First-generation Biofuels Research Articles

Evolution of global water footprints of crop production in 1990–2019

Abstract Crop production has the largest water footprint (WF) of all economic sectors and ranks as a leading cause of water scarcity. Despite this, our understanding of historical changes in global WFs of crops remains limited. In this study, we analyse the recently published dataset on green and blue WFs of 175 individual crops in 1990–2019. We explore the main changes in unit WFs (expressed in m3t−1 yr−1) and WFs of production (m3 yr−1) and connect the observed changes to various physical and socio-economic drivers. We find that nearly 80% of crops reduced global average unit WFs (required less water per tonne) as crop yields improved and cultivation centred around more productive areas. However, the total WF of crop production increased by 30% as these productivity gains were insufficient to compensate for cropland expansion of mostly water-intensive crops. Close to 90% of the increase occurred between 2000–2019 likely driven by accelerated economic growth, globalisation, changing diets, and production of first-generation biofuels. Among crops, we observe the largest increases for oil palm fruit, soya beans, and maize as they became the main providers of crop-based nutrients, animal feed, and biofuels for the modern economy. Among regions, most of the increase occurred across the tropics, mainly in Indonesia, Brazil, and Nigeria. However, India, China, and the USA had the largest WFs of production over the study period. Humanity consumed 6.8 trillion m3 of water (87.1% green) to produce crops in 2019. This number is likely to increase in the future which may exacerbate already existing environmental and socio-economic issues. Thus, it is important to transition to more water-sustainable agrifood systems. Much potential still exists in increasing crop water productivity, shifting production to less water-scarce geographies, and rethinking our dietary and industrial consumption patterns.

Impact of agricultural and energy prices on the biofuels market through a VAR-VEC model

This study uses a Vector Autoregression - Error Correction Model to examine the price dynamics of Fatty Acid Methyl Ester (FAME) in the Portuguese market. The importance of this research is that failure to meet the targets of the Renewable Energy Directive jeopardizes Portugal's efforts to improve the sustainability of the transport sector. The results suggest that FAME prices are susceptible to fluctuations in agricultural commodities, ethanol, and fossil fuels, particularly diesel. Specifically for soy, FAME prices did not return to baseline levels by the end of the period, indicating a persistent impact. The volatility of FAME prices in response to ethanol and agricultural commodity prices underscores the need for strategic interventions to optimize these relationships. In the case of ethanol, this correlation could be strengthened, while in the case of agricultural commodities, feedstock diversification is essential to decouple FAME from first-generation biofuel sources and avoid competition with food crops. Moreover, biodiesel FAME, which serves as substitute and a complement to diesel, has a price sensitivity to changes in diesel prices. Policies and incentives to diversify feedstocks and promote advanced biofuels are essential for maintaining FAME's competitiveness and mitigating diesel price impacts.

Physical-Chemical Properties of First-Generation Biofuel Aiming Application in Diesel Locomotive

Theoretical framework: A biodiesel fuel is made from long-chain fatty acids derived from vegetable oil or animal fat. Similarities between physical-chemical characteristics of diesel and biodiesel make their mixture feasible. Environmental benefits achieved by using biofuels to drive machines has increased their contribution in energetic matrixes. Objective: The aim of this research is to produce soybean and sunflower biodiesel in the laboratory using a transesterification reaction and to examine the biodiesel specifications for utilization in compression ignition engines. Method: The physical-chemical properties of the biodiesel measured in the present work are density, viscosity, cetane index, flash point, pour point, and cloud point. Results and conclusion: For soybean and sunflower biodiesel, density (867 kg/m³, 860 kg/m³), viscosity (5.29 mm²/s, 5.30 mm²/s), Centane index (53.88, 55.66), flash point (187°C and 135.6°C) are reported respectively. Regarding the pour point, cloud point, were only determined for sunflower biodiesel, respectively, -2°C and 13°C. The results indicate that these properties, density, kinematic viscosity, flash point, as determined from the soybean and sunflower biodiesel are within the limits established by The Brazilian National Agency of Petroleum, Natural Gas and Biofuels, Resolution No. 45 of the ANP of 08/25/2014 – DOU 08/26/2014. These values are, respectively, 850-900 kg/m³, 3-6 mm²/s, at least 100°C.The produced biodiesel presented behavior similar to diesel S10 proving its viability of use. Research implications: As a result of such thorough research, we are able to compare many characteristics of soybean and sunflower biodiesel with commercial diesel S10. This research is critical to the performance evaluation of a compression ignition engine and the potential reduction in greenhouse gas emissions associated with conventional diesel.

Comparative Analysis of Acidic and Alkaline Pretreatment Techniques for Bioethanol Production from Perennial Grasses

This review paper examines acid and alkaline pretreatments on perennial grasses for second-generation (2G) bioethanol production, a relatively unexplored area in this field. It compares the efficiency of these pretreatments in producing fermentable sugar and bioethanol yield. This study finds that alkaline pretreatment is more effective than acidic pretreatment in removing lignin and increasing sugar yield, leading to higher ethanol yields. However, it is costlier and requires longer reaction times than acidic pretreatment, while acidic pretreatment often leads to the formation of inhibitory compounds at higher temperatures, which is undesirable. The economic and environmental impacts of lignocellulosic biomass (LCB) are also assessed. It is revealed that LCB has a lower carbon but higher water footprint and significant costs due to pretreatment compared to first-generation biofuels. This review further explores artificial intelligence (AI) and advanced technologies in optimizing bioethanol production and identified the gap in literature regarding their application to pretreatment of perennial grasses. This review concludes that although perennial grasses hold promise for 2G bioethanol, the high costs and environmental challenges associated with LCB necessitate further research. This research should focus on integrating AI to optimize the pretreatment of LCB, thereby improving efficiency and sustainability in 2G biofuel production.

Technology Research and Development Prospects of Biofuels

The energy consumption that results from economic growth and the pollution it releases into the environment has been the subject of widespread concern in academics and society in recent years, and they have grown in importance as the times progress. There is a growing need for renewable and alternative energy sources due to the possible depletion of non-renewable fossil energy sources like coal and oil as well as the acceleration of global climate change. One of the hottest areas of study right now is the hunt for clean, renewable, and alternative energy sources. A thorough analysis of the biofuels industry's present level of growth indicates a dynamic environment fueled by the rising demand for sustainable energy throughout the world. This review aims to analyze in detail the research background, significance, and rationale for selecting biofuels. It will start with first-generation biofuels and focus on the current third-generation biofuels. Biofuels derived from renewable bioresources have emerged as a promising alternative because of the need to address environmental issues associated with traditional fossil fuels. The dual impact of biofuels on reducing greenhouse gas emissions and enhancing energy security is explored. The choice to focus on third-generation biofuels emphasizes the commitment to innovation and is in line with the United Nations sustainable development goals, in particular those related to clean energy, climate action, and environmental protection.

Performance of the Polish Biofuel Industry after Accession to the European Union in the Area of Sustainable Development Concepts

Poland is an important producer of rapeseed used in the biofuel industry. The rate of production of the biofuel industry increased after Poland’s accession to the European Union (EU). The reasons for these changes are numerous, of which the European Union’s energy policy is the most important. This paper aims to analyze the performance of the biofuel industry in Poland in view of changes in the market. Moreover, I evaluated changes in the biofuel industry after Poland’s accession to the EU. In addition, I analyzed the fixed and current assets of the Polish biofuel. The hypothesis that the price of rapeseed oil is the key determinant of profitability in the biodiesel industry was formulated. A statistical analysis proved the second hypothesis stating that the net profit of biodiesel companies depends on biodiesel production to the greatest extent. The time range of the analysis was 2005–2021. To analyze the economic performance of the biofuel industry in Poland, these changes were used. A regression analysis to find factors influencing the economic performance of the biofuel industry was used. More and more oils are used for the production of first-generation biofuels. Refined rapeseed oil also increased from 386.5 thousand tons to 780.6 thousand tons. Such numbers demonstrate the development of biofuel markets.

Biofuels an alternative to traditional fossil fuels: A comprehensive review

Biofuels are fossil fuel alternatives produced from agricultural biomass or other organic matter; considered sustainable, eco-friendly, and bioeconomic biofuels have come up as a topic of discussion for over a decade. Their practical use depends on the production methods, low cost-technology implementation, and substrate used. This review gives an insight into different generations of biofuels with their applications and implications. First-generation biofuels are produced from edible biomass, but even in highly efficient processes, their yield isn't enough to cast them as a better alternative to conventional fuels. The second-generation biofuels are produced from non-edible biomass, where the substrate is eco-friendly and provides a sustainable use of solid waste, but the pretreatment is overpriced and sophisticated technology is needed to carry out the process. Third-generation biofuels are produced from substrates like seaweed or microalgae for which no specific area or separate cultivation process is required. Biofuels such as biohydrogen produced through microbial dark fermentation, bio-syngas generated via gasification, and biodiesel obtained through transesterification, have emerged as promising and environmentally friendly alternatives to conventional fuels. These biofuels have the potential to pave the way for a bioeconomic system of fuel production, offering economic viability and efficiency. However, extensive research conducted in the field of bioenergy, several challenges persist, hindering their commercialization prospects. To overcome the problems of first, second and third-generation biofuels, fourth-generation biofuels are under development using techniques like co-culturing, nanotechnology, and genetically modified organisms. Future generations of biofuels would set a system for a circular bioeconomic pathway for sustainable development in the fuel industry.

Production of first and second-generation biodiesel for diesel engine operation: A review

Researchers are looking at alternative cleaner technologies to fulfill the rising need for greener fuels. For this reason, alternatives like bioethanol and biodiesel have become commercially available. Renewable fuels are classified as either "first generation," "second generation," or "third generation" depending on the feedstock used in their manufacture. Over the past decade, society's reliance on first-generation biofuel feedstocks has created an inbuilt rivalry between food and fuel. Second-generation biofuel feed-stocks, such as non-edible agricultural waste products, energy crops, and crop residues, have been illuminated by emerging technical prospects. Technologies for producing biofuels have been proposed and developed in multiple stages, with first-generation technologies being the most developed. In several nations, including the United States, corn grain is used as feedstock in bio-refineries. There is a risk that food and fuel prices will rise as a result of the usage of edible materials in crops like corn. Second-generation biofuel manufacturing technology that utilizes crop residues has been developed to deal with this kind of problem. This study investigates and evaluates the economic viability and environmental sustainability of the proposed solution for the production of second-generation biodiesel.

ANALYSIS OF PROSPECTIVE DIRECTIONS FOR USING UKRAINE’S BIOMASS POTENTIAL FOR ENERGY

The purpose of the work is a comprehensive assessment of Ukraine’s bioenergy potential. The task of the work is to develop recommendations for the practical implementation of promising directions for the potential utilisation. The research methods include calculations, study and analysis of literature, statistics and other data. The availability of considerable biomass potential for the production of various types of biofuel and energy is one of the main prerequisites for the successful development of bioenergy in Ukraine. Results of the assessment based on 2021 data show that the potential of biomass for energy in the country amounts to nearly 26 Mtoe/year. A comprehensive assessment of the potential was carried out for such components as solid biomass, biofuelі and biogas. Sources of solid biomass are various agricultural residues, various types of wood biomass and energy crops (provided they are grown on unused agricultural land). Solid biomass in the amount of more than 16 Mtoe/year is the largest component of the country's biomass energy potential accounting for 62% of the total. Expert assessments indicate the possibility of increasing this potential to about 44 Mtoe/year in the period until 2050. A scenario for the long-term use of the biomass potential for energy and biofuel production has been developed taking into account sustainability issues. To implement this scenario, it is necessary to overcome a number of barriers existing in the bioenergy sector, primarily the main ones. It also seems necessary to temporarily liberalize for Ukraine the strict sustainability criteria established by the EU RED II. This mitigation should include postponing the requirement to reduce greenhouse gas emissions (65% for biofuels and biogas for transport produced in installations that started operation from 01.01.2021); establishing a special limit for Ukraine until 2030 on the use of energy from first-generation biofuels in transport (up to 7%); expanding for Ukraine the list of feedstock for the production of advanced biofuels, including regulation of possibility to obtain raw material for biofuel production on polluted, unused, low-productivity and degraded lands.

Supporting Second Generation Biofuel Development: Thermophilic Anaerobic Digestion of Vinasse for Harmonizing with Molasses Based Bioethanol Plant Capacity

First-generation biofuel is environmental quandary due to its impact to the forest conversion into plantation area. Not only environmental sector, first-generation biofuel has other issues on socioeconomic sector. It consumes crops as its feedstock which will be a conflict between food and energy source. This conflict will impact the vulnerable people as the raising food price. Molasses-based bioethanol is second-generation biofuel which more beneficial from environmental, economic, and social aspect. Molasses-based bioethanol production process generates waste named vinasse. Vinasse can’t be directly discharged to the environment due to its high organic matter concentration which is harmful to the waterbody, soil, and air. On the other hand, high organic matter contained in vinasse can be converted into biogas and is higher potential for molasses-based bioethanol plant. This study was preliminary study for processing vinasse using thermophilic anaerobic digestion specifically by temperature direct escalation and starvation method to the mesophilic originated inoculum. The result shows robust performance of thermophilic microbia which is an averment of compatible method for enriching thermophilic anaerobic microbia in mesophilic originated inoculum.

Microbial Enzyme Systems in the Production of Second Generation Bioethanol

The primary contributor to global warming has been the careless usage of fossil fuels. Urbanization’s threat to the depletion of these resources has made it necessary to find alternatives due to the rising demand. Four different forms of biofuels are now available and constitute a possible replacement for fossil fuels. The first generation of biofuels is generated from the edible portion of biomass, the second generation is made from the non-edible portion of biomass, the third generation is made from algal biomass, and the fourth generation is made using molecular biology to improve the algal strain. Second-generation biofuels are extremely important because they are derived from non-edible biomass, such as agricultural and agro-industrial wastes rich in cellulose, hemicellulose, pectin, and starch impregnated with lignin, and are hydrolyzed after delignification by physio-chemical or biological pretreatments using ligninases. The enzymes involved in the hydrolysis of feedstocks for the production of second-generation bioethanol, a highly acceptable biofuel, are discussed in this article. Furthermore, the article discusses various fermentation technologies as well as significant developments in second-generation biofuel production by combining various microbial enzyme systems.

TRANSFORMATION OF SOLID WASTE INTO RENEWABLE ENERGY: PERSPECTIVES FOR THE PRODUCTION OF 2G BIOFUELS

Turning residual biomass into bioenergy promotes rational environmental waste disposal and turn it into a source of energy. In the last decade, the idea of using lignocellulosic biomass to make second-generation (2G) biofuels has become more popular in the energy industry. Thus, this study aimed to show the potential of residual lignocellulosic biomass as raw material for clean and sustainable energy and the technological advances focused on making it economically viable. A narrative review was adopted, in which the material used in the bibliographic survey was organized from scientific sources collected in high-relevance databases. The various factors presented in the review guarantee that the use of lignocellulosic biomass is considered a promising substrate. Furthermore, it indicates a solution to the competition between food supply and fuel production, which occurs with first-generation biofuels, which in the long term seem to be unsustainable. However, despite technological advances for its production and commercialization on a large scale, investment in scientific research is necessary to make the adopted technologies viable.

Bacterial metabolic engineering for the production of second-generation (2G) bioethanol and biobutanol; a review.

The second generation (2G) biofuels were introduced to solve the issues associated with first-generation biofuel (dependency on food materials) and fossil fuels such as reservoirs diminution, high demand, price fluctuation, and lethal greenhouse gases emission. Butanol and ethanol are the main 2G biofuels. They are used as a disinfectant, antiseptic, and chemical solvent in pharmaceutical, plastic, textiles, cosmetics, and fuel industries. Currently, their bacterial biological production from lignocellulosic material at the industrial level with primitive microorganisms is under development and not economical and qualitative compatible as compared to that of fossil origin, due to slow growth rate, low titer, recalcitrant nature of lignocellulose, strain intolerance to a higher amount of butanol and ethanol, and strain inability to tolerate inhibitors accumulated during pretreatment of lignocellulosic materials. Therefore, metabolic engineering strategies such as redirection of carbon flux, knocking out competing pathways, enhancing strain robustness and wide range of substrate utilization ability, and overexpression of enzymes involved in their biological synthesis have been applied to bacteria for enhancing their ability for 2G ethanol and butanol production in a highly cost-effective amount from lignocellulosic materials. Herein, we summarized and reviewed the progress in metabolic engineering of bacterial species such as clostridium spp, E. coli, and Z. moibilis for the synthesis of 2G butanol and ethanol, especially from lignocellulosic materials.

Zero Till Water Use Efficient Rabi Sorghum (Sorghum bicolour L. Moench), an Effective Alternative to Water Guzzling Summer Rice (Oryza sativa), under Changing Climatic Scenario

As temperature rises, the yields of food and cash crops in South Asia are expected to decline, putting pressure on food security in the region. India, home to 1.4 billion people, is ranked 101 out of 116 countries in the Global Hunger Index, indicating a serious problem. Scientists and researchers project that a 2.5 to 4.90C increase in temperature across the country could lead to a decrease of 41%-52% in the wheat yield, and 32%-40% in rice. Under changing climate conditions, hybrid sorghum is an effective solution for food security, which can withstand high temperatures and grow with less water over water guzzling summer rice. It has versatile utility as food grains, feed, fodder, and an important feedstock for first-generation biofuel or bioethanol production. Zero till hybrid sorghum cultivars CSH 14, CSH 16, and CSH 23 were sown after Kharif rice in jute-rice-Rabi sorghum sequence, in winter, on 1st January 2010. The crop matured with 52.5 cm irrigation water at 120 days (30th April) and consumed 7 irrigations, 7.5 cm each. The highest sorghum grain yield was obtained from cv. CSH 14 i.e., 6.5 tonnes/ha. Its water productivity was high, 808 litre water/kg grain whereas for summer rice with the same productivity (6.5t/ha) the water productivity was low, 2308 litre water/kg rice grain (irrigation requirement 150 cm). Thus, with the same water, the area under sorghum will be thrice over summer rice. Gross return from hybrid sorghum was Rs.193050/ha over Rs. 132600/ha from summer rice. Rabi sorghum saved 65% (97.5 cm/ha) of irrigation water which is drawn from groundwater only. From 6.5 tons of sorghum grain, approximately 2470 litre of ethanol can be produced/ha which is used as biofuel. Replacement of summer rice by profitable drought-resistant Rabi sorghum will ensure food security under changing climatic scenarios and maintain a sustainable groundwater position in traditional rice growing belts.

Three Pillars of Advanced Biofuels’ Sustainability

Today, reducing GHG emissions is an important goal worldwide. Initially, first-generation biofuels were considered as a solution; however, they created a conflict between food and fuel. Advanced biofuels, which use non-edible materials, have emerged and are becoming more widespread, thus resolving this conflict. The paper aimed to investigate the three pillars of advanced biofuels’ sustainability (economic, environmental, and social). In the frame of a systematic literature review, 41 out of the initially screened 3407 articles were analyzed in depth. The economic aspect of sustainability was the most frequently occurring topic, followed by the environmental aspect, while the number of articles related to the social aspect was limited. From the economic point of view, all the analyzed articles agreed that advanced biofuels are far from commercialization at this stage; however, there are promising options related to different feedstocks or production technologies. Advanced biofuels perform unequivocally better environmentally than even conventional biofuels. For third-generation biofuels, negative net GHG emissions can even be possible, while fourth-generation biofuels can theoretically be produced from CO2. With respect to the social pillar, job creation was the core element of the articles analyzed. This can be experienced at the farm, production, and research levels. Although the commercialization of advanced biofuel production will take time, humanity must turn to them in order to avoid the food versus fuel problem, as well as to successfully fight against climate change and global warming.

Implementasi Minyak Wijen Sebagai Bahan Bakar Alternatif Untuk Kendaraan Matic Terhadap Pelaku Bengkel Di Sambi Kerep Surabaya

Biofuels include energy-enriched chemicals produced directly through biological processes or derived from the chemical conversion of the biomass of previously living organisms. Biofuels can be classified into two categories: primary and secondary biofuels. The main biofuels are produced directly from burning woody plant material or cellulose and dry animal dung. Secondary biofuels can be classified into three generations, and each is produced indirectly from plant and animal materials. The first-generation biofuel is ethanol derived from starch-rich food crops or biodiesel, extracted from animal fat wastes such as cooking oil. The second generation is bioethanol derived from non-food cellulosic biomass and biodiesel derived from oil-rich plant seeds such as soybean or jatropha. The third generation is a biofuel produced from cyanobacteria, microalgae, and other microbes, which is the most promising approach to meet global energy demand. This community service aims to explain innovation and provide knowledge to technology players, namely technicians, operators, supervisors, and workshop supervisors, about the use of alternative fuels of sesame oil for small-capacity automatic gasoline engines. The counseling results show that the performance and exhaust gas results are optimal so that the technology actors know the quality and quantity of the alternative energy.

Comparison of the Combustion Process Parameters in a Diesel Engine Powered by Second-Generation Biodiesel Compared to the First-Generation Biodiesel

The use of biofuels to power compression–ignition engines makes it possible to reduce emissions of certain harmful components of exhaust gases. The purpose of this study was to determine the influence of second-generation biofuels on the course of indicator graphs and heat release characteristics of the Perkins 1104D-44TA compression–ignition engine. For comparative purposes, the same tests were carried out by feeding the engine with first-generation biofuel and diesel fuel. Babassu butyl esters (BBuE) were used as the second-generation biofuel. The second fuel was a first-generation biofuel—rapeseed oil methyl esters (RME). Analysis of the results made it possible to draw conclusions about the effect of using 2nd and 1st generation biofuels on the parameters of the combustion process. When the DF engine was powered, the lowest fuel dose per work cycle was obtained. In the case of RME and BBuE fuels, it depends on the engine load. For low loads, higher consumption is for RME, and for higher loads, fuel consumption for BBuE in-creases most often. This is due to the lower calorific value of the esters. The results of these tests indicate that feeding the engine with BBuE and RME fuel in most loads resulted in higher maximum combustion pressures compared to feeding the engine with DF which may be directly related to the higher cetane number of these fuels compared to DF and the oxygen content of these fuels. Feeding the engine with BBuE and RME esters compared to DF did not result in large differences in the maximum heat release rates HRmax. However, the values of the first and second maximum heat release rates x1max and x2max, in addition to the type of fuel, are strongly influenced by the operating conditions, especially the engine load. Analyzing the combustion angles of 5, 10, 50, and 90% of the fuel dose, it can be seen that feeding the engine with BBuE and RME esters for most measurement points results in faster combustion of the fuel dose compared to DF.

The Analysis on the Current Situation of the Utilization Mode of Microalgal Biomass Materials

In recent years, global warming caused by the greenhouse effect has become one of the greatest threats to mankind. This will have a serious impact on the environment and human body, such as land desertification, increase in ocean acidity, sea level rise, and increase in pests and diseases; affect people’s normal work and rest; and make people feel dizzy and nauseated. Excessive emissions of carbon dioxide (CO2), the main component of the greenhouse gas, have contributed to the continued rise in Earth’s temperature. Although the world is vigorously developing clean energy to reduce carbon emissions, it will not replace fossil fuels in the short term. The conversion of biomass into energy is the most important way of energy utilization. Biomass energy refers to the solar energy stored in biomass in the form of chemical energy and is the fourth major energy source after oil, coal, and natural gas. At present, biofuels have gone through three developmental stages, which can be divided into first-generation biofuels, second-generation biofuels, and third-generation biofuels according to the types of raw materials and development history. The first generation of biofuels produced from food crops, such as bioethanol derived from sucrose and starch, has already entered the energy market. However, because the first generation of biofuels uses food crops as raw materials, there is a phenomenon of “competing with people for food,” and it is difficult to achieve large-scale application. To avoid the problem of food shortages, second-generation biofuels produced from nonfood crops, such as wood fiber, have been developed. Microalgae biomass energy is favored by governments and scholars all over the world because of its unique advantages of fast reproduction speed and high oil content. The cultivation of microalgae does not occupy traditional farmland, and the marginal land such as mountains, oceans, and deserts can cultivate microalgae, or develop microalgae cultivation in the air through the innovation of microalgae photosynthetic reactors. When municipal wastewater, food industry wastewater, and aquaculture wastewater are used as the medium for large-scale cultivation of microalgae, and waste gas from biogas power generation, flue gas from coal power plants, and industrial waste gas from fermentation are used as the CO2 gas source for large-scale cultivation of microalgae, it can be further reduced. The comprehensive production cost of microalgae bioenergy plays a significant emission reduction effect. Combining the above advantages, the use of microalgae to produce first- or second-generation bioenergy has become a new research direction. This study focuses on the review of microalgal biomass in fuel, nonfuel, wastewater treatment, and fuel cell.

Biofuels Production and Processing Technology

The negative global warming impact and global environmental pollution due to fossil fuels mean that the main challenge of modern society is finding alternatives to conventional fuels. In this scenario, biofuels derived from renewable biomass represent the most promising renewable energy sources. Depending on the biomass used by the fermentation technologies, it is possible obtain first-generation biofuels produced from food crops, second-generation biofuels produced from non-food feedstock, mainly starting from renewable lignocellulosic biomasses, and third-generation biofuels, represented by algae or food waste biomass. Although biofuels appear to be the closest alternative to fossil fuels, it is necessary for them to be produced in competitive quantities and costs, requiring both improvements to production technologies and diversification of feedstock. This Special Issue is focused on technological innovations, which include but are not limited to the utilization of different feedstock; different biomass pretreatments; fermentation strategies, such as simultaneous saccharification and fermentation (SSF) or separate hydrolysis and fermentation (SHF); different applied microorganisms used as monoculture or co-culture; and different setups for biofuel fermentation processes.

On quantifying sources of uncertainty in the carbon footprint of biofuels: crop/feedstock, LCA modelling approach, land-use change, and GHG metrics

Biofuel systems may represent a promising strategy to combat climate change by replacing fossil fuels in electricity generation and transportation. First-generation biofuels from sugar and starch crops for ethanol (a gasoline substitute) and from oilseed crops for biodiesel (a petroleum diesel substitute) have come under increasing levels of scrutiny due to the uncertainty associated with the estimation of climate change impacts of biofuels, such as due to indirect effects on land use. This analysis estimates the magnitude of some uncertainty sources: i) crop/feedstock, ii) life cycle assessment (LCA) modelling approach, iii) land-use change (LUC), and iv) greenhouse gas (GHG) metrics. The metrics used for characterising the different GHGs (global warming potential-GWP and global temperature change potential-GTP at different time horizons) appeared not to play a significant role in explaining the variance in the carbon footprint of biofuels, as opposed to the crop/feedstock used, the inclusion/exclusion of LUC considerations, and the LCA modelling approach (p<0.001). The estimated climate footprint of biofuels is dependent on the latter three parameters and, thus, is context-specific. It is recommended that these parameters be dealt with in a manner consistent with the goal and scope of the study. In particular, it is essential to interpret the results of the carbon footprint of biofuel systems in light of the choices made in each of these sources of uncertainty, and sensitivity analysis is recommended to overcome their influence on the result.