Mass Cultivation Of Microalgae Research Articles

Mass Cultivation of Microalgae III: A Philosophical and Economic Exploration of Carbon Capture and Utilization

This article discusses an innovative carbon capture and utilization project from societal, economic, and ethical perspectives. UiT—The Arctic University of Norway and the ferrosilicon producer Finnfjord AS, both located in Northern Norway, collaborate to develop sustainably produced fish feed by cultivating microalgae (diatoms) that feed on CO2 from the factory fume. The microalgae biomass, when added to fish feed applied in the aquaculture industry, contributes nutrients that are essential to human and fish health. The project carries the potential to contribute to the operationalization of the Sustainable Development Goals. The present study is intended as a contribution to the literature focusing on CO2 utilization as a means of achieving a sustainable “green” transition in the industry. By viewing the utilization of CO2 through the lenses of biotechnology, a circular economy, ethics and philosophy, our research findings are relevant to sustainability scholars, industrial actors, and policy makers. It also presents future perspectives on how the aquaculture and manufacturing industries can contribute to the operationalizing of the Sustainable Development Goals in a rapidly evolving industrial environment that is now undergoing a paradigm shift.

Towards Sustainable Energy: Harnessing Microalgae Biofuels for a Greener Future

Bioenergy productions from microalgae have received wide attention recently and have a high potential to replace fossil fuels. Moreover, due to the high photosynthetic efficiency, microalgae mass cultivation and scale-up are believed to efficiently reduce the impact of greenhouse gas emissions. This review article explores the potential of microalgae as a reliable and sustainable source of bioenergy feedstock. The current review article contains an in-depth discussion of the various methods of producing energy using microalgae, viz. algal fuel cell (AFC), microbial fuel cell (MFC), bioethanol and biodiesel, and various other applications. This article discussed the different aspects of AFC and MFC, such as fuel cell configurations, reaction mechanisms at electrodes, reactor design factors affecting the efficiencies, and strategies to enhance the efficiencies. Moreover, microalgae cultivation, value-added compounds (pigments, polysaccharides, unsaturated fatty acids), liquid fuel production, limitations, the global scenario of microalgae biomass-based energy, and significant advancements in this field. In a nutshell, this review serves as a valuable resource for identifying, developing, and harnessing the potential of microalgae as a promising biofuel source.

Folate-mediated one-carbon metabolism as a potential antifungal target for the sustainable cultivation of microalga Haematococcus pluvialis

BackgroundMicroalgae are widely considered as multifunctional cell factories that are able to transform the photo-synthetically fixed CO2 to numerous high-value compounds, including lipids, carbohydrates, proteins and pigments. However, contamination of the algal mass culture with fungal parasites continues to threaten the production of algal biomass, which dramatically highlights the importance of developing effective measures to control the fungal infection. One viable solution is to identify potential metabolic pathways that are essential for fungal pathogenicity but are not obligate for algal growth, and to use inhibitors targeting such pathways to restrain the infection. However, such targets remain largely unknown, making it challenging to develop effective measures to mitigate the infection in algal mass culture.ResultsIn the present study, we conducted RNA-Seq analysis for the fungus Paraphysoderma sedebokerense, which can infect the astaxanthin-producing microalga Haematococcus pluvialis. It was found that many differentially expressed genes (DEGs) related to folate-mediated one-carbon metabolism (FOCM) were enriched in P. sedebokerense, which was assumed to produce metabolites required for the fungal parasitism. To verify this hypothesis, antifolate that hampered FOCM was applied to the culture systems. Results showed that when 20 ppm of the antifolate co-trimoxazole were added, the infection ratio decreased to ~ 10% after 9 days inoculation (for the control, the infection ratio was 100% after 5 days inoculation). Moreover, application of co-trimoxazole to H. pluvialis mono-culture showed no obvious differences in the biomass and pigment accumulation compared with the control, suggesting that this is a potentially algae-safe, fungi-targeted treatment.ConclusionsThis study demonstrated that applying antifolate to H. pluvialis culturing systems can abolish the infection of the fungus P. sedebokerense and the treatment shows no obvious disturbance to the algal culture, suggesting FOCM is a potential target for antifungal drug design in the microalgal mass culture industry.

Light and carbon limited photosynthesis of Chlorella sorokiniana

Carbon dioxide (CO2) and light are essential for high photosynthetic rates of microalgal cultures. Microalgal photosynthetic behavior at low CO2 concentrations has not been revealed yet at the same level of detail as leaf photosynthesis. In the present study, we investigated the short-term photosynthetic response of suspended Chlorella sorokiniana to limiting light intensity and CO2 concentration. We used a novel CO2-based photosynthesis monitor originating from leaf research but equipped with an aquatic chamber sparged with CO2 enriched air. Photosynthesis was measured by employing a steady-state CO2 mass balance over the chamber. Light and carbon response curves were determined under constant pH, temperature, dissolved oxygen, light intensity or dissolved carbon dioxide. We determined the volumetric mass transfer coefficient of the aquatic chamber to accurately convert gaseous CO2 partial pressure into aqueous CO2 concentration to evaluate the CO2 response measurements.Light response measurements on dilute algal cultures revealed a high photosynthetic capacity on a time scale of minutes which by far exceeded the average CO2 uptake on a time scale of hours (cell growth). Light response measurements with dense and fully absorbing cultures provided accurate insight into the response of microalgal mass culture to changing incident irradiance, including the efficiency of photosynthesis of the algal culture as a whole. CO2 response measurements demonstrated severe CO2 limitation at dissolved CO2 levels of <20 μM giving a concrete target for optimization of CO2 supply in large-scale cultivation systems. Measurements at a background of either 21 % O2 (air) or 2 % O2 indicated the existence of photorespiration in Chlorella. Moreover, the magnitude of photorespiration first increased and then decreased again while reduced dissolved CO2 levels, indicating the activation of a carbon concentrating mechanism at low CO2. Simultaneous measurement of the quantum yield of PSII linear electron transport (ϕPSII) and CO2 uptake revealed the transition of CO2 limited photosynthesis towards light-limited photosynthesis.

Biopolymer treatment of ammonium-rich industrial effluents for the mass cultivation of microalgae

Although wastewater reutilization for microalgae culturing can meet the dual goals of wastewater treatment and biomass production, some effluents with high contaminant concentrations are toxic to microalgae, necessitating pretreatment protocols to lower the toxicity before bioremediation. The present study aimed to bioremediate the industrial effluents of El Delta Co. for Fertilizers and Chemical Industries (Mansoura, Egypt), using sodium alginate as a pretreatment to enable reuse as a growth medium for microalgae culturing. Various water quality parameters signified the inferior state of the effluent with an ammonia-N concentration of 185.76 mg L−1. Toxicity investigations of the raw industrial effluents revealed toxicity to Chlorella sorokiniana, Scenedesmus vacuolatus and Pseudokirchneriella subcapitata. Effluent bioremediation was adopted using different concentrations of the biopolymer sodium alginate, and 1.0 g L−1 sodium alginate resulted in the highest removal of both ammonia-N and heavy metals. Chlorella sorokiniana and S. vacuolatus successfully grew in the 1.0 g L−1 alginate-treated effluent. Chlorella sorokiniana removed 87.8% of the ammonia-N, 75% of the copper, and 100% of the phosphorus. Scenedesmus vacuolatus consumed 85.7% of the ammonia-N, 66.7% of the copper, and 100% of the phosphorus. Adjusting the N:P mass ratio to 9.9 resulted in high tolerance of C. sorokiniana and S. vacuolatus to the effluent toxicity, with an EC50 > 100%. The 1.0 g L−1 sodium alginate-treated effluent stimulated C. sorokiniana and S. vacuolatus growth relative to the control. Additionally, C. sorokiniana and S. vacuolatus had the highest biomass production and protein content, reaching 1.42 and 0.74 g L−1 and 57.04 ± 0.04% and 52.19 ± 0.02%, respectively, in the treated effluent. Therefore, it was concluded that this bioremediation approach using the 1.0 g L−1 alginate pretreatment followed by microalgal cultivation (C. sorokiniana and S. vacuolatus) successfully treated the industrial effluent, representing a promising protocol for bioremediation practices.

High density cultivation and CO2 uptake by panel arrays of the macrophytic red alga Gracilaria vermiculophylla in a 100 L raceway pond

New approaches are needed for land-based cultivation of macrophytic red algae that reduce costly aeration requirements for biomass suspension and enable high-density cultivation. The goal of this study was to demonstrate the high-density cultivation of the carbohydrate-rich macrophytic red alga Gracilaria vermiculophylla on vertical arrays of panels deployed in an open channel raceway configuration similar to those developed for mass cultivation of microalgae. A clonal culture of G. vermiculophylla, consisting of branched, cylindrical thallus tissues of 8–10 cm length, was mechanically blended using a Waring blender into 2–3 cm fragments and then fluidically injected onto a 3 mm polypropylene mesh support. Immobilized G. vermiculophylla mesh panels were spaced 6.5 cm apart and aligned parallel to flowing seawater medium at nominal bulk velocity of 20 cm s−1 in a 100 L raceway pond of 20 cm liquid depth. This raceway was equipped with real-time measurement of CO2 concentration in the inlet and outlet gas for determination of CO2 uptake dynamics. Specific rates for CO2 uptake became saturated at 8000 ppm CO2. To match CO2 demand by the biomass under nutrient-replete conditions at 21 °C, the inlet gas CO2 was increased from 1000 to 4000 ppm (day 7–14), and then to 8000 ppm (day 14–23) at 0.010 L gas L−1 liquid min−1 gas flow. Over the 23 day cultivation, biomass on the panel increased by a factor of 48, with final biomass loading exceeding 10 kg FW m−2 panel area, and cumulative CO2 capture of 65%. The cumulative average areal productivity within the panel zone of the raceway exceeded 60 g AFDW m−2 day−1, and final biomass density nearing 7.2 g AFDW L−1 (47 g FW L−1) was achieved after 23 days. Overall, these outcomes demonstrate the potential for land-based raceway cultivation of clonal red macroalgae of present and future commercial significance.

Manipulation of fatty acid profile and nutritional quality of Chlorella vulgaris by supplementing with citrus peel fatty acid

Microalgae could be an excellent resource of functional and essential fatty acids. To achieve viable microalgal biomass production, mass cultivation of microalgae is required; however, the high cost of nutrients is the obstacle. An inexpensive and nutritious material is required to feed Chlorella vulgaris in the pharmaceutical and food sectors. Citrus peel waste with a valuable nutritional quality could be one of the promising and inexpensive candidates. In this study, the fatty acid extract from different citrus peels was used as the organic nutrient source for the cultivation of Chlorella. The proximate composition of bitter orange, sweet orange, grapefruit, and mandarin peels were determined, and their nutritional quality was evaluated. Total fatty acids from the citrus peel were prepared by acidic methanol hydrolysis and hexane extraction. Fourier transforms infrared (FT-IR) and gas chromatography–mass spectrometry (GC–MS) was used to analyze the fatty acid composition and nutrient composition. Fatty acids from the citrus peels were added to the Chlorella culture medium to study their influences on biomass, lipid production, fatty acid profile, and nutritional quality of Chlorella. The most predominant citrus peel fatty acids were linoleic, palmitic, oleic, linolenic, and stearic acids. The citrus peels contain polyunsaturated, saturated, and monounsaturated fatty acids. The most unsaturated fatty acids were omega-6, omega-3, omega-9, and omega-7. The citrus peel had acceptable atherogenicity, thrombogenicity, omega-6/omega-3, peroxidizability, hypocholesterolemic, and nutritive value indices. The major fatty acids of Chlorella were palmitic, linoleic, oleic, alpha-linolenic, gamma-linolenic, 4,7,10,13-hexadecatetraenoic, palmitoleic, 7,10-hexadecadienoic, 7,10,13-hexadecatrienoic, lauric and 5,8,11,14,17-eicosapentaenoic acids. Chlorella contains polyunsaturated, saturated, and monounsaturated fatty acids. The most unsaturated fatty acids contain omega-6, omega-3, omega-9, and omega-7. Chlorella had acceptable atherogenicity, thrombogenicity, omega-6/omega-3, hypocholesterolemic, peroxidizability, and nutritive value indices. Supplementation of Chlorella with citrus peels fatty acid increases total biomass, lipid content, and nutritional quality of Chlorella. The present research shows that citrus peels have good nutritional quality and could be used for the inexpensive cultivation of Chlorella biomass with potential utility for food application.

Malaysian Virgin Soil Extracts as Natural Growth Enhancer for Targeted Green Microalgae Species

The microalgae-based industries are trending upwards, particularly as the feed ingredient for aquaculture. Therefore, a sustainable and reasonably priced source of nutrients to support the mass cultivation of microalgae is in great demand. The present study explored the feasibility of using extracts from virgin soil as natural growth-promoting nutrients for the cultivation of Nannochloropsis oculata, Nannochloropsis oceanica, and Chlorella sorokiniana. The extracts were obtained from Bera Lake Forest using five different treatment methods. The greatest retrieval of dissolved organic carbon, total dissolved nitrogen, and total dissolved phosphorus were observed with the autoclave treatment method at 121 °C twice, yielding a respective concentration of 336.56 mg/L, 13.40 mg/L, and 0.14 mg/L, respectively. The highest growth was recorded with Nannochloropsis oculata resulting in an optical density of 0.488 ± 0.009 (×103 cell mL−1), exhibiting 43% and 44% enhanced growth in comparison to Nannochloropsis oceanica and Chlorella sorokiniana, respectively. The specific growth rate (0.114 a ± 0.007 d−1) was the highest for Nannochloropsis oculata when the 24 h-extraction method was used, whereas the utilization of the autoclave 121 °C twice treatment method contributed to the highest specific growth of Nannochloropsis ocenica (0.069 a ± 0.003 d−1) and Chlorella sorokiniana (0.080 a ± 0.001 d−1). Collectively, these findings suggested that the addition of soil extracts which is sustainable and inexpensive promoted the growth of microalgae compared to the control system. A further study investigating the optimum culture conditions for enhanced microalgae growth will be carried out for the mass production of microalgae biomass.

Mass Cultivation of Microalgae: I. Experiences with Vertical Column Airlift Photobioreactors, Diatoms and CO2 Sequestration

From 2015 to 2021, we optimized mass cultivation of diatoms in our own developed vertical column airlift photobioreactors using natural and artificial light (LEDs). The project took place at the ferrosilicon producer Finnfjord AS in North Norway as a joint venture with UiT—The Arctic University of Norway. Small (0.1–6–14 m3) reactors were used for initial experiments and to produce inoculum cultures while upscaling experiments took place in a 300 m3 reactor. We here argue that species cultivated in reactors should be large since biovolume specific self-shadowing of light can be lower for large vs. small cells. The highest production, 1.28 cm3 L−1 biovolume (0.09–0.31 g DW day−1), was obtained with continuous culture at ca. 19% light utilization efficiency and 34% CO2 uptake. We cultivated 4–6 months without microbial contamination or biofouling, and this we argue was due to a natural antifouling (anti-biofilm) agent in the algae. In terms of protein quality all essential amino acids were present, and the composition and digestibility of the fatty acids were as required for feed ingredients. Lipid content was ca. 20% of ash-free DW with high EPA levels, and omega-3 and amino acid content increased when factory fume was added. The content of heavy metals in algae cultivated with fume was well within the accepted safety limits. Organic pollutants (e.g., dioxins and PCBs) were below the limits required by the European Union food safety regulations, and bioprospecting revealed several promising findings.

Bright as day and dark as night: light-dependant energy for lipid biosynthesis and production in microalgae.

Microalgae are photosynthetic organisms functioning as the green bio-factories for various pharmaceutical and biofuel products. To date, numerous attempts have been carried out to manipulate culture conditions to maximize the production of the desired metabolites. Because light is the energy source of microalgae for their growth and metabolites biosynthesis, it has been one of the most investigated variables emphasized on the deep understanding of how microalgae respond towards light changes as an external stimulus. This review discusses the effects of different light sources, light intensities, light wavelengths and length of photoperiod on various microalgae species, especially in terms of biomass and lipid productivity. Additionally, the relationship between photoregulation processes and lipid productivity of microalgae are also deliberated. The current available approaches of microalgae mass cultivation, including different types of open and closed systems are recapitulated with the intention to highlight the significant insights for the design of future photoreactors.

Productivity analysis in tubular photobioreactors using a dynamic photosynthesis model coupled to computational fluid dynamics particle tracking

Tubular photobioreactors (TPBRs) are closed devices used for the mass culture of microalgae. TPBRs are supposed to be well-mixed, but the influence of their specific fluid dynamics in photosynthesis efficiency has never been studied in detail. Here, we use Computational Fluid Dynamics (CFD) coupled to a dynamic photosynthesis model to analyze the efficiency of the photosynthetic response in the loop of TPBRs of different sizes (14, 24, 44, 64, and 84 mm) and circulation velocities (0.4 to 1 m s−1). The results show that only the smallest diameters cause enough radial mixing for a photosynthesis-enhancing light regime (integration factor Γ = 0.199 for D = 14 mm and v = 1 m s−1) while high circulation velocities in larger diameters (up to 1 m s−1) increase operating costs but do not enhance photosynthetic productivity. It is also shown the relevance of the characteristic frequency of the strain (β), which is crucial for high productivity.

Fish farm effluent as a nutrient source for algae biomass cultivation

One of the challenges of microalgae biotechnology is the cost of growth media nutrients, with microalgae consuming enormous quantities of fertilisers, more than other oil crops. The traditional use of synthetic fertilisers in mass cultivation of microalgae is associated with rising prices of crude oil and competition from traditional agriculture. The fact that fish farm wastewater (FFW) nutrients are released in the form preferred by microalgae (NH3 for nitrogen and PO4-3 for phosphate), and the ability of microalgae to use nitrogen from different sources, can be exploited by using fish farm effluent rich in nutrients (nitrogen and phosphorus) in the cultivation of cheaper microalgae biomass for production of biodiesel. The cultivation of algae biomass in FFW will also serve as wastewater treatment. We reviewed the benefits and potential of fish effluent in algae cultivation for the production of biodiesel. Microalgae can utilise nutrients in FFW for different applications desirable for the production of biomass, including the accumulation of lipids, and produce a fuel with desirable properties. Also, treating wastewater and reducing demand for fresh water are advantageous. The high lipid content and comparable biodiesel properties of Chlorella sorokiniana and Scenedesmus obliquus make both species viable for FFW cultivation for biodiesel production.&#x0D; Significance:&#x0D; &#x0D; The cost associated with microalgae growth media nutrients can be saved by using fish farm wastewater, which contains nutrients (nitrogen and phosphorus) suitable for microalgae cultivation.&#x0D; Fish farm wastewater has lower nutrient concentrations when compared to standard growth media suitable for higher lipid accumulation.&#x0D; Microalgae used as a biodiesel feedstock, cultivated in fish farm wastewater, has added benefits, including wastewater treatment.&#x0D;

Variables Governing Photosynthesis and Growth in Microalgae Mass Cultures

Since the 1950s, microalgae have been grown commercially in man-made cultivation units and used for biomass production as a source of food and feed supplements, pharmaceuticals, cosmetics and lately biofuels, as well as a means for wastewater treatment and mitigation of atmospheric CO2 build-up. In this work, photosynthesis and growth affecting variables—light intensity, pH, CO2/O2 exchange, nutrient supply, culture turbulence, light/dark cell cycling, biomass density and culture depth (light path)—are reviewed as concerns in microalgae mass cultures. Various photosynthesis monitoring techniques were employed to study photosynthetic performance to optimize the growth of microalgae strains in outdoor cultivation units. The most operative and reliable techniques appeared to be fast-response ones based on chlorophyll fluorescence and oxygen production monitoring, which provide analogous results.

Interaction between the cell walls of microalgal host and fungal carbohydrate-activate enzymes is essential for the pathogenic parasitism process.

Fungi can parasitize microalgae, exerting profound impacts on both the aquatic ecosystems and microalgal mass cultures. In this study, the unicellular green alga Haematococcus pluvialis and the blastocladialean fungus Paraphysoderma sedebokerense were used as a model system to address the mechanisms underlying the fungal parasitism on the algal host. High-throughput metabolic assay indicated that P. sedebokerense can utilize several carbon sources with a preference for mannose, glucose and their oligosaccharides, which was compatible with the profile of the host algal cell walls enriched with glucan and mannan. The results of dual transcriptomics analysis suggested that P. sedebokerense can upregulate a large number of putative carbohydrate-activate enzymes (CAZymes) encoding genes, including those coding for the endo-1,4-β-glucanase and endo-1,4-β-mannanase during the infection process. The cell walls of H. pluvialis can be decomposed by both P. sedebokerense and commercial CAZymes (e.g. cellulase and endo-1,4-β-mannanase) to produce mannooligomers, while several putative parasitism-related genes of P. sedebokerense can be in turn upregulated by mannooligomers. In addition, the parasitism can be blocked by interfering the selected CAZymes including glucanase, mannanase and lysozyme with the specific inhibitors, which provided a framework for screening suitable compounds for pathogen mitigation in algal mass culture.

Effect of commercial NPK fertilizer on growth and biomass of Navicula sp. and Nannochloropsis sp

Microalgae as a source of biodiesel precursor are promising by pointing out several advantages of its cultivation, such as able to be cultivated in non-arable land, high growth rate with high biomass yield, high lipid content, and renewable. Mass cultivation of microalgae requires large amount of nutrients which makes it economically impractical. To overcome this problem, an alternative medium which contains cheaper nutrients sources should be addressed. In this research, the growth and biomass productivity of Navicula sp. and Nannochloropsis sp. were compared in the commonly used F/2 medium and modified medium containing commercial NPK fertilizer. The results indicated that Navicula sp. and Nannochloropsis sp. can thrive in modified F/2-NPK medium under continuous illumination, while NPK-only medium didn’t show any significant increase in growth and biomass accumulation for both strains compared to initial cell inoculation. Cell optical density at 750 nm and biomass dry weight of 80% F/2 and 50% F/2 medium were comparable to that in F/2 control medium for both strains, indicating that Navicula sp. and Nannochloropsis sp. have a similar requirement for nutrients types. Furthermore, higher specific growth rate of Nannochloropsis sp. than Navicula sp. seen in both modified medium showed its favorable condition for growth.

Analysis of productivity in raceway photobioreactor using computational fluid dynamics particle tracking coupled to a dynamic photosynthesis model

Raceway photobioreactors (RWPs) are the most common and affordable device for the mass culture of microalgae but due to geometry and the requirement of low input power, its photosynthetic performance is low. The fluid dynamics of RWPs have been studied for information such as energy dissipation and shear rate, CFD has never been used to analyze photosynthesis efficiency by coupling dynamic photosynthesis models with microalgae trajectories. In this work, we investigate by CFD simulation the effect of circulation velocities between 0.2 and 0.8 m s-1in a 0.15 m−1 deep RWPs under standard outdoor conditions to shows that in all circumstances the RWP from the point o view of photosynthesis operates as a perfectly segregated device (no mixing) and that the average growth rate is the result of the integration of the local growth rates at different depths (integration factor Γ = 0).

Improvement of Photoautotrophic Algal Biomass Production after Interrupted CO2 Supply by Urea and KH2PO4 Injection

Microalgae-derived biomass is currently considered a sustainable feedstock for making biofuels, including biodiesel and direct combustion fuel. The photoautotrophic cultivation of microalgae using flue gas from power plants has been continuously investigated to improve the economic feasibility of microalgae processes. The utilization of waste CO2 from power plants is advantageous in reducing carbon footprints and the cost of carbon sources. Nonetheless, the sudden interruption of CO2 supply during microalgal cultivation leads to a severe reduction in biomass productivity. Herein, chemical fertilizers including urea and KH2PO4 were added to the culture medium when CO2 supply was halted. Urea (5 mM) and KH2PO4 (5 mM) were present in the culture medium in the form of CO2/NH4+ and K+/H2PO4−, respectively, preventing cell growth inhibition. The culture with urea and KH2PO4 supplementation exhibited 10.02-fold higher and 7.28-fold higher biomass and lipid productivity, respectively, compared to the culture with ambient CO2 supply due to the maintenance of a stable pH and dissolved inorganic carbon in the medium. In the mass cultivation of microalgae using flue gas from coal-fired power plants, urea and KH2PO4 were supplied while the flue gas supply was shut off. Consequently, the microalgae were grown successfully without cell death.

Resource recovery through bioremediation of wastewaters and waste carbon by microalgae: a circular bioeconomy approach.

Microalgal biomass-based biofuels are a promising alternative to fossil fuels. Microalgal biofuels' major obstacles are the water and carbon sources for their cultivation and biomass harvest from the liquid medium. To date, an economically viable process is not available for algal based biofuels. The circular bioeconomy is an attractive concept for reuse, reduce, and recycle resources. The recovery of nutrients from waste and effluents by microalgae could significantly impact the escalating demands of energy and nutraceutical source to the growing population. Wastewaters from different sources are enriched with nutrients and carbon, and these resources can be recovered and utilized for the circular bioeconomy approach. However, the utilization of wastewaters and waste seems to be an essential strategy for mass cultivation of microalgae to minimizing freshwater consumption, carbon, nutrients cost, nitrogen, phosphorus removal, and other pollutants loads from wastewater and generating sustainable biomass for value addition for either biofuels or other chemicals. Hence, the amalgamation of wastewater treatment with the mass cultivation of microalgae improved the conventional treatment process and environmental impacts. This review provides complete information on the latest progress and developments of microalgae as potential biocatalyst for the remediation of wastewaters and waste carbon to recover resources through biomass with metabolites for various industrial applications and large-scale cultivation in wastewaters, and future perspectives are discussed.

Productivity Analysis in Tubular Photobioreactors Using a Dynamic Photosynthesis Model Coupled to Computational Fluid Dynamics Particle Tracking

Tubular photobioreactors (TPBRs) are closed devices widely used for the mass culture of microalgae. TPBRs are supposed to be well-mixed, high-efficiency devices, but the influence of their fluid dynamics in photosynthesis has never been studied in detail. We use CFD coupled to a dynamic photosynthesis model to analyze the efficiency of the photosynthetic in the loop of TPBRs of different sizes (14, 24, 44, 64, and 84 mm) and circulation velocities (0.4 to 1 m s-1 ). The results show that only the smallest diameters cause enough radial mixing for a photosynthesis-enhancing light regime (integration factor Γ =0.199 for D=14 mm and v=1 m s-1 ) while high circulation velocities in larger diameters (up to 1 m s-1) do not enhance photosynthetic productivity. It is also explained how the characteristic frequency of the strain ( β ) is crucial for high productivity and that there is room for improvement.

Computerized Optimization of Microalgal Photosynthesis and Growth

ABSTRACT We describe the use of a novel, computerized, multiple outdoor microalgal growth system to achieve conditions maximizing high photosynthesis and biomass production rates. We applied this system to determine the effects of multiple environmental and culture parameters such as light, temperature, pH, and mode of mixing and CO2 supply, and their combinations on the rates of algal photosynthesis, respiration, and growth. We continuously monitored the following parameters: pH, temperature, dissolved oxygen, and light, concomitantly with algal growth and biomass production rates. In particular, we likewise monitored and determined the dramatic effects of CO2 supply, mixing by paddle wheel or bubbling air modes, on algal biomass production. The isolated and synergistic effects of each factor and operation regime were measured and are discussed. We found that the diel range of maxima to minimal pH and oxygen levels strongly correlated with container performance, and were controllable by CO2 supply and mixing regime. We conclude that mixing by bubble aeration was the most important growth-rate controlling factor. It limited the build-up of high oxygen and pH levels that reduce photosynthesis that were measured by O2 evolution. In this study, OD measurements calibrated with biomass concentrations were used to calculate growth rates and estimate the photosynthetic rates of the microalgae. The potential of algae as a source of food, feed, biofuel, and fine chemicals has been widely recognized, but their competitiveness depends on areal yields. Our results allow us to recommend culture parameters that increase areal biomass yields, regardless of the algal species, thereby bringing microalgal mass culture closer to economic viability.