Biochar production from microalgae: a new sustainable approach to wastewater treatment based on a circular economy.

The generation of wastewater due to human activities are the main responsible for environmental problems. These problems are caused by the large amount of organic and inorganic pollutants related to the presence of pesticides, metals, pathogens, drugs and dyes. The photosynthetic treatment of effluents emerges as a sustainable and low-cost alternative for developing wastewater treatment systems based on a circular economy. Chemical compounds present in wastewater can be recovered and reused as a source of nutrients in microalgae cultivation to produce value-added bioproducts. The microalgal biomass produced in the cultivation with effluents has the potential to produce biochar. Biochar is carbon-rich charcoal that can be obtained by converting microalgae biomass through thermal decomposition of organic raw material under limited oxygen supply conditions. Pyrolysis, torrefaction, and hydrothermal carbonization are processes used for biochar synthesis. The application of microalgal biochar as an adsorbent material to remove several compounds present in effluents is an effective and fast treatment. This effectiveness is usually related to the unique physicochemical characteristics of the biochar, such as the presence of functional groups, ion exchange capacity, thermal stability, and high surface area, volume, and pore area. In addition, biochar can be reused in the adsorption process or applied in agriculture for soil correction. In this context, this review article describes the production, characterization, and use of microalgae biochar through a sustainable approach to wastewater treatment, emphasizing its potential in the circular economy. In addition, the article approaches the potential of microalgal biochar as an adsorbent material and its reuse after the adsorption of contaminants, as well as highlights the challenges and future perspectives on this topic.

Renewal of nanofibers in Chlorella fusca microalgae cultivation to increase CO2 fixation.

This study explored strategies to increase the CO2 fixation ability of microalgae by renewing polymeric nanofibers in cultures of Chlorella fusca LEB 111. Nanofibers composed of 10% (w v-1) polyacrylonitrile (PAN)/dimethylformamide (DMF) containing 4% (w v-1) iron oxide nanoparticles (NPsFe2O3) were added to photobioreactors. The nanomaterial was renewed in the test cultures as follows: renewal only on day 7; renewal only on day 15; or renewal on both days 7 and 15 (i.e., double renewal). The highest biomass concentration (2.53 g L-1) and CO2 biofixation rate (141.5 mg L-1 d-1) were obtained by cultivating with double renewal, resulting in values 21.6% and 23% higher, respectively, than those obtained by cultivation without renewal. The application of nanofiber renewal in the cultivation of C. fusca LEB 111 shows the potential to increase CO2 biofixation, which may contribute to reducing the atmospheric concentrations of this main greenhouse gas intensifier.

Green alga cultivation with nanofibers as physical adsorbents of carbon dioxide: Evaluation of gas biofixation and macromolecule production.

The objective of this study was to evaluate the biofixation and production of biocompounds by Chlorella fusca LEB 111 cultivated with different concentrations of carbon dioxide (CO2) adsorbent nanofibers in their free form or retained. Cultures were grown in 15% (v v-1) CO2 with 0.1, 0.3 and 0.5 g L-1 nanofibers developed with 10% (w v-1) polyacrylonitrile (PAN)/dimethylformamide (DMF), with or without nanoparticles; retained or not. The addition of 0.1 g L-1 nanofibers with nanoparticles in their free form to the cultures promoted the accumulation of approximately 3 times more carbon in the medium (46.6 mg L-1), a 45% higher biofixation rate (89.2 mg L-1 d-1) and increased carbohydrate production by approximately 2.3% (w w-1) of that observed in cultures grown without nanofibers. Therefore, nanofibers showed promising potential as physical adsorbents of CO2 in the cultivation to increase gas fixation and promote the synthesis of macromolecules.

Innovative nanofiber technology to improve carbon dioxide biofixation in microalgae cultivation.

The aim of this study was to develop nanofibers containing nanoparticles with potential for the biological fixation of CO2 together with the microalgae Chlorella fusca LEB 111. An electrospinning technique was used for the production of polymeric nanofibers with different concentrations of iron oxide nanoparticles: 0, 2, 4, 6, 8, and 10% (w v-1). Nanofibers with a nanoparticle concentration of 4% (w v-1) were selected for use in the microalgal cultivation due to their smaller diameter (434 nm), high specific surface area (13.8 m2 g-1) and higher CO2 adsorption capacity (164.2 mg g-1). The microalgae C. fusca LEB 111 presented a higher CO2 biofixation rate of 216.2 mg L-1 d-1 when cultivated with these nanofibers. The results demonstrated the potential of electrospun nanofibers as physical adsorbents of CO2 since they can increase the contact time between the gas and the microorganism and consequently increase the CO2 biofixation by the microalgae.

Nanoencapsulation of the Bioactive Compounds of Spirulina with a Microalgal Biopolymer Coating.

Microalgae have been studied in biotechnological processes due to the various biocompounds that can be obtained from their biomasses, including pigments, proteins, antioxidants, biopeptides, fatty acids and biopolymers. Microalgae biopolymers are biodegradable materials that present similar characteristics to traditional polymers, with the advantage of being rapidly degraded when discarded. In addition, nanoencapsulation is capable of increasing the availability of bioactive compounds by allowing the release of these biocompounds to occur slowly over time. The use of polymers in the nanoencapsulation of active ingredients can mask the undesired physicochemical properties of the compounds to be encapsulated, thereby enhancing consumer acceptability. This covering also acts as a barrier against several foreign substances that can react with bioactive compounds and reduce their activity. Studies of the development of poly-3-hydroxybutyrate (PHB) nanocapsules from microbial sources are little explored; this review addresses the use of nanotechnology to obtain bioactive compounds coated with biopolymer nanocapsules, both obtained from Spirulina biomasses. These microalgae are Generally Recognized as Safe (GRAS) certified, which guarantees that the biomass can be used to obtain high added value biocompounds, which can be used in human and animal supplementation.

Use of Solid Waste from Thermoelectric Plants for the Cultivation of Microalgae

ABSTRACT The aim of this study was to analyze the influence of solid waste on the cultivation of the microalgae Spirulina sp. LEB 18 and Chlorella fusca LEB 111 with 0, 40, 80 and 120 ppm of mineral coal ash. The addition of the ash did not inhibit the cultivation of microalgae at the tested concentrations, showing that it could be used for the cultivation of these microalgae due to the minerals present in the ash, which might substitute the nutrients needed for their growth.

Biologically Active Metabolites Synthesized by Microalgae.

Microalgae are microorganisms that have different morphological, physiological, and genetic traits that confer the ability to produce different biologically active metabolites. Microalgal biotechnology has become a subject of study for various fields, due to the varied bioproducts that can be obtained from these microorganisms. When microalgal cultivation processes are better understood, microalgae can become an environmentally friendly and economically viable source of compounds of interest, because production can be optimized in a controlled culture. The bioactive compounds derived from microalgae have anti-inflammatory, antimicrobial, and antioxidant activities, among others. Furthermore, these microorganisms have the ability to promote health and reduce the risk of the development of degenerative diseases. In this context, the aim of this review is to discuss bioactive metabolites produced by microalgae for possible applications in the life sciences.

Biological effects of Spirulina (Arthrospira) biopolymers and biomass in the development of nanostructured scaffolds.

Spirulina is produced from pure cultures of the photosynthetic prokaryotic cyanobacteria Arthrospira. For many years research centers throughout the world have studied its application in various scientific fields, especially in foods and medicine. The biomass produced from Spirulina cultivation contains a variety of biocompounds, including biopeptides, biopolymers, carbohydrates, essential fatty acids, minerals, oligoelements, and sterols. Some of these compounds are bioactive and have anti-inflammatory, antibacterial, antioxidant, and antifungal properties. These compounds can be used in tissue engineering, the interdisciplinary field that combines techniques from cell science, engineering, and materials science and which has grown in importance over the past few decades. Spirulina biomass can be used to produce polyhydroxyalkanoates (PHAs), biopolymers that can substitute synthetic polymers in the construction of engineered extracellular matrices (scaffolds) for use in tissue cultures or bioactive molecule construction. This review describes the development of nanostructured scaffolds based on biopolymers extracted from microalgae and biomass from Spirulina production. These scaffolds have the potential to encourage cell growth while reducing the risk of organ or tissue rejection.