Conversion Of Algal Biomass Research Articles

Advancements in algal biorefineries for sustainable agriculture: Biofuels, high-value products, and environmental solutions

Micro- and macroalgal biomass conversion into valuable products is central to biorefinery research, addressing global challenges in energy and sustainability. This review details recent advancements in algal biomass conversion, focusing on the enhancement of conversion technologies to increase commercial value. Methods such as pyrolysis and catalytic bioconversion are examined for their efficiency in producing biofuels and biochemicals. The utilization of specialized algal strains for effective bioremediation and the role of algal-derived biofertilizers and biostimulants in providing sustainable alternatives to chemical fertilizers are discussed. These alternatives significantly improve soil health and plant growth. The review also highlights advanced extraction techniques, including supercritical CO2 and enzyme-assisted extraction, expanding the application of algal derivatives beyond traditional agricultural uses. Despite the potential, challenges such as high cultivation and processing costs remain, necessitating further optimization of algae-based biofuels for commercial viability. The crucial roles of genetic engineering and synthetic biology are emphasized in enhancing algal productivity and tailoring bioproduct synthesis. The review stresses the need for continued research and technological advancements to overcome these barriers, thus promoting the broader adoption of algal biorefineries and contributing to sustainable agricultural practices and enhanced global energy security.

Conversion of algal biomass into renewable fuel: A mini review of chemical and biochemical processes

Microalgae are a vital resource for the coming years to address the concern of decrease in oil reserves and the negative impacts of fossil fuels on the environment. Their utilization is crucial for a wide range of industrial applications. Depending on the strain, microalgae contain a variety of chemical components and can be treated biochemically or thermochemically. This review thus focuses on the biochemical mechanisms that are used to convert algal biomass into sustainable fuel, including the challenges and potential of those processes. Microalgae have been shown to be a viable third-generation alternative to conventional biofuel feedstocks. The optimum production of biofuel depends on the proper selection of microalgae species based on their lipid, carbohydrate, and protein content in order to produce high-quality, sustainable biofuel. Nannochloropsis gaditana can contribute to a maximum biodiesel yield of 96.47%, whereas Nannochloropsis oculata can produce the least (25%) through the biochemical process of transesterification. Higher yields of microalgae-derived gaseous, solid and liquid fuels can be achieved by pre-treating microalgal biomass and then employing bioconversion processes such as photo-fermentation and hydrothermal carbonization.

Advanced thermochemical conversion of algal biomass to liquid and gaseous biofuels: A comprehensive review of recent advances

Algal biomass is considered to be one of the most promising feedstocks of importance for conversion into biofuels. With their benefits over other biomass feedstocks, such as sustainability, renewability and productivity, microalgae are one of the most promising biomass resources for use in thermochemical conversion processes. With this review, we hope to present the most recent information available on the commonly used thermochemical conversion procedures, which are hydrothermal liquefaction, pyrolysis, and gasification processes. The study evaluated both the quality and yield of liquid products (bio-oil) as well as gaseous products (syngas) derived by thermochemical conversion processes, to truly comprehend the effectiveness and feasibility of each method. It was found that the yield of bio-oil obtained through hydrothermal liquefaction was lower than the yield achieved through pyrolysis. However, the energy density, fuel properties and storage stability of hydrothermal liquefaction bio-oil are superior to those of pyrolysis bio-oil. This study also demonstrated that the gasification process has been the most energy-saving approach for the transformation of microalgae to syngas. Microalgae supercritical water gasification might be a good way to turn microalgae into high-heating-value gas without having to dry it first. Finally, the prospects and obstacles of converting microalgal biomass to biofuels were discussed. Overall, the purpose of this work is to present a comprehensive assessment of the most recent developments in microalgal biomass thermochemical conversion for the production of liquid and gaseous biofuels.

Comparative study of different catalysts mediated FAME conversion from macroalga Padina tetrastromatica biomass and hydrothermal liquefaction facilitated bio-oil production

Marine macroalgae offer an endurable source of renewable biomass, which do not require cultivable area, fertilizers for cultivation for bioproducts production. In this study, marine brown macroalga Padina tetrastromatica as an alternate sustainable feedstock for the production of liquid fuels. Padina tetrastromatica biomass was collected from Mandapam; the coastal region of Rameswaram, Tamil Nadu, India. and the algal oil was extracted using sequential extractions using various solvents. Petroleum ether (PE) and dichloromethane (DCM) solvent fractions were found to have high lipids and further utilized for biodiesel production, wherein four different heterogeneous nanocatalysts (TiO2, Bio-Fe, GO, and MgO) and commercial homogeneous catalysts (HCl and NaOH) were employed for the transesterification. High fatty acid methyl ester (FAME) recovery (92.3%) was achieved from TiO2 mediated transesterification than the other conventional catalysts. Further, the conversion of algal biomass into bio-oil and by-products was carried out using hydrothermal liquefaction (HTL). Subsequently, the compounds were characterized by FT-IR and GC-MS analysis. The quality parameters of liquid biofuels were examined and they are in accordance with the international fuel standards. Thus, brown macroalga Padina tetrastromatica may be considered as an alternate feedstock for biofuel and other bioproducts production and TiO2 would be a suitable catalyst for the conversion of FAME.

Effect of novel Ni2P-loaded catalysts on algal pyrolysis bio-oil

This study focused on conversion of algal biomass to bio-oil through in-situ catalytic fast pyrolysis. In particular, novel Ni2P-loaded and unmodified (zeolite, activated carbon and chicken manure biochar) catalysts were evaluated to determine their effect on in-situ upgrading of algal pyrolysis products. Among the catalysts evaluated, Ni2P-loaded zeolite achieved the highest bio-oil hydrocarbon (34.97 %) and calorific value (32.66 MJ/kg), and the lowest O/C (0.075) and N/C (0.074) ratios. There was a 137 % increase of the aliphatic hydrocarbon fraction and a 72 % increase of the biochar specific surface area (SSA) with the loading of Ni2P to zeolite. Additionally, unfavourable major oxygen- and nitrogen-containing compound, phytol and tetradecanamide, decreased seven- and six-fold, respectively, compared to the non-catalytic baseline case. Ni2P-loaded biochar achieved a reduction in the bio-oil acidity from a pH of 4.52–6.78 and a 41 % decrease of the carboxylic acids content. Biochar produced from the zeolite formulations exhibited especially favourable sorbent quality with SSA greater than 500 m2/g. According to the proposed catalytic mechanism, the generation of n-heptadecane and hexadecanamide may be due to the decomposition of phytol and tetradecanamide, and the catalytic activity was correlated to the pore size of the catalyst (22.22 Å). Direct addition reactions were the dominant pathway in the formation of liquid hydrocarbons. These results suggest that it is feasible to develop an in-situ multi-catalyst system to achieve high-quality bio-oil production. Thus, the development of novel Ni2P-loaded catalysts addressed a promising approach for biomass conversion into hydrocarbon-rich products with low risk to the environment.

Monochromatic light filters to enhance biomass and carotenoid productivities of Dunaliella salina in raceway ponds

Monochromatic blue and red wavelengths are more efficient for light to algal biomass conversion than full-spectrum sunlight. In this study, monochromatic light filters were used to down-regulate natural sunlight to blue (400–520 nm) and red (600–700 nm) wavelengths to enhance biomass productivity of Dunaliella salina in outdoor raceway ponds. Growth indices such as cell size, pigment concentrations, biomass yield, photosynthetic efficiency, and major nutritional compositions were determined and compared against a control receiving unfiltered sunlight. Results showed that red light increased biomass productivity, lipid, and carotenoid contents but decreased cell volume, chlorophyll production, and cell weight. Conversely, blue light increased cell volume by 200%, cell weight by 68%, and enhanced chlorophyll a and protein contents by 35% and 51%, respectively, over red light. Compared to the control treatment, photoinhibition of D. salina cells at noon sunshine was decreased 60% by utilizing optical filters on the pond’s surface.

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.

Effect of reaction temperature on the conversion of algal biomass to bio-oil and biochar through pyrolysis and hydrothermal liquefaction

Thermochemical methods namely pyrolysis, gasification/hydrothermal gasification, combustion, hydrothermal liquefaction and hydrothermal carbonization are widely practiced to convert algal biomass into fuels. Among the methods, pyrolysis, and hydrothermal liquefaction are most commonly practised to convert numerous algal biomasses into bio-oil and/or biochar to substitute crude oil in petroleum refinery. In this regard, this review is focused on the conversion of various microalgal; and cyanobacterial biomasses into bio-oil, and solid char products through pyrolysis and hydrothermal liquefaction. Initially, pyrolysis and hydrothermal liquefaction of algal biomass on bio-oil and biochar yield have been reviewed. As the composition and yield of bio-oil from algae depends on the reaction temperature, detailed account of the impact of temperature on the quantity and quality of bio-oil and solid char obtained from pyrolysis and hydrothermal liquefaction were comprehensively presented in the review. Eventually, this article provides opportunities and scope in the pyrolysis and hydrothermal liquefaction of algae for further research.

Activation strategies for biochar to use as an efficient catalyst in various applications

Microalgae and macroalgae are known for their use in food and fuel applications. Recently, tremendous interest on algal biomass for biochar production has been increased. Biochar are well known for its catalytic activity to produce many finished products such as alternative fuels, treat environmental waste water and act as an input for agricultural applications. Three routes are commonly adopted for alternative fuel production from algal biomass namely, biochemical, chemical, and thermochemical techniques. Recently, thermochemical methods for the conversion of algal biomass to biochar are employed to use biochar based catalyst. Biochar must be activated before used as a potential catalyst. Therefore, this review has given broad information of various activation strategies for biochar modification. Different activation methods such as physical and chemical modes are being practiced to modify the biochar for efficient catalyst in alternative fuel production.

Immobilization of β-1,3-xylanase on pitch-based hyper-crosslinked polymers loaded with Ni2+ for algal biomass manipulation

β-1,3-xylanase plays an important role in the conversion of algal biomass into renewable chemical commodities and functional xylooligosaccharides. Efficient immobilization of the target enzymes that could integrate the separation, purification, and immobilization in one-step may have great potentials. The cheap and easily obtained pitch was adopted as the raw material to prepare the hyper-cross-linked polymers with the specific surface areas of 560 m2/g and the Ni2+ loading about 80 mg/g. As a carrier, it could immobilize and purify the β-1,3-xylanases directly from the crude cell debris with the activity recovery of (80.66 ± 0.87) %. The half-life of the immobilized β-1,3-xylanases was 50 min at 50 °C, which was significantly longer than the free ones with only 14 min. The immobilized β-1,3-xylanases could retain 65 % of the activity after stored at 30 ℃ for 80 h, they could also retain 87 % of the original activity after 15 cycles of reuse. In terms of potential applications in the manipulation of algae Caulerpa lentillifera, the immobilized β-1,3-xylanases could release 30 % more reducing sugar in 85 h. The method proposed here is promising for algal biomass manipulation because of its low cost, stable storage, convenient recycling and excellent reusability.

Kinetic Analysis of Algae Gasification by Distributed Activation Energy Model

Conversion of algal biomass into energy products via gasification has attracted increasing research interests. A basic understanding of the gasification kinetics of algal biomass is of fundamental importance. Distributed activation energy model (DAEM), which provides the information of energy barrier distribution during the gasification process, is a promising tool to study the kinetic process of algae gasification. In this study, DAEM model was used to investigate Chlorella vulgaris and Spirulina gasification. The activation energy of Chlorella vulgaris gasification was in the range from 370 to 650 kJ mol−1. The range of activation energy for Spirulina gasification was a bit wider, spanning from 330 to 670 kJ mol−1. The distribution of activation energy for both Chlorella vulgaris and Spirulina showed that 500 kJ mol−1 had the most components, and these components were gasified at around 300 °C. The DAEM algorithm was validated by the conversion and conversion rate from experimental measurement, demonstrating that DAEM is accurate to describe the kinetics of algal biomass gasification.

Microalgae for biofuel production and removal of heavy metals: a review

Removal of heavy metals from wastewaters using microalgae is gaining interest because microalgae also assimilate carbon, nitrogen and phosphorus. Here, we review algal metabolism and cultivation; algal biomass conversion to biodiesel, bioethanol, biohydrogen, methane, electricity and fertilizers; and removal of metals with microalgae. The mixotrophic approach enables the effective treatment of both organic and inorganic wastes in water. For cultivation, photobioreactors are found efficient due to the control of operational conditions. Bioremediation of heavy metals by physiochemical processes appears to be more efficient than algal uptake.

Third-generation biorefineries: a sustainable platform for food, clean energy, and nutraceuticals production

Sustainable transformation of biomass into a wide range of valuable chemicals, fuels, and materials is the eventual goal of a biorefinery. Algal feedstock (microalgae and macroalgae) is a principal component of third-generation (3G) biorefinery empowering the bio-renewables industry. While first-generation (1G) biorefineries are commercially viable, products (fuels and commodity chemicals) from second-generation (2G) and 3G biorefinery are not yet commercially competitive due to the gross technical challenges, scalable and production cost issues. Because of the inherently diversified nature of feedstock used in 3G biorefineries, a myriad of specific bioproducts can be produced. Furthermore, stable food/feed supply, environmental concerns, climate change, and geopolitical issues have necessitated the exploration of 3G feedstocks into fuels and renewable chemicals. Considerable success has been seen in research laboratories in the last two or three decades which led to mature technical developments in algal biomass conversion. However, the scale-up issues are still posing a big challenge for the commercial exploitation of algal feedstock into fuels and chemicals. Nevertheless, various products such as nutraceuticals, pharmaceuticals, and cosmetics are successfully being produced from algal feedstock. This review paper describes the technical developments, industrial scenario, environmental issues, and range of diversified products from 3G biorefineries. Specially, we focus on the exploration of algal biomass into fuels and biochemicals via multidisciplinary technological routes.

Efficient saccharification of microalgal biomass by Trichoderma harzianum enzymes for the production of ethanol

Microalgal and/or cyanobacterial biomass could be more advantageous than current plant feedstocks for the production of ethanol and/or other fermentation products. Enzymatic saccharification of microalgal biomass currently requires harsh pretreatments and significant amounts of expensive hydrolytic enzymes. The purpose of this study was: i) to analyze the quality of biomass of a cell-wall deficient microalga as a saccharification substrate for enzymatic hydrolysis; and ii) to identify an alternative source of enzymes for the saccharification of algal biomass. We showed that a newly isolated strain of the fungus Trichoderma harzianum was able to grow at the expense of intact cells of the alga Chlamydomonas reinhardtii as a sole source of nutrients. The fungal spent medium exhibited pectinolytic, amylolytic, cellulolytic, and proteolytic activities and efficiently saccharified either dry and milled biomass or intact cells of the microalga. Biomass of a cell-wall deficient C. reinhardtii strain was saccharified at a similar efficiency than biomass of the parental strain with T. harzianum enzymes, indicating full capacity of these enzymes to circumvent the cell-wall recalcitrance to hydrolysis. Algal biomass saccharification yielded up to 22.4 g reducing sugars·L−1 and could be quantitatively converted into ethanol by fermentation with Saccharomyces cerevisiae. The efficiency of conversion of algal biomass into ethanol showed in this study is among the highest reported so far and encourages research for scaling up production of T. harzianum enzymes as well as the evaluation of biomass of other algal strains as feedstocks for the production of ethanol.

Conversion of green algal biomass into bioenergy by pyrolysis. A review

Climate change issues are calling for the design of renewable sources of energy. In particular, biomass energy from algae is encouraging because production of algae at the commercial scale can be done successfully with various techniques. Here, we review the conversion of algal biomass into energy by fast, slow, microwave and catalytic pyrolysis. The article details algae classification; cultivation of macroalgae and microalgae; pyrolysis parameters; production of biochar, bio-oil and biogas; and types of pyrolysis.

Efficient enzymatic saccharification of macroalgal biomass using a specific thermostable GH 12 endoglucanase from Aspergillus terreus JL1.

Stranded green macroalgae represents an important and renewable biomass that remains under valorized despite the numerous environmental problems generated by their accumulation in coastal regions. This work describes the isolation of a filamentous thermophile fungus identified as Aspergillus terreus JL1 that produces an efficient cellulolytic activity for green macroalgae saccharification. The characterization of the endoglucanase activity obtained after submerged fermentation showed a differential induction depending on the carbon source used with a unique isoform released when Ulva lactuca was used as inducer. The crude extract obtained hydrolyzed efficiently the untreated algal biomass (70.5%) compared to other cellulolytic extracts. The unique endoglucanase released was then purified to homogeneity (Yield: 49.6%; Specific activity: 30.1 U/mg; Purification fold: 4.36) and characterized biochemically. Its peptidic sequence was then determined and showed its belonging to the GH12. The described enzyme represents a promising biotechnological tool for algal biomass conversion.

A comparative analysis of hydrogen production from the thermochemical conversion of algal biomass

Gasification has the potential to convert biomass into gaseous mixtures that can be used for hydrogen production. Thermal gasification and supercritical water gasification are commonly used thermochemical methods for conversion of biomass to hydrogen. Supercritical water gasification handles wet biomass, thus eliminating the capital cost-intensive drying step. Thermal gasification is considered as an alternative means of producing hydrogen from microalgae where biomass has to be dried before gasification. The authors developed techno-economic models for assessment of the production of hydrogen through supercritical gasification and thermal gasification processes. Techno-economic assessment was based on developed process models. Equipment was sized and costs were estimated using the developed process models, and the product value was determined assuming 20 years of plant life. The economic assessment of supercritical water and thermal gasification show that 2000 dry tonnes/day plant requires total capital investments of 277.8 M$ and 215.3 M$ for hydrogen product values of $4.59 ± 0.10/kg and $5.66 ± 0.10/kg, respectively. The relatively higher yield obtained in supercritical water gasification compared to thermal gasification results in lower product value of hydrogen for supercritical water gasification, thereby making it more desirable. This cost of hydrogen is about 4 times the cost of hydrogen from natural gas. The sensitivity analysis indicates that biomass cost and yield are the most sensitive parameters in the economics of the supercritical or thermal gasification process; this signifies the importance of algal biomass availability. The techno-economic assessment helps to identify options for the production of hydrogen fuel through these novel technologies.

Fate and reuse of nitrogen-containing organics from the hydrothermal conversion of algal biomass

Hydrothermal (HT) conversion is a promising and suitable technology for the generation of biofuels from microalgae. Besides the fact that water is used as a “green” reactant and solvent and that no biomass drying is required, the technology offers a potential nutrient source for microalgae culture using an aqueous effluent very rich in essential inorganic nutrients. However, upon continuous and multiple recycling of this HT effluent, the recalcitrant organic fraction is likely to increase and may potentially attain toxic thresholds for microalgae use. In this work, we show the presence of recalcitrant N-containing organic compounds (NOC's) in the HT effluent. The most prominent NOC's in the extracts were carefully examined for their effect on microalgae, namely 2-pyrrolidinone and β-phenylethylamine (β-PEA). The first set of experiments consisted in testing these two substances at three different concentrations (10, 50 and 150 ppm) using three different microalgae strains: Phaeodactylum tricornutum, Chlorella sorokiniana and Scenedesmus vacuolatus. The confirmed half maximal inhibitory concentration (IC50) was approximately 75 ppm for all tested species. In the second set of experiments, P. tricornutum was grown using diluted HT effluent. Experimental conditions were set by adjusting the nitrogen concentration in the HT effluent to be equal to a known commercial medium. The concentrations of specific NOC's were lowered to concentrations of 8.5 mg/L 2-pyrrolidinone and 0.5 mg/L β-PEA after dilution. The growth of P. tricornutum using the diluted HT solution was kept constant with no evidence of inhibition or consumption of NOC's, as the concentration of the specific compounds remains the same before and after growth. Therefore, in order to avoid effects of accumulation of NOC's upon continuous recycling, the HT effluent was pumped through the existing hydrothermal gasification unit as a water clean-up step. The conversion of NOC's to ammonium was successfully achieved.

A review on sustainable microalgae based biofuel and bioenergy production: Recent developments

Abstract Climate changes induced by anthropogenic greenhouse gas emissions (mainly carbon dioxide) is one of the major threats of the modern era. Primary causes are the high reliance on fossil fuels for power generation, transportation, manufacturing and the intensive land usage (deforestation). The current share of renewable biofuel production in the overall fuel demand has been found insufficient to replace fossil fuels. Microalgae can deliver a sustainable and complementary biofuel platform with some important advantages. This review aims to offer a state-of-the art review of algal biomass conversion methods into various biofuel products, including biodiesel, syngas, biogas, bioethanol. Emerging more sustainable biofuel/bioenergy production technologies are highlighted. Attention is also paid to sustainable cultivation methods, including wastewater treatment and bioremediation to capture CO2 and fix nitrogen and phosphorus, produced from industrial, agricultural and municipal sources. Finally, a light is shed on the important role of algae metabolic engineering.

Demonstration of parallel algal processing: production of renewable diesel blendstock and a high-value chemical intermediate

Demonstration of a novel integrated algal biomass conversion process for fuels and chemicals.