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The global energy system is undergoing an evolutionary change to cope with the highly inevitable threats caused by the climatic changes and global warming. The large dependence on fossil fuels has largely led to the emissions of harmful greenhouse gases which impacted global warming and its consequential environmental and climatic effects. The biofuels and other renewable energy sources have been presently considered by the world countries as economically viable and productive alternatives for mitigating carbon footprints and eventually, ensuring energy securities. In the past, the transition to renewable energy sources mainly pursued aiming for economic and foreign exchange objectives when countries undertook to invest in biofuels to lessen their dependence on imported fossil fuels. In recent years, national policies at the global level have increasingly focused on climate resilience sustainability, and environmental conservation. "The Book" thoroughly imparts biofuel production and deployment advanced techniques from the perspective of science, technology and policy. The chapters dealt in this book throw light on the ecological advantages of biofuel, underlining the fact that they are not only reducing air pollution but also improving the wellbeing of the entire world through sustainable activities for healthy ecosystems. Besides, the economic benefits of biofuels on environment, especially its role in increasing agricultural production, creating jobs, developing rural areas and contributing to GDP growth has been acknowledged by environmentalist and economist/policy makers. Additionally, this book elaborated different biofuel products bioethanol, biodiesel, biogas and policies adopted in several countries, reflecting diverse strategies and ambitious goals of bioethanol and biodiesel. Importantly, this book focused on sources of biofuel crops, genetic improvement of crops and sustainable agricultural practices that support the cultivation of biofuel crops and which are crucial as they help in the minimization of environmental trade-offs while enabling land and resource use. Biofuel crops do not compete with food crops, commercial crops since the targeted areas are marginal lands and the land not used for cultivation including adjoining area of forest. The production and supply of bioethanol and biodiesel in major countries and globally arebpresented with figures and data. The potential feedstock sources for ethanol production are sugarcane and maize serving as primary crops which are highly consumed in Brazil and the United States. The biodiesel production in Europe is also discussed with their major oilseed crops. Second-generation biofuels do not compete with food crops because they are produced from non-food

As global climate change becomes an increasingly urgent concern, the search for sustainable and renewable energy sources has intensified. Among the alternatives to fossil fuels, biofuels have emerged as a promising solution due to their potential to reduce greenhouse gas emissions and dependence on petroleum. Biofuels are derived from organic matter, such as crops, agricultural residues and other biomass, which can be converted into energy sources like ethanol, biodiesel, and biogas. For instance, crops like corn and soybeans contain oil extracts that can be processed into biofuels, offering a renewable and environmentally friendly alternative to traditional fossil fuels (Demirbas, 2009). However, the potential of biofuels extends beyond these conventional sources, as researchers explore a wide range of organic materials that can be sustainably regrown and harvested, minimizing ecological impacts (Naik et al., 2010). Biofuels have gained significant importance in both developed and developing economies, driven by their potential to enhance energy security and reduce carbon footprints. In 2023, the United States led global biofuel production with 15,550 million gallons, followed by Brazil with 8,260 million gallons. India ranked third, producing 1,430 million gallons of bioethanol and achieving an E11.7 blend rate during the 2022–2023 period. This blend was sourced from various feedstocks, including sugarcane juice (5%), cane molasses (5%), and damaged food grains (DFG) (1.7%). Historically, India’s ethanol production has relied heavily on sugarcane molasses, but the National Biofuel Policy (NBP) of 2018 has been instrumental in promoting the use of biofuels to reduce fossil fuel dependence, mitigate greenhouse gas emissions, and strengthen energy security (Ministry of Petroleum and Natural Gas, 2018). India, the third-largest energy-consuming nation globally, faces considerable challenges due to its heavy dependence on imported oil, posing risks to both economic stability and strategic security. With its share of global energy consumption projected to double by 2050, the country is actively seeking domestic alternatives to curb this reliance. Ethanol, produced within India, has emerged as a viable substitute. Since its initial pilot in 2001, ethanol-blended petrol has demonstrated notable environmental advantages, with every 10 million liters reducing CO2 emissions by 8,000–17,000 tonnes compared to conventional

Introduction  Maize (Zea mays L.) which belongs to the Poaceae family, has its roots in the American continent where it was once grown by ancient cultures like the Indians, Magyars, and Aztecs. Today, maize is one of the most widely cultivated crops globally, with the largest productions in countries such as the US, China, India, and Brazil. As a monocotyledonous and cross-pollinated annual plant, maize is an angiosperm with seeds enclosed in a fruit or shell. The root system of maize is fibrous, reaching up to 60 cm. in soil depth. Maize is a warm-season crop with specific agro climatic requirements for successful cultivation. It thrives in warm temperatures and requires a minimum temperature of around 10°C (50°F) for germination. The ideal temperature range for its growth is between 20°C and 30°C (68°F to 86°F). However, maize is sensitive to frost, and exposure to freezing temperatures can damage or kill the crop. Adequate and well-distributed rainfall is crucial during its growing season, as maize needs about 500 to 1000 mm. (20 to 40 inches) of rainfall to support its development, with higher water requirements during flowering and grain-filling stages. While the crop is moderately droughttolerant, moisture stress at critical growth stages can significantly impact yield. Maize is a sun-loving crop and requires long daylight hours with ample sunshine for efficient photosynthesis and plant growth. The soil should be well-drained, loamy or sandy, rich in organic matter, and have a pH ranging from 5.8 to 7.0 (Greaves et al., 1996). Avoiding waterlogged or compacted soils is crucial, as they can impede root development and nutrient uptake. Maize can be cultivated at varying altitudes, but its suitability is generally limited to elevations below 2,500 meters (8,200 feet) above sea level. The crop typically requires 90 to 120 days from planting to maturity, although some varieties with shorter growing seasons are available for regions with limited frost-free periods. High salinity can result in decreased plant leaves, green weight, fresh weight, shorter shoots, and root length but salt-tolerant varieties have been developed.

Introduction Sugarcane (Saccharum officinarum Linn.) is a remarkable tall, perennial grass characterized by its thick, jointed stalks and long linear leaves. This remarkable plant, known for its ability to efficiently photosynthesize in warm climates, is a C4 plant. The propagation of sugarcane primarily occurs through stem cuttings, as it seldom produces flowers and seeds. It finds roots in regions with tropical and subtropical climates featuring warm temperatures, abundant sunshine, and well-drained fertile soil (Shukla et al., 2017). Cultivated for its sweet juice, rich in sucrose, sugarcane serves as the primary raw material for the production of sugar, ethanol, and various other valuable products. Its lifecycle comprises several growth stages, including germination, tillering, grand growth, and maturation, culminating in the harvesting of its valuable juice. Continuous advancements in botany and genetics have contributed to the improvement of sugarcane cultivation, enhancing yield and resistance to pests and diseases. The origins and domestication of sugarcane can be traced back to Southeast Asia, particularly in regions encompassing Papua New Guinea, Indonesia, and their vicinity. The domestication of sugarcane is believed to have commenced thousands of years ago when early human populations in these regions recognized the sweetness of the cane and began cultivating it for its edible properties. Over time, through selective breeding and propagation of plants with desirable traits, these early cultivators played a pivotal role in shaping the sugarcane we know today. This indigenous Southeast Asian plant spread to other parts of the world through trade and exploration. Historical records indicate that sugarcane found its way to India around 500 BC and reached China in the 6th century AD. Subsequently, it traversed the Middle East, the Mediterranean region, and eventually reached the Americas during the early voyages of exploration and colonization (Grivet et al., 2004). Christopher Columbus played a significant role in introducing sugarcane to the Caribbean islands during his second voyage in 1493, and from there, it made its way to other parts of the New World, including Brazil and various South American countries. The cultivation of sugarcane emerged as an essential industry in these regions, profoundly influencing their economic and social landscapes. The domestication and widespread cultivation of sugarcane have left an indelible mark on the global economy, trade, and human history. Today, sugarcane remains one of the most significant crops globally, with major producing countries, including Brazil, India, China, Thailand, and others. It stands not only as a pivotal

Introduction  Sorghum bicolor L. Moench, commonly known as sorghum, has emerged as a significant and promising candidate for both sugar and lignocellulosic biofuel production. Cultivated sorghum varieties exhibit a wide range of phenotypic and morphological characteristics, and based on their intended use, they have been categorized into four distinct groups: grain, forage, energy, and sweet sorghum. Grain sorghum varieties typically stand between three to six feet in height, featuring large ear heads. Their primary role is to serve as a source of food for humans or livestock feed. These varieties play a crucial role in providing sustenance and nutrition to both people and animals. Sweet sorghum, also known as sweet stalk sorghum, represents a unique group of genotypes that accumulate soluble sugars within their stalks. These varieties can grow impressively tall, reaching up to twenty feet, and produce significantly higher biomass yields compared to grain sorghum (Murray et al., 2009). Sweet sorghum’s stems are characterized by their thickness and fleshiness, although they do tend to have relatively lower seed yields. Despite this, sweet sorghum offers substantial advantages in terms of bioethanol production due to the high sucrose content present in its stalks (Srinivasa Rao et al. 2009). It has garnered recognition as an ideal candidate for bioenergy crop cultivation in tropical and temperate regions around the world, particularly in the southern United States. When compared to other bioenergy crops such as corn, wheat, sugarcane, sugar beet, cassava, and sweet potatoes, sweet sorghum presents several noteworthy benefits (Disasa et al., 2016). It is notably drought-tolerant and requires significantly less water than many other crops, such as one-third of the water needed for sugarcane and half of that required for corn. Furthermore, it exhibits tolerance to salinity, enabling its cultivation in marginal regions that are not traditionally suitable for crop production. Additionally, sweet sorghum boasts lower greenhouse gas emissions on a life-cycle basis, contributing to a more sustainable and environmentally friendly biofuel production process. The applications of sweet sorghum are diverse, with its stalks being used for various purposes. In Brazil and India, the stalk is chewed fresh or processed for the production of food-grade syrup and alcohol. Its high sucrose content makes it an excellent candidate for bioethanol production, with the potential to yield up to 8,000 liters per hectare, surpassing the ethanol yield of corn by approximately twofold and outperforming

Introduction  Castor bean (Ricinus communis L.) is a species of annual and perennial flowering plant in the spurge family, Euphorbiaceae (USDA, 2016). It is the sole species in the monotypic genus, Ricinus, and subtribe, Ricininae. The evolution of castor and its relation to other species are currently being studied using modern genetic tools (Institute for Genome Sciences, 2009). Castor reproduces with a mixed pollination system that favors selfing by geitonogamy but can also be pollinated by wind (anemophily) or insects (entomophily) (Rizzardo et al.,2012). Native to the southeastern Mediterranean Basin, Eastern Africa, and India, castor is now widespread throughout tropical regions (Phillips & Rix, 2002). The plant is known for its seeds, which contain 40-60% oil, primarily composed of triglycerides such as ricinolein. However, the seeds also contain ricin, a watersoluble toxin present in lower concentrations throughout the plant. Ricinus communis exhibits significant variability in its growth habit and appearance, with cultivars selected for leaf and flower colours as well as oil production. Castor bean is a fast-growing shrub that can reach up to 12 meters in height, although it is not cold hardy. Its stems spherical, spiny seed capsules also vary in pigmentation. In some varieties, the fruit capsules are more attractive than the flowers. Ongoing research aims to better understand the plant’s evolution and its relationship to other species, while its unique characteristics and diverse uses make it an important subject of study. The monoecious castor plant bears unisexual male and female flowers in terminal panicle-like inflorescences (Fig :1). Male flowers are yellowish-green with creamy stamens, while fewer female flowers have prominent red stigmas (Oliver and Lee, 2010). The spiny capsule fruit contains large, oval, poisonous seeds with a caruncle that aids ant-mediated dispersal. Improving castor bean (Ricinus communis) cultivation for biodiesel production involves a combination of genetic, agronomic, and technological strategies aimed at enhancing yield, oil quality and sustainability. Genetic improvement focuses on developing high-yielding and disease-resistant varieties through traditional breeding, molecular techniques like marker-assisted selection (MAS), and advanced tools such as CRISPR-Cas9 for targeted gene editing. Efforts are directed at optimizing oil content, improving fatty acid profiles for biodiesel, and reducing toxins like ricin. Agronomic practices play a crucial role, including the adoption of efficient planting densities, intercropping systems, and soil and

Rapeseed Rapeseed (Brassica napus L.), a member of the Brassicaceae family, is one of the primary oilseed crops cultivated for biodiesel production, particularly in Europe and Canada (Hoekman et al., 2012; Demirbas, 2009). Its seeds contain 40-45% oil, making it one of the most efficient oil crops for biofuel production (Ramos et al., 2009). The extracted oil is known as canola oil, which is preferred for both food and fuel applications due to its low erucic acid and glucosinolate content (Atabani et al., 2012). Rapeseed (Brassica napus L.), is one of the biofuel species that has achieved global attention, primarily due to its high yield, climatic versatility as well as its low environmental impact than fossil fuels (Singh et al., 2010). The crop is being grown all over the temperate region because its ability to resist cold temperatures and pests is a major advantage for the practice of sustainable agriculture. Moreover, the rapeseed has been positively affected by the development of biotechnology and the utilization of hybrid breeding that has been significantly increasing the oil yield and disease resistance of rapeseed, thus, facilitating the biodiesel production from this plant (Zanetti et al., 2013). Biodiesel from rapeseed has ecological advantages, significantly reducing greenhouse gas emissions by up to 50% compared to regular diesel (Hill et al., 2006). It also supports rural economic development through the diversification of farmer income and diminishing reliance on imported petroleum (FAO, 2021). The increasing price of the biofuel, chiefly supported by sustainable energy policies and reducing carbon footprint policies, is one of the driving factors for increasing demand of rapeseed as global demand for renewable energy sources rises (Euopean Commission 2021). Sunflower Sunflower (Helianthus annuus L.) is an important oilseed crop used for biodiesel production, especially in temperate regions like Europe and North America (Demirbas, 2009). The oil content of sunflower seeds ranges from 25-50%, making it a suitable feedstock for biofuel (Atabani et al., 2012). The characteristics of sunflower oil, such as the high content of unsaturated fatty acids, lead to better cold flow properties of its biodiesel (Ramos et al., 2009). In addition, the creation of high-oleic sunflower varieties allowed considerable improvement in oxidative stability and led to the fact that sunflower biodiesel is more suitable for storage and combustion (Dimitrijevic et al., 2017). A second

Introduction Oil palm (Elaeis guineensis Jacq.), a tropical perennial tree native to West Africa, is the most productive oilseed crop for biodiesel, yielding up to 5 tons of oil per hectare (Mekhilef et al., 2011). Indonesia and Malaysia are the largest global producers, accounting for over 85% of the world’s palm oil (Atabani et al., 2012). Palm oil is extracted from the fruit of the oil palm and is widely used in both food and fuel applications. However, its cultivation has raised environmental concerns, including deforestation, habitat loss, and carbon emissions (Gui et al., 2008). Efforts are being made to promote sustainable palm oil production to mitigate these impacts (Mekhilef et al., 2011). Deforestation, habitat loss, and carbon emissions are only a few of the serious environmental issues brought on by its cultivation (Fargione et al., 2008). Oil palm plantation growth has been connected to a decline in biodiversity, especially in tropical rainforests that are home to endangered species like Sumatran tigers and orangutans (Fitzherbert et al., 2008). According to Carlson et al. (2013), the conversion of peatlands for the production of oil palm contributes to climate change by increasing greenhouse gas emissions. History of Oil Palm as Biodiesel Feedstock Oil palm has been used for cooking and lighting for thousands of years in Africa and Southeast Asia (Obahiagbon, 2012). Research into its use as a biodiesel feedstock began in the 1980s, with Malaysia pioneering biodiesel development (Zainal et al.,2017). • 1982: The Palm Oil Research Institute of Malaysia (PORIM) successfully tested palm oil-based biodiesel in diesel engines (Yusoff, 2006). • Early 2000s: Commercial production expanded in Indonesia and Malaysia, driven by government policies and renewable fuel demand (Mekhilef, 2011). • Sustainability challenges have led to the establishment of certification schemes such as the Roundtable on Sustainable Palm Oil (RSPO) (Ruysschaert & Salles, 2014).

Introduction  Jatropha, a genus belonging to the Euphorbiaceae family, comprises 175 species and has its origins in tropical America and Mexico, later spreading to the tropics and subtropics of Asia and Africa (Divakara et al., 2010). In Asian countries, India, China, and Myanmar account for more than 85% of Jatropha cultivation, while Africa and Latin American countries like Brazil and Mexico make up 12% and 2%, respectively. India stands as the largest cultivator of Jatropha (Kumar and Sharma, 2008). Historically, Jatropha has been utilized for various purposes, including storm protection, soil erosion control, firewood, hedges, and traditional medicines (Openshaw, 2000; Gubitz et al., 1999; Heller, 1996; Kaushik and Kaushik, 2011). The seed oil of Jatropha has also been used as lamp fuel, soap manufacturing ingredient, paints, and lubricant (Gubitz et al., 1999; Achten et al., 2007; Brittaine and Lutaladio, 2010). The characteristics of Jatropha seed oil closely resemble those of diesel (Pramanik, 2003; Foidl et al., 1996; Augustus et al., 2002), earning it the title of a biodiesel plant (Pandey et al., 2012). Jatropha thrives on diverse wastelands without requiring agricultural inputs like irrigation and fertilization and its seeds contain 40 to 60% oil content (Pandey et al., 2012; Achten et al., 2007). The plant’s easy propagation, rapid growth, drought tolerance, pest resistance, higher oil content compared to other oil crops, adaptation to a wide range of environmental conditions, short gestation period and optimal plant size and architecture which facilitate seed collection (Divakara et al., 2010), make it a promising crop for biofuel production (Abou Kheira and Atta, 2009; Fairless, 2007). The oil extracted from Jatropha curcas L. is primarily converted into biodiesel for use in diesel engines. The protein-rich cake resulting from oil extraction can be used as fish or animal feed after detoxification. Additionally, it serves as a biomass feedstock for electricity generation or biogas production and is a high-quality organic fertilizer (Gubitz et al., 1999). Crop improvement in Jatropha curcas L. focuses on enhancing its potential as a biodiesel feedstock by addressing challenges like low yield, variable oil content and narrow adaptability. Efforts in selection and breeding aim to identify highyielding genotypes with desirable traits such as high oil content, early maturity and resistance to pests and diseases. Hybridization and mutation breeding are used to introduce genetic diversity and develop improved varieties suited to diverse environmental conditions. Biotechnological approaches, including genetic engineering and marker-assisted selection are employed to accelerate

Introduction  In recent years, the global demand for sustainable and renewable energy sources has intensified due to the continuous depletion of fossil fuel reserves, rising fuel prices, and environmental concerns. Bioethanol, a renewable fuel derived from the fermentation of plant biomass, is considered a promising alternative to petroleum-based fuels. Among various feedstocks, tuber crops such as cassava, sweet potato, and potato have gained significant attention due to their high starch content and relatively low competition with food supply in certain regions. Bioethanol production is broadly categorized into four generations based on the type of feedstock and technology involved: First-Generation Bioethanol is derived from food crops such as maize, sugarcane, and tuber crops. Despite its wide application, it has been criticized for contributing to rising food prices (Khairati, 2024). Second-Generation Bioethanol is produced from non-food lignocellulosic biomass like agricultural residues, which reduces the food vs. fuel conflict (Sharma et al., 2020). Third- Generation Bioethanol is derived from algal biomass, offering higher yields and lower competition with land use (Brennan & Owende, 2010). Fourth-Generation Bioethanol combines biomass conversion with carbon capture and storage technologies, providing the highest environmental benefits (Yoon et al., 2012). Further the trend in world ethanol production during the year 20020–2025 is given in Figure 1. Tuber crops such as cassava, sweet potato, and potato are promising feedstocks due to their high starch content and lower food competition in certain regions. Recent studies highlight the efficiency of bioethanol production from these crops: Cassava is considered the most efficient tuber crop for bioethanol production due to its high starch yield and low production cost (Jagatee et al., 2015). Sweet Potato studies report ethanol yields of up to 138.6 g/kg under optimized fermentation conditions using co-fermentation techniques (Dash et al., 2017). Industrial potato waste has been successfully utilized for bioethanol production, with pilotscale experiments yielding up to 68.68% ethanol concentration (Sehsah et al., 2015). Bioethanol production from tuber crops presents several environmental and economic benefits. Life Cycle Assessment studies indicate that bioethanol reduces GHG emissions compared to gasoline, particularly in second-generation production systems (Farahani & Asoodar, 2017). Utilizing agricultural waste

Cellulosic ethanol refers to the production of ethanol, an alcohol fuel, from cellulose found in plant fibers rather than from seeds or fruits. This biofuel can be derived from various sources such as grasses, wood, and other plants. The fibrous components of these plants are mostly from crop residues and other sources indigestible for animals, except for ruminants like cows and sheep, as well as hindgut fermenters like horses, rabbits, and rhinos. The interest in cellulosic ethanol stems from its potential economic value. Plant growth and cellulose formation serve as a mechanism to capture and store solar energy in a chemically stable manner, facilitating easy transport and storage of the resulting supplies. Moreover, the ability of grasses and trees to grow in temperate regions makes cellulosic ethanol commercially viable and offers a potential solution from non-food sources other than grain and tuber starch. This cellulosic ethanol development in the biofuel industry presents an opportunity to derive carbonaceous liquid fuels and petrochemicals, which are vital for our current standard of living, in a balanced and renewable manner by recycling carbon from the surface and atmosphere through any kind of plant orgin or any plant or tree species, Additionally, commercially viable cellulosic ethanol could mitigate the issue associated with conventional biofuels based on grains, which compete with food production and may lead to increased food prices. However, the production of cellulosic ethanol is currently economically feasible and has been implemented on a large scale in India. Several 2G ethanol plants are being developed by companies like Indian Oil Corporation Limited (IOCL), Bharat Petroleum Corporation Limited (BPCL) and Hindustan Petroleum Corporation Limited (HPCL). Different types of biomass contain varying amounts of sugars, and the complexity of the biomass is determined by the structural and carbohydrate components. Plant biomass mainly consists of lignin (13.6-28.1%), cellulose (40.6-51.2%) and hemicellulose (28.5-37.2%), which serve as the raw materials for fuel production. The conversion of biomass into sugars is a crucial step in biofuel production. Therefore, selecting an appropriate pretreatment process based on the biomass type is essential to achieve optimal sugar yield with minimal energy input.

Microalgae have long been recognized as good potential sources for biofuel production due to their relatively high oil content and rapid biomass production (Schenk et al., 2008; Hu et al., 2008). These photosynthetic organisms thrive in a variety of aquatic habitats, including lakes, rivers, oceans, and even sewage, demonstrating their adaptability to diverse environmental conditions. They can tolerate a wide range of temperatures, salinities, and pH levels, as well as varying light intensities and aquatic or desert conditions. Additionally, microalgae can grow independently or in symbiosis with other organisms, making them highly versatile for various cultivation systems (Mutanda et al., 2011). Algae are generally grouped into three major categories: Rhodophyta (red algae), Phaeophyta (brown algae), and Chlorophyta (green algae), and are further classified by size into macroalgae and microalgae. Macroalgae are large, multicellular organisms visible to the naked eye, while microalgae consist of microscopic single cells that can be either prokaryotic, similar to cyanobacteria, or eukaryotic, similar to green algae (Fields et al., 2014; Maltsev & Maltseva, 2021). Microalgae are capable of producing a wide array of valuable bioproducts, including polysaccharides, lipids, pigments, proteins, vitamins, bioactive compounds, and antioxidants. They grow at a much faster rate compared to terrestrial crops and can be cultivated on non-agricultural land using non-potable saltwater or wastewater, reducing competition with food crops and ensuring sustainability (Lee et al., 2014). This has made microalgae an increasingly attractive alternative feedstock for biodiesel production, which relies heavily on the high lipid content of microalgae. The majority of these lipids are stored in the form of triacylglycerols, a type of oil that is ideal for biodiesel production. Beyond biodiesel, microalgae can also be utilized in various other energy production pathways. Some microalgal strains can produce hydrogen gas under specific growth conditions, while algal biomass can be combusted like wood or digested anaerobically to produce methane biogas, which can be used for heat and power generation. Additionally, algal biomass can be processed into crude bio-oil through pyrolysis, further expanding its applications as a renewable energy source (Mumtaz et al., 2019).

Algae are organisms that grow in an aquatic environment and use light and carbon dioxide (CO2) to produce biomass. There are two categories of algae: macroalgae and microalgae. Macroalgae, measured in inches, are large multicellular algae that often grow in ponds. Macroalgae refers to thousands of macroscopic and multicellular seaweed species. The term includes some species of macroalgae such as Rhodophyta (red), Phaeophyta (brown), and Chlorophyta (green). Algae species such as kelp provide important breeding habitats for fisheries and other marine species, thereby protecting food sources; Other species such as plankton algae play an essential role in carbon sequestration and produce up to 90% of the Earth’s oxygen. Macroalgae, or large seaweeds, grow very rapidly and can reach extraordinary lengths up to 60 meters (McHugh, 2003). Their growth rates are much higher compared to many land plants. For example, wild brown algae can yield between 3.3 and 11.3 kg of dry biomass per square meter each year, and cultivated varieties can produce up to 13.1 kg in just seven months. In contrast, sugarcane, which is known for its high productivity, typically produces 6.1 to 9.5 kg of fresh biomass per square meter per year (Kraan. 2010). Additionally, macroalgae are available naturally in water bodies on a seasonal basis, and farming them in the ocean does not require traditional farming land or fertilizers. This makes them a promising option for addressing energy needs, as they are not only used for food and hydrocolloid extraction but also have potential for ethanol production. Humans have a long history of growing algae for uses such as food, food additives, feed, textiles and papers, bio-plastics. In recent years, seaweed farming has become a worldwide agricultural practice, providing food and feedstock for various chemical uses such as carrageenan, animal feed, biofertilizers and growth promoters. Due to its importance in marine ecology and carbon uptake, recent attention has focused on kelp farming as a potential climate change mitigation strategy for carbon dioxide biocapture, along with other benefits, such as reduced nutrient loads and increased habitat for coastal aquatic species, and reduced local ocean acidification in addition to biofuel opportunities. The seven most commonly cultivated algal taxa are Eucheuma spp., Kappaphycus alvarezii, Gracilaria spp., Saccharina japonica, Undaria pinnatifida, Pyropia spp. and Sargassum fusiform. Eucheuma and K. alvarezii are cultivated for carrageenan (a gelling agent); Gracilaria is grown for agar; while the rest is grown for food. Macroalgae production has become a cornerstone of global aquaculture, serving diverse industries such as food, biofuels, and pharmaceuticals

Introduction  Tree-based biofuels, which are made from non-edible oilseeds of perennial trees, have emerged as a renewable energy source with considerable environmental and economic benefits. Unlike annual biofuel crops, tree-based biofuels have the potential for long-term yields, soil conservation benefits, and the ability to survive on marginal terrain (Dwivedi et al.,2011). Various tree species have been identified globally for their biofuel potential, with an emphasis on sustainability and low competition with food crops (Pandey et al., 2012). In India, there is a diverse range of over 100 tree species that produce seed oil suitable for biodiesel. These oil tree species can be cultivated on non-agricultural lands, ensuring that they do not compete with food and fodder production. Globally, tree-based biofuels are crucial for energy security. Palm, jatropha, pongamia, and mahua are among the feedstocks investigated by the US, Brazil, and Europe for biodiesel production. Tree-borne oilseeds (TBOs) are critical for biodiesel generation in India, which relies heavily on fossil fuel imports. India has implemented both the National Biofuel Policy (2009) and the National Agroforestry Policy (2014). The former policy aims to replace fossil fuels with biofuels, targeting a 5% replacement by 2012, 10% by 2017, and exceeding 10% beyond 2017. The latter policy focuses on integrated land use options for livelihood, environment, and energy security. Notably, important tree-borne oilseeds (TBOs) such as Jatropha, Karanj, Mahua, and Simarouba have been efficiently incorporated into agroforestry systems, yielding beneficial results and providing a significant source of non-edible oilseeds from trees. The need for alternatives to fossil fuels is particularly urgent for countries like India, which have a vibrant economy and high consumption of fossil fuels, heavily relying on imports. Biofuels, as renewable liquid fuels derived from biological sources, have proven to be promising substitutes for oil in the energy sector (Mahapatra et al.,2021). In India, the focus on biofuels is primarily on non-edible oils obtained from tree species’ seeds since oils from food crops like corn, sweet sorghum, and soybean cannot be diverted for biodiesel production (Raju et al., 2012). Tree-borne oilseeds (TBOs) are cultivated across the country in various agro-climatic conditions, including forest and non-forest areas, as well as wastelands, deserts, and hilly regions. India has a vast potential for oilseeds derived from trees, such as Mahua (Madhuca indica), Neem (Azadirachta indica),

Fourth-generation biofuels, also known as advanced liquid biofuels, represent a progression of biofuel production leveraging advanced technologies (Chiaramonti & Maniatis, 2020). They incorporate the concept of “carbon capture and storage (CCS)” at both the feedstock and processing levels. Utilizing non-competitive feedstocks like algal biomass, cellulosic materials, and genetically engineered microorganisms, 4G biofuels ensure renewable and sustainable production without relying on arable land or food crops. The feedstock is designed not only to enhance processing efficiency but also to capture more carbon dioxide as the crop grows. Thermochemical processing methods are coupled with CCS technologies, which direct the generated carbon dioxide into geological formations or storage areas such as depleted oil fields or mineral storage as carbonates (International Renewable Energy Agency [IRENA], 2021). Fourth-generation biofuels have the potential to significantly reduce greenhouse gas (GHG) emissions and can even achieve carbon neutrality or negativity compared to previous generations of biofuels. This concept aligns with the idea of “Bioenergy with Carbon Storage (BECS)” (Demirbas, 2010). These advanced biofuels are currently in the development and experimental stages, encompassing various applications related to technology, processing, and feedstock. The primary feedstock for fourth-generation biofuels production consists of genetically engineered high-yielding biomass with low lignin and cellulose contents, addressing the challenges encountered in second-generation biofuels production. Alternatively, metabolically engineered crop plants with lower lignin, high oil contents facilitate enhanced carbon capture capabilities, and improved cultivation, harvesting, and fermentation processes and can significantly enhance biofuels production (Dutta et al., 2014).

Biofuel crops play a crucial role in the global transition towards renewable energy. With increasing concerns about climate change and energy security, biofuels have emerged as a viable alternative to fossil fuels. However, their economic viability is influenced by various factors, including production costs, market demand, government policies, and environmental implications. The United States has been the most prominent fuel ethanol producer since 2007, followed by Brazil. Together the United States and Brazil account for 84% of the global ethanol production. European Union, China and Canada are the other leading fuel ethanol producers. Fuel ethanol production and consumption continue to rise, regardless of variations in crude oil prices. The United States is the largest producer, generating 60 billion liters primarily from corn, while Brazil follows with 33 billion liters, mainly derived from sugarcane (https://www.statista.com.) Ethanol production in India started in 1938 with recommendations to convert molasses into alcohol, eventually resulting in the enactment of the Power Alcohol Act in 1948. The Ethanol Blending Programme (EBP), introduced in 2003, mandated a 5% ethanol blend (E5). However, due to supply shortages in 2004-2005, the blending requirement was made optional. In the 2013-14 period, a total of 38 crore liters of ethanol was procured for blending with petrol. This amount significantly increased to 567 crore liters in the Ethanol Supply Year (ESY) 2022-23, achieving an ethanol blend level of E11.7. Acknowledging the substantial progress in the ethanol fuel blending initiative for a greener transition and Atmanirbhar Bharat, the government revised the target to E20 by 2025–26 and set an E30 goal for 2030 (NAAS, 2024). The proposed share of E20 is from sugarcane-based ethanol 10%, maize 7% and other damaged food grains 3.0%. The recently reported data during Jan 2025 showed the achievement of 19.6% blending in petrol (PIB, GOI, 2025)

Introduction  Biofuels have emerged as a key solution in the energy transition toward sustainable energy, reducing dependence on fossil fuels and cutting greenhouse gas (GHG) emissions. The demand for biofuels has been steadily increasing due to environmental concerns, government promotional policies, and technological advancements. The factors driving biofuel demand, current market trends, and future projections are the global demand for biofuels is experiencing rapid growth due to government policies, energy security concerns, and advancements in sustainable biofuel production. As more countries implement biofuel mandates and invest in next-generation biofuels, demand is expected to rise significantly in the coming years, positioning biofuels as a critical component of the global energy transition. Governments worldwide have implemented various policies to promote biofuel production and consumption. These policies aim to reduce greenhouse gas emissions, enhance energy security, and support rural economies. Ethanol remains the most widely used biofuel, with major producers like the U.S., Brazil, and China increasing production to meet rising demand. The U.S. and Brazil collectively account for over 80% of global ethanol production. Bioethanol production originated in Brazil in the early 20th century, where sugarcane was used to produce ethanol as a fuel additive. However, the United States also played a significant role in the large-scale commercialization of bioethanol, especially from corn, starting in the 1970s during the oil crisis. Brazil remains a global leader in sugarcane-based ethanol, while the U.S. leads in corn-based ethanol production. Biodiesel demand is growing, particularly in the European Union, Indonesia, and Argentina. Indonesia’s B30 program (30% biodiesel blending) has significantly boosted demand. Between 2005 and 2015, the biodiesel production experienced a sevenfold increase and is projected to grow by an additional 35% by 2025 (OECD/ FAO, 2014). Biofuel policies have played a crucial role in shaping the growth of biofuel production worldwide. Since their inception, these policies have provided financial incentives, blending mandates, and research support, which have driven large-scale production. The impact of these policies varies across major biofuelproducing nations, including the United States, Brazil, the European Union, China, and India (Table 1). The U.S. biofuel industry expanded significantly due to the