Bioethanol Production from Lignocellulosic Biomass-Challenges and Solutions

Cofactor engineering in Thermoanaerobacterium aotearoense SCUT27 for maximizing ethanol yield and revealing an enzyme complex with high ferredoxin-NAD+ reductase activity

Thermoanaerobacterium aotearoense SCUT27 is a prominent producer of biofuels from lignocellulosic materials. To provide sufficient NAD(P)H for ethanol production, redox-related genes, including lactate dehydrogenase (ldh), redox-sensing transcriptional repressor (rex), and hydrogenase (hfsB), were knocked out. However, the growth of strain PRH (Δldh/Δrex/ΔhfsB) was suppressed due to the intracellular redox state imbalance with the increased NADH concentration. Coincidentally, when the Bcd-EtfAB (BCD) complex was overexpressed, the resulting strain PRH-B3 (Δldh/Δrex/ΔhfsB::BCD) grew rapidly and produced ethanol with a high yield. With lignocellulosic hydrolysates, PRH-BA (Δldh/Δrex/ΔhfsB::BCD::adhE) demonstrated high ethanol productivity and yield, reaching levels of 0.45-0.51 g/L/h and 0.46-0.53 g/g sugars, respectively. The study results shed light on the cofactor balance for cell stability and the high ferredoxin-NAD+ reductase activity of the BCD complex under an intracellular low redox state. They also provide an essential reference for developing strains for improved biofuel production.

Phytostabilization of fly ash from a coalmine in Botswana and biovalorisation of the recovered Napier grass (Pennisetum purpureum Schumach.)

The disposal of fly ash (FA) from coal power plants polluting the air, soil, and groundwater is a major environmental concern. Phytoremediation to rehabilitate fly ash dumpsites is a promising alternative but has practical concerns about the disposal of harvested biomass. This study investigated the effect of supplementing fly ash with fresh sewage sludge (FSS), aged sewage sludge, food waste, and compost (COM) to enhance the phytoremediation potential of Napier grass and its subsequent utilization for ethanol production. The highest removal of Mn (1196.12 g ha-1) and Ni (128.06 g ha-1) from FA could be obtained when Napier is grown in the presence of FSS and inorganic fertilizer (NPK). In addition, the highest bioethanol yield (19.31 g L-1) was obtained from Napier grown in fly ash with COM + NPK, thus providing additional economic benefits aside from the remediation process. Given the significant levels of heavy metals present in the pulp and bio-slurry after ethanol production, further research is required in this area to determine the best ways to utilize this waste such as converting it into biochar.

Lignocellulosic materials valorization in second generation biorefineries: an opportunity to produce fungal biopigments

Second generation biorefineries play an important role in the production of renewable energy and fuels, utilizing forest and agro-industrial residues and by-products as raw materials. The integration of novel bioproducts, such as: xylitol, β-carotene, xylooligosaccharides, and biopigments into the biorefinery's portfolio can offer economic benefits in the valorization of lignocellulosic materials, particularly cellulosic and hemicellulosic fractions. Fungal biopigments, known for their additional antioxidant and antimicrobial properties, are appealing to consumers and can have applications in various industrial sectors, including food and pharmaceuticals. The use of lignocellulosic materials as carbon and nutrient sources for the growth medium helps to reduce production costs, increasing the competitiveness of fungal biopigments in the market. In addition, the implementation of biopigment production in biorefineries allows the utilization of underutilized fractions, such as hemicellulose, for value-added bioproducts. This study deals with the potential of fungal biopigments production in second generation biorefineries in order to diversify the produced biomolecules together with energy generation. A comprehensive and critical review of the recent literature on this topic has been conducted, covering the major possible raw materials, general aspects of second generation biorefineries, the fungal biopigments and their potential for incorporation into biorefineries.

Cloning, expression and purification of cellobiohydrolase gene from Caldicellulosiruptor bescii for efficient saccharification of plant biomass

Anthropogenic activities have led to a drastic shift from natural fuels to alternative renewable energy reserves that demand heat-stable cellulases. Cellobiohydrolase is an indispensable member of cellulases that play a critical role in the degradation of cellulosic biomass. This article details the process of cloning the cellobiohydrolase gene from the thermophilic bacterium Caldicellulosiruptor bescii and expressing it in Escherichia coli (BL21) CondonPlus DE3-(RIPL) using the pET-21a(+) expression vector. Multi-alignments and structural modeling studies reveal that recombinant CbCBH contained a conserved cellulose binding domain III. The enzyme's catalytic site included Asp-372 and Glu-620, which are either involved in substrate or metal binding. The purified CbCBH, with a molecular weight of 91.8 kDa, displayed peak activity against pNPC (167.93 U/mg) at 65°C and pH 6.0. Moreover, it demonstrated remarkable stability across a broad temperature range (60-80°C) for 8 h. Additionally, the Plackett-Burman experimental model was employed to assess the saccharification of pretreated sugarcane bagasse with CbCBH, aiming to evaluate the cultivation conditions. The optimized parameters, including a pH of 6.0, a temperature of 55°C, a 24-hour incubation period, a substrate concentration of 1.5% (w/v), and enzyme activity of 120 U, resulted in an observed saccharification efficiency of 28.45%. This discovery indicates that the recombinant CbCBH holds promising potential for biofuel sector.

The Future of Graphene: Preparation from Biomass Waste and Sports Applications

At present, the main raw material for producing graphene is graphite ore. However, researchers actively seek alternative resources due to their high cost and environmental problems. Biomass waste has attracted much attention due to its carbon-rich structure and renewability, emerging as a potential raw material for graphene production to be used in sports equipment. However, further progress is required on the quality of graphene produced from waste biomass. This paper, therefore, summarizes the properties, structures, and production processes of graphene and its derivatives, as well as the inherent advantages of biomass waste-derived graphene. Finally, this paper reviews graphene's importance and application prospects in sports since this wonder material has made sports equipment available with high-strength and lightweight quality. Moreover, its outstanding thermal and electrical conductivity is exploited to prepare wearable sensors to collect more accurate sports data, thus helping to improve athletes' training levels and competitive performance. Although the large-scale production of biomass waste-derived graphene has yet to be realized, it is expected that its application will expand to various other fields due to the associated low cost and environmental friendliness of the preparation technique.

Nano-based biofuel production from low-cost lignocellulose biomass: environmental sustainability and economic approach

The use of nanomaterials in biofuel production from lignocellulosic biomass offers a promising approach to simultaneously address environmental sustainability and economic viability. This review provides an overview of the environmental and economic implications of integrating nanotechnology into biofuel production from low-cost lignocellulosic biomass. In this review, we highlight the potential benefits and challenges of nano-based biofuel production. Nanomaterials provide opportunities to improve feedstock pretreatment, enzymatic hydrolysis, fermentation, and catalysis, resulting in enhanced process efficiency, lower energy consumption, and reduced environmental impact. Conducting life cycle assessments is crucial for evaluating the overall environmental footprint of biofuel production. An economic perspective that focuses on the cost implications of utilizing nanomaterials in biofuel production is also discussed. A comprehensive understanding of both environmental and economic dimensions is essential to fully harness the potential of nanomaterials in biofuel production from lignocellulosic biomass and to move towards sustainable future energy.

A Network of Processes for Biorefining Burdock Seeds and Roots

In this work, a novel sustainable approach was proposed for the integral valorisation of Arctium lappa (burdock) seeds and roots. Firstly, a preliminary recovery of bioactive compounds, including unsaturated fatty acids, was performed. Then, simple sugars (i.e., fructose and sucrose) and phenolic compounds were extracted by using compressed fluids (supercritical CO2 and propane). Consequently, a complete characterisation of raw biomass and extraction residues was carried out to determine the starting chemical composition in terms of residual lipids, proteins, hemicellulose, cellulose, lignin, and ash content. Subsequently, three alternative ways to utilise extraction residues were proposed and successfully tested: (i) enzymatic hydrolysis operated by Cellulases (Thricoderma resei) of raw and residual biomass to glucose, (ii) direct ethanolysis to produce ethyl levulinate; and (iii) pyrolysis to obtain biochar to be used as supports for the synthesis of sulfonated magnetic iron-carbon catalysts (Fe-SMCC) to be applied in the dehydration of fructose for the synthesis of 5-hydroxymethylfurfural (5-HMF). The development of these advanced approaches enabled the full utilisation of this resource through the production of fine chemicals and value-added compounds in line with the principles of the circular economy.

Catalytic Supercritical Water Gasification of Canola Straw with Promoted and Supported Nickel-Based Catalysts

Lignocellulosic biomass such as canola straw is produced as low-value residue from the canola processing industry. Its high cellulose and hemicellulose content makes it a suitable candidate for the production of hydrogen via supercritical water gasification. However, supercritical water gasification of lignocellulosic biomass such as canola straw suffers from low hydrogen yield, hydrogen selectivity, and conversion efficiencies. Cost-effective and sustainable catalysts with high catalytic activity for supercritical water gasification are increasingly becoming a focal point of interest. In this research study, novel wet-impregnated nickel-based catalysts supported on carbon-negative hydrochar obtained from hydrothermal liquefaction (HTL-HC) and hydrothermal carbonization (HTC-HC) of canola straw, along with other nickel-supported catalysts such as Ni/Al2O3, Ni/ZrO2, Ni/CNT, and Ni/AC, were synthesized for gasification of canola straw on previously optimized reaction conditions of 500 °C, 60 min, 10 wt%, and 23-25 MPa. The order of hydrogen yield for the six supports was (10.5 mmol/g) Ni/ZrO2 > (9.9 mmol/g) Ni/Al2O3 > (9.1 mmol/g) Ni/HTL-HC > (8.8 mmol/g) Ni/HTC-HC > (7.7 mmol/g) Ni/AC > (6.8 mmol/g) Ni/CNT, compared to 8.1 mmol/g for the non-catalytic run. The most suitable Ni/ZrO2 catalyst was further modified using promotors such as K, Zn, and Ce, and the performance of the promoted Ni/ZrO2 catalysts was evaluated. Ni-Ce/ZrO2 showed the highest hydrogen yield of 12.9 mmol/g, followed by 12.0 mmol/g for Ni-Zn/ZrO2 and 11.6 mmol/g for Ni-K/ZrO2. The most suitable Ni-Ce/ZrO2 catalysts also demonstrated high stability over their repeated use. The superior performance of the Ni-Ce/ZrO2 was due to its high nickel dispersion, resilience to sintering, high thermal stability, and oxygen storage capabilities to minimize coke deposition.

Theoretical insight of reactive oxygen species scavenging mechanism in lignin waste depolymerization products

Apart from natural products and synthesis, phenolic compounds can be produced from the depolymerization of lignin, a major waste in biofuel and paper production. This process yields a plethora of aryl propanoid phenolic derivatives with broad biological activities, especially antioxidant properties. Due to its versatility, our study focuses on investigating the antioxidant mechanisms of several phenolic compounds obtained from renewable and abundant resources, namely, syringol (Hs), 4-allylsyringol (HAs), 4-propenylsyringol (HPns), and 4-propylsyringol (HPs). Employing the density functional theory (DFT) approach in conjunction with the QM-ORSA protocol, we aim to explore the reactivity of these compounds in neutralizing hydroperoxyl radicals in physiological and non-polar media. Kinetic and thermodynamic parameter calculations on the antioxidant activity of these compounds were also included in this study. Additionally, our research utilizes the activation strain model (ASM) for the first time to explain the reactivity of the HT and RAF mechanisms in the peroxyl radical scavenging process. It is predicted that HPs has the best rate constant in both media (1.13 × 108 M-1 s-1 and 1.75 × 108 M-1 s-1, respectively). Through ASM analysis, it is observed that the increase in the interaction energy due to the formation of intermolecular hydrogen bonds during the reaction is an important feature for accelerating the hydrogen transfer process. Furthermore, by examining the physicochemical and toxicity parameters, only Hs is not suitable for further investigation as a therapeutic agent because of potential toxicity and mutagenicity. However, overall, all compounds are considered potent HOO˙ scavengers in lipid-rich environments compared to previously studied antioxidants.

Rice straw hydrolysis using in-situ produced enzymes: Feedstock influences fungal enzyme composition and hydrolytic efficiency

Trichoderma reesei RUT-C30 was cultivated on differentially pretreated rice straw and pure cellulose as a carbon source/inducer for cellulase production, and the enzymes were evaluated for hydrolysis of sequential acid and alkali pretreated rice straw. Growth on pretreated rice straw enhanced protein secretion and cellulase activities compared to pure cellulose as a carbon source. The yield of cellulolytic enzymes was higher for alkali pretreated rice straw (ALP-RS), while H2O2-treated (HP-RS) could not induce cellulases to a larger level compared to pure cellulose. Protein concentration was 3.5-fold higher on ALP-RS as compared to pure cellulose, with a maximum filter-paper cellulase (FPase) activity of 1.76 IU/ml and carboxy-methyl cellulase (CMCase) activity of 40.16 IU/ml (2.18 fold higher). Beta-glucosidase (BGL) activity was more or less the same with the different substrates and supplementation of heterologous BGL could result in a quantum jump in hydrolytic efficiencies, which in the case of ALP-RS induced enzymes was 34% (increased from 69.26% to 92.51%). The use of lignocellulosic biomass (LCB) itself as a substrate for the production of cellulase is advantageous not only in terms of raw material costs but also for obtaining a more suitable enzyme profile for biomass hydrolysis.

Independent metabolism of oligosaccharides is the keystone of synchronous utilization of cellulose and hemicellulose in Myceliophthora

The effective utilization of cellulose and hemicellulose, the main components of plant biomass, is a key technical obstacle that needs to be overcome for the economic viability of lignocellulosic biorefineries. Here, we firstly demonstrated that the thermophilic cellulolytic fungus Myceliophthora thermophila can simultaneously utilize cellulose and hemicellulose, as evidenced by the independent uptake and intracellular metabolism of cellodextrin and xylodextrin. When plant biomass serviced as carbon source, we detected the cellodextrin and xylodextrin both in cells and in the culture medium, as well as high enzyme activities related to extracellular oligosaccharide formation and intracellular oligosaccharide hydrolysis. Sugar consumption assay revealed that in contrast to inhibitory effect of glucose on xylose and cellodextrin/xylodextrin consumption in mixed-carbon media, cellodextrin and xylodextrin were synchronously utilized in this fungus. Transcriptomic analysis also indicated simultaneous induction of the genes involved in cellodextrin and xylodextrin metabolic pathway, suggesting carbon catabolite repression (CCR) is triggered by extracellular glucose and can be eliminated by the intracellular hydrolysis and metabolism of oligosaccharides. The xylodextrin transporter MtCDT-2 was observed to preferentially transport xylobiose and tolerate high cellobiose concentrations, which helps to bypass the inhibition of xylobiose uptake. Furthermore, the expression of cellulase and hemicellulase genes was independently induced by their corresponding inducers, which enabled this strain to synchronously utilize cellulose and hemicellulose. Taken together, the data presented herein will further elucidate the degradation of plant biomass by fungi, with implications for the development of consolidated bioprocessing-based lignocellulosic biorefinery.

Transformations of bamboo into bioethanol through biorefinery

The increasing demand for energy has prompted scholars to research alternative energy sources. Bamboo is a species of woody perennial grass that belongs to the Gramineae family and the Bambuseae subfamily. It could be considered a possible lignocellulosic substrate for the production of bioethanol due to its favourable environmental effects and increased yearly biomass yield. Non-renewable fossil fuels cannot provide enough energy to meet the needs of contemporary societies. Among the various alternative energy sources, bioethanol has drawn a lot of attention from people all around the world. This paper reviews the cost and process parameters for the synthesis of bioethanol from bamboo. This review aims to increase the effectiveness of the entire ethanol production process by focusing on pretreatment, enzymatic hydrolysis, and fermentation. The emphasis of this review is on the efficient process for producing bioethanol while maintaining environmental sustainability. When compared to other NaOH pretreatment techniques, bamboo substrates prepared with NaOH and ultra-high-pressure explosion (UHPE) exhibit higher enzymatic hydrolyzability when processed under optimal conditions, such as 100 MPa, 121 °C, and 70 rpm for 2 h, yielding 89.7-95.1% ethanol after 24 h. The article lists the bamboo species responsible for creating each product, making it straightforward for producers to study and select the species based on whatever value-added product they wish to produce bioethanol with different parameters.

Exploring the diverse applications of Carbohydrate macromolecules in food, pharmaceutical, and environmental technologies

Carbohydrates are a class of macromolecules that has significant potential across several domains, including the organisation of genetic material, provision of structural support, and facilitation of defence mechanisms against invasion. Their molecular diversity enables a vast array of essential functions, such as energy storage, immunological signalling, and the modification of food texture and consistency. Due to their rheological characteristics, solubility, sweetness, hygroscopicity, ability to prevent crystallization, flavour encapsulation, and coating capabilities, carbohydrates are useful in food products. Carbohydrates hold potential for the future of therapeutic development due to their important role in sustained drug release, drug targeting, immune antigens, and adjuvants. Bio-based packaging provides an emerging phase of materials that offer biodegradability and biocompatibility, serving as a substitute for traditional non-biodegradable polymers used as coatings on paper. Blending polyhydroxyalkanoates (PHA) with carbohydrate biopolymers, such as starch, cellulose, polylactic acid, etc., reduces the undesirable qualities of PHA, such as crystallinity and brittleness, and enhances the PHA's properties in addition to minimizing manufacturing costs. Carbohydrate-based biopolymeric nanoparticles are a viable and cost-effective way to boost agricultural yields, which is crucial for the increasing global population. The use of biopolymeric nanoparticles derived from carbohydrates is a potential and economically viable approach to enhance the quality and quantity of agricultural harvests, which is of utmost importance given the developing global population. The carbohydrate biopolymers may play in plant protection against pathogenic fungi by inhibiting spore germination and mycelial growth, may act as effective elicitors inducing the plant immune system to cope with pathogens. Furthermore, they can be utilised as carriers in controlled-release formulations of agrochemicals or other active ingredients, offering an alternative approach to conventional fungicides. It is expected that this review provides an extensive summary of the application of carbohydrates in the realms of food, pharmaceuticals, and environment.

Isolation, screening and identification of ethanol producing yeasts from Ethiopian fermented beverages

The growing demand for renewable energy sources such as bioethanol is facing a lack of efficient ethanologenic microbes. This study aimed to isolate and screen ethanologenic yeasts from Ethiopian fermented beverages. A progressive screening and selection approach was employed. Selected isolates were evaluated for bioethanol production using banana peel waste as substrate. A total of 102 isolates were obtained. Sixteen isolates were selected based on their tolerance to stress conditions and carbohydrate fermentation and assimilation capacity. Most found moderately tolerant to 10 %, but slightly tolerant at 15 and 20 % (v/v) ethanol concentration. They yield 15.3 to 20.1 g/L and 9.1 ± 0.6 to 12.9 ± 1.3 g/L ethanol from 2 % (w/v) glucose and 80 g/L banana peel, respectively. Molecular characterization identified them as Saccharomyces cerevisiae strains. Results demonstrate insight about their potential role in the ethanol industry. Optimization of the fermentation conditions is recommended.

Physicochemical Pretreatment of Vietnamosasa pusilla for Bioethanol and Xylitol Production

The consumption of fossil fuels has resulted in severe environmental consequences, including greenhouse gas emissions and climate change. Therefore, transitioning to alternative energy sources, such as cellulosic ethanol, is a promising strategy for reducing environmental impacts and promoting sustainable low-carbon energy. Vietnamosasa pusilla, an invasive weed, has been recognized as a high potential feedstock for sugar-based biorefineries due to its high total carbohydrate content, including glucan (48.1 ± 0.3%) and xylan (19.2 ± 0.4%). This study aimed to examine the impact of NaOH pretreatment-assisted autoclaving on V. pusilla feedstock. The V. pusilla enzymatic hydrolysate was used as a substrate for bioethanol and xylitol synthesis. After treating the feedstock with varying concentrations of NaOH at different temperatures, the glucose and xylose recovery yields were substantially higher than those of the untreated material. The hydrolysate generated by enzymatic hydrolysis was fermented into bioethanol using Saccharomyces cerevisiae TISTR 5339. The liquid byproduct of ethanol production was utilized by Candida tropicalis TISTR 5171 to generate xylitol. The results of this study indicate that the six- and five-carbon sugars of V. pusilla biomass have great potential for the production of two value-added products (bioethanol and xylitol).

Special Issue "Lignocellulosic Biomass II"

As a result of human population growth, the availability of residual lignocellulosic materials from agriculture, forestry, food- and wood-processing industries, and other waste streams is continuously increasing [...].

Bioethanol production from alkali-pretreated rice straw: effects on fermentation yield, structural characterization, and ethanol analysis

Current ethanol production technology has a dire need for efficient conversion of lignocellulosic biomass to fermentable sugars. The conversion requires pretreatment of the biomass, one of the most expensive steps, and thus it is quite necessary to identify the most cost-effective and high-efficiency conversion method. In this study, rice straw (RS) biomass was pretreated using 4% NaOH alkali, soaked for 4 h, and autoclaved for 30 min. The structural and morphological changes were examined using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and scanning electron microscopy (SEM) analysis in both native and alkali-treated RS. The FTIR analysis revealed that native RS contains a considerable amount of lignin that was removed after the pretreatment process. The XRD pattern of the RS revealed an increasing crystallite size of the pretreated lignocellulosic biomass. The study of SEM clearly showed the distorted structure and surface porosity after the pretreatment process. Enzymatic hydrolysis efficiency was checked by comparing the commercial enzymes and microbial hydrolysis extracted from a fungal isolate. The best-reducing sugar yield obtained was 0.62 g/L, achieved at optimized conditions from the commercial enzymes. Fermentation efficiency was checked using the yeast isolate Saccharomyces cerevisiae in both the native and pretreated substrate, and the highest ethanol concentration (21.45%) was achieved using 20% w/v biomass loading, enzyme loading (2:1:1), and fermentation for a week at 30°C and pH 4.5. This concentration was higher than that of the untreated RS (3.67%). The ethanol thus produced was further checked for analysis by the 1H and 13C nuclear magnetic resonance (NMR) methods.

Municipal green waste as substrate for the microbial production of platform chemicals

In Germany alone, more than 5·106 tons of municipal green waste is produced each year. So far, this material is not used in an economically worthwhile way. In this work, grass clippings and tree pruning as examples of municipal green waste were utilized as feedstock for the microbial production of platform chemicals. A pretreatment procedure depending on the moisture and lignin content of the biomass was developed. The suitability of grass press juice and enzymatic hydrolysate of lignocellulosic biomass pretreated with an organosolv process as fermentation medium or medium supplement for the cultivation of Saccharomyces cerevisiae, Lactobacillus delbrueckii subsp. lactis, Ustilago maydis, and Clostridium acetobutylicum was demonstrated. Product concentrations of 9.4 gethanol L-1, 16.9 glactic acid L-1, 20.0 gitaconic acid L-1, and 15.5 gsolvents L-1 were achieved in the different processes. Yields were in the same range as or higher than those of reference processes grown in established standard media. By reducing the waste arising in cities and using municipal green waste as feedstock to produce platform chemicals, this work contributes to the UN sustainability goals and supports the transition toward a circular bioeconomy.

Enhancing saccharification of bamboo shoot shells by rapid one-pot pretreatment of hydrated deep eutectic solvent

In this work, a rapid one-pot hydrated deep eutectic solvent (DES) pretreatment was proposed to facilitate the conversion of carbohydrates from lignocellulosic biomass to monosaccharides. Specifically, the pure and hydrated DES based on benzyl triethylammonium chloride (BTEAC), formic acid (FA) and water was used to pretreat bamboo shoot shells (BSS) by microwave heating. The pretreated solid residues were enzymatically saccharified to produce fermentable sugars, and the hydrolyzed carbohydrates and lignin remained in the hydrolyzate. The results showed that the yield of monosaccharides from the hydrated DES hydrolyzate (193.7-228.4 g/kg) was significantly higher than that (45.9-66.1 g/kg) of pure DES. The 30% hydrated DES pretreatment achieved the best glucose yield (89.03%) and a total monosaccharides yield of 555.4 g/kg, which corresponded to a conversion ratio of carbohydrates to monosaccharides of 87.0%. The proposed process is a robust method for the efficiently convert carbohydrates from BSS into monosaccharides.

Microalgae to Bioenergy: Optimization of Aurantiochytrium sp. Saccharification

Microalgae are a promising feedstock for bioethanol production, essentially due to their high growth rates and absence of lignin. Hydrolysis-where the monosaccharides are released for further fermentation-is considered a critical step, and its optimization is advised for each raw material. The present study focuses on the thermal acid hydrolysis (with sulfuric acid) of Aurantiochytrium sp. through a response surface methodology (RSM), studying the effect of acid concentration, hydrolysis time and biomass/acid ratio on both sugar concentration of the hydrolysate and biomass conversion yield. Preliminary studies allowed to establish the range of the variables to be optimized. The obtained models predicted a maximum sugar concentration (18.05 g/L; R² = 0.990) after 90 min of hydrolysis, using 15% (w/v) biomass/acid ratio and sulfuric acid at 3.5% (v/v), whereas the maximum conversion yield (12.86 g/100 g; R² = 0.876) was obtained using 9.3% (w/v) biomass/acid ratio, maintaining the other parameters. Model outputs indicate that the biomass/acid ratio and time are the most influential parameters on the sugar concentration and yield models, respectively. The study allowed to obtain a predictive model that is very well adjusted to the experimental data to find the best saccharification conditions for the Aurantiochytrium sp. microalgae.

Different pre-treatments and kinetic models for bioethanol production from lignocellulosic biomass: A review

Lignocellulosic biomass is the generally explored substrate to produce bioethanol for environmental sustainability due to its availability in abundance. However, the complex network of cellulose-hemicellulose-lignin present in it makes its hydrolysis as a challenging task. To boost the effectiveness of conversion, biomass is pre-treated before enzymatic hydrolysis to alter or destroy its original composition. Enzymes like Cellulases are widely used for breaking down cellulose into fermentable sugars. Enzymatic hydrolysis is a complex process involving many influencing factors such as pH, temperature, substrate concentration. This review presents major four pre-treatment methods used for hydrolysing different substrates under varied reaction conditions along with their mechanism and limitations. A relative comparison of data analysis for most widely studied 10 kinetic models is briefly explained in terms of substrates used to get the brief insight about hydrolysis rates. The summary of pre-treatment methods and hydrolysis rates including cellulase enzyme kinetics will be the value addition for upcoming researchers for optimising the hydrolysis process.

Lignocellulosic residues from bioethanol production: a novel source of biopolymers for laccase immobilization

The full utilization of the main components in the lignocellulosic biomass is the major goal from a biorefinery point of view, giving not only environmental benefits but also making the process economically viable. In this sense the solid residue obtained in bioethanol production after steam explosion pretreatment, enzymatic hydrolysis, and fermentation of the lignocellulosic biomass, was studied for further valorization. Two different residues were analyzed, one generated by the production of cellulosic ethanol from an energy crop such as switchgrass (Panicum virgatum) and the other, from wood (Eucalyptus globulus). The chemical composition of these by-products showed that they were mainly composed of lignin with a total content range from 70 to 83% (w/w) and small amounts of cellulose and hemicellulose. The present work was focused on devising a new alternative for processing these materials, based on the ability of the ionic liquids (IL) to dissolve lignocellulosic biomass. The resulting mixture of biopolymers and IL constituted the raw material for developing new insoluble biocatalysts. Active hydrogels based on fungal laccase from Dichostereum sordulentum 1488 were attained. A multifactorial analysis of the main variables involved in the immobilization process enabled a more direct approach to improving hydrogel-bound activity. These hydrogels achieved a 97% reduction in the concentration of the estrogen ethinylestradiol, an emerging contaminant of particular concern due to its endocrine activity. The novel biocatalysts based on fungal laccase entrapped on a matrix made from a by-product of second-generation bioethanol production presents great potential for performing heterogeneous catalysis offering extra value to the ethanol biorefinery.

Valorization of Delonix regia Pods for Bioethanol Production

Delonix regia (common name: Flame tree) pods, an inexpensive lignocellulosic waste matrix, were successfully used to produce value-added bioethanol. Initially, the potentiality of D. regia pods as a lignocellulosic biomass was assessed by Fourier-transform infrared spectroscopy (FTIR), which revealed the presence of several functional groups belonging to cellulose, hemicellulose, and lignin, implying that D. regia pods could serve as an excellent lignocellulosic biomass. Response Surface Methodology (RSM) and Central Composite Design (CCD) were used to optimize pretreatment conditions of incubation time (10–70 min), H2SO4 concentration (0.5–3%), amount of substrate (0.02–0.22 g), and temperature (45–100 °C). Then, RSM-suggested 30 trials of pretreatment conditions experimented in the laboratory, and a trial using 0.16 g substrate, 3% H2SO4, 70 min incubation at 90 °C, yielded the highest amount of glucose (0.296 mg·mL−1), and xylose (0.477 mg·mL−1). Subsequently, the same trial conditions were chosen in the downstream process, and pretreated D. regia pods were subjected to enzymatic hydrolysis with 5 mL of indigenously produced cellulase enzyme (74 filter per unit [FPU]) at 50 °C for 72 h to augment the yield of fermentable sugars, yielding up to 55.57 mg·mL−1 of glucose. Finally, the released sugars were fermented to ethanol by Saccharomyces cerevisiae, yielding a maximum of 7.771% ethanol after 72 h of incubation at 30 °C. Conclusively, this study entails the successful valorization of D. regia pods for bioethanol production.

Bioconversion of a Lignocellulosic Hydrolysate to Single Cell Oil for Biofuel Production in a Cost-Efficient Fermentation Process

Cutaneotrichosporon oleaginosus is a highly efficient single cell oil producer, which in addition to hexoses and pentoses can metabolize organic acids. In this study, fed-batch cultivation with consumption-based acetic acid feeding was further developed to integrate the transformation of an industrial paper mill lignocellulosic hydrolysate (LCH) into yeast oil. Employing pentose-rich LCH as a carbon source instead of glucose significantly improved both biomass formation and lipid titer, reaching 55.73 ± 5.20 g/L and 42.1 ± 1.7 g/L (75.5% lipid per biomass), respectively. This hybrid approach of using acetic acid and LCH in one process was further optimized to increase the share of bioavailable carbon from LCH using a combination of consumption-based and continuous feeding. Finally, the techno-economic analysis revealed a 26% cost reduction when using LCH instead of commercial glucose. In summary, we developed a process leading to a holistic approach to valorizing a pentose-rich industrial waste by converting it into oleochemicals.

Co-feeding enhances the yield of methyl ketones

The biotechnological production of methyl ketones is a sustainable alternative to fossil-derived chemical production. To date, the best host for microbial production of methyl ketones is a genetically engineered Pseudomonas taiwanensis VLB120 ∆6 pProd strain, achieving yields of 101 mgg-1 on glucose in batch cultivations. For competitiveness with the petrochemical production pathway, however, higher yields are necessary. Co-feeding can improve the yield by fitting the carbon-to-energy ratio to the organism and the target product. In this work, we developed co-feeding strategies for P. taiwanensis VLB120 ∆6 pProd by combined metabolic modeling and experimental work. In a first step, we conducted flux balance analysis with an expanded genome-scale metabolic model of iJN1463 and found ethanol as the most promising among five cosubstrates. Next, we performed cultivations with ethanol and found the highest reported yield in batch production of methyl ketones with P. taiwanensis VLB120 to date, namely, 154 mg g-1 methyl ketones. However, ethanol is toxic to the cell, which reflects in a lower substrate consumption and lower product concentrations when compared to production on glucose. Hence, we propose cofeeding ethanol with glucose and find that, indeed, higher concentrations than in ethanol-fed cultivation (0.84 g Laq-1 with glucose and ethanol as opposed to 0.48 g Laq-1 with only ethanol) were achieved, with a yield of 85 mg g-1. In a last step, comparing experimental with computational results suggested the potential for improving the methyl ketone yield by fed-batch cultivation, in which cell growth and methyl ketone production are separated into two phases employing optimal ethanol to glucose ratios.

ONE-SENTENCE SUMMARY

By combining computational and experimental work, we demonstrate that feeding ethanol in addition to glucose improves the yield of biotechnologically produced methyl ketones.