Bioconversion of sugarcane biomass into ethanol: an overview about composition, pretreatment methods, detoxification of hydrolysates, enzymatic saccharification, and ethanol fermentation.

Bioconversion of lignocellulosic biomass (agro residues, grasses, wood, weed, dedicated energy crops and others) into biofuels and other value-added products offers numerous geopolitical, environmental, and strategic benefits. Lignocellulosic biomass (LB) is the most abundant renewable organic resources (~200 billion tons annually) on earth that are readily available for conversion to biofuels and other value-added products (industrial enzymes, organic acids, pharmaceuticals, commodity chemicals, and food/feed). However, they have not yet been tapped for the commercial production of these products. The last three decades witnessed the success made in research and development for the conversion of LB into biofuels and other commercially viable products. Despite the success achieved in the laboratory, there are several challenges for the successful bioconversion of lignocellulosic substrates into value-added products at commercial scale. The future of lignocellulosics conversion is expected to lie in improvement in pretreatment technologies, cellulolytic enzymes producing microorganisms, fullest exploitation of biomass components, and process integration. Further, advancement in system-biology-based “OMICS” approaches may provide new breakthroughs for the development of biocatalysts/enzyme titers for the cost effective production of commodity chemicals and fuels from biomass. This special issue presents a diverse range of experimental advancements on biomass pretreatment, enzymatic saccharification, production of cellulosic biofuels, polyhydroxyalkanoates (PHA), polyhydroxybutyrate (PHB), and lovastatin and blends of polyacrylonitrile (PAN) and lignin. Authors here report on process variables including feedstock types (grasses and sugarcane-based agro residues), bioprocess engineering simulations, multivisual structural analysis of lignocellulosics after pretreatment, improvements in cellulase-mediated hydrolysis, and modification in fermentation strategies for the production of a range of value-added products. Selection of suitable lignocellulosic substrates plays a key role for the economic cellulosic ethanol production. Factors such as availability of feedstock and presence of high amount of carbohydrates and lignin amounts are critical for biofuels production at large scale under the biorefinery concept. Of particular interest in this regard is the use of sugarcane residues, corn stover, and grasses as a second-generation feedstock. L. Canilha et al. comprehensively reviewed the technologies (pretreatment methods, detoxification, hydrolysis, fermentation, and end-product distillation) for second-generation (2G) ethanol production from sugarcane residues (sugarcane bagasse and straw). Grasses are another excellent feedstock for 2G ethanol production in countries like Thailand. J. Wongwatanapaiboon et al. collected data on composition of cellulose, hemicellulose, and lignin in 18 types of grasses followed by the alkaline peroxide mediated pretreatment. The pretreated materials were evaluated for ethanol production under simultaneous saccharification and fermentation approach employing yeasts cocultures. J. Lu et al. explored the Reed as a primary source for 2G ethanol production. They presented the data on sugar recovery after liquid hot water pretreatment followed by enzymatic hydrolysis and conversion of sugars into ethanol under separate hydrolysis and fermentation. J. E. Jessen and J. Orlygsson examined the 2G ethanol production from various feedstocks (hemp stem, grass, wheat straw, newspaper, and cellulose) employing a new thermophilic isolate, Thermoanaerobacter J1, from a hot spring in Iceland in addition to the exploration of a mechanism of electron-scavenging systems on end-product formation. For the economization of biofuel or any value-added product formation from lignocellulosic materials, the efficient bioconversion of cellulose and hemicellulose into monomeric sugars is inevitable. In this line, A. D. Eckard et al. demonstrated the mechanism of casein (skimmed milk protein) action to improve the enzymatic saccharification of corn stover. Pretreatment is the key technology for the direct methanation of agroresidues. Y. Feng et al. investigated the changes in the maize straw characteristics during the methanation process. M. A. K. M. Zahari et al. optimized major influential parameters for poly(3-hydroxybutyrate) production from oil palm frond (OPF) juice by Cupriavidus necator CCUG52238T and concluded that OPF juice could be a competitive carbon source for the economic production of PHB. P. Chakraborty et al. presented the data on modified feeding strategies using a mixture of volatile fatty acids and artificial rumen fluid to maximize the PHA production by Ralstonia eutropha. Towards the pharmaceuticals intermediate production, M. F. Jahromi et al. investigated the lovastatin production by Aspergillus terreus under solid-state fermentation using rice straw and oil palm frond. M. O. Seydibeyoglu examined the properties of blends of polyacrylonitrile (PAN) and lignin followed by the structural analysis employing modern structural tools. We sincerely hope readers will find these papers helpful to their research pursuits. It has been our pleasure to put together this special issue in Journal of Biomedicine and Biotechnology.

Flexible heat integration system in first-/second-generation ethanol production via screening pinch-based method and multiperiod model

Pretreatment of biomass is one of the most challenging steps in the process of second-generation (2G) ethanol and biochemical production. Dilute acid pretreatment is a widely adapted and convenient method to recover pentose (C5) as well as hexose (C6) sugars due to its featured solubilization of hemicellulose and cellulose before and after enzymatic saccharification, respectively. In the present study, dilute sulfuric acid (H2SO4) pretreatment of sugarcane bagasse (SCB) was statistically optimized using the face-centered composite design (FCCD) of response surface methodology (RSM) in terms of acid concentration (0.1–3% v/v), solid loading (5–20% w/v) and residence time (15–60 min) at constant temperature of 121 °C followed by enzymatic hydrolysis using commercial cellulase (Novozymes Cellic CTec2) for enhanced combined sugar yield (CSY) comprising of C5 and C6 sugars in pretreated as well as saccharified hydrolysates. Optimized process parameters found in the study were 2.18% (v/v) acid; 14.35% (w/v) solid loading; and 29.49 min residence time. CSY under optimized conditions was found to be 521.42 ± 7.2 g/kg raw SCB with 72.06 ± 1.0% sugars recovered out of the maximum theoretical sugars present in the raw biomass. Total reducing sugar yields in pretreated and saccharified hydrolysates were found to be 215.28 ± 2.4 and 306.14 ± 5.3 g/kg raw SCB, respectively. Morphological and structural changes in optimized pretreated and saccharified biomass further validated the efficiency of optimized pretreatment applied in the present study. The maximum ethanol concentration, volumetric productivity and yield from released sugars were calculated as 10.82 ± 2.2 g/L, 0.45 ± 0.9 g/L/h and 0.42 g/g-glucose consumed or 71.45 ± 2.5 g/kg raw SCB, respectively. Ethanol yield obtained from the fermentation of dilute H2SO4-pretreated SCB was corresponding to 82.4% of the theoretical ethanol yield.

BackgroundSugarcane is the most efficient crop for production of (1G) ethanol. Additionally, sugarcane bagasse can be used to produce (2G) ethanol. However, the manufacture of 2G ethanol in large scale is not a consolidated process yet. Thus, a detailed economic analysis, based on consistent simulations of the process, is worthwhile. Moreover, both ethanol and electric energy markets have been extremely volatile in Brazil, which suggests that a flexible biorefinery, able to switch between 2G ethanol and electric energy production, could be an option to absorb fluctuations in relative prices. Simulations of three cases were run using the software EMSO: production of 1G ethanol + electric energy, of 1G + 2G ethanol and a flexible biorefinery. Bagasse for 2G ethanol was pretreated with a weak acid solution, followed by enzymatic hydrolysis, while 50% of sugarcane trash (mostly leaves) was used as surplus fuel.ResultsWith maximum diversion of bagasse to 2G ethanol (74% of the total), an increase of 25.8% in ethanol production (reaching 115.2 L/tonne of sugarcane) was achieved. An increase of 21.1% in the current ethanol price would be enough to make all three biorefineries economically viable (11.5% for the 1G + 2G dedicated biorefinery). For 2012 prices, the flexible biorefinery presented a lower Internal Rate of Return (IRR) than the 1G + 2G dedicated biorefinery. The impact of electric energy prices (auction and spot market) and of enzyme costs on the IRR was not as significant as it would be expected.ConclusionsFor current market prices in Brazil, not even production of 1G bioethanol is economically feasible. However, the 1G + 2G dedicated biorefinery is closer to feasibility than the conventional 1G + electric energy industrial plant. Besides, the IRR of the 1G + 2G biorefinery is more sensitive with respect to the price of ethanol, and an increase of 11.5% in this value would be enough to achieve feasibility. The ability of the flexible biorefinery to take advantage of seasonal fluctuations does not make up for its higher investment cost, in the present scenario.

An increasing demand for energy and depleting petroleum sources has elevated the need for producing alternative renewable resources. Owing to the prominence of lignocellulosic biomass as bio-renewable and the most abundant resource on Earth, this critical review provides perceptions into the potential of lignocellulosic biomass for production of second generation (2G) ethanol and value added products in a biorefinery manner. The efficient utilization of all three components of lignocellulosic biomass (i.e., cellulose, hemicellulose and lignin) would play a significant role in the economic viability of cellulosic ethanol. The pretreatment method is the key to the success of bioconversion processes and greatly influences the economics of biorefinery process. Biotechnology tools and process engineering play pivotal roles in development of integrated processes for production of biofuels, biochemicals and biomaterials from lignocellulosic biomass. Although, lignocellulosic biorefinery has ample scopes, commercial production of biofuels and chemicals is still challenging. In this context, this review entails concept of lignocellulose biorefinery, latest developments in 2G ethanol production process, importance and market potential of 2G ethanol as renewable fuel and value added chemicals, integration of processes, challenges for integrated production of fuel together with value added chemicals and future directions.

A novel process intensification strategy for second-generation ethanol production from sugarcane bagasse in fluidized bed reactor

The use of agroindustrial residues for the production of biofuels and other value-added products has been the subject of research in Brazil and in the world, being the sugarcane bagasse (SCB) one of the most studied by-products. In this context, the present work investigated the alkaline pre-treatment of SCB, followed by saccharification using commercial enzyme Cellic Ctec3 (under variable conditions of time and percentage of bagasse) and the alcoholic fermentation with commercial Saccharomyces cerevisiae and Galactomyces geotrichum UFVJM-R150 yeasts in the production of second generation ethanol (2G ethanol). The pre-treatment of the SCB with sodium hydroxide (NaOH 2%) was efficient for the removal of lignin, with a reduction of 58.15% in pre-treated bagasse (PTB). It was also observed that the cellulosic fraction was conserved and there was an increase of the porosity in the fibers in PTB. Concerning hemicelluloses, there was a removal of 31.66% in PTB. After saccharification, the concentrations of total reducing sugars (TRS) by the colorimetric method were quantified using 3.5 dinitrosalicylic acid (DNS) and the monosaccharides by high performance liquid chromatography (HPLC). The highest concentrations of TRS (73.96 g.L -1 ), and D-glucose and D-xylose (31.78 and 10.85 g.L -1 , respectively) were obtained in the hydrolysate containing 10% PTB after 72 hours of hydrolysis. Then, alcoholic fermentations were performed, in which cell viability (CV) and ethanol production were evaluated. The greatest results were also obtained after the fermentations using the hydrolysate with 10% PTB (72 hours): G. geotrichum UFVJM-R150 with a peak of CV of 1.23x10 10 cells.mL - and maximum ethanol production of 9.99 g.L - 1 (volumetric productivity -QP de 0,42 g.L -1 .h - yield of ethanol as a function of the substrate -YP/S of 0.27 gethanol.gsugar - ) and S. cerevisiae with 7.76x 10 9 cells.mL - and 16.15 g.L -1 of ethanol (QP of 0.67 g.L -1 .h - and YP/S of 0.48 gethanol.gsugar - ). It was observed that, besides ethanol G. geotrichum UFVJM-R150 was able to produce other value-added products, such as galacturonic acid, propionic acid, isoamyl alcohol. These compounds were produced in different concentrations in the fermentations of hydrolysates 10% PTB (72 hours), YPX and model solution. The production of these secondary metabolites may enable the application of G. geotrichum UFVJM-R150 in biorefineries. In addition, the values of yield and productivity in ethanol and the consumption of D-glucose and D-xylose by G. geotrichum UFVJM-R150 were quite satisfactory. This is the first study which reports the 2G ethanol production and other byproducts by G. geotrichum UFVJM-R150 from PTB hydrolysates.

Effect of a novel method for in-house cellulase production on 2G ethanol yields

The water consumption of sugarcane bagasse post-washing after protic ionic liquid pretreatment and its impact on 2G ethanol production

BackgroundIn the sugarcane industry, large amounts of lignocellulosic residues are generated, which includes bagasse, straw, and tops. The use of the whole sugarcane lignocellulosic biomass for the production of second-generation (2G) ethanol can be a potential alternative to contribute to the economic viability of this process. Here, we conducted a systematic comparative study of the use of the lignocellulosic residues from the whole sugarcane lignocellulosic biomass (bagasse, straw, and tops) from commercial sugarcane varieties for the production of 2G ethanol. In addition, the feasibility of using a mixture of these residues from a selected variety was also investigated.ResultsThe materials were pretreated with dilute acid and hydrolyzed with a commercial enzymatic preparation, after which the hydrolysates were fermented using an industrial strain of Saccharomyces cerevisiae. The susceptibility to enzymatic saccharification was higher for the tops, followed by straw and bagasse. Interestingly, the fermentability of the hydrolysates showed a different profile, with straw achieving the highest ethanol yields, followed by tops and bagasse. Using a mixture of the different sugarcane parts (bagasse-straw-tops, 1:1:1, in a dry-weight basis), it was possible to achieve a 55% higher enzymatic conversion and a 25% higher ethanol yield, compared to use of the bagasse alone. For the four commercial sugarcane varieties evaluated using the same experimental set of conditions, it was found that the variety of sugarcane was not a significant factor in the 2G ethanol production process.ConclusionsAssessment of use of the whole lignocellulosic sugarcane biomass clearly showed that 2G ethanol production could be significantly improved by the combined use of bagasse, straw, and tops, when compared to the use of bagasse alone. The lower susceptibility to saccharification of sugarcane bagasse, as well as the lower fermentability of its hydrolysates, can be compensated by using it in combination with straw and tops (sugarcane trash). Furthermore, given that the variety was not a significant factor for the 2G ethanol production process within the four commercial sugarcane varieties evaluated here, agronomic features such as higher productivity and tolerance of soil and climate variations can be used as the criteria for variety selection.

Second-generation (2G) ethanol production has been increasingly evaluated, and the use of sugarcane bagasse as feedstock has enabled the integration of this process with first-generation (1G) ethanol production from sugarcane. The pretreatment of bagasse generates pentose liquor as a by-product, which can be anaerobically processed to recover energy and value-added chemicals. The potential to produce biohydrogen and organic acids from pentose liquor was assessed using a mesophilic (25 °C) upflow anaerobic packed-bed bioreactor in this study. An average organic loading rate of 11.1 g COD·L−1·d−1 was applied in the reactor, resulting in a low biohydrogen production rate of 120 mL·L−1 d−1. Meanwhile, high lactate (38.6 g·d−1), acetate (31.4 g·d−1), propionate (50.1 g·d−1), and butyrate (50.3 g·d−1) production rates were concomitantly obtained. Preliminary analyses indicated that the full-scale application of this anaerobic acidogenic technology for hydrogen production in a medium-sized 2G ethanol distillery would have the potential to completely fuel 56 hydrogen-powered vehicles per day. An increase of 24.3% was estimated over the economic potential by means of chemical production, whereas an 8.1% increase was calculated if organic acids were converted into methane for cogeneration (806.73 MWh). In addition, 62.7 and 74.7% of excess organic matter from the 2G ethanol waste stream could be removed with the extraction of organic acid as chemical commodities or their utilization as a substrate for biomethane generation, respectively.

Several economies around the world are using second-generation (2G) ethanol produced from agricultural residues, like sugarcane straw and bagasse, as a sustainable solution to replace petroleum products. Since first-generation (1G) ethanol uses the sugars of sugarcane, an integrated 1G–2G production would enable the production of more ethanol from the same amount of sugarcane without leading to increased use of arable land. The ethanol production process is complex, involving different high-energy consumption operations such as evaporation and distillation. The economic competitiveness of this process depends heavily on the amount of thermal and electrical energy produced using sugarcane straw and bagasse as input. Thus, the objective of this study was to use the mean-variance methodology to determine the optimal allocation of residual sugarcane biomass between 2G ethanol and bioelectricity productions, with simultaneous objectives of maximizing the return and minimizing the risk for investors of this sector. In this paper, four scenarios are analyzed. The first one is the base scenario that represents the current state of production costs and investments. scenarios 2, 3, and 4 considered four cuts of 10%, 20%, and 40% in the production cost of ethanol 2G, respectively. The results show the optimum biomass allocations and the growth rates of returns as a function of risk growth. It can be concluded that from scenario 4, the production of 2G ethanol becomes financially advantageous for the investor, presenting greater returns with smaller risks.

ABSTRACTThe use of different lignocellulosic residues for the production of cellulosic ethanol is an alternative for the expanding demand of this fuel without increasing the planting area of traditional carbohydrate crops. One of the proposed alternatives is the use of pineapple leaf fibers (PALF) residues, which is a material rich in cellulose that can be used as raw material for second-generation (2G) ethanol production. In this study, the PALF was pretreated using an alkaline medium combined with a steam explosion and the 2G ethanol produSction was analyzed by two-way processes to enzymatic hydrolysis using separated hydrolysis and fermentation (SHF) or simultaneous saccharification and fermentation (SSF). Using SHF, the alcoholic fermentation process with addition of molasses provided good fermentability and can handle larger loads of carbohydrate in shorter fermentation time. The SSF was a better method for 2G ethanol production from PALF yielding 96.12%. Therefore, PALF is presented as good raw material for production of 2G ethanol, with all the environmental and social advantages of such approach.

The use of sugarcane bagasse hemicellulosic hydrolysates presents an interesting alternative to second generation (2G) ethanol production. Techniques to enhance the fermentation process, e.g., the use of immobilized cells, is one of the key factors for efficient production. Here, the effect of two important parameters (cell concentration in immobilized system and stirring rate) on the 2G ethanol production using the wild Brazilian yeast S. shehatae UFMG-HM 52.2 immobilized in calcium alginate matrix are presented. A 2(2) full factorial design of experiments was carried out to evaluate the effect of cell concentrations in sodium alginate solution for immobilized bead production (3.0, 6.0, and 9.0g/L) and stirring rate (150, 200, and 250rpm) for 2G ethanol production. Statistical analysis showed that the use of both variables at low levels enhanced ethanol yield (YP/S). Under these process conditions, YP/S of 0.31g/g and ethanol productivity (Qp) of 0.12g/Lh were achieved. Results showed the potential of this immobilized yeast in 2G ethanol production from C5 sugars and demonstrate the importance of adequate cell concentration in immobilized systems, a finding that stands to increase bioprocesses yields and productivity.

Selection and improvement of Saccharomyces cerevisiae by direct and mass mating for integrated first and second generation (1G + 2G) ethanol production