Microalgae biomass products are gaining popularity due to their diverse applications in various sectors. However, the costs associated with media ingredients and cell harvesting pose challenges to the scale-up of microalgae cultivation. This study evaluated the growth and nutrient removal efficiency (RE) of immobilized microalgae Tetradesmus obliquus in sodium alginate beads cultivated in swine manure-based wastewater compared to free cells. The main findings of this research include (i) immobilized cells outperformed free cells, showing approximately 2.3 times higher biomass production, especially at 10% effluent concentration; (ii) enhanced organic carbon removal was observed, with a significant 62% reduction in chemical oxygen demand (383.46-144.84 mg L-1) within 48 h for immobilized cells compared to 6% in free culture; (iii) both immobilized and free cells exhibited efficient removal of total nitrogen and total phosphorus, with high REs exceeding 99% for phosphorus. In addition, microscopic analysis confirmed successful cell dispersion within the alginate beads, ensuring efficient light and substrate transfer. Overall, the results highlight the potential of immobilization techniques and alternative media, such as biodigested swine manure, to enhance microalgal growth and nutrient RE, offering promising prospects for sustainable wastewater treatment processes.

A great technological advent is the use of renewable energies with the objective of promoting the migration of the world energy matrix. For this, alternatives to generate and store energy are sought. Among them, the use of hydrogen stands out - the most abundant chemical element in our universe - produced from various sources, such as natural gas, biomass and water electrolysis, making it a viable option as a renewable fuel, in addition to being considered a source of clean energy, as its burning does not emit gases such as carbon dioxide (CO2), one of the main responsible for global warming. In addition, hydrogen can be used in a range of applications, including transportation, power generation, heating and industry, making it versatile with fossil fuels. Its intrinsic properties such as its high energy density become advantageous from the perspective of the economy based on hydrogen. When used in fuel cells, it can generate electricity efficiently and without pollutants, after all, the only emission from the fuel cell system is water. The most common way to produce hydrogen is from natural gas, through a process called steam reforming, where methane from natural gas is combined with water vapor to produce hydrogen and carbon dioxide as a by-product. However, this approach still emits CO2, in a smaller amount, when compared to the direct burning of fossil fuels. Another option is the production of hydrogen from biomass, such as agricultural and forestry waste, through gasification processes or anaerobic fermentation, which can be neutral in terms of CO2 emissions, as the carbon released during production is offset by the carbon absorbed. by plants during their growth. In addition, water electrolysis, which uses electricity to split water into hydrogen and oxygen, is another option for producing hydrogen without CO2 emissions when the electricity used comes from renewable sources. With its vast production, hydrogen can be used as a form of renewable energy storage, after all, one of the main limitations of renewable energies, such as solar and wind, is their intermittency, that is, energy generation depends on climatic conditions. Hydrogen can be produced when there is a surplus of renewable energy available, being stored in liquid or gaseous form, in large spoons, facilitating its transport for later use, and also, meeting the growing world energy demand.

The increase of wastewater follows the expansion of the world population generating a deficit in basic sanitation and in the sewage collection provided. It is widely known that the United Nations (UN) instituted the 2030 Agenda, a plan for the sustainability of the planet, improvement of people's lives and world prosperity. There are 17 Sustainable Development Goals (SDGs) in the 2030 Agenda. We highlight the SDG 6: “Clean water and sanitation”, which is aimed at basic sanitation and access to drinking water. Currently, the treatment system is divided into three stages: primary, secondary and tertiary. In the secondary stage, one makes use of microorganisms to remove organic matter from the medium, such as microalgae or bacteria. Preference has been given to the use of microalgae, classified as microorganisms of rapid cell growth with photoautotrophic capacity. However, the free state physical dimension of a microalgae makes the treatment process more expensive and potentially, impacts the treatment time, thus burdening the treatment. With that in mind, a method of immobilization of microalgae and the elaboration of a photobioreactor for the treatment of effluents was developed. Immobilization is a practice that consists of fixing algae within small spheres, which simplifies the separation methodology of microorganisms from the treated effluent. The immobilizing medium provides mechanical resistance and protects the culture from possible contamination. In order to demonstrate the functionality of the system, as a means of effluent treatment, a mathematical modeling of the effluent treatment was conceived. Fortran was the programming language used to solve nonlinear differential equations through temporal discretization. Runge-Kutta was the numerical method chosen to solve the equations of the model that are based on Monod’s model. Monod’s model predicts the growth parameters during the life cycle determining the amount of substrates and the number of microalgae along the lag phase, log phase and stabilization level. It also expresses the consumption of the substrates. Thus, the model allows the visualization of the biomass growth, consumption of inorganic substances and the treatment time under study.

Algae are ubiquitous organisms whose capabilities have drawn much attention as of late in the bioengineering field due to their potential to enable a wide range of bioproducts. Microalgae are ideal organisms for the application of the biorefinery concept since they can be grown in wastewater and, at the same time, produce many products of commercial interest. These microorganisms are also known for their resilience to extreme environmental conditions and suitable cell growth rates. Beyond the known potential for biofuel production, these microorganisms can still produce other compounds, being lipids, pigments, vitamins, proteins, and polysaccharides, whose applications go from pharmaceutical to agricultural industries. Recently, the research focus has been directed to the biopolymer-producing ability of both micro- and macroalgae, as they can be rather varied and useful to many applications. However, this is still an ongoing research field, and new data are frequently added in the literature, notably on biomass processing, which can be done with the intent of use into dyes, bioplastics, paints, and even as biochar in solid fuel cells. Microalgae-based biopolymers can be used in a wide range of products, nevertheless, the resulting process efficiency and yields depend on the extraction process utilized, as well as on the microalgae species used and the culture conditions. Furthermore, the polymer extraction can be done directly with common solvents at atmospheric pressure or with other fluids, such as supercritical CO2 or subcritical solvents, and assisted by specific treatments, e.g., ultrasound and microwave. The residual biomass can still be used to produce other less valuable products, such as feedstock, and energy via combustion. In this sense, the present work aims to provide a state-of-the-art review on microalgae biopolymers. Issues related to the efficiency of current treatment methods, industrial applications, and environmental performance are presented and discussed. Besides, the perspectives in this area of knowledge are also a contribution of the present work, the extent to which scientific research is still under development.

The objective of this paper is to determine if it is possible to refrigerate an area by means of a heat source. Theory determines that an absorption refrigerator can work as a possible solution through a refrigeration fluid. According to it, the system works by the evaporation or condensation of the working fluid. The traditional process consists of using engine fuel to run an electric compressor and by its means achieve refrigeration. That process has its toll on fuel economy and engine efficiency and the refrigeration fluid damages the ozone layer or is based on the transportation of ice previously bought on shore. The technological improvement will be equipped on fishing boats, in order to make the trip last longer due to the possibility of not needing to buy and transport ice and for the purpose of lowering the fishing industry cost. Absorption refrigeration can augment engine efficiency by using heat energy that is normally wasted and the system could reach temperatures of freezing water, meaning that it could be possible to follow Brazilian and international standards. The methodology of this work consists of an energy analysis of an absorption refrigerator, which is the determination of the heat transfer equations on the ammonia evaporator, condenser and exhaust/ammonia. Furthermore, it should be analyzed if it’s possible to determine to which working parameters the system will have an optimum operation. From the mathematical analysis, the system shows that with the equations it is possible to operate an absorption refrigeration based on the exhaust gases of fishing boats. Furthermore, the process can be operated on a wide range of temperatures, being possible to determine according to a few dimensionless parameters to which temperature levels the process of refrigeration shows the best removal of heat.

O aquecimento global é uma questão considerável que vem sendo discutida recentemente e, devido às altas taxas de emissão de gases de efeito estufa (GEE), tem sido um dos principais fatores que pode comprometer a segurança hídrica, alimentar e energética mundial.Dessa maneira, é imprescindível atuar por meio de estratégias e aplicações sustentáveis a fim de minimizar esses impactos negativos.Este capítulo compila informações a respeito de análise de ciclo de vida (ACV) aplicada à processos e produtos a partir do cultivo de microalgas.O trabalho salienta que são necessárias investigações para compreender melhor os prejuízos causados pelas