Improvement of acetone, butanol, and ethanol production from woody biomass using organosolv pretreatment

Comparative assessment on lignocellulose degrading enzymes and bioethanol production from spent mushroom substrate of Calocybe indica and Volvariella volvacea

In the current study, we compared the production of extracellular lignocellulose degrading enzymes and bioethanol from the spent mushroom substrate (SMS) of Calocybe indica and Volvariella volvacea. From SMS at different stages of the mushroom development cycle, ligninolytic and hydrolytic enzymes were analysed. The activities of lignin-degrading enzymes, including lignin peroxidase (LiP), laccase, and manganese peroxidase (MnP) were maximal in the spawn run and primordial stages, while hydrolytic enzymes including xylanase, cellobiohydrolase (CBH), and carboxymethyl cellulase (CMCase) showed higher activity during fruiting bodies development and at the end of the mushroom growth cycle. SMS of V. volvacea showed relatively lower ligninase activity than the SMS of C. indica, but had the maximum activity of hydrolytic enzymes. The enzyme was precipitated with acetone and further purified with the DEAE cellulose column. The maximum yield of reducing sugars was obtained after hydrolysis of NaOH (0.5 M) pretreated SMS with a cocktail of partially purified enzymes (50% v/v). After enzymatic hydrolysis, the total reducing sugars were 18.68 ± 0.34 g/l (SMS of C. indica) and 20.02 ± 0.87 g/l (SMS of V. volvacea). We observed the highest fermentation efficiency and ethanol productivity (54.25%, 0.12 g/l h) obtained from SMS hydrolysate of V. volvacea after 48 h at 30 ± 2 °C, using co-culture of Saccharomyces cerevisiae MTCC 11,815 and Pachysolen tannophilus MTCC 1077.

Fungal behavior and recent developments in biopulping technology

Biological pretreatment of wood chips by fungi is a well-known approach prior to mechanical- or chemical pulp production. For this biological approach, a limited number of white-rot fungi with an ability to colonize and selectively degrade lignin are used to pretreat wood chips allowing the remaining cellulose to be processed for further applications. Biopulping is an environmentally friendly technology that can reduce the energy consumption of traditional pulping processes. Fungal pretreatment also reduces the pitch content in the wood chips and improves the pulp quality in terms of brightness, strength, and bleachability. The bleached biopulps are easier to refine compared to pulps produced by conventional methodology. In the last decades, biopulping has been scaled up with pilot trials towards industrial level, with optimization of several intermediate steps and improvement of economic feasibility. Nevertheless, fundamental knowledge on the biochemical mechanisms involved in biopulping is still lacking. Overall, biopulping technology has advanced rapidly during recent decades and pilot mill trials have been implemented. The use of fungi as pretreatment for pulp production is in line with modern circular economy strategies and can be implemented in existing production plants. In this review, we discuss some recent advances in biopulping technology, which can improve mechanical-, chemical-, and organosolv pulping processes along with their mechanisms.

Wood waste valorization: Ethanol based organosolv as a promising recycling process

Wood waste is a valuable material that could constitute an abundant and inexpensive source for the production of new materials the recovery of energy. In Europe, about 46% of wood waste is recycled to particleboard and fiberboard, while the other fraction is incinerated. However, a considerable quantity of wood waste shows potential for its transformation into value-added products due to its compositional quality. In this work, wood waste collected at a mechanical treatment plant underwent organosolv treatment to produce a cellulose pulp suitable for manufacturing containerboard. Three variables (temperature, acid concentration, and ethanol concentration) were investigated to find an optimal solution to produce wood pulp by means of Design of Experiment. Wood waste was microwave-heated at 160 °C for 15 min using an acidified ethanol-water solution (2% w/w H2SO4 and 0.8 w/w ethanol concentration), producing pulp with an average cellulose content of 76% where 93% of initial cellulose was retained. Thanks to a one-pot approach, ethanol was totally recovered, 62% of initial lignin was precipitated, and 20 g/l of hemicellulose-derived sugars solution was obtained. Finally, three wood waste samples collected in different periods of the year yielded comparable outcomes, suggesting a good reproducibility of the organosolv process. ANOVA test with a significance level of 0.01 showed a p-value of 0.029 and 0.235 for cellulose content and cellulose recovery, respectively. This study paves the way for an industrial symbiosis between recycling centers and paper mills located in the same territory.

Clostridium as microbial cell factory to enable the sustainable utilization of three generations of feedstocks

The sustainable production of chemicals and biofuels from non-fossil carbon sources is considered key to reducing greenhouse gas (GHG) emissions. Clostridium sp. can convert various substrates, including the 1st-generation (biomass crops), the 2nd-generation (lignocellulosic biomass), and the 3rd-generation (C1 gases) feedstocks, into high-value products, which makes Clostridia attractive for biorefinery applications. However, the complexity of lignocellulosic catabolism and C1 gas utilization make it difficult to construct efficient production routes. Accordingly, this review highlights the advances in the development of three generations of feedstocks with Clostridia as cell factories. At the same time, more attention was given to using agro-industrial wastes (lignocelluloses and C1 gases) as the feedstocks, for which metabolic and process engineering efforts were comprehensively analyzed. In addition, the challenges of using agro-industrial wastes are also discussed. Lastly, several new synthetic biology tools and regulatory strategies are emphasized as promising technologies to be developed to address the aforementioned challenges in Clostridia and realize the efficient utilization of agro-industrial wastes.

Post-hydrolysis of cellulose oligomers by cellulase immobilized on chitosan-grafted magnetic nanoparticles: A key stage of butanol production from waste textile

The recently developed technologies for immobilization of cellulase may address the challenges in costly hydrolysis of cellulose for cellulosic butanol production. In this study, a "hybrid" hydrolysis was developed based on chemical hydrolysis of cellulose to its oligomers followed by enzymatic post-hydrolysis of the resulting "soluble oligomers" by cellulase immobilized on chitosan-coated Fe₃O₄ nanoparticles. This hybrid hydrolysis stage was utilized in the process of biobutanol production from a waste textile, jeans waste, leading to selective formation of glucose and high yield of butanol production by Clostridium acetobutylicum. After validating the immobilization process, the optimum immobilization parameters including enzyme concentration and time were achieved on 8 h and 15.0 mg/mL, respectively. The reusability of immobilized enzyme showed that immobilized cellulase could retain 51.5% of its initial activity after three times reuses. Dilute acid hydrolysis of regenerated cellulose at 120-180 °C for 60 min 0.5-1.0% phosphoric acid led to less than 10 g/L glucose production, and enzymatic post-hydrolysis of the oligomers resulted in up to 51.5 g/L glucose. Fermentation of the hydrolysate was accompanied by 5.3 g/L acetone-butanol-ethanol (ABE) production. The simultaneous co-saccharification and fermentation (SCSF) of soluble and insoluble oligomers of cellulose led to 17.4 g/L ABE production.

Efficient Co-Utilization of Biomass-Derived Mixed Sugars for Lactic Acid Production by Bacillus coagulans Azu-10

Lignocellulosic and algal biomass are promising substrates for lactic acid (LA) production. However, lack of xylose utilization and/or sequential utilization of mixed-sugars (carbon catabolite repression, CCR) from biomass hydrolysates by most microorganisms limits achievable titers, yields, and productivities for economical industry-scale production. This study aimed to design lignocellulose-derived substrates for efficient LA production by a thermophilic, xylose-utilizing, and inhibitor-resistant Bacillus coagulans Azu-10. This strain produced 102.2 g/L of LA from 104 g/L xylose at a yield of 1.0 g/g and productivity of 3.18 g/L/h. The CCR effect and LA production were investigated using different mixtures of glucose (G), cellobiose (C), and/or xylose (X). Strain Azu-10 has efficiently co-utilized GX and CX mixture without CCR; however, total substrate concentration (>75 g/L) was the only limiting factor. The strain completely consumed GX and CX mixture and homoferemnatively produced LA up to 76.9 g/L. On the other hand, fermentation with GC mixture exhibited obvious CCR where both glucose concentration (>25 g/L) and total sugar concentration (>50 g/L) were the limiting factors. A maximum LA production of 50.3 g/L was produced from GC mixture with a yield of 0.93 g/g and productivity of 2.09 g/L/h. Batch fermentation of GCX mixture achieved a maximum LA concentration of 62.7 g/L at LA yield of 0.962 g/g and productivity of 1.3 g/L/h. Fermentation of GX and CX mixture was the best biomass for LA production. Fed-batch fermentation with GX mixture achieved LA production of 83.6 g/L at a yield of 0.895 g/g and productivity of 1.39 g/L/h.

Removal of Diclofenac in Wastewater Using Biosorption and Advanced Oxidation Techniques: Comparative Results

Wastewater treatment is a topic of primary interest with regard to the environment. Diclofenac is a common analgesic drug often detected in wastewater and surface water. In this paper, three commonly available agrifood waste types (artichoke agrowaste, olive-mill residues, and citrus waste) were reused as sorbents of diclofenac present in aqueous effluents. Citrus-waste biomass for a dose of 2 g·L−1 allowed for removing 99.7% of diclofenac present in the initial sample, with a sorption capacity of 9 mg of adsorbed diclofenac for each gram of used biomass. The respective values obtained for olive-mill residues and artichoke agrowaste were around 4.15 mg·g−1. Advanced oxidation processes with UV/H2O2 and UV/HOCl were shown to be effective treatments for the elimination of diclofenac. A significant reduction in chemical oxygen demand (COD; 40–48%) was also achieved with these oxidation treatments. Despite the lesser effectiveness of the sorption process, it should be considered that the reuse and valorization of these lignocellulosic agrifood residues would facilitate the fostering of a circular economy.

Synergy of municipal solid waste co-processing with lignocellulosic waste for improved biobutanol production

Co-processing of lignocellulosic wastes, e.g., garden and paper wastes, and the organic matters fraction of municipal solid waste (OMSW) in an integrated bioprocess is a possible approach to realize the potential of wastes for biobutanol production. Dilute acid pretreatment is a multi-functional stage for breaking the recalcitrant lignocellulose's structure, hydrolyzing hemicellulose, and hydrolyzing/solubilizing starch, leading to a pretreated solid and a rich hydrolysate. In this study, dilute-acid pretreatment of the combination of wastepaper and OMSW, composite I, as well as garden waste and OMSW, composite II, at severe conditions resulted in "pretreatment hydrolysates" containing 33.7 and 19.4 g/L sugar along with 18.9 and 33.2 g/L soluble starch, respectively. In addition, the hydrolysis of solid remained after the pretreatment of composite I and II resulted in "enzymatic hydrolysates" comprising 19.4 and 33 g/L sugar, respectively. The fermentation of the pretreatment hydrolysates and enzymatic hydrolysates resulted in 3.5 and 6.4 g/L ABE from composite I and 15 and 5.2 g/L ABE from composite II, respectively. In this process, 148 and 173 g ABE (60 and 100 g gasoline equivalent/kg) was obtained from each kg composite I and composite II, respectively, where co-processing of OMSW with lignocellulosic wastes resulted in 10 and 49% higher ABE than that produced from the individual substrates.

Acetone, butanol, and ethanol production from puerariae slag hydrolysate through ultrasound-assisted dilute acid by Clostridium beijerinckii YBS3

In this study, puerariae slag (PS) was evaluated as a renewable raw material for acetone-butanol-ethanol (ABE) fermentation. To accelerate the hydrolysis of PS, the method of ultrasound-assisted dilute acid hydrolysis (UAAH) was used. With this effort, 0.69 g reducing sugar was obtained from 1 g raw material under the optimal pretreatment condition. Subsequently, the butanol and total solvent production of 8.79 ± 0.16 g/L and 12.32 ± 0.26 g/L were obtained from the non-detoxified diluted hydrolysate, and the yield and productivity of butanol were 0.19 g/g and 0.12 g/L/h, respectively. Additionally, the changes in the structure of PS after different pretreatment methods were observed using SEM and FT-IR. UAAH resulted in more severe and distinct damage to the dense structure of PS. This study suggests that the UAAH is an attainable but effective pretreatment method, thereby is a promising technique for lignocellulose hydrolysis and improve butanol production.

Towards continuous industrial bioprocessing with solventogenic and acetogenic clostridia: challenges, progress and perspectives

The sustainable production of solvents from above ground carbon is highly desired. Several clostridia naturally produce solvents and use a variety of renewable and waste-derived substrates such as lignocellulosic biomass and gas mixtures containing H2/CO2 or CO. To enable economically viable production of solvents and biofuels such as ethanol and butanol, the high productivity of continuous bioprocesses is needed. While the first industrial-scale gas fermentation facility operates continuously, the acetone-butanol-ethanol (ABE) fermentation is traditionally operated in batch mode. This review highlights the benefits of continuous bioprocessing for solvent production and underlines the progress made towards its establishment. Based on metabolic capabilities of solvent producing clostridia, we discuss recent advances in systems-level understanding and genome engineering. On the process side, we focus on innovative fermentation methods and integrated product recovery to overcome the limitations of the classical one-stage chemostat and give an overview of the current industrial bioproduction of solvents.

Progress in the development of alkali and metal salt catalysed lignocellulosic pretreatment regimes: Potential for bioethanol production

Lignocellulosic biomass (LCB) is well suited to address present day energy and environmental concerns, since it is abundant, environmentally benign and sustainable. However, the commercial application of LCB has been limited by its recalcitrant structure. To date, several biomass pretreatment systems have been developed to address this major bottleneck but have shown to be toxic and costly. Alkali and metal salt pretreatment regimes have emerged as promising non-toxic and low-cost treatments. This paper examines the progress made in lignocellulosic pretreatment using alkali and metal salts. The reaction mechanism of alkali and metal chloride salts on lignocellulosic biomass degradation are reviewed. The effect of salt pretreatment on lignin removal, hemicellulose solubilization, cellulose crystallinity, and physical structural changes are also presented. In addition, the enzymatic digestibility and inhibitor profile from salt pretreated lignocellulosic biomass are discussed. Furthermore, the challenges and future prospects on lignocellulosic pretreatment and bioethanol production are highlighted.

Smart fermentation engineering for butanol production: designed biomass and consolidated bioprocessing systems

There is a renewed interest in acetone-butanol-ethanol (ABE) fermentation from renewable substrates for the sustainable and environment-friendly production of biofuel and platform chemicals. However, the ABE fermentation is associated with several challenges due to the presence of heterogeneous components in the renewable substrates and the intrinsic characteristics of ABE fermentation process. Hence, there is a need to select optimal substrates and modify their characteristics suitable for the ABE fermentation process or microbial strain. This "designed biomass" can be used to establish the consolidated bioprocessing systems. As there are very few reports on designed biomass, the main objectives of this review are to summarize the main challenges associated with ABE fermentation from renewable substrates and to introduce feasible strategies for designing the substrates through pretreatment and hydrolysis technologies as well as through the establishment of consolidated bioprocessing systems. This review offers new insights on improving the efficiency of ABE fermentation from designed renewable substrates.

Enhancing delignification and subsequent enzymatic hydrolysis of corn stover by magnesium oxide-ethanol pretreatment

Corn stover pretreatment by MgO-ethanol was investigated to improve sugar recovery by reducing sugar degradation and enhance enzymatic hydrolysis by improving delignification and reducing inhibitor formation. Results showed MgO as an effective additive and Lewis base, functioned to neutralize the acids released from hemicellulose during pretreatment, reduce monosaccharide degradation and inhibitor formation, and enhance delignification. The optimal pretreatment conditions were 50% ethanol, 0.08 mol/L MgO, and 10% solid loading at 190 °C for 40 min. Under optimal conditions, 98% glucose and 92% xylose were recovered with 89% glucan and 71% xylan recoveries and 60% lignin removal. A total sugar yield of 63% on a received biomass basis after enzymatic hydrolysis was obtained with 78% glucose and 41% xylose yields. The resulting biomass slurry was near-neutral and free of furfural and 5-hydroxymethylfurfural. Thus, the process to isolate high-purity value-added lignin and recover sugars from biomass liquor can be largely simplified.

Semi-hydrolysate of paper pulp without pretreatment enables a consolidated fermentation system with in situ product recovery for the production of butanol

Utilization of lignocellulosic biomasses for biobutanol fermentation usually requires costly processes of pretreatment and enzymatic hydrolysis. In this study, paper pulp (93.2% glucan) was used as a starting biomass material to produce biobutanol. We conducted enzymatic semi-hydrolysis of paper pulp without pretreatment and with low enzyme loading, which produced high concentrations of cellobiose (13.9 g L^-1) and glucose (21.3 g L^-1). In addition, efficient fermentation of the semi-hydrolysate was achieved similar to that with the use of commercial sugars without inhibitors. Finally, we designed a novel non-isothermal simultaneous saccharification and fermentation with in situ butanol recovery, which was composed of a repeated semi-hydrolysis process and successive butanol-extractive fermentation process under the respective optimal conditions. The consolidated system improved butanol production, butanol yields, and butanol productivities and enabled repeated use of medium when compared with other integrated hydrolysis and fermentation processes.

Progress and Opportunities in the Characterization of Cellulose - An Important Regulator of Cell Wall Growth and Mechanics

The plant cell wall is a dynamic network of several biopolymers and structural proteins including cellulose, pectin, hemicellulose and lignin. Cellulose is one of the main load bearing components of this complex, heterogeneous structure, and in this way, is an important regulator of cell wall growth and mechanics. Glucan chains of cellulose aggregate via hydrogen bonds and van der Waals forces to form long thread-like crystalline structures called cellulose microfibrils. The shape, size, and crystallinity of these microfibrils are important structural parameters that influence mechanical properties of the cell wall and these parameters are likely important determinants of cell wall digestibility for biofuel conversion. Cellulose-cellulose and cellulose-matrix interactions also contribute to the regulation of the mechanics and growth of the cell wall. As a consequence, much emphasis has been placed on extracting valuable structural details about cell wall components from several techniques, either individually or in combination, including diffraction/scattering, microscopy, and spectroscopy. In this review, we describe efforts to characterize the organization of cellulose in plant cell walls. X-ray scattering reveals the size and orientation of microfibrils; diffraction reveals unit lattice parameters and crystallinity. The presence of different cell wall components, their physical and chemical states, and their alignment and orientation have been identified by Infrared, Raman, Nuclear Magnetic Resonance, and Sum Frequency Generation spectroscopy. Direct visualization of cell wall components, their network-like structure, and interactions between different components has also been made possible through a host of microscopic imaging techniques including scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. This review highlights advantages and limitations of different analytical techniques for characterizing cellulose structure and its interaction with other wall polymers. We also delineate emerging opportunities for future developments of structural characterization tools and multi-modal analyses of cellulose and plant cell walls. Ultimately, elucidation of the structure of plant cell walls across multiple length scales will be imperative for establishing structure-property relationships to link cell wall structure to control of growth and mechanics.

Pretreatment and hydrolysis of lignocellulosic wastes for butanol production: Challenges and perspectives

Butanol is acknowledged as a drop-in biofuel that can be used in the existing transportation infrastructure, addressing the needs for sustainable liquid fuel. However, before becoming a thoughtful alternative for fossil fuel, butanol should be produced efficiently from a widely-available, renewable, and cost-effective source. In this regard, lignocellulosic materials, the main component of organic wastes from agriculture, forestry, municipalities, and even industries seems to be the most promising source. The butanol-producing bacteria, i.e., Clostridia sp., can uptake a wide range of hexoses, pentoses, and oligomers obtained from hydrolysis of cellulose and hemicellulose content of lignocelluloses. The present work is dedicated to reviewing different processes containing pretreatment and hydrolysis of hemicellulose and cellulose developed for preparing fermentable hydrolysates for biobutanol production.

Semi-hydrolysis with low enzyme loading leads to highly effective butanol fermentation

To improve butanol fermentation efficiencies, semi-hydrolysate with low enzyme loading using H₂SO₄ pretreated rice straw was designed, which preferably produced cellobiose with xylose (instead of glucose). Fermentation of semi-hydrolysates avoided carbon catabolite repression (CCR) and produced higher butanol yield to enzyme loading (0.0290 g U^-1), a newly proposed parameter, than the conventional glucose-oriented hydrolysate (0.00197 g U^-1). Further, overall butanol productivity was improved from 0.0628 g L^-1 h^-1 to 0.265 g L^-1 h^-1 during fermentation of undetoxified semi-hydrolysate by using high cell density. A novel simultaneously repeated hydrolysis and fermentation (SRHF) was constructed by recycling of enzymes and cells, which further improved butanol yield to enzyme loading by 183% and overall butanol productivity by 6.04%. Thus, semi-hydrolysate with SRHF is a smartly designed biomass for efficient butanol fermentation of lignocellulosic materials.

Detoxification of Organosolv-Pretreated Pine Prehydrolysates with Anion Resin and Cysteine for Butanol Fermentation

Bioconversion of lignocellulose to biofuels suffers from the degradation compounds formed during pretreatment and acid hydrolysis. In order to achieve an efficient biomass to biofuel conversion, detoxification is often required before enzymatic hydrolysis and microbial fermentation. Prehydrolysates from ethanol organosolv-pretreated pine wood were used as substrates in butanol fermentation in this study. Six detoxification approaches were studied and compared, including overliming, anion exchange resin, nonionic resin, laccase, activated carbon, and cysteine. It was observed that detoxification by anion exchange resin was the most effective method. The final butanol yield after anion exchange resin treatment was comparable to the control group, but the fermentation was delayed for 72 h. The addition of Ca(OH)₂ was found to alleviate this delay and improve the fermentation efficiency. The combination of Ca(OH)₂ and anion exchange resin resulted in completion of fermentation within 72 h and acetone-butanol-ethanol (ABE) production of 11.11 g/L, corresponding to a yield of 0.21 g/g sugar. The cysteine detoxification also resulted in good detoxification performance, but promoted fermentation towards acid production (8.90 g/L). The effect of salt on ABE fermentation was assessed and the possible role of Ca(OH)₂ was to remove the salts in the prehydrolysates by precipitation.

Fractionation of lignocellulosic biopolymers from sugarcane bagasse using formic acid-catalyzed organosolv process

A one-step formic acid-catalyzed organosolv process using a low-boiling point acid-solvent system was studied for fractionation of sugarcane bagasse. Compared to H₂SO₄, the use of formic acid as a promoter resulted in higher efficiency and selectivity on removals of hemicellulose and lignin with increased enzymatic digestibility of the cellulose-enriched solid fraction. The optimal condition from central composite design analysis was determined as 40 min residence time at 159 °C using water/ethanol/ethyl acetate/formic acid in the respective ratios of 43:20:16:21%v/v. Under this condition, a 94.6% recovery of cellulose was obtained in the solid with 80.2% cellulose content while 91.4 and 80.4% of hemicellulose and lignin were removed to the aqueous-alcohol-acid and ethyl acetate phases, respectively. Enzymatic hydrolysis of the solid yielded 84.5% glucose recovery compared to available glucan in the raw material. Physicochemical analysis revealed intact cellulose fibers with decreased crystallinity while the hemicellulose was partially recovered as mono- and oligomeric sugars. High-purity organosolv lignin with < 1% sugar cross-contamination was obtained with no major structural modification according to Fourier-transform infrared spectroscopy. The work represents an alternative process for efficient fractionation of lignocellulosic biomass in biorefineries.

Co-fermentation of the main sugar types from a beechwood organosolv hydrolysate by several strains of Bacillus coagulans results in effective lactic acid production

Bacillus coagulans is an interesting facultative anaerobic microorganism for biotechnological production of lactic acid that arouses interest. To determine the efficiency of biotechnological production of lactic acid from lignocellulosic feedstock hydrolysates, five Bacillus coagulans strains were grown in lignocellulose organosolv hydrolysate from ethanol/water-pulped beechwood. Parameter estimation based on a Monod-type model was used to derive the basic key parameters for a performance evaluation of the batch process. Three of the Bacillus coagulans strains, including DSM No. 2314, were able to produce lactate, primarily via uptake of glucose and xylose. Two other strains were identified as having the ability of utilizing cellobiose to a high degree, but they also had a lower affinity to xylose. The lactate yield concentration varied from 79.4 ± 2.1 g/L to 93.7 ± 1.4 g/L (85.4 ± 4.7 % of consumed carbohydrates) from the diluted organosolv hydrolysate.

Organosolv Fractionation of Softwood Biomass for Biofuel and Biorefinery Applications

Softwoods represent a significant fraction of the available lignocellulosic biomass for conversion into a variety of bio-based products. Its inherent recalcitrance, however, makes its successful utilization an ongoing challenge. In the current work the research efforts for the fractionation and utilization of softwood biomass with the organosolv process are reviewed. A short introduction into the specific challenges of softwood utilization, the development of the biorefinery concept, as well as the initial efforts for the development of organosolv as a pulping method is also provided for better understanding of the related research framework. The effect of organosolv pretreatment at various conditions, in the fractionation efficiency of wood components, enzymatic hydrolysis and bioethanol production yields is then discussed. Specific attention is given in the effect of the pretreated biomass properties such as residual lignin on enzymatic hydrolysis. Finally, the valorization of organosolv lignin via the production of biofuels, chemicals, and materials is also described.

Process optimization of biogas energy production from cow dung with alkali pre-treated coffee pulp

Biogas production from cow dung with co-substrate agricultural waste is one of the most demanding technologies for generating energy in a sustainable approach considering eco-friendly. In the present study, coffee pulp (CP) was pre-treated with 1% NaOH and combined with various proportions of cow dung (CD) to explore its biogas producing potentiality. The optimization of the process was studied using Response surface methodology. Statistics based on 3-D plots were generated to evaluate the changes in the response surface and to understand the relationship between the biogas yield and other parameters. The highest methane production (144 mL/kg) was achieved after 90 h of incubation with 1:3 of CP and CD at 40 °C. Gas chromatography analyzes the chemical compositions of the generated biogas and its post combustion emissions. The chemical composition of the substrates before digestion and after fermentation (biogas spent sludge) were measured in terms of fiber content and the values were noted as, total solids (0.53%), ash content (9.2%), volatile fatty acid (100 mg/L), organic carbon (46%) and a total carbohydrate (179 mg/g). The results of the optimization of biogas production presented in this work found to have significance with the process parameters. The outcome of the study has supported the fact of conventional combustion technology that has to be upgraded to prevent these hazardous emissions into the atmosphere.

New Insight into Sugarcane Industry Waste Utilization (Press Mud) for Cleaner Biobutanol Production by Using C. acetobutylicum NRRL B-527

In the present study, press mud, a sugar industry waste, was explored for biobutanol production to strengthen agricultural economy. The fermentative production of biobutanol was investigated via series of steps, viz. characterization, drying, acid hydrolysis, detoxification, and fermentation. Press mud contains an adequate amount of cellulose (22.3%) and hemicellulose (21.67%) on dry basis, and hence, it can be utilized for further acetone-butanol-ethanol (ABE) production. Drying experiments were conducted in the temperature range of 60-120 °C to circumvent microbial spoilage and enhance storability of press mud. Furthermore, acidic pretreatment variables, viz. sulfuric acid concentration, solid to liquid ratio, and time, were optimized using response surface methodology. The corresponding values were found to be 1.5% (v/v), 1:5 g/mL, and 15 min, respectively. In addition, detoxification studies were also conducted using activated charcoal, which removed almost 93-97% phenolics and around 98% furans, which are toxic to microorganisms during fermentation. Finally, the batch fermentation of detoxified press mud slurry (the sample dried at 100 °C and pretreated) using Clostridium acetobutylicum NRRL B-527 resulted in a higher butanol production of 4.43 g/L with a total ABE of 6.69 g/L.

Sustainable biobutanol production from pineapple waste by using Clostridium acetobutylicum B 527: Drying kinetics study

Present investigation explores the use of pineapple peel, a food industry waste, for acetone-butanol-ethanol (ABE) production using Clostridium acetobutylicum B 527. Proximate analysis of pineapple peel shows that it contains 35% cellulose, 19% hemicellulose, and 16% lignin on dry basis. Drying experiments on pineapple peel waste were carried out in the temperature range of 60-120°C and experimental drying data was modeled using moisture diffusion control model to study its effect on ABE production. The production of ABE was further accomplished via acid hydrolysis, detoxification, and fermentation process. Maximum total sugar release obtained by using acid hydrolysis was 97g/L with 95-97% and 10-50% removal of phenolics and acetic acid, respectively during detoxification process. The maximum ABE titer obtained was 5.23g/L with 55.6% substrate consumption when samples dried at 120°C were used as a substrate (after detoxification).

Beneficial effects of Trametes versicolor pretreatment on saccharification and lignin enrichment of organosolv-pretreated pinewood

Fungi-treated pinewood yields more organosolv lignin rich in p-hydroxyphenyl (H) subunits.

Influence of surfactant-free ionic liquid microemulsions pretreatment on the composition, structure and enzymatic hydrolysis of water hyacinth

This study investigated the pretreatment performance of surfactant-free ionic liquid microemulsions (ILMs) on water hyacinth. Pretreatment effects were evaluated in terms of lignocellulosic composition, structure and enzymatic hydrolysis. Analysis of the regenerated water hyacinth indicated that the content of the lignocellulosic composition changed, and the surface became more porous. After being pretreated with ILM(a) (mass ratio of toluene: ethanol: 1-ethyl-3-methylimidazolium acetate ([Emim]Ac)=0.35:0.3:0.35) at 70°C for 12h, the maximum delignification of 63.6% was observed. The cellulose of the water hyacinth was well protected and retained during the pretreatment process. After being enzymatically hydrolyzed for 48 h, the reducing sugar yield of the water hyacinth pretreated with ILM(a) at 70°C for 6 h was 563.7 mg/g, and its hydrolysis yield (86.1%) was nearly four and a half times of that of the untreated one (20.2%). In conclusion, the designed surfactant-free ILMs exhibit promising potential application in biomass pretreatment.

A critical review of analytical methods in pretreatment of lignocelluloses: Composition, imaging, and crystallinity

Lignocelluloses are widely investigated as renewable substrates to produce biofuels, e.g., ethanol, methane, hydrogen, and butanol, as well as chemicals such as citric acid, lactic acid, and xanthan gum. However, lignocelluloses have a recalcitrance structure to resist microbial and enzymatic attacks; therefore, many physical, thermal, chemical, and biological pretreatment methods have been developed to open up their structure. The efficiency of these pretreatments was studied using a variety of analytical methods that address their image, composition, crystallinity, degree of polymerization, enzyme adsorption/desorption, and accessibility. This paper presents a critical review of the first three categories of these methods as well as their constraints in various applications. The advantages, drawbacks, approaches, practical details, and some points that should be considered in the experimental methods to reach reliable and promising conclusions are also discussed.