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Algal Biomass and Biofuel Production
Abstract
Primary nonrenewable sources of energy like coal, petroleum, and natural gas are constantly depleting due to their perpetual usage in industrial and transport sectors. Besides, these fuels have emerged out as precarious category of sources of pollutants, displaying hostile effects on both human health and the dynamism of ecosystems, due to forgo of hazardous and toxic gases. Moreover, level of greenhouse gases has exponentially augmented in the post‐industrialization period by 25% of total through emission of chlorofluoro‐hydrocarbons and CO 2 . As a result, across the globe, the climate conditions have perilously transmuted and have become a matter of concern and debate. Therefore, improved fuel transformation strategies with better adeptness, eco‐friendly, and renewable nature are required to meet the energy supply demand for the ever‐growing population. Owing to all this, there is desideratum for the sustainable alternative sources of renewable energy. Diverse array of biomass from heterogeneous sources like forestry, agricultural, and aquatic systems have been considered for a variety of biofuel production, viz., bio‐hydrogen, biogas, bio‐oil, bioethanol, and biodiesel. The utilization of first‐generation biofuels obtained from oil seeds (soybean, and rapeseed) and food‐based crops (corn, and sugar molasses) are restricted due to the climate change as well as economic concerns. Second‐generation biofuels obtained from lignocellulosic biomass, municipal solid wastes, manures, agricultural and forest wastes, e.g. jatropha, cassava, poplar, and so on, are additionally delimited because of the processing and high production cost quandary. Microalgae, comprises of third‐generation biofuels, are found to be very promising in the engenderment of biofuels. Microalgae, harbor metabolic toolbox to, act as a solar‐driven energy factory for production of raw materials for biofuels. Also photosynthetic machinery of microalgae enables CO 2 sequestration from atmosphere and ergo diminishes the relinquishment of unfavorable and toxic substances in the environment. Microalgae, therefore, could be plausible keystone to provide a solution to meet global energy demand along with sustaining invulnerable and carbon‐neutral environment. This chapter fixates on the biofuels production by these minute photoautotrophs, their cultivation, harvesting, processing as well as other by‐products and the promising applications of microalgae.
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In the wake of intensive fossil fuel usage and CO2 accumulation in the environment, research is targeted toward sustainable alternate bioenergy that can suffice the growing need for fuel and also that leaves a minimal carbon footprint. Oil production from microalgae can potentially be carried out more efficiently, leaving a smaller footprint and without competing for arable land or biodiverse landscapes. However, current algae cultivation systems and lipid induction processes must be significantly improved and are threatened by contamination with other algae or algal grazers. To address this issue, we have developed an efficient two-stage cultivation system using the marine microalga Tetraselmis sp. M8. This hybrid system combines exponential biomass production in positive pressure air lift-driven bioreactors with a separate synchronized high-lipid induction phase in nutrient deplete open raceway ponds. A comparison to either bioreactor or open raceway pond cultivation system suggests that this process potentially leads to significantly higher productivity of algal lipids. Nutrients are only added to the closed bioreactors, while open raceway ponds have turnovers of only a few days, thus reducing the issue of microalgal grazers.
Roadmaps towards sustainable bioeconomy, including the production of biofuels, in many EU countries mostly rely on biomass use. However, although biomass is renewable, the efficiency of biomass production is too low to be able to fully replace the fossil fuels. The use of land for fuel production also introduces ethical problems in increasing the food price. Harvesting solar energy by the photosynthetic machinery of plants and autotrophic microorganisms is the basis for all biomass production. This paper describes current challenges and possibilities to sustainably increase the biomass production and highlights future technologies to further enhance biofuel production directly from sunlight. The biggest scientific breakthroughs are expected to rely on a new technology called "synthetic biology", which makes engineering of biological systems possible. It will enable direct conversion of solar energy to a fuel from inexhaustible raw materials: sun light, water and CO2. In the future, such solar biofuels are expected to be produced in engineered photosynthetic microorganisms or in completely synthetic living factories.
Ultrasonication has recently received attention as a novel bioprocessing tool for process intensification in many areas of downstream processing. Ultrasonic intensification (periodic ultrasonic treatment during the fermentation process) can result in a more effective homogenization of biomass and faster energy and mass transfer to biomass over short time periods which can result in enhanced microbial growth. Ultrasonic intensification can allow the rapid selective extraction of specific biomass components and can enhance product yields which can be of economic benefit. This review focuses on the role of ultrasonication in the extraction and yield enhancement of compounds from various microbial sources, specifically algal and cyanobacterial biomass with a focus on the production of biofuels. The operating principles associated with the process of ultrasonication and the influence of various operating conditions including ultrasonic frequency, power intensity, ultrasonic duration, reactor designs and kinetics applied for ultrasonic intensification are also described.
Sustainable and renewable energy resources are highly essential to replace the vanishing petroleum fossil fuels. Biofuels play a vital role in mitigating CO 2 emission, reducing global warming and bringing down the hike in oil prices. Biodiesel has become a recent attraction since it is biodegradable, renewable and non toxic. The objective of the paper is to study the potential of microalgae as an alternative raw material for biodiesel generation. Microalga has been chosen as a biodiesel producer due to high mass productivity and faster lipid production. Production of biodiesel from microalgae could be a greater alternative to oil crops due to economical instability, jeopardizing agricultural lands and insufficient oil crops. This review article focusses on the technical improvements in cultivation of different microalgal species, lipid content in various algal species, modes and efficiency of harvesting and transesterification methods. This paper thus serves the researchers to further enhance the production and commercialization of biodiesel.
• Biofuels, in conjunction to their positive carbon balance with regards to fossil fuels, also represent a significant potential for sustainability and economic growth of industrialized countries because they can be generated from locally available renewable material. • Biofuels are usually classified as follows: 1. First-generation biofuels are directly related to a biomass that is generally edible. 2. Second-generation biofuels are defined as fuels produced from a wide array of different feedstock, ranging from lignocellulosic feedstocks to municipal solid wastes. 3. Third-generation biofuels are, at this point, related to algal biomass but could to a certain extent be linked to utilization of CO2 as feedstock. • Scaling second- and third-generation biofuel processes thus requires solid economics that are directly dependent on optimized carbon utilization that relies on the production of fuels (commodities), as well as high value co-products.
The world seems to be raising its energy needs owing to an expanding population and people's desire for higher living standards. Diversification biofuel sources have become an important energy issue in recent times. Among the various resources, algal biomass has received much attention in the recent years due to its relatively high growth rate, its vast potential to reduce greenhouse gas (GHG) emissions and climate change, and their ability to store high amounts of lipids and carbohydrates. These versatile organisms can also be used for the production of biofuel. In this review, sustainability and the viability of algae as an up-coming biofuel feedstock have been discussed. Additionally, this review offers an overview of the status of biofuel production through algal biomass and progress made so far in this area.
One of the major challenges associated with algal biofuels production in a biorefinery-type setting is improving biomass utilization in its entirety, increasing the process energetic yields and providing economically viable and scalable co-product concepts. We demonstrate the effectiveness of a novel, integrated technology based on moderate temperatures and low pH to convert the carbohydrates in wet algal biomass to soluble sugars for fermentation, while making lipids more accessible for downstream extraction and leaving a protein-enriched fraction behind. We studied the effect of harvest timing on the conversion yields, using two algal strains; Chlorella and Scenedesmus, generating biomass with distinctive compositional ratios of protein, carbohydrate, and lipids. We found that the late harvest Scenedesmus biomass had the maximum theoretical biofuel potential at 143 gasoline gallon equivalent (GGE) combined fuel yield per dry ton biomass, followed by late harvest Chlorella at 128 GGE per ton. Our experimental data show a clear difference between the two strains, as Scenedesmus was more successfully converted in this process with a demonstrated 97 GGE/ton. Our measurements indicated a release of > 90% of the available glucose in the hydrolysate liquors and an extraction and recovery of up to 97% of the fatty acids from wet biomass. Techno-economic analysis for the combined product yields indicates that this process exhibits the potential to improve per-gallon fuel costs by up to 33% compared to a lipids-only process for one strain, Scenedesmus, grown to the mid-point harvest condition.
Concern over the economics of accessing fossil fuel reserves, and widespread acceptance of the anthropogenic origin of rising CO2 emissions and associated climate change from combusting such carbon sources, is driving academic and commercial research into new routes to sustainable fuels to meet the demands of a rapidly rising global population. Here we discuss catalytic esterification and transesterification solutions to the clean synthesis of biodiesel, the most readily implemented and low cost, alternative source of transportation fuels to meet future societal demands.
A nonrenewable fuel like petroleum has been used from centuries and its usage has kept on increasing day by day. This also contributes to increased production of greenhouse gases contributing towards global issues like global warming. In order to meet environmental and economic sustainability, renewable, carbon neutral transport fuels are necessary. To meet these demands microalgae are the key source for production of biodiesel. These microalgae do produce oil from sunlight like plants but in a much more efficient manner. Biodiesel provides more environmental benefits, and being a renewable resource it has gained lot of attraction. However, the main obstacle to commercialization of biodiesel is its cost and feasibility. Biodiesel is usually used by blending with petro diesel, but it can also be used in pure form. Biodiesel is a sustainable fuel, as it is available throughout the year and can run any engine. It will satisfy the needs of the future generation to come.
Fossil fuel energy resources are depleting rapidly and most importantly the liquid fossil fuel will be diminished by the middle of this century. In addition, the fossil fuel is directly related to air pollution, land and water degradation. In these circumstances, biofuel from renewable sources can be an alternative to reduce our dependency on fossil fuel and assist to maintain the healthy global environment and economic sustainability. Production of biofuel from food stock generally consumed by humans or animals can be problematic and the root cause of worldwide dissatisfaction. Biofuels production from microalgae can provide some distinctive advantages such as their rapid growth rate, greenhouse gas fixation ability and high production capacity of lipids. This paper reviews the current status of biofuel from algae as a renewable source.
Biofuels are particularly important as an alternative fuel option for transportation. The sustainability of biofuels will depend on the development of viable, sustainable technologies that do not appear to be yet commercially viable. Successful development of algae-based biofuels and co-products industry requires the optimum combination of technical innovations in systems and processes, coupled with economic feasibility in the practical implementation and integrated scale-up for commercial production and marketing.
This article discusses the importance of algae-based biofuels together with the different opinions regarding its future. Advantages and disadvantages of these types of biofuels are presented. Algal growth drives around the world with special emphasis to Egypt are outlined. The article includes a brief description of the concept of algal biorefineries. It also declares the five key strategies to help producers to reduce costs and accelerate the commercialization of algal biodiesel. The internal strengths and weaknesses, and external opportunities, and threats are manifested through the SWOT analysis for micro-algae. Strategies for enhancing algae based-fuels are outlined. New process innovations and the role of genetic engineering in meeting these strategies are briefly discussed. To improve the economics of algal biofuels the concept of employing algae for wastewater treatment is presented.
Micro-algae have received considerable interest as a potential feedstock for producing sustainable transport fuels (biofuels). The perceived benefits provide the underpinning rationale for much of the public support directed towards micro-algae research. Here we examine three aspects of micro-algae production that will ultimately determine the future economic viability and environmental sustainability: the energy and carbon balance, environmental impacts and production cost. This analysis combines systematic review and meta-analysis with insights gained from expert workshops.We find that achieving a positive energy balance will require technological advances and highly optimised production systems. Aspects that will need to be addressed in a viable commercial system include: energy required for pumping, the embodied energy required for construction, the embodied energy in fertilizer, and the energy required for drying and de-watering. The conceptual and often incomplete nature of algae production systems investigated within the existing literature, together with limited sources of primary data for process and scale-up assumptions, highlights future uncertainties around micro-algae biofuel production. Environmental impacts from water management, carbon dioxide handling, and nutrient supply could constrain system design and implementation options. Cost estimates need to be improved and this will require empirical data on the performance of systems designed specifically to produce biofuels. Significant (>50%) cost reductions may be achieved if CO2, nutrients and water can be obtained at low cost. This is a very demanding requirement, however, and it could dramatically restrict the number of production locations available.
Sub-critical water gasification by partial oxidation of glucose was carried out in the presence of various alkali catalysts; NaOH, KOH, Ca(OH)2, Na2CO3, K2CO3 and NaHCO3. Experiments were carried out in a closed batch reactor under sub-critical water conditions of 330°C temperature and 13.5MPa pressure. Hydrogen gas yield in relation to the alkali catalyst was in the following order; NaOH>KOH>Ca(OH)2>K2CO3>Na2CO3>NaHCO3. The metal hydroxides produced higher H2 gas yield than the carbonates or bicarbonate. Carbon dioxide was the predominant gas product in the presence of metal carbonate and bicarbonates. Catalysts of the hydroxide ion group, NaOH, KOH and Ca(OH)2, were selected to react with representative food processing wastes in the form of molasses and rice bran under hydrothermal condition. The results indicated that NaOH, KOH and Ca(OH)2 could promote biomass decomposition and improve the amount of H2 product via the water-gas shift reaction by intermediate formation of formate salts. In addition, NaOH, KOH and Ca(OH)2 inhibited and suppressed tar and char formation. NaOH was also effective in capturing the CO2 formed, thereby shifting the water-gas shift reaction equilibrium in the forward direction. In addition, results showed that hydrothermal gasification at low temperature depended not only on the metal ion (Na+, K+ and Ca2+) but also on their species and concentrations. It is suggested that the basicity strengths of the aqueous solutions of alkali additives may have enhanced the initial decomposition of biomass into gasifiable intermediates, especially during the heat-up period.
Microalgae Dunaliella tertiolecta were studied for production of bio-oil through a sub- and supercritical water liquefaction process. The effects of liquefaction temperature, holding time, and feedstock ratio on the yields of the products were investigated. The maximum bio-oil yield is about 36.9%, obtained at a reaction temperature of 360 °C and a holding time of 30 min, with a feedstock ratio of materials to water of 1:10. The various physical and chemical characteristics of bio-oil obtained under the most suitable conditions were determined, and detailed chemical compositional analysis of bio-oil was performed using an elemental analyzer, Fourier transform infrared spectroscopy, and gas chromatography–mass spectrometry. The empirical formula of bio-oil with a heating value of 26.62 MJ kg−1 was established as CH1.38O0.43N0.07, and bio-oil was composed of hexadecanoic acid, palmitamide, and fatty acid methyl ester. Overall, the bio-oil obtained from microalgae Dunaliella tertiolecta were presented as a potentially valuable and environmentally friendly feedstock candidate for biofuels and chemicals.
Biodiesel production using microalgae is attractive in a number of respects. Here a number of pros and cons to using microalgae for biofuels production are reviewed. Algal cultivation can be carried out using non-arable land and non-potable water with simple nutrient supply. In addition, algal biomass productivities are much higher than those of vascular plants and the extractable content of lipids that can be usefully converted to biodiesel, triacylglycerols (TAGs) can be much higher than that of the oil seeds now used for first generation biodiesel. On the other hand, practical, cost-effective production of biofuels from microalgae requires that a number of obstacles be overcome. These include the development of low-cost, effective growth systems, efficient and energy saving harvesting techniques, and methods for oil extraction and conversion that are environmentally benign and cost-effective. Promising recent advances in these areas are highlighted.
Rapid depletion of fossil fuel reserves has posed a serious challenge to meet future energy requirement. Biodiesel with low carbon footprint has emerged as a potential candidate that can replace the need of fossil fuels. Biofuel derived from algae offers best alternative due to their high lipid content, robust nature, and noncompetitive nature toward food crops. The downstream production of biodiesel from feedstock is, however, facing challenges due to energy-intensive nature and higher production cost. A new and rapidly emerging field of nanotechnology has given a choice to built robust nanobiocatalytic systems with long-term stability and low input cost. Earlier studies reported that the addition of nanomaterials in algal culture system improved microalgal growth as well as induced lipid accumulation. Moreover, with the application of nanomaterials, the lipid extraction efficiency could also be enhanced. This chapter is aimed to review the current and significant applications of nanotechnology in the field of algal biodiesel production. Development of innovative technologies dealing with nanotechnological application in algal cultivation, lipid accumulation, harvesting, and transesterification has been critically reviewed.
Diatom algae are known to play an important role as primary producers in many diverse ecosystems including artificial aquaculture ponds were they also aid in maintaining water quality by consuming excess nutrients. But factors influencing their growth are still poorly understood. In the present study the effect of micro nutrients, N: P ratio and silica concentration on benthic diatom Synedra sp. grown in fish pond waste water was studied along with nutrient removal efficiency. We have studied 9 different treatments of which addition of micronutrient mixture Nualgi along with adjusted N:P to 6:1 has resulted in highest cell density followed by Silicate enrichment were as only N:P adjustment and Nualgi addition has no significant effect on diatom growth. At the end of growth experiment, the N removal efficiency of treatment groups (50.23%–65.44%) were significantly higher (P < 0.05) than control group (43.56%) were as phosphate removal efficiency was significantly higher (P < 0.05) with Nualgi and N:P adjustment (53.37%–68.98%). The silicate consumption was significantly higher in control group at 63.87%, than other experimental groups. These results will give us a new insight in to important factors influencing beneficial algae growth and simultaneous nutrient removal from aquaculture waste water.
The global energy demand has been increasing rapidly due to depletion of fossil fuels, continuous growth of world population and industrialized economy. India has surpassed to Japan and Russia and become the third largest oil consumer in the world. Unfortunately, India’s primary energy consumption has increased due to reduced oil and gas production. The increased consumption of imported oil could lead to turbulence in economic growth. Due to increasing demand of oil fuels and consequent impact of global warming issues, development of alternate energy is a top priority in research and developments sector. The bioenergy produced from the biomass is being a sustainable alternate energy source which received high acceptance in various sectors include public, industries and government policies. from the Government, public, industries and researches for its sustainability. This review focuson bioprospecting of biomass from terrestrial and marine resources for non conventional energy production and the stepping stones of biofuel for near future. These carbohydrates can be converted into various forms of biofuels either directly or indirectly by exploiting microorganisms. However, the production process and chemical transformation is being an expensive process and therefore commercial supply of biofuel in largescale is not yet successful. Hence an economic and efficient production process is essential to commercialize biomass based biofuels. This article highlights the overview of sustainable and renewable resources for biofuel and stepping stones of biofuel commercialization.
This paper assesses the economics of heat and power production from the anaerobic digestion (AD) of brown algae (Laminaria japonica) at a plant scale of 400,000 dry tons/year. The conversion process was simulated in Aspen Plus v.8.6 to obtain rigorous heat and material balance for energy assessments and the development of a techno-economic model. The breakeven electricity selling price (BESP) was found to be 18.81 ¢/kWh assuming 30 years of plant life and a 10% internal rate of return. The results show that the AD unit has the highest energy demand in the entire process and consumes approximately 14% of all electricity produced. In addition, the seaweed cost of 11.95 ¢/kWh is the largest cost component that contributes to the calculated BESP, which means that a reduction in the cost of seaweed cultivation can significantly decrease the electricity production cost. A sensitivity analysis was performed on the economic and process parameters in order to assess the impact of possible variations and uncertainties in these parameters. Results showed that solids loading, anaerobic digestion yield, and time, respectively, have the highest impact on BESP.
In a scenario with growing population, increasing demand for energy and volatile prices of fossil fuel, there is a high incentive for the use of biofuels, especially those produced from waste material. In this context, second and third generation bioethanol (2G/3G) are interesting alternatives, as they can be produced from different raw material such as corn and rice straw, sugarcane bagasse, waste from pulp industry and microalgae. This paper presents an overview of the available technologies for both 2G and 3G bioethanol production, including lignocellulosic biomass feedstock, biocatalysts and co-generation processes.
Due to growing interest in biofuels as alternative renewable energy sources, several recent studies have assessed the sustainability of their production. Emergy is a widely used environmental indicator for this purpose, as it counts exploitation of natural resources and direct and indirect solar energy requirements of biofuel production. Depending on whether a biofuel is first, second or third generation, its production system differs in nature and the indications derived from emergy evaluations vary as well. This article aims to provide guidelines on how to interpret and properly use the results of emergy evaluation of first, second and third generation biofuels. These guidelines are useful for correct emergy assessment of biofuels and clarify the actual meaning of emergy evaluation outcomes.
Brown algae have been considered as renewable biomass for bioethanol production because of high growth rate and sugar level. Saccharification of brown algae biomass is relatively easy due to the absence of lignin. Among the major sugar components of brown algae, alginate cannot be directly used because industrial microorganisms are not able to metabolize alginate. This problem has been overcome by the development of metabolically engineered microbes to efficiently utilize alginate. This review analyzes and evaluates recent research activities related to bioethanol production from brown algae. This review mainly deals with the recent development and potential of a metabolically engineered microbial cell factory and bioethanol production from brown algae biomass including alginate as the main carbohydrate. Future researches for cost-effective bioethanol production from brown algae are discussed.
The characterization of photobiological hydrogen production for four marine green algae by sulfur-deprived and treated with uncoupler after dark anaerobic incubation was investigated. The four marine green algae couldn't produce any hydrogen gas by sulfur-deprived from medium during direct light illumination. Four marine green algae were treated with 5 μmol/L uncoupler CCCP after dark anaerobic incubation of 32 hours, Platymonas subcordiformis could photoproduce a significant amount of hydrogen gas, Dunaliella salina and Marine Chlamydomonas only could photoproduce extremely small amount of hydrogen gas, and Pyramidomonas sp hardly could photoproduce any hydrogen gas. The change of hydrogen photoproduction rate and PS II photochemical activity of P subcordiformis indicated that part inhibition the PS II photochemical activity makes the photosynthetic oxygen evolution lower than the oxygen consumption by mitochondrion and the system can maintain anaerobic condition, at the same time, algae cells must keep some photochemical activity, which can supply enough electrons to hydrogenase for hydrogen production.
Algae are some of the fastest growing organisms in the world, with up to 90% of their weight made up from carbohydrate, protein and oil. As well as these macromolecules, microalgae are also rich in other high-value compounds, such as vitamins, pigments, and biologically active compounds, All these compounds can be extracted for use by the cosmetics, pharmaceutical, nutraceutical, and food industries, and the algae itself can be used for feeding of livestock, in particular fish, where on-going research is dedicated to increasing the percentage of fish and shellfish feed not derived from fish meal. Microalgae are also applied to wastewater bioremediation and carbon capture from industrial flue gases, and can be used as organic fertilizer. So far, only a few species of microalgae, including cyanobacteria, are under mass cultivation. The potential for expansion is enormous, considering the existing hundreds of thousands of species and subspecies, in which a large gene-pool offers a significant potential for many new producers. Completely revised, updated and expanded, and with the inclusion of new Editor, Qiang Hu of Arizona State University, the second edition of this extremely important book contains 37 chapters. Nineteen of these chapters are written by new authors, introducing many advanced and emerging technologies and applications such as novel photobioreactors, mass cultivation of oil-bearing microalgae for biofuels, exploration of naturally occurring and genetically engineered microalgae as cell factories for high-value chemicals, and techno-economic analysis of microalgal mass culture. This excellent new edition also contains details of the biology and large-scale culture of several economically important and newly-exploited microalgae, including Botryococcus, Chlamydomonas, Nannochloropsis, Nostoc, Chlorella, Spirulina,Haematococcus, and Dunaniella species/strains. Edited by Amos Richmond and Qiang Hu, each with a huge wealth of experience in microalgae, its culture, and biotechnology, and drawing together contributions from experts around the globe, this thorough and comprehensive new edition is an essential purchase for all those involved with microalgae, their culture, processing and use. Biotechnologists, bioengineers, phycologists, pharmaceutical, biofuel and fish-feed industry personnel and biological scientists and students will all find a vast amount of cutting-edge information within this Second Edition. Libraries in all universities where biological sciences, biotechnology and aquaculture are studied and taught should all have copies of this landmark new edition on their shelves. This edition first published 2013
Due to diminishing petroleum reserves and deleterious environmental consequences of exhaust gases from fossil-based fuels, research on renewable and environment friendly fuels has received a lot of impetus in the recent years. However, the availability of the non-edible crops serve as the sources for biofuel production are limited and economically not feasible. Algae are a promising alternative source to the conventional feedstocks for the third generation biofuel production. There has been a considerable discussion in the recent years about the potential of microalgae for the production of biofuels, but there may be other more readily exploitable commercial opportunities for macroalgae and microalgae. This review, briefly describes the biofuels conversion technologies for both macroalgae and microalgae. The gasification process produces combustible gases such as H2, CH4, CO2 and ammonia, whereas, the product of pyrolysis is bio-oil. The fermentation product of algae is ethanol, that can be used as a direct fuel or as a gasohol. Hydrogen can be obtained from the photobiological process of algal biomass. In transesterification process, algae oil is converted into biodiesel, which is quite similar to those of conventional diesel and it can be blended with the petroleum diesel. This study, also reviewed the production of high value byproducts from macroalgae and microalgae and their commercial applications. Algae as a potential renewable resource is not only used for biofuels but also for human health, animal and aquatic nutrition, environmental applications such as CO2 mitigation, wastewater treatment, biofertilizer, high-value compounds, synthesis of pigments and stable isotope biochemicals. This review is mainly an attempt, to investigate the biorefinery concept applied on the algal technology, for the synthesis of novel bioproducts to improve the algal biofuels as even more diversified and economically competitive.
Microscopic algae ("microalgae") have great potential as a future source of biological lipids for use in biodiesel fuel production. We are investigating the biochemistry and molecular biology of lipid biosynthesis in these organisms, and are developing genetic transformation systems that should allow us to genetically engineer microalgal strains for enhanced biodiesel production capabilities. As a result of these studies, we have isolated a full-length gene for the key lipid biosynthetic enzyme acetyl-CoA carboxylase. In addition, we have isolated portions of the genes that encode nitrate reductase and acetolactate synthase as a first step in the development of homologous selectable markers for microalgal transformation.
In many developed and developing countries, algal biomass is no doubt considered a significant source of energy to be used for local industry and transportation but the fact remains that the information on current utilization of algal biomass is still estimated and partial. Much more information will have to be gathered on the use and availability of algal biomass; particularly the limitations of first and second generation biofuel have given rise to the current interest in algae as a promising alternative to these conventional biofuel sources. It is therefore in this context that the present communication focuses its efforts to have region based database able to provide information on specific biomass production, their utilization with the respect to sectors like region, industries, transportation, etc., also taking into consideration the strong need for research on third generation biofuel production. In the present review, a comprehensive survey on algal biomass resource for future, is addressed.
Microalgae can efficiently fix carbon dioxide through their phototropic metabolism, and have been recognized as a promising bioresource for animal feed, health food, fuel, cosmetic, and pharmaceutical products. However, since microalgae in cultivated medium have a low biomass concentration (0.1–1% w/w), both harvesting and concentration of microalgal biomass are often required prior to the production of commercial products. Efficient and cost-effective dewatering and drying methods for microalgae heavily affect the overall energy consumption and production cost of microalgal products. This review describes the characteristics of commonly used dewatering and drying technologies, and critically evaluates the feasibility for their use to treat microalgal biomass. No single dewatering or drying method can satisfactorily handle all types of microalgae. The suitability of each method depends on the properties of the microalgae suspension, the required process design, the quality of the end product, and the related capital and production costs.
Brown algae, considered as the third generation biomass, offer several advantages over lignocellulosic biomass. However, the current high cost of seaweed cultivation hampers the industrialization of macroalgae-based biofuel production. The aim of this study is to determine the maximum dry seaweed price (MDSP) as an upper limit for purchasing price of brown algae at bioethanol plant gates. In addition, a minimum ethanol-selling price (MESP) was calculated by considering the state-of-the-art bioethanol production technology and current brown algae-cultivation costs. A new simple pretreatment process was economically validated and compared with the traditional acid thermal hydrolysis known as combined pretreatment. The processes were simulated at the scales of 80,000 and 400,000 ton/year of dry brown algae using the Aspen Plus v.8.4 software, and techno-economic models were developed based on mass and energy balance. MDSP for the simple and combined processes was calculated as 64.6 and 26 /ton (400,000 ton/year), respectively. In addition, MESP for the simple and combined processes was determined as 2.39 and 2.85 /gal (400,000 ton/year), respectively. These results indicate that the simple pretreatment is economically superior to the combined pretreatment. A comprehensive sensitivity analysis showed that seaweed price had the highest impact on MESP, thereby confirming that the cost-effective large-scale seaweed cultivation is the key to the success of macroalgae-based biofuel production.
Microalgal cultivation combined with anaerobic digestion at wastewater treatment plants is promising to recover energy. This study investigated the growth and anaerobic digestion characteristics of microalgae cultivated using nutrients in sewage. Microalgae were cultivated using primary effluent, secondary effluent, and dewatering filtrate. Microscopic observation indicated that Chlorella was cultivated using dewatering filtrate of anaerobic digestion without controlling the type of species. Batch anaerobic digestion experiments with digested sludge showed that the methane conversion ratio of the cultivated mixture was approximately 40-65%. Different cultivation time did not affect the microalgal contents. Methane recovery mass was 0.13NL-methane/L-cultivation liquor. The C/N ratio of the cultivated mixture was approximately 3-5, but the apparent ammonia release ratio was smaller than that of sewage sludge during digestion. These results proved the applicability of methane recovery from microalgae cultivated using nutrients included in anaerobically digested sludge.
Biodiesel, defined as the monoalkyl esters of vegetable oils and animal fats, can be derived from other triacylglycerol-containing feedstocks. Algae are being considered for this purpose due to their claimed high production potential. However, there are no comprehensive reports regarding the fuel properties of biodiesel obtained from algal oils. Algal oils, with examples of some exceptions also mentioned here, often contain significant amounts of saturated and highly polyunsaturated (≥4 double bonds) fatty acid chains which influence fuel properties of the resulting biodiesel. In this connection, the relevant fuel properties of biodiesel from algal oils and the important fuel properties of highly polyunsaturated fatty acid methyl esters as they would occur in many biodiesel fuels obtained from algal oils, have not yet been reported. To fill this gap, in the present work for the first time two neat highly polyunsaturated fatty acid methyl esters with more than three double bonds, methyl 5(Z),8(Z),11(Z),14(Z)-eicosatetraenoate (C20:4) and methyl 4(Z),7(Z),10(Z),13(Z),16(Z),19(Z)-docosahexaenoate (C22:6), were investigated. The cetane numbers were determined as 29.6 for C20:4 and 24.4 for C22:6. Kinematic viscosity values were observed as 3.11 mm2/s for C20:4 and 2.97 mm2/s for C22:6, while oxidative stability values were below 0.1 h for both by the Rancimat test while densities were above 0.9 g/cm3. Two polyunsaturated C20 methyl esters, methyl 11(Z),14(Z)-eicosadienoate and 11(Z),14(Z),17(Z)-eicosatrienoate, were also studied for kinematic viscosity, density, and oxidative stability to expand the database on these properties of C20 compounds and provide additional data to predict the properties of other highly polyunsaturated fatty acid methyl esters. Properties of biodiesel from algal oils are predicted with cetane numbers expected in the low to upper 40s and kinematic viscosity between 3 and 4 mm2/s for most algal biodiesel.
This study investigates the influence of heating and cooling rate on liquefaction of lignocellulosic biomass in subH2O (subcritical water) or in scEtOH (supercritical ethanol), in dependency of final reaction temperatures (250–350 °C) and residence times (1–40 min). The heating rate has been identified as a crucial parameter in the subH2O-based liquefaction, whereas it has marginal influence in the scEtOH-based liquefaction. Detailed characterization of gas, liquid and solid products enables to identify the individual reaction steps, which results in a new insight into the reaction mechanisms, depending on the liquefaction solvents and conditions. Similar to fast pyrolysis, hydrothermal liquefaction consists of beneficial primary reactions (pyrolytic & hydrolytic degradation) and non-beneficial secondary reactions i.e. recombination and secondary cracking. In scEtOH, biomass was decomposed by pyrolysis and alcoholysis at relatively high reaction temperatures while the recombination of reaction intermediates are retarded by the unique reactions of scEtOH such as hydrogen donation and hydroxylalkylation.
One of the most important dilemmas of the modern world is to supply enough energy with minimal environmental impact. On this demand bioenergy from renewable biofuels is of growing public and private interest.Recent developments in the scientific researches show that microalgae have potential as a source of bioenergy. With their exception of being one of the oldest residents of the Earth and playing a vital role in building up the atmosphere, microalgae have a variety of diversified strains, biochemical routes and products that can be used for biofuel processing. An increasing number of researchers, academics, entrepreneurs and investors are now working on new technologies to adapt microalgae originated energy into our daily life.The aim of this review is to focus on microalgae based biofuels under the main titles of biodiesel, biohydrogen, bioethanol and biomethane.For evolution in bioenergy that started with the first generation way through the third generation and today stepping on the concept of fourth generation, microalgae will be a good candidate for an alternative energy source.
The challenges, progress and prospects of green algae hydrogen production were discussed. The photosynthetic ability of green alga to generate molecular hydrogen was utilized for hydrogen production. The improvements needed to maintain continuity of production and optimize solar conversion efficiency were analyzed. The hydrogen metabolism pathways, methods for the recycling of photobioreactor components and minimizing the costs of alga growth nutrients were also described as important challenges to be overcome.
Nineteen different amino acids were liquefied by reaction at 300°C for 1 h to study distribution of nitrogen in amino acids and reaction products. Oil yields of the amino acids except tryptophan were less than 10%. Nitrogen contents of oil were less than 13%. All of the amino acids were unstable and most of the amino acid, except tryptophan, was converted to water soluble nitrogen compounds other than amino acids, so that the residue of nitrogen in feedstock amino acids in the oil was less than 7%. For tryptophan, oil yield was 66% and the distribution of nitrogen to the oil was 50%.
The economically significant production of carbon-neutral biodiesel from microalgae has been hailed as
the ultimate alternative to depleting resources of petro-diesel due to its high cellular concentration of lipids,
resources and economic sustainability and overall potential advantages over other sources of biofuels.
Pertinent questions however need to be answered on the commercial viability of large scale
production of biodiesel from microalgae. Vital steps need to be critically analysed at each stage. Isolation
of microalgae should be based on the question of whether marine or freshwater microalgae, cultures
from collections or indigenous wild types are best suited for large scale production. Furthermore, the
determination of initial sampling points play a pivotal role in the determination of strain selection as well
as strain viability. The screening process should identify, purify and select lipid producing strains. Are
natural strains or stressed strains higher in lipid productivity? The synergistic interactions that occur naturally
between algae and other microorganisms cannot be ignored. A lot of literature is available on the
downstream processing of microalgae but a few reports are available on the upstream processing of microalgae
for biomass and lipid production for biodiesel production. We present in this review an empirical
and critical analysis on the potential of translating research findings from laboratory scale trials to full
scale application. The move from laboratory to large scale microalgal cultivation requires careful planning.
It is imperative to do extensive pre-pilot demonstration trials and formulate a suitable trajectory
for possible data extrapolation for large scale experimental designs. The pros and cons of the two widely
used methods for growing microalgae by photobioreactors or open raceway ponds are discussed in detail.
In addition, current methods for biomass harvesting and lipid extraction are critically evaluated. This
would be novel approach to economical biodiesel production from microalgae in the near future. Globally,
microalgae are largest biomass producers having higher neutral lipid content outcompeting terrestrial
plants for biofuel production. However, the viscosities of microalgal oils are usually higher than that
of petroleum diesel.
In this study, pyrolysis of microalgal remnants was investigated for recovery of energy and nutrients. Chlorella vulgaris biomass was first solvent-extracted for lipid recovery then the remnants were used as the feedstock for fast pyrolysis experiments using a fluidized bed reactor at 500°C. Yields of bio-oil, biochar, and gas were 53, 31, and 10wt.%, respectively. Bio-oil from C. vulgaris remnants was a complex mixture of aromatics and straight-chain hydrocarbons, amides, amines, carboxylic acids, phenols, and other compounds with molecular weights ranging from 70 to 1200Da. Structure and surface topography of the biochar were analyzed. The high inorganic content (potassium, phosphorous, and nitrogen) of the biochar suggests it may be suitable to provide nutrients for crop production. The bio-oil and biochar represented 57% and 36% of the energy content of the microalgae remnant feedstock, respectively.