Advances in Lignocellulosic Biofuel Production Systems

By Ramesh C. Ray

Advances in Lignocellulosic Biofuel Production Systems focuses on general topics such as novel pretreatment strategies, lignocellulosic biomass as a suitable feedstock for biofuels, lifecycle assessment and integrated biorefineries. Furthermore, the book focuses on more advanced topics such as genetically engineered feedstocks, metabolically engineered microbes, bioreactor design and configuration, cell immobilization strategies, artificial intelligence applications and nanotechnology. This book will guide readers through all aspects of lignocellulosic biofuel production rather than simply covering a single topic.

• Provides information on the most advanced and innovative technologies for biomass valorization, including the design and configuration of bioreactors
• Identifies research gaps in the application of artificial intelligence, nanotechnology, cell immobilization, metabolic engineering, kinetic assessment and genetically engineered feedstocks for enhancing lignocellulosic bioprocessing and biofuel yield
• Presents a global overview of the supply chain for biofuels production from lignocellulosic biomass
• Includes techno-economic analysis, along with environmental and socioeconomic impact assessments of various technologies

• Language: English
• Publisher: Elsevier Science
• Release date: Apr 27, 2023
• ISBN: 9780323913447

Book preview

Preface

Preshanthan Moodley, Ramesh C. Ray and Evariste B. Gueguim Kana

Population growth, increasing urbanization, the depletion of fossil fuel sources, the necessity for energy security, and the incredible amount of waste produced are some of the inherent problems linked to the current fossil-based linear economy. Exploring and identifying alternative technologies, methods, and feedstocks that can transition to a circular economy is urgently needed, given the trajectory of the current scenario. The world’s economy is progressively shifting from one that is dependent on fossil fuels to one that is circular and sustainable. Alternative and sustainable methods for producing liquid and gaseous biofuels are crucial to aid in this paradigm shift. The production of biofuels utilizing residues as a feedstock has emerged as a method for generating sustainable energy. Biofuels are a temporary and natural by-product of numerous biochemical processes powered by microorganisms, supporting environment-friendly and sustainable manufacturing. Climate change and the enormous amounts of waste being produced are concerns that cannot be overlooked. The massive amounts of biogenic waste that are produced may be viewed as a potential fuel for the bio-based economy’s structure.

This book is divided into five sections and it is a collection of expertly curated chapters that provide a snapshot of the lignocellulosic biofuel landscape, with a specific focus on current advances. Section I is the introductory chapter which provides an overview of lignocellulosic biofuel processes with a brief look at the contents of each chapter in the book. Section II deals with feedstock and processing. The first chapter in this section provides a detailed account of lignocellulosic biomass as a feedstock to support the circular economy; this is followed by a chapter on genetically engineered feedstocks to enhance biofuel yields. Subsequent chapters deal with pretreatment technologies, application of microwave processing, and role of enzymes for enhanced saccharification. It also presents a case study examining acid mine drainage as a potential pretreatment agent for lignocellulosic biomass. Section III details recent trends in bioprocessing with the first chapter focusing metabolic engineering of microorganisms followed by chapters on insight into microbial factories and then cell immobilization strategies to enhance process yields. Section IV contains chapters dealing with advances in modeling and development, specifically artificial intelligence, integrated biorefineries, two-stage anaerobic digestion, farm to biorefinery, and life cycle assessment. The last section (V) details public policy for a circular economy with a specific focus on Mexico as a cast study.

The editors of this book would like to express their sincere thanks to all the authors for their high-quality contributions. The successful completion of this book has been the result of the cooperation of many people and we would therefore like to express our sincere thanks and gratitude to all of them.

We genuinely hope that the present discourse on biofuels research will significantly advance readers’ understanding of the cutting-edge technical potential in this area as well as to inspire others to build upon the ground-breaking research that has been laid.

Section I

Introduction

Outline

1 Current status of lignocellulosic biofuel production system—an overview

1

Current status of lignocellulosic biofuel production system—an overview

Preshanthan Moodley and Cristina Trois,    SARCHI Chair Waste and Climate Change, School of Engineering, University of KwaZulu-Natal, Durban, South Africa

Abstract

Second-generation biofuels derived from lignocellulosic biomass (LCB) have the innate ability to compete with fossil fuels if proper cost-effective and efficient production strategies are utilized. As agriculture is practiced globally and millions of tons of biomass are generated annually, the generation of biofuel from these wastes might be an ecologically benign way to fulfill the growing energy demand. Rigid lignocellulose must be converted into usable biofuel by applying various technologies and processes, which is challenging. This chapter provides an overview of the current status of lignocellulosic biofuel production systems, including feedstock pretreatment, enzymatic hydrolysis and saccharification, biorefinery systems, genetic engineering, and artificial intelligence. It further details the status of bioethanol, biohydrogen, biogas, and sustainable aviation fuel production from LCB.

Keywords

Aviation fuels; biomass; consolidated bioprocessing; lignocellulose; bioethanol; biogas; biohydrogen

1.1 Introduction

Due to the energy industry's growing environmental, economic, and social consequences, experts and researchers are motivated to explore biofuels. According to model forecasts in recent research, the value of the global biofuels market is expected to approach US$201.21 billion by 2030, rising at a compound annual growth rate of 8.3% between 2021 and 2030. There has been a fundamental movement among nations toward higher usage of biofuel to promote a circular economy and aid in the fight against climate change brought on by excessive carbon emissions. The United Nations issued 17 sustainable development objectives (goals), addressing all countries globally. Among these, the aspirational objectives of achieving clean, inexpensive energy and combating climate change provide a bold plan for a better world. The necessity for sustainable development has been acknowledged by national governments worldwide. Countries like the United States, Brazil, Europe, France, India, and China are among those preparing to reduce greenhouse gas (GHG) emissions by boosting the use of biofuels (Wei et al., 2021). The International Air Transport Association has set high goals for its members, including encouraging the construction of carbon-neutral infrastructure and reducing CO2 emissions by half by 2050. The development of outstanding, cost-effective biofuel production technologies may be ensured by significant infrastructure investment and improved government policy.

It is essential to employ cutting-edge techniques to produce biofuels in an environmentally responsible, cost-competitive, and sustainable way. Biofuels made from biomass resources using ecologically friendly processes are attracting growing attention from scientists and academics. Many liquid and gaseous biofuels may be created from biomass, including ethanol, biodiesel, methane, methanol, biohydrogen, and sustainable aviation fuel (SAF). With the help of these biofuels, future energy security, and sustainability may be attained. Furthermore, biofuels lessen total pollution load and environmental effects by lowering GHG emissions, primarily CO2, in addition to reducing air pollutants during combustion. Most renewable energy-generating alternatives rely on resources that can provide electrical energy and displace fossil fuels, including wind, solar, tidal, hydropower, and geothermal. However, the platform for energy consumption is still dominated by liquid fuels, and the infrastructure and technologies needed to convey these renewables are still in their infancy. For this reason, many experts consider it a viable choice to gradually replace fossil fuels with liquid biofuels, including ethanol, methanol, butanol, and biokerosene (Kazemi Shariat Panahi et al., 2019).

With a strategic growth in biofuel production from about 16 billion liters in 2000 to 143 billion liters in 2016, which includes a production growth of 65% for bioethanol, 25% for biodiesel, and 10% for other biofuels, the use of liquid biofuels has increased from 1% of the world’s total biomass-derived bioenergy supply in 2000 to 6% in 2016 (Tursi, 2019). These biofuels are often combined with gasoline at a specific ratio to fuel automobiles. For example, India aims to mix 20% of ethanol with gasoline by 2025 (Sarwal et al., 2021), compared to Brazil’s requirement of 27% (BRAZIL: FUELS: BIOFUELS, 2021).

It will take several million years to rebuild the depleted oil and natural gas supplies. Thus it is vital to turn to carbon-based materials that can produce energy quickly and continuously. One such feedstock that satisfies the criteria is lignocellulosic biomass (LCB) (Popp et al., 2021). All types of plant and animal materials may be classified as biomass, with plant biomass being the most prevalent (Woiciechowski et al., 2020). Although there are many choices for using biomass to produce energy, it’s critical to identify those biomasses that are both economical and provide a sufficient and reliable quantity of energy to be able to replace energy from fossil fuels. One of the primary issues in the production of energy and transportation is cost (Sarkar et al., 2021).

Waste biomass and residues are byproducts of the processing and consumption of raw materials, as opposed to biomass that is generated particularly for energy generation. Using waste biomass in energy production adds value to biomass leftovers and increases the profitability of the energy production process since waste biomass, such as agricultural and agro-industrial wastes, is plentiful and, if improperly disposed of, causes environmental difficulties. Agro-biomass, also known as agricultural lignocellulose waste biomass has recently attracted attention since it is produced in vast quantities each year and has a high calorific value (Abdeshahian et al., 2020). Lignocellulosic plant biomass, which is widely accessible, is thought to be an upcoming feedstock for the production of biofuels (Parakh et al., 2020). Plants are comprised of lignocellulose, which contains cellulose, hemicellulose, and lignin as their primary constituents and forms a complex structure that is highly recalcitrant (Deshavath et al., 2019). Agricultural LCB production relies on several variables, including seasonal availability, composition, pretreatment, and fermentation techniques.

1.2 Lignocellulosic biomass: an ideal candidate feedstock for biofuels

The imbalance between global supply and demand for energy resources has raised concerns on a global scale. Utilizing LCB as an energy source might be a great choice in this situation. However, different kinds of biomass have not been fully used for energy recovery. Despite its widespread availability, waste biomass is one kind of LCB that has not been used for energy recovery. On the other hand, improper management of waste biomass disposal led to a wide range of environmental issues. Despite the billion tons of agricultural leftovers that are produced yearly across the globe, most of them are either burnt in open fields or dumped as garbage. Depending on their composition, waste biomasses may be divided into woody and nonwoody biomass (Roy et al., 2022).

The three primary components of LCB are cellulose, hemicellulose, and lignin (Zadeh et al., 2020). Fig. 1.1 provides a broad representation of the LCB structure where lignin encases the sugar polymers while hemicellulose is woven between the cellulose chains. More details on the composition of LCB are given in Chapter 2 of this book.

Figure 1.1 General lignocellulosic structure of biomass.

Cellulose is a linear polymer made up of chains of β-(1bis4)-glucopyranose units. It is an unbranched polymer. Cellulose crystallinity has an impact on the enzymatic digestibility of LCB because highly organized regions are physically more compact and inherently resistant to enzymes, acids, and swelling underwater. Studies have demonstrated that amorphous cellulose might hydrolyze more rapidly and at a faster rate than crystalline cellulose (Ravindran and Jaiswal, 2016). The degree of polymerization of cellulose also reveals the biomass’s resistance. The rate of cellulose hydrolysis increases with the length of the cellulose chain. One of the first stages involved in the conversion of biomass to biofuels is pretreatment.

1.2.1 Pretreatment

Owing to the recalcitrant nature of LCB, pretreatment has become synonymous with lignocellulosic processes. The primary goal of pretreatment is to destabilize and disrupt the complex matrix, removing lignin and enhancing access to the sugar-rich polymers of cellulose and hemicellulose. Pretreatment can be broadly categorized into either physical, chemical, or biological strategies while a combination of these options has routinely been employed as well, as illustrated in Fig. 1.2. Chemical methods such as acid and alkali are the most commonly employed, albeit coupled with many disadvantages. These include high cost and toxicity, environmental concerns, production of inhibitors, and degradation of sugars. For this reason, the development of newer, more environmentally-friendly technologies is being pursued, as illustrated in Table 1.1. Given the integral role that pretreatment plays in the biofuel production process, selecting and optimizing a pretreatment is critical to the overall outlook of the process (Moodley et al., 2020).

Figure 1.2 Overview of commonly considered pretreatment methods.

Table 1.1

1.2.2 Bioethanol

The world’s biggest producer of gasoline-ethanol is the United States. In 2020, it was projected that the United States would generate 13.8 billion gallons of ethanol. In conventional cars, ethanol or grain alcohol may be mixed up to 10% with gasoline (Sonnichsen, 2021). India Glycols Ltd. in Kashipur, Uttarakhand, has constructed a second-generation ethanol demonstration facility for the first time using a range of feedstocks, such as cotton stalk, sugarcane bagasse, and rice straw. On the National Institute for Interdisciplinary Science and Technology campus, Thiruvananthapuram, India, a prototype plant with a feeding capacity of 50 kg/day was built as part of continuing efforts to create second-generation ethanol (Sukumaran et al., 2010). China was Asia’s biggest ethanol producer, with 2.1 billion liters of gasoline-ethanol produced in 2012. China has long developed ethanol for use as a vehicle fuel. To decrease its reliance on oil, China plans to promote ethanol-based fuel and establish a new market for its excess grain. In China, corn, cassava, and rice make up the majority of the sources of grain-based bioethanol, making up around 80% of the nation's overall output.

Most of the ethanol produced in the United States is made from starch-based crops that are either processed in dry or wet mills. It was estimated that by 2020 there would be 208 ethanol production facilities in the United States, with an installed capacity of 17.44 billion gallons annually. The total output in 2020 was 13.8 billion gallons, a 12.7% decrease from the record-breaking 15.8 billion gallons produced the year before (Renewable Fuels Association, 2021). In 2020, Canada was ranked as the sixth-largest bioethanol producer worldwide and contributed 1.6% to the world's ethanol production. Corn and wheat were the two most significant feedstocks for manufacturing bioethanol, each contributing 1534.3 million liters and 360.7 million liters, respectively (Renewables Fuels Association, 2020). In 2020, Brazil’s ethanol output was anticipated to make up 26.7% of global ethanol production. On the other hand, Argentina produced 1.0% of the world's ethanol production in 2020, placing it ninth in the globe (New Energy Blue, 2021). Colombia produced 0.44% of the total ethanol produced worldwide in 2020, ranking it 13th in the world (Renewables Fuels Association, 2022). The entire amount of ethanol produced in the EU in 2020 made up 4.8% of global production. Due to the country’s expanding economy, Vietnam has recently used a substantial volume of gasoline to manufacture biofuels. The United States Department of Agriculture reports that Vietnam’s gasoline consumption has increased by 4%–5% in recent years. In addition to its output, Vietnam is anticipated to have spent $2.5 billion in the first quarter of 2020 on crude oil and petroleum products, including bioethanol. Among the top ethanol producers in the world, India is placed in the sixth position. The country’s average ethanol blending rate in gasoline was anticipated to reach 7.5% in 2021 due to increased government initiatives to divert more raw materials toward ethanol. Therefore India’s ethanol production was projected to reach 3.17 billion liters in 2021, up 7% from 2020, due to excess sugarcane production (India Biofuels Annual Report, 2020).

While there have been some great strides toward developing second-generation bioethanol processes, there are still several bottlenecks facing the commercialization of bioethanol production processes from LCB. Some of these include identifying the best feedstock, efficient and cost-effective pretreatment strategy, employing highly efficient enzymes to hydrolyze the feedstock, selecting a suitable microbial strain, optimizing the fermentation process, and furthering the downstream processing. Once these shortfalls are addressed in an integrated manner, the process in its entirety can potentially transition towards a commercial scale.

1.2.3 Biohydrogen

By using biological processes, hydrogen generation is fundamentally environmentally beneficial and sustainable. Hydrogen may be produced from a wide variety of feedstocks, including household trash, industrial effluents, agricultural residue, municipal solid waste, and even water. Direct biophotolysis, indirect biophotolysis, photo-fermentation, dark fermentation, and microbial electrolysis are the typical methods of producing biohydrogen.

Dark fermentation is one of the most promising clean technologies for producing biohydrogen since it can convert a variety of organic waste into biohydrogen under moderate fermentation conditions. However, its poor biohydrogen yields limit dark fermentation’s commercial use. Only a portion of the substrates may be converted to biohydrogen throughout the dark fermentation process, and the majority of them (60%–70%) are still present as volatile fatty acids and alcohols. The highest biohydrogen output, where acetic acid is the sole byproduct, is 4 mol/mol glucose. According to reports, the production of biohydrogen by dark fermentation was often only 1–3 mol/mol glucose (Sekoai et al., 2020). So, in recent years, research has been conducted to improve biohydrogen generation in the dark fermentation process using various cutting-edge technologies, such as innovative microbial culture selection, genetic engineering, cell immobilization, and nanotechnology. Consequently, there is a huge opportunity to research the expansion of these areas.

Briefly, investigations into microbial selection continue to be extensively studied to enhance biohydrogen yields. For instance, a study by Nizzy et al. (2020) discovered that it is possible to produce biohydrogen from sago industrial wastewater using a newly isolated pure culture of Enterobacter cloacae NASGE 02 and Clostridium sartagoforme NASGE01. With a maximal biohydrogen production of 1.26 mol H2/mol glucose, C. sartagoforme NASGE 01 was capable of degrading up to 56.7% of the substrate. Additionally, novel microbial species (Bacillus coagulans MO11 and Clostridium beijerinckii CN) with efficient biohydrogen production capacity from molasses and ethanol refinery effluent were successfully screened by Lertsriwong and Glinwong (2020). In a recent study, two pure Bacillus cereus strains (B. cereus RTUA and RTUB strains) capable of producing several enzymes were isolated from an anaerobic digester and shown to be prospective candidates for biohydrogen generation from various substrates (Saleem et al., 2020). However, it is challenging to maintain a pure culture free of contamination because of different toxins from biowaste and wastewater.

Nanotechnology is another field that has shown immense promise in biohydrogen production. According to Seelert et al. (2015), Clostridium beijerinckii NCIMB8052 was immobilized on magnetite nanoparticles, which decreased the lag period of microbial growth and later increased the generation yield of biohydrogen. When nanoparticles are combined with carbon-based materials like activated carbon and biochar, the activity of microorganisms and enzymes may be enhanced synergistically (Yang and Wang, 2019). Due to their complementary roles and the release of additional Fe²+ from the Fe⁰ nanoparticle-biochar microelectrolysis, biochar and Fe⁰ nanoparticles together had the predicted synergetic impact on the improvement of biohydrogen generation from grass fermentation (Yang and Wang, 2019).

1.2.4 Sustainable aviation fuel

Lower carbon alternatives may be produced from LCB sources (agricultural residues, waste organics, etc.) and nonfossil derived CO2 materials as diverse feedstocks for creating biokerosene, sustainable aviation fuel (SAF) has lately gained a lot of interest. Common organic chemical components of jet fuel include paraffin, aromatics, olefins, and naphthenes. Triglyceride-based sources such as vegetable oil used cooking oil, and animal fats are promising feedstocks to manufacture diesel equivalent fuel since commercial-level SAF production is often constrained. The SAF meets the requirements set out by the American Society for Testing and Materials (ASTM) for jet fuel standards to be approved as a drop-in and distillate fuel. For instance, D1655 is a jet range fuel having synthetic and conventional mix components, while D7566 is an aircraft turbine fuel. Furthermore, according to the Sustainable Development Scenario of the International Energy Agency (IEA), biofuel production should be able to cover the energy needs of 10% of aviation fuel by 2030 and 20% by 2040. Catalytic hydrothermolysis, the sixth process for SAF production as certified by the ASTM in 2020, is one of the most effective techniques found. However, Biokerosene is often produced as the primary feedstock for aircraft turbine fuel by the conversion of a range of biogenic wastes and hydrotreated vegetable oil (Eswaran et al., 2021). Finding alternate feedstock materials and different biorefining processes has received a lot of interest due to the difficulties associated with adopting the food versus fuel idea (Ghatalam, 2020). The two probable methods for producing biokerosene from lignocellulose are as follows:

1. Hydrolyzing the feedstock directly to produce sugars, followed by the production of biokerosene.

2. Thermochemically treating the feedstock to produce intermediate products, which are subsequently upgraded to biokerosene.

However, compared to traditional fossil fuels, the high cost of biokerosene further hinders product development for large-scale commercial use (Thilo, 2018). These problems might be resolved by establishing effective intergovernmental agreements to lower tariffs related to the supply of biofuels and by creating alternative pathways for the manufacture of biokerosene, coupled with useful byproducts that can result in practical affordability.

1.2.5 Biogas

Anaerobic processing of LCB can lead to the production of biogas. However, hydrolysis is a relatively slow process for lignocellulosic materials and is affected by the type and composition of the feedstock. Hydrolysis is the rate-limiting phase for lignocellulosic material that breaks down the complex organic polymer components during anaerobic digestion (AD) (Dahadha et al., 2017). In recent years, there has been a lot of research done on the biogas produced by the AD of lignocellulosic materials. For instance, Khan and Ahring (2019) employed the leftovers from the enzymatic hydrolysis and wet explosion pretreatment steps that remove carbohydrates. The findings demonstrated that lignin from biorefineries might be a suitable substrate for biogas generation, with the greatest severity pretreatment producing the maximum methane output. In a relatively recent paper, modeling, and experiments were employed for the first time to suggest a potential cleaner thermochemical conversion of LCB to biomethane (Yun et al., 2019). Predicted values of CH4, H2, and plant thermal efficiency were equivalent to modeled efficiencies reported in the literature for wood gasification based on the autothermal plant’s simulation findings. A study exploring the potential for converting waste products from bioethanol manufacturing into gaseous biofuels in a biorefinery setting demonstrated that waste from bioethanol has a high energetic value and may help boost the total energy produced by biomass (Rocha-Meneses et al., 2019).

The variability and low density of lignocellulosic materials further hinder the AD process by causing a floating layer to develop on the surface of AD reactors (Tian et al., 2015). As a result, the microorganisms have difficulty accessing the substrate, which worsens mass and heat transmission and lowers the methane output (Wang et al., 2018). High carbon-to-nitrogen (C/N) ratios have been shown to restrict the amount of LCB that can be digested (Sawatdeenarunat et al., 2015). However, this may be overcome by adding additional nitrogen sources or co-digesting with the substrate that contains more nitrogen. Increased biogas output may offset these additional expenses, making LCB a profitable AD feed for methane production.

1.3 Biorefineries

A single definition of the phrase biorefinery is challenging to come up with since it encompasses a wide range of industries, including those in the transportation, chemical, energy, agricultural, and forestry sectors. Biorefining, for example, is described by the International Energy Agency (IEA) as "the sustainable processing of biomass into a spectrum of marketable bio-based products and bioenergy/biofuels, as an innovative and efficient approach to use available biomass resources for the synergistic co-production of power, heat, and biofuels alongside food and feed ingredients, pharmaceuticals, chemicals, materials, minerals, and short-cycle CO2" (Lindorfer et al., 2019). The concept of a biorefinery is not new, and there are now several industrial facilities in use that may be seen as exemplary examples of actual biorefineries. Most of them are associated with food, pulp, and paper and likely constitute the first examples of technical applications to transform biomass into valuable goods. In the so-called product-driven biorefineries, these facilities are concentrated on the manufacture of relatively limited quantities of higher value-added bio-based goods, and they typically generate energy (bioenergy) as a byproduct (ETIP, 2017). However, in recent years the idea of a biorefinery has expanded to include a broader range of feedstocks, processing methods, and end products to maximize the sustainable and efficient use of all biomass components. Utilizing a broad variety of biomasses (including woody and herbaceous energy crops, byproducts from forestry and agricultural sectors, urban garbage, and aquaculture) to create a variety of products and energy is a crucial component of the advanced biorefinery method. Depending on the feedstock and product needed, LCB may go through several processing methods in a biorefinery. Numerous technologies must often be used simultaneously or successively to create the desired result. Thermochemical, biochemical, chemical, and mechanical/physical processes can be used to transform LCB into a wide range of products, including materials, chemicals, organic acids, polymers and resins, and biopolymers, as well as energy-related products (gaseous, solid, and liquid biofuels). Cellulosic ethanol is one of the most significant examples of the advancements made in this field. Currently, it is close to full commercialization. Over the past few decades, a significant portion of the research and development effort carried out in the field of LCB has been focused on fuels and other energy-related products. However, it is also recognized that its manufacturing costs are still too high to be competitive, necessitating the search for creative solutions that lower costs. Recent developments in biocatalysts and microbial strains used in the conversion pathway, applied through the use of tools like high-throughput screening, metagenomics techniques, metabolic engineering, and synthetic biology, may enhance the potential for increased production and contribute to reaching a more competitive product from an economic point of view. Such cutting-edge technology has also made it possible to enhance the manufacturing of bio-based goods from lignocellulosic feedstocks meant to replace their equivalents produced by fossil fuels (Duque et al., 2021). A general LCB is illustrated in Fig. 1.3.

Figure 1.3 The general flow of bioconversion of lignocellulosic biomass.

1.4 Genetic engineering of feedstocks and fermenting microorganisms

Major contributors to the generation of biofuel are microorganisms. However, the native strains’ inadequate yield of the product makes it essential to modify and enhance them using the strategies of metabolic engineering and genetic engineering. To maximize levels of productivity and energy value at a lower cost of production, recent research has concentrated on using metabolic engineering to analyze strain development. There is a good chance that database mining will provide more distinct metabolic pathways for the synthesis of biofuels shortly. Therefore any obstacles to using LCBs as renewable fermentation feedstock may be removed by implementing these routes in commercial fermentation hosts. By inserting useful genes into the genome or deleting obstructive ones, metabolic engineers need to take advantage of the most cutting-edge technologies currently available, such as the omic technologies and CRISPER/Cas9 system, to design and create novel strains of microbial species with the enhanced ability to produce biofuels from a variety of feedstocks (Adegboye et al., 2021).

Through the use of diverse breeding techniques, progress has also been achieved in addressing the engineering of lignocellulosic feedstocks, specifically cell wall recalcitrance, improving biomass output and the quality of bioenergy crops. The methods primarily aim to modify the composition of plant cell walls. Various biofuel crops have been improved using a variety of plant breeding strategies, including molecular and marker-assisted selection, genetic engineering, and resistance to biotic and abiotic challenges. There have been produced crops that can withstand a variety of biotic and abiotic challenges, such as pests, weeds, diseases, drought, heat, and salt (Wang et al., 2016). Recombinant DNA technology has been a key technique in genetic engineering’s alteration of plant cell walls to overcome biomass recalcitrance, leading to improved saccharification and ultimately higher yields of bioethanol. To increase feedstock output and quality in various plants, genetic modification efforts have focused on changing the structure of enzymes and overexpressing or silencing genes involved in various processes. Gene discovery will continue to be a crucial task for genetic modification using both conventional breeding methods and genetic engineering since several genes are known to affect various processes in the production, breakdown, and regulation of the plant cell wall. Modern biotechnological technologies that enable comparative genomic investigations of the transfer of genes across distantly related species may also be used for gene discovery (Wang et al., 2021).

1.5 Artificial intelligence in biofuel production

Artificial intelligence (AI) technology has advanced in recent years to the point where researchers are starting to pay more attention to it, especially in the field of bioenergy and biofuel research. Given the significance of AI in this particular area of bioenergy, many AI technologies for improving current systems and solving issues in bioenergy production have been discussed. For effective use of resources, environmental awareness, and efficient production from natural resources, AI offers numerous sophisticated mechanisms in bioenergy production technologies (Williams et al., 2015). Similar to other sectors, bioenergy might use AI to assist its long-term goals. AI offers a variety of optimization tools, like the ASPEN Plus simulator (Okolie et al., 2021) and artificial neural network (ANN)-genetic algorithm (GA)-based modeling (Liao and Yao, 2021), which makes it simple to examine the economics of different types of bio-oil and syngas production based plants. The user of AI-based optimization tools may also benefit from assistance with economic forecasting and the large-scale commercialization of bioenergy conversion technology. With the use of AI, risks or disruptive events that may potentially occur across the supply chain can be quickly assessed and more effectively minimized. A bioenergy production facility's whole supply chain management is heavily reliant on resource evaluation, logistical planning, and power plant design. By keeping a multiscale feedstock database with information on the characteristics, availability, demand, and logistics of feedstocks, among other things, AI provides various significant applications in the management of supply chains.

1.6 Bioreactor configuration for enhanced biofuel processes

A favorable environment for microbial growth, biocatalysis, the generation of microbial metabolites, and energy conversion is provided by bioreactors. Due to its potential for simple operation, improved reaction parameter control, sustainability, low input of raw materials and energy cost, and maximum carbon footprint conversion, bioreactor technology has attracted a lot of interest in the process development of microbial cultivations and biofuel conversion. For fermentation to proceed efficiently, sugar must be transformed into a useful product. As a result, a crucial factor that depends on the kind of substrate that will be fermented into the desired product is microbial selection. These bacteria convert C6 or C5 carbohydrates into biofuels in a bioreactor under regulated conditions.

For the large-scale production of renewable and sustainable biofuels, energy-efficient reactors that provide a stable and regulated biological environment are crucial, and their optimization focuses on lowering energy consumption and waste gas emissions. Photobioreactors were created for the cultivation of algae or microalgae, and the bioreactors might be either anaerobic or aerobic (Xu et al., 2018). Various modeling techniques for bioreactor design have been developed due to the high expense of manufacturing large volumes of bioreactors. The development of super microbial factories with maximum productivity and metabolic pathway flux is also essential to the development of the optimal biofuel reactor (Keasling et al., 2021). Every biological process requires the use of bioreactors, and they are even thought of as the center of bioprocesses. The structures in which a reaction or biological process takes place are called bioreactors. To ensure a high output of the bioprocess and to meet the needs of the biological system (enzyme, microbe, or cell), the bioreactor must offer the ideal conditions.

1.7 Current status of global energy recovery from lignocelluloses

Biomass has historically been a significant source of energy. The biomass sector has substantial, regional, and international impacts on society and the environment. Numerous disputes and problems have been linked to the use of biomass as an energy source. There is a lot of promise for balancing global trade imbalances, assuring global energy security, and ensuring global food security using a modern biofuel manufacturing technique that extracts energy from biomass. Several efforts are now underway globally to transition the present energy supply system from traditional to contemporary biomass conversion. Renewable Energy Statistics (2021) states that the capacity and output of renewable energy for 2020 was 2799094 MW. Hydropower (1331889 MW) was the most significant energy source, followed by solid biofuels and renewable trash (102852 MW). The leading nations in terms of biofuel capacity are North America (623.000 barrels of oil equivalent per day), South and Central America (446,000 barrels of oil equivalent per day), Asia Pacific (310,000 barrels of oil equivalent per day), and Europe (295,000 barrels of oil equivalent per day). Between 2007 and 2017, the output of biofuels grew by 11.4% worldwide. The IEA reports that the output of biofuels globally hit a record 154 billion liters in 2018. Forecasts indicate that it will expand by 25% by 2024, with an average annual growth rate of 3%. In addition to financial and political concerns, the bioenergy industry faces several obstacles and uncertainties, particularly concerning changes in the price of crude oil. Additionally, it has been challenging to commercialize advanced biofuels due to technical challenges. Despite these obstacles, the biofuel business is still expanding, which adds to the rise in world energy demand. About 2.8 million employment opportunities have been made possible by bioenergy, suggesting its significance for job creation. All of these indicate that lignocellulosic biofuel systems have been advancing at a precipitous rate; however, more research is required to bridge the gap between experimentation and commercialization.

1.8 Conclusion and future perspectives

The potential for producing biofuels effectively has been established by recent advances in lignocellulose bioconversion processes. With the use of contemporary synthetic biology technology, it is possible to synthesize biofuel feedstock that is not naturally generated. In any case, the use of genetic and metabolic engineering will be regarded as an important and cutting-edge strategy that modifies and examines metabolic pathways to improve the production of biofuels. Future research should concentrate on low-cost pretreatment methods, metabolic engineering approaches, and modeling for large-scale commercial lignocellulose biofuel production. Additionally, more effective methods must be created to completely remove the refractory characteristic and maximize the usage of lignocellulose components in fuel production. All of these mentioned fields as well as other areas for improvement are presented and discussed in further detail in this book.

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