Bioethanol from Spirulina platensis biomass and the use of residuals to produce biomethane: An energy efficient approach

Biological effects of culture medium on Tetraselmis chuii and Dunaliella tertiolecta: Implications for emerging pollutants degradation

In this study, laboratory-scale cultivation of T. chuii and D. tertiolecta was conducted using Conway, F/2, and TMRL media to evaluate their biochemical composition and economic costs. The highest cell density (30.36 × 106 cells/mL) and dry weight (0.65 g/L) for T. chuii were achieved with Conway medium. This medium also produced biomass with maximum lipid content (25.65%), proteins (27.84%), and total carbohydrates (8.45%) compared with F/2 and TMRL media. D. tertiolecta reached a maximum cell density of 17.50 × 106 cells/mL in F/2 medium, which was notably lower than that of T. chuii. Furthermore, the media cost varied from US$0.23 to US$0.74 for each 1 L of media, primarily due to the addition of Na3PO4, KNO3, and cyanocobalamin. Thus, biomass production rates varied between US$38.81 and US$128.80 per kg on a dry weight basis. These findings comprehensively compare laboratory conditions and the costs associated with biomass production in different media. Additionally, this study explored the potential of T. chuii and D. tertiolecta strains, as well as their consortia with bacteria, for the degradation of various emerging pollutants (EPs), including caffeine, salicylic acid, DEET, imidacloprid, MBT, cimetidine, venlafaxine, methylparaben, thiabendazole, and paracetamol. Both microalgal strains demonstrated effective degradation of EPs, with enhanced degradation observed in microalgae-bacterial consortia. These results suggest that the symbiotic relationship between microalgae and bacteria can be harnessed for the bioremediation of EPs, thereby offering valuable insights into the environmental applications of microalgal cultivation.

Use of Residual Lignocellulosic Biomass and Algal Biomass to Produce Biofuels

Efforts are intensifying to identify new biofuel sources in response to the pressing need to mitigate environmental pollutants, such as greenhouse gases, which are key contributors to global warming and various worldwide calamities. Algae and microalgae present themselves as excellent alternatives for solid-gaseous fuel production, given their renewable nature and non-polluting characteristics. However, making biomass production from these organisms economically feasible remains a challenge. This article collates various studies on the use of lignocellulosic waste, transforming it from environmental waste to valuable organic supplements for algae and microalgae cultivation. The focus is on enhancing biomass production and the metabolites derived from these biomasses.

Valorization of coffee bean processing waste for bioethanol production: comparison and evaluation of mass transfer effects in fermentations using free and encapsulated cells of Saccharomyces cerevisiae

Coffee husk, an agricultural waste abundant in carbohydrates and nutrients, is typically discarded through landfills, mixed with animal fodder, or incinerated. However, in alignment with sustainable development principles, researchers worldwide are exploring innovative methods to harness the value of coffee husk, transforming it into profitable products. One such avenue is the biotechnological approach to bioethanol production from agricultural wastes, offering an eco-friendly alternative to mitigate the adverse effects of fossil fuels. This study delves into the feasibility of utilizing coffee husk as a substrate for bioethanol production, employing and comparing various hydrolysis methods. The enzymatic hydrolysis method outshone thermochemical and thermal approaches, yielding 1.84 and 3.07 times more reducing sugars in the hydrolysate, respectively. In examining bioethanol production, a comparison between free and encapsulated cells in enzyme hydrolysate revealed that free-cell fermentation faced challenges due to cell viability issues. Under specific fermentation conditions, bioethanol yield (0.59 and 0.83 g of bioethanol/g of reducing sugar) and productivity (0.1 and 0.12 g/L h) were achieved for free and encapsulated cells, respectively. However, it was noted that bioethanol production by encapsulated cells was more significantly influenced by internal mass transfer effects, as indicated by the Thiele modulus and effectiveness factor. In conclusion, our findings underscore the potential of coffee husk as a valuable substrate for bioethanol production, showcasing its viability in contributing to sustainable and eco-friendly practices.

Restoration of mitochondrial function by Spirulina polysaccharide via upregulated SOD2 in aging fibroblasts

Reactive oxygen species (ROS), such as superoxide, are crucial factors involved in the stimulation of cellular aging. Mitochondria, which are important organelles responsible for various metabolic processes in cells, produce ROS. These ROS impair mitochondrial function, thereby accelerating aging-related cellular dysfunction. Herein, we demonstrated that the Spirulina polysaccharide complex (SPC) restores mitochondrial function and collagen production by scavenging superoxide via the upregulation of superoxide dismutase 2 (SOD2) in aging fibroblasts. We observed that SOD2 expression was linked to inflammatory pathways; however, SPC did not upregulate the expression of most inflammatory cytokines produced as a result of induction of LPS in aging fibroblasts, indicating that SPC induces SOD2 without activation of inflammatory pathways. Furthermore, SPC stimulated endoplasmic reticulum (ER) protein folding by upregulating ER chaperones expression. Thus, SPC is proposed to be an antiaging material that rejuvenates aging fibroblasts by increasing their antioxidant potential via the upregulation of SOD2.

Fruit residues as biomass for bioethanol production using enzymatic hydrolysis as pretreatment

The commercialization of fruits in markets generates a large amount of waste because they are perishable and have a short shelf life, so, they are discarded. This study aimed to provide a noble end to discarded fruits that have fermentable sugars. Banana, apple, mango and papaya residues were collected from supermarkets and underwent an enzymatic hydrolysis process. The ability of four pectinases, two amylases, one xylanase and one cellulase to release reducing sugars from fruit biomass before fermentation with two yeast strains (S. cerevisiae CAT-1 and S. cerevisiae Angel) for bioethanol production was investigated, obtaining a total of RS (Reducing sugar) of 268.08 mg/mL in banana residues. A fermentation with yeast S. cerevisiae CAT-1 resulted in 98% consumption of RS and the production of a total of 28.02 g/L of ethanol. Furthermore, fermentation with the yeast S. cerevisiae Angel, resulted in 97% RS consumption and 31.87 g/L ethanol production, which was the best result obtained throughout all the tests of hydrolysis, highlighting the banana residue as a promising biomass for the production of bioethanol.

A review on the sustainable procurement of microalgal biomass from wastewaters for the production of biofuels

The feasibility of microalgal biomass as one of the most promising and renewable sources for the production of biofuels is being studied extensively. Microalgal biomass can be cultivated under photoautotrophic, heterotrophic, photoheterotrophic, and mixotrophic cultivation conditions. Photoautotrophic cultivation is the most common way of microalgal biomass production. Under mixotrophic cultivation, microalgae can utilize both organic carbon and CO2 simultaneously. Mixotrophic cultivation depicts higher biomass productivity as compared to photoautotrophic cultivation. It is evident from the literature that mixotrophic cultivation yields higher quantities of polyunsaturated fatty acids as compared to that photoautotrophic cultivation. In this context, for economical biomass production, the organic carbon of industrial wastewaters can be valorized for the mixotrophic cultivation of microalgae. Following the way, contaminants' load of wastewaters can be reduced while concomitantly producing highly productive microalgal biomass. This review focuses on different aspects covering the sustainable cultivation of different microalgal species in different types of wastewaters.

Use of carbohydrate-directed enzymes for the potential exploitation of sugarcane bagasse to obtain value-added biotechnological products

Microorganisms, such as fungi and bacteria, are crucial players in the production of enzymatic cocktails for biomass hydrolysis or the bioconversion of plant biomass into products with industrial relevance. The biotechnology industry can exploit lignocellulosic biomass for the production of high-value chemicals. The generation of biotechnological products from lignocellulosic feedstock presents several bottlenecks, including low efficiency of enzymatic hydrolysis, high cost of enzymes, and limitations on microbe metabolic performance. Genetic engineering offers a route for developing improved microbial strains for biotechnological applications in high-value product biosynthesis. Sugarcane bagasse, for example, is an agro-industrial waste that is abundantly produced in sugar and first-generation processing plants. Here, we review the potential conversion of its feedstock into relevant industrial products via microbial production and discuss the advances that have been made in improving strains for biotechnological applications.

Microalgae-derived polysaccharides: Potential building blocks for biomedical applications

In recent years, the increasing concern about human health well-being has strongly boosted the search for natural alternatives that can be used in different fields, especially in biomedicine. This has put microalgae-based products in evidence since they contain many bioactive compounds, of which polysaccharides are attractive due to the diverse physicochemical properties and new or improved biological roles they play. Polysaccharides from microalgae, specially exopolysaccharides, are critically important for market purposes because they can be used as anti-inflammatory, immunomodulatory, anti-glycemic, antitumor, antioxidant, anticoagulant, antilipidemic, antiviral, antibacterial, and antifungal agents. Therefore, to obtain higher productivity and competitiveness of these naturally available compounds, the cultivation parameters and the extraction/purification processes must be better optimized in order to bring perspectives for the exploitation of products in commercial and clinical practice. In this sense, the objective of the present review is to elucidate the potential biomedical applications of microalgae-derived polysaccharides. A closer look is taken at the main polysaccharides produced by microalgae, methods of extraction, purification and structural determination, biological activities and their applications, and current status.

Low Indirect Land Use Change (ILUC) Energy Crops to Bioenergy and Biofuels—A Review

Energy crops are dedicated cultures directed for biofuels, electricity, and heat production. Due to their tolerance to contaminated lands, they can alleviate and remediate land pollution by the disposal of toxic elements and polymetallic agents. Moreover, these crops are suitable to be exploited in marginal soils (e.g., saline), and, therefore, the risk of land-use conflicts due to competition for food, feed, and fuel is reduced, contributing positively to economic growth, and bringing additional revenue to landowners. Therefore, further study and investment in R&D is required to link energy crops to the implementation of biorefineries. The main objective of this study is to present a review of the potential of selected energy crops for bioenergy and biofuels production, when cultivated in marginal/degraded/contaminated (MDC) soils (not competing with agriculture), contributing to avoiding Indirect Land Use Change (ILUC) burdens. The selected energy crops are Cynara cardunculus, Arundo donax, Cannabis sativa, Helianthus tuberosus, Linum usitatissimum, Miscanthus × giganteus, Sorghum bicolor, Panicum virgatum, Acacia dealbata, Pinus pinaster, Paulownia tomentosa, Populus alba, Populus nigra, Salix viminalis, and microalgae cultures. This article is useful for researchers or entrepreneurs who want to know what kind of crops can produce which biofuels in MDC soils.

Metabolic and Evolutionary Engineering of Diploid Yeast for the Production of First- and Second-Generation Ethanol

Despite a growing preference for second-generation (2G) ethanol in industries, its application is severely restricted owing to a major obstacle of developing a suitable yeast strain for fermentation using feedstock biomasses. In this study, a yeast strain, Saccharomyces cerevisiae A31Z, for 2G bioethanol production was developed from an industrial strain, Angel, using metabolic engineering by the incorporation of gene clusters involved in the xylose metabolism combined with adaptive evolution for evolving its anti-inhibitory properties. This strain outcompeted its ancestors in xylose utilization and subsequent ethanol production and manifested higher tolerance against common inhibitors from lignocellulosic hydrolysates, and also it lowered the production of glycerol by-product. Furthermore, A31Z outperformed in ethanol production using industrial hydrolysate from dried distillers grains with solubles and whole corn. Overall, this study provided a promising path for improving 2G bioethanol production in industries using S. cerevisiae.

Microalgae-based carbohydrates: A green innovative source of bioenergy

Microalgae contribute significantly to the global carbon cycle through photosynthesis. Given their ability to efficiently convert solar energy and atmospheric carbon dioxide into chemical compounds, such as carbohydrates, and generate oxygen during the process, microalgae represent an excellent and feasible carbohydrate bioresource. Microalgae-based biofuels are technically viable and, delineate a green and innovative field of opportunity for bioenergy exploitation. Microalgal polysaccharides are one of the most versatile groups for biotechnological applications and its content can be increased by manipulating cultivation conditions. Microalgal carbohydrates can be used to produce a variety of biofuels, including bioethanol, biobutanol, biomethane, and biohydrogen. This review provides an overview of microalgal carbohydrates, focusing on their use as feedstock for biofuel production, highlighting the carbohydrate metabolism and approaches for their enhancement. Moreover, biofuels produced from microalgal carbohydrate are showed, in addition to a new bibliometric study of current literature on microalgal carbohydrates and their use.

A review on cyanobacteria cultivation for carbohydrate-based biofuels: Cultivation aspects, polysaccharides accumulation strategies, and biofuels production scenarios

Cyanobacterial biomass has constituted a crucial third and fourth-generation biofuel material, with great potential to synthesize a wide range of metabolites, mainly carbohydrates. Lately, carbohydrate-based biofuels from cyanobacteria, such as bioethanol, biohydrogen, and biobutanol, have attracted attention as a sustainable alternative to petroleum-based products. Cyanobacteria can perform a simple process of saccharification, and extracted carbohydrates can be converted into biofuels with two alternatives; the first one consists of a fermentative process based on bacteria or yeasts, while the second alternative consists of an internal metabolic process of their own in intracellular carbohydrate content, either by the natural or genetic engineered process. This study reviewed carbohydrate-enriched cyanobacterial biomass as feedstock for biofuels. Detailed insights on technical strategies and limitations of cultivation, polysaccharide accumulation strategies for further fermentation process were provided. Advances and challenges in bioethanol, biohydrogen, and biobutanol production by cyanobacteria synthesis and an independent fermentative process are presented. Critical outlook on life-cycle assessment and techno-economical aspects for large-scale application of these technologies were discussed.

Phycoremediation and biomass production from high strong swine wastewater for biogas generation improvement: An integrated bioprocess

This study investigated the phycoremediation process from swine digestate integrated with photosynthetic biomass and biogas production in the context of circular economy. Effects of total ammonia nitrogen (TAN) and pH on biomass productivity and nutrients removal, using a central rotational composite design, were evaluated. pH showed a significant effect on biomass productivity and phosphate removal. The strain Chlorella sorokiniana (LBA#39) was able to tolerate up to 1300 mg TAN L^-1 at neutral pH, with maximum biomass productivity of 198 mg DW L^-1 d^-1 and removal of 90 and 70 (%) of phosphate and nitrogen, respectively. The biomass harvested after phycoremediation from digestate showed high content of volatile solids (95.4%) and proteins (59.5%). Biochemical methane potential (BMP) from microalgae monodigestion was 292 ± 10 mL_NCH4 g_VSadd^-1. The use microalgae biomass addition in the biodigestion process increased up to 32.1% in biogas production. It is an attractive approach to integrating raw materials into existing agro-industrial facilities and improving biogas production, adopting the concept of circular economy and mitigating greenhouse gas emissions.

Production of biofuels from soybean straw and hull hydrolysates obtained by subcritical water hydrolysis

The objective of this study was to evaluate the ethanol production by Wickerhamomyces sp. using soybean straw and hull hydrolysates obtained by subcritical water hydrolysis and, afterward, the biogas production using the fermented hydrolysates. Ethanol was produced using the straw and hull hydrolysates diluted and supplement with glucose, reaching 5.57 ± 0.01 g/L and 6.11 ± 0.11 g/L, respectively. The fermentation in a bioreactor with changing the pH to 7.0 allowed achieving maximum ethanol production of 4.03 and 3.60 g/L for straw and hull hydrolysates at 24 h, respectively. The biogas productions obtained for the fermented hydrolysates of straw with and without changing the pH were 739 ± 37 and 652 ± 34 NmL/gVSad, respectively. The fermented hydrolysate of hull without changing the pH presented 620 ± 26 NmL/gVSad. The soybean residues produced biofuels, indicating these residues show potential as raw material for renewable energy production.

Optimization of Chlamydomonas reinhardtii cultivation with simultaneous CO2 sequestration and biofuels production in a biorefinery framework

Algal biomass is regarded as a sustainable energy feedstock for the future. Enhancement of the biomass and metabolite production of microalgae increases the economic feasibility of the biofuel production process. The present study encompasses on bioethanol production from Chlamydomonas reinhardtii through a biorefinery approach. The biomass and carbohydrate productivity of C. reinhardtii UTEX 90 and CC 2656 were enhanced by optimizing the physico-chemical parameters. The following conditions were found suitable for the improvement of biomass and metabolite content of C. reinhardtii: pH 6.5-7.0, incubation temperature 30 °C, initial acetate and ammonium chloride concentration of 1.56 g L^-1 and 100-200 mg L^-1, respectively. Under the optimized operational condition biomass and carbohydrate productivity of C. reinhardtii UTEX 90 and CC 2656 were 512 mg L^-1 d^-1 & 266.24 mg L^-1 d^-1 and 364 mg L^-1 d ^-1 & 163.80 mg L^-1 d^-1, respectively. The amount of CO₂ sequestered during the cultivation process by UTEX 90 and CC 2656 were 113 mg L^-1 d^-1 and 74.95 mg L^-1 d^-1, respectively. The depigmented and defatted carbohydrate rich biomass was considered as raw material for bioethanol production. The bioethanol yield range was 90-94% of the theoretical yield using Saccharomyces cerevisiae INVSC-1 in a double jacket reactor. To improve the viability of the process, the spent media after ethanol fermentation was subsequently used for methane production using mixed microbial consortium. The energy recovery from the process was 40.39% and 39.7% for UTEX 90 and CC 2656, respectively when C. reinhardtii biomass was used as substrate for biofuel production. The present investigation concedes with the potentiality of algae as a favourable 3rd generation feedstock to address the existing challenges of clean energy production with concomitant CO₂ sequestration.

Bioethanol Production by Enzymatic Hydrolysis from Different Lignocellulosic Sources

As the need for non-renewable sources such as fossil fuels has increased during the last few decades, the search for sustainable and renewable alternative sources has gained growing interest. Enzymatic hydrolysis in bioethanol production presents an important step, where sugars that are fermented are obtained in the final fermentation process. In the process of enzymatic hydrolysis, more and more new effective enzymes are being researched to ensure a more cost-effective process. There are many different enzyme strategies implemented in hydrolysis protocols, where different lignocellulosic biomass, such as wood feedstocks, different agricultural wastes, and marine algae are being used as substrates for an efficient bioethanol production. This review investigates the very recent enzymatic hydrolysis pathways in bioethanol production from lignocellulosic biomass.

Microalgae starch: A promising raw material for the bioethanol production

Ethanol is currently the most successful biofuel and can be produced from microalgal biomass (third-generation). Ethanol from microalgal biomass has advantages because it does not use arable land and reduces environmental impacts through the sequestration of CO₂ from the atmosphere. In this way, micro and macroalgal starch, which is structurally similar to that from higher plants can be considered a promise raw material for the production of bioethanol. Thus, strategies can be used to intensify the carbohydrate concentration in the microalgal biomass enabling the production of third-generation bioethanol. The microalgae biomass can be destined to biorefineries so that the residual biomass generated from the extraction processes is used for the production of high value-added products. Therefore, the process will have an impact on reducing the production costs and the generation of waste. In this context, this review aims to bring concepts and perspectives on the production of third-generation bioethanol, demonstrating the microalgal biomass potential as a carbon source to produce bioethanol and supply part of the world energy demand. The main factors that influence the microalgal cultivation and fermentation process, as well as the processes of transformation of biomass into the easily fermentable substrate are also discussed.

Advances in the Biotechnological Potential of Brazilian Marine Microalgae and Cyanobacteria

Due the worldwide need to improve care for the environment and people, there is a great demand for the development of new renewable, sustainable, and less polluting technologies for food, health, and environmental industries. The marine environment is one of the main areas investigated in the search for alternatives to the raw materials currently used. Thereby, cyanobacteria and marine microalgae are microorganisms that are capable of producing a diverse range of metabolites useful for their cellular maintenance, but that also represent a great biotechnological potential. Due its great potential, they have an enormous appeal in the scientific research where, the biological activity of metabolites produced by these microorganisms, such as the antioxidant action of sterols are, some examples of biotechnological applications investigated around the world. Thereby, Brazil due to its extensive biodiversity, has high potential as a raw material supplier of marine waters, researching cyanobacteria and microalgae metabolites and their applications. Thus, this rapid review intends to present some important contributions and advances from Brazilian researchers, using the biomass of Brazilian cyanobacteria and marine microalgae, in order to illustrate the value of what has already been discovered and the enormous potential of what remains unexplored so far.

Microalgal biomass pretreatment for integrated processing into biofuels, food, and feed

Microalgae are sources of nutritional products and biofuels. However, their economical processing is challenging, because of (i) the inherently low concentration of biomass in algal cultures, below 0.5%, (ii) the high-water content in the harvested biomass, above 70%; and (iii) the variable intracellular content and composition. Cell wall structure and strength vary enormously among microalgae, from naked Dunaliella cells to robust Haematococcus cysts. High-value products justify using fast and energy-intensive processes, ranging from 0.23 kWh/kg dry biomass in high-pressure homogenization, to 6 kWh/kg dry biomass in sonication. However, in biofuels production, the energy input must be minimized, requiring slower, thermal or chemical pretreatments. Whichever the primary fraction of interest, the spent biomass can be processed into valuable by-products. This review discusses microalgal cell structure and composition, how it affects pretreatment, focusing on technologies tested for large scale or promising for industrial processes, and how these can be integrated into algal biorefineries.

Process optimization for the production of high-concentration ethanol with Scenedesmus raciborskii biomass

Scenedesmus raciborskii WZKMT was subjected to fed-batch enzymatic hydrolysis and fermentation to facilitate the saccharification of high-solid-loading substrate for high-concentration ethanol. In this work, process factors affecting enzymatic hydrolysis, including enzyme loading, temperature, pH, and solid loading, were optimized. Results showed that 58.03 g L^-1 glucose, 12.57 g L^-1 xylose, and 1.45 g L^-1 cellobiose were obtained after the enzymatic hydrolysis of 330 g L^-1 substrates under the optimal conditions of 30 FPU g^-1 enzyme loading, 50 °C, and pH 5.5. Meanwhile, 89.60% yield and 30.43 g L^-1 content of ethanol were obtained after the fermentation of 330 g L^-1 hydrolysate. The maximum ethanol concentration of 79.38 g L^-1 could be achieved through repeated fed-batch process, indicating that S. raciborskii WZKMT is a promising feedstock for ethanol production.

Algae biorefinery: Review on a broad spectrum of downstream processes and products

Algae biomass comprises variety of biochemicals components such as carbohydrates, lipids and protein, which make them a feasible feedstock for biofuel production. However, high production cost mainly due to algae cultivation remains the main challenge in commercializing algae biofuels. Hence, extraction of other high value-added bioproducts from algae biomass is necessary to enhance the economic feasibility of algae biofuel production. This paper is aims to deliberate the recent developments of conventional technologies for algae biofuels production, such as biochemical and chemical conversion pathways, and extraction of a variety of bioproducts from algae biomass for various potential applications. Besides, life cycle evaluation studies on microalgae biorefinery are presented, focusing on case studies for various cultivation techniques, culture medium, harvesting, and dewatering techniques along with biofuel and bioenergy production pathways. Overall, the algae biorefinery provides new opportunities for valorisation of algae biomass for multiple products synthesis.

Assessment of upstream bioprocessing

Depending on the purpose and use, bioprocesses are carried out in order to reduce, maintain or increase the molar O/C ratio of biomass as the initial substrate. Cascade use considers the holistic and efficient use of biomass. In the current debate of biomass use, however, one may admit that an efficient use of biomass can further be based on the maintenance of initially present molar O/C ratio and functionality. In this regard, what compound should be formed that possesses highest functionality and similar molar O/C ratio as the substrate? How much energy should be spent on bioprocesses for the conversion of biomass under aerobic or anaerobic conditions? This study discusses and contributes to the efficiency assessment of aerobic and anaerobic bioprocesses based on chemical functionality and molar O/C ratio and their scale-depended energy need for creating appropriate environmental conditions for biological agents.