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An Overview of Existing Individual Unit Operations
Abstract
This chapter presents an overview of the different unit operations of biochemical platforms used in biorefineries producing ethanol and butanol. Biochemical platforms primarily convert lignocellulosic biomass into mixed sugars and then liquid fuels. Biochemical conversion processes rely on biocatalysts, such as enzymes and microorganisms, in combination with heat, chemical catalysts, and solvents, to convert the carbohydrate fraction of lignocellulosic biomass (hemicellulose and cellulose) into an intermediate sugar stream, which serves as the substrate for ethanol and butanol fermentation. Future biorefineries can benefit from the various combinations of diverse raw materials, conversion processes, technologies, and product portfolios associated with these platforms. Biochemical conversion routes apply biocatalysts, such as enzymes and microbial cells, plus heat and chemicals, to convert biomass into an intermediate sugar mix stream and then to ethanol or butanol. Thermochemical conversion technologies use heat and/or physical catalysts to convert biomass into a gaseous intermediate that primarily consists of H2 and CO, and a subsequent chemical or biological step converts the intermediate into biofuels. Fully understanding these processes requires knowledge of each step. Therefore, this chapter offers a summary of the individual unit operations involved in these processes.
... Physical pretreatment results in the generation of several inhibitory and toxic compounds, such as acetic acid, formic acid, levulinic acid, furfural, vanillin, etc. that affect the subsequent saccharification and fermentation process (Tye et al., 2016). Other limitations of physical pretreatment include high implementation cost at an industrial scale, excessive energy demand, environmental concern, and less delignification (Aslanzadeh et al., 2014). Altogether, this pretreatment affects the economic aspects of substrate conversion into their respective products at a large scale (Tye et al., 2016). ...
... Chemical pretreatment is an extremely selective process for specific biomass components and demands intense conditions. The chemical method is inappropriate for biorefinery as it negatively affects the downstream approach (Aslanzadeh et al., 2014). Likewise, chemicals are released in this pretreatment that adversely affects the environment causing harmful effects on flora and fauna. ...
... Further, chemical pretreatment, like using dilute acid, results in the formation of polysaccharide degradation byproducts at higher temperatures, which negatively affect the microbial growth considered for the fermentation process, resulting in low biofuel yield. Similarly, high cost is required for the recycling process of concentrating the acid as well as for corrosive-resistant equipment that negatively affects the downstream economics (Aslanzadeh et al., 2014). Further, the undesired breakdown of the cellulose generates some toxic phenolic compounds. ...
... In physical pretreatment, the biomass is reduced into particles of smaller size via mechanical comminution, or the surface area of the biomass is increased without size-reduction (Aslanzadeh et al., 2014). Vibratory ball milling has been found to be more effective in breaking down the cellulose 231 4 Pretreatments of agro-industrial residues crystallinity of spruce and aspen chips and improving the digestibility of the biomass than ordinary ball milling (Nystrom, 1975;Sun & Cheng, 2002). ...
... Another advantage is that there is no use of hazardous chemicals, so it is environmentally friendly. However, these pretreatments require high energy input, and it has no ability to remove lignin, which limits the access of enzymes to cellulose (Aslanzadeh et al., 2014). ...
... The chemical pre-treatment is the most studied technique among various pre-treatments used for delignification of cellulosic materials . Generally, chemical pretreatment technologies display a high degree of selectivity for the biomass constituents, and they require quite harsh reaction conditions, which may not be desirable for integration into a biorefinery scheme (Aslanzadeh et al., 2014). Some chemical pre-treatment techniques for waste biomass include ozonolysis for lignin degradation, acid and base pre-treatment, ionic liquids for solubilizing crystalline 232 ...
Phenolics are among the most studied compounds due to their beneficial implications in human health. The conventional methods applied in the extraction of these compounds include maceration, distillation, Soxhlet, among others, and the extraction capacity depends on several factors, such as the extraction solvent and respective concentration, time, and temperature. The incorporation of green chemistry in the development of more sustainable products and processes has promoted the use of new solvents that would replace conventional ones and the application of more eco-sustainable technologies (e.g., supercritical fluids, pulsed electric fields, and ultrasounds). Green solvents, coupled with conventional extraction methods, present excellent stability for food, pharmaceutical, and cosmetic industries because they are non-toxic, non-volatile, recyclable, biodegradable, and imply lower energy cost of synthesis. In this chapter, traditional and eco-sustainable methods based on solid–liquid extraction will be revised, as well as safety issues, life-cycle assessment, and economic aspects.
... As it can be seen, the reported pretreatment methods can be classified as: physical (targeted for thermochemical and biochemical conversion) and chemical and/or biological (targeted specifically for biochemical conversion). Physical pretreatment reduces the particle size to increase surface area and pore size, and chemical pretreatment is based on the use of compounds (organic and inorganic) to disrupt biomass structure and crystallinity [31]. Βiological pretreatment involves fungi that produce enzymes that degrade, depolymerize and cleave the contents of biomass [32]. ...
... The purpose of pretreatment methods is to reduce moisture, remove impurities, increase H/C ratios and energy content and improve the overall fuel property of biomass (such as heating value, moisture content, ash content, etc.) [29,30]. In the case of lignocellulosic feedstocks, additional pretreatment processes should also be applied toward changing the structure of the lignocellulose in order to make cellulose more accessible [31]. The general classification scheme of biomass pretreatment has been reported by Anukam et al. (Figure 2) [32]. ...
... As it can be seen, the reported pretreatment methods can be classified as: physical (targeted for thermochemical and biochemical conversion) and chemical and/or biological (targeted specifically for biochemical conversion). Physical pretreatment reduces the particle size to increase surface area and pore size, and chemical pretreatment is based on the use of compounds (organic and inorganic) to disrupt biomass structure and crystallinity [31]. Biological pretreatment involves fungi that produce enzymes that degrade, depolymerize and cleave the contents of biomass [32]. ...
The present work aims to identify alternative liquid biofuel value chain scenarios utilizing heavy metal (HM)-contaminated biomass feedstocks. The analysis is based on breaking down existing liquid biofuel value chains, focusing on the required adaptations needed for clean biofuel production. State-of-the-art and emerging liquid biofuel production options are reviewed. The potential implications caused by the HM load in the biomass feedstock are analyzed along the whole biofuel production chain, which includes pre-processing, conversion and post-processing stages. The fate of the most common HM species present in contaminated biomass is identified and graphically represented for advanced (second generation) biofuel conversion processes. This information synthesis leads to the description of alternative value chains, capable of producing HM-free biofuel. This work goes a step further than existing reviews of experiments and simulations regarding heavy metal-contaminated biomass (HMCB) valorization to biofuels since feasible value chains are described by synthesizing the findings of the several studies examined. By defining the adapted value chains, the “road is paved” toward establishing realistic process chains and determining system boundaries, which actually are essential methodological steps of various critical evaluation and optimization methodologies, such as Life Cycle Assessment, supply chain optimization and techno-economic assessment of the total value chain.
... Physicochemical treatment technology is nothing but combined methods involving both physical and chemical pretreatment techniques (Table 3.1). The lignocellulosic biomass is subjected to chemical modification and the cell wall structure is physically broken (Aslanzadeh et al. 2014). The high pressure and temperatures used in these types of processes increase the costs of applying them in a biorefinery type system. ...
... The high pressure and temperatures used in these types of processes increase the costs of applying them in a biorefinery type system. Steam pretreatment is the most common method applied to biomass due to their wide ranging application on various types of biomass, however in case of recalcitrant biomass sources, it may necessitates additional treatment using acid or SO 2 (Aslanzadeh et al. 2014). During steam explosion, fermentation inhibitors are generated such as HMF, weak acids and phenolic compounds. ...
... This method requires a high amount of energy and involves elevated operation costs (Peral 2016). Ionic 68 I. Covarrubias-García and S. Arriaga liquids are effective in decrystallizing the cellulose, fractionating lignin and polysaccharide contents into separate streams, making the following hydrolysis step much easier (Aslanzadeh et al. 2014). ...
Food loss and waste (FLW) is becoming a general environmental and societal problem as well as an opportunity for its valorisation to a plethora of energy vectors, chemicals and bio-based materials. Food loss is related to the primary and industrial sectors (i.e., farms and fish farms, factories), while food waste is produced by retailers and consumers. This leads not only to direct FLW but also indirect loss of energy and resources devoted to food production. While societal and political awareness is rising, with the subsequent actions resulting in an efficiency boost along the food supply chain, unavoidable FLW amounting to more than 1000 Mtons/year exists due to personal preferences, safety issues and supply inefficiencies. Likewise, huge amounts of plant biomass by-products (pomace, bagasse, straw, stover, peels and pulp) over 5000 Mtons/year are generated. First, second and third-generation biorefineries can be built based on such biomass as well as that from forest, cattle, fish and algae. Biorefineries are based on thermal, physical, chemical and biological treatments and can produce a great variety of energy vectors, namely hydrogen, biogas, bioethanol, biokerosene, biodiesel and biochar; chemicals (similar to petrochemicals), materials (biomonomers and biopolymers) and energy (heat). Even feed and food products could be considered as biorefinery products, ultimately.
... Physicochemical treatment technology is nothing but combined methods involving both physical and chemical pretreatment techniques (Table 3.1). The lignocellulosic biomass is subjected to chemical modification and the cell wall structure is physically broken (Aslanzadeh et al. 2014). The high pressure and temperatures used in these types of processes increase the costs of applying them in a biorefinery type system. ...
... The high pressure and temperatures used in these types of processes increase the costs of applying them in a biorefinery type system. Steam pretreatment is the most common method applied to biomass due to their wide ranging application on various types of biomass, however in case of recalcitrant biomass sources, it may necessitates additional treatment using acid or SO 2 (Aslanzadeh et al. 2014). During steam explosion, fermentation inhibitors are generated such as HMF, weak acids and phenolic compounds. ...
... This method requires a high amount of energy and involves elevated operation costs (Peral 2016). Ionic 68 I. Covarrubias-García and S. Arriaga liquids are effective in decrystallizing the cellulose, fractionating lignin and polysaccharide contents into separate streams, making the following hydrolysis step much easier (Aslanzadeh et al. 2014). ...
The development of anaerobic digestion (AD) plants has been considered as a solution to overcome the depletion of fossil resources and the increasing environmental pollution caused by the over-use of fossil fuels. However, there are some challenges which may undermine the sustainability of the AD including its associated up- and downstream strategies. In order to sustain the development of AD plants it is necessary to calculate the environmental hotspots through their whole life cycle and represent the possible solutions to mitigate the potential pollution. Among different methods, life cycle assessment (LCA) is widely employed to quantify and evaluate the environmental impacts of AD and its related up- and downstream technologies. This chapter comprehensively summarizes the environmental impacts of AD plants from an LCA point of view and proposes advanced strategies to alleviate the negative impacts and bring biogas plants into sustainable circular bio-economy.
... Physicochemical treatment technology is nothing but combined methods involving both physical and chemical pretreatment techniques (Table 3.1). The lignocellulosic biomass is subjected to chemical modification and the cell wall structure is physically broken (Aslanzadeh et al. 2014). The high pressure and temperatures used in these types of processes increase the costs of applying them in a biorefinery type system. ...
... The high pressure and temperatures used in these types of processes increase the costs of applying them in a biorefinery type system. Steam pretreatment is the most common method applied to biomass due to their wide ranging application on various types of biomass, however in case of recalcitrant biomass sources, it may necessitates additional treatment using acid or SO 2 (Aslanzadeh et al. 2014). During steam explosion, fermentation inhibitors are generated such as HMF, weak acids and phenolic compounds. ...
... This method requires a high amount of energy and involves elevated operation costs (Peral 2016). Ionic 68 I. Covarrubias-García and S. Arriaga liquids are effective in decrystallizing the cellulose, fractionating lignin and polysaccharide contents into separate streams, making the following hydrolysis step much easier (Aslanzadeh et al. 2014). ...
Biogas can be considered as one of the primary renewable energy sources to generate electricity regarding the grid connection and feed-in tariffs in industrial plants. The present study is focused on introducing biogas systems on electricity production and what environmental policies should be assessed to minimize the air’s biogas component emission. Micro-gas turbine (MGT) systems, combined heat and power (CHP) systems, solid oxide fuel cells (SOFC), and organic Rankine cycle (ORC) systems are the most applicable renewable energy systems that can utilize biogas. Combinations of technologies as a hybrid and novel system give the engineers chance to optimize the biogas conversion to electricity for specified industrial purposes. Moreover, environmental features of biogas emissions from industrial plants were discussed and explained.
... Physical pretreatment generates a large number of cellulose inhibitory compounds, which negatively affects the enzymatic saccharification and fermentation processes [2,49]. The major drawback of physical pretreatment is its inability in removal of lignin and partial degradation of hemicellulose and lignincarbohydrate matrix, which decreases the enzymatic accessibility to cellulose [50]. Other limitations of physical pretreatment include high energy requirement, excessive large-scale implementation cost, and enormous environmental safety concerns, which highly affect the economy of biomass conversion at large scale [49,50]. ...
... The major drawback of physical pretreatment is its inability in removal of lignin and partial degradation of hemicellulose and lignincarbohydrate matrix, which decreases the enzymatic accessibility to cellulose [50]. Other limitations of physical pretreatment include high energy requirement, excessive large-scale implementation cost, and enormous environmental safety concerns, which highly affect the economy of biomass conversion at large scale [49,50]. ...
... Similarly, chemical pretreatment is highly selective for respective biomass constituents, i.e., demands quite severe conditions, which makes it unsuitable for biorefinery scheme due to adverse effect on downstream process [50]. Secondly, chemicals released after the chemical pretreatment are harmful for the environment causing negative effects on the flora and fauna. ...
Open rice straw burning has created hazardous effects on the environment and human health. Biological pretreatment of rice straw has been proven as an environmental-benign and economical feasible process for the production of biofuels and value-added products under milder and greener conditions by avoiding harmful chemicals and toxic reagents. A consolidated bioprocess for the production of cellulolytic enzymes and biological pretreatment was developed to achieve a cost-effective saccharification of rice straw. Biodegradation of biomass was slightly enhanced with increase in cultivation time of microbial pretreatment. Furthermore, the modification in biomass due to biological pretreatment weakened the interaction between hemicellulose and lignin that resulted in significant reduction in lignin using Bacillus subtilis subsp. subtilis JJBS300, Myceliophthora thermophila BJTLRMDU3, and Aspergillus oryzae SBS50 for biological pretreatment of rice straw. Bacterial culture produced maximum FPase, CMCase, and β-glucosidase of 28, 17, and 20.36 U/g DMR after 2 days during pretreatment process, whereas M. thermophila produced maximum FPase (85.10 U/g DMR), CMCase (96.89 U/g DMR), and β-glucosidase (91.92 U/g DMR) after 9 days. The mold A.oryzae SBS50 also produced maximum FPase (57.41 U/g DMR), CMCase (55.36 U/g DMR), and β-glucosidase (48.04 U/g DMR) after 9 days of pretreatment. Maximum amount of reducing sugars of 52.41, 86.74, and 49.59 mg/g substrate were liberated from 6-, 5-, and 3-day-old biological pretreated rice straw by B. subtilis, M. thermophila, and A. oryzae, respectively, after enzymatic hydrolysis for 6 h at 60 oC and pH 5.0. Laccase-pretreated rice straw followed by enzymastic saccharification resulted in liberation of 162.82 mg/g reducing sugars at pH 5.0 and 60 °C after 6h using 20 U/g cellulase. Simultaneous laccase pretreatment and saccharification (SLPS) process further enhanced the liberated reducing sugars, i.e., 179.47 mg/g substrate. FTIR, XRD, and SEM analyses showed marked morphological changes as a result of delignification after biological pretreatment of rice straw. Biological pretreatment being an environmental-benign process causing no harm to the environment in comparison to physical and chemical pretreatments of lignocellulosic biomass could be a better pretreatment strategy for bioremediation of lignocellulosic substrates.
... physical pretreatment decreases cellulose crystallinity and degree of polymerization. It is a vital step prior to both the biochemical and thermochemical conversion of biomass [7,26]. However, there is limited information about the mode of action of physical pretreatment processes, particularly with respect to how the chemical composition of biomass is modified or how its structure is affected. ...
... Other shortcomings include high energy consumption and the prohibitive cost of scale-up for commercial purposes. Studies [26,27] have shown that the process of lignin removal from LCB materials could be one of the major reasons for the high energy demand of physical pretreatment techniques hence the overall energy efficiency of a bio refinery process may be ultimately affected by this pretreatment method [26]. ...
... Other shortcomings include high energy consumption and the prohibitive cost of scale-up for commercial purposes. Studies [26,27] have shown that the process of lignin removal from LCB materials could be one of the major reasons for the high energy demand of physical pretreatment techniques hence the overall energy efficiency of a bio refinery process may be ultimately affected by this pretreatment method [26]. ...
Biomass has the potential to replace conventional fuels in a number of applications,
particularly in biofuel production. It is an abundantly available renewable
material with great potential as a feedstock for bioconversion processes for the
production of energy, fuels, and a variety of chemicals. Due to its biogenic origin,
the carbon dioxide released from its combustion process does not impact atmospheric
carbon dioxide. Despite these merits, a major problem hindering its widespread
use has always been its recalcitrant nature, in terms of its inherent
characteristics, which are unfavorable to its use in bioconversion and biorefinery
processes. This makes it necessary for biomass to be pretreated before use in any
conversion process for maximum product recovery. However, a major issue with
regards to biomass pretreatment is the lack of rapid, high throughput and reliable
tools for assessing and tracing biopolymer components of biomass relevant to the
energy production potential of the biomass. This chapter, therefore, presents an
overview of the pretreatment and characterization of biomass relevant to energy,
fuels, and chemicals production. The information provided will bequeath readers
with the basic knowledge necessary for finding an auspicious solution to
pretreatment problems and the production of energy from pretreated biomass.
... It has been shown that the application of physical pretreatment alone, generally increases the biohydrogen, methane, and ethanol by 5-25% compared to the non-treated biomass [22,82,84] . However, the noticeable drawback of the physical pretreatment is its incapacity to eliminate the lignin structure, which thus limits the access of the enzymatic reactions to cellulose [82,85] . Besides, these methods consume high energy amounts which don't correlate with the low hydrogen yield produced during the dark fermentative process. ...
... Besides, these methods consume high energy amounts which don't correlate with the low hydrogen yield produced during the dark fermentative process. It is costly from its industrial application perspective and is always accompanied by environmental and safety concerns [82,85,86] . ...
Currently, fossil fuels are the world’s primary form of energy. The huge consumption of fossil fuel-based energy is along with the rapid growth of the global population, which is always accompanied by growing industrialization. Excessive exploitation of fossil fuels reduces fossil fuel reserves and emits a large amount of carbon dioxide, which deepens environmental pollution and CO2-driven climate change, including global warming. Therefore, it is very necessary to develop a sustainable, economical, and eco-friendly renewable energy source as a substitute for fossil fuels to eliminate the world’s dependence on fossil fuel-based energy and alleviate the CO2-driven environmental issues.
Therefore, biohydrogen (H2) energy has attracted worldwide interest compared to other types of energy resources. It is the cleanest energy carrier, combustible with high calorific value and its combustion process produces zero carbon emissions. Therefore, producing bioH2 from a renewable resource such as agricultural waste could be a sustainable and cost-effective method for carbon neutrality. In that regard, dark fermentation (DF) has been extensively applied as a promising eco-friendly technique to produce bioH2 from lignocellulosic agricultural wastes. However, the recalcitrant and stubborn anti-degradation characteristics of the lignocellulose structure which hinder the microbial hydrolysis reactions, the proliferation of hydrogenotrophic methanogens in the formed biofilm that utilizes the generated H2 for their survival, and the accumulation of acid-rich intermediate by-products including Volatile fatty acids (VFAs) that couldn’t further be oxidized in fermentation process strictly hampered the practical application of fermentation technology for biohydrogen evolution.
To overcome the above-mentioned barriers, this study proposes a suitable pretreatment of agricultural straw waste to improve the substrate digestibility; it used thermal-pretreated activated sludge as a potential biocatalyst as a strategy to suppress methanogens and integrate microbial electrolysis cells (MEC) to dark fermentation to provide the additional energy input required for the continuous decomposition of dead-end products namely VFAs. Through bio-electrochemical processes, MEC can enhance H2 generation in the DF reactors by accelerating the decomposition of complex organic wastes including lignocellulosic agricultural wastes, and promote further utilization of the VFAs. Particularly, the applied voltage to the electrical circuit of MEC drives released electrons during the oxidation of the substrate (waste biomass) from the anode to the cathode and supports hydrogen generation at the cathode. However, to date, there is still a gap of knowledge and a lack of relevant research work exploring the feasibility of producing fermentative-bioH2 energy from real recalcitrant feedstocks without the additional use of commercial chemical catalysts. The main research results of this project are as follows:
(1) The wheat straw biomass-fed MEC performance was remarkably affected by the applied voltage. The experimental results revealed that the optimum applied voltage was 0.8V, and achieved a high H2 production which was ~28.2% and ~9.8% higher than that of 0.5V and 1V respectively. Moreover, the MEC performed under 0.8V (MEC0.8) attained a high COD removal rate of ~73.4%. Both anodic biofilm viability and microbial cell shape were less affected at low voltage but largely damaged at high voltages. The MEC (V=1.0) depicted a high charge transfer resistance of 16.06 Ω which was ~22.1% and ~73.7 % higher than that of MEC(V=0.8) and MEC(V=0.5) respectively.
(2) Using thermal-pretreated activated sludge as a potential alternative to expensive chemical catalysts and a coupled DF-MEC system significantly enhanced hydrogen production from wheat straw wastes. The overall system produced a maximum hydrogen production of 5.416 mmol H2/g straw with an energy recovery efficiency of 94.4% and a coulombic efficiency (CE) of 74%. Moreover, the DF-MEC integrated system favored the further bio-transformation of both lignocellulosic straw fibers and VFAs into biohydrogen, with 81.32% and 42.25% for COD and NH3-H removal efficiency respectively.
(3) The operating temperature of the DF-MEC integrated system significantly shaped the mixed microbial consortia structure during the conversion of lignocellulosic agricultural wheat straw biomass into biohydrogen. The results revealed that the bioreactor operating at higher temperature conspicuously promoted the thermophilic hydrogen-producing microbial growth, and the formed anodic biofilm was mainly composed of Proteobacteria (37.82%), Thermotogota (35.94%), and Coprothermobacteria (8.3%), whereas the reactors operated in the mesophilic environment was enriched more diverse microbial communities and promoted the proliferation of the methanogenic archaeal genera.
(4) Utilizing the wastewater residue from the DF-MEC process as a new potential biological fertilizer remarkably promoted plant growth. The collected bio-electrohydrogenesis left-over residues were enriched with plant growth-promoting flora including Bacillus (0.44 ± 0.11%), Azospirillum (0.11 ± 0.02%), Achromobacter (0.16 ± 0.07%), Bradyrhizobium (0.12 ± 0.02%), Allorhizobium-NeorhizobiumPararhizobium-Rhizobium (0.06 ± 0.02%), Methylobacterium-Methylorubrum (0.07 ± 0.01%), and Mesorhizobium (0.1 ± 0.03%). They also contained phosphate-solubilizing and nitrogen-fixing microorganisms as well as large amounts of nitrogen, phosphorus, potassium and other trace elements essential for plant growth. Herein, the collected DFMEC effluent was directly used to grow three plant crops including tomato, chilli and brinjal as fertilizer, and the growth and development of plants and the flowering and fruiting processes were significantly promoted. For instance, the plant heights of tomato, chilli, and brinjal species grown in the DF-MEC effluent-used protocol were ~2.03, ~1.2 and 2.7 times that of the control group, respectively.
Overall findings suggest that producing hydrogen energy using lignocellulosic straw waste as the substrate in a DF-MEC integrated system could be a promising approach to increasing the world's energy supply and reducing atmospheric greenhouse gases (GHG). Furthermore, this work provides sustainable solutions for agricultural waste management and encourages the use of the remaining generated residues as a cheap bio-fertilizer to replace the expensive commercial chemical fertilizers, thereby improving soil quality for agricultural production.
... The step after this kind of pretreatment is the enzymatic hydrolysis, in which enzymes are applied to hydrolyze cellulose into glucose monomers. From there, sugars can be used in bioprocesses to produce various products [7]. ...
... After physical-chemical pretreatment, an additional step should be carried out by using enzymes to hydrolyze the recalcitrant structure and to release monomeric sugars from the cellulosic fraction [6,7]. Enzymes such as: endoglucanases, exoglucanases, b-glucosidases, and oxidoreductases are used in this step, breaking cellulose into glucose. ...
The development of technologies to ferment carbohydrates (mainly glucose and xylose) obtained from the hydrolysis of lignocellulosic biomass for the production of second-generation ethanol (2G ethanol) has many economic and environmental advantages. The pretreatment step of this biomass is industrially performed mainly by steam explosion with diluted sulfuric acid and generates hydrolysates that contain inhibitory compounds for the metabolism of microorganisms, harming the next step of ethanol production. The main inhibitors are: organic acids, furan, and phenolics. Several strategies can be applied to decrease the action of these compounds in microorganisms, such as cell immobilization. Based on data published in the literature, this overview will address the relevant aspects of cell immobilization for the production of 2G ethanol, aiming to evaluate this method as a strategy for protecting microorganisms against inhibitors in different modes of operation for fermentation. This is the first overview to date that shows the relation between inhibitors, cells immobilization, and fermentation operation modes for 2G ethanol. In this sense, the state of the art regarding the main inhibitors in 2G ethanol and the most applied techniques for cell immobilization, besides batch, repeated batch and continuous fermentation using immobilized cells, in addition to co-culture immobilization and co-immobilization of enzymes, are presented in this work.
... It has been shown that the application of physical pretreatment alone, generally increases the biohydrogen, methane, and ethanol by 5-25% compared to the non-treated biomass [29,90,92]. However, the noticeable drawback of the physical pretreatment is its incapacity to eliminate the lignin structure, which thus limits the access of the enzymatic reactions to cellulose [90,93,94]. Besides, these methods consume high energy amounts which don't correlate with the low hydrogen yield produced during the dark fermentative process. ...
... Inhibitors are generated during conversion processes (e.g., cellulose realignment) [13] environmental and safety concerns [90,93,95]. ...
The continuous surge in global energy demand, fossil fuel depletion, and related climate change issues have oriented the worldwide researchers' endeavors to the investigation and development of sustainable and co-effective technology to satisfy the global energy needs. Referring to the non-toxic properties of hydrogen, it is considered as a suitable renewable energy source that could replace fossil fuel-based energy. It is the cleanest energy carrier, combustible with high calorific value, high energy yield. Producing biohydrogen energy from renewable resources such as lignocellulosic agricultural residues could be a sustainable carbon-neutral most cost-effective approach. Dark fermentation has been widely applied as a promising eco-friendly technique to produce biohydrogen from agricultural residues. However, it has shown drawbacks owing to the recalcitrance of ligno-cellulose structure, and the accumulation of acid-rich intermediate by-products. Microbial electrolysis cells use bio-electrochemical reactions to upgrade H 2 production in a dark fermentation reactor by promoting further decomposition of the generated volatile fatty acids. Therefore, integrating microbial electrohydrogenesis with dark fermentation can be a promising strategy to optimize the straw biomass conversion to biohydrogen. This review aims in delineating the structural composition and recalcitrance of the agricultural residues and their major effects on biohydrogen production. It summarizes all possible pre-treatment methods of the lignocellulosic agricultural residues; elucidates the stable operational conditions of microbial electrolysis cell and dark fermentation integrated system and discusses its performance for biohydrogen production. This study also reviewed the current technical challenges of this integrated system application and suggested sustainable solutions towards its industrial implementation.
... Wood-decay fungi are generally classified based on the decay type of mushroom, including brown rot, soft rot, and white rot, each with unique enzymatic activities and environmental preferences [10]. Brown-rot and soft-rot fungi primarily degrade cellulose and may induce minor changes to lignin, whereas white-rot fungi focus on breaking down lignin [28,54]. Overall, these considerations are crucial for ensuring the safety and suitability of the MBCs fabrication for various applications. ...
Mycelium-based green composites (MBCs) represent an eco-friendly material innovation with vast potential across diverse applications. This paper provides a thorough review of the factors influencing the production and properties of MBCs, with a particular focus on interdisciplinary collaboration and long-term sustainability goals. It delves into critical aspects such as fungal species selection, substrate type selection, substrate preparation, optimal conditions, dehydrating methods, post-processing techniques, mold design, sterilization processes, cost comparison, key recommendations, and other necessary factors. Regarding fungal species selection, the paper highlights the significance of considering factors like mycelium species, decay type, hyphal network systems, growth rate, and bonding properties in ensuring the safety and suitability of MBCs fabrication. Substrate type selection is discussed, emphasizing the importance of chemical characteristics such as cellulose, hemicellulose, lignin content, pH, organic carbon, total nitrogen, and the C: N ratio in determining mycelium growth and MBC properties. Substrate preparation methods, optimal growth conditions, and post-processing techniques are thoroughly examined, along with their impacts on MBCs quality and performance. Moreover, the paper discusses the importance of designing molds and implementing effective sterilization processes to ensure clean environments for mycelium growth. It also evaluates the costs associated with MBCs production compared to traditional materials, highlighting potential cost savings and economic advantages. Additionally, the paper provides key recommendations and precautions for improving MBC properties, including addressing fungal strain degeneration, encouraging research collaboration, establishing biosecurity protocols, ensuring regulatory compliance, optimizing storage conditions, implementing waste management practices, conducting life cycle assessments, and suggesting parameters for desirable MBC properties. Overall, this review offers valuable insights into the complex interplay of factors influencing MBCs production and provides guidance for optimizing processes to achieve sustainable, high-quality composites for diverse applications.
... Ethanol and water are soluble in each other, so distillation is required for the separation and concentration of ethanol from the fermentation broth. It is not possible to obtain 100% purity through simple distillation because of the azeotrope between water and ethanol; there is a strong hydrogen bond that exists between water and ethanol, which causes water to be attached to ethanol as it pulls out when heated and, therefore, about 95% of ethanol can be recovered through this process, which finds relevance in the solvent, chemical, cosmetic, and pharmaceutical industries [73]. To obtain 99.9% ethanol, i.e., anhydrous ethanol, further drying of ethanol or a dehydration step is required [37]. ...
Biofuels are clean and renewable energy resources gaining increased attention as a potential replacement for non-renewable petroleum-based fuels. They are derived from biomass that could either be animal-based or belong to any of the three generations of plant biomass (agricultural crops, lignocellulosic materials, or algae). Over 130 studies including experimental research, case studies, literature reviews, and website publications related to bioethanol production were evaluated; different methods and techniques have been tested by scientists and researchers in this field, and the most optimal conditions have been adopted for the generation of biofuels from biomass. This has ultimately led to a subsequent scale-up of procedures and the establishment of pilot, demo, and large-scale plants/biorefineries in some regions of the world. Nevertheless, there are still challenges associated with the production of bioethanol from lignocellulosic biomass, such as recalcitrance of the cell wall, multiple pretreatment steps, prolonged hydrolysis time, degradation product formation, cost, etc., which have impeded the implementation of its large-scale production, which needs to be addressed. This review gives an overview of biomass and bioenergy, the structure and composition of lignocellulosic biomass, biofuel classification, bioethanol as an energy source, bioethanol production processes, different pretreatment and hydrolysis techniques, inhibitory product formation, fermentation strategies/process, the microorganisms used for fermentation, distillation, legislation in support of advanced biofuel, and industrial projects on advanced bioethanol. The ultimate objective is still to find the best conditions and technology possible to sustainably and inexpensively produce a high bioethanol yield.
... They can offer green pretreatments, in which the product (hydrolyzate) can be directly utilized to generate sugars. Still, physical methods, such as mechanical comminution and pyrolysis, have been considered to be too expensive for a full-scale process due to their high energy consumption; however, the main disadvantage of physical pretreatment methods is their inability to degrade the structure of lignin [56,82]. ...
Lignocellulose consists of cellulose, hemicellulose, and lignin and is a sustainable feedstock for a biorefinery to generate marketable biomaterials like biofuels and platform chemicals. Enormous tons of lignocellulose are obtained from agricultural waste, but a few tons are utilized due to a lack of awareness of the biotechnological importance of lignocellulose. Underutilizing lignocellulose could also be linked to the incomplete use of cellulose and hemicellulose in biotransformation into new products. Utilizing lignocellulose in producing value-added products alleviates agricultural waste disposal management challenges. It also reduces the emission of toxic substances into the environment, which promotes a sustainable development goal and contributes to circular economy development and economic growth. This review broadly focused on lignocellulose in the production of high-value products. The aspects that were discussed included: (i) sources of lignocellulosic biomass; (ii) conversion of lignocellulosic biomass into value-added products; and (iii) various bio-based products obtained from lignocellulose. Additionally, several challenges in upcycling lignocellulose and alleviation strategies were discussed. This review also suggested prospects using lignocellulose to replace polystyrene packaging with lignin-based packaging products, the production of crafts and interior decorations using lignin, nanolignin in producing environmental biosensors and biomimetic sensors, and processing cellulose and hemicellulose with the addition of nutritional supplements to meet dietary requirements in animal feeding.
... strains , whereas thermochemical conversion involves gasification, pyrolysis, and liquefaction. Although carbonaceous materials are commonly gasified, lignocellulosic biomass gasification is still a relatively new technology (Aslanzadeh et al. 2014). As a result, the main purpose of this chapter is to discuss different agricultural biomass that can be used to produce biobutanol. ...
The main objective of the study was to isolate and characterize microalgae from Vellar estuary south coast of India. The isolated eight microalgal species were cultured in CHU 10 broth to find the efficient culture media under laboratory conditions. The growth rate, pH, and biomass for lipid production under different conditions were studied from the eight microalgal species isolated and incubated in different media. On the other hand, the physicochemical properties of sewage water were analyzed, and the suitable environmental condition was adopted for culturing. Microalgae showed good growth, and the biomass was taken for further study among which Nitzschia species was selected based on biomass and lipid production. Further, enhancement was carried out by supplementing media with different carbon (glucose and starch) and nitrogen (urea and yeast) sources. Nitzschia species resulted in a maximum growth rate (2.08) and biomass (0.17 g L−1) with glucose as carbon source, while supplemented yeast as nitrogen source yielded a maximum growth rate (1.118) and urea favored the maximum biomass (0.16 g L−1). Maximum lipid content about 0.058 and 0.046 g was witnessed when supplementing the glucose and yeast along with the diatom media components (0.025 g). The oil was characterized by FT-IR spectroscopy, and different active functional groups were recorded. In Nitzschia, 98% of different fatty acids were recorded. The present study concluded that the culture conditions, especially the nature of carbon and nitrogen sources, influence the yield on growth, biomass, and lipid production of Nitzschia sp.KeywordsMicroalgaeSewage waterBiomassNitzschia sp.LipidMedia components
... strains , whereas thermochemical conversion involves gasification, pyrolysis, and liquefaction. Although carbonaceous materials are commonly gasified, lignocellulosic biomass gasification is still a relatively new technology (Aslanzadeh et al. 2014). As a result, the main purpose of this chapter is to discuss different agricultural biomass that can be used to produce biobutanol. ...
Weeds are invasive or unwanted plants that are non-native to the ecosystem grow along with food crops threatening the food security, health, economic development and biodiversity. They are competitive, able to persist and grow under any stressed conditions with high propagating capability. India having temperate to tropical zones possesses rich plant diversity spread across different crop and non-croplands. Weeds grow everywhere consuming the nutrients, soil moisture, space, etc., meant for food crops and thus ultimately affect the crop productivity adversely. Parthenium is a weed that invaded India with imported food grains in the mid-1950s. This weed alone was reported (2001–2007) to invade over 14.5 million hectares of farmland in India (Directorate of Weed Science Research—DWSR). It was also opined that the swift growth of this weed is a threat to environment, biodiversity and country’s economy. Various strategies involving many voluntary organizations, individuals and government agencies in the weed management on a regional scale were organized. Though several eradication measures were undertaken in this regard, not a single method is still a choice for the complete eradication of weed. Therefore, the status of weed controlling is envisaged with respect to “large-scale utilization”. Over a century, several studies have been reported that weed can be a potential biomass. Weed can be used as a green manure, biocontrol agent, soil ameliorate, compost which in turn improves physical, chemical and biological composition of the soil and also in the generation of significant quantities of energy. In this age of renewable energy, there is an ever-rising demand for the alternative energy source which calls for exploring and exploiting new sources of energy biomethanation is a process of production of biogas (methane), during which the organic matter is converted into an alternative fuel. Biomethanation offers an effective way to manage the weed biomass in eco-friendly and cost-effective way.
... strains , whereas thermochemical conversion involves gasification, pyrolysis, and liquefaction. Although carbonaceous materials are commonly gasified, lignocellulosic biomass gasification is still a relatively new technology (Aslanzadeh et al. 2014). As a result, the main purpose of this chapter is to discuss different agricultural biomass that can be used to produce biobutanol. ...
Bioenergy is energy produced from organic material of plant and animal sources, mainly agricultural residues, wood, energy crops, and organic wastes. Bioenergy is the most common renewable energy source globally, accounting for roughly 70% of all critical renewable energy sources. Since biomass is organic, it is one of the most dependable energy sources. Traditional biomass is used by about 2.5 billion people worldwide and about 1.3 million public, specifically children and women, every year prematurely die. Biological resources are agricultural residues, industrial waste, municipal solid waste, and terrestrial and aquatic crops grown only for energy purposes. Agricultural residues are an essential energy source, and rice is a chief crop in several emerging countries, especially Asia. Rice bran and rice straw, which are remnants of this crop, have a high potential for bioenergy production. The source of bioenergy is rice grass, lignocellulosic biomass, lignin, cellulose, and hemicellulose. Rice straw is also used to generate electricity; the fundamental method is a thermochemical one that generates steam via direct combustion of biomaterials. This form, however, is highly undesirable due to the detrimental effects on the environment caused by the release of carbon dioxide and methane gas. Consequently, it is imperative to progress a method of extracting energy from rice straw to generate electricity. It is an excellent approach to dispose of rice straw and uses heat is helpful for power generation. Eventually, rice straw can be used in high-efficiency, energy production, and affordable agro-biometry to generate electricity and evaluate bioenergy and its impacts in the sense of the particular framework of which it is a part, as well as their direct and broader impacts on the environment and economy.
... Physical pre-treatment is one of the most common methods of pre-treatment involved during biofuel production from rice. In this method, plant biomass is reduced or ground into fine particles, which enhances the accessible surface area of biomass [126]. The typical physical pre-treatment methods are grinding and milling, steaming, pressure, temperature, and irradiation. ...
Rice is the prominent food grain required by more than half of the world's population to fulfll their nutritional demand. With the continuous growth in the population at the global level, rice production has also been elevated. However, high rice production also creates a new problem in waste management worldwide. Rice straw, generated after rice harvest, possesses meager nutritional value, due to which it is less preferred as fodder and burned in the field. Paddy burning is one of the major causes of air pollution, leading to lung, heart, eye, and skin-related diseases and even premature death. This stubble burning also decreases soil fertility. In this review article, we have discussed the various economic uses of paddy straw which will help to reduce air pollution through the decline in paddy straw burning. Biochar is produced from paddy straw, which can be mixed into the soil to restore fertility and reduce toxic metals' bioavailability. The generation of biofuels such as biobutanol, bioethanol, and biogas from rice straw with their mechanism of synthesis is also discussed in this article. Rice straw can also be utilized in the preparation of solid fuel. Along with this, mushroom cultivation in paddy straw houses is also described. Paddy straw can be used for the pulp and paper industries, which will help to reduce the tree dependence of these industries.
Apart from this, a bibliometric analysis of the Scopus database on rice straw uses for the last 20 years was done, including a bibliographic keyword analysis to show published documents' trends. This review will give an elaborated overview of the
alternative uses of rice straw with a quantitative analysis of air pollution caused by paddy straw burning. This review will also help to improve the current uses of paddy straw for industrial and commercial benefits to make it more economical.
... In enzymatic reaction, the influence caused by the substrate concentration is complex and affects the primary rate and yield of enzymatic hydrolysis [33]. The reaction rate can be expected to enhance with increasing of substrate concentrations, on the contrary higher substrate concentrations can result in inhibition of enzyme activity leading to decrease of hydrolysis rate [34]. ...
A state-of-the-art strategy for the determination of lipase activity in pancreatic preparations using flow injection analysis (FIA) with electrochemical detection (FIA-ED) is described. The procedure is based on the enzymatic reaction of a specific substrate (1,3-dilinoleoyl-glycerol) with lipase from porcine pancreas and determination of enzymatically formed linoleic acid (LA) at +0.4 V by applying a cobalt (II) phthalocyanine-multiwalled carbon-nanotubes modified carbon paste electrode (Co(II)PC/MWCNT/CPE). In order to get a high-performance analytical method, sample preparation, flow system, and electrochemical conditions were optimized. Under optimized conditions the lipase activity of porcine pancreatic lipase was calculated to be 0.47 units per mg lipase protein based on the definition that 1 unit hydrolyses 1 microequivalent linoleic acid from 1,3-dilinoleoyl-glycerol per 1 min at pH 9 and 20 °C (kinetic measurement: 0-25 min). Moreover, the developed procedure was shown to be easily adaptable for the fixed-time assay (incubation time 25 min) as well. In this case, linear correlation between flow signal and lipase activity was found in the range from 0.8 to 18 U L-1. LOD and LOQ were determined to be 0.3 U L-1 and 1 U L-1, respectively. The kinetic assay was further preferred for the determination of lipase activity in commercially available pancreatic preparations. The lipase activities of all preparations obtained by the present method were found to be in good correlation with those obtained by the titrimetric method and declared by manufacturers.
... Physical pretreatments aim at reducing particle size and crystallinity, increasing the contact surface, and thus the efficiency of possible downstream pretreatments [128]. It is considered as an essential step prior to chemical or biochemical pretreatment, for an improvement of the subsequent yields [131]. Three types are commonly considered, namely, mechanical treatment, microwave treatment and ultrasound treatment [132]. ...
Seaweeds represent a promising and sustainable feedstock for biofuel production which raises increasing research interests. Their high availability, easy fermentable composition, and good degradation potential make them a suitable candidate for alternating fossil fuels as an advantageous energy resource. This comprehensive review aims to summarize and discuss data from the literature on the biochemical composition of seaweeds and its potential for biomethane and biohydrogen production, as well as to investigate the effect of the common pretreatment methods. Satisfactory yields comparable to terrestrial biomass could be obtained through anaerobic digestion; concerning dark fermentation, the challenge remains to better define the operating conditions allowing a stable production of biohydrogen. Finally, we propose a potential energy production scheme with the seaweed found by the Caribbean Islands of Guadeloupe and Martinique, as well as current techno-economic challenges and future prospects. An annual energy potential of 66 GWh could be attained via a two-stage biohythane production process, this tends to be promising in terms of energetic valorization and coastal management.
... Therefore, the reaction of hemicellulose constituents and impregnation chemicals have been considered. It was detected that, presumably, some of the primary sugars of the softwoods' hemicelluloses, mannose and/or glucose (Aslanzadeh et al. 2012), reacted with sorbitol citrate. However, that is not a proof of the reaction between unhydrolyzed hemicellulose and SorCA. ...
In recent years, a wood treatment system based on sorbitol and citric acid (SorCA) has emerged as a promising alternative to already commercialized modification processes of European-grown wood species. The improvement of dimensional stability and biological durability have been reported. However, the mode of action behind the changes in wood structure leading to these improvements has not been well defined yet, as the research was based on the infrared spectroscopy, which cannot distinguish nor compare the effect of cell wall bulking (CWB), covalent bonding and cross-linking. Moreover, most of the assumptions regarding the reaction mechanism have resulted from the studies of citric acid reactions with wood and wood-based products. Therefore, in this study different analytical chemistry methods have been used to explain the interaction between SorCA and wood at two polymerization temperatures (120 and 140°C). It has been confirmed that the curing temperature is a crucial parameter for achieving the desired fixation. Subsequently, liquid chromatography-mass spectrometry (LC-MS), cross-polarization/ magic angle spinning (CP/MAS 13 C-NMR) spectroscopy and pyrolysis gas chromatography-mass spectrometry (Py-GC/MS) have been used to determine the contribution caused by an in-situ formation of high molecular-weight SorCA polyesters (resulting in CWB) and a higher rate of esterification of wood polymers.
... A low conversion rate is caused by a high substrate saturation level i.e. oversupplied with the excess substrate may be toxic to the organisms [33]. Cell growth is reduced as a result of partial dehydration, which is caused due to an elevated substrate concentration [34]. In this study, substrate inhibition increased with a glycerol concentration of 25 g/L. ...
Global attention caused by pollutants and greenhouse gas emissions leads to alternative fuels that decrease the dependence on fossil fuels and reduce the carbon footprint that preceded the development of biodiesel production. Glycerol residue is generated more signi cantly from the biodiesel industry as a byproduct and is left as waste. In this study, we utilized glycerol residue from the biodiesel industry as an excellent opportunity to convert ethanol by bioconversion. e waste glycerol was used as a good and cheap carbon source as a substrate to synthesize ethanol by immobilizing E. coli cells. e screening of parameters such as mass substrate, temperature, inoculum size, and fermentation time was carried out using the one-factor-at-a-time (OFAT) technique. e Taguchi model employed optimization of fermentation parameters. e process parameters showed the mass substrate glycerol of 20 g with an inoculum size of 20%, and 12 hours yielded the ethanol concentration of 10.0 g/L.
... A low conversion rate is caused by a high substrate saturation level i.e. oversupplied with the excess substrate may be toxic to the organisms [33]. Cell growth is reduced as a result of partial dehydration, which is caused due to an elevated substrate concentration [34]. In this study, substrate inhibition increased with a glycerol concentration of 25 g/L. ...
Global attention caused by pollutants and greenhouse gas emissions leads to alternative fuels that decrease the dependence on fossil fuels and reduce the carbon footprint that preceded the development of biodiesel production. Glycerol residue is generated more significantly from the biodiesel industry as a byproduct and is left as waste. In this study, we utilized glycerol residue from the biodiesel industry as an excellent opportunity to convert ethanol by bioconversion. The waste glycerol was used as a good and cheap carbon source as a substrate to synthesize ethanol by immobilizing E. coli cells. The screening of parameters such as mass substrate, temperature, inoculum size, and fermentation time was carried out using the one-factor-at-a-time (OFAT) technique. The Taguchi model employed optimization of fermentation parameters. The process parameters showed the mass substrate glycerol of 20 g with an inoculum size of 20%, and 12 hours yielded the ethanol concentration of 10.0 g/L.
... It was found that depending on the selected end-point ( Figure 2b and Table S1 in the Supplementary Materials, Section S2) Km mean value fluctuated from 14 to 17 mM. Nevertheless, considering that high substrate concentrations can result in enzyme activity inhibition [21] decreasing the hydrolysis rate, 10 mM of NPA were used as the substrate concentration. Km is an important parameter representing the substrate concentration (on this occasion NPA) at which the reaction velocity is equal to half the maximal velocity of the reaction (1/2 Vmax). ...
Pancreatic lipase (PNLIP, EC 3.1.1.3) plays a pivotal role in the digestion of dietary lipids,
a metabolic pathway directly related to obesity. One of the effective strategies in obesity treatment is the inhibition of PNLIP, which is possible to be achieved by specific phenolic compounds occurring in high abundance in some plants. In this study, a multidisciplinary approach is presented investigating the PNLIP inhibitory effect of 33 plants belonging in the Asteraceae botanical family. In the first stage of the study, a rapid and cost-efficient PNLIP assay in a 96-microwell plate format was developed and important parameters were optimized, e.g., the enzyme substrate. Upon PNLIP assay optimization, aqueous and dichloromethane Asteraceae plant extracts were tested and a cut-off inhibition level was set to further analyze only the samples with a significant inhibitory effect (inhibitory rate > 40%), using an ultra-high-performance liquid chromatography hybrid quadrupole time-of-flight mass spectrometry (UHPLC-q-TOF-MS) method. Specifically, a metabolomic suspect screening was performed and 69 phenolic compounds were tentatively identified,
including phenolic acids, flavonoids, flavonoid-3-O-glycosides, and flavonoid-7-O-glycosides, amongst others. In the case of aqueous extracts, phytochemicals known for inducing PNLIP inhibitory effect, e.g., compounds containing galloyl molecules or caffeoylquinic acids, were monitored in Chrysanthemum morifolium, Grindella camporum and Hieracium pilosella extracts. All in all, the presented approach combines in vitro bioactivity measurements to high-end metabolomics to identify phenolic compounds with potential medicinal and/or dietary applications.
... Nevertheless, the time needed to reach the maximum production rate (t max ) also increases with the increase in substrate concentration. The delay arises from the increasing lag phase period due to the reduced mass transfer at high solid loadings [79]. Another reason is the substrate inhibition encountered by the microorganism involved at a high substrate concentration. ...
This paper presents a new multi-scale kinetic model built upon the multi-stage growth Hypothesis for predicting biohydrogen production. The proposed model represents the significant factors affecting biohydrogen production using a sum of first-order kinetic terms with varying dynamics from slow to fast one. The current work investigates 52 case studies of biohydrogen production that show the double first-order kinetic model provides the best modeling fitness (R² > 0.99). This result suggests two prevalent pathways or microbial groups with distinct dynamics (i.e., fast and slow modes) in biohydrogen production. An increase in temperature (30 °C–43 °C) or substrate concentration (10 g/L to 40 g/L) and the use of simple substrates or mixed cultures can increase the fast-mode dominance up to 100% contribution. Model analysis suggests that the fast mode corresponds to the butyrate production pathway, the growth-associated hydrogen-producing activity, the easily-biodegradable substrates, or the quick hydrogen-producing groups.
... This is followed by cementing the hydrophobic fatty acid and the hydrophilic protein moiety. The increase in substrate concentration induces the substrate inhibition that significantly lowers the enzymatic hydrolysis of AF and thereby reduces the CLB production at high substrate concentration (Aslanzadeh et al., 2014). An analogous interaction was also observed between time and temperature surface plot (Fig. 1b). ...
Bioremediation of municipal landfill leachate (MLL) is often intricate due to presence of refractory lignin. In the present study, it was attempted to tailor the histidine rich protein moiety of cationic lipoprotein biosurfactant (CLB) to sequester the lignin from MLL. Animal fleshing (AF), the solid waste generated in tanning industry was utilized for the production of histidine rich CLB by de novo substrate dependent synthesis pathway involving Bacillus tropicus. The optimum conditions for the maximum production of CLB were determined using response surface methodology. At the optimized conditions, the maximum yield of CLB was 217.4 mg/g AF (on dry basis). The produced histidine rich CLB was purified using Immobilized metal affinity chromatography at the optimum binding and elution conditions. The histidine residues were more pronounced in the CLB, as determined by HPLC analysis. The CLB was further characterized by SDS-PAGE, Zeta potential, XRD, FT-IR, Raman, NMR, GC-MS and TG analyses. The CLB was immobilized onto functionalized nanoporous activated bio carbon (FNABC) and the optimum immobilization capacity was found to be 211.6 mg/g FNABC. The immobilization of CLB onto FNABC was confirmed using SEM, FT-IR, XRD and TG analyses. The isotherm models, kinetic and thermodynamics studies of CLB immobilization onto FNABC were performed to evaluate its field level application. Subsequently, the CLB-FNABC was then applied for the sequestration of lignin in MLL. The maximum lignin sequestration was achieved by 92.5 mg/g CLB-FNABC at the optimized sequestration time, 180 min; pH, 5; temperature, 45 °C and mass of CLB-FNABC, 1.0 g. The sequestration of lignin by CLB- FNABC was confirmed by SEM, FT-IR and UV-Vis analyses. Further, the mechanistic study revealed the anchoring of CLB onto the surface of lignin through electrostatic interaction.
... However, that study achieved greater degradation at an initial concentration of 3% WCO over 3 days, compared with around 40% over 7 days in the current study. The inhibition of degradation associated with high concentrations of substrate may indicate suppression of key enzymes [85]. This is known to be the case especially in the biodegradation of hydrocarbons that are composed of aromatic elements [86]. ...
Hydrocarbons can cause pollution to Antarctic terrestrial and aquatic ecosystems, both through accidental release and the discharge of waste cooking oil in grey water. Such pollutants can persist for long periods in cold environments. The native microbial community may play a role in their biodegradation. In this study, using mixed native Antarctic bacterial communities, several environmental factors influencing biodegradation of waste canola oil (WCO) and pure canola oil (PCO) were optimised using established one-factor-at-a-time (OFAT) and response surface methodology (RSM) approaches. The factors include salinity, pH, type of nitrogen and concentration, temperature, yeast extract and initial substrate concentration in OFAT and only the significant factors proceeded for the statistical optimisation through RSM. High concentration of substrate targeted for degradation activity through RSM compared to OFAT method. As for the result, all factors were significant in PBD, while only 4 factors were significant in biodegradation of PCO (pH, nitrogen concentration, yeast extract and initial substrate concentration). Using OFAT, the most effective microbial community examined was able to degrade 94.42% and 86.83% (from an initial concentration of 0.5% (v/v)) of WCO and PCO, respectively, within 7 days. Using RSM, 94.99% and 79.77% degradation of WCO and PCO was achieved in 6 days. The significant interaction for the RSM in biodegradation activity between temperature and WCO concentration in WCO media were exhibited. Meanwhile, in biodegradation of PCO the significant factors were between (1) pH and PCO concentration, (2) nitrogen concentration and yeast extract, (3) nitrogen concentration and PCO concentration. The models for the RSM were validated for both WCO and PCO media and it showed no significant difference between experimental and predicted values. The efficiency of canola oil biodegradation achieved in this study provides support for the development of practical strategies for efficient bioremediation in the Antarctic environment.
... BG is the most abundant cellulose degradation enzyme in soil and is essential for the carbon cycle [46]. The BG enzyme activity is influenced by the substrate concentration [47]. BG activity increased with the amount of OM, which is a substrate, but the OM was not significantly affected by lime treatment, so there was no difference between the experimental plots. ...
Soil acidification caused by anthropogenic activities adversely affects forest ecosystems by altering soil pH, which is an important factor in soil quality and function. Liming is one suggested way to solve this problem. This study was performed to evaluate the effects of liming in acidic forest soils by determining soil microbial biomass, microbial community structure, and extracellular enzyme activities associated with carbon, nitrogen, and phosphorus cycling. Lime treatment increased soil pH by up to 40%, significantly increased organic matter (OM) content at some sites, and altered the enzyme activity of the soil. With liming, the microbial biomass appeared to be affected by the chemical properties of the soil, such as pH, Ca²⁺, Mg²⁺, K⁺, and exchangeable aluminum (Ale) levels, although there were no significant differences at the site level. Enzymatic activity was found to be affected by pH, Ca²⁺, Mg²⁺, electrical conductivity (EC), and Ale; and acid phosphatase (AP) and phenol oxidase (POX) activity were significantly affected by lime treatment. AP activity decreased from 0.62 to 0.66, and POX activity increased from 1.75 to 3.00 in part of the sites. The bacterial community richness was influenced by pH as a direct effect of lime treatment. The fungal community richness was associated with changes in K⁺ that were not due to lime treatment. The bacterial community structure was affected by soil OM, total nitrogen (TN), pH, and Ca²⁺; and the fungal community structure was affected by pH, Mg²⁺, and K⁺. In conclusion, changes in soil environmental conditions by liming can affect soil microbial communities and functions through direct or indirect processes, further changing ecosystem processes.
... The concentration of glucose used in the study was 60 g/l which is a very large amount and in some cases may even lead to inhibition of microorganisms due to high concentration of substrate [52][53][54][55]. In order to overcome this problem, the concentration of glucose was varied from 10 to 70 g/l to check for maximum production of exopolysaccharide, and the product formed was estimated in terms of total carbohydrate present in the sample by phenol-sulphuric acid test. ...
Microbial exopolysaccharides, especially from thermophiles, are gaining attention due to their thermostability and reduced viscosity at elevated temperatures which make them suitable candidates for pharmaceutical, cosmetics and food industries. This study aims to identify potential of a novel thermophile for the production of high amounts of exopolysaccharide. It also reports suitable process parameters for growth of novel thermophile in exopolysaccharide production medium and determination of optimum glucose concentration as its production generally requires high amount of glucose making the process cost intensive. Thermophilic bacteria, from a local hot spring, were screened for the production of exopolysaccharide, and growth kinetics of the best producer, Brevibacillus borstelensis MK878423, was studied. The growth study of bacterium revealed optimum time of production as 40 h, and maximum product was formed at 30 g/l glucose. The logistic growth curve of the bacterium was analysed, and kinetic rate constants for substrate utilization were estimated by modified Luedeking-Piret kinetic model. The specific growth rate of the bacterium was calculated to be 0.0166 h−1 with kinetic rate constants as − 18.953 (α) and 90.655 (β) for Luedeking-Piret substrate. This is the first report on the production of exopolysaccharide by a strain of Brevibacillus borstelensis. Understanding the kinetic rate constants for substrate consumption will help in extrapolating the system of microbial exopolysaccharide production from agricultural wastes with high glucose content. The determination of optimal glucose concentration will also help in utilizing biowastes as substrates for exopolysaccharide production following biorefinery concept as wastes are utilized for the production of value-added chemicals.
... The biomass surface area increases through reduction of size and crystallinity of particles through mechanical pretreatments (Liu et al., 2020). Typical comminution methods includes milling, grinding, and chipping, which is often conducted before chemical or biochemical processing (Aslanzadeh et al., 2014). Among these, ball milling is widely used for fine particle that the lignin G-unit in eucalyptus easily depolymerize at a low temperature (e.g. 120 ℃) during the IL pretreatment. ...
The demands of energy sustainability drive efforts to bio-chemical conversion of biomass into biofuels through pretreatment, enzymatic hydrolysis, and microbial fermentation. Pretreatment leads to significant structural changes of the complex lignin polymer that affect yield and productivity of the enzymatic conversion of lignocellulosic biomass. Structural changes of lignin after pretreatment include functional groups, inter unit linkages and compositions. These changes influence non-productive adsorption of enzyme on lignin through hydrophobic interaction and electrostatic interaction as well as hydrogen bonding. This paper reviews the relationships between structural changes of lignin and enzymatic hydrolysis of pretreated lignocellulosic biomass. The formation of pseudo-lignin during dilute acid pretreatment is revealed, and their negative effect on enzymatic hydrolysis is discussed.
... Moreover, it the most important step where the availability of biomass for the cellulose enzyme is increased, their digestability and product availability is increased. Thus, it is highly important for the researchers to keep in mind about the present condition of the biofuel production so that the researchers can accordingly work for the improved better future toward biorefinery (Aslanzadeh, Ishola, Richards, & Taherzadeh, 2014). Initially, the production of biofuel was based on two different routes, biochemical routes and thermochemical routes. ...
Different pretreatment techniques help to overcome many barriers in achieving desirable bioproducts at low cost as well as at lower energy requirement. This review predominantly aims to summarize all the pretreatment methods for the production of biofuel from biomass. The massive use of fossil fuel led to several huge problems Predominantly, Bioenergy has attained great importance due to rapid depletion in fossil fuel because biofuels are considered to be one of the promising alternatives of nonrenewable sources. The main objective of pretreatment methods is enhancement of sugar production by hydrolyzing the biomass and help in achieving maximum yield. Pretreatment is a significant tool for the conversion of cellulose as well as it is also very important to change the structure of cellulosic biomass. All the major pretreatment techniques are broadly classified into physical, chemical, physicochemical and biological methodologies which includes techniques like Mechanical Comminution, Acid hydrolysis, steam explosion, microwave pretreatment etc. The motive of these pretreatments is to make cellulose more available to the enzymes that assist in the conversion of carbohydrate polymers into fermentable sugars. Biological pretreatments have been analyzed to have immense advantages over physical and chemical pretreatments. Presently, Biomass almost produce about more than 13% of the world's energy. There are many high‐throughput testing ideas and processing technologies which can add up additional values for a better biomass processing in future. Thus, a systemic and computational approach can combine multistage formulation with multistage problem solving so that novel technology can be encouraged for the biorefinery production. This review has done extensive literature study of the various pretreatment technologies which will assist us to produce bioethanols and other biofuels that can be helpful in reducing the adverse effect on the environment.
Practical Applications
Predominantly, Bioenergy has attained great importance due to rapid depletion in fossil fuel because biofuels are considered to be one of the promising alternatives of nonrenewable sources. Biofuel Production and Food Processing of various pretreatment technologies produce environmentally friendly methods. All methods of pretreatment help to overcome many barriers and achieving desirable products at low cost as well as lower energy requirement with efficient yield. This article assists us to produce bioethanols and other biofuels that can be helpful in reducing the adverse effect on the environment and on the diminishing amount of fossil fuel.
... Physiochemical pretreatment is a combination of physical and chemical methods, where LC biomass is simultaneously chemically modified and the cell wall structure is physically altered [74]. Well known physicochemical pretreatment methods are steam explosion, CO 2 explosion pretreatment, ammonia fiber expansion (AFEX), and liquid hot water (LHW) pretreatment. ...
Lignin is a natural polymer, one that has an abundant and renewable resource in biomass. Due to a tendency towards the use of biochemicals, the efficient utilization of lignin has gained wide attention. The delignification of lignocellulosic biomass makes its fractions (cellulose, hemicellulose, and lignin) susceptible to easier transformation to many different commodities like energy, chemicals, and materials that could be produced using the biorefinery concept. This review gives an overview of the field of lignin separation from lignocellulosic biomass and changes that occur in the biomass during this process, as well as taking a detailed look at the influence of parameters that lead the process of dissolution. According to recent studies, a number of ionic liquids (ILs) have shown a level of potential for industrial scale production in terms of the pretreatment of biomass. ILs are perspective green solvents for pretreatment of lignocellulosic biomass. These properties in ILs enable one to disrupt the complex structure of lignocellulose. In addition, the physicochemical properties of aprotic and protic ionic liquids (PILs) are summarized, with those properties making them suitable solvents for lignocellulose pretreatment which, especially, target lignin. The aim of the paper is to focus on the separation of lignin from lignocellulosic biomass, by keeping all components susceptible for biorefinery processes. The discussion includes interaction mechanisms between lignocellulosic biomass subcomponents and ILs to increase the lignin yield. According to our research, certain PILs have potential for the cost reduction of LC biomass pretreatment on the feasible separation of lignin.
The marine environment is an abundant source of organisms which are rich in functional/bioactive compounds. Many of these compounds exhibit a remarkable potential for medical, industrial and biotechnological applications. Handled appropriately, with a focus on sustainability, these organisms and compounds can offer new and renewable feedstocks for a variety of industries. The biomass from marine organisms also offers opportunities for clean and sustainable fuel generation, carbon sequestration and wastewater remediation.
Focusing on the use of biomass from marine algae (both macro and micro), bacteria and yeasts this book looks at opportunities for producing high value chemicals with applications across multiple industries. It is an essential read for researchers interested in innovative, green feedstock sources, sustainability and the circular economy.
Purpose of Review
Lignocellulosic biomass, as a green and sustainable resource, can be used in biorefineries to produce bio-based products. The complex and resistant structure of lignocellulose prevents microorganisms access to carbohydrates in the biorefinery’s main processes, necessitating pretreatment. Different conventional pretreatment methods (physical, physico-chemical, chemical, and biological methods) and also novel advanced oxidation processes (AOPs) and their sustainability, environmental impact, economic viability, energy efficiency and, commercialization state are investigated in this review.
Recent Findings
Due to various reviews and studies on conventional pretreatment methods, they are briefly described with proper data. As the mechanisms and principle of operation of AOPs were investigated, during the AOPs pretreatment methods, hydroxyl radicals (·OH) are generated sufficiently to decompose lignocellulosic structure through oxidation. In this paper, we review the different AOPs, i.e., Fenton process, ozonation, photochemical, wet air oxidation, ultrasound, and electrochemical, which are recently used in the pretreatment of lignocellulose. Also, the achievement of different AOPs pretreatment research studies and general trends governing the process operating conditions are presented briefly in tables. Moreover, lignocellulosic biomass pretreatment sustainability assessment approaches such as life cycle assessment (LCA) and economic value and environmental impact (EVEI) are discussed. Although no study compared the sustainability aspects of different AOPs with conventional methods, this review generally addresses them. Further, environmental, energetic, and economic aspects of AOPs methods have been compared as important criteria in selecting a pretreatment method.
Summary
This review provides a thorough insight into the biorefinery’s bottleneck, pretreatment, and comprehensively investigated mechanisms, principle of operation, sustainability, environmental, economic, energy, and commercialization state of AOPs methods.
Due to increased exploitation of energy resources and environmental issues, there is a need for a fuel which is sustainable and environment friendly in order to meet the world’s future energy needs. Second-generation biofuels can be an attractive option for the society and may encourage them to shift toward the green fuels, also known as advance biofuels. It can be produced from non-food biomass which includes agricultural residues generated as waste during or after processing of agricultural crops without compromising the food security. These agricultural residues comprised of lignocellulosic materials, providing a unique natural resource at a large scale that is renewable and a cost-effective alternative for biobutanol production. Generally, two strategies are followed for the conversion of biomass into biobutanol that enhances the target yield from the raw materials being utilized; first is the thermochemical processing and biochemical processing. This chapter will provide an overview of the technical details being utilized for the conversion of residual biomass into biobutanol that are currently employed. This chapter will also cover the emerging advancements in the two primary conversion techniques, i.e., thermochemical process including gasification, liquefaction, and pyrolysis and biochemical process including fermentative pathways. The review will summarize the integration of biochemical and thermochemical conversion routes for the efficient production of biobutanol also their individual pros and cons will be discussed.KeywordsAgricultural wasteThermochemicalBiochemicalBiofuels
Dark fermentation (DF) is a promising process for mitigating environmental pollution and producing “green” H2. However, wider implementation and scaling of this technology is hampered by insufficient process efficiency. In this work, for the first time, the effect of innovative pretreatment of cheese whey (CW) in a vortex layer apparatus (VLA) on characteristics and DF of CW was studied. Pretreatment in VLA resulted in a heating of the CW, slight increase in pH, volatile fatty acids, iron, and reduction in fat, sugar, and chemical oxygen demand (COD). The biochemical hydrogen potential test and analysis of H2 production kinetics confirmed the significant potential of using VLA in enhancement of dark fermentative H2 production. The maximum potential H2 yield (202.4 mL H2/g COD or 3.4 mol H2/mol hexose) was obtained after pretreatment in VLA for 45 s and was 45.8% higher than the control. The maximum H2 production rate after 5 and 45 s of pretreatment was 256.5 and 237.2 mL H2/g COD/d, respectively, which is 8.06 and 7.46 times higher than in the control. The lag phase was more than halved as a function of the pretreatment time. The pretreatment time positively correlated with the total final concentration of Fe2+ and Fe3+ and negatively with the lag phase, indicating a positive effect of pretreatment in VLA on the start of H2 production.
The Brazilian Amazon is the largest biome of the country. Fruit production is one of the most important fields in Brazilian agriculture, and this industry produces a lot of waste with technological potentials. Secondary metabolites of vegetable components have shown antioxidant activity due to their bioactive nature. The extraction of bioactive chemicals is a critical stage in the process, and there are numerous traditional (solvent) and unconventional (ultrasound, supercritical extraction, etc.) approaches. Due to its advantages of environmental compatibility, high efficiency, and ease of processing, enzyme-assisted extraction is a viable alternative for the release of bioactive components from plant materials. Hydrolytic enzymes, such as cellulase and pectinase, are often employed to hydrolyze and dissolve cell wall elements and increase the release of intracellular content. Because these enzymes can degrade cell walls, they are ideal for extracting polyphenols from a variety of plant sources.
The depletion of fossil fuels and their environmental impact has motivated the research on alternative sources of energy. Lignocellulosic wastes are potential substrates for bioenergy and biochemicals production due to the carbohydrate content in the cell wall, which is composed of cellulose (40–80%), hemicellulose (10–40%), and lignin (5–25%). The sugar content of lignocellulosic biomass can be converted into fermentable monomeric sugars by physicochemical or enzymatic process. The hydrolysates produced during those processes have a high content of inhibitory substances such as phenolic and furanic compounds, i.e. syringaldehyde, vanillin, furfural and 5 hydroxymethylfurfural. Thus, the need of a detoxification pretreatment of hydrolysates before the fermentation process should be addressed. There are several detoxification processes reported such as overliming, ion exchange, membranes, use of enzymes or microorganisms and adsorption. Adsorption processes with nanomaterials have emerged as a promising technique for the removal of such inhibitors. This chapter shows the potential methods to detoxify hydrolysates, specifically using the adsorption process with potential adsorbents such as nanomaterials. Furthermore, inhibitors should not be just considered as obstacles for fermentation and hydrolysis, but could also be viewed as valuable chemicals for other industries which is also highlighted in this chapter.
Malaysia is the second-largest palm oil producer in the world. Nevertheless, limited research was found on using oil palm trunk (OPT) for glucose production. The objective of this study is to optimise the glucose production from OPT via simultaneous enzymatic process. Response Surface Methodology (RSM) was adopted to optimise the mass of OPT, stirring speed, and the hydrolysis time for glucose production. All the three parameters were significant with p < 0.001. Quadratic regression model well described the experiment data with predicted R² = 0.9700 and adjusted R² = 0.8828. Meanwhile, artificial neuron network (ANN) predicted the data with correlation R = 0.9612 and mean square error = 0.0021. The highest concentration of glucose, 30.1 mmol/L, was produced by using 30 g of OPT, 225 rpm for 16 h at 60 ℃. The prediction from both RSM and ANN are comparable and highly accurate.
Global energy demand is expected to increase by 48% in the next 20 years owing to the precipitous increase in the global population. Currently, 80% of the energy demand is met by fossil fuels. However, rapidly depleting fossil fuel reserves coupled with the negative environmental impacts has driven research toward biofuels. Biorefineries have recently attracted significant attention owing to their system dynamics where multiple products can be generated from a singular waste feedstock. Bioethanol, biohydrogen, bio-jet fuel, biomethane, and biodiesel have all been examined in different combinations in a biorefinery system, and have shown great potential. There are obstacles that inhibit the complete advancement of this technology such as the development of effective yet low-cost pretreatment strategies. Bioethanol has emerged as a valuable competitor to fossil-derived fuel owing to its compatibility with current infrastructure and its clean burning nature. Lignocellulosic biorefineries have the potential to contribute to a circular and green economy but more research is needed to propel this technology forward.
Biorefineries are mechanisms for adapting modern technologies toward the goals of recovery and aggregation of biomass value by creating processes that are renewable and environmentally friendly. The transformation of biorefineries to industrial realities is an area of intense study worldwide. Creation of more efficient systems requires hydrolysis processes that maximize the fractionation of biomass structure to produce high yields of several products. Scientific studies search to fill gaps in previously developed hydrolysis methods that may be coupled to biorefinery processes. There is great interest in advances in biomass enzymatic hydrolysis technologies that aim to convert complex compounds efficiently in innovative clean technology. This review will explore current scientific works that search integration of multiple processes through efficient hydrolysis methods for converting biomass, finally realizing the biorefinery concepts.
Lignocellulosic biomass can be used as a source for energy, fuel and valuable chemical production. From all available technologies, biological approaches have been recognized as the most environmentally friendly and sustainable ones. At the same time, high conversion costs, low efficiency and environmental issues still hinder the introduction of biological processes into industrial scale manufacturing. The aim of this study was to determine the most suitable enzyme cocktail recovery conditions from a biomass–fungal culture of the white-rot basidiomycete Irpex lacteus. Subsequent evaluation of the overall enzyme cocktail efficiency to release fermentable carbohydrates from biomass showed that prolonged fungal cultivation decreases the quality of the produced enzyme cocktail. At the same time, introduction of ultrasound pre-treatment during enzyme extraction improved the recovered enzyme cocktail efficiency in converting biomass to fermentable sugars, yielding up to 0.25 g of fermentable sugar per g dry hay biomass and up to 0.11 g per g dried straw or microalgae substrates. The results demonstrated that the production of lignocellulose-degrading enzymes from fungi is more sensitive than previously described, especially in terms of fungal growth, culture sterility and incubation conditions.
The study evaluates wood and non-wood lignocellulosic conversion into biofuels and renewable intermediate chemical products, on the basis of material efficiency, heat content in final products (lower heating value) and properties of fuel components, as related to their use, existing cars and storage. This type of conversion efficiency analysis can be viewed as a first step in biorefinery route optimization. The upgrading routes considered here include gasification, pyrolysis with subsequent gasification, ethanol, anaerobic acetic acid and ABE-fermentation, digestion and chemical conversion of sugars into fuel. The material efficiency is calculated on the basis of potential yields. In addition, the subsequent conversion of these intermediate products to fuel components through chemical reactions has been considered. Intermediate chemicals, such as ethylene, propylene, ethyl acetate and acetic acid, have also been analyzed. Chemical upgrading of sugars, acetic acid fermentation and gasification converted most of the raw material heat content in the products. The components with good properties containing some oxygen, such as butanol, methyltetrahydrofuran (MTHF) and ethers, appeared as promising from the viewpoint of both fuel properties and biomass conversion.
The use of gas fermentation for the production of low carbon biofuels such as ethanol or butanol from lignocellulosic biomass is an area currently undergoing intensive research and development, with the first commercial units expected to commence operation in the near future. In this process, biomass is first converted into carbon monoxide (CO) and hydrogen (H2)-rich synthesis gas (syngas) via gasification, and subsequently fermented to hydrocarbons by acetogenic bacteria. Several studies have been performed over the last few years to optimise both biomass gasification and syngas fermentation with significant progress being reported in both areas. While challenges associated with the scale-up and operation of this novel process remain, this strategy offers numerous advantages compared with established fermentation and purely thermochemical approaches to biofuel production in terms of feedstock flexibility and production cost. In recent times, metabolic engineering and synthetic biology techniques have been applied to gas fermenting organisms, paving the way for gases to be used as the feedstock for the commercial production of increasingly energy dense fuels and more valuable chemicals.
Growing concerns over the availability and cost of extracting fossil fuel resources have increased interest in renewable resources. Therefore, interest in producing numerous needed chemicals from renewable biomass resources has increased. The focus of this comprehensive review is on managing greenhouse gas emissions (GHG) in biorefinery production chains. To highlight the results of the content analysis an attempt is made to summarize the findings in a climate impact management matrix. In particular, three topics from the matrix are put forward: (1) uncertainties in assessing GHG emissions of feedstock cultivation, harvesting and logistics; (2) found GHG emissions in biorefinery chains; and (3) a short comparative analysis of two potential technologies to improve the GHG and carbon balance of biorefinery operations. In addition, benefits of lignocellulosic biomass, residuals, organic waste and algae are highlighted, sustainability issues of the field are discussed and research gaps are identified. Uncertainties in assessing the sustainability of biofuels supply chains support a more diversified renewable resource base and production of multiple chemicals in biorefinery chains.
Isobutanol is an important target for biorefinery research as a next-generation biofuel and a building block for commodity chemical production. Metabolically engineered microbial strains to produce isobutanol have been successfully developed by introducing the Ehrlich pathway into bacterial hosts. Isobutanol-producing baker's yeast (Saccharomyces cerevisiae) strains have been developed following the strategy with respect to its advantageous characteristics for cost-effective isobutanol production. However, the isobutanol yields and titers attained by the developed strains need to be further improved through engineering of S. cerevisiae metabolism.
Two strategies including eliminating competing pathways and resolving the cofactor imbalance were applied to improve isobutanol production in S. cerevisiae. Isobutanol production levels were increased in strains lacking genes encoding members of the pyruvate dehydrogenase complex such as LPD1, indicating that the pyruvate supply for isobutanol biosynthesis is competing with acetyl-CoA biosynthesis in mitochondria. Isobutanol production was increased by overexpression of enzymes responsible for transhydrogenase-like shunts such as pyruvate carboxylase, malate dehydrogenase, and malic enzyme. The integration of a single gene deletion lpd1Delta and the activation of the transhydrogenase-like shunt further increased isobutanol levels. In a batch fermentation test at the 50-mL scale from 100 g/L glucose using the integrated strains, the isobutanol titer reached 1.62 +/- 0.11 g/L and 1.61 +/- 0.03 g/L at 24 h after the start of fermentation, which corresponds to the yield at 0.016 +/- 0.001 g/g glucose consumed and 0.016 +/- 0.0003 g/g glucose consumed, respectively.
These results demonstrate that downregulation of competing pathways and metabolic functions for resolving the cofactor imbalance are promising strategies to construct S. cerevisiae strains that effectively produce isobutanol.
Agricultural biomass as an energy resource has several environmental and economical advantages and has potential to substantially contribute to present days’ fuel demands. Currently, thermochemical processes for agricultural biomass to energy transformation seem promising and feasible. The relative advantage of thermochemical conversion over others is due to higher productivity and compatibility with existing infrastructure facilities. However, the majority of these processes are still under development phase and trying to secure a market share due to various challenges, right from suitable infrastructure, raw material, technical limitations, government policies, and social acceptance. The knowledge at hand suggests that biomass can become a sustainable and major contributor to the current energy demands, if research and development are encouraged in the field of thermochemical conversion for various agricultural biomass types. This paper intends to explore the physical and chemical characteristics of biofuel substitutes of fossil fuels, potential biomass sources, and process parameters for thermochemical conversion.
The effect of gross fiber characteristics on enzyme accessibility and hydrolysis of Douglas fir kraft pulp substrates was investigated. The average fiber size and coarseness of the substrate had a significant effect on the enzyme adsorption capacity. This was primarily due to the increased specific surface area of small fibers and fines. The observed adsorption capacities were in agreement with the hydrolysis rates and yields because the substrates with the lower average fiber size were hydrolyzed both at a faster rate and more completely. The observed changes in fiber-length distribution and fiber coarseness suggested that the effect of fiber size was most influential during the initial stages of hydrolysis. The small fibers and fines present in heterogeneous, lignocellulosic substrates were hydrolyzed rapidly, yielding a high initial rate of hydrolysis.
Sheer enormity of lignocellulosics makes them potential feedstock for biofuel production but, their conversion into fermentable sugars is a major hurdle. They have to be pretreated physically, chemically, or biologically to be used by fermenting organisms for production of ethanol. Each lignocellulosic substrate is a complex mix of cellulose, hemicellulose and lignin, bound in a matrix. While cellulose and hemicellulose yield fermentable sugars, lignin is the most recalcitrant polymer, consisting of phenyl-propanoid units. Many microorganisms in nature are able to attack and degrade lignin, thus making access to cellulose easy. Such organisms are abundantly found in forest leaf litter/composts and especially include the wood rotting fungi, actinomycetes and bacteria. These microorganisms possess enzyme systems to attack, depolymerize and degrade the polymers in lignocellulosic substrates. Current pretreatment research is targeted towards developing processes which are mild, economical and environment friendly facilitating subsequent saccharification of cellulose and its fermentation to ethanol. Besides being the critical step, pretreatment is also cost intensive. Biological treatments with white rot fungi and Streptomyces have been studied for delignification of pulp, increasing digestibility of lignocellulosics for animal feed and for bioremediation of paper mill effluents. Such lignocellulolytic organisms can prove extremely useful in production of bioethanol when used for removal of lignin from lignocellulosic substrate and also for cellulase production. Our studies on treatment of hardwood and softwood residues with Streptomyces griseus isolated from leaf litter showed that it enhanced the mild alkaline solubilisation of lignins and also produced high levels of the cellulase complex when growing on wood substrates. Lignin loss (Klason lignin) observed was 10.5 and 23.5% in case of soft wood and hard wood, respectively. Thus, biological pretreatment process for lignocellulosic substrate using lignolytic organisms such as actinomycetes and white rot fungi can be developed for facilitating efficient enzymatic digestibility of cellulose.
Background
Succinic acid is one of the key platform chemicals which can be produced via biotechnology process instead of petrochemical process. Biomass derived bio-oil have been investigated intensively as an alternative of diesel and gasoline fuels. Bio-oil could be fractionized into organic phase and aqueous phase parts. The organic phase bio-oil can be easily upgraded to transport fuel. The aqueous phase bio-oil (AP-bio-oil) is of low value. There is no report for its usage or upgrading via biological methods. In this paper, the use of AP-bio-oil for the production of succinic acid was investigated.
Results
The transgenic E. coli strain could grow in modified M9 medium containing 20 v/v% AP-bio-oil with an increase in OD from 0.25 to 1.09. And 0.38 g/L succinic acid was produced. With the presence of 4 g/L glucose in the medium, succinic acid concentration increased from 1.4 to 2.4 g/L by addition of 20 v/v% AP-bio-oil. When enzymatic hydrolysate of corn stover was used as carbon source, 10.3 g/L succinic acid was produced. The obtained succinic acid concentration increased to 11.5 g/L when 12.5 v/v% AP-bio-oil was added. However, it decreased to 8 g/L when 50 v/v% AP-bio-oil was added. GC-MS analysis revealed that some low molecular carbon compounds in the AP-bio-oil were utilized by E. coli.
Conclusions
The results indicate that AP-bio-oil can be used by E. coli for cell growth and succinic acid production.
Bioconversion of lignocellulose by microbial fermentation is typically preceded by an acidic thermochemical pretreatment step designed to facilitate enzymatic hydrolysis of cellulose. Substances formed during the pretreatment of the lignocellulosic feedstock inhibit enzymatic hydrolysis as well as microbial fermentation steps. This review focuses on inhibitors from lignocellulosic feedstocks and how conditioning of slurries and hydrolysates can be used to alleviate inhibition problems. Novel developments in the area include chemical in-situ detoxification by using reducing agents, and methods that improve the performance of both enzymatic and microbial biocatalysts.
Great disparities exist between organisms with regard to the relative ease of chromosomal mutagenesis and manipulation. In Chromosomal Mutagenesis, a team of experts provide a variety of chromosomal manipulation techniques, including insertional gene disruptions, gene knockouts, stimulated homologous recombination techniques and other novel tools, for both prokaryotic and eukaryotic organisms, and attempt to expand the genetic toolbox beyond model organisms. Following the format of the highly successful Methods in Molecular Biology™ format, each chapter offers step-by-step laboratory instructions, lists of the necessary equipment and reagents, and tips on troubleshooting and avoiding known pitfalls.
Comprehensive and cutting-edge, Chomosomal Mutagenesis covers state-of-the-art techniques that are staged to expand, if not revolutionize, genetic analysis in the long neglected and relevant cell types.
Different strategies to overcome inhibitor problems in the production of bio-ethanol from lignocellulose hydrolyzates with the yeast were examined. The strategies included detoxification prior to fermentation and in situ detoxification of furfural. Fractions collected from strong anion exchangers with styrene-based matrices showed the best fermentability and the lowest inhibitor concentrations. The results show that during fermentative and respiratory growth, the maximum specific conversion rate of furfural in dynamic experiments was significantly higher than the rate obtained in the steady-state experiments.
Important aspects of ethanol production from undetoxified dilute acid liginocellulose hydrolysate, are discussed with emphasis on the use of Saccharomyces cerevisiae (Baker's yeast) as the biocatalyst. Saccharomyces hydrolysate ATCC 96581 distinguishes itself as a possible candidate for a commercial process, since it has high tolerance to inhibiting medium. It can function in a satisfactory way under relatively stressful conditions. In addition, extremely low specific growth rates could be combined with relatively high ethanol yields for extended periods of time.
Some topics discussed are the following: a historical perspective; the current status and the future outlook; raw material selection and preparation; fermentation; alcohol recovery; fermentation waste treatment and by-product recovery; integrated alcohol plant design and economics; ethanol market history; and conclusions on the outlook for fermentative ethanol.
Ethanol production from lignocellulosic materials is a major global task in producing liquid fuel by sustainable processes. The structure of the lignocellulose is usually opened by dilute-acid hydrolysis or steam explosion in a pretreatment step, while the resulting cellulose and hemicelluloses can be cleaved to the monomers (sugars) by acid or enzymatic hydrolyses. The hydrolyzates are then fermented to ethanol by using baker's yeast or other microorganisms. The acid hydrolysis suffers from a number of inhibitory by-products including furans, phenolic compounds and carboxylic acids, whereas the enzymatic one is still expensive and slow. Very good progress has been made within the last two decades on development of pretreatments, hydrolyses, fermentation techniques and recombinant microorganisms. These advances are briefly reviewed here.
Physical pretreatment of woody biomass or wood size reduction is a prerequisite step for further chemical or biochemical processing in forest biorefinery. However, wood size reduction is very energy intensive which differentiates woody biomass from herbaceous biomass for biorefinery. This chapter discusses several critical issues related to wood size reduction: (1) factors affecting mechanical energy consumption and the post-pretreatment wood size-reduction approach to significantly reduce energy consumption, (2) biomass substrate specific surface area for substrate size characterization and the wet imaging technique for woody substrate size/specific surface measurements, (3) the effect of biomass substrate size/specific surface on enzymatic cellulose hydrolysis, and (4) the concept of substrate "surface productivity" for the determination of optimal degree of size reduction and energy efficient wood size reduction.
The application of biotechnology to the production of commodity products (fuels, chemicals, and materials) offering benefits in terms of sustainable resource supply and environmental quality is an emergent area of intellectual endeavor and industrial practice with great promise. Such “biocommodity engineering” is distinct from biotechnology motivated by health care at multiple levels, including economic driving forces, the importance of feedstocks and cost-motivated process engineering, and the scale of application. Plant biomass represents both the dominant foreseeable source of feedstocks for biotechnological processes as well as the only foreseeable sustainable source of organic fuels, chemicals, and materials. A variety of forms of biomass, notably many cellulosic feedstocks, are potentially available at a large scale and are cost-competitive with low-cost petroleum whether considered on a mass or energy basis, and in terms of price defined on a purchase or net basis for both current and projected mature technology, and on a transfer basis for mature technology. Thus the central, and we believe surmountable, impediment to more widespread application of biocommodity engineering is the general absence of low-cost processing technology. Technological and research challenges associated with converting plant biomass into commodity products are considered relative to overcoming the recalcitrance of cellulosic biomass (converting cellulosic biomass into reactive intermediates) and product diversification (converting reactive intermediates into useful products). Advances are needed in pretreatment technology to make cellulosic materials accessible to enzymatic hydrolysis, with increased attention to the fundamental chemistry operative in pretreatment processes likely to accelerate progress. Important biotechnological challenges related to the utilization of cellulosic biomass include developing cellulase enzymes and microorganisms to produce them, fermentation of xylose and other nonglucose sugars, and “consolidated bioprocessing” in which cellulase production, cellulose hydrolysis, and fermentation of soluble carbohydrates to desired products occur in a single process step. With respect to product diversification, a distinction is made between replacement of a fossil resource-derived chemical with a biomass-derived chemical of identical composition and substitution of a biomass-derived chemical with equivalent functional characteristics but distinct composition. The substitution strategy involves larger transition issues but is seen as more promising in the long term. Metabolic engineering pursuant to the production of biocommodity products requires host organisms with properties such as the ability to use low-cost substrates, high product yield, competitive fitness, and robustness in industrial environments. In many cases, it is likely to be more successful to engineer a desired pathway into an organism having useful industrial properties rather than trying to engineer such often multi-gene properties into host organisms that do not have them naturally. Identification of host organisms with useful industrial properties and development of genetic systems for these organisms is a research challenge distinctive to biocommodity engineering. Chemical catalysis and separations technologies have important roles to play in downstream processing of biocommodity products and involve a distinctive set of challenges relative to petrochemical processing. At its current nascent state of development, the definition and advancement of the biocommodity field can benefit from integration at multiple levels. These include technical issues associated with integrating unit operations with each other, integrating production of individual products into a multi-product biorefinery, and integrating biorefineries into the broader resource, economic, and environmental systems in which they function. We anticipate that coproduction of multiple products, for example, production of fuels, chemicals, power, and/or feed, is likely to be essential for economic viability. Lifecycle analysis is necessary to verify the sustainability and environmental quality benefits of a particular biocommodity product or process. We see biocommodity engineering as a legitimate focus for graduate study, which is responsive to an established personnel demand in an industry that is expected to grow in the future. Graduate study in biocommodity engineering is supported by a distinctive blend of intellectual elements, including biotechnology, process engineering, and resource and environmental systems.
Natural molecular biomass plays an important role in the field of renewable polymers, as they can be directly used or derivatized as monomers for controlled polymerization, in a way similar to many petroleum-derived monomers. We deliver this perspective primarily based on a monomer approach. Biomass-derived monomers are separated into four major categories according to their natural resource origins: (1) oxygen-rich monomers including carboxylic acids (lactic acid, succinic acid, itaconic acid, and levulinic acid) and furan; (2) hydrocarbon-rich monomers including vegetable oils, fatty acids, terpenes, terpenoids and resin acids; (3) hydrocarbon monomers (bio-olefins); and (4) non-hydrocarbon monomers (carbon dioxide). A variety of emerging synthetic tools (controlled polymerization and click chemistry) are particularly summarized. An overview on future opportunities and challenges, which are critical to promote biorefinery in the production of renewable chemicals and polymers, is given.
The chemical and physical changes of lignocellulosic biomass after subjecting to various pretreatment conditions were investigated in this current work. Subsequently, the effects of biomass changes on digestibility of cellulose to fermentable sugar (glucose) by enzyme were studied. Oil palm frond (OPF), the chosen biomass in this study was pretreated using ionic liquid (IL) 1-butyl-3-methylimidazolium chloride ([BMIM]Cl) at different pretreatment conditions before subjected to analysis and subsequent enzymatic hydrolysis process. The pretreatment variables studied in this work are temperature, retention time and solid loading. Results showed that OPF experienced changes in lignin, cellulose and hemicellulose content after pretreatment due to dissolution as well as depolymerization process occurring during pretreatment. In addition to that, the recalcitrance of lignocellulosic biomass was effectively disrupted by ionic liquid pretreatment at various pretreatment conditions as cellulose digestibility of OPF was largely enhanced after pretreatment.
Hydrogenase activity plays an important role in the fermentation of biomass-generated syngas (containing CO, CO2, and H2) to obtain ethanol and other biofuels. One process efficiency issue for producing biofuels from syngas fermentation is the ability of key cellular enzymes to produce reducing equivalents from syngas. For microbes using the Wood–Ljungdahl pathway, inhibition of the hydrogenase enzyme would decrease reducing equivalent production from H2, thus potentially reducing carbon conversion efficiency and biofuel production. During biomass gasification to produce syngas, several impurities are generated. These impurities, such as ammonia (NH3), can potentially impact the fermentation process. In this work, it was shown that NH3 rapidly converts to ammonium ion (NH4+) following exposure of fermentation media to NH3. The accumulated NH4+ also inhibited hydrogenase activity and cell growth. A kinetic model for hydrogenase activity that included inhibition effects from NH4+ was developed. Model parameters included KH2KH2 (Michaelis–Menten constant) and KNH4+ (the inhibition constant for NH4+). Experimental results showed that NH4+ is a non-competitive inhibitor for hydrogenase activity with KNH4+ of (649 ± 35) mol m−3. As part of the work to distinguish the unique aspect of NH4+ inhibition, additional work showed that potassium and phosphate ions had no effect on hydrogenase activity. Since NH4+ can easily be accumulated in fermentation media and transport across the cell membrane, it is necessary to remove NH3 impurity from raw syngas to minimize the reduction in hydrogenase activity.
Second-generation ethanol production from various lignocellulosic materials based on enzymatic hydrolysis of cellulose has moved from research in lab scale to pilot- and demo scale but has not yet reached commercial scale. One of the crucial process steps is the pretreatment of the biomass, which has as primary aim to make the biomass accessible to enzymatic attack, as it has a large impact on all the other steps in the process. Several pretreatment methods have been developed, comprising methods working at low pH, i.e., acid based, at medium pH (without addition of catalysts), or at high pH, i.e., with a base as catalyst. Many methods result in high sugar yields, above 90% of theoretical for agricultural residues while more recalcitrant materials like hardwood, and especially softwood, require dilute-acid pretreatment to reach high sugar yields. However, most studies on pretreatment have been assessed by enzymatic hydrolysis at low solids content and high enzyme dosages. The various pretreatment methods need in the future to be reassessed at more industrial-like conditions considering the whole integrated process taking into consideration the influence on all process steps. In this review, various pretreatment methods are discussed and how assessment should be performed to reach optimal conditions.
Pretreatment of sweet sorghum bagasse (SSB) through microwave radiation was evaluated at four lime doses (0, 0.1, 0.15, and 0.2 g/g SSB), two water content of 10 or 20 ml/g SSB, and three exposure times as 2, 4, and 6 min. Optimal pretreatment condition was identified as 0.1 g lime and 10 ml water per g SSB in 4 min. Under this condition, sugar yield of 32.2 g/100 g SSB (equivalent to 52.6% of maximal potential sugars) was achieved. With the same water content and exposure time, but without lime, sugar yield of 39.8 g/100 g SSB (equivalent to 65.1% of maximal total sugars) was observed. The higher sugar recovery without lime was mainly due to high sugar release during pretreatment. But with lime, sugar degradation took place, which resulted in less sugar yield though lime did make cellulose more accessible to enzymes as evidenced by higher percentage of increase of total reducing sugars during enzymatic hydrolysis. Results from this study were strongly supported by FTIR and SEM images. Overall, in a very short time and simple setup, microwave radiation shows great promise to be a leading pretreatment technique for SSB.
The pretreatment of softwood with sulfuric acid impregnation in the production of ethanol, based on enzymatic hydrolysis, has been investigated. The parameters investigated were: H2SO4 concentration (0.5 – 4.4% w/w liquid), temperature (180 – 240°C), and residence time (1-20 minutes). The combined severity (log Ro-pH) was used to combine the parameters into a single reaction ordinate. The highest yields of fermentable sugars, i.e., glucose and mannose, were obtained at a combined severity of 3. At this severity, however, the fermentability declined and the ethanol yield decreased. In a comparison with previous results, SO2 impregnation was found to be preferable, since it resulted in approximately the same sugar yields, but better fermentability.
Bioconversion of renewable lignocellulosic biomass to biofuel and value added products are globally gaining significant prominence. Market forces demonstrate a drive towards products benign to natural environment increasing the importance of renewable materials. The development of second generation bioethanol from lignocellulosic biomass serves many advantages from both energy and environmental point of views. Biomass an inexpensive feedstock considered sustainable and renewable, is an option with the potential to replace a wide diversity of fossil based products within the energy sector; heat, power, fuels, materials and chemicals. Lignocellulose is a major structural component of woody and non-woody plants and consists of cellulose, hemicellulose and lignin. The effective utilization of all the three components would play a significant role in the economic viability of cellulosic ethanol. Biomass conversion process involves five major steps, choice of suitable biomass, effective pretreatment, production of saccharolytic enzymes-cellulases and hemicellulases, fermentation of hexoses and pentoses and downstream processing. Within the context of production of fuels from biomass, pretreatment has come to denote processes by which cellulosic biomass is made amenable to the action of hydrolytic enzymes. The limited effectiveness of current enzymatic process on lignocellulose is thought to be due to the relative difficulties in pretreating the feedstocks. The present review is a comprehensive state of the art describing the advancement in recent pretreaments, metabolic engineering approaches with special emphasis on the latest developments in consolidated biomass processing, current global scenario of bioethanol pilot plants and biorefinery concept for the production of biofuels and bioproducts.
An immobilized cell reactor for producing acetone butanol ethanol (ABE or solvents) when using Clostridium beijerinckii BA101 demonstrated reactor productivities of 3.49, 5.99 and 16.13 gl−1h−1 at dilution rates of 0.29, 1.00 and 2.00 h−1, respectively. These dilution rates are based on the total volume of the reactor. The reactor was scaled up successfully as these productivities are close to those achieved in small reactor. Dilution rate based on the void volume increased reactor productivity from 16.13 to 34.76 g I−1 h−1. The packed bed reactor blocked after a period of 2302 h of continuous operation due to excessive cell growth. Nutrient limitation was applied as a means of reducing cell growth while keeping the reactor productive; however, this approach was not successful. It was found that most of the cell growth in adsorbed cell bioreactors occurs on the surface of the cell support. The free cell continuous reactor demonstrated much lower reactor productivity. In the immobilized cell reactor only a fraction of the biomass was in the solventogenic state. A significant amount of biomass was present as inactive biomass (spores). It is suggested that sporulation be blocked in C. beijerinckii BA101 in order for reactors to be more productive. It is postulated that once such a culture is developed nutrient limitation should be attempted to avoid reactor blockage due to excessive cell growth.
Using fermentation to replace chemical processes in the production of acetone and butanol depends largely on the availability of inexpensive and abundant raw materials and efficient conversion of these materials to solvents. In this study solvent production of Clostridium acetobutylicum ATCC824 from nano-membrane concentrated hemicellulosic hydrolysate was investigated. Alkali pretreatment methods were applied to improve fermentability of nano-membrane concentrated hemicellulosic hydrolysate and solvent production by ATCC824. Results demonstrated that though nanofiltration could remove nearly all small molecular organic acids (acetic acid, formic acid), furfural and HMF, the resulting hydrolysate found to be still inhibiting solvent production of C. acetobutylicum. Solid particles separated from filtering hydrolysate were found not toxic to cells when xylose or glucose was used as carbon resource. Overliming treatment can significantly improve the ultimate butanol concentration to 7 g l−1 from 0.8 g l−1. Providing cells with more carbon source at the final stage of fermentation was found to have no impact on butanol production, but acetic acid and butyric acid production were found to increase significantly. The reasons leading to low solvent yield at later fermentation stages is not cell degeneration, but the toxicity of butanol and inhibitors remaining in the hydrolysate.
The synergistic effect of pre-impregnation by sulphuric acid and steam explosion has been investigated. Sugar recovery by water extraction and cellulose digestibility by enzymes have been considered. The acid diffusion inside a representative particle, having thickness of 0.7mm, has been modelled on the basis of available models and diffusion coefficients. The experiments of acid impregnation have pointed out a plateau of the acid uptake after 10min corresponding to an acid adsorption of 22g/kg of dry stover. An experiment of acid desorption from the pre-impregnated biomass particles to a new bulk of pure water (reverse diffusion), has confirmed that only a small fraction of the uptaken acid remained free, while most has been consumed by the substrate. Nine conditions have been tested for the steam explosion treatment selecting the temperature of 180, 190, 200°C and sulphuric acid loadings of 0, 1.5, 3wt.%. The maximum sugar recovery by water extraction is produced by a SE treatment of 190°C for 5min and an acid loading of 1.5wt.%; at these conditions 25% of the sugars in the feedstock can be recovered as monomers or oligomers. The acid has greatly improved the sugar solubility, e.g. at 180°C the sugar recovery has been only 1.5% without acid, while by using 3wt.% of acid the sugar recovery has increased to 16.8%. Also the cellulose digestibility has been improved by the acid pre-impregnation, after 48h of digestion the yield of glucose reached 93% of the theoretical by using the substrate that was pre-impregnated with 3wt.% of acid an treated at 190°C. The high acid loading has also been required to achieve the best recovery of glucose (85% of the initial glucan) as sum of water extraction and 48h hydrolysis.
The influence of the severity of dilute sulfuric acid hydrolysis of spruce (softwood) on sugar yield and on the fermentability of the hydrolysate by Saccharomyces cerevisiae (Baker’s yeast) was investigated. Fermentability was assessed as the ethanol yield on fermentable sugars (mannose and glucose) and the mean volumetric productivity (4 h). The hydrolysis conditions, residence time, temperature, and sulfuric acid concentration were treated as a single parameter, combined severity (CS). When the CS of the hydrolysis conditions increased, the yield of fermentable sugars increased to a maximum between CS 2.0–2.7 for mannose, and 3.0–3.4 for glucose above which it decreased. The decrease in the yield of monosaccharides coincided with the maximum concentrations of furfural and 5-hydroxymethylfurfural (5-HMF). With the further increase in CS, the concentrations of furfural and 5-HMF decreased while the formation of formic acid and levulinic acid increased. The yield of ethanol decreased at approximately CS 3; however, the volumetric productivity decreased at lower CS.
The effect of acetic acid, formic acid, levulinic acid, furfural, and 5-HMF on fermentability was assayed in model fermentations. Ethanol yield and volumetric productivity decreased with increasing concentrations of acetic acid, formic acid, and levulinic acid. Furfural and 5-HMF decreased the volumetric productivity but did not influence the final yield of ethanol. The decrease in volumetric productivity was more pronounced when 5-HMF was added to the fermentation, and this compound was depleted at a lower rate than furfural. The inhibition observed in hydrolysates produced in higher CS could not be fully explained by the effect of the by-products furfural, 5-HMF, acetic acid, formic acid, and levulinic acid.
Commercially available zeolites (CBV28014, CBV901) with a high Si/Al ratio were tested as adsorbents to recover 1-butanol from aqueous solutions such as acetone–butanol–ethanol (ABE) fermentation broth. It was found that these zeolites can quickly and almost completely adsorb 1-butanol from aqueous solutions containing ∼1wt% of 1-butanol. The binding capacity of the zeolites appeared to be around 0.12g 1-butanol/g zeolite, and remained constant till equilibrium concentration as low as 0.04wt% 1-butanol in water. Extrudates were prepared and tested in a column set-up to get an impression of the suitability of these zeolites for industrial applications. Extrudates of 80% zeolite and 20% alumina binder with 16–24 mesh (0.7–1.0mm) size showed the best adsorption results in a packed bed column with up-flow of ABE broth. The adsorbent loading at 10% breakthrough was calculated to be 0.085g 1-butanol/g zeolite (9.3min residence time). A subsequent temperature swing leads to desorption. By choosing the temperature program carefully, it was possible to separate the water/ethanol/acetone and 1-butanol fractions. The resulting 1-butanol concentration in the 1-butanol fraction was 84.3wt% and thus a concentration factor of 65 was achieved in one step, which is a higher value compared to other isolation techniques. Only 80% of adsorbed 1-butanol could be recovered, the remainder could only be desorbed at higher temperatures as butene. However, this should not be a problem in an industrial process as all stronger binding, catalytic sites will be blocked after the first adsorption/desorption round. A mathematical model was developed to simulate the breakthrough data and a mass transfer coefficient (kpa) of 0.052min−1 was obtained. Comparison of simulated kpa for different sizes of extrudates clearly indicated that the adsorption rate is determined by solid phase diffusion.
This paper presents experimental results on the gasification of several wastes using high temperature steam. Four cellulose-rich surrogate wastes (paper, cardboard, and wood pellets) were gasified with preheated steam at different temperatures in the range of 700 to 1100°C. Gasification is an efficient method for clean conversion of waste to hydrogen rich gas with moderate heating value product gas stream containing negligible soot and tars. Although the gasification is a relatively old technique, it has not been examined at ultra high gasification temperatures. Paper, cardboard and other cellulose-rich wastes represent their considerable shares in Municipal Solid Wastes. A basic chemistry of gasification and main reactions propelling the process are presented. The experimental facility used provided pure steam or steam-oxygen mixtures from the combustion of hydrogen and oxygen at very high temperatures. The role of feedstock property (ultimate analysis, chemical formulas, steam/feedstock ratio) and gasifying agent property (flow rate, temperatures) have been determined. The results obtained have been compared with the equilibrium calculations using Equil software - part of Chemkin software. The experimental results for hydrogen and carbon monoxide yield are compared with the numerical simulation results. The results reveal information on the operating parameters for high hydrogen yield from cellulose-rich wastes. The results show high hydrogen yield of over 36% at 1000°C gasification temperatures using paper. At higher gasification temperatures the yield of hydrogen decreased due to its dissociation. For other biomass wastes, only 24% hydrogen was obtained at 900°C. The heating value of the gases produced was high at higher gasification temperatures for all wastes. Although the experimental results showed good comparison with calculations, the experimentally determined magnitude of hydrogen and CO obtained was smaller than the calculation results.
The direct conversion of synthesis gas to ethanol and the indirect reaction of synthesis gas with methanol to yield ethanol (homologation) have been studied as possible alternative processes for the production of ethanol from coal. Experimental evidence indicates an unusually general catalytic method for methanol homologation occurring in methanol solutions of amines at synthesis gas pressures near 300 atm and temperatures near 200°C. Significantly, methanol is homologated while ethanol is essentially unaffected. In each case, carbon dioxide is the oxygenated byproduct, and ethanol is formed. Since observation of this type of reaction using Fe(CO)â catalyst, we have become aware of the method's generality extending to several diverse metal centers. This study represents an accumulated detailed knowledge of the mechanism for the iron carbonyl system. More important, however, a clear picture of a common pathway of a number of the complexes has emerged. In general, all of the catalytic reactions use methyl-ammonium ions as methyl carriers, transition-metal complex anions as nucleophilic methyl acceptors, and catalytic decomposition of formic acid to remove protons generated in hydrogen activation steps.
Pervaporative separation of n-butanol from dilute aqueous solutions (<0.5 wt%) using a silicalite-filled poly(dimethyl siloxane) composite membrane was investigated. The effects of operating conditions (e.g., feed composition, temperature) on the permeation flux, separation factor and pervaporation separation index were evaluated. It was shown that at a given temperature, water flux increased almost linearly with an increase in feed butanol concentration, whereas the butanol flux increased in a concave fashion due to silicalite fillers that have a strong affinity to butanol molecules. Consequently, the permeate butanol concentration initially increased and then gradually leveled off when the feed butanol concentration was high enough, and the leveling off started to occur at a lower butanol concentration at a higher temperature. The temperature dependence of permeation flux followed a typical Arrhenius relation, and a variation in temperature would increase or decrease the membrane selectivity, depending on feed butanol concentration. These results are especially important for potential use of the membrane for in situ butanol extraction from fermentation where butanol becomes inhibitory at a low concentration of 4-6 g/L.
Poly(1-trimethylsilyl-1-propyne) (PTMSP) was synthesized using a TaCl5–Al(i-Bu)3 catalysis system. Pervaporation and sorption of n-butanol–water mixtures were studied, and the peculiarities of water and butanol co-permeation are discussed. The strong dependence of water partial flux (with a minimum at 1wt.% butanol in feed) on butanol concentration in feed was observed. S-shaped isotherms of butanol and total sorption were found for PTMSP in 0–1wt.% concentration range. It appears that blocking of PTMSP nanopores by high sorbing organic molecules controls the pervaporation of butanol from dilute aqueous solutions. Data are discussed in regard with PTMSP morphology.
Saccharomyces cerevisiae is an important model to understand the eukaryotic cells control mechanisms. In this Letter, an approach based on in vivo13C NMR and mathematical modelling was presented to develop a basis for a deeper understanding of eukaryotic responses to environmental stresses. Despite the few metabolites included, the model describes correctly the dynamical behaviour of glucose degradation and ethanol production, providing a qualitative and quantitative description of the response of S. cerevisiae metabolism to stressful concentrations of ethanol. The data and the model highlight that an exogenous stress is able to influence the cellular activity and the ethanol production rate constant.
This article reviews developments in the technology for ethanol produc- tion from lignocellulosic materials by "enzymatic" processes. Several methods of pretreatment of lignocelluloses are discussed, where the crystalline structure of lignocelluloses is opened up, making them more accessible to the cellulase enzymes. The characteristics of these enzymes and important factors in enzymatic hydrolysis of the cellulose and hemicellulose to cellobiose, glucose, and other sugars are discussed. Different strategies are then described for enzymatic hydrolysis and fermentation, including separate enzymatic hydrolysis and fermentation (SHF), simultaneous saccharification and fermentation (SSF), non-isothermal simultaneous saccharification and fermentation (NSSF), simultaneous saccharification and co-fermentation (SSCF), and consolidated bioprocessing (CBP). Furthermore, the by-products in ethanol from lignocellulosic materials, wastewater treatment, commercial status, and energy production and integration are reviewed.
CSTR and packed-column models are presented for the biological production of liquid and gaseous fuels from coal synthesis gas.
Alcohols can be used directly as fuels and fuel additives or as intermediates to form high octane or high cetane ethers. Catalysts have been improved to synthesize the higher alcohols, especially isobutanol, from coal- or natural gas-derived H2/CO synthesis gas, and reaction engineering approaches are being investigated to further increase the activities and selectivities of the reactions forming the higher alcohols. These approaches include (a) using a dual catalyst bed reactor for gas phase conversions and (b) employing a slurry phase reaction system for increasing the reaction rate of the exothermic synthesis reactions. These developments have led to higher alcohol productivities. For example, with double bed Cs/Cu/ZnO/Cr2O3 catalysts, productivities of isobutanol and total alcohols as high as 202 and 947g/kg catalyst/h, respectively, have been achieved. However, declining petroleum prices over the last three years have pushed the economic break-even point to even greater productivity levels of isobutanol and of a mixture of the higher alcohols. It is shown that alcohols and certain ethers have desirable properties as octane enhancers, while other ethers could be used as additives to enhance the cetane number of diesel fuel.
The presumed high cost of cellulase enzymes is seen as a major economic hurdle in ethanol fuel production from lignocellulosic biomass. One way to reduce enzyme cost is to use much less enzyme per unit of biomass hydrolysed. The ammonia fiber explosion (AFEX) process produces a highly reactive biomass but the relationship between AFEX treatment conditions, enzyme loadings and hydrolysis yields has never been thoroughly explored. We report here the effects of AFEX treatment on the initial rates and 24 h hydrolysis yields for several crop residues and lignocellulosic materials using low enzyme levels (1–5 IU/g dry biomass). Near theoretical sugar yields are obtained for some AFEX treatment conditions at 1 IU/g for corn fiber and 5 IU/g for switchgrass. Implications of the experimental results are discussed.
A method and apparatus for converting waste gases from industrial processes such as oil refining, carbon black, coke, ammonia, and methanol production, into useful products is disclosed. The method includes introducing the waste gases into a bioreactor where they are fermented to various product, such as organic acids, alcohols H.sub.2, SCP, and salts of organic acids by anaerobic bacteria within the bioreactor. These valuable end products are then recovered, separated and purified.
A method for isolating succinic acid producing bacteria is provided comprising increasing the biomass of an organism which lacks the ability to catabolize pyruvate, and then subjecting the biomass to glucose-rich medium in an anaerobic environment to enable pyruvate-catabolizing mutants to grow. The invention also provides for a mutant that produces high amounts of succinic acid, which as been derived from a parent which lacked the genes for pyruvate formate lyase and lactate dehydrogenase, and which belongs to the E.coli Group of Bacteria.
This chapter summarizes the major inhibitors in different ethanol processes, as well as different methods to avoid the inhibition effects or remove the inhibitors. Inhibition in ethanol production may be caused by many factors, including the high concentrations of sugars, ethanol, and salts, as well as the raw materials such as limonene in citrus wastes, or the materials formed in the pretreatment/hydrolysis, such as carboxylic acids, furans, and phenolic compounds. The inhibition effects can be reduced or removed by choosing a suitable level of the components in the substrates and choosing the correct methods and optimizing the pretreatment and hydrolysis steps to reduce the inhibitors, or doing a detoxification prior to the fermentation. However, if the inhibitors enter the bioreactors, choosing the right strategy for the fermentation mode of operation, a tolerant organism, or an organism that can convert the inhibitors might be a suitable method.
