Bioethanol from microalgae and cyanobacteria: A review and technological outlook

Role of cultivation parameters in carbohydrate accretion for production of bioethanol and C-phycocyanin from a marine cyanobacterium Leptolyngbya valderiana BDU 41001: A sustainable approach

The investigation aimed to augment carbohydrate accumulation in the marine cyanobacterium Leptolyngbya valderiana BDU 41001 to facilitate bioethanol production. Under the standardised physiochemical condition (SPC), i.e. 90 µmol photon m-2 s-1 light intensity, initial culture pH 8.5, 35 °C temperature and mixing at 150 rpm increased the carbohydrate productivity ∼70 % than the control, while a 47 % rise in content was obtained under the nitrate (N)-starved condition. Therefore, a two-stage cultivation strategy was implemented, combining SPC at the 1st stage and N starvation at the 2nd stage, resulting in 80 % augmentation of carbohydrate yield, which enhanced the bioethanol yield by ∼86 % as compared to the control employing immobilised yeast fermentation. Moreover, biomass utilisation was maximised by extracting C-phycocyanin, where a ∼77 % rise in productivity was recorded under the SPC. This study highlights the potential of L. valderiana for pilot-scale biorefinery applications, advancing the understanding of sustainable biofuel production.

Microalgae to bioenergy production: Recent advances, influencing parameters, utilization of wastewater - A critical review

Fossil fuel limitations and their influence on climate change through atmospheric greenhouse gas emissions have made the excessive use of fossil fuels widely recognized as unsustainable. The high lipid content, carbon-neutral nature and potential as a biofuel source have made microalgae a subject of global study. Microalgae are a promising supply of biomass for third-generation biofuels production since they are renewable. They have the potential to produce significant amounts of biofuel and are considered a sustainable alternative to non-renewable energy sources. Microalgae are currently incapable to synthesize algal biofuel on an extensive basis in a sustainable manner, despite their significance in the global production of biofuels. Wastewater contains nutrients (both organic and inorganic) which is essential for the development of microalgae. Microalgae and wastewater can be combined to remediate waste effectively. Wastewater of various kinds such as industrial, agricultural, domestic, and municipal can be used as a substrate for microalgal growth. This process helps reduce carbon dioxide emissions and makes the production of biofuels more cost-effective. This critical review provides a detailed analysis of the utilization of wastewater as a growth medium for microalgal - biofuel production. The review also highlights potential future strategies to improve the commercial production of biofuels from microalgae.

Microalgae as fishmeal alternatives in aquaculture: current status, existing problems, and possible solutions

Fishmeal is an indispensable ingredient for most aquatic animals. However, the finite supply and escalating price of fishmeal seriously limit its use in aquaculture. Thus the development of new, sustainable protein ingredients has been a research focus. Microalgae are potential fishmeal alternatives owing to their high protein content and balanced amino acid profile. Studies suggest that suitable replacement of fishmeal with microalgae is beneficial for fish growth performance, but excessive replacement would induce poor growth and feed utilization. Therefore, this paper aims to review research on the maximum substitutional level of fishmeal by microalgae and propose the main issues and possible solutions for fishmeal replacement by microalgae. The maximum replacement level is affected by microalgal species, fish feeding habits, quality of fishmeal and microalgal meals, and supplemental levels of fishmeal in the control group. Microalgae could generally replace 100%, 95%, 95%, 64.1%, 25.6%, and 18.6% fishmeal protein in diets of carp, shrimp, catfish, tilapia, marine fish, and salmon and trout, respectively. The main issues with fishmeal replacement using microalgae include low production and high production cost, poor digestibility, and anti-nutritional factors. Possible solutions to these problems are recommended in this paper. Overall, microalgae are promising fishmeal alternatives in aquaculture.

Microalgae-assisted green bioremediation of food-processing wastewater: A sustainable approach toward a circular economy concept

Wastewater disposal is a major environmental issue that pollutes water, causing eutrophication, habitat destruction, and economic impact. In Mexico, food-processing effluents pose a huge environmental threat due to their excessive nutrient content and their large volume discharged every year. Some of the most harmful residues are tequila vinasses, nejayote, and cheese whey. Each liter of tequila generates 13-15 L of vinasses, each kilogram of cheese produces approximately 9 kg of cheese whey, and each kilogram of nixtamalized maize results in the production of 2.5-3.3 L of nejayote. A promising strategy to reduce the contamination derived from wastewater is through microalgae-based wastewater treatment. Microalgae have a high adaptability to hostile environments and they can feed on the nutrients in the effluents to grow. Moreover, to increase the viability, profitability, and value of wastewater treatments, a microalgae biorefinery could be proposed. This review will focus on the circular bioeconomy scheme focused on the simultaneous food-processing wastewater treatment and its use to grow microalgae biomass to produce added-value compounds. This strategy allows for the revalorization of wastewater, decreases contamination of water sources, and produces valuable compounds that promote human health such as phycobiliproteins, carotenoids, omega-3 fatty acids, exopolysaccharides, mycosporine-like amino acids, and as a source of clean energy: biodiesel, biogas, and bioethanol.

Cellulose Synthase in Atacama Cyanobacteria and Bioethanol Production from Their Exopolysaccharides

Cyanobacteria produce exopolysaccharides (EPSs) as an adaptative mechanism against ultraviolet radiation and desiccation. Cellulose is present in the extracellular polymeric substance in some cyanobacteria genera and it has been proposed as a raw material for biofuel production. The goal of this work was to evaluate the cellulose presence in EPS of Atacama cyanobacteria strains and its use as an alternative and innovative biological source to produce bioethanol. The presence of cellulose was evaluated using techniques of molecular biology, bioinformatics, and electronic microscopy. The conserved motif D,D,D,35QXXRW, characteristic of processive β-glycosyltransferase in all cellulose-producing organisms, was identified in the genome of the LLA-10 strain. This is evidence that cellulose synthase in the LLA-10 strain is a functional enzyme. EPS from Atacama cyanobacteria was hydrolyzed by β-glucosidases (cellobiase and cellulase) and the released glucose was yeast-fermented to ethanol. Ethanol production reached 172.69 ± 0.02 mg ethanol/g EPS after 48 h of incubation. These results are the first step in the evaluation of EPS produced by native cyanobacteria isolated from northern Chile for future biotechnological applications such as the production of bioethanol.

Microalgal co-cultivation -recent methods, trends in omic-studies, applications, and future challenges

The burgeoning human population has resulted in an augmented demand for raw materials and energy sources, which in turn has led to a deleterious environmental impact marked by elevated greenhouse gas (GHG) emissions, acidification of water bodies, and escalating global temperatures. Therefore, it is imperative that modern society develop sustainable technologies to avert future environmental degradation and generate alternative bioproduct-producing technologies. A promising approach to tackling this challenge involves utilizing natural microbial consortia or designing synthetic communities of microorganisms as a foundation to develop diverse and sustainable applications for bioproduct production, wastewater treatment, GHG emission reduction, energy crisis alleviation, and soil fertility enhancement. Microalgae, which are photosynthetic microorganisms that inhabit aquatic environments and exhibit a high capacity for CO2 fixation, are particularly appealing in this context. They can convert light energy and atmospheric CO2 or industrial flue gases into valuable biomass and organic chemicals, thereby contributing to GHG emission reduction. To date, most microalgae cultivation studies have focused on monoculture systems. However, maintaining a microalgae monoculture system can be challenging due to contamination by other microorganisms (e.g., yeasts, fungi, bacteria, and other microalgae species), which can lead to low productivity, culture collapse, and low-quality biomass. Co-culture systems, which produce robust microorganism consortia or communities, present a compelling strategy for addressing contamination problems. In recent years, research and development of innovative co-cultivation techniques have substantially increased. Nevertheless, many microalgae co-culturing technologies remain in the developmental phase and have yet to be scaled and commercialized. Accordingly, this review presents a thorough literature review of research conducted in the last few decades, exploring the advantages and disadvantages of microalgae co-cultivation systems that involve microalgae-bacteria, microalgae-fungi, and microalgae-microalgae/algae systems. The manuscript also addresses diverse uses of co-culture systems, and growing methods, and includes one of the most exciting research areas in co-culturing systems, which are omic studies that elucidate different interaction mechanisms among microbial communities. Finally, the manuscript discusses the economic viability, future challenges, and prospects of microalgal co-cultivation methods.

Aerosolization flux, bio-products, and dispersal capacities in the freshwater microalga Limnomonas gaiensis (Chlorophyceae)

Little is known on the spreading capacities of Limnomonas gaiensis across freshwater lakes in Northern Europe. In this study, we show that the species could successfully be aerosolized from water sources by bubble bursting (2-40 particles.cm-3), irrespectively of its density in the water source or of the jet velocity used to simulate wave breaking. The species viability was impacted by both water turbulences and aerosolization. The survival rate of emitted cells was low, strain-specific, and differently impacted by bubble busting processes. The entity "microalga and bionts" could produce ethanol, and actively nucleate ice (principally ≤-18 °C) mediated soluble ice nucleation active proteins, thereby potentially impacting smog and cloud formation. Moreover, smallest strains could better cope with applied stressors. Survival to short-term exposure to temperatures down to -21 °C and freezing events further suggest that L. gaiensis could be air dispersed and contribute to their deposition.

Mechanism and kinetic model of microalgal enzymatic hydrolysis for prospective bioethanol conversion

Tetraselmis chuii is a potential microalgae that is in consideration for producing bioethanol owing to its large content of carbohydrates. The glucose production from T. chuii through an enzymatic process with cellulase and xylanase (pretreatment process) and α-amylase and glucoamylase (saccharification process) was studied. The mechanism of the enzymatic process was developed and the kinetic models were then evaluated. For the pretreatment process, enzymes with 30% concentration reacted at 30 °C for 40 min resulted in 35.9% glucose yield. For the saccharification process, the highest glucose yield of 90.03% was obtained using simultaneous α-amylase (0.0006%) and glucoamylase (0.01%) enzymes at 55 °C and for 40 min. The kinetic models fitted well with the experimental data. The model also revealed that the saccharification process performed better than the pretreatment process with a higher kinetic constant and lower activation energy. The proposed kinetic model plays an important role in implementing processes at a larger scale.

Physiological responses to pH in the freshwater microalga Limnomonas gaiensis

The ecological niche of the recently described limnic microalga Limnomonas gaiensis (Chlamydomonadales) in Northern Europe remains unknown. To decipher the species tolerance capacity to pH, the effects of hydrogen ions on the physiological response of L. gaiensis were investigated. Results showed that L. gaiensis could tolerate exposure from pH 3 up to pH 11, with an optimal survival at pH 5-8. Its physiological response to pH was strain specific. Globally the southernmost strain was more alkaliphilic, had a slightly rounder shape, a slowest growth rate, and a lowest carrying capacity. Despite strain discrepancies among lakes, Swedish strains exhibited similar growth rates, faster at more acidic conditions. The extreme pH conditions affected its morphological features such as the eye spot and papilla shape, especially at acidic pH, and the cell wall integrity, at more alkaline pH. The wide range tolerance of L. gaiensis to pH would not be a hindrance to its dispersal in Swedish lakes (pH 4-8). Notably, the storage of high-energetic reserves over a wide range of pH conditions, as numerous starch grains and oil droplets, makes L. gaiensis a good candidate for bioethanol/fuel industrial production and a key resource to sustain aquatic food chain and microbial loop.

Copper multifaceted interferences during swine wastewater treatment in high-rate algal ponds: alterations on nutrient removal, biomass composition and resource recovery

Microalgae cultivation in swine wastewater (SW) allows the removal of nutrients and biomass production. However, SW is known for its Cu contamination, and its effects on algae cultivation systems such as high-rate algal ponds (HRAPs) are poorly understood. This gap in the literature limits the proposition of adequate concentrations of Cu to optimise SW treatment and resource recovery in HRAPs. For this assessment, 12 HRAPs installed outdoors were operated with 800 L of SW with different Cu concentrations (0.1-4.0 mg/L). Cu's interferences on the growth and composition of biomass and nutrient removal from SW were investigated through mass balance and experimental modelling. The results showed that the concentration of 1.0 mg Cu/L stimulated microalgae growth, and above 3.0 mg Cu/L caused inhibition accompanied by an accumulation of H₂O₂. Furthermore, Cu affected the contents of lipids and carotenoids observed in the biomass; the highest concentration was observed in the control (16%) and 0.5 mg Cu/L (1.6 mg/g), respectively. An innovative result was verified for nutrient removal, in which increased Cu concentration reduced the N-NH₄⁺ removal rate. In contrast, the soluble P removal rate was enhanced by 2.0 mg Cu/L. Removal of soluble Cu in treated SW reached 91%. However, the action of microalgae in this process was not associated with assimilation but with a pH increase resulting from photosynthesis. A preliminary evaluation of economic viability showed that the commercialisation of biomass considering the concentration of carotenoids obtained in HRAPs with 0.5 mg Cu/L could be economically attractive. In conclusion, Cu affected the different parameters evaluated in this study in a complex way. This can help managers consort nutrient removal, biomass production, and resource recovery, providing information for possible industrial exploitation of the generated bioproducts.

Botryococcus terribilis Ethanol Extract Exerts Anti-inflammatory Effects on Murine RAW264 Cells

The present study aimed to evaluate the effects of Botryococcus terribilis ethanol extract (BTEE) on lipopolysaccharide (LPS)-induced inflammation in RAW264 cells. BTEE significantly attenuated LPS-induced nitric oxide production and inflammatory cytokines release, including Ccl2, Cox2, and Il6. On the other hand, several anti-inflammatory mediators, such as Pgc1β and Socs1, were increased in BTEE-treated cells. Further, we performed an untargeted whole-genome microarray analysis to explore the anti-inflammatory molecular mechanism of BTEE. Enrichment analysis showed BTEE significantly downregulated ‘response to stimulus’, ‘locomotion’, and ‘immune system response’ and upregulated ‘cell cycle’ gene ontologies in both 6- and 17-h post-LPS stimulation conditions. Pathway analysis revealed BTEE could downregulate the expressions of chemokines of the CC and CXC subfamily, and cytokines of the TNF family, TGFβ family, IL1-like, and class I helical. PPI analysis showed AXL receptor tyrosine kinase (Axl), a receptor tyrosine kinase from the TAM family, and its upstream transcription factors were downregulated in both conditions. Node neighborhood analysis showed several Axl coexpressed genes were also downregulated. Further, kinase enrichment and chemical perturbation analyses supported Axl inhibition in BTEE-treated conditions. Altogether, these findings suggest anti-inflammatory effects of BTEE that are mediated via the suppression of pro-inflammatory cytokines and predict its potential as an Axl inhibitor.

Optimization of the culture of Chlorella sorokiniana PA.91 by RSM: effect of temperature, light intensity, and MgAC-NPs

The unique physicochemical properties of magnesium amino clay nanoparticles (MgAC-NPs) tends to be beneficial in the application as a co-additive in treating microalgae. Also, MgAC-NPs can create oxidative stress in the environment, concurrently elective control bacteria in mixotrophic culture, and stimulate CO₂ biofixation. The condition of the cultivation of newly isolated strains, Chlorella sorokiniana PA.91, was optimized for the first time for MgAC-NPs at various temperatures and light intensities in the culture medium of municipal wastewater (MWW) by central composite design in the response surface methodology (RSM-CCD). This study examined synthesized MgAC-NP with their FE-SEM, EDX, XRD, and FT-IR characteristics. The synthesized MgAC-NPs were naturally stable, cubic shaped, and within the size range of 30-60 nm. The optimization results show that at culture conditions of 20 °C, 37 μmol m^-2 s^-1, and 0.05 g L^-1, microalga MgAC-NPs have the best growth productivity and biomass performance. Maximum dry biomass weight (55.41%), specific growth rate (30.26%), chlorophyll (81.26%), and carotenoids (35.71%) were achieved under the optimized condition. Experimental results displayed that C.S. PA.91 has a high capacity for lipid extraction (1.36 g L^-1) and significant lipid efficiency (45.1%). Also, in 0.2 and 0.05 g L^-1 of the MgAC-NPs, COD removal efficiency 91.1% and 81.34% from C.S. PA.91 showed, respectively. These results showed the potential of C.S. PA.91-MgAC-NPs for nutrient removal in wastewater treatment plants and their quality as sources of biodiesel.

An Alternative Exploitation of Synechocystis sp. PCC6803: A Cascade Approach for the Recovery of High Added-Value Products

Microalgal biomass represents a very interesting biological feedstock to be converted into several high-value products in a biorefinery approach. In this study, the cyanobacterium Synechocystis sp. PCC6803 was used to obtain different classes of molecules: proteins, carotenoids and lipids by using a cascade approach. In particular, the protein extract showed a selective cytotoxicity towards cancer cells, whereas carotenoids were found to be active as antioxidants both in vitro and on a cell-based model. Finally, for the first time, lipids were recovered from Synechocystis biomass as the last class of molecules and were successfully used as an alternative substrate for the production of polyhydroxyalkanoate (PHA) by the native PHA producer Pseudomonas resinovorans. Taken together, our results lead to a significant increase in the valorization of Synechocystis sp. PCC6803 biomass, thus allowing a possible offsetting of the process costs.

Challenges and opportunities for third-generation ethanol production: A critical review

In recent decades, third-generation (3G) biofuels have become a more attractive method of fuel production, as algae cultivation does not infringe on resources needed for food production. Additionally, algae can adapt to different environments, has high photosynthetic efficiency (CO2 fixation), and has a high potential for carbohydrate accumulation. The prevalence of algae worldwide demonstrates its ability to adapt to different environments and climates, proving its biodiversity and versatility. Algae can be grown in wastewater, seawater, and even sewage, thus ensuring a lower water footprint and greater energy efficiency during algal biomass production. Because of this, the optimization of 3G ethanol production appears to be an excellent alternative to mitigate environmental impacts and increase energy and food security. This critical review presents (i) the stages of cultivation and processing of micro and macroalgae; (ii) the selection of yeasts (through engineering and/or bioprospecting) to produce ethanol from these biomasses; (iii) the potential of seawater-based facilities to reduce water footprint; and (iv) the mass and energy balances of 3G ethanol production in the world energy matrix. This article is, above all, a brainstorm on the environmental viability of algae bioethanol.

Role of microalgae in achieving sustainable development goals and circular economy

In 2015, the United Nations General Assembly (UNGA) set out 17 Sustainable Development Goals (SDGs) to be achieved by 2030. These goals highlight key objectives that must be addressed. Each target focuses on a unique perspective crucial to meeting these goals. Social, political, and economic issues are addressed to comprehensively review the main issues combating climate change and creating sustainable and environmentally friendly industries, jobs, and communities. Several mechanisms that involve judicious use of biological entities are among instruments that are being explored to achieve the targets of SDGs. Microalgae have an increasing interest in various sectors, including; renewable energy, food, environmental management, water purification, and the production of chemicals such as biofertilizers, cosmetics, and healthcare products. The significance of microalgae also arises from their tendency to consume CO2, which is the main greenhouse gas and the major contributor to the climate change. This work discusses the roles of microalgae in achieving the various SDGs. Moreover, this work elaborates on the contribution of microalgae to the circular economy. It was found that the microalgae contribute to all the 17th SDGs, where they directly contribute to 9th of the SDGs and indirectly contribute to the rest. The major contribution of the Microalgae is clear in SDG-6 "Clean water and sanitation", SDG-7 "Affordable and clean energy", and SDG-13 "Climate action". Furthermore, it was found that Microalgae have a significant contribution to the circular economy.

Robust Control Based on Modeling Error Compensation of Microalgae Anaerobic Digestion

Microalgae are used to produce renewable biofuels (biodiesel, bioethanol, biogas, and biohydrogen) and high-value-added products, as well as in bioremediation and CO2 sequestration tasks. In the case of anaerobic digestion of microalgae, biogas can be produced from mainly proteins and carbohydrates. Anaerobic digestion is a complex process that involves several stages and is susceptible to operational instability due to various factors. Robust controllers with simple structure and design are necessary for practical implementation purposes and to achieve a proper process operation despite process variabilities, uncertainties, and complex interactions. This paper presents the application of a control design based on the modeling error compensation technique for the anaerobic digestion of microalgae. The control design departs from a low-order input–output model by enhancement with uncertainty estimation. The results show that achieving desired organic pollution levels and methanogenic biomass concentrations as well as minimizing the effect of external perturbations on a benchmark case study of the anaerobic digestion of microalgae is possible with the proposed control design.

Recent Advances in Micro-/Nanoplastic (MNPs) Removal by Microalgae and Possible Integrated Routes of Energy Recovery

Reliance on plastic has resulted in the widespread occurrence of micro-/nanoplastics (MNPs) in aquatic ecosystems, threatening the food web and whole ecosystem functions. There is a tight interaction between MNPs and microalgae, as dominant living organisms and fundamental constituents at the base of the aquatic food web. Therefore, it is crucial to better understand the mechanisms underlying the interactions between plastic particles and microalgae, as well as the role of microalgae in removing MNPs from aquatic ecosystems. In addition, finding a suitable route for further utilization of MNP-contaminated algal biomass is of great importance. The present review article provides an interdisciplinary approach to elucidate microalgae-MNP interactions and subsequent impacts on microalgal physiology. The degradation of plastic in the environment and differences between micro- and nanoplastics are discussed. The possible toxic effects of MNPs on microalgal growth, photosynthetic activity, and morphology, due to physical or chemical interactions, are evaluated. In addition, the potential role of MNPs in microalgae cultivation and/or harvesting, together with further safe routes for biomass utilization in biofuel production, are suggested. Overall, the current article represents a state-of-the-art overview of MNP generation and the consequences of their accumulation in the environment, providing new insights into microalgae integrated routes of plastic removal and bioenergy production.

Versatile Applications of Cyanobacteria in Biotechnology

Cyanobacteria are blue-green Gram-negative and photosynthetic bacteria which are seen as one of the most morphologically numerous groups of prokaryotes. Because of their ability to fix gaseous nitrogen and carbon dioxide to organic materials, they are known to play important roles in the universal nutrient cycle. Cyanobacteria has emerged as one of the promising resources to combat the issues of global warming, disease outbreaks, nutrition insecurity, energy crises as well as persistent daily human population increases. Cyanobacteria possess significant levels of macro and micronutrient substances which facilitate the versatile popularity to be utilized as human food and protein supplements in many countries such as Asia. Cyanobacteria has been employed as a complementary dietary constituent of feed for poultry and as vitamin and protein supplement in aquatic lives. They are effectively used to deal with numerous tasks in various fields of biotechnology, such as agricultural (including aquaculture), industrial (food and dairy products), environmental (pollution control), biofuel (bioenergy) and pharmaceutical biotechnology (such as antimicrobial, anti-inflammatory, immunosuppressant, anticoagulant and antitumor); recently, the growing interest of applying them as biocatalysts has been observed as well. Cyanobacteria are known to generate a numerous variety of bioactive compounds. However, the versatile potential applications of cyanobacteria in biotechnology could be their significant growth rate and survival in severe environmental conditions due to their distinct and unique metabolic pathways as well as active defensive mechanisms. In this review, we elaborated on the versatile cyanobacteria applications in different areas of biotechnology. We also emphasized the factors that could impede the implementation to cyanobacteria applications in biotechnology and the execution of strategies to enhance their effective applications.

On reducing the emissions of CO, HC, and NOx from gasoline blended with hydrogen peroxide and ethanol: Optimization study aided with ANN-PSO

The use of ethanol blending for gasoline has been found to have a significant effect in reducing emissions without any loss in the performance of a spark ignition engine. However, an increase in the emissions of oxides of nitrogen (NO_x) may be seen due to the increased oxygen content in the fuel. On the contrary, emulsifying fuel with hydrogen peroxide (H₂O₂) has shown a substantial effect in reducing all the emissions, including NO_x in a compression ignition (CI) engine. In this study, 10% ethanol is blended with gasoline (E10) and further emulsified with H₂O₂ up to 1.5%. When compared to neat gasoline, a 4.8% increase in brake thermal efficiency (BTE) is obtained with 10% ethanol and 1.5% H₂O₂. The corresponding average decrease in the emissions of carbon monoxide (CO), hydrocarbons (HC), and NO_x were 80%, 43%, and 17%, respectively. The results of the experimental trials are used to model an artificial neural network (ANN) to derive a relationship between the input factors of ethanol concentration, H₂O₂ concentration, and engine speeds with the output responses of BTE, CO, HC, and NO_x. The ANN models of each response are optimized using a multi-objective particle swarm optimization (PSO) for maximizing BTE and minimizing emissions of CO, HC, and NO_x. The PSO results showed that operating the engine at 2000 rpm using ethanol blending between 4 and 6% and H₂O₂ emulsification of 1.5% are the best optimal conditions.

Sustainable Microalgae and Cyanobacteria Biotechnology

Marine organisms are a valuable source of new compounds, many of which have remarkable biotechnological properties, such as microalgae and cyanobacteria, which have attracted special attention to develop new industrial production routes. These organisms are a source of many biologically active molecules in nature, including antioxidants, immunostimulants, antivirals, antibiotics, hemagglutinates, polyunsaturated fatty acids, peptides, proteins, biofuels, and pigments. The use of several technologies to improve biomass production, in the first step, industrial processes schemes have been addressed with different accomplishments. It is critical to consider all steps involved in producing a bioactive valuable compound, such as species and strain selection, nutrient supply required to support productivity, type of photobioreactor, downstream processes, namely extraction, recovery, and purification. In general, two product production schemes can be mentioned; one for large amounts of product, such as biodiesel or any other biofuel and the biomass for feeding purposes; the other for when the product will be used in the human health domain, such as antivirals, antibiotics, antioxidants, etc. Several applications for microalgae have been documented. In general, the usefulness of an application for each species of microalgae is determined by growth and product production. Furthermore, the use of OMICS technologies enabled the development of a new design for human therapeutic recombinant proteins, including strain selection based on previous proteomic profiles, gene cloning, and the development of expression networks. Microalgal expression systems have an advantage over traditional microbial, plant, and mammalian expression systems for new and sustainable microalga applications, for responsible production and consumption.

Machine Learning Methods Modeling Carbohydrate-Enriched Cyanobacteria Biomass Production in Wastewater Treatment Systems

One-stage production of carbohydrate-enriched microalgae biomass in wastewater is a promising option to obtain biofuels. Understanding the interaction of water quality parameters such as nutrients, carbon, internal carbohydrates, and microbial composition in the culture is crucial for efficient operation and viable large-scale cultivation. Bioprocess models are an essential tool for studying the simultaneous effect of complex factors on carbohydrate accumulation, optimizing the process, and reducing operational costs. In this sense, we use a dataset obtained from an empirical model that analyzed the accumulation of carbohydrates in a single process (simultaneous growth and accumulation) from real wastewater. In this experiment, there were no ideal conditions (limiting nutrient conditions), but rather these limitations are guaranteed by the operating conditions (hydraulic retention times/nutrient or carbon loads). Thus, the model integrates 18 variables that are affected and not only carbohydrates. The effect of these variables directly influences the accumulation of carbohydrates. Therefore, this paper analyzes artificial intelligence (AI) algorithms to develop a model to forecast biomass production in wastewater treatment systems. Carbohydrates were modeled using five artificial intelligence methods: (1) Artificial Neural Networks (ANNs), (2) Convolutional Neural Networks (CNN), (3) Long Short-Term Memory Network (LSTMs), (4) K-Nearest Neighbors (kNN), and (5) Random Forest (RF)). The AI methods allow learning how several components interact and if their combinations work faster than building the physical experiments over the same period of time. After comparing the five learning models, the CNN-1D model obtained the best results with an MSE (Mean Squared Error) = 0.0028. This result shows that the model adequately approximates the system’s dynamics.

R, Maitra S, Tarafdar A, Alphy MP, Kumar AN, Madhavan A, Sirohi R, Awasthi MK, Sindhu R, Varjani S, Binod P. Waste-Derived Fuels and Renewable Chemicals for Bioeconomy Promotion: A Sustainable Approach

Bio-based fuels and chemicals through the biorefinery approach has gained significant interest as an alternative platform for the petroleum-derived processes as these biobased processes are noticed to have positive environmental and societal impacts. Decades of research was involved in understanding the diversity of microorganisms in different habitats that could synthesize various secondary metabolites that have functional potential as fuels, chemicals, nutraceuticals, food ingredients, and many more. Later, due to the substrate-related process economics, the diverse low-value, high-carbon feedstocks like lignocellulosic biomass, industrial byproducts, and waste streams were investigated to have greater potential. Among them, municipal solid wastes can be used as the source of substrates for the production of commercially viable gaseous and liquid fuels, as well as short-chain fattyacids and carboxylic acids. In this work, technologies and processes demanding the production of value-added products were explained in detail to understand and inculcate the value of municipal solid wastes and the economy, and it can provide to the biorefinery aspect.

Algal biomass valorisation to high-value chemicals and bioproducts: Recent advances, opportunities and challenges

Algae are considered promising biomass resources for biofuel production. However, some arguments doubt the economical and energetical feasibility of algal cultivation, harvesting, and conversion processes. Beyond biofuel, value-added bioproducts can be generated via algae conversion, which would enhance the economic feasibility of algal biorefineries. This review primarily focuses on valuable chemical and bioproduct production from algae. The methods for effective recovery of valuable algae components, and their applications are summarized. The potential routes for the conversion of lipids, carbohydrates, and proteins to valuable chemicals and bioproducts are assessed from recent studies. In addition, this review proposes the following challenges for future algal biorefineries: (1) utilization of naturally grown algae instead of cultivated algae; (2) fractionation of algae to individual components towards high-selectivity products; (3) avoidance of humin formation from algal carbohydrate conversion; (4) development of strategies for algal protein utilisation; and (5) development of efficient processes for commercialization and industrialization.

Wastewater-based microalgal biorefineries for the production of astaxanthin and co-products: Current status, challenges and future perspectives

The freshwater microalgae Haematococcus pluvialis and Chlorella zofingiensis are attractive biorefinery feedstocks in view of their ability to simultaneously synthesize astaxanthin and other valuable metabolites. Nonetheless, there are concerns regarding the sustainability of such biorefineries due to the high freshwater footprint of microalgae cultivation. The integration of wastewater as an alternative growth media is a promising approach to reduce freshwater demand. Wastewater-based cultivation enables the recovery of essential nutrients required for microalgae growth and consequently results in phycoremediation of wastewater, thus promoting the concept of a circular economy and further enhancing the sustainability of the process. In this review, recent developments in wastewater-integrated cultivation of H. pluvialis and C. zofingiensis for astaxanthin production are discussed. Furthermore, prospective strategies for overcoming the inherent challenges of wastewater-based cultivation are reviewed. Moreover, the biorefinery potential of wastewater-grown H. pluvialis and C. zofingiensis is delineated and future perspectives of wastewater-based biorefineries are outlined.

Role of Biofuels in Energy Transition, Green Economy and Carbon Neutrality

Modern civilization is heavily reliant on petroleum-based fuels to meet the energy demand of the transportation sector. However, burning fossil fuels in engines emits greenhouse gas emissions that harm the environment. Biofuels are commonly regarded as an alternative for sustainable transportation and economic development. Algal-based fuels, solar fuels, e-fuels, and CO2-to-fuels are marketed as next-generation sources that address the shortcomings of first-generation and second-generation biofuels. This article investigates the benefits, limitations, and trends in different generations of biofuels through a review of the literature. The study also addresses the newer generation of biofuels highlighting the social, economic, and environmental aspects, providing the reader with information on long-term sustainability. The use of nanoparticles in the commercialization of biofuel is also highlighted. Finally, the paper discusses the recent advancements that potentially enable a sustainable energy transition, green economy, and carbon neutrality in the biofuel sector.

Current Trends and Future Prospects of Nanotechnology in Biofuel Production

Biofuel is one of the best alternatives to petroleum-derived fuels globally especially in the current scenario, where fossil fuels are continuously depleting. Fossil-based fuels cause severe threats to the environment and human health by releasing greenhouse gases on their burning. With the several limitations in currently available technologies and associated higher expenses, producing biofuels on an industrial scale is a time-consuming operation. Moreover, processes adopted for the conversion of various feedstock to the desired product are different depending upon the various techniques and materials utilized. Nanoparticles (NPs) are one of the best solutions to the current challenges on utilization of biomass in terms of their selectivity, energy efficiency, and time management, with reduced cost involvement. Many of these methods have recently been adopted, and several NPs such as metal, magnetic, and metal oxide are now being used in enhancement of biofuel production. The unique properties of NPs, such as their design, stability, greater surface area to volume ratio, catalytic activity, and reusability, make them effective biofuel additives. In addition, nanomaterials such as carbon nanotubes, carbon nanofibers, and nanosheets have been found to be cost effective as well as stable catalysts for enzyme immobilization, thus improving biofuel synthesis. The current study gives a comprehensive overview of the use of various nanomaterials in biofuel production, as well as the major challenges and future opportunities.

Biorefinery Gets Hot: Thermophilic Enzymes and Microorganisms for Second-Generation Bioethanol Production

To mitigate the current global energy and the environmental crisis, biofuels such as bioethanol have progressively gained attention from both scientific and industrial perspectives. However, at present, commercialized bioethanol is mainly derived from edible crops, thus raising serious concerns given its competition with feed production. For this reason, lignocellulosic biomasses (LCBs) have been recognized as important alternatives for bioethanol production. Because LCBs supply is sustainable, abundant, widespread, and cheap, LCBs-derived bioethanol currently represents one of the most viable solutions to meet the global demand for liquid fuel. However, the cost-effective conversion of LCBs into ethanol remains a challenge and its implementation has been hampered by several bottlenecks that must still be tackled. Among other factors related to the challenging and variable nature of LCBs, we highlight: (i) energy-demanding pretreatments, (ii) expensive hydrolytic enzyme blends, and (iii) the need for microorganisms that can ferment mixed sugars. In this regard, thermophiles represent valuable tools to overcome some of these limitations. Thus, the aim of this review is to provide an overview of the state-of-the-art technologies involved, such as the use of thermophilic enzymes and microorganisms in industrial-relevant conditions, and to propose possible means to implement thermophiles into second-generation ethanol biorefineries that are already in operation.

Bio-products from algae-based biorefinery on wastewater: A review

Increasing resource demand, predicted fossil resources shortage in the near future, and environmental concerns due to the production of greenhouse gas carbon dioxide have motivated the search for alternative 'circular' pathways. Among many options, microalgae have been recently 'revised' as one of the most promising due to their high growth rate (with low land use and without competing with food crops), high tolerance to nutrients and salts stresses and their variability in biochemical composition, in so allowing the supply of a plethora of possible bio-based products such as animal feeds, chemicals and biofuels. The recent raising popularity of Circular Bio-Economy (CBE) further prompted investment in microalgae, especially in combination with wastewater treatment, under the twofold aim of allowing the production of a wide range of bio-based products while bioremediating wastewater. With the aim of discussing the potential bio-products that may be gained from microalgae grown on urban wastewater, this paper presents an overview on microalgae production with particular emphasis on the main microalgae species suitable for growth on wastewater and the obtainable bio-based products from them. By selecting and reviewing 76 articles published in Scopus between 1992 and 2020, a number of interesting aspects, including the selection of algal species suitable for growing on urban wastewater, wastewater pretreatment and algal-bacterial cooperation, were carefully reviewed and discussed in this work. In this review, particular emphasis is placed on understanding of the main mechanisms driving formation of microalgal products (such as biofuels, biogas, etc.) and how they are affected by different environmental factors in selected species. Lastly, the quantitative information gathered from the articles were used to estimate the potential benefits gained from microalgae grown on urban wastewater in Campania Region, a region sometimes criticized for poor wastewater management.

Optimization of microwave-assisted carbohydrate extraction from indigenous Scenedesmus sp. grown in brewery effluent using response surface methodology

The use of wastewater as a nutrient source for microalgae cultivation is considered as a cost-effective approach for algal biomass and biofuel production. The microalgal biomass contains carbohydrates that can be processed into bioethanol through different extraction methods. The objective of this study is to optimize the microwave-assisted extraction (MAE) of carbohydrates from the indigenous Scenedesmus sp. grown on brewery effluent. Optimization of independent variables, such as acid concentration (0.1–5 N), microwave power (800–1200 W), temperature (80–180 °C) and extraction time (5–30 min) performed by response surface methodology. It was found that all independent variables had a significant and positive effect on microwave-assisted carbohydrate extraction. The quadratic model developed on the basis of carbohydrate yield had F value of 112.05 with P < 0.05, indicating that the model was significant to predict the carbohydrate yield. The model had a high value of R² (0.9899) and adjusted R² (0.9811), indicating that the fitted model displayed a good agreement between the predicted and actual carbohydrate yield. An optimum carbohydrate yield obtained was 260.54 mg g⁻¹ under the optimum conditions of acid concentration (2.8 N), microwave power (1075 W), temperature (151 °C) and extraction time (22 min). The validation test showed that the model has adequately described the microwave-assisted extraction (MAE) of carbohydrates from microalgal biomass. This study demonstrated that the indigenous Scenedesmus sp. grown on brewery effluent provides a promising result in carbohydrate production for bioethanol feedstock.

Single-phase and two-phase cultivations using different light regimes to improve production of valuable substances in the anoxygenic photosynthetic bacterium Rhodopseudomonas faecalis PA2

This study aimed to improve biomass, carotenoid, bacteriochlorophyll, protein, lipid, and carbohydrate contents of Rhodopseudomonas faecalis PA2 using different light regimes. Light intensity (4000, 6000, 8000, and 10,000 lx), together with photoperiod (24:0, 16:8, 12:12, and 8:16 h light/dark), was assigned as single-phase (SP) cultivation while two-phase (TP) cultivation used two light intensities (using 4000 lx as the first phase), together with the control of phase shift (3, 6, and 9 days) and photoperiod. Biomass, carotenoid, and bacteriochlorophyll contents were maximized by SP cultivation; light at 8000 lx with light-dark cycle of 24:0 was optimal for pigments synthesis. In contrast, TP was useful to enhance storage compounds; protein, lipid, and carbohydrate productivities were significantly increased by 121.69%, 101.69%, and 92.44%, respectively, in TP when compared with SP. This indicates that the novel light strategy proposed in this study was able to manipulate the production of valuable substances in this strain.

Cyanobacteria-From the Oceans to the Potential Biotechnological and Biomedical Applications

Cyanobacteria are photosynthetic prokaryotic organisms which represent a significant source of novel, bioactive, secondary metabolites, and they are also considered an abundant source of bioactive compounds/drugs, such as dolastatin, cryptophycin 1, curacin toyocamycin, phytoalexin, cyanovirin-N and phycocyanin. Some of these compounds have displayed promising results in successful Phase I, II, III and IV clinical trials. Additionally, the cyanobacterial compounds applied to medical research have demonstrated an exciting future with great potential to be developed into new medicines. Most of these compounds have exhibited strong pharmacological activities, including neurotoxicity, cytotoxicity and antiviral activity against HCMV, HSV-1, HHV-6 and HIV-1, so these metabolites could be promising candidates for COVID-19 treatment. Therefore, the effective large-scale production of natural marine products through synthesis is important for resolving the existing issues associated with chemical isolation, including small yields, and may be necessary to better investigate their biological activities. Herein, we highlight the total synthesized and stereochemical determinations of the cyanobacterial bioactive compounds. Furthermore, this review primarily focuses on the biotechnological applications of cyanobacteria, including applications as cosmetics, food supplements, and the nanobiotechnological applications of cyanobacterial bioactive compounds in potential medicinal applications for various human diseases are discussed.

Recycling industrial wastewater for improved carbohydrate-rich biomass production in a semi-continuous photobioreactor: Effect of hydraulic retention time

This study aimed to investigate a mixed microalgae culture's capacity to simultaneously remove nutrients and organic matter from industrial effluents while producing carbohydrate-rich biomass. A culture initially dominated by filamentous cyanobacteria Geitlerinema sp. was inoculated in a lab-scale stirred tank photobioreactor, operating at 10, 8, and 6 days hydraulic retention time (HRT). The results show that different HRT led to different inorganic carbon profiles and N:P ratios in the culture, influencing microbial changes, and carbohydrate content. Hence, higher N-NH₄⁺ removal efficiencies were obtained at HRT of 10 d and decreased with decreasing HRT. Whereas, complete depletion of P-PO₄^3- was achieved only at HRT of 8 d and 6 d. Also, the highest COD removal efficiency (60%) was achieved at 6 d of HRT. The maximum accumulation of carbohydrates was achieved at HRT of 8 d, which presented an N:P ratio of 22:1 and carbon availability, recording a constant carbohydrate content of 57% without any additional carbon source. Furthermore, this operational condition reached the best biomass production of 0.033 g L^-1d^-1 of easy-settling cyanobacteria dominated culture. According to the results, this process presents an alternative to recycling industrial effluents and, at the same time, grow valuable biomass, closing a loop for sustainable economy.

Bioprospecting of wild type ethanologenic yeast for ethanol fuel production from wastewater-grown microalgae

BACKGROUND

Wild-type yeasts have been successfully used to obtain food products, yet their full potential as fermenting microorganisms for large-scale ethanol fuel production has to be determined. In this study, wild-type ethanologenic yeasts isolated from a secondary effluent were assessed for their capability to ferment saccharified microalgae sugars.

RESULTS

Yeast species in wastewater were identified sequencing the Internal Transcribed Spacers 1 and 2 regions of the ribosomal cluster. Concurrently, microalgae biomass sugars were saccharified via acid hydrolysis, producing 5.0 ± 0.3 g L^-1 of fermentable sugars. Glucose consumption and ethanol production of yeasts in hydrolyzed-microalgae liquor were tested at different initial sugar concentrations and fermentation time. The predominant ethanologenic yeast species was identified as Candida sp., and glucose consumption for this strain and S. cerevisiae achieved 75% and 87% of the initial concentration at optimal conditions, respectively. Relatively similar ethanol yields were determined for both species, achieving 0.45 ± 0.05 (S. cerevisiae) and 0.46 ± 0.05 g ethanol per g glucose (Candida sp.).

CONCLUSION

Overall, the results provide a first insight of the fermentation capacities of specific wild-type Candida species, and their potential role in ethanol industries seeking to improve their cost-efficiency.

Biochemical and phylogenetic characterization of the wastewater tolerant Chlamydomonas biconvexa Embrapa|LBA40 strain cultivated in palm oil mill effluent

The increasing demand for water, food and energy poses challenges for the world´s sustainability. Tropical palm oil is currently the major source of vegetable oil worldwide with a production that exceeds 55 million tons per year, while generating over 200 million tons of palm oil mill effluent (POME). It could potentially be used as a substrate for production of microalgal biomass though. In this study, the microalgal strain Chlamydomonas biconvexa Embrapa|LBA40, originally isolated from a sugarcane vinasse stabilization pond, was selected among 17 strains tested for growth in POME retrieved from anaerobic ponds of a palm oil industrial plant located within the Amazon rainforest region. During cultivation in POME, C. biconvexa Embrapa|LBA40 biomass productivity reached 190.60 mgDW • L-1 • d-1 using 15L airlift flat plate photobioreactors. Carbohydrates comprised the major fraction of algal biomass (31.96%), while the lipidic fraction reached up to 11.3% of dry mass. Reductions of 99% in ammonium and nitrite, as well as 98% reduction in phosphate present in POME were detected after 5 days of algal cultivation. This suggests that the aerobic pond stage, usually used in palm oil industrial plants to reduce POME inorganic load, could be substituted by high rate photobioreactors, significantly reducing the time and area requirements for wastewater treatment. In addition, the complete mitochondrial genome of C. biconvexa Embrapa|LBA40 strain was sequenced, revealing a compact mitogenome, with 15.98 kb in size, a total of 14 genes, of which 9 are protein coding genes. Phylogenetic analysis confirmed the strain taxonomic status within the Chlamydomonas genus, opening up opportunities for future genetic modification and molecular breeding programs in these species.

Improvement of ethanol production using green alga Chlorococcum minutum

Incessant depletion of fossil fuels urges the governments and non-governmental organizations to invest more on renewable energy sectors including generation of biofuels such as bioethanol. Production of ethanol from algal feedstock has been an interesting area of research in recent times. In the present investigation, feedstock of a green alga Chlorococcum minutum was selected for ethanol production and compared with feedstock of model alga Chlamydomonas reinhardtii. Both the species were grown under in vitro conditions using universal tris-acetate-phosphate (TAP) medium with various concentrations and combinations of vitamins such as thiamin, biotin and cobalamin (B1, B7 and B12) to enhance the biomass in turn reducing sugars in both the algal cultures. Later, these algal feedstocks were used for the production of ethanol under fermentation conditions using yeast. Reducing sugars were more in both the algal cultures grown in Cr3 or Cm3 media (TAP with 0.8 g/L of B1, 0.004 g/L of B7 & 0.004 g/L of B12) and also in Cr2 or Cm2 media (TAP with 0.4 g/L of B1, 0.002 g/L of B7 & 0.002 g/L of B12). In extent, the enhancement of ethanol production was noticed in C. reinhardtii (33.57 g/L) and C. minutum (46.97 g/L) from the feedstocks grown in Cr3 or Cm3 media when compared with feedstocks grown in other vitamin combinations or without vitamin assistance. Specifically, feedstock of C. minutum generated more output at 48 h when compared with model alga. The present work may be useful for the production of ethanol at a commercial level.

Biofuels from Micro-Organisms: Thermodynamic Considerations on the Role of Electrochemical Potential on Micro-Organisms Growth

Biofuels from micro-organisms represents a possible response to the carbon dioxide mitigation. One open problem is to improve their productivity, in terms of biofuels production. To do so, an improvement of the present model of growth and production is required. However, this implies an understanding of the growth spontaneous conditions of the bacteria. In this paper, a thermodynamic approach is developed in order to highlight the fundamental role of the electrochemical potential in bacteria proliferation. Temperature effect on the biosystem behaviour has been pointed out. The results link together the electrochemical potential, the membrane electric potential, the pH gradient through the membrane, and the temperature, with the result of improving the thermodynamic approaches, usually introduced in this topic of research.

Producing Energy-Rich Microalgae Biomass for Liquid Biofuels: Influence of Strain Selection and Culture Conditions

Energy-storage metabolites such as neutral lipids and carbohydrates are valuable compounds for liquid biofuel production. The aim of this work is to elucidate the main biological responses of two algae species known for their effective energy-rich compound accumulation in nitrogen limitation and day–night cycles: Nannochloropsis gaditana, a seawater species, and Parachlorella kessleri, a freshwater species. Lipid and carbohydrate production are investigated, as well as cell resistance to mechanical disruption for energy-rich compound release. Nitrogen-depleted N. gaditana showed only a low consumption of energy-storage molecules with a non-significant preference for neutral lipids (TAG) and carbohydrates in day–night cycles. However, it did accumulate significantly fewer carbohydrates than P. kessleri. Following this, the highest levels of productivity for N. gaditana in chemostat cultures at four levels of nitrogen limitation were found to be 3.4 and 2.2 × 10−3 kg/m2·d for carbohydrates and TAG, respectively, at 56%NO3 limitation. The cell disruption rate of N. gaditana decreased along with nitrogen limitation, from 75% (at 200%NO3) to 17% (at 13%NO3). In the context of potentially recoverable energy for biofuels, P. kessleri showed good potential for biodiesel and high potential for bioethanol; by contrast, N. gaditana was found to be more efficient for biodiesel production only.

A New Model of Alcoholic Fermentation under a Byproduct Inhibitory Effect

Despite the advantages of continuous fermentation whereby ethanol is selectively removed from the fermenting broth to reduce the end-product inhibition, this process can concentrate minor secondary products to the point where they become toxic to the yeast. This study aims to develop a new mathematical model do describe the inhibitory effect of byproducts on alcoholic fermentation including glycerol, lactic acid, acetic acid, and succinic acid, which were reported as major byproducts during batch alcoholic fermentation. The accumulation of these byproducts during the different stages of batch fermentation has been quantified. The yields of total byproducts, glycerol, acetic acid, and succinic acid per gram of glucose were 0.0442, 0.023, 0.0155, and 0.0054, respectively. It was found that the concentration of these byproducts linearly increases with the increase in glucose concentration in the range of 25-250 g/L. The results have also showed that byproduct concentration has a significant inhibitory effect on specific growth coefficient (μ) whereas no effect was observed on the half-velocity constant (K s). A new mathematical model of alcoholic fermentation was developed considering the byproduct inhibitory effect, which showed a good performance and more accuracy compared to the classical Monod model.

Isolation of Industrial Important Bioactive Compounds from Microalgae

Microalgae are known as a rich source of bioactive compounds which exhibit different biological activities. Increased demand for sustainable biomass for production of important bioactive components with various potential especially therapeutic applications has resulted in noticeable interest in algae. Utilisation of microalgae in multiple scopes has been growing in various industries ranging from harnessing renewable energy to exploitation of high-value products. The focuses of this review are on production and the use of value-added components obtained from microalgae with current and potential application in the pharmaceutical, nutraceutical, cosmeceutical, energy and agri-food industries, as well as for bioremediation. Moreover, this work discusses the advantage, potential new beneficial strains, applications, limitations, research gaps and future prospect of microalgae in industry.

Algae: Biomass to Biofuel

Worldwide demand for ethanol alternative fuel has been emerging day by day owing to the rapid population growth and industrialization. Culturing microalgae as an alternative feedstock is anticipated to be a potentially significant approach for sustainable bioethanol biofuel production. Microalgae are abundant in nature, which grow at faster rates with a capability of storing high lipid and starch/cellulose contents inside their cells. This process offers several environmental advantages, including the effective utilization of land, good CO2 sequestration without entering into "food against fuel" dispute. This chapter focuses on the methods and processes used for the production of bioethanol biofuels from algae. Thus, it also covers significant achievements in the research and developments on algae bioethanol production, mainly including pretreatment, hydrolysis, and fermentation of algae biomass. The processes of producing biodiesel, biogas, and hydrogen have also been discussed.

The Application of Catalytic Processes on the Production of Algae-Based Biofuels: A Review

Over the last decades, microalgal biomass has gained a significant role in the development of different high-end (nutraceuticals, colorants, food supplements, and pharmaceuticals) and low-end products (biodiesel, bioethanol, and biogas) due to its rapid growth and high carbon-fixing efficiency. Therefore, microalgae are considered a useful and sustainable resource to attain energy security while reducing our current reliance on fossil fuels. From the technologies available for obtaining biofuels using microalgae biomass, thermochemical processes (pyrolysis, Hydrothermal Liquefaction (HTL), gasification) have proven to be processed with higher viability, because they use all biomass. However, due to the complex structure of the biomass (lipids, carbohydrates, and proteins), the obtained biofuels from direct thermochemical conversion have large amounts of heteroatoms (oxygen, nitrogen, and sulfur). As a solution, catalyst-based processes have emerged as a sustainable solution for the increase in biocrude production. This paper’s objective is to present a comprehensive review of recent developments on the catalyst-mediated conversion of algal biomass. Special attention will be given to operating conditions, strains evaluated, and challenges for the optimal yield of algal-based biofuels through pyrolysis and HTL.

A Cyanobacteria-Based Biofilm System for Advanced Brewery Wastewater Treatment

Algal/cyanobacterial biofilm photobioreactors provide an alternative technology to conventional photosynthetic systems for wastewater treatment based on high biomass production and easy biomass harvesting at low cost. This study introduces a novel cyanobacteria-based biofilm photobioreactor and assesses its performance in post-treatment of brewery wastewater and biomass production. Two different supporting materials (glass/polyurethane) were tested to investigate the effect of surface hydrophobicity on biomass attachment and overall reactor performance. The reactor exhibited high removal efficiency (over 65%) of the wastewater’s pollutants (chemical oxygen demand, nitrate, nitrite, ammonium, orthophosphate, and total Kjeldahl nitrogen), while biomass per reactor surface reached 13.1 and 12.8 g·m−2 corresponding to 406 and 392 mg·L−1 for glass and polyurethane, respectively, after 15 days of cultivation. The hydrophilic glass surface favored initial biomass adhesion, although eventually both materials yielded complete biomass attachment, highlighting that cell-to-cell interactions are the dominant adhesion mechanism in mature biofilms. It was also found that the biofilm accumulated up to 61% of its dry weight in carbohydrates at the end of cultivation, thus making the produced biomass a suitable feedstock for bioethanol production.

Sustainable Production of Microbial Isoprenoid Derived Advanced Biojet Fuels Using Different Generation Feedstocks: A Review

As the fastest mode of transport, the aircraft is a major driver for globalization and economic growth. The development of alternative advanced liquid fuels is critical to sustainable development within the sector. Such fuels should be compatible with existing infrastructure and derived from second generation feedstocks to avoid competition with food markets. With properties similar to petroleum based fuels, isoprenoid derived compounds such as limonene, bisabolane, farnesane, and pinene dimers are of increasing interest as "drop-in" replacement jet fuels. In this review potential isoprenoid derived jet fuels and progress toward their microbial production was discussed in detail. Although substantial advancements have been achieved, the use of first generation feedstocks remains ubiquitous. Lignocellulosic biomass is the most abundant raw material available for biofuel production, however, technological constraints associated with its pretreatment and saccharification hinder its economic feasibility for low-value commodity production. Non-conventional microbes with novel characteristics including cellulolytic bacteria and fungi capable of highly efficient lignocellulose degradation and xylose fermenting oleaginous yeast with enhanced lignin-associated inhibitor tolerance were investigated as alternatives to traditional model hosts. Finally, innovative bioprocessing methods including consolidated bioprocessing and sequential bioreactor approaches, with potential to capitalize on such unique natural capabilities were considered.