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Microalgae-based CO2 capture has potential as an industrial-scale solution to climate change challenges while also amassing usable microalgae biomass. Computational fluid dynamics (CFD) can optimize CO2 extraction in microalgae growing systems, especially when paired with phytohormone-regulated growth. This paper examines the use of CFD to predict fluid flow, nutrient distribution, light intensity, and mass transfer in microalgae-based systems, which are crucial for improving photosynthetic efficiency and fixing CO2. The focus is on how phytohormones, such as auxins and cytokinin, influence microalgal growth and their subsequent involvement in increasing carbon sequestration. Furthermore, this review discusses CFD applications in reactor design, where fluid dynamics and biological kinetics interact to increase biomass yield. The focus on scaling up and transitioning from laboratory to industrial application with the possible integration of computational fluid dynamics with experiment data to enhance simulation precision is addressed. The assessment demonstrates CFD's potential as an important tool for sustainable CO2 fixation. [ABSTRACT FROM AUTHOR]

Growing population, industrialisation, and demand for resources put pressure on the delicate balance of the planet's ecosystems. From alternative sources of energy, healthier foods, cleaner water, and an overall more sustainable economy, the integration of microalgae in various industries, that otherwise are based on practices that hurt the environment, could be a successful solution. To reach that goal, further research is required on the complex relationship between microalgae and growth parameters (temperature, light intensity and spectrum, nutrient distribution, inhibiting factors, and so on). The scientific community successfully used microalgae to produce healthier foods, pigments, biofuel, animal fodder, methods for sequestering heavy metals, toxic compounds from water, and much more. In this review article, we approach the use of microalgae in municipal wastewater treatment, mainly for using nitrogen and phosphorous present in water as nutrients. Data were collected from articles published in the last 7 years (2018–2024). The results show that microalgae are very efficient at using N and P compounds from wastewater, as well as carbon, converting them in high-value substances (proteins, lipids, carbohydrates, etc.) with further applications in multiple industries. [ABSTRACT FROM AUTHOR]

The treatment of wastewater using microalgae is regarded as a green and potential technology. However, its engineering application has been largely hindered because of the limitation of microalgae separation and harvesting. Therefore, immobilization technology has been widely used to embed microalgae for wastewater treatment. In this paper, sodium alginate (SA) and polyvinyl alcohol (PVA) as the common immobilized carriers were used to immobilize ankistrodesmus falcatus for simulated slaughtering wastewater (SSW) treatment. The experimental results of the mass transfer and adsorption of immobilized carriers were found to show that the mass transfer of SA-SiO2 gel balls (SS-GB) was better than PVA-SA gel balls (PS-GB) and that the adsorption of PS-GB was better than SS-GB. When immobilizing microalgae with the two kinds of carriers, it was found that SA-SiO2 microalgal spheres (SS-MS) were better than PVA-SA microalgal spheres (PS-MS) for the maintenance of microalgal cell activity and that PS-MS were better than SS-MS for the resistance to biodegradation. This is because the carrier of PS-MS had a thick shell and dense structure, while the carrier of SS-MS had a thin shell and loose structure. The results of SSW treatment by PS-MS and SS-MS were found to show that the total phosphorus (TP) removal rates of PS-MS and SS-MS were 90.31% and 86.60%, respectively. This indicates that the TP removal effect of PS-MS was superior to that of SS-MS. The adsorption kinetics simulation showed that the adsorption of TP onto PS-GB was controlled by chemisorption and that the adsorption of TP onto SS-GB was controlled by physical adsorption. The chemical oxygen demand (COD) and ammonium nitrogen (NH4+-N) removal of PS-MS were 9.30% and 10.70%, respectively, and the COD and NH4+-N removal of SS-MS were 54.60% and 62.08%, respectively. This indicates that the COD and NH4+-N removal effect of SS-MS were superior to PS-MS. This is the result of the combined action of the degradation by microalgal cells and adsorption by the carrier. [ABSTRACT FROM AUTHOR]

A comprehensive numerical model is developed to simulate the growth of microalgae under light/dark cycling conditions. The purpose of this study is to predict the growth rate of Chlorella vulgaris cultivated in photobioreactors (PBRs) in order to improve the light conditions for microalgae and enhance the photosynthetic efficiency. Computational fluid dynamics (CFD) is used to simulate its internal hydrodynamic behaviors. The Lagrangian method is employed to track the movement of microalgae cells. The radiative transfer equation (RTE) is used to obtain light intensity distribution. The combination of light radiation field and microalgae cell motions is used to construct the light history and they are integrated into the model of the photosynthetic units (PSU) to calculate the microalgae growth rate. The numerical results demonstrate that enhanced light/dark cycling frequency with ordered mixing can promote efficient microalgae cultivation. The effect of the vortex flow field generated by the baffles in an air-lift PBR is analyzed for increasing microalgae growth rate. When using the 1:1 baffle spacing, the biomass production of microalgae is increased by 41.8% compared to the original PBR. [ABSTRACT FROM AUTHOR]

Based on the flow modeling and operational experience of the previous cylindrical loop reactor, we designed a sheet reactor combined with a loop reactor. The design with a cylindrical cross-section was applied to an equivalent cross-section (sheet) of several squares arranged next to each other. In accordance with the sedimentation processes experienced in the outlet branch, we created an algae trap, thereby reducing the flow to the level necessary for sedimentation. With this, I would like to achieve the already experienced, nearly 10-fold increase in algae concentration compared to the one in the mainstream.

Abstract The paper deals with the application of microalgae in building’s façade, regard to the broader project comprising the aspects of the environmental comfort of academic spaces and the energy consumption with on-grid photovoltaic generation, as well as the investigation of alternatives for the improvement of the performance of the building envelopes. Thus, its main objective is the application of interdisciplinary concepts involving Architecture and Biotechnology, as known by Black Ecologies, referring to an investigative interest to explore a new approach of nature, not only related to architectural space, but an emergent environmental focus. This relationship is performed by using photobioreactors with microalgae, installed on the façades of buildings for educational use. The present work presents the methodological outline of the research, based on literature review and case studies; complementary experimental methodologies are also presented to contextualize the subject and its application and feasibility. The current state of art showed an emergent approach in terms of international level, but in the Brazilian context any further research was identified yet. In addition to thermal and energy performance, the strategies will allow the process of sequestration of carbon dioxide and other GHG (greenhouse gases) that impacts on the process of climate change and can contribute to reach the sustainable development. This subject coincides with the discussions of the 2050 scenarios and emission reduction, which were faced at the recent COP-27 and its connections with an integrative way to contribute to the United Nations Sustainable Development Goals.

Background Microalgae-based products offer a sustainable solution for food, fuel, and agricultural inputs, presenting environmental benefits and economic opportunities. A comprehensive assessment is needed to understand their potential in supporting sustainability goals, considering the complex interplay between production methods, energy sources, and environmental impacts. Methods This study evaluated the environmental impacts of three microalgae-derived products – biodiesel, fish feed, and biofertilizer – through a comprehensive life cycle assessment. Nine scenarios were explored comparing three electricity profiles (current Thai mix, 50% renewable/50% current mix hybrid, 100% renewable) across the three products. The assessment evaluated environmental impacts and potential economic benefits of transitioning to these microalgae-based alternatives. Results and discussion All products demonstrated potential for significant environmental benefits under increased renewable energy scenarios. Fish feed consistently exhibited the lowest environmental impacts across all categories examined, showing substantial improvements with increased renewable energy use. With an annual demand of 0.4 million tonnes, fish feed could generate USD 560 million in revenue and reduce CO 2 emissions by 1.1 million tonnes. Fulfilling the projected biodiesel demand of 4,015 million liters per year through microalgae production could yield approximately USD 3.5 billion in revenue and reduce CO 2 emissions by 30 million tonnes compared to conventional fossil-based diesel. Additionally, algal biofertilizer production could meet a 5 million tonnes annual demand, offering USD 2 billion in revenue while reducing CO 2 emissions by 6 million tonnes yearly. Collectively, these products could offset 37 million tonnes of CO 2, representing about 14% of Thailand’s total CO 2 emissions, contributing significantly to the country’s Nationally Determined Contribution (NDC) target of 20-30% greenhouse gas emissions reduction. Conclusion Transitioning to microalgae-based products could transform the aquaculture, energy, and agricultural sectors, potentially supporting the national climate change mitigation goals, if implemented.

Reducing greenhouse gas emissions remains a topical issue in fundamental and applied scientific research, including in terms of analyzing developed and applied CO2 capture technologies. The main focus is on methods of carbon dioxide burial in stable geological formations, absorption, filtration, etc. The absorption of carbon dioxide during photosynthesis is usually associated with terrestrial biota, although aquatic organisms have a higher productivity of photosynthesis. The use of microalgae as photosynthetic agents is determined mainly by their value for obtaining high-quality food and feed additives, pharmaceutical products, and biofuels, but it is important to consider their effectiveness in the associated absorption of CO2. When producing products with a long carbon sequestration period, this method can be included in the list of effective carbon capture technologies. To estimate the specific energy costs for CO2 absorption, proven cultivation methods were considered: open-plane cultivators (microalgae Arthrospira platensis, growth rate from 20 to 40 g/m2 per day on dry matter) and cylindrical closed photobioreactors (microalgae Chlorella vulgaris, growth rate 0.7 g/dm3 per day in dry matter). Based on experimental results of microalgae cultivation under conditions of elevated CO2 concentrations, it is shown that specific energy consumption is in the range from 27 to 768 GJ/t when cultivating A. platensis microalgae and from 59 to 373 GJ/t in microalgae cultivation of C. vulgaris. The greatest energy costs are required for heating and lighting microalgae plantations as well as for separating biomass from the culture liquid for microalgae with small cell sizes. Specific energy consumption can be reduced by maximizing the use of natural light and waste heat from industrial facilities and optimizing biomass collection systems. [ABSTRACT FROM AUTHOR]

Certain secondary carotenoids, such as astaxanthin and canthaxanthin, are of growing economic interest in the fields of human nutrition, food, health and cosmetics, as well as feed and aquaculture, particularly due to their numerous biological activities, such as their remarkable antioxidant properties. The present study was devoted to assessing, in a photobioreactor, the feasibility of cultivating newly isolated Dysmorphococcus strains from the biodiversity of Reunion Island for the production of these valuable xanthophylls. The results showed that all these strains were capable of producing and accumulating canthaxanthin and astaxanthin in response to environmental stresses. Among them, a strain which presented interesting morphological, genetic and biochemical properties as compared to the other Dysmorphococcus strains was further cultivated in a 3 L benchtop photobioreactor and was found to produce maximum carotenoid-rich biomass concentrations and productivities of about 4 g L−1 dw and 0.055 g L−1 d−1 dw, respectively. We also found that the biomass contained up to 1.2 mg g−1 dw of canthaxanthin and 0.7 mg g−1 dw of different forms of astaxanthin, mainly astaxanthin monoesters. The productivity of these carotenoids was found to be lower than those observed for other microalgal species previously reported, and we suggested that further optimizations with respect to the cultivation and the carotenogenesis induction processes are needed to improve productivities and to make this locally isolated Dysmorphococcus strain useful for future commercial production of natural canthaxanthin and astaxanthin. [ABSTRACT FROM AUTHOR]

This study investigates the effects of continuous and short-term direct current (DC) stimulation on the growth and nutrient composition of Nitzschia closterium f. minutissima, a marine diatom with significant potential in aquaculture feed. We explored the optimal conditions of DC stimulation by applying both short-term and continuous treatments at varying voltages (0 V, 1 V, 3 V, 5 V, 10 V for short-term; 0 V, 0.05 V, 0.5 V, 1 V for continuous). The results demonstrated that short-term DC stimulation significantly enhanced cell density and lipid accumulation, with maximum cell density increasing by 13.14% under 1 V stimulation compared to the control. However, continuous stimulation was less effective and showed growth inhibition in several cases. Nutrient analysis revealed that short-term stimulation, particularly at 3 V, led to a 67.66% increase in lipid content, while moderate continuous stimulation (0.5 V) showed a 39.47% increase in biomass dry weight. These findings suggest that short-term DC stimulation is a promising approach to optimize microalgal growth and nutrient accumulation for large-scale aquaculture production. [ABSTRACT FROM AUTHOR]

Animal production wastes and effluents are among the most highly produced wastewaters, containing high concentrations of nutrients and microbes that could lead to contamination and eutrophication of water sources. Large-scale enterprises in cattle breeding face challenges in storing and removing a substantial volume of liquid manure (LM). Therefore, the management of LM becomes an economic burden for producers. In this case, the question arises as to whether a more economical and sustainable treatment method can be employed by utilizing LM from animal production in algal growth, which has emerged as a renewable raw material source in recent years. In this study, a microalgae Ankistrodesmus sp. was employed for nutrient removal from dairy LM at concentrations of 10%, 20%, and 30% over 35 days. The total nitrogen reduction rates in the reactors with 10%, 20%, and 30% LM were 72.8%, 69.1%, and 71%, respectively, while the total phosphorus reduction rates were 65.7%, 52.6%, and 31.5%, respectively. Overall, integrating microalgae cultivation into wastewater treatment processes shows promise for nutrient removal and biomass production. By leveraging the nutrient-rich characteristics of LM from cattle farming, microalgae provide a sustainable and effective approach to reduce environmental pollution and enhance resource recovery in agriculture. Further research and development in this field are essential for optimizing treatment methods and improving the environmental sustainability of livestock operations. [ABSTRACT FROM AUTHOR]

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While global population growth drives increased production efficiency in animal agriculture, there is a growing demand for environmentally friendly practices, particularly in reducing air pollutant emissions from concentrated animal feeding operations. This study explores the potential of cultivating microalgae in photobioreactors (PBRs) as an eco-friendly and cost-effective approach to mitigate NH3 and CO2 emissions from pig barns. Unlike traditional physicochemical mitigation systems, microalgae offer a renewable solution by converting pollutants into valuable biomass. The research focused on Scenedesmus dimorphus growth under typical NH3 and CO2 concentrations found in the indoor air of pig barns. Four NH3 (0, 12, 25, and 50 ppm) and four CO2 concentrations (350, 1200, 2350, and 3500 ppm) were tested using photobioreactors. Results showed a maximum specific growth rate of 0.83 d−1 with 12 ppm NH3 and 3500 ppm CO2. The dry biomass concentration was significantly higher (1.16 ± 0.08 g L−1; p < 0.01) at 25 ppm NH3 and 2350 ppm CO2 than other test conditions. S. dimorphus demonstrated the peak NH3 and CO2 fixation rates (23.8 ± 2.26 mg NH3 L−1 d−1 and 432.24 ± 41.09 mg CO2 L−1 d−1) at 25 ppm NH3 and 2350 ppm CO2. These findings support the feasibility of using algae to effectively remove air pollutants in pig barns, thereby improving indoor air quality. [ABSTRACT FROM AUTHOR]

The ocean is the largest carbon reservoir on Earth and serves as a significant sink for atmospheric CO2. Of the known mechanisms for ocean CO2 absorption, the biological pump is considered the most important for carbon sequestration due to its economic and efficient advantages. Using microalgae to capture CO2 has several advantages, including a short cultivation period, high carbon sequestration efficiency, and a low investment cost. This article provides an overview of the methods used to screen algae species in microalgal carbon sequestration technology, as well as the expected effects of carbon sequestration. This article analyzes the appropriate cultivation conditions for algae, including the type of photobioreactor, light intensity, CO2 concentration, and nutritional requirements. The article contends that achieving accurate control of multiple environmental factors during microalgal cultivation and optimizing the internal structure of the cultivation device are key components for improving microalgal biomass production and CO2 fixation ability. The results of life-cycle assessments (LCA) indicate that the production of high-value compounds using microalgae is capable of achieving negative carbon emissions. Finally, this paper evaluates the practicality and economic feasibility of microalgae carbon sequestration and also discusses the future challenges and prospects for the development of this technology. [ABSTRACT FROM AUTHOR]

Microalgae and cyanobacteria are photosynthetic microorganisms with significant biotechnological potential for the production of bioactive compounds, making them a promising resource for diverse industrial applications. This study presents the development and validation of a modular, droplet-based microfluidic photobioreactor (µPBR) designed for high-throughput screening and cultivation under controlled light conditions. The µPBR, based on polytetrafluoroethylene (PTFE) tubing and a 4-channel LED illumination system, enables precise modulation of light intensity, wavelength, and photoperiod, facilitating dose–response experiments. Synechococcus elongatus UTEX 2973 and Chlorella vulgaris were used to demonstrate the system's capacity to support photosynthetic growth under various conditions. The results indicate that continuous illumination, particularly under blue and mixed blue-red light, promotes higher autofluorescence and chlorophyll a content in cyanobacteria Synechococcus elongatus UTEX2973, while Chlorella vulgaris achieved optimal growth under a 16:8 light-dark cycle with moderate light intensity. This µPBR offers not only a flexible, scalable platform for optimizing growth parameters but also allows for the investigation of highly resolved dose response screenings of environmental stressors such as salinity. The presented findings highlight its potential for advancing microalgal biotechnology research and applications. [ABSTRACT FROM AUTHOR]

The paper deals with the application of microalgae in building's façade, regard to the broader project comprising the aspects of the environmental comfort of academic spaces and the energy consumption with on-grid photovoltaic generation, as well as the investigation of alternatives for the improvement of the performance of the building envelopes. Thus, its main objective is the application of interdisciplinary concepts involving Architecture and Biotechnology, as known by Black Ecologies, referring to an investigative interest to explore a new approach of nature, not only related to architectural space, but an emergent environmental focus. This relationship is performed by using photobioreactors with microalgae, installed on the façades of buildings for educational use. The present work presents the methodological outline of the research, based on literature review and case studies; complementary experimental methodologies are also presented to contextualize the subject and its application and feasibility. The current state of art showed an emergent approach in terms of international level, but in the Brazilian context any further research was identified yet. In addition to thermal and energy performance, the strategies will allow the process of sequestration of carbon dioxide and other GHG (greenhouse gases) that impacts on the process of climate change and can contribute to reach the sustainable development. This subject coincides with the discussions of the 2050 scenarios and emission reduction, which were faced at the recent COP-27 and its connections with an integrative way to contribute to the United Nations Sustainable Development Goals. [ABSTRACT FROM AUTHOR]

This methodology paper introduces an illuminated culture flask-based 3D-printed bioreactor system (FlaskLED) based on Arduino, Grove ecosystem and LED sticks. The Arduino microcontroller allows extensibility and future upgrades via programming and other modifications. We provide the 3D printer files, video presentation of assembly instructions and a detailed description of the INO code and wiring scheme. The INO code presented can be used to produce different light colors and patterns of varying intensity and durations (intermittent/flashing/pulsing light). The system was validated by examining the toxicity of Au3+ ions on Phaeodactylum tricornutum growth. The capabilities of the system offer unique applications for laboratory and industrial research. Our aim is to provide a low-cost and open-source tool to promote and improve cultivation of microalgae and other photosynthetic organisms under different laboratory and experimental setups. [ABSTRACT FROM AUTHOR]

To improve the durability of the photobioreactor antibiofouling surface for microalgal cultivation, a series of photoreactive poly(2,2,2-trifluoroethyl methacrylate) (PTFEMA) were successfully synthesized and used to modify ethylene-vinyl acetate (EVA) films by a surface coating and UV light grafting method. Fourier transform infrared (FT-IR) spectra, X-ray photoelectron spectroscopy analysis (XPS) and fluorescence microscopy results indicated that PTFEMA were fixed successfully onto the EVA film surface through a covalent bond. During the microalgal adhesion assay, the number of EVA-PTFEMA film-adhered microalgae was 41.4% lower than that of the EVA film. Moreover, the number of microalgae attached to the EVA-PTFEMA film decreased by 61.7% after cleaning, while that of EVA film decreased by only 49.1%. It was found that the contact angle of EVA-PTFEMA film surface increased, and remained stable when immersed in acid and alkali solution for up to 90 days. HIGHLIGHTS: Durable photobioreactor antibiofouling surfaces for microalgal cultivation were prepared successfully. The contact angle of antibiofouling coating surface remained stable in acid and base environment for 90 days. The attached microalgae on antibiofouling surface decreased 41.4% than those of unmodified surface. The attached microalgae on antibiofouling surface could be cleaned by 61.7% through changing the flow velocity of microalgal suspension. [ABSTRACT FROM AUTHOR]

Since the Industrial Revolution, nearly 700 Gt of carbon (GtC) have been emitted into the atmosphere as CO2 derived from human activities, of which 292 GtC remain uncontrolled. By the end of this century, the atmospheric CO2 concentration is predicted to surpass 700 ppm. The effects of this sudden carbon release on the worldwide biogeochemical cycles and balances are not yet fully understood, but global warming and climate change are undeniable, with this gas playing a starring role. Governmental policies and international agreements on emission reduction are not producing results quickly enough, and the deadline to act is running out. Biological CO2 capture is a fast-acting carbon cycle component capable of sequestering over 115 GtC annually through photosynthesis. This study analyses a hypothetical scenario in which this biological CO2 capture is artificially enhanced through the large-scale cultivation of phytoplankton in partially natural photobioreactors (PBRs). To develop this approach, the current figures of the carbon cycle have been updated, and the key aspects of phytoplankton cultivation technology have been analysed. Our results show that a global increase of 6.5% in biological capture, along with the subsequent stabilization of the produced biomass, could counteract the current CO2 emission rate and maintain atmospheric levels of this gas at their current levels. Based on a review of the available literature, an average production rate of 17 g/m2·day has been proposed for phytoplankton cultivation in horizontal PBRs. Using this value as a key reference, it is estimated that implementing a large-scale production system would require approximately 2.1 × 106 km2 of the Earth's surface. From this, a production system model is proposed, and the key technological and political challenges associated with establishing these extensive cultivation areas are discussed. [ABSTRACT FROM AUTHOR]

Third-generation biofuels derived from microalgae offer a sustainable solution to meet rising energy demands while minimizing competition with food resources and reducing greenhouse gas emissions. Microalgae are a raw material with high potential for their use in the production of biodiesel. This study investigates the effect of nitrogen deprivation on lipid accumulation in Chlorella sp., a promising microalga for biodiesel production, identifying in the process the optimal conditions for production, being the main goal to compare biomass and lipid production between these controlled conditions and environmental ones using a bioreactor. The results showed that nitrogen deprivation increased lipid content by 7.7 % in Chlorella sp., demonstrating its potential for biodiesel enhancement. The optimal conditions for biodiesel production, including temperature (24.74 °C), pH (8.25), and light intensity (6600 lux), were identified using factorial design. Under optimized laboratory conditions (pH 8.25, light intensity 6600 lux, temperature 24.74 °C), maximum biodiesel yield was achieved at 79 %. Under environmental conditions in Arequipa, biodiesel production achieved 21.21 % lipid content, demonstrating comparable efficiency to laboratory conditions (21.24 %). Environmental and laboratory conditions yielded similar biodiesel outputs, highlighting the feasibility of outdoor production.

Background Microalgae-based products offer a sustainable solution for food, fuel, and agricultural inputs, presenting environmental benefits and economic opportunities. A comprehensive assessment is needed to understand their potential in supporting sustainability goals, considering the complex interplay between production methods, energy sources, and environmental impacts. Methods This study evaluated the environmental impacts of three microalgae-derived products – biodiesel, fish feed, and biofertilizer – through a comprehensive life cycle assessment. Nine scenarios were explored comparing three electricity profiles (current Thai mix, 50% renewable/50% current mix hybrid, 100% renewable) across the three products. The assessment evaluated environmental impacts and potential economic benefits of transitioning to these microalgae-based alternatives. Results and discussion All products demonstrated potential for significant environmental benefits under increased renewable energy scenarios. Fish feed consistently exhibited the lowest environmental impacts across all categories examined, showing substantial improvements with increased renewable energy use. With an annual demand of 0.4 million tonnes, fish feed could generate USD 560 million in revenue and reduce CO 2 emissions by 1.1 million tonnes. Fulfilling the projected biodiesel demand of 4,015 million liters per year through microalgae production could yield approximately USD 3.5 billion in revenue and reduce CO 2 emissions by 30 million tonnes compared to conventional fossil-based diesel. Additionally, algal biofertilizer production could meet a 5 million tonnes annual demand, offering USD 2 billion in revenue while reducing CO 2 emissions by 6 million tonnes yearly. Collectively, these products could offset 37 million tonnes of CO 2, representing about 14% of Thailand’s total CO 2 emissions, contributing significantly to the country’s Nationally Determined Contribution (NDC) target of 20-30% greenhouse gas emissions reduction. Conclusion Transitioning to microalgae-based products could transform the aquaculture, energy, and agricultural sectors, potentially supporting the national climate change mitigation goals, if implemented.

Life on earth depends on photosynthetic primary producers that exploit sunlight to fix CO2 into biomass. Approximately half of global primary production is associated with microalgae living in aquatic environments. Microalgae also represent a promising source of biomass to complement crop cultivation, and they could contribute to the development of a more sustainable bioeconomy. Photosynthetic organisms evolved multiple mechanisms involved in the regulation of photosynthesis to respond to highly variable environmental conditions. While essential to avoid photodamage, regulation of photosynthesis results in dissipation of absorbed light energy, generating a complex trade-off between protection from stress and light-use efficiency. This work investigates the impact of the xanthophyll cycle, the light-induced reversible conversion of violaxanthin into zeaxanthin, on the protection from excess light and on biomass productivity in the marine microalgae of the genus Nannochloropsis. Zeaxanthin is shown to have an essential role in protection from excess light, contributing to the induction of nonphotochemical quenching and scavenging of reactive oxygen species. On the contrary, the overexpression of zeaxanthin epoxidase enables a faster reconversion of zeaxanthin to violaxanthin that is shown to be advantageous for biomass productivity in dense cultures in photobioreactors. These results demonstrate that zeaxanthin accumulation is critical to respond to strong illumination, but it may lead to unnecessary energy losses in light-limiting conditions and accelerating its reconversion to violaxanthin provides an advantage for biomass productivity in microalgae.

The failure of mass production of Spirulina plateaus can be attributed to an imbalance of nutrients (C:N) and an increase in accumulated sodium ions, coupled with the traditional harvesting process. The current study aims at the recovery of stressed and red cultures of Spirulina platensis as well as enhanced phycocyanin accumulation. The stressed Spirulina platensis cultures were obtained from a local Egyptian Spirulina production farms, which were further subjected to water analyses after removing the Spirulina biomass. Optimization was performed within 300-ml water path photobioreactor. Spirulina platensis samples were incubated with Zarrouk medium comparing with those modified using ammonium bicarbonate or ammonium acetate instead of sodium bicarbonate. Continuous batching was performed every 12 days during three sequenced batches. Growth measurements (dry weight and pigments) were performed along the incubation time. It was found that carbon content of the growth medium seems to be more effective in Spirulina growth and biomass characteristics. Under different carbon sources, acetate resulted in the maximum dry weight of 1.48 g·l−1 and recovery percentage of 463.3%. Such effect was extended along the different incubation batches. Various carbon concentrations revealed that moderate concentration of carbon in the form of acetate (0.699 g·l−1) leads to the maximum growth under the same nitrogen content. A similar trend was observed with chlorophyll and phycocyanin accumulation, while carotenoids showed the opposite manner. [ABSTRACT FROM AUTHOR]

Cyanobacteria are oxygen-evolving prokaryotes that can be engineered for biofuel production from solar energy, CO 2, and water. Isobutanol (IB) has the potential to serve as an alternative fuel and important chemical feedstock. The research involves engineering Synechocystis sp. PCC 6803, for photosynthetic isobutanol production via the 2-keto-acid pathway and their cultivation in lab-scale photobioreactors. This synthetic pathway involves the heterologous expression of two enzymes, α-ketoisovalerate decarboxylase (Kivd) and alcohol dehydrogenase (Yqhd), under a strong light-inducible promotor, psbA2, known to show increased gene expression under high light. The use of psbA2 could be a valuable strategy for isobutanol production as economic scaling up demands the utilization of natural sunlight, which also provides very high light intensity at midday, facilitating increased production. The study reports isobutanol production from engineered strains containing both pathway genes and with only kivd. In shake flask studies, the highest isobutanol titre of 75 mg L−1 (12th day) was achieved from an engineered strain DM12 under optimized light intensity. DM12 was cultivated in a 2 L flat panel photobioreactor, resulting in a maximum isobutanol titre of 371.8 mg L−1 (10th day) with 2 % CO 2 and 200 μmol photons m−2 s−1. Cultivation of DM12 in a photobioreactor under mimic diurnal sunlight demonstrated the highest productivity of 39 mg L−1 day−1 with the maximum titre of 308.5 mg L−1 (9th day). This work lays the foundation for sustainable, large-scale biobutanol production using solar energy. • Isobutanol production was achieved from engineered Synechocystis sp. PCC 6803. • Light-inducible psbA2 promoter showed light intensity dependent butanol production. • Isobutanol titer was 371.8 mg L−1 under 200 μmol photons m−2 s−1 light in PBR. • Under simulated sunlight isobutanol productivity was 39 mg L−1 day−1 in PBR. [ABSTRACT FROM AUTHOR]

The cheese industry produces substantial amounts of raw cheese whey wastewater (RW), which requires effective treatment prior to environmental disposal. This study presents an innovative sequential batch system that combines macrophyte and microalgal cultivation for RW remediation. The efficacy of Lemna minor MO23 in first-line photobioreactors (PBR-1) and Chlorella sp. MC18 (CH) or Scenedesmus sp. MJ23-R (SC) in second-line photobioreactors (PBR-2) for pollutant removal was evaluated. The nutrient removal capacity of L. minor, CH, and SC was assessed at optimal tolerance concentrations, alongside nutrient recovery from treated RW (TRW) by PBR-1 for microalgae biomass production. The results demonstrate that all three species effectively purified the cheese whey wastewater. L. minor efficiently removed COD, nitrate, phosphate, and sulfate from RW, producing TRW effluent suitable for microalgal growth. CH and SC further purified TRW, enhancing biomass production. CH outperformed SC with a 4.79% higher maximum specific growth rate and 20.95% higher biomass yield. Biochemical analyses revealed the potential of CH and SC biomass for applications such as biofuels and aquaculture. After treatment, the physicochemical parameters of the effluent were within the regulatory limits. This demonstrates that the PBR-1 and PBR-2 series-coupled system effectively purifies and recovers dairy effluents while complying with discharge standards. [ABSTRACT FROM AUTHOR]

The attached microalgal–bacterial consortium (microalgae–bacteria biofilm, MBBF) has been increasingly recognized in wastewater treatment for its superior pollutant removal efficiency, resilience to toxic substances, and improved harvesting performance. This review initially discusses the advantages of MBBFs compared to activated sludge and suspended microalgal–bacterial consortia. These advantages stem from the coexistence of pollutant removal pathways for the bacteria and microalgae in MBBFs, as well as the synergistic interactions between the microalgae and bacteria that enhance pollutant removal and resilience capabilities. Subsequently, the establishment of the MBBF system is emphasized, covering the establishment process, influencing factors of MBBF formation, and the utilization of photobioreactors. Lastly, the challenges associated with implementing MBBFs in wastewater treatment are deliberated. This study aims to present a detailed and comprehensive overview of the application of MBBFs for wastewater treatment and biomass production. [ABSTRACT FROM AUTHOR]

Microalgae have unique properties that allow them to thrive in unconventional spaces, making them suitable for areas that are not normally suitable for crop growth. This is due to their ability to multiply rapidly, grow easily and adapt to different environments at low cost. As a result, the present study aims to analyze the potential of microalgae as a source of agricultural nutrition, as well as the health benefits they can provide. The following research was conducted on an experimental scale using a closed system (photobioreactor) for the cultivation of microalgae, its physicochemical characterization of the cultures and dry biomass. It can be observed the percentages of 11 N; 1.4 P; 0.3 K and its micronutrients are essential for plant growth, since microalgae-based biofertilizers are considered as a sustainable, cost-effective and environmentally friendly alternative to chemical fertilizers. The use of microalgae biomass as a biofertilizer in agriculture can increase fertility, reduce soil erosion and nutrient loss, and improve soil quality over time. It also benefits plants, vegetables and greens, as it contains nitrogen, phosphorus and potassium, which are necessary for growth. [ABSTRACT FROM AUTHOR]

The availability of light and its efficient utilisation is a major limiting factor in large scale algal cultures. While algae predominantly use the blue and red spectral regions, a significant amount of incoming light energy remains untapped outside these ranges. Converting this unused light into usable wavelengths could enhance photosynthesis. This study aimed to identify the optimal spectral converter among Lumogen Red (LR), Rhodamine 8G (R8G), and Lumogen Yellow (LY), providing efficient light utilisation for algal cultivation. Chlamydomonas reinhardtii was cultivated in double-jacketed cylindrical photo-bioreactors (PBRs) using 30% UV-a and 5% UV-b fluorescent tubes. The R8G dye displayed a slight wavelength shift with a sharp peak at about 498 nm. The LY dye demonstrated several sharp peaks at the green and blue light spectra evident of photo-degradation. The LR dye maintained better photo-stability compared to R8G and LY. Carbohydrate, lipid and protein were produced early, whereas biomass increased after day 4, as a result of photo-acclimation. The LR dye converted and emitted 3.17 × 10-19 J photon-1, enhancing biomass production and increasing photochemical energy utilisation [Y(II)] while decreasing regulated energy dissipation [Y(NPQ)]. Pigment biosynthesis was initially increased and then reduced to counteract heightened irradiation as a means of photo-protection. LR had a 1.6- and 2.9-fold up-regulation of the RuBisCo gene expression. The dye-based system correlated with improved growth, lipid, protein, carbohydrate, and pigment production. The dye-based wavelength conversion system was interlinked to the sustainable development goals addressing environmental, economic, and social aspects. [ABSTRACT FROM AUTHOR]

This study aims to reveal how height/diameter ratio of column photobioreactors affect the growth and lipid content of microalgae. For this purpose, Chlorella variabilis cells were grown in aerated column photobioreactors with height/diameter ratio of 1, 2, and 3 in defined (BG11) culture medium. Results obtained showed that maximum microalgae biomass concentration, cell productivity, cell doubling time, and lipid productivity were found to increase as the height/diameter of photobioreactor increased. After 15 days of cultivation, the highest cell productivity (0.139 gdw/L.day), cell lipid content (21.1%) and lipid productivity (29.33 mg/L.day) were obtained in the photobioreactor with the highest height/diameter ratio (3), whereas the highest specific growth rate (0.045 h-1) was obtained in the photobioreactor with the smallest height/diameter ratio (1). These findings contribute to the knowledge on photobioreactor design and pave way for more efficient use of column type photobioreactors in producing microalgae. [ABSTRACT FROM AUTHOR]

Mass transfer of bubbles is important in microalgae cultivation. In this study, aiming to improve the microalgae culturing efficiency, computational fluid dynamics (CFD) was adopted to study the influence of the aeration manners on mass transfer of bubbles within ascending columns in multi‐column airlift photobioreactor (PBR) and the hydrodynamic conditions within the PBR under different aeration manners. In addition, the bubble generation time, the detachment diameter, and the average volumetric mass transfer coefficient of bubbles in ascending columns were analyzed. Furthermore, the experimental results were compared with the simulation results obtained from microalgae cultivation. The results showed that the whole aeration manner yields the lowest mixing strength and mass transfer efficiency of bubbles at an aeration rate of 0.2 vvm. Conversely, both the mixing strength of the liquid and mass transfer coefficient of bubbles were enhanced under the half and alternate aeration manners. However, the results demonstrated that the distribution of the flow field was not uniform under the half aeration manner and there were obvious high‐speed and low‐speed zones. In contrast, the flow field distribution in the PBR was more uniform under the alternate aeration manner, which was suitable for microalgae cultivation at high concentration. This study effectively enhanced the mixing strength and CO2 transfer rate in the PBR. [ABSTRACT FROM AUTHOR]

Summary: Diatoms are a diverse group of phytoplankton usually dominating areas characterized by rapidly shifting light conditions. Because of their high growth rates and interesting biochemical profile, their biomass is considered for various commercial applications. This study aimed at identifying strains with superior growth in a photobioreactor (PBR) by screening the natural intraspecific diversity of ecotypes isolated from different habitats. We investigated the effect of PBR light fluctuating on a millisecond scale (FL, simulating the light in a PBR) on 19 ecotypes of the diatom Skeletonema marinoi isolated from the North Sea–Baltic Sea area.We compare growth, pigment ratios, phylogeny, photo‐physiological variables and photoacclimation strategies between all strains and perform qPCR and absorption spectra analysis on a subset of strains.Our results show that the ecotypes responded differently to FL, and have contrasting photo‐physiological and photoprotective strategies. The strains from Kattegat performed better in FL, and shared common photoacclimation and photoprotection strategies that are the results of adaptation to the specific light climate of the Kattegat area.The strains that performed better with FL conditions had a high light (HL)‐acclimated phenotype coupled with unique nonphotochemical quenching features. Based on their characteristics, three strains were identified as good candidates for growth in PBRs. [ABSTRACT FROM AUTHOR]

The treatment of industrial waste water using cyanobacteria in photobioreactor for the removal of sulphide, COD and phenol. The microorganisms were collected from the effluent treatment plant of a petroleum refinery and a biofilm was developed in nutrient medium. The reactor was fed with cyanobacteria. After biofilm formation and acclimatization, the same procedure was followed for 16 days in a rectangular tray type photo bioreactor for the treatment of industrial waste water. From continuous mode of operation, it was found that the phototrophic microorganisms can degrade the pollutants present in industrial waste water. The removal efficiency of hardness 75 %, sulphide 95.8 %, COD 98.7 %, phenol 99.9 % and nitrate 83.7 % was studied. The present works shows that it is feasible to use cyanobacteria in a photo bioreactor for the treatment of industrial waste water. [ABSTRACT FROM AUTHOR]

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