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Biohydrogen production from thermochemically pretreated corncob using a mixed culture bioaugmented with Clostridium acetobutylicum
Abstract
Bovine ruminal fluid (BRF) bioaugmented with Clostridium acetobutylicum (Clac) was assessed for hydrolyzing cellulose and produce biohydrogen (BioH2) simultaneously from pretreated corncob in a single step, without the use of external hydrolytic biocatalysts. The corncob was pretreated using three thermochemical methods: H2SO4 2%, 160 °C; NaOH 2%, 140 °C; NaOCl 2%, 140 °C; autohydrolysis: H2O, 190 °C. Subsequently, BioH2 production was carried out using the pretreated material with the highest digestibility applying a Taguchi experimental array to identify the optimal operating conditions. The results showed a higher glucose released from pretreated corncob with H2SO4 (134.7 g/L) compared to pretreated materials by autohydrolysis, NaOH and NaOCl (123 g/L, 89.8 g/L and 52.9 g/L, respectively). The mixed culture was able to hydrolyze the pretreated corncob and produce 575 mL of H2 (at 35 °C, pH 5.5, 1:2 ratio of BRF:Clac and 5% of solids loading) equivalent to 132 L H2/Kg of biomass.
... DES (ChCl-glycerol) by coordinating FeCl 3 was mainly attributed to 78.9% of lignin removal and 93.6% of hemicellulose dissolution of Hybrid Pennisetum under 140°C for 9 h [18]. The main pretreatment methods of corncob include microwave irradiation, acid and alkali pretreatments, and thermochemical pretreatment [25][26][27]. However, few studies focused on hydrogen production from corncob enhanced by DES pretreatment. ...
... Moreover, biohydrogen production from various sources was compared, and the results are shown in Table 3. Hydrogen yield from DES-pretreated corncob was much higher than that of giant reed pretreated by ionic liquids [39], sugarcane bagasse pretreated by hydrochloric acid [50], wheat straw pretreated by hydrothermal alkali [49], and corncob pretreated by acid steamexplosion [44,[46][47][48]. The hydrogen yields of corn stalk pretreated by 2% NaOH [5] and corncob pretreated thermochemically by 2% H 2 SO 4 [25] were similar to the yields obtained in the present study. However, the best hydrogen yield from corncob was achieved with ultrafine grinding pretreatment [42] was best. ...
Deep eutectic solvent pretreatment with different temperatures and durations was applied to corncob to increase hydrogen yield via photo-fermentation. The correlation of composition, enzymatic hydrolysis, and hydrogen production in pretreated corncobs, as well as energy conversion was evaluated. Deep eutectic solvent pretreatment effectively dissolved lignin, retained cellulose, and enhanced both enzymatic hydrolysis and hydrogen production. The maximum cumulative hydrogen yield obtained under a pretreatment condition of 50°C and 12 h was 677.45 mL; this was 2.72 times higher than that of untreated corncob, and the corresponding lignin removal and enzymatic reduction of sugar concentration were 79.15% and 49.83 g/L, respectively; the highest energy conversion efficiency was 12.08%. The hydrogen production delay period was shortened, and the maximum shortening time was 18.9 h. Moreover, the cellulose content in pretreated corncob was positively correlated with both reducing sugar concentration and hydrogen yield and had the strongest influence on hydrogen production.
... BioH(d) [186] Agave hydrolyzate Clostridium acetobutylicum --150.00 BioH(d) [187] Wheat straw Anaerobic sludge --250.50 BioMeth(e) [188] Rice straw Bovine rumen fluid --165.00 ...
Lignocellulose consists of cellulose, hemicellulose, and lignin and is a sustainable feedstock for a biorefinery to generate marketable biomaterials like biofuels and platform chemicals. Enormous tons of lignocellulose are obtained from agricultural waste, but a few tons are utilized due to a lack of awareness of the biotechnological importance of lignocellulose. Underutilizing lignocellulose could also be linked to the incomplete use of cellulose and hemicellulose in biotransformation into new products. Utilizing lignocellulose in producing value-added products alleviates agricultural waste disposal management challenges. It also reduces the emission of toxic substances into the environment, which promotes a sustainable development goal and contributes to circular economy development and economic growth. This review broadly focused on lignocellulose in the production of high-value products. The aspects that were discussed included: (i) sources of lignocellulosic biomass; (ii) conversion of lignocellulosic biomass into value-added products; and (iii) various bio-based products obtained from lignocellulose. Additionally, several challenges in upcycling lignocellulose and alleviation strategies were discussed. This review also suggested prospects using lignocellulose to replace polystyrene packaging with lignin-based packaging products, the production of crafts and interior decorations using lignin, nanolignin in producing environmental biosensors and biomimetic sensors, and processing cellulose and hemicellulose with the addition of nutritional supplements to meet dietary requirements in animal feeding.
... Clostridium acetobutylicum ATCC 824 was propagated under anaerobic conditions in 120 mL glass bottles containing 70 mL of a synthetic medium at pH 6.7 and 35 • C as described by Oliva-Rodríguez et al. [11] for 72 h. The synthetic medium was formulated as described by Medina-Morales et al. [29] using glucose as carbon source at a concentration of 60 g/L. ...
Different strategies have been assessed for the revalorization of guishe to obtain biomolecules. The juice obtained after the mechanical extraction of guishe is rich in phytochemicals and sugars which can be converted to other products. The objective of the present study was to evaluate the production of hydrogen and butanol at different guishe juice concentrations (and therefore, different sugar concentrations) via fermentation in batch mode using Clostridium acetobutylicum ATCC 824. Fermentation assays were performed in triplicate under anaerobic conditions at 35 °C for 142 h. Guishe juice was supplemented with all components of synthetic medium (salts, vitamins and reducing agents), except glucose, and diluted at different concentrations: 20%, 40%, 60%, 80% and 100%. For comparison purposes, a control was carried out in a synthetic medium using glucose as carbon source. Results showed a maximum butanol concentration of 5.39 g/L using 80% guishe juice, corresponding to a productivity and yield of 0.04 g/L h−1 and 0.24 g/g, respectively. Meanwhile, the highest productivity (1.16 L H2/L d−1; 1.99 mmol H2/L h−1) and yield (18.4 L/kg) of hydrogen were obtained with 40% guishe juice. This study demonstrates the potential of guishe juice to be used as a low-cost substrate for hydrogen and butanol production.
... After hydrolysis with cellulase, 80 (IU/g), and xylanase, 234.58 (IU/g), a significant increase in the glucose yield from 193.190 to 342.51 ± 17.45 mg/g BM was achieved in the acid-treated Pj pods (Table S2). The glucose release during enzymatic hydrolysis could be attributed to the high separation of lignin, hemicellulose, and cellulose from the Pj pods during the pretreatment with sulfuric acid [21]. The glucose produced during enzymatic hydrolysis from Pj pods pretreated with NaOH, ammonia, and citric acid was lower than acid hydrolysis. ...
The present study evaluated the hybrid enzymatic hydrolysis and fermentation of Prosopis juliflora pods (Pj pods) for the enhanced biohydrogen production from the activated anaerobic sludge through the waste to energy approach (WtE). The pretreatment effect of sulfuric acid, citric acid, sodium hydroxide, and ammonia has been studied on the Pj pods to make cellulose more accessible for enzyme hydrolysis. The sulfuric acid pretreatment obtained the maximum glucose, 193.19 mg/g BM. The cellulolytic enzyme cocktail comprising cellulase, 80 IU/g, and xylanase, 234.58 IU/g from the newly isolated Trichoderma harzianum BPGF1, is used to hydrolyze the sulfuric acid-treated Pj pods. After the separate enzymatic hydrolysis, the acid-treated Pj pods produced 342.51 mg/g BM glucose. The hybrid enzymatic hydrolysis and fermentation of Pj pods with activated anaerobic sludge was optimized using the central composite design (CCD). The microbial consortium in the anaerobic sludge was identified by next-generation sequencing (NGS) through metagenomic analysis, and the hydrogen was analyzed by gas chromatography. The maximum biohydrogen yield of 1552.25 ± 53.61 mM/L was achieved in the medium containing Pj pods, 13.6% w/v, vitamin solutions, 1.44% v/v, cellulase, 62.74 IU/g BM, and inoculum, 8.67% v/v at an initial pH of 6.49 under anaerobic conditions.
... Corncobs have a distinctive lignocellulosic composition with a higher xylan content and lower lignin and structural ash content compared to other biomass types (Rabemanolontsoa and Saka, 2013). The average reported biomass composition of corncobs derived from NREL analysis methods (NREL, 2021) is, Cellulose 38.9 %, hemicellulose 28. 5 %, and lignin 20. 5 % (Dai et al., 2019;Thangavelu et al., 2018;Li et al., 2018;Medina-Morales et al., 2021;Bu et al., 2021;Dasgupta et al., 2021;Mengstie and Habtu, 2020). a comparative lignocellulose-composition of diferent second-generation bioethanol feedstocks, such as corncob, corn stover, sugar cane bagasse, wheat straw, and rice straw showed cellulose content up to 36 %, 37 %, 39 %, 36 %, 36 % respectively, hemicellulose content up to 38 %, 30 %, 25 %, 30 %, 27 % respectively, and lignin content up to 11 %, 20 %, 21 %, 17 %, 9 % respectively (Ioelovich, 2013). ...
Bioethanol is highly produced and most used biofuel, with lignocellulosic biomass as an ideal choice of feedstock. This study particularly highlights various strategies of second-generation (2 G)-bioethanol production from corncobs. A detailed account of the effects of different pretreatment methods, detoxification methods and fermentation approaches on ethanol yield obtained from corncobs is given to make the reader understand the possibilities of further research improvements in this field. About 31 % of the works, reported dilute sulphuric acid pretreatment. H2SO4, NaOH and their combination pretreatments collectively accounted for 50 % of the total reports. Most other pretreatments were either less reported or completely missing. A combination of acid and alkali pretreatments along with a proper detoxification step is proven to achieve ethanol yield as high as 100 % of the theoretical yield. Techno-economic analysis (TEA), established that the overall cost of operation is essentially comprised of chemical cost and energy consumption. Hence pretreatment and detoxification are key steps in determining process economics. Genetic engineering to construct inhibitor tolerant and consolidated bioprocessing (CBP) compatible microbes for ethanol fermentation is another way to achieve an economical process. Techno economic analysis (TEA) and life cycle assessment (LCA) studies suggested that the key to achieving an overall sustainable corncob-biorefinery is to simultaneously valorize xylan and lignin along with glucan. Based on the market value of the final products, xylooligosaccharides (XOS) are much more beneficial than xylose based ethanol. Hence an ideal corncob-biorefinery would involve the production of high valued end-products from lignocellulose components. However, methods for uniform research data representation, greener pretreatment technologies, and integrated approaches to put together TEA and LCA studies are yet to be developed to assess the corncob-based 2 G bioethanol technologies.
... Another enhancement study involved the use of microorganisms present in bovine ruminal fluid in presence of Clostridium acetobutylicum resulting in the yield of greater than 40 g/L glucose from agave biomass ultimately leading to a total yield of 150 L of hydrogen per Kg of the biomass [51]. In comparison, corncob treated with 2% sulphuric acid before the addition of bovine ruminal fluid with Clostridium acetobutylicum were able to produce 575 mL of hydrogen which was equivalent to 132 L H 2 /Kg of biomass [52]. Hydrogen production from the organic fraction of the municipal solid waste pretreated with Bacillus subtilis in a combination of bacteria/sludge ratio of 0.25 led to a volumetric hydrogen production of 564.4 ± 10.9 mL [53]. ...
Biohydrogen (BioH2) is a low-carbon fuel with high energy efficiency. Although it can be produced using various technologies, the biological method has been deemed more sustainable and economically feasible. Extensive research has also led to identifying of lignocellulosic feedstocks (LCFs) as the highly abundant and renewable raw material for BioH2 production. Although there are many hurdles, the use of microbes-dependent processes for BioH2 production could bring down the operational cost and waste produced, and is efficient enough to meet future energy demands. In this review, the latest developments made in recent years regarding the biological conversion of LCFs to BioH2 are discussed. The microorganisms involved in the technologies of biological pretreatment, photo- and dark fermentation are presented. The recent developments made with genetic engineering and other factors (like pH, temperature, external additives, and nanomaterials) for enhancing the BioH2 production from microorganisms using the LCFs are discussed in detail. Each parameter has been explored and analysed to highlight its effects on maximizing hydrogen yield and enhancing the production rate. This aims to contribute to the ongoing research about the potential of these individual parameters to improve BioH2production. Furthermore, future perspectives on integration and improvement required to enhance the lignocellulosic-biohydrogen production process are also reviewed.
... The biohydrogen yield was improved by 80.94% through microwave treatment compared with the untreated corncob. Other studies have reported efficient production of biohydrogen through microbial valorization of corncob using different strategies such as the use of mixed cultures to ferment thermochemically treated corncob (Medina-Morales et al., 2021) and co-production of biohydrogen and methane from 2-stage fermentation process . ...
Creation of novel products and processes from corncob to achieve goals 3, 6, 7, 9 and 13 of the SDG.
Abstract
Huge amount of renewable biomass in excess of 140 billion metric tons is generated annually due to agro-industrial activities. The agrowastes are often disposed indiscriminately or burnt off, thereby constituting environmental menace and contribute to global warming through the generation of greenhouse gases. Most frequently, the biomasses despite their richness in nutrients are also not found suitable for deserving applications. Among the agrowastes, generation of corncob occupies a prime position due to large scale cultivation of maize worldwide, as more than 200 million tons of corncobs are produced yearly. In recent times, to achieve environmental sustainability, value-addition to wastes, and promotion of advances in bio- and circular economy, agrowastes are now being investigated for valorization through biotechnological route. The preponderance of microbes with their concomitant production of different varieties of degradative enzymes makes them suitable for bioconversion of agrowastes to viable bioproducts in eco-friendly manner. The valorization of agrowastes is in direct responses to achieving five of the goals of SDG; particularly good health and wellbeing (SDG 3), clean water and sanitation (SDG 6), affordable and clean energy (SDG 7), industry and innovation (SDG 9), and climate action (SDG 13). In this review, we present recent activities on biotechnological valorization of corncob to create new range of bio- and nanoproducts to stimulate more research endeavours in this area.
Agricultural industries are the largest waste producer that comprises a major problem worldwide due to the adverse effect of agro-waste on the environment, economy, and social life. Annually 1300 million tons of trash are produced from the agricultural fields, out of which up to 50% are raw materials dumped without treatment. Therefore, minimising agricultural solid waste is imperative to combat its detrimental effects on the health of humans and other animals. Furthermore, agro-waste contains different bioactive compounds such as lignin, cellulose, chitin, and polyphenolic compounds; therefore, it can be envisaged as a potential source for producing biofertiliser, biofuel, biogas, enzymes, vitamins, antioxidants, and other value-added products. Additionally, utilising agro-waste as a raw material diminishes production costs and provides the scope of additional revenue for the reliant industries. Also, the synchronised recovery of renewable energy and wastewater treatment through bioelectrochemical systems (BES) utilising agro-waste products as feedstock demonstrates a waste biorefinery approach leading towards a sustainable circular bioeconomy. Therefore, this chapter elucidates the application of different agro-waste products in the field of BES and their effects on bioenergy production and other value-added product recoveries. Moreover, this chapter aims to enlighten the readers on the advancements in biochemical processes for agro-waste remediation and biochemical conversion technologies to recover valuable biochemicals. In addition, different roadblocks associated with biochemical conversion technologies, considering recommendations and future perspectives, are also highlighted. Additionally, recent developments in potential imminent research areas of agro-waste-assisted BES have also been covered to make this nascent technology ready for large-scale implementation.
In the dark fermentation of hydrogen, development of production host is crucial as bacteria act on substrates and produce hydrogen. The present study aimed to improve hydrogen production through the development of Clostridium acetobutylicum as a superior biohydrogen producer. Glyceraldehyde-3-phosphate dehydrogenase (GAPDH), which produces NADH/NADPH for metabolites and energy in primary pathways, was introduced to enhance hydrogen production. The strain CAC824-G containing gapC that encodes GAPDH showed a 66.3 % higher hydrogen production than the wild-type strain, with increased NADH and NADPH pools. Glucose consumption and other byproducts, such as acetone, butanol, and ethanol, were also high in CAC824-G. Overexpression of gapC resulted in increased hydrogen production with sugars obtained from different biomass, even in the presence of inhibitors such as vanillin, 5-hydroxymethylfufural, acetic acid, and formic acid. Our results imply that overexpression of gapC in Clostridium is possible to expand the production of the reported biochemicals to produce hydrogen.
In the direction of sustainable and zero carbon energy production, hydrogen is considered as a potential fuel with high heating value and energy content compared to other fossil fuels. The present review focuses on conventional and advanced biohydrogen production by utilizing low-cost biomass feedstock through dark fermentation, photo fermentation, bio-photolysis, microbial electrochemical cell, as well as integrated and co-fermentation approaches. Different substrate pretreatment methods, such as thermo-aero-size reduction, acid–alkali or biocatalyst, and combined pretreatment methods are investigated, which can potentially enhance hydrogen productivity multiple-fold. This review explores the application of various hydrogen-selective polymeric membranes, which improves biohydrogen production yield and reduces purification costs. Techno-economic assessment of different biohydrogen production technologies is reviewed based on technological advancements for improved production yield and energy efficiency as well as economic performance enhancement depending upon a minimum selling price, capital cost, operating cost, and profitability. Furthermore, an extensive investigation of the continent or country-specific biohydrogen production challenges is presented. These findings of the current study will explore novel biohydrogen production processes with an aspect of energy efficiency, economics, and environmental footprint.
Industries are working to minimize their reliance on petrochemicals and petroleum-based industrial components and replace them with biobased, sustainable, and environmentally friendly alternatives due to the global warming emergency caused by the uncontrolled production of greenhouse gases. The agricultural waste provides large volumes of lignocellulosic biomass, a sustainable resource material to develop a wide portfolio of bioproducts. Recent developments in integrated biorefineries have enhanced the utilization of waste lignocellulose components to generate biofuels, platform chemicals, resins, bioplastics, additives, and other biobased materials for a variety of applications. Here in this review, we have summarized recent advancements in the processing of lignocellulosic biomass from agricultural waste. Additionally, this review thoroughly discussed the recent technological advancements in the utilization of various lignocellulose biomass constituents for biofuels, biocomposites, and bioplastics. Finally, an assessment of the currently existing literature gaps and prospective future perspectives for the development of lignocellulosic biomass from agricultural waste has been conducted.
Lignocellulosic biomass (LCB) waste materials are abundant in nature, and because of their high cellulose content, they rank among the most widely accessible and preferred feedstocks for the development of cost-effective biorefineries. The main obstacle to the long-term viability of this waste valorization at the pilot size, however, is the complexity of the structural composition of these wastes and the lack of a suitable bioprocess for their economical and efficient biotransformation. The current review investigates the potential for economically viable and environmentally friendly biotransformation of LCB wastes into cellulolytic enzymes and biofuels generation technologies. The review focuses on the efficient synthesis of enzymes and energy from LCB wastes through biotransformation. Based on the update progress, the information of the complexity constraint that currently exists in the LCB structure and the successful limitation surmounted have also been evaluated. To improve the overall bioprocess on a sustainable scale, other possible sustainable recommendations have also been proposed. Such LCB waste valorizations can contribute to the circular economy for sustainable future applications.
Hydrogen is an important industrial material and ideal secondary energy. It is widely used in petrochemical, electronics, metallurgy, food processing, fine organic synthesis, and clean energy. Currently, most of the hydrogen consumed comes from reforming fossil fuels, which results in significant emissions. In comparison, biohydrogen production is environmentally friendly and green, without additional carbon emissions. However, until now, the biohydrogen production system is relatively unstable, hindering its industrialization. Therefore, in this review, the key problems in biohydrogen production, including current measures from the aspects of hydrogenase, hydrogen-producing organisms, hydrogen-evolving reactions, biohydrogen-producing culture and production systems, are summarized. It is concluded that a single microbial strain or hydrogen production method seems difficult for stable production. Instead, coupling hydrogen production with organic waste treatment and multi-type combination is an economically feasible way for scale production, which will be based on suitable waste and depend on the robust strains and appropriate microbial communities.
Continuous environmental degradation, volatility in the oil market, and unimpressive functioning of fossil-based (FB) fuels in compression ignition engines have expanded the tempo of the search for alternative fuels. Due to the astronomical rise in global population, improved agricultural, commercial, and manufacturing activities, enhanced farming and other food production and utilization ventures, agricultural waste generation, renewable fuel consumption, and emission of toxic gases. The need for cost-effective, readily available, and environmentally benign agricultural waste to biofuels has never been more crucial. Biofuels are renewable, biodegradable, low-cost, and eco-friendly fuels that are produced by microorganisms from waste lignocellulosic biomass. Conversion of agricultural wastes to biofuel does not exacerbate food security, contributes to waste management, prevents environmental degradation, and ensures energy security. This study reviews the conversion of agricultural wastes into biofuels with special emphasis on bioethanol, biohydrogen, biobutanol, biomethane, biomethanol, and biodiesel for various applications. It is safe to conclude that wastes generated from agricultural activities and processes are useful and can be harnessed to meet the affordable and accessible global renewable energy target. The result of this investigation will improve the body of knowledge and provide novel strategies and pathways for the utilization of agricultural wastes. Going forward, more collaborative and interdisciplinary studies are required to evolve state-of-the-art, ecofriendly, and cost-effective conversion pathways for agricultural wastes to promote the utilization of the generated renewable fuels. More human, financial, and infrastructural investments are desirable to motivate the conversion of agricultural waste into biofuels to ensure environmental sanitation and sustainability, promote renewable fuel utilization, and avert the raging implosion of our planet.
Lignocellulosic materials (LCM) have garnered attention as feedstocks for second-generation biofuels and platform chemicals. With an estimated annual production of nearly 200 billion tons, LCM represent an abundant source of clean, renewable, and sustainable carbon that can be funneled to numerous biofuels and platform chemicals by sustainable microbial bioprocessing. However, the low bioavailability of LCM due to the recalcitrant nature of plant cell components, the complexity and compositional heterogeneity of LCM monomers, and the limited metabolic flexibility of wild-type product-forming microorganisms to simultaneously utilize various LCM monomers are major roadblocks. Several innovative strategies have been proposed recently to counter these issues and expedite the widespread commercialization of biorefineries using LCM as feedstocks. Herein, we critically summarize the recent advances in the biological valorization of LCM to value-added products. The review focuses on the progress achieved in the development of strategies that boost efficiency indicators such as yield and selectivity, minimize carbon losses via integrated biorefinery concepts, facilitate carbon co-metabolism and carbon-flux redirection towards targeted products using recently engineered microorganisms, and address specific product-related challenges, to provide perspectives on future research needs and developments. The strategies and views presented here could guide future studies in developing feasible and economically sustainable LCM-based biorefineries as a crucial node in achieving carbon neutrality.
The torrefaction pretreatment technology with different temperature varying from 160℃ to 240℃ was utilized to enhance the enzymatic saccharification and hydrogen production potential of corn stover. The composition characteristics, Crystal Intensity (CrI), reducing sugars yield and hydrogen production of the pretreated corn stover were detected to explore the torrefaction pretreatment effectiveness. Results revealed that the reducing sugar yield and hydrogen production from corn stover were improved significantly through torrefaction pretreatment, both the maximum reducing sugar yield of 427.86±19 mg/g Total solid(TS) and hydrogen yield of 123.72 mL/g TS were obtained at 200 ℃, increased by 46.41% and 70.79%, respectively. The kinetic parameters from Gompertz model showed torrefaction pretreatment could shorten the lag phase time of enzymatic saccharification and hydrogen production. The reducing sugar data can be fitted well by fractal-like kinetic model and Gompertz model.
Deep eutectic solvent (DES), a new green solvent, was used to pretreat corncob to enhance biohydrogen production. As a result of the pretreatment, lignin was effectively removed, and the maximum delignification efficiency of 83.12% was achieved. Moreover, the contents of cellulose in the pretreated corncob significantly increased. DES pretreatment effect improved with increasing liquid-solid ratio. The pretreated corncob’s enzymatic saccharification activity and hydrogen production were promoted due to the lower content of lignin. The best result was observed at a ratio of 25:1 (DES:corncob, g/g), in which the reducing sugar concentration (53.91 g/L) and the hydrogen yield (151 mL/g) was 6.8 and 3.1 times than that of untreated corncob, respectively. In addition, the lag time of hydrogen production was obviously shortened to 16.53 h due to the utilization of abundant available fermentable sugars, which accelerated hydrogen production.
Pretreatment of biomass helps to enhance reducing sugar yield from biomass during enzyme hydrolysis tests. Ultrafine grinding was applied to pretreat corncob. The effect of affecting factors including milling time, initial particle size and ball to power weight on the reducing sugar yield from corncob was investigated firstly. And then, an GM(1,N) model was constructed to model the ultrafine grinding pretreatment system predicting the reducing sugar yield from corncob based on experimental data, the results demonstrate GM(1,N) could predict the reducing sugar yield accurately and effectively without depending on the number of samples. The initial particle size was the most critical influential factor affecting reducing sugar yield according to the driving coefficient. The cumulative hydrogen yield was significantly affected by ultrafine grinding pretreatment, the hydrogen yield of pretreated corncob was 153.60±5.8 mL/g total solids, which was higher than that of untreated corncob (113.20±3.2 mL/g total solids).
The xylan richness and comparatively lower extractives, and ash, make the corncob lignocellulose an excellent source for many Biorefinery products and objectives. The unique packing of lignocellulose material in corncob made it susceptible to different pretreatment approaches, that are otherwise less effective on other types of biomasses. Achieving Highest 99% delignification 99%, 100% hemicellulose solubilization (100%), and around 95% cellulose recovery. This led to the application of corncob derived platforms into conventional as well as newer products like super capacitors. Platform sugars and ethanol have been the major products from corncob derived cellulose and hemicellulose, whereas the production of xylooligosaccharides is the second most reported objective. Corncob lignin is mostly valorised for its phenols. Traditional, as well as emerging pretreatment approaches, were reported, and in some reports, corncob-lignocellulose is valorised without a pretreatment. In this review, we compiled all the pretreatment methodologies, employed on corncobs, by collecting the data reported over the past fifty years, through SCOPUS database search. A detailed report has been compiled by comparing the efficiencies of different pretreatment methodologies, and their effect on downstream yields.
Innovative processes to transform plant biomass into renewable chemicals are needed to replace fossil fuels and limit climate change. Clostridium acetobutylicum is of industrial interest because it ferments sugars into acetone, butanol and ethanol (ABE). However, this organism is unable to depolymerize cellulose, limiting its use for the direct transformation of lignocellulose. In this study, the freely secreted family 5 cellulase cphy2058 from Clostridium phytofermentans was efficiently expressed in C. acetobutylicum to enhance cellulolysis. RT-qPCR confirmed the transcription of the cellulase gene, and galactomannan and carboxymethyl cellulose plate assays showed endoglucanase and mannanase activity of cphy2058. ABE titers by the recombinant, cellulase-expressing C. acetobutylicum reached 85.83 mM in cellobiose cultures, whereas ABE titers by wild-type were 44.52 mM. ABE titers by the cellulase-expressing strain were similarly elevated relative to wild-type in cellulose and galactomannan cultures. These results demonstrate a novel strategy to enhance complex substrate utilization by heterologous cellulase expression in C. acetobutylicum.
The lignocellulosic biomass, such as provided by the sugarcane, is an abundant source of raw materials for energy production. Milling and pretreatments can be employed to alter the structure of the materials, remove lignin, and hemicellulose. This pretreatment effect exposes the cellulose and raises its accessibility, which is one of the most important properties to ensure enzymatic digestibility. However, the biomass generated from the sugarcane has different physicochemical characteristics, giving different responses to the pretreatments. In this context, this study aimed to verify the effects of lignin and hemicellulose removal from the sugarcane biomass (external fraction, node, internode, and leaf) on cellulose accessibility. Each fraction was pretreated with acid (5, 10, and 20% w/w, at 121 °C/30 min), alkali (5, 10, 20, and 30% NaOH w/w) and oxidative (0.5, 1, 2, and 3 h charged with 30% sodium chlorite). Accessibility was determined by dye adsorption of Direct Orange (external specific surface) and Direct Blue (internal specific surface). Enzymatic hydrolysis was used to verify the effects of pretreatments and cellulose accessibility on the glucose yield. Delignification by sodium chlorite (oxidative) resulted in lignin removal, with almost complete removal from leaf samples. Accessibility determined indicated that pretreatments that are more aggressive improved cellulose accessibility. The less recalcitrant fraction, the internode, showed 1333.3 mg/g of Direct Orange adsorbed and 746.3 mg/g of Direct Blue. Glucose yield during enzymatic hydrolysis improved with higher cellulose accessibility. Lignin and xylan removal (down to 10% and 1%, respectively) resulted in higher glucose yield, with delignified internode samples showing almost complete cellulose conversion. Hemicellulose and lignin removal by the pretreatments directly influenced cellulose accessibility, resulting in better enzymatic hydrolysis across all fractions. This study successfully showed that lignin and hemicellulose removal of 15% and 10%, respectively, resulting in at least 60% of glucose yield, reaching desired accessibility levels based on dye adsorption of 2079.6 mg/g.
Corncobs are lignocellulosic biomass that has received widespread attention as a promising raw material for bioethanol production because of its abundance and low-cost. They also relieve the predicament and ethics involved in using consumable food crops such as corn for bio-ethanol production when there are serious food shortages in many parts of the world. Corncobs have a high cellulose and hemicellulose content, high-molecular-weight constituents of lignocellulosic residues that can break down into simple sugars for microbial growth. Pretreatment of corncobs is necessary for lignin removal and the breakdown of cellulosic matter. Enzymes or acids act on the lignocelluloses to break down the cellulose into glucose monomers which are utilized by micro-organisms for conversion into ethanol through metabolic pathways. Large-scale production of bio-ethanol is stalled, attributed to the cost of production. The selection of a suitable pretreatment strategy will offset costs but is challenging as different methods offer different advantages over others in improving the overall efficiency of enzymatic saccharification and downstream processing costs. The current review accounts for strategies developed for bio-ethanol production using corncobs since pre-treating corncobs have been thoroughly researched and documented. The review hopes to establish the future of corncobs as a valuable commodity in the bioethanol industryby acting as knowledge or material source of the important processes to assist in designing a cost-effective ethanol production for industrial-scale production.
Graphic Abstract
Ethanol production from cellulosic material is considered one of the most promising options for future biofuel production contributing to both the energy diversification and decarbonization of the transport sector, especially where electricity is not a viable option (e.g., aviation). Compared to conventional (or first generation) ethanol production from food and feed crops (mainly sugar and starch based crops), cellulosic (or second generation) ethanol provides better performance in terms of greenhouse gas (GHG) emissions savings and low risk of direct and indirect land-use change. However, despite the policy support (in terms of targets) and significant R&D funding in the last decade (both in EU and outside the EU), cellulosic ethanol production appears to be still limited. The paper provides a comprehensive overview of the status of cellulosic ethanol production in EU and outside EU, reviewing available literature and highlighting technical and non-technical barriers that still limit its production at commercial scale. The review shows that the cellulosic ethanol sector appears to be still stagnating, characterized by technical difficulties as well as high production costs. Competitiveness issues, against standard starch based ethanol, are evident considering many commercial scale cellulosic ethanol plants appear to be currently in idle or on-hold states.
Valuable biomass conversion processes are highly dependent on the use of effective pretreatments for lignocellulose degradation and enzymes for saccharification. Among the nowadays available treatments, chemical delignification represents a promising alternative to physical-mechanical treatments. Banana is one of the most important fruit crops around the world. After harvesting, it generates large amounts of rachis, a lignocellulosic residue, that could be used for second generation ethanol production, via saccharification and fermentation. In the present study, eight chemical pretreatments for lignin degradation (organosolv based on organic solvents, sodium hypochlorite, hypochlorous acid, hydrogen peroxide, alkaline hydrogen peroxide, and some combinations thereof) have been tested on banana rachis and the effects evaluated in terms of lignin removal, material losses, and chemical composition of pretreated material. Pretreatment based on lignin oxidation have demonstrated to reach the highest delignification yield, also in terms of monosaccharides recovery. In fact, all the delignified samples were then saccharified with enzymes (cellulase and beta-glucosidase) and hydrolysis efficiency was evaluated in terms of final sugars recovery before fermentation. Analysis of Fourier transform infrared spectra (FTIR) has been carried out on treated samples, in order to better understand the structural effects of delignification on lignocellulose. Active chlorine oxidations, hypochlorous acid in particular, were the best effective for lignin removal obtaining in the meanwhile the most promising cellulose-to-glucose conversion.
Anaerobic fungi (phylum Neocallimastigomycota), an early branching family of fungi, are commonly encountered in the digestive tract of mammalian herbivores. To date, isolates from ten described genera have been reported, and several novel taxonomic groupings are detected using culture-independent molecular methods. Anaerobic fungi are recognized as playing key roles in the decomposition of lignocellulose (up to 50% of the ingested and untreated lignocellulose), with their physical penetration and extracellular enzymatical secretion of an unbiased diverse repertoire of cell-wall-degrading enzymes. The secreted cell-wall-degrading enzymes of anaerobic fungi include both free enzymes and extracellular multi-enzyme complexes called cellulosomes, both of which have potential as fiber degraders in industries. In addition, anaerobic fungi can provide large amounts of substrates such as hydrogen, formate, and acetate for their co-cultured methanogens. Consequently, large amounts of methane can be produced. And thus, it is promising to use the co-culture of anaerobic fungi and methanogens in the biogas process to intensify the biogas yield owing to the efficient and robust degradation of recalcitrant biomass by anaerobic fungi and improved methane production from co-cultures of anaerobic fungi and methanogens.
Agave has recently shown its potential as a bioenergy feedstock with promising features such as higher biomass productivity than leading bioenergy feedstock while at the same time being drought-resistant with low water requirements and high sugar to ethanol conversion using ionic liquid (IL) pretreatment. IL pretreatment was studied to develop the first direct side-by-side comparative recalcitrance assessment of the agro-industrial residues from five Agave species [Agave americana (AME), A. angustifolia (ANG), A. fourcroydes (FOU), A. salmiana (SAL), and A. tequilana (TEQ)] using compositional analysis, X-ray diffraction, and the lignin syringyl/guaiacyl subunit ratio (S/G) by pyrolysis molecular beam mass spectrometry (PyMBMS). Prominent calcium oxalate peaks were found only in unpretreated AME, SAL, and TEQ. The S/G ratios of all five unpretreated Agave species were between 1.27 and 1.57 while the IL-pretreated samples were from 1.39 to 1.72. The highest overall sugar production was obtained with IL-pretreated FOU with 492 mg glucose/g biomass and 157 mg xylose/g biomass at 120 °C and 3 h using 1-ethyl-3-methylimidazolium acetate ([C2C1Im][OAc]). An estimated theoretical ethanol yield from the studied agro-industrial residues from the five Agave species was in the range of 1060 to 5800 L ethanol/ha/year. These comparison results demonstrate the potential of the Agave spp. as a suitable biofuel feedstock which can be employed within a biorefinery scheme.
Agave lechuguilla cogollos (heart or pulpy central stem with attached leaf bases) were used as feedstock for production of second generation bioethanol following a scheme based on pretreatment by autohydrolysis, enzymatic saccharification and fermentation of hydrolysates. Autohydrolysis was carried out in a Parr reactor at different severity factors with a solid/liquid ratio of 1/6 (w/v) and 200 rpm. Solid fraction obtained was hydrolyzed using the commercial cellulase Accellerase 1500 (Genencor®). Hydrolysate was fermented with the Saccharomyces cerevisiae ATCC 4126 yeast. Using a severity factor of 4.127 (190 °C during 30 min) it was possible to preserve most of the glucans while increasing its enzymatic digestibility. Enzymatic hydrolysis of the solid fraction showed a maximum yield of 60.85%, with a final glucose concentration of 59 g/L. Ethanol concentration at the end of the fermentation was 25.4 g/L (91% of the theoretical ethanol yield). © 2017, Universidad Autonoma Metropolitana Iztapalapa. All rights reserved.
Background
Limited availability of corn stover due to the competing uses (organic manure, animal feed, bio-materials, and bioenergy) presents a major concern for its future in the bio-economy. Furthermore, biomass research has exhibited different results due to the differences in the supply of enzymes and dissimilar analytical methods. The effect of the two leading pretreatment techniques (dilute acid and alkaline) on glucose yield from three corn stover fractions (cob, stalk, and leaf) sourced from a single harvest in Uganda were studied at temperatures 100, 120, 140, and 160 °C over reaction times of 5, 10, 30, and 60 min. ResultsFrom this study, the highest glucose concentrations obtained from the dilute acid (DA) pretreated cobs, stalks, and leaves were 18.4 g/L (66.8% glucose yield), 16.2 g/L (64.1% glucose yield), and 11.0 g/L (49.5% glucose yield), respectively. The optimal pretreatment settings needed to obtain these yields from the DA pretreated samples were at a temperature of 160 °C over an incubation time of 30 min. The highest glucose concentrations obtained from the alkaline (AL) pretreated cobs, stalks, and leaves were 24.7 g/L (81.73% glucose yield), 21.3 g/L (81.23% glucose yield), and 15.0 g/L (51.92% glucose yield), respectively. To be able to achieve these yields, the optimal pretreatment settings for the cobs and stalks were 140 °C and for a retention time of 30 min, while the leaves require optimal conditions of 140 °C and for a retention time of 60 min. Conclusions
The study recommends that the leaves could be left on the field during harvesting since the recovery of glucose from the pretreated cobs and stalks is higher.
Using response surface method, 20 runs of experiments were carried out to investigate the effects of initial pH variation (5–8), temperature (25–40°C), and glucose concentration (4–12 g/l) on biohydrogen production in dark fermentation method by Clostridium acetobutylicum (PTCC 1492). Results show that the raise of temperature to 37°C leads to increase of hydrogen production volume and yield. It is also observed that while the increase of pH to 6.5 increases hydrogen production, further increment of pH declines volume and yield. Finally, it is found that increase of glucose concentration from 8g/l leads to decrease of yield and increase of production volume.
Maximizing the amount of monomeric sugar yield from lignocellulosic materials requires an effective pretreatment process and identification of an optimal enzyme loading for cost-effectiveness. In this work, a microwave-diluted sulfuric acid pretreatment was applied prior to enzymatic hydrolysis of sago palm bark (SPB). Characterization of the solid fraction was completed before and after the pretreatment process. Analysis of SPB ash showed a presence of 6.8% silica. There was a 32% reduction in lignin content, an increased crystallinity from 29% to 47%, and clear damage and fragmentation to the surface structure of SPB after the pretreatment. Inhibitors were not detectable in the liquor after the microwave-acid pretreatment. The enzymatic hydrolysis of SPB was employed by adding 6 to 42 FPU/g of cellulase and 50 U/g of β-glucosidase to identify the optimal cellulase loading at fixed β-glucosidase loading. The maximum total monomeric sugar yield and total reducing sugar (using DNS method) at 77 mg/g and 378 mg/g were achieved using 24 FPU/g of cellulose, respectively. Thus, this enzyme loading can be recommended for further microwave-acid pretreatment and enzymatic hydrolysis of SPB.
The present work aimed at establishing an efficient degradation and energy recovery system form sugarcane bagasse (SCB) through hydrogen peroxide-acetic acid (HPAC) pretreatment, thermophilic hydrogen production and mesophilic methane production. The degradation ratio of HPAC pretreated SCB (HPAC-SCB, 2%, w/v) exceeded 90% under the biological hydrolysis of C. thermocellum without enzyme addition. The hydrogen yield in the co-culture fermentation of T. thermosaccharolyticum and C. thermocellum from HPAC-SCB (2%, w/v) reached 226 mL/g substrate. The long-term hydrogen fermentation was successfully established with 1.59 L/(L·d), 0.159 L/g substrate for average hydrogen productivity and yield, respectively. Methane production of 0.341 L/g COD (chemical oxygen demand)added was recovered by semi-continuous methane fermentation from hydrogen-producing effluent at 12 days of hydraulic retention time (HRT). Average energy recovery of 8.79 MJ/kg SCB was obtained under the optimal conditions. The present work indicated the promising application of the established process in valorization of lignocellulosic bio-waste.
A comparison between microwave and ultrasound irradiations in the agave pretreatment using dilute sulfuric acid as catalyst was assessed for the first time. Pretreatments were performed using a Taguchi Orthogonal Array L9 (34) to improve the hemicellulose removal and the agave digestibility. The results showed that under optimal conditions, the hemicellulose removal was superior in the pretreatment assisted with microwave (77.5%) compared to ultrasound (28.2%). Enzymatic hydrolysis yield of agave pretreated with microwave (MWOC) was 2-fold higher than agave pretreated with ultrasound (USOC). The relatively mild conditions of pretreatment with MWOC allowed to obtain a hydrolyzed free of inhibitors with a high glucose concentration (47.7 g/L) at low solids loading (10% w/v). However, these conditions did not have a significant effect over the agave pretreated with ultrasound. The pretreatment assisted with MWOC allowed to reduce time and temperature of the process compared to pretreatment with conventional heating.
Lignocellulosic biomass is one of the most abundant renewable resources, and their transformation into bioenergy is an effective approach to alleviate energy shortage and recycle organic wastes. This review summarized the rumen microorganisms and related enzymes, and rumen digestion strategies and mechanisms for improvement of anaerobic rumen digestion in engineering application. Main related literatures were searched on sciencedirect and web of science, systematically summarized, compared and analyzed. Rumen microorganisms accomplish the hydrolysis, acidogenisis and methanogenesis of lignocellulosic biomass, which mainly depends on the synergy of microorganisms and enzymes. Rumen bacteria are the main players and anaerobic fungi play an indispensable role in the hydrolysis and acidogenesis of lignocelluloses. The interaction of different microorganisms promotes the efficiency of lignocelluloses conversion to renewable energy in rumen digestion system, especially protozoa and methanogens. Rumen microorganisms secrete the cellulases, hemicellulases and ligninases, which have their own unique structure and action mode and synergistically promote the lignocellulose degradation. Anaerobic digestion reactor cannot be simply designed through simulating the rumen structure and environment, while the simulation of rumen digestion strategies according to the physicochemical properties and microbial community is more important. The substrate structure and additives significantly improve the rumen digestion of lignocellulosic biomass as a potential design strategy. Finally, the current challenges, future works, and prospects on biological conversion of lignocellulose to bioenergy with rumen microorganisms are outlined.
Stages of waste corn cobs processing leading to the production of biohydrogen via dark fermentation are presented and discussed in this paper. Firstly, the effects of pre-treatment conditions i.e. alkaline, alkaline-oxidizing and Fenton oxidizing pre-treatment of lignocellulosic biomass on the removal of lignin were examined. The solid residue obtained in the first stage was subjected to saccharification by means of enzymatic hydrolysis. The composition of enzymatic hydrolysates and fermentation broths were investigated in order to determine the content of sugars as well as phenolic compounds and fermentation broth composition containing organic acids. The dark fermentation process of the obtained hydrolysates was carried using mixed wastewater sludge from the municipal sewage treatment plant. The highest hydrogen production was obtained for alkaline pre-treated hydrolysates. The effects of investigated chemical pre-treatment methods were discussed in terms of the obtained saccharification efficiency and composition of the gas phase formed during the fermentation, and the composition of fermentation broth.
Consolidated bioprocessing (CBP) by using microbial consortium was considered as a promising approach to achieve direct biofuel production from lignocellulose. In this study, the interaction mechanism of microbial consortium consisting of Thermoanaerobacterium thermosaccharolyticum M5 and Clostridium acetobutylicum NJ4 was analyzed, which could achieve efficient butanol production from xylan through CBP. Strain M5 possesses efficient xylan degradation capability, as 19.73 g/L of xylose was accumulated within 50 h. The efficient xylose utilization capability of partner strain NJ4 could relieve the substrate inhibition to hydrolytic enzymes of xylanase and xylosidase secreted by strain M5. In addition, the earlier solventogenesis of strain NJ4 was observed due to the existence of butyrate generated by strain M5. The mutual interaction of these two strains finally gave 13.28 g/L of butanol from 70 g/L of xylan after process optimization, representing a relatively high butanol production from hemicellulose. Moreover, 7.61 g/L of butanol was generated from untreated corncob via CBP. This successfully constructed microbial consortium exhibits efficient cooperation performance on butanol production from lignocellulose, which could provide a platform for the emerging butanol production from lignocellulose.
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Consolidated bioprocessing (CBP) has been considered as a cost-effective strategy for the efficient bioconversion of lignocellulosic biomass into valuable chemicals. Microbial consortium can complete the complex CBP process through the cooperation within different microorganisms. In this study, a proof-of-concept CBP microbial consortium was designed, which is composed of a hemicellulase-producing bacterium Thermoanaerobacterium thermosaccharolyticum M5 and a succinic acid production specialist Actinobacillus succinogenes 130Z. The continuous conversion of xylan to xylose by T. thermosaccharolyticum could maintain a high hydrolyzing rate, which would facilitate the following succinic acid production by A. succinogenes 130Z. After the process optimization including inoculation time, pH etc., 32.50 g/L of succinic acid with yield of 0.39 g/g was obtained from xylan through CBP, representing the highest succinic acid production directly from hemicellulose materials. In addition, 12.51 g/L of succinic acid was directly produced from 80 g/L of untreated corn cob. These results demonstrated that the proof-of-concept application of this CBP based microbial co-cultivation system could be readily adopted for bioconversion of lignocellulosic biomass into other valuable bio-chemicals.
Biohydrogen production was evaluated using cassava processing wastewater (CPW) and two microbial consortia (Vir and Gal) from different Brazilian environments. The biohydrogen production was optimized using a Box-Behnken design (T, pH, C/N, and % v/v inoculum). Maximum yields were obtained with hydrolyzed substrate: 4.12 and 3.80 mol H2 / for Vir and Gal, respectively. Similarly, the kinetic parameters µ, k, and q were higher with hydrolyzed CPW in both consortia. The molecular analysis of the consortia through Illumina high-throughput sequencing showed the presence of bacteria from the families Porphyromonadaceae, Clostridiaceae, Ruminococcaceae, and Enterococcaceae. The relative abundance of microbial families varies as fermentation progresses. In both consortia, Clostridiaceae reached the maximum relative abundance in the media between 16 and 24 h, interval in which approximately 90% of the biohydrogen is generated.
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The potential of lignocellulosic feedstock has been widely studied, mainly for biofuels production, which usually requires an enzymatic step on the process. Cellulolytic enzymes have been studied as input for bioconversion and as a product from lignocellulose fermentation. The integration of these two perspectives may lead to an economically viable approach for second generation biofuels production, which is nowadays difficult due to high cost of commercial cellulase. Conversely, enzyme production by fermentation of lignocellulosic substrates is inexpensive and the hydrolytic activity of enzymes produced on these substrates, which are to be hydrolyzed, may be better than those enzymes produced on other materials, such as cellulose. Many studies have defined the ideal conditions for cellulase production and saccharification processes separately. In contrast, few reports have developed a unique and integrated process, based on the same feedstock. This review is focused on current advances and innovation in on-site cellulolytic enzymes production using plant biomass, and application of the enzymes in lignocellulose conversion to fermentable sugars for biofuel production.
Biohydrogen is a promising low-carbon energy vector because its high energetic density, and emerging technologies has been studied aiming achieving higher efficiency and competitive H2 production, as is the case of dark fermentation. The objective of this paper is to review dark fermentative biohydrogen production from lignocellulosic biomass, presenting insights of biomass pretreatment methods, influential factors in dark fermentation, and environmental and economic aspects. Rice, corn, and wheat residues have been the main lignocellulosic sources studied, and biohydrogen production ranged from 12 to 7019 mL H2/L. This wide variation is due to the source of lignocellulosic and its pretreatment method, the source and treatment conditions of the inoculum, and the operational conditions of dark fermentation. Acid hydrolysis has been the most applied method to breakdown the complex structure of lignocellulosic biomass, and enzymatic hydrolysis has been used in sequence to improve the process. Moreover, additives (mainly metal materials) have been studied to enhance dark fermentation and lignocellulosic biomass pretreatment. Heat-treated mixed culture is the main used source of inoculum – 100 °C for 30 min is the most usual condition. Temperature, pH, and hydraulic retention time (HRT) have also high influence in the biohydrogen production and yield. Mesophilic temperatures (around 37 °C), pH near 7.0, and HRT of 72 h, are recurrent parameters of dark biohydrogen fermentation. Finally, most studies focused on laboratory scale, which suggest advanced studies on a large scale, and alternatives to improve lignocellulosic biomass pretreatment and biohydrogen production is necessary to make this technology efficient, economical and sustainable.
Lignocellulosic biomass is an inexpensive renewable source that can be used to produce biofuels and bioproducts. The recalcitrance nature of biomass hampers polysaccharide accessibility for enzymes and microbes. Several pretreatment methods have been developed for the conversion of lignocellulosic biomass into value-added products. However, these pretreatment methods also produce a wide range of secondary compounds, which are inhibitory to enzymes and microorganisms. The selection of an effective and efficient pretreatment method discussed in the review and its process optimization can significantly reduce the production of inhibitory compounds and may lead to enhanced production of fermentable sugars and biochemicals. Moreover, evolutionary and genetic engineering approaches are being used for the improvement of microbial tolerance towards inhibitors. Advancements in pretreatment and detoxification technologies may help to increase the productivity of lignocellulose-based biorefinery. In this review, we discuss the recent advancements in lignocellulosic biomass pretreatment technologies and strategies for the removal of inhibitors.
The biological production of H2 represents a renewable and eco-friendly energy alternative compared to fossil fuels. However, its production from lignocellulose involves the use of expensive enzymatic complexes. In the present work, the production of H2 from pretreated agave biomass was evaluated by means of a Consolidated Bioprocess (CBP). This strategy was carried through the interaction of cellulose-degrading microorganisms obtained from bovine ruminal fluid (BRF) capable of enhancing H2 production by Clostridium acetobutylicum. The results obtained show the capacity of BRF to hydrolyze the acid pretreated agave, improving the production of H2 in the experiments where the inoculum of Clostridium was greater. According to the results, production of H2 is significantly affected by the increase of the solids loading, obtaining a maximum H2 production at a 10% of solids loading, pH 5.5 and 35 °C, representing a yield of 150 L of H2 per Kg of biomass in 264 h.
Pretreatment is an essential step prior to the effective valorization of lignocellulosic biomass. However, depending on the pretreatment method, it can be costly and originate potential environmental threats. In this study, green pretreatments, namely Liquid Hot Water (LHW) and 1-butyl-3-methylimidazolium chloride (BmimCl), as well as low concentrated sodium hydroxide solution (NaOH), were applied individually and in combination to pretreat corncob, and their effects on physicochemical properties of fibers were analyzed. The pretreated samples were dissolved in ionic liquid and attempts to prepare regenerated cellulose films have been made. While NaOH was efficient to removal lignin, LHW presented higher solubilization hemicellulose. By combining these treatments, the biomass was fractionated in a complementary way, and a solid enrich-cellulose fraction with high thermal stability and crystallinity was obtained. The BmimCl did not significantly change the chemical composition of biomass and, independent of the treatment applied in combination, samples were regenerated as amorphous cellulose coexisting with lesser amount of cellulose crystalline I. This structural conversion was also confirmed through thermogravimetric analysis, from which a decrease in thermal stability was verified. This latter property was markedly affected by the presence of hemicellulose remained after some pretreatments. The obtained results indicate that each pretreatment performed can meet different application requirements. The LHW-NaOH pretreated sample was the only one suitable to produce regenerated films, which exhibited good mechanical properties to be used in value-added applications, such as packaging.
In this study, tobacco stalk (TS), the solid residue from tobacco industry, was utilized as the raw material for the production of bioethanol through combining processes of alkaline pretreatment or acid-catalyzed (AC) steam pretreatment followed by enzymatic hydrolysis and fermentation. The results indicate that both the two pretreatment strategies could efficiently improve the enzymatic digestibility of TS. Compared to alkaline pretreatment, AC steam pretreatment solubilized more xylan into the liquid phase while preserving more lignin in the pretreated solid substrate. Following enzymatic saccharification of whole pretreated materials from two pretreatment methods at a modest enzyme loading of 15 mg protein/g glucan, the slurry from alkaline pretreatment achieved a slightly higher total monomeric sugar yields than that of AC steam pretreatment. The sugars in the obtained enzymatic hydrolysates from both the two pretreatment technologies showed good sugar-to-ethanol conversion during fermentation with Saccharomyces cerevisiae Lg8-1 strain. The overall mass balances showed that yields of ethanol were 2.75 and 2.69 kg per 10 kg of untreated TS for alkaline and AC steam pretreatments, respectively.
Under the situation of increasingly severe challenge of energy consumption, it is of great importance to make full use of bioresources such as forestry and agricultural residues. Herein, the corncob residues generated after processing corncob were enzymatically hydrolyzed to yield fermentable sugars. To overcome the recalcitrance of corncob residues, three kinds of pretreatment methods, i.e., sulfonation, PFI refining, and wet grinding, were applied; their effects on enzymatic hydrolysis and main characteristics of corncob residues substrate were investigated. The results showed that the enzymatic digestibility of the substrate was greatly enhanced by employing each method. The wet grinding exhibited obvious advantages, e.g., the conversion yield of cellulose to glucose and glucose concentration reached 96.7% and 32.2 g/L after 59 h of enzymatic hydrolysis, respectively. The improvement in enzymatic hydrolysis was mainly attributed to the altered characteristics of the substrate such as swelling ability, specific surface area, and particle size and distribution.
Biohydrogen production from waste lignocellulosic biomass serves the dual purpose of converting waste into valuable products and alleviates waste disposal issues. In this study, waste date seeds were valorized for biohydrogen production via consolidated bioprocessing by Clostridium thermocellum ATCC 27405. Effect of various surfactants (PEG1000, surfactin, Triton X-100) and sodium carbonate (buffering agent) on biohydrogen production from the acid pre-treated substrate was examined. Among the various surfactants, addition of Triton X-100 resulted in the maximum biohydrogen yield of 103.97 mmol/L at an optimal dosage of 0.75% w/v. Triton X-100 supplementation favoured the production of ethanol and acetate as co-metabolites than butyrate. Addition of Na2CO3 to date seed fermentation medium at a concentration of 15 mM enhanced the biohydrogen production by 33.16%. Also, Na2CO3 buffering supported the glycolytic pathway and subsequent ethanol production than acetate/butyrate formation. Combined effect of the optimal dosages of Triton X-100 and Na2CO3 resulted in high hydrogen productivity up to 72 h (0.443 mmol/g h of H2) with a total increase in hydrogen yield of 40.6% at the end of 168 h, as compared to fermentation supplemented with Triton X-100 alone. Further analysis revealed that the combined effects of the additives resulted in better substrate degradation, favourable pH window and cell growth promotion which ensured enhanced hydrogen productivity and yield. Thus, the study highlights a novel stimulatory approach for enhanced biohydrogen production from a new substrate.
In an effort to find a suitable genetic background for efficient cellulolytic secretion, genetically diverse strains were transformed to produce core fungal cellulases namely, β-glucosidase (BGLI), endoglucanase (EGII) and cellobiohydrolase (CBHI) in various combinations and expression configurations. The secreted enzyme activity levels, gene copy number, substrate specificities, as well as hydrolysis and fermentation yields of the transformants were analysed. The effectiveness of the partially cellulolytic yeast transformants to convert two different pre-treated corn residues, namely corn cob and corn husk was then explored. Higher secretion titers were achieved by cellulolytic strains with the YI13 genetic background and cellulolytic transformants produced up to 1.34 fold higher glucose concentrations (g/L) than a control composed of equal amounts of each enzyme type. The transformant co-producing BGLI and EGII in a secreted ratio of 1:15 (cellulase activity unit per gram dry cell weight) converted 56.5% of the cellulose present in corn cob to glucose in hydrolysis experiments and yielded 4.05 g/L ethanol in fermentations. We demonstrate that the choice of optimal genetic background and cellulase activity secretion ratio can improve cellulosic ethanol production by consolidated bioprocessing yeast strains.
The mechanism for enhancing enzymatic hydrolysis during microwave-assisted deep eutectic solvent (Mw-DES)pretreatment in deconstruction of plant cell wall was proposed by combining wet chemical analysis and microscopic measurements. Mw-DES pretreatment achieved significantly higher enzymatic conversion of 81.90% with lower lignin and comparable xylan removal (42.81% and 74.73%, respectively). While DES pretreated sample with higher lignin and xylan removal (66.59% and 74.93%, respectively)obtained limited sugar yield (45.67%). There were no significant differences with respect to chemical structures of lignin fraction between DES and Mw-DES pretreatment but primary discrepancies of topochemical and morphological changes were observed. Non- or low-substituted xylan was directly removed from secondary walls (SW)exposed more cellulose for enzyme attacking after Mw-DES pretreatment. Meanwhile, high-substituted xylan and lignin were synergistically dissolved from cell corner middle lamella (CCML). These topochemical changes of components resulted in cracked and porous cell wall structure, thus facilitating the accessibility of cellulose.
Biohydrogen production via dark fermentation using fermentable sugars from biomass materials is a sustainable way of procuring biohydrogen. Lignocellulosic biomass is a potential renewable feedstock for dark fermentation, but its use is challenged by the recalcitrant nature and generation of certain fermentation inhibitors resulting in compromised fermentation performance. Consolidated bioprocessing (CBP), the successful integration of hydrolysis and fermentation of lignocellulosic biomass to desirable products, has received tremendous research attentions in recent years to boost renewable fuel production in an economically feasible way. A microbial strain capable of both biomass hydrolysis and hydrogen fermentation is critical for successful CBP-based hydrogen fermentation. This review provides comprehensive information on dark fermentation for hydrogen production using lignocellulosic biomass as a potential feedstock with a CBP approach. Consolidated bioprocessing of lignocellulosic biomass for biohydrogen production via native and recombinant microbial strains is discussed in detail. Potential bottlenecks in the above mentioned processes are critically analyzed and future research perspectives are presented.
The porous particulate carriers of activated carbon, bagasse and brick were used for Clostridium acetobutylicum immobilization for coproduction of hydrogen and butanol. The dense microbial population was growing on the carrier surface with the biofilms formed during fermentation. The homogeneous array of the microbial cells on the surface looks some interesting behaviors. The cells have the ability to shuttle between holes in bagasse. Higher efficiency of cell immobilization could be achieved accordingly. The cell concentration during immobilized fermentation was about one order magnitude higher than that during free cell fermentation. Enhanced fermentation for hydrogen and butanol has been achieved during the immobilized fermentation. The highest yield of hydrogen was 1.81 mol/mol when brick was used as immobilization carrier, while the highest butanol yield of 0.22 g/g was achieved during fermentation with bagasse as immobilization carrier. Hydrogen productivity and butanol productivity were up to 403.2 ml/L/h and 0.44 g/L/h, respectively. Hydrogen and butanol production behaved differently in organic and inorganic carrier materials.
Consolidated bioprocessing (CBP) is a promising approach for hydrogen production from lignocellulose owing to its lower cost and higher efficiency. In this study, the newly isolated theromphilic Thermoanaerobacterium sp. strain F6 exhibited the capability of direct utilization of various hemicellulosic and cellulosic materials for hydrogen production, including xylan, Avicel and filter paper etc. Especially, the maximum cumulative hydrogen production reached 370.7 mmoL/L from 60 g/L of xylan. In addition, natural lignocellulosic materials, such as corn cob and sugarcane bagasse without any hydrolytic pretreatment could also be directly utilized as the sole carbon source for hydrogen production. 1822.6 and 826.3 mL H 2 /L of hydrogen were produced from corn cob and sugarcane bagasse, respectively. The high hydrogen production from cellulosic and hemicellulosic materials were both benefit from its efficient secretion of hydrolytic enzymes. Thus, Thermoanaerobacterium sp. strain F6 is a potential candidate for effective conversion of lignocellulose to hydrogen through CBP.
The present work focused in assessing the hydrogen production from pretreated wastes of the paper industry (PIW) by simultaneous saccharification and fermentation (SSF) using anaerobic biofilms developed in natural fibers (ixtle) at different conditions. Anaerobic sludge from brewery wastewater treatment was used for biofilms and they were developed in plastic spheres covered with fiber cord from ixtle. The solid wastes of paper industry were previously pretreated with H2SO4 at 2.5% (v/v) at 120 °C by 30 min. The solids pretreated were hydrolyzed and fermented in batch reactors. All reactors were kept at an initial pH of 5.0 and three levels of enzyme loadings (10, 40 and 70 FPU/mL) and temperatures (35, 45, 55 °C) were assessed. The maximum hydrogen obtained (60.75 mmol/h*g volatile solids) was at 45 °C and 70 FPU/mL, moreover, no methane was detected in all cases.
In this work, three Clostridium strains were tested for butanol production from Agave lechuguilla hydrolysates to select one for co-culturing. The agave hydrolysates medium was supplemented with nutrients and reducing agents to promote anaerobiosis. Clostridium acetobutylicum ATCC 824 had the highest butanol production (6.04 g/L) and was selected for further analyses. In the co-culture process, Bacillus subtilis CDBB 555 was used to deplete oxygen and achieve anaerobic conditions required for butanol production. The co-culture was prepared with C. acetobutylicum and B. subtilis without anaerobic pretreatment. Butanol production in co-culture from agave hydrolysates was compared with experiments using synthetic medium with glucose and a pure culture of C. acetobutylicum. The maximum butanol concentration obtained was 8.28 g/L in the co-cultured hydrolysate medium. Results obtained in the present work demonstrated that agave hydrolysates have the potential for butanol production using a co-culture of B. subtilis and C. acetobutylicum without anaerobic pretreatment.
In second-generation bioethanol production, pretreatment and saccharification have been considered one of the most expensive steps. Thus, we present an approach to improve bioethanol yield by using surfactant concomitantly with corncob pretreatment and saccharification. A response surface methodology (RSM) evaluated the Tween 80 (0%, 5.0%, and 10.0% w/w), in both corncob pretreatment and saccharification, and the enzyme dosage (CellicCTec2: 5.0, 17.5, and 30.0 FPU/gdry matter) on enzymatic digestibility of the acid pretreated biomass. According to the results, higher glucose yields (∼80-85%) could be obtained by reducing the highest enzyme dosage to 41.67% concomitantly by reducing the Tween 80 to 34.2% or 63% by adding it (10% w/w) into only the pretreatment or saccharification, respectively. The RSM suggested applying enzyme dosage between 17.5 and 25.5 FPU/gdry matter associated with the highest Tween 80 amount to improve glucose yield. For statistical validation model, the maximum glucose (80.54%) and xylose (70.66%) yields were obtained for 10.0% of surfactant in both pretreatment and saccharification (25.50 FPU/gdry matter). The hydrolysate was supplemented and fermented by Scheffersomyces stipitis CBS 6054. This yeast fermented the sugars glucose (98.95%), xylose (64.90%), and cellobiose (60.12%) efficiently into ethanol with high yield (0.37 g/g) and volumetric productivity (1.02 gethanol/L.h).
The fermentation characteristics, structural carbohydrate degradation and enzymatic hydrolysis of rice straw ensiled with hemicellulase and Lactobacillus plantarum were examined. Fresh rice straw was ensiled in 1-L laboratory silos with no additive control (CK), L. plantarum (L), hemicellulase (HC) and hemicellulase + L. plantarum (HCL) for 6, 15, 30 and 60 days. All additives increased lactic acid concentration, and reduced pH and lignocellulosic content of the resulting silage relative to the control. The highest organic acid and residual sugar contents and lignocellulose degradation were observed in HCL silage. Hemicellulase alone or combined with L. plantarum improved the enzymatic hydrolysis with higher glucose yield and cellulose convertibility. Fresh rice straw ensiled with the combined additives increased feedstock preservation and cellulose conversion, and is thus recommended as a biological pretreatment for subsequent biofuel production.
Agave lechuguilla is a common plant of Northern Mexico that can be used as feedstock in the context of a biorefinery without competition for food use. In this work, the production of fermentable sugars from this biomass has been studied for the first time using dilute sulfuric acid pretreatment. An experimental design and response surface methodology were applied with temperature (160–200 °C) and acid concentration (0.5–1.5% w/v) chosen as factors. The pretreatment conditions were expressed in a combined severity factor, which ranged from −0.75 to 2.38. According to an optimization criterion that maximizes hemicellulosic sugar recovery in the prehydrolysate and glucose recovery by enzymatic hydrolysis, optimal conditions for acid pretreatment of agave were found to be 180 °C and 1.24% (w/v) H2SO4 at 10% biomass loading. These optimal conditions yielded 87% hemicellulosic sugar recovery and 68 g glucose/100 g glucose in raw agave. The whole slurry resulting from acid pretreatment of agave at optimal conditions was enzymatically saccharified yielding a sugar solution that was co-fermented by the ethanologenic Escherichia coli MM160. This process configuration allowed the fermentation of all sugars in raw A. lechuguilla in a single step reaching an ethanol yield of 73.3%.
Cassava stem is one of the prominent lignocellulosic wastes and has potential as a feedstock for fermentable sugar production. In this study, response surface methodology (RSM) with Box-Behnken design (BBD) was employed to investigate optimum conditions for microwave assisted alkaline pretreatment of cassava stem. Effect of four variables such as reaction time (60–120 s), NaOH concentration (2–4% w/v), solid to liquid ratio (1:25–1:75 g/ml), and microwave frequency (360–720 Hz) were evaluated to improve the sugar recovery. The quadratic model indicated that, reaction time of 116.4 s, NaOH concentration of 3.21% (w/v), substrate to liquid ratio of 1:62.07 g/ml and microwave frequency of 719.86 Hz was found to be optimum and obtained a maximum yield of 43.60 μg/ml of reducing sugar and 91.71 μg/ml of xylose. Under this condition, the cellulose content of cassava stem was increased from 33.27% to 52.34%, while the hemicellulose and lignin content was decreased from 32.30% to 27.15% and 27.15% 14.59%, respectively. Moreover, to evaluate the effectiveness of the pretreatment, Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) and scanning electron microscope (SEM) analysis were employed on the untreated and pretreated cassava stem. These results suggest that the microwave assisted alkaline NaOH pretreatment (MAASHP) influences the fermentable sugar production significantly and further it can be utilized effectively for bioethanol production.
Grass clipping, a cellulose-rich raw material, has great potential to produce biofuels, but must be firstly hydrolyzed to liberate fermentable sugars. In this study, grass clipping was pretreated with ultrasound (US), Ca(OH)2, NaOH, US-Ca(OH)2 and US-NaOH at relatively low temperature to enhance its enzymatic hydrolysis. The solubilization of hemicellulose and lignin, and crystallinity index of cellulose increased after US-alkaline pretreatment, leading to a significant increase of enzyme accessibility to cellulose. Compared with another four pretreatments, US-Ca(OH)2 pretreatment of grass clipping showed the best improvement for reducing sugar yield. X-ray diffraction (XRD) determination and scanning electron microscope (SEM) observation showed that the crystallinity index of grass clipping increased and the grass clipping surface suffered from serious erosion after US-Ca(OH)2 pretreatment. Then, the operating conditions of US-Ca(OH)2 pretreatment and enzymatic hydrolysis were systematically optimized, and the suitable operating conditions were as follows: US power density of 0.65 W/ml, US pretreatment time of 30 min, Ca(OH)2 concentration of 0.75%, pretreatment temperature of 75 °C, enzyme loading of 125 FPU/g, and hydrolysis time of 72 h. The reducing sugar yield of grass clipping pretreated by US-Ca(OH)2 reached 414 mg/g, increasing by 3.5 times compared with that of raw grass clipping. The US-Ca(OH)2 pretreatment of grass clipping at low temperature significantly enhanced the potential of grass clipping as a promising raw material to produce biofuels.
Both autohydrolysis and acidic pretreatments have already been commercialised to allow for the bioconversion of lignocellulosic biomass to valuable products. Recent fundamental research has shown that the pretreatment of lignocellulosic biomass can be enhanced by the suppression of lignin repolymerisation. This work evaluates the application potential of a carbocation scavenger additive that prevents lignin repolymerisation for the autohydrolysis and acidic pretreatment of woody biomass. The results show that the enhancing effect of the scavenger is strongly dependent on the type of biomass. While it proved hardly beneficial in the pretreatment of hardwoods, the pretreatment of recalcitrant softwoods could be greatly enhanced. Softwood has an exceptionally high recalcitrance to biochemical conversion compared to other biomass types, though the reasons for this behaviour have hardly been understood so far. Our study revealed that lignin repolymerisation is a major factor accounting for the exceptional softwood recalcitrance. A sensitivity analysis of pretreatment temperature and time showed that the scavenger can enhance the enzymatic digestibility of softwood cellulose by up to 113% in autohydrolysis and up to 142% in dilute acid pretreatments. The scavenger proved effective for both softwood sawdust and wood chips. Its mode of action in pretreatment was shown to be particularly suitable for the implementation in two-stage pretreatments, which are of high commercial relevance.
This study evaluated the effectiveness of different pretreatments methodologies of hydrogen peroxide, alkaline hydrolysis (calcium hydroxide or sodium hydroxide), alkaline peroxide oxidation (hydrogen peroxide/calcium hydroxide or hydrogen peroxide/sodium hydroxide), and dilute acid hydrolysis (10%(w/w) sulphuric acid) on corn cob biomass waste potential for biofuel and biocommodities utilization. The structure and elemental compositions of treated solid biomass waste fraction were characterised by different analytical techniques such as gravimetry, steremicroscopy, scanning electron microscopy, Light microscopy, Fourier transform infrared spectroscopy, and carbon, hydrogen, nitrogen, sulphur, and oxygen analyser. The solid fractions were also estimated based on cellulose enhancement, hemicellulose solubilization and lignin removal. The liquid fractions were evaluated with atomic absorption spectrophotometry for heavy metals presence and high performance liquid chromatograph (HPLC) for the monosaccharides. In all the pretreatments, the performance of alkaline peroxide oxidation (hydrogen peroxide/sodium hydroxide) was superior to all other methods evaluated with the highest lignin removal (about 78%(w/w)), cellulose was also enhanced (up to 59%(w/w)) from an initial 16%(w/w), and hemicellulose solubilized up to 79%(w/w). More of the sugars were solubilized in the acid pretreated hydrolyzate. The pretreatment methods considered in this study established the economic viability of the corn cob for biocommodities and biofuel production.
The aim of the present work was to assess the autohydrolysis pretreatment of Agave tequilana bagasse for ethanol production. The pretreatment was conducted using a one-liter high pressure Parr reactor under different severity factors (SF) at a 1:6 w/v ratio (solid:liquid) and 200 rpm. The solids obtained under the selected autohydrolysis conditions were subjected to enzymatic hydrolysis with a commercial cellulase cocktail, and the enzymatic hydrolysate was fermented using Saccharomyces cerevisiae. The results obtained from the pretreatment process showed that the glucan content in the pretreated solid was mostly preserved, and an increase in the digestibility was observed for the case with a SF of 4.13 (190 °C, 30 minutes). Enzymatic hydrolysis of the pretreated solids showed a yield of 74.3%, with a glucose concentration of 126 g/L, resulting in 65.26 g/L of ethanol after 10 h of fermentation, which represent a 98.4% conversion according to the theoretical ethanol yield value.
We attempted to develop a pretreatment method for methane fermentation of lignocellulosic biomass using cattle rumen fluid, treated as slaughterhouse waste. When rapeseed (Brassica napus L.) was added to the methane fermentation after being solubilized with rumen fluid, 1.5 times more methane was produced compared with untreated rapeseed. Analysis of the bacterial flora during rumen fluid treatment using the MiSeq next-generation sequencer showed that the predominant phylum shifted from Bacteroidetes, composed of amylolytic Prevotella spp., to Firmicutes, composed of cellulolytic and xylanolytic Ruminococcus spp., in only 6 h. In total, 7 cellulolytic, 25 cello-oligosaccharolytic, and 11 xylanolytic bacteria were detected after investigating the most abundant sequences of detected taxa. The relative abundance of two Ruminococcus species (Ruminococcus albus and R. flavefaciens), known as cellulolytic, cello-oligosaccharolytic, and xylanolytic bacteria, increased with increasing cellulose and hemicellulose degradation rates, and, finally, comprised 48% of all operational taxonomic units. The chronological observation of enzyme activities showed that cellulolytic and xylanolytic activities increased 6 h later, and that oligosaccharolytic activity increased 24 h later. This study detected six bacteria that participate in the degradation of aromatics derived from lignin, which have rarely been reported in rumen fluid. The constitution of the detected bacteria suggests that the aromatics were converted into acetate via benzoate. The list of microbes that cover all lignocellulose-degrading candidates will provide fundamental knowledge for future studies focusing on rumen microbes.
The following study reports bioconversion of corncob into ethanol using hybrid approach for co-utilization of dilute acid hydrolysate (pentose rich stream) and hexose rich stream obtained by enzymatic saccharification employing commercial cellulase Cellic CTec2 as well as in-house cellulase preparations derived from Malbranchea cinnamomea, Scytalidium thermophilium and a recombinant Aspergillus strain. Acid hydrolysis (1% H2SO4) of corncob at 1:15 solid liquid ratio led to removal of 80.5% of hemicellulosic fraction. The solid glucan rich fraction (63.5% glucan, 8.3% pentosans and 27.9% lignin) was hydrolysed at 10% substrate loading rate with different enzymes for 72 h at 50 °C resulting in release of 732 and 535 (mg/g substrate) total sugars by Cellic CTec2 and M. cinnamomea derived enzymes, respectively. The fermentation of enzyme hydrolysate with co-culture of Saccharomyces cerevisiae and Pichia stipitis added in sequential manner resulted in 3.42 and 2.50% (v/v) ethanol in hydrolysate obtained from commercial Cellic CTec2 and M. cinnamomea, respectively. Employing a hybrid approach, where dilute acid hydrolysate stream was added to solid residue along with enzyme Cellic CTec2 during staggered simultaneous saccharification and fermentation at substrate loading rate of 15% resulted in 252 g ethanol/kg corncob.
With the increasing energy crisis and rising concern over climate change, the development of clean alternative energy sources is of great importance. Biohydrogen produced from lignocellulosic biomass is a promising candidate, because of its positives such as readily available, no harmful emissions, environment friendly, efficient, and renewable. However, obstacles still exist to enable the commercialization of biological hydrogen production from lignocellulosic biomass. Thus the objective of this work is to provide update information about the recent progress on lignocellulosic hydrogen conversion via dark fermentation. In this review, the most important technologies associated with lignocellulosic hydrogen fermentation were covered. Firstly, pretreatment methods for better utilization of lignocellulosic biomass are presented, at the same time, hydrolysis methods assisting to achieve efficient hydrogen fermentation were discussed. Afterwards, issues related to bioprocesses for hydrogen production purposes were presented. Additionally, the paper gave challenges and new insights of lignocellulosic biohydrogen production.
The effects of alkaline pretreatment with NaOH, KOH, Ca(OH)2, and NaOCl at varying temperatures and concentrations on the production of sugars, changes in the morphological structure, and the chemical composition of rice straw were evaluated. Enzymatic saccharification of 2% (w/v) KOH-treated rice straw with autoclaving at 121°C, 15 psi, 20 min, gave a maximum yield of 59.90 g/L of reducing sugars, which was slightly higher than that of NaOH (55.48 g/L) with the same conditions. Chemical composition analysis of the rice straw showed that the cellulose content was increased to 71% and 66% after pretreatments with NaOH and KOH, respectively. Fourier Transform Infrared (FTIR) spectroscopy revealed that solubilization and removal of the lignin component also took place. The scanning electron microscope (SEM) analysis showed a marked change in the morphological structure of the treated rice straw compared to the untreated rice straw. These results suggested that pretreatment of rice straw with either 2% (w/v) NaOH or KOH at high temperature could be a promising pretreatment method for sugars production.
Hydrothermal pretreatment of corncobs in aqueous media under non-isothermal conditions is an effective means for solubilizing hemicellulose fractions and improving cellulose hydrolysis. The effects of a range of pretreatment severities (temperatures of 170 to 230 degrees C) on the conversion of corncobs into fermentable sugars were examined. The major differences between the conversions of untreated and pretreated corncobs were the dissolution of hemicelluloses into the prehydrolyzate and the partial removal and relocation of lignin on the external surface of biomass particles (in the form of recondensed droplets) in the pretreated corncobs. Hemicellulose dissolution increased with pretreatment temperature. The maximum sugar recovery (272.3 g/kg raw material) and the minimum accumulation of inhibitory compounds in the prehydrolyzate were observed following treatment at 190 degrees C. While the fibrils of the untreated raw material remained largely intact, serious disruption of the cell wall was observed in SEM images of the surfaces of pretreated samples. Accordingly, the cellulose digestibilities of residues increased from 26.8% for the raw material to almost 100% for the 190 degrees C-treated sample. It was concluded that low severity hydrothermal pretreatment can be successfully applied to corncobs to obtain high cellulose digestibility while operating at low enzyme charges.