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This review comprehensively examines the various applications of microalgae, focusing on their significant potential in producing biodiesel and hydrogen, serving as sustainable food sources, and their efficacy in treating both municipal and food-related wastewater. While previous studies have mainly focused on specific applications of microalgae, such as biofuel production or wastewater treatment, this review covers these applications comprehensively. It examines the potential for microalgae to be applied in various industrial sectors such as energy, food security, and environmental management. By bridging these different application areas, this review differs from previous studies in providing an integrated and multifaceted view of the industrial applications of microalgae. Since it is essential to increase the productivity of the process to utilize microalgae for various industrial applications, research trends in different microalgae cultivation processes, including the culture system (e.g., open ponds, closed ponds) or environmental conditions (e.g., pH, temperature, light intensity) to improve the productivity of biomass and valuable substances was firstly analyzed. In addition, microalgae cultivation technologies that can maximize the biomass and valuable substances productivity while limiting the potential for contamination that can occur when utilizing these systems have been described to maximize CO2 reduction. In conclusion, this review has provided a detailed analysis of current research findings and technological innovations, highlighting the important role of microalgae in addressing global challenges related to energy, food supply, and waste management. It has also provided valuable insights into future research directions and potential commercial applications in several bio-related industries, and illustrated how important continued exploration and development in this area is to realize the full potential of microalgae. [ABSTRACT FROM AUTHOR]

Recognized as the third-generation biomass of the future, microalgae are increasingly viewed as a promising solution for the sustainable production of biofuels, often referred to as "green gold." Extensive research is being conducted across the upstream, midstream, and downstream sectors to develop fundamental technologies that enable efficient and economical large-scale microalgae cultivation. Recent studies suggest that microalgae-based biofuels have the potential to meet global energy demands. However, challenges such as spatial constraints in site selection and the high cost of transporting CO2—an essential component for pH regulation and photosynthesis—pose obstacles. Here, this study demonstrates that by supplementing air-only medium with CaCO3, Chlorella sorokiniana can effectively utilize airborne CO2 to produce biomass. In laboratory-scale culture conditions supplied only with air, adding 5 mM CaCO3 (pH 7.8) could maintain the pH stably compared to the untreated conditions (pH 9.5) and improved the biomass concentration and lipid content by 17.68-fold and 9.58-fold, respectively. In bench-scale conditions, cultures supplemented with 5 mM CaCO3 exhibited a 9-fold increase in the biomass and a 7.15-fold increase in the lipid concentrations compared to those cultivated with air alone. With microalgae emerging as an essential resource for future generations, cultivation technology utilizing CaCO3 will be a critical technology that enables commercial-scale microalgae cultivation using only air, without artificial CO2 supply facilities. [ABSTRACT FROM AUTHOR]

[Display omitted] • Studies are introduced to reduce carbon emissions under large-scale culture system. • Downstream systems to maximize microalgae-based biomass productivity were reviewed. • Efficient biohydrogen production strategies that reduce carbon emissions are needed. • The methods of hydrogen production and storage from microalgae are presented. • Additional cost-effective strategies are needed to mass-produce hydrogen. Hydrogen as a clean fuel is receiving attention because it generates only water and a small amount of nitrogen oxide upon combustion. Biohydrogen production using microalgae is considered to be a highly promising carbon–neutral technology because it can secure renewable energy while efficiently reducing CO 2 emissions. However, previous studies have mainly focused on improving the biological performance of microalgae; these approaches have struggled to achieve breakthroughs in commercialization because they do not heavily consider the complexity of the entire production process with microalgae, including large-scale cultivation, biomass harvest, and biomass storage. This work presents an in-depth analysis of the state-of-the-art technologies focused on large-scale cultivation systems with efficient downstream processes. Considering the individual processes of biohydrogen production, strategies are discussed to minimize carbon emissions and improve productivity simultaneously. A comprehensive understanding of microalgae-derived biohydrogen production suggests future directions for realizing environmental and economic sustainability. [ABSTRACT FROM AUTHOR]

Novel 3D-printed buoyant structures can be applied in various environmental processes because of their considerable advantages. Microalgae cultivation in photobioreactors, directly supplemented by industrial CO 2 , enables environmental pollution mitigation/cleanup and sustainable energy production. However, in photobioreactor systems, biofilm formation due to gas bubbling decreases microalgal productivity. Therefore, in this study, we aimed to develop a novel 3D-printed buoyant structure to suppress biofilm formation. The 10 mm-sized spherical buoyant structure reduced the height and area of the biofilm by 58.3% and 82.5%, respectively. The structure decreased space where bubble burst occurred and controlled the bubble size, reducing the overall biomass loss by 58.7%. It did not reduce photobioreactor performance noticeably during semi-continuous cultivation, indicating the possibility of long-term applicability. In large-scale outdoor microalgae cultivation using flue gas CO 2 , the buoyant structure improved the cell density and biodiesel production potential without contamination. This study provides a promising strategy to contribute to biological CO 2 mitigation through the utilization of flue gas CO 2 for enhanced microalgal production, paving the way for energy and environmental sustainability. [Display omitted] • 3D-printed buoyant structure prevented biofouling in a polymeric photobioreactor. • The 10 mm-sized spherical structure decreased the height and area of the biofilm. • Buoyant structure prevented bursting of bubbles and generation of large bubbles. • Biofouling was controlled in semi-continuous culture without structure replacement. • Biofouling suppression contributed to microalgal valorization of flue gas CO 2. [ABSTRACT FROM AUTHOR]