Nitric Acid Pretreatment of Jerusalem Artichoke Stalks for Enzymatic Saccharification and Bioethanol Production

Effect of Apple Cultivar and Selected Technological Treatments on the Quality of Apple Distillate

Apple producers are looking for new markets to dispose of their harvest surpluses. One of the solutions may be the production of apple spirits by small distilleries. This study aimed to evaluate the influence of apple cultivars and technological treatments, i.e., pasteurization, depectinization, and deacidification, on the fermentation efficiency and quality of the distillates. Samples for fermentation were prepared from Polish apple cultivars (Antonówka, Delikates, Kosztela, Kronselska). The control samples were raw pulp-based samples. After fermentation, the samples were analyzed for ethanol, residual sugars, and by-product content by the HPLC technique. The distillates were tested for volatile compounds by the GC-MS method and their sensory evaluation was performed. Raw pulp-based samples, independent of the apple cultivar, showed fermentation efficiencies between (75.77 ± 4.69)% and (81.36 ± 4.69)% of the theoretical yield. Depectinization of apple pulp prior to fermentation resulted in the highest ethanol concentration and yield up to approximately 89%. All tested apple distillates were rich in volatile aroma compounds and met the requirements of the EU regulation for hydrogen cyanide content. The obtained results indicate that the tested apple cultivars can be used for the efficient production of apple spirits, providing producers with an opportunity for brand development.

Two-Stage Pretreatment of Jerusalem Artichoke Stalks with Wastewater Recycling and Lignin Recovery for the Biorefinery of Lignocellulosic Biomass

Jerusalem artichoke (Helianthus tuberosus L.) is emerging as one of the energy plants considered for biofuel production. Alkali and alkali-involved pretreatment methods have been widely used for the bioconversion of cellulosic materials due to their high sugar yield and low inhibitor release. However, the recovery and treatment of wastewater (black liquor) have been poorly studied. Here, we present a novel two-stage pretreatment process design for recycling black liquor. Jerusalem artichoke stalk (JAS) was first treated with 2% (w/v) NaOH, after which lignin was recovered by H2SO4 at pH 2.0 from the black liquor. The recycled solutions were subsequently used to treat the NaOH-pretreated JAS for the second time to dissolve hemicellulose. CO-pretreated JAS, hydrolysates, and acid-insoluble lignin were obtained after the above-mentioned two-stage pretreatment. A reducing sugar yield of 809.98 mg/g Co-pretreated JAS was achieved after 48 h at 5% substrate concentration using a cellulase dosage of 25 FPU/g substrate. In addition, hydrolysates containing xylose and acid-insoluble lignin were obtained as byproducts. The pretreatment strategy described here using alkali and acid combined with wastewater recycling provides an alternative approach for cellulosic biorefinery.

Valorization of Cheese Whey as a Feedstock for Production of Cyclosporin A by Tolypocladium inflatum

Food waste-based biorefineries are considered an essential concept for the implementation of a sustainable circular economy. In this study, cheese whey powder (CWP), a dairy industry waste, was utilized to produce cyclosporin A (CsA). As it is difficult to valorize CWP because its components vary depending on the origin, a process for sugar conversion via acid hydrolysis was designed to obtain reproducible results using refined whey powder (WP) of a consistent quality. Acid hydrolysis was carried out using 2% (w/w) HCl and biomass loading of 50 g/L at 121 °C for 20 min. CWP hydrolysates were utilized to ferment Tolypocladium inflatum ATCC 34921. CsA production was found to be 51.3 mg/L at 12 days, a 1.4-fold increase compared to the control (commercial glucose, 36.3 mg/L). Our results showed that 100 g CWP can be converted to 81.8 mg of CsA. This finding demonstrated that CWP can be used as a sustainable feedstock for biorefineries.

Cellulosic Ethanol Production Using Waste Wheat Stillage after Microwave-Assisted Hydrotropic Pretreatment

One of the key elements influencing the efficiency of cellulosic ethanol production is the effective pretreatment of lignocellulosic biomass. The aim of the study was to evaluate the effect of microwave-assisted pretreatment of wheat stillage in the presence of sodium cumene sulphonate (NaCS) hydrotrope used for the production of second-generation bioethanol. As a result of microwave pretreatment, the composition of the wheat stillage biomass changed significantly when compared with the raw material used, before treatment. Microwave-assisted pretreatment with NaCS effectively reduced the lignin content and hemicellulose, making cellulose the dominant component of biomass, which accounted for 42.91 ± 0.10%. In post pretreatment, changes in biomass composition were also visible on FTIR spectra. The peaks of functional groups and bonds characteristic of lignins (C-O vibration in the syringyl ring, asymmetric bending in CH₃, and aromatic skeleton C-C stretching) decreased. The pretreatment of the analyzed lignocellulosic raw material with NaCS resulted in the complete conversion of glucose to ethanol after 48 h of the process, with yield (in relation to the theoretical one) of above 91%. The highest observed concentration of ethanol, 23.57 ± 0.10 g/L, indicated the high effectiveness of the method used for the pretreatment of wheat stillage that did not require additional nutrient supplementation.

Ethanolic Fermentation of Rye Mashes: Factors Influencing the Formation of Aldehydes and Process Efficiency

High concentrations of aldehydes may result in poor-quality agricultural distillate. We investigate the influence of the method of mash preparation, the initial pH of the mashes, and different yeast strains on the fermentation efficiency and concentration of aldehydes from C2 (acetaldehyde) to C7 (enanthaldehyde) in rye mashes. The tested factors were revealed to have a differentiated influence on both the process efficiency and the concentrations of aldehydes, especially in the case of the dominant acetaldehyde. Mashes obtained from steamed rye grain showed significantly higher fermentation efficiencies than those prepared by the pressureless method. Increasing the pH of the sweet mashes from 4.5 to 6.0 resulted in significantly higher concentrations of acetaldehyde, especially in the case of steamed rye grain. Moreover, an increase in the concentrations of other aldehydes, i.e., from C3 (propionaldehyde) to C5 (valer- and isovaleraldehyde) was observed. A high fermentation efficiency and the lowest acetaldehyde concentrations were obtained from steamed rye mashes with an initial pH of 4.5, fermented using the yeast strains DistilaMax GW and DistilaMax HT. DistilaMax HT yeast also provided a relatively low concentration of acetaldehyde in mashes with an initial pH in the range of 4.5–5.5 prepared by the energy-saving pressureless method.

Pretreatment of Jerusalem artichoke stalk using hydroxylammonium ionic liquids and their influences on 2,3-butanediol fermentation by Bacillus subtilis

Pretreatment of lignocellulose is a vital step for biological production of bio-chemicals and bio-fuels. In this work, the pretreatment of Jerusalem artichoke stalk (JAS) by hydroxylammonium ionic liquids was evaluated based on pretreatment efficiency including polysaccharide recovery and enzymatic digestibility, and influence of ionic liquids on 2,3-butanediol fermentation using Bacillus subtilis. The results showed ethanolammonium acetate (EOAA) was efficient in JAS pretreatment, and maximum cell density was increased 25% when EOAA concentration was not greater than 0.3 mol/L in medium, while the total concentration of acetoin and 2,3-butanediol was 15% greater than the control at 0.1 mol/L EOAA. After the pretreatment under optimized conditions of 170 °C for 5-h and liquid-solid ratio of 18, about 87% cellulose and 75% hemicellulose were recovered, and glucose yield of 64% and xylose of 66% were obtained after 24-h hydrolysis of JAS residue by cellulase (15 FPU/g) with solid loading of 10 wt%.

Exploring Use of the Metschnikowia pulcherrima Clade to Improve Properties of Fruit Wines

Mixed fermentation using Saccharomyces cerevisiae and non-Saccharomyces yeasts as starter cultures is well known to improve the complexity of wines and accentuate their characteristics. This study examines the use of controlled mixed fermentations with the Metschnikowia pulcherrima clade, Saccharomyces cerevisiae Tokay, and non-conventional yeasts: Wickerhamomyces anomalus and Dekkera bruxellensis. We investigated the assimilation profiles, enzyme fingerprinting, and metabolic profiles of yeast species, both individually and in mixed systems. The chemical complexity of apple wines was improved using the M. pulcherrima clade as co-starters. M. pulcherrima with S. cerevisiae produced a wine with a lower ethanol content, similar glycerol level, and a higher level of volatilome. However, inoculation with the Dekkera and Wickerhamomyces strains may slightly reduce this effect. The final beneficial effect of co-fermentation with M. pulcherrima may also depend on the type of fruit must.

Acid-based lignocellulosic biomass biorefinery for bioenergy production: Advantages, application constraints, and perspectives

The production of chemicals and fuels from renewable biomass with the primary aim of reducing carbon footprints has recently become one of the central points of interest. The use of lignocellulosic biomass for energy production is believed to meet the main criteria of maximizing the available global energy source and minimizing pollutant emissions. However, before usage in bioenergy production, lignocellulosic biomass needs to undergo several processes, among which biomass pretreatment plays an important role in the yield, productivity, and quality of the products. Acid-based pretreatment, one of the existing methods applied for lignocellulosic biomass pretreatment, has several advantages, such as short operating time and high efficiency. A thorough analysis of the characteristics of acid-based biomass pretreatment is presented in this review. The environmental concerns and future challenges involved in using acid pretreatment methods are discussed in detail to achieve clean and sustainable bioenergy production. The application of acid to biomass pretreatment is considered an effective process for biorefineries that aim to optimize the production of desired products while minimizing the by-products.

Bioethanol Production from Sugarcane Press-Mud: Assessment of the Fermentation Conditions to Reduce Fusel Alcohol

Within a biorefinery context, bioethanol is a promising platform molecule since it can be used as raw material to produce a wide spectrum of valuable industrial products such as H2 and light olefins. However, the presence of impurities limits the conversion of bioethanol in these products. Herein, we aimed to determine the proper pretreatment and fermentation conditions to yield bioethanol with a low content of impurities, such as 3-methyl-1-butanol, by using sugarcane press-mud as feedstock. To do so, a Box-Behnken methodology was employed to select proper pretreatment and fermentation conditions. Factors assessed were temperature, stirring, and pH during fermentation of hydrolysates coming from two different pretreatment methods named as hydrothermal and acid hydrolysis. Results showed that the fermentation temperature should be kept between 26–30 °C to assure at least 91 g/L ethanol. The fusel alcohol content would be reduced by 22% at 30 °C, pH = 4.5, and 200 rpm if sugarcane press-mud is pretreated under acid hydrolysis conditions (T = 130 °C, t = 1 h, 16 g HNO3/kg solid). Further studies should aim to integrate these conditions within a biorefinery concept to yield valuable products such as H2 and ethylene.

Study of biorefineries based on experimental data: production of bioethanol, biogas, syngas, and electricity using coffee-cut stems as raw material

Energy-driven biorefineries can be designed considering biotechnological and thermochemical conversion pathways. Nevertheless, energy and environmental comparisons are necessary to establish the best way to upgrade lignocellulosic biomass and set the requirements of these processes in different scenarios. This paper aims to evaluate experimentally a biorefinery producing energy vectors using coffee-cut stems (CCS) as feedstock. The obtained yields were the basis for energy and environmental analysis, in two different biorefinery scenarios: (i) production of bioethanol and biogas and (ii) production of syngas and electricity. The energy results indicated that the overall energy efficiency calculated in the first scenario was only 9.15%. Meanwhile, the second biorefinery configuration based on thermochemical routes presented an energy efficiency value of 70.89%. This difference was attributed to the higher consumption of utilities in the biorefinery based on biotechnological routes. The environmental results showed that the impact category of climate change for the first biorefinery (i.e., 0.0193 kg CO₂ eq./MJ) had a lower value than that of the second process (i.e., 0.2377 kg CO₂ eq./MJ). Thus, the biorefinery based on the biotechnological route presented a better environmental performance. Additionally, the results for both biorefineries allowed concluding that the inclusion of by-products and co-products in the calculation of the environmental analysis can dramatically affect the results.

Different nitrogen forms differentially affect Cd uptake and accumulation in dwarf Polish wheat (Triticum polonicum L.) seedlings

This study investigated the effects of different nitrogen (N) forms on Cadmium (Cd) uptake and accumulation in dwarf Polish wheat (DPW) seedlings, which were grown under Cd stress with N-Null, NH₄⁺-N, NO₃^--N and NH₄⁺-N + NO₃^--N. We measured plant growth and determined Cd uptake, translocation, accumulation, subcellular distribution and chemical forms in the roots and shoots of DPW seedlings. We also analyzed saccharide concentrations, and the transcript levels of genes encoding metal transporters in the roots of DPW seedlings. In the absence of NO₃^--N, addition of NH₄⁺-N reduced roots Cd concentration, F_CW (Cd in cell wall), F_S (Cd in soluble fraction) and F_E (inorganic Cd) concentrations, and induced the expression of four genes encoding metal transporters in roots, while it promoted Cd translocation to shoots. In the presence of NO₃^--N, addition of NH₄⁺-N increased roots Cd concentration, F_CW and F_W concentrations, and induced the expression of 22 genes encoding metal transporters in roots. Regardless of NH₄⁺-N level, addition of NO₃^--N increased roots Cd concentration, F_CW, F_S, F_W (water-soluble Cd), F_NaCl (pectates and protein Cd), F_HAc (undissolved Cd phosphate) and lactose concentrations, and also induced the expression of genes encoding metal transporters in roots. Overall, NH₄⁺-N differently regulated Cd uptake and accumulation in DPW seedlings in the absence or presence of NO₃^--N, while NO₃^--N greatly increased Cd uptake and accumulation in the presence of NH₄⁺-N compared to the absence of NH₄⁺-N. These patterns of Cd alteration likely arose due to different N forms altering Cd subcellular distribution and chemical forms, lactose concentration and the expression of metal transporter genes.

Lignocellulosic Biomass as a Substrate for Oleaginous Microorganisms: A Review

Microorganisms capable of accumulating lipids in high percentages, known as oleaginous microorganisms, have been widely studied as an alternative for producing oleochemicals and biofuels. Microbial lipid, so-called Single Cell Oil (SCO), production depends on several growth parameters, including the nature of the carbon substrate, which must be efficiently taken up and converted into storage lipid. On the other hand, substrates considered for large scale applications must be abundant and of low acquisition cost. Among others, lignocellulosic biomass is a promising renewable substrate containing high percentages of assimilable sugars (hexoses and pentoses). However, it is also highly recalcitrant, and therefore it requires specific pretreatments in order to release its assimilable components. The main drawback of lignocellulose pretreatment is the generation of several by-products that can inhibit the microbial metabolism. In this review, we discuss the main aspects related to the cultivation of oleaginous microorganisms using lignocellulosic biomass as substrate, hoping to contribute to the development of a sustainable process for SCO production in the near future.

Bioethanol Production from Azolla filiculoides by Saccharomyces cerevisiae, Pichia stipitis, Candida lusitaniae, and Kluyveromyces marxianus

Ethanol was produced by separate hydrolysis and fermentation using Azolla filiculoides as a biomass. Thermal acid hydrolysis and enzymatic saccharification were used as pretreatment methods to produce monosaccharides from Azolla. The optimal content for thermal acid hydrolysis of 14% (w/v) Azolla weed slurry produced 16.7-g/L monosaccharides by using 200 mM H₂SO₄ at 121 °C for 60 min. Enzymatic saccharification using 16 U/mL Viscozyme produced 61.6 g/L monosaccharide at 48 h. Ethanol productions with ethanol yield coefficients from Azolla weed hydrolysate using Kluyveromyces marxianus, Candida lusitaniae Saccharomyces cerevisiae, and Pichia stipitis were 26.8 g/L (Y_EtOH = 0.43), 23.2 g/L (Y_EtOH = 0.37), 18.2 g/L (Y_EtOH = 0.29), and 13.7 g/L (Y_EtOH = 0.22), respectively. Saccharomyces cerevisiae produces the lowest yield as it utilized only glucose. Bioethanol from Azolla weed hydrolysate can be successfully produced by using Kluyveromyces marxianus because it consumed the mixture of glucose and xylose completely within 60 h.

Microwave-Assisted Degradation of Biomass with the Use of Acid Catalysis

The aim of the study was to assess the effectiveness of microwave pretreatment combined with acid catalysis in the decomposition of various types of biomass (pine and beech chips and hemp stems). It was clearly demonstrated that sulfuric acid was a catalyst enabling the most effective decomposition of the tested plant biomass, guaranteeing the highest concentrations of simple sugars released. Acid catalysis with 1% v/v sulfuric acid combined with microwave radiation provided high glucose concentrations of 89.8 ± 3.4, 170.4 ± 2.4 and 164.6 ± 4.6 mg/g for pine chips, beech chips and hemp stems, respectively. In turn, the use of nitric acid promoted the degradation of hemicellulose, which resulted in high concentrations of galactose and xylose, i.e., 147.6 ± 0.6, 163.6 ± 0.4 and 134.9 ± 0.8 mg/g of pine chips, beech chips and hemp stems, respectively, while glucose levels remained relatively low. It was also demonstrated that the undesirable dehydration of sugars such as glucose and xylose is more pronounced in sulfuric acid than nitric acid processes. The use of H2SO4 and increased pressure generated 5-hydroxymethylfurfural (5-HMF) and furfural at a concentration of ca. 12 and 6 mg/g, 10 and 45 mg/g and 14 and 30 mg/g, of pine chips, beech chips and hemp shoots, respectively. Our studies confirmed the usefulness of the combined use of microwaves and acid catalysis in the degradation of softwood, hardwood and non-wood plant biomass. It should be emphasized that obtaining high concentrations of released simple sugars (as potential substrates in biosynthesis), while maintaining low levels of toxic by-products (inhibitors), requires precise selection of process parameters such as pressure, exposition time and type of acid catalyst.

A Two-Step Ferric Chloride and Dilute Alkaline Pretreatment for Enhancing Enzymatic Hydrolysis and Fermentable Sugar Recovery from Miscanthus sinensis

A two-step process was proposed to enhance enzymatic hydrolysis of Miscanthus sinensis based on a comparative study of acid/alkaline pretreatments. Ferric chloride pretreatment (FP) effectively removed hemicellulose and recovered soluble sugars, but the enzymatic hydrolysis was not efficient. Dilute alkaline pretreatment (ALP) resulted in much better delignification and stronger morphological changes of the sample, making it more accessible to enzymes. While ALP obtained the highest sugar yield during enzymatic hydrolysis, the soluble sugar recovery from the pretreatment stage was still limited. Furthermore, a two-step ferric chloride and dilute alkaline pretreatment (F-ALP) has been successfully developed by effectively recovering soluble sugars in the first FP step and further removing lignin of the FP sample in the second ALP step to improve its enzymatic hydrolysis. As a result, the two-step process yielded the highest total sugar recovery (418.8 mg/g raw stalk) through the whole process.

Conversion of Potato Industry Waste into Fodder Yeast Biomass

In this study, we evaluate potato pulp waste as a potential raw material for obtaining yeast biomass. A portion of the carbohydrates in the potato pulp waste can thereby be converted into more valuable protein. The potato pulp waste was analyzed in terms of protein and ash content, dry mass, simple sugars, and starch content. Two kinds of hydrolysis were performed (thermo-acidic and enzymatic) to produce media for cultivating Candida guilliermondii and Pichia stipitis. The hydrolysates and post-cultivation leachates were analyzed by High Performance Liquid Chromatography (HPLC). The highest biomass yield after 48 h (39.3%) was noted for Candida guilliermondii yeast grown on enzymatic hydrolysate-based medium. Our results prove that potato waste pulp is a promising raw material for the production of yeast single-cell protein (SCP).

Production of Methane, Hydrogen and Ethanol from Secale cereale L. Straw Pretreated with Sulfuric Acid

The study describes sulfuric acid pretreatment of straw from Secale cereale L. (rye straw) to evaluate the effect of acid concentration and treatment time on the efficiency of biofuel production. The highest ethanol yield occurred after the enzyme treatment at a dose of 15 filter paper unit (FPU) per gram of rye straw (subjected to chemical hydrolysis with 2% sulfuric acid (SA) at 121 °C for 1 h) during 120 h. Anaerobic digestion of rye straw treated with 10% SA at 121 °C during 1 h allowed to obtain 347.42 L methane/kg volatile solids (VS). Most hydrogen was released during dark fermentation of rye straw after pretreatment of 2% SA, 121 °C, 1 h and 1% SA, 121 °C, 2 h—131.99 and 134.71 L hydrogen/kg VS, respectively. If the rye straw produced in the European Union were processed into methane, hydrogen, ethanol, the annual electricity production in 2018 could reach 9.87 TWh (terawatt-hours), 1.16 TWh, and 0.60 TWh, respectively.

One-Step or Two-Step Acid/Alkaline Pretreatments to Improve Enzymatic Hydrolysis and Sugar Recovery from Arundo Donax L

Energy crops are not easily converted by microorganisms because of their recalcitrance. This necessitates a pretreatment to improve their biodigestibility. The effects of different pretreatments, as well as their combination on the enzymatic digestibility of Arundo donax L. were systematically investigated to evaluate its potential for bioconversion. Dilute alkaline pretreatment (ALP) using 1.2% NaOH at 120 °C for 30 min resulted in the highest reducing sugar yield in the enzymatic hydrolysis process because of its strong delignification and morphological modification, while ferric chloride pretreatment (FP) was effective in removing hemicellulose and recovering soluble sugars in the pretreatment stage. Furthermore, an efficient two-step ferric chloride-alkaline pretreatment (FALP) was successfully developed. In the first FP step, easily degradable cellulosic components, especially hemicellulose, were dissolved and then effectively recovered as soluble sugars. Subsequently, the FP sample was further treated in the second ALP step to remove lignin to enhance the enzymatic hydrolysis of the hardly degradable cellulose. As a result, the integrated two-step process obtained the highest total sugar yield of 420.4 mg/g raw stalk in the whole pretreatment and enzymatic hydrolysis process; hence, the process is a valuable candidate for biofuel production.

Feasibility Assessment of a Bioethanol Plant in the Northern Netherlands

Due to the exhaustion and increased pressure regarding the environmental and political aspects of fossil fuels, the industrial focus has switched towards renewable energy resources. Lignocellulosic biowaste can come from several sources, such as industrial waste, agricultural waste, forestry waste, and bioenergy crops and processed into bioethanol via a biochemical pathway. Although much research has been done on the ethanol production from lignocellulosic biomass, the economic viability of a bioethanol plant in the Northern Netherlands is yet unknown, and therefore, examined. In this thesis, the feasibility study of a bioethanol plant treating sugar beet pulp, cow manure, and grass straw is conducted using the simulation software SuperPro Designer. Results show that it is not economically viable to treat the tested lignocellulosic biomass for the production of bioethanol, since all three original cases result in a negative net present value (NPV). An alternative would be to exclude the pretreatment step from the process. Although this results in a lower production of bioethanol per year, the plant treating sugar beet pulp (SBP) and grass straw (GS) becomes economically viable since the costs have significantly decreased.

Two-Stage Pretreatment to Improve Saccharification of Oat Straw and Jerusalem Artichoke Biomass

Pretreatment is a necessary step when lignocellulosic biomass is to be converted to simple sugars; however single-stage pretreatment is often insufficient to guarantee full availability of polymeric sugars from raw material to hydrolyzing enzymes. In this work, the two-stage pretreatment with use of acid (H2SO4, HNO3) and alkali (NaOH) was applied in order to increase the susceptibility of Jerusalem artichoke stalks (JAS) and oat straw (OS) biomass on the enzymatic attack. The effect of the concentration of reagents (2% and 5% w/v) and the order of acid and alkali sequence on the composition of remaining solids and the efficiency of enzymatic hydrolysis was evaluated. It was found that after combined pretreatment process, due to the removal of hemicellulose and lignin, the content of cellulose in pretreated biomass increased to a large extent, reaching almost 90% d.m. and 95% d.m., in the case of JAS and OS, respectively. The enzymatic hydrolysis of solids remaining after pretreatment resulted in the formation of up to 45 g/L of glucose, for both JAS and OS. The highest glucose yield was achieved after pretreatment with 5% nitric acid followed by NaOH, and 90.6% and 97.6% of efficiency were obtained, respectively for JAS and OS.

Effect of dilute acid pretreatment on the saccharification and fermentation of rye straw

This research shows the effect of dilute acid pretreatment with various sulfuric acid concentrations (0.5-2.0% [wt/vol]) on enzymatic saccharification and fermentation yield of rye straw. After pretreatment, solids of rye straw were suspended in Na citrate buffer or post-pretreatment liquids (prehydrolysates) containing sugars liberated after hemicellulose hydrolysis. Saccharification was conducted using enzymes dosage of 15 or 25 FPU/g cellulose. Cellulose saccharification rate after rye straw pretreatment was enhanced by performing enzymatic hydrolysis in sodium citrate buffer in comparison with hemicellulose prehydrolysate. The maximum cellulose saccharification rate (69%) was reached in sodium citrate buffer (biomass pretreated with 2.0% [wt/vol] H₂ SO₄ ). Lignocellulosic complex of rye straw after pretreatment was subjected to separate hydrolysis and fermentation (SHF) or separate hydrolysis and co-fermentation (SHCF). The SHF processes conducted in the sodium citrate buffer using monoculture of Saccharomyces cerevisiae (Ethanol Red) were more efficient compared to hemicellulose prehydrolysate in respect with ethanol yields. Maximum fermentation efficiency of SHF processes obtained after rye straw pretreatment at 1.5% [wt/vol] H₂ SO₄ and saccharification using enzymes dosage of 25 FPU/g in sodium citrate buffer, achieving 40.6% of theoretical yield. However, SHCF process using cocultures of pentose-fermenting yeast, after pretreatment of raw material at 1.5% [wt/vol] H₂ SO₄ and hydrolysis using enzymes dosage of 25 FPU/g, resulted in the highest ethanol yield among studied methods, achieving 9.4 g/L of ethanol, corresponding to 55% of theoretical yield.

Biofuel and Bioenergy Technology

Biomass is considered as a renewable resource because of its short life cycle, and biomass-derived biofuels are potential substitutes to fossil fuels [...]