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Abstract: Light energy directly affects microalgae growth and productivity. Microalgae in natural environments receive light through solar fluxes, and their duration and distribution are highly variable over time. Consequently, microalgae must adjust their photosynthetic processes to avoid photo limitation and photoinhibition and maximize yield. Considering these circumstances, adjusting light capture through artificial lighting in the main culture systems benefits microalgae growth and induces the production of commercially important compounds. In this sense, this review provides a comprehensive study of the role of light in microalgae biotechnology. For this, we present the main fundamentals and reactions of metabolism and metabolic alternatives to regulate photosynthetic conversion in microalgae cells. Light conversions based on natural and artificial systems are compared, mainly demonstrating the impact of solar radiation on natural systems and lighting devices, spectral compositions, periodic modulations, and light fluxes when using artificial lighting systems. The most commonly used photobioreactor design and performance are shown herein, in addition to a more detailed discussion of light-dependent approaches in these photobioreactors. In addition, we present the principal advances in photobioreactor projects, focusing on lighting, through a patent-based analysis to map technological trends. Lastly, sustainability and economic issues in commercializing microalgae products were presented.

Microalgae produce many metabolites with diversified structures that play important roles in their development. This work evaluated the effects of different climatic variables, seasons, and light/dark phases in the production of volatile organic compounds by Scenedesmus obliquus CPCC05, focusing on the simulation of climatic variables (average temperature, maximum light intensity, and light hours per day) of the extreme geographical positions of Brazil based on tropical Am, tropical Aw, and subtropical Cfa climates found in Joao Pessoa-PB, Rio Branco-AC, Boa Vista-RR, and Rio Grande-RS, in summer and winter seasons. For the best condition in this first step, the light/dark phases together with the residence time of the culture were evaluated. A total of 45 compounds were identified in all conditions studied. The main volatile groups found were hydrocarbons, aldehydes, ketones, alcohols, and terpenes identified in both geographic locations. Among these, hydrocarbons were the main biomarkers of the subtropical Cfa climate, while the ketone group was produced mainly in warmer climates, such as the Aw tropical climate. In the experiments of light/dark phases, a total of 34 compounds were identified. 2-Pentenol and decanal were only produced in the light phase, while 1-pentanol and 2-ethyl hexanol were only found in the dark phase. The main volatile compound found was 3-methylbutanol reaching a total area abundance of 14.10%. The major compounds detected during the cultures were originated and derived from the terpenoid pathways, fatty acids, and amino acid derivates.

Aware of the uncontrolled increase in greenhouse gas emissions, and designated as the main contributor, carbon dioxide (CO2), until now, has been the hottest point in research on gaseous waste management. Thus, the use of CO2 is attracting more and more interest in renewable fuel generation processes. In this sense, this chapter aims to compile a wide range of applications for the use of CO2 as an essential raw material in the conversion of fuels. Beyond briefly discussing the technologies for direct chemical conversion of CO2 for the generation of alternative fuels, our approach focused on examining in more detail the biological use of CO2, through microalgae-based processes. Finally, the chapter presents some recommendations for the future exploration of CO2 generation technologies for fuels.

Microalgae are considered to be a promising renewable resource to manufacture both low-value bulk commodities and high added-value fine chemicals. However, on a large scale, these products in the context of microalgae biorefinery face several obstacles, which make commercial competitiveness unfeasible. Therefore, the central objective of this chapter is to present the technological bottlenecks in establishing microalgal biorefineries. Firstly, we provide an overview of these facilities, emphasizing unit processing operations of the upstream and downstream stages. The core of the chapter is a critical discussion of the hottest spots, usually attributed to the technical-economic aspects found in a microalgae biorefinery. In the end, recent developments, some potential solutions, and a patent landscape, in an attempt to resolve such bottlenecks, are addressed.

Currently, the most important microalgae-based product for use as bioactive food compound is single-cell protein (whole dried biomass) sold directly as dietary supplements. However, chemical specialties, such as pigments and fatty acids derived from microalgae are consolidating their market share of bioactive compounds for use as food coloring, food additive, and food supplement. Also, several emerging bioactive compounds (phycoerythrin, fucoxanthin, beta-glucan, and exocellular polysaccharides), not yet marketed, are shifting their research and development status to achieve commercial exploitation in the coming years. Microalgae-based products are prominent players in the bioactive food compounds industry. In this sense, this work aims to present a current opinion on bioactive food compounds from microalgae through a biorefinery approach.

The increasing demand by energy and the current need of the replace fossil resources it is leading the research and development (R&D) sector to search by renewable feedstock and renewable processes. Thus, major emphasis is being put into sustainable technologies and environmentally benign. In this context, microalgae have been extensively exploited for their versatility and capacity of the produce a broad spectrum of bioproducts. In particular, the viability of these microorganisms to generate electrical energy from organic and inorganic residues is an attractive technological route. The use of microalgae in electrochemical systems has the potential to produce bioelectricity associated with bioremediation and wastewater treatment. This integration could be advantageously exploited to the development of a self-sustaining biobased system. In this sense, this chapter is intended to provide a overview of various aspects associated with the bioelectricity production from microalgae.

The production of bioproducts from cyanobacteria with techno-economic feasibility is a challenge to these biotechnological processes. The choice of low-cost raw materials is of great importance for the overall economy of bioprocesses, as they represent a significant percentage in the final cost of the product. The objective of this work was to study the operational parameters of cultivation (exogenous sources of organic carbon and absolute amount of nutrients) to optimize productivity in bioproducts by Aphanothece microscopica Nägeli, for further evaluation of stirring speed. The experiments were performed in a bubble column bioreactor, operating at 30°C, pH of 7.6, C/N ratio of 20, 100 mg/L of inoculum, continuous aeration of 1 volume of air per volume of culture per minute (VVM), and absence of light. The results indicate that absolute amounts of 5,000/250 using cassava starch resulted in improved system performance, reaching biomass productivity of 36.66 mg/L/h in parallel with lipid productivity of 6.65 mg/L/h. Finally, experiments with variation in stirring speed indicate that 200 rpm resulted in better average rate of substrate consumption (44.01 mg/L/h), in parallel to biomass productivity of 39.27 mg/L/h. However, the increase of stirring speed had a negative effect on lipid productivity of the process. The technological route developed indicates potential to production of biomass and bulk oil, as a result of the capacity of cyanobacteria to adapt their metabolism in varying culture conditions, which provides opportunities to modify, control, and thereby maximize the formation of targeted compounds.

O objetivo do estudo foi avaliar a produção de biodiesel pela cianobactéria Phormidium autumnale a partir do efluente cervejeiro como plataforma de produção. Os experimentos foram realizados em um reator de coluna de bolhas, operando à temperatura constante de 30°C, pH de 7,6, em diferentes razões C/N (20, 40, 60 e 80), 100 mg.L-1 de inóculo, aeração constante de 1VVM (volume de ar por volume de cultura por minuto) e ausência de luz. Os resultados indicam que a razão C/N de 80 resultou em um melhor desempenho do sistema, atingindo produtividade celular de 25,97 mg/L.h em paralelo com teor lipídico de 6,33%. A composição do óleo é predominantemente saturado (53,38%) e monoinsaturado (25,98%), adequado para a síntese de biodiesel (teor de éster de 89,87%, número de cetano de 62,93, índice de iodo de 50,13 g100gI2-1, grau de insaturação de 47%, índice de saponificação de 195,54, fator saturados de cadeia longa de 6,74%, ponto de entupimento do filtro a frio em 4,7°C, ponto de névoa em 12°C, equivalente de posição alílica de 33, equivalente de posição bis-alílicos de 17,37, estabilidade oxidativa de 13,81h, calor de combustão de 35,13, viscosidade cinemática 3,091 mm² s-1 e densidade cinemática de 0,78 g cm-³).