is suitable for high quality of biodiesel, suggesting that it can be practicably utilized for mass production of algal biofuel.

Improvement of Squalene Production from CO2 in Synechococcus elongatus PCC 7942 by Metabolic Engineering and Scalable Production in a Photobioreactor

The push-and-pull strategy for metabolic engineering was successfully demonstrated in Synechococcus elongatus PCC 7942, a model photosynthetic bacterium, to produce squalene from CO₂. Squalene synthase (SQS) was fused to either a key enzyme (farnesyl diphosphate synthase) of the methylerythritol phosphate pathway or the β-subunit of phycocyanin (CpcB1). Engineered cyanobacteria with expression of a fusion CpcB1-SQS protein showed a squalene production level (7.16 ± 0.05 mg/L/OD₇₃₀) that was increased by 1.8-fold compared to that of the control strain expressing SQS alone. To increase squalene production further, the gene dosage for CpcB1·SQS protein expression was increased and the fusion protein was expressed under a strong promoter, yielding 11.98 ± 0.49 mg/L/OD₇₃₀ of squalene, representing a 3.1-fold increase compared to the control. Subsequently, the best squalene producer was cultivated in a scalable photobioreactor (6 L) with light optimization, which produced 7.08 ± 0.5 mg/L/OD₇₃₀ squalene (equivalent to 79.2 mg per g dry cell weight). Further optimization for photobioprocessing and strain development will promote the construction of a solar-to-chemical platform.

Optimizing gas transfer to improve growth rate of Haematococcus pluvialis in a raceway pond with chute and oscillating baffles

Up-down chute and oscillating (UCO) baffles were used to generate vortex and oscillating flow field to improve growth rate of Haematococcus pluvialis in a raceway pond. Effects of gas flow rate, solution velocity, and solution depth on solution mass transfer coefficient and mixing time were evaluated using online pH and dissolved oxygen probes. Mass transfer coefficient increased by 1.3 times and mixing time decreased by 33% when UCO baffles were used in the H. pluvialis solution, resulting in an 18% increase in biomass yield with 2% CO2. The H. pluvialis biomass yield further increased to 1.5g/L, and astaxanthin composition accumulated to 29.7mg/L under relatively higher light intensity and salinity.

Astaxanthin-Producing Green Microalga Haematococcus pluvialis: From Single Cell to High Value Commercial Products

Many species of microalgae have been used as source of nutrient rich food, feed, and health promoting compounds. Among the commercially important microalgae, Haematococcus pluvialis is the richest source of natural astaxanthin which is considered as "super anti-oxidant." Natural astaxanthin produced by H. pluvialis has significantly greater antioxidant capacity than the synthetic one. Astaxanthin has important applications in the nutraceuticals, cosmetics, food, and aquaculture industries. It is now evident that, astaxanthin can significantly reduce free radicals and oxidative stress and help human body maintain a healthy state. With extraordinary potency and increase in demand, astaxanthin is one of the high-value microalgal products of the future.This comprehensive review summarizes the most important aspects of the biology, biochemical composition, biosynthesis, and astaxanthin accumulation in the cells of H. pluvialis and its wide range of applications for humans and animals. In this paper, important and recent developments ranging from cultivation, harvest and postharvest bio-processing technologies to metabolic control and genetic engineering are reviewed in detail, focusing on biomass and astaxanthin production from this biotechnologically important microalga. Simultaneously, critical bottlenecks and major challenges in commercial scale production; current and prospective global market of H. pluvialis derived astaxanthin are also presented in a critical manner. A new biorefinery concept for H. pluvialis has been also suggested to guide toward economically sustainable approach for microalgae cultivation and processing. This report could serve as a useful guide to present current status of knowledge in the field and highlight key areas for future development of H. pluvialis astaxanthin technology and its large scale commercial implementation.

The water footprint of biofilm cultivation of Haematococcus pluvialis is greatly decreased by using sealed narrow chambers combined with slow aeration rate

OBJECTIVE

Biofilm cultivation of microalgae has great potential in many applications. However, the water footprint for this method has not been well assessed. This issue was explored with the microalga Haematococcus pluvialis.

RESULTS

Only 1.25 l water is sufficient to support 1 m(2) biofilm cultivation surface. To produce 1 kg Haematococcus biomass and astaxanthin, the water footprint could be as low as 35.7 and 1440 l, respectively, by sealing the biofilm in a narrow chamber and supplying the proper amount of nutrients if the evaporation water loss was not considered. However, when loss of water by evaporation was considered, the water footprint was as low as 66.9 and 2700 l, respectively, if the chamber was aerated with CO2 at 0.014 vvm. These water footprint values are much lower than values obtained in other research work.

CONCLUSIONS

The water footprint of biofilm microalgal cultivation can be potentially reduced by more than 90% if the biofilm is sealed in a narrow chamber and supplied with a slow aeration of CO2 as carbon source.

The effective photoinduction of Haematococcus pluvialis for accumulating astaxanthin with attached cultivation

As the optimal source of astaxanthin, Haematococcus pluvialis was cultured for commercial production of astaxanthin through two continuous phases: cell growth and astaxanthin induction. In this study, the efficiency of an attached system for producing astaxanthin from H. pluvialis was investigated and compared to that of the suspended system (bubble column bioreactor) under various conditions. Results showed that this attached system is more suitable for photoinduction of H. pluvialis than the suspended bioreactor. Under the optimal conditions, the astaxanthin productivity of the attached system was 65.8 mg m(-2)d(-1) and 2.4-fold of that in the suspended system. This attached approach also offers other advantages over suspended systems, such as, producing astaxanthin under a wide range of light intensities and temperatures, saving water, ease to harvest cells, resisting contamination. Therefore, the attached approach can be considered an economical, environmentally friendly and highly-efficient technology for producing astaxanthin from H. pluvialis.

Attached cultivation of Haematococcus pluvialis for astaxanthin production

Haematococcus pluvialis, the best natural source for astaxanthin, was cultivated with an immobilized biofilm method, viz. "attached cultivation", which was high in photosynthetic efficiency. A practical operational protocol for this "attached cultivation" method was investigated by studying the effects of inoculum density, light intensity, nitrogen quantity as well as medium volume on growth and astaxanthin accumulation. Results indicated the optimized inoculum density and light intensity were 10 g m(-2) and 100 μmol m(-2)s(-1), respectively. The optimized nitrogen supply strategy was circulating ca. 30 L of BG-11 medium with initial sodium nitrate concentration of ca. 1.8mM for 1m(2) of cultivation surface. With this strategy, the maximum astaxanthin productivity reached ca. 160 mg m(-2)d(-1) which is much higher than many other indoor researches. Both of the red and green cells were found in the biofilm with red cells on the top.