Biobutanol production from rice straw by a non acetone producing Clostridium sporogenes BE01

The Effect of Technological Conditions on ABE Fermentation and Butanol Production of Rye Straw and the Composition of Volatile Compounds

The objective of this study was to evaluate the effect of pretreatment and different technological conditions on the course of ABE fermentation of rye straw (RS) and the composition of volatile compounds in the distillates obtained. The highest concentration of ABE and butanol was obtained from the fermentation of pretreated rye straw by alkaline hydrolysis followed by detoxification and enzymatic hydrolysis. After 72 h of fermentation, the maximum butanol concentration, productivity, and yield from RS were 16.11 g/L, 0.224 g/L/h, and 0.402 g/g, respectively. Three different methods to produce butanol were tested: the two-step process (SHF), the simultaneous process (SSF), and simultaneous saccharification with ABE fermentation (consolidation SHF/SSF). The SHF/SSF process observed that ABE concentration (21.28 g/L) was higher than in the SSF (20.03 g/L) and lower compared with the SHF (22.21 g/L). The effect of the detoxification process and various ABE fermentation technologies on the composition of volatile compounds formed during fermentation and distillation were analyzed.

Investigation of pre-treatment techniques on spent substrate of Pleurotus ostreatus for enhanced biobutanol production using Clostridium acetobutylicum MTCC 11274

Addressing global energy demand, researchers sought eco-friendly biobutanol production from lignocellulosic waste biomass. In the present research work, five different pre-treatment methods viz., Microwave, Ultrasound, Alkali, Acid, and Hybrid, were investigated to explore its biobutanol production potential by utilizing Pleurotus ostreatus spent as substrate. The compositional and physico-chemical changes of the pre-treated Spent Mushroom Substrate (SMS) were assessed using SEM, FTIR, and XRD. Hybrid pre-treatment (Microwave, Alkali, Ultrasound) showed higher delignification when compared to conventional pre-treatment method. Hybrid pre-treated SMS resulted in higher total reducing sugars (521.53 ± 1.84 mg/g) than indigenous SMS (267.89 ± 1.53 mg/g). Fermentation of hybrid pre-treated SMS with Clostridium acetobutylicum MTCC 11274 produced the highest biobutanol concentration (9.84 ± 0.03 g/L) and yielded 0.38 ± 0.02 g/g of biobutanol. This study revealed that hybrid pre-treatment could be a promising solution for enhanced biobutanol production using SMS biomass.

Heterologous expression of NoxA confers aerotolerance in Clostridium sporogenes

Clostridium is a genus of gram-positive obligate anaerobic bacteria. Some species of Clostridium, including Clostridium sporogenes, may be of use in bacteria-mediated cancer therapy. Spores of Clostridium are inert in healthy normoxic tissue but germinate when in the hypoxic regions of solid tumors, causing tumor regression. However, such treatments fail to completely eradicate tumors partly because of higher oxygen levels at the tumor's outer rim. In this study, we demonstrate that a degree of aerotolerance can be introduced to C. sporogenes by transfer of the noxA gene from Clostridium aminovalericum. NoxA is a water-forming NADH oxidase enzyme, and so has no detrimental effect on cell viability. In addition to its potential in cancer treatment, the noxA-expressing strain described here could be used to alleviate challenges related to oxygen sensitivity of C. sporogenes in biomanufacturing.

Production of butanol from lignocellulosic biomass: recent advances, challenges, and prospects

Due to energy and environmental concerns, biobutanol is gaining increasing attention as an alternative renewable fuel owing to its desirable fuel properties. Biobutanol production from lignocellulosic biomass through acetone-butanol-ethanol (ABE) fermentation has gained much interest globally due to its sustainable supply and non-competitiveness with food, but large-scale fermentative production suffers from low product titres and poor selectivity. This review presents recent developments in lignocellulosic butanol production, including pretreatment and hydrolysis of hemicellulose and cellulose during ABE fermentation. Challenges are discussed, including low concentrations of fermentation sugars, inhibitors, detoxification, and carbon catabolite repression. Some key process improvements are also summarised to guide further research and development towards more profitable and commercially viable butanol fermentation.

Biochemical biorefinery: A low-cost and non-waste concept for promoting sustainable circular bioeconomy

The transition from a fossil-based linear economy to a circular bioeconomy is no longer an option but rather imperative, given worldwide concerns about the depletion of fossil resources and the demand for innovative products that are ecocompatible. As a critical component of sustainable development, this discourse has attracted wide attention at the regional and international levels. Biorefinery is an indispensable technology to implement the blueprint of the circular bioeconomy. As a low-cost, non-waste innovative concept, the biorefinery concept will spur a myriad of new economic opportunities across a wide range of sectors. Consequently, scaling up biorefinery processes is of the essence. Despite several decades of research and development channeled into upscaling biorefinery processes, the commercialization of biorefinery technology appears unrealizable. In this review, challenges limiting the commercialization of biorefinery technologies are discussed, with a particular focus on biofuels, biochemicals, and biomaterials. To counteract these challenges, various process intensification strategies such as consolidated bioprocessing, integrated biorefinery configurations, the use of highly efficient bioreactors, simultaneous saccharification and fermentation, have been explored. This study also includes an overview of biomass pretreatment-generated inhibitory compounds as platform chemicals to produce other essential biocommodities. There is a detailed examination of the technological, economic, and environmental considerations of a sustainable biorefinery. Finally, the prospects for establishing a viable circular bioeconomy in Nigeria are briefly discussed.

Valorisation of xylose to renewable fuels and chemicals, an essential step in augmenting the commercial viability of lignocellulosic biorefineries

Biologists and engineers are making tremendous efforts in contributing to a sustainable and green society. To that end, there is growing interest in waste management and valorisation. Lignocellulosic biomass (LCB) is the most abundant material on the earth and an inevitable waste predominantly originating from agricultural residues, forest biomass and municipal solid waste streams. LCB serves as the renewable feedstock for clean and sustainable processes and products with low carbon emission. Cellulose and hemicellulose constitute the polymeric structure of LCB, which on depolymerisation liberates oligomeric or monomeric glucose and xylose, respectively. The preferential utilization of glucose and/or absence of the xylose metabolic pathway in microbial systems cause xylose valorization to be alienated and abandoned, a major bottleneck in the commercial viability of LCB-based biorefineries. Xylose is the second most abundant sugar in LCB, but a non-conventional industrial substrate unlike glucose. The current review seeks to summarize the recent developments in the biological conversion of xylose into a myriad of sustainable products and associated challenges. The review discusses the microbiology, genetics, and biochemistry of xylose metabolism with hurdles requiring debottlenecking for efficient xylose assimilation. It further describes the product formation by microbial cell factories which can assimilate xylose naturally and rewiring of metabolic networks to ameliorate xylose-based bioproduction in native as well as non-native strains. The review also includes a case study that provides an argument on a suitable pathway for optimal cell growth and succinic acid (SA) production from xylose through elementary flux mode analysis. Finally, a product portfolio from xylose bioconversion has been evaluated along with significant developments made through enzyme, metabolic and process engineering approaches, to maximize the product titers and yield, eventually empowering LCB-based biorefineries. Towards the end, the review is wrapped up with current challenges, concluding remarks, and prospects with an argument for intense future research into xylose-based biorefineries.

Role of Biofuels in Energy Transition, Green Economy and Carbon Neutrality

Modern civilization is heavily reliant on petroleum-based fuels to meet the energy demand of the transportation sector. However, burning fossil fuels in engines emits greenhouse gas emissions that harm the environment. Biofuels are commonly regarded as an alternative for sustainable transportation and economic development. Algal-based fuels, solar fuels, e-fuels, and CO2-to-fuels are marketed as next-generation sources that address the shortcomings of first-generation and second-generation biofuels. This article investigates the benefits, limitations, and trends in different generations of biofuels through a review of the literature. The study also addresses the newer generation of biofuels highlighting the social, economic, and environmental aspects, providing the reader with information on long-term sustainability. The use of nanoparticles in the commercialization of biofuel is also highlighted. Finally, the paper discusses the recent advancements that potentially enable a sustainable energy transition, green economy, and carbon neutrality in the biofuel sector.

Improving probiotic spore yield using rice straw hydrolysate

Spore-forming Bacillus sp. has been extensively studied for their probiotic properties. In this study, an acid-treated rice straw hydrolysate was used as carbon source to produce the spores of Bacillus coagulans. The results showed that this hydrolysate significantly improved the spore yield compared with other carbon sources such as glucose. Three significant medium components including rice straw hydrolysate, MnSO₄ and yeast extract were screened by Plackett-Burman design. These significant variables were further optimized by response surface methodology (RSM). The optimal values of the medium components were rice straw hydolysate of 27% (v/v), MnSO₄ of 0·78 g l^-1 and yeast extract of 1·2 g l^-1 . The optimized medium and RSM model for spore production were validated in a 5 l bioreactor. Overall, this sporulation medium containing acid-treated rice straw hydrolysate has a potential to be used in the production of B. coagulans spores.

Biobutanol production from municipal solid waste: Technical and economic analysis

Novel processes for the production of acetone-butanol-ethanol (ABE) from municipal solid waste (MSW) were developed and simulated using Aspen Plus®. In scenario 1, a conventional distillation system was used, while a gas stripping system was coupled with a fermenter in scenario 2. In scenario 3, pervaporation (PV) and gas stripping systems right after the fermentation reactor were applied. Gas stripping increased the total ABE produced while the addition of the PV module decreased the number of distillation columns from 6 to 2 as well as created 6.4% increments in the amount of butanol in comparison with scenario 1. Economical evaluation resulted in having payout periods of 15.9, 4.4, and 2.9 years for scenarios 1 to 3, respectively. These results show that using MSW as an inexpensive sugar-rich feedstock together with gas stripping PV system is a promising solution to overcome the major obstacles in the way of the ABE production.

Isolation of Clostridium from Yunnan-Tibet hot springs and description of Clostridium thermarum sp. nov. with lignocellulosic ethanol production

Lignocellulose is considered a major source of renewable energy that serve as an alternative to the fossil fuels. Members of the genus Clostridium are some of the many microorganisms that have the ability to degrade lignocellulose efficiently to sugar, which can be further converted to biofuel. In this study, we isolated twelve Clostridium strains from hot spring samples of Yunnan and Tibet, of which isolates SYSU GA15002^T and SYSU GA17076 showed low 16S rRNA gene sequence identity profiles to any of the validly named Clostridium strains (<94.0%). Studies using a polyphasic taxonomy approach concluded that the two isolates represent one novel species of the genus Clostridium, for which we propose the name Clostridium thermarum sp. nov., with SYSU GA15002^T as the type strain of the species. Isolate SYSU GA15002^T has an optimum growth temperature at 45°C. Fermentation of the substrates cellobiose, cellulose, xylan and untreated straw powder by this strain results in the production of ethanol, along with acetate and formate. The complete pathways for the conversion of cellulose and xylan to ethanol is also predicted from the genome of isolate SYSU GA15002^T, which revealed a single step conversion of lignocellulosic biomass through consolidated bioprocessing. This paper is a comprehensive study encompassing isolation, polyphasic taxonomy, lignocellulose biodegradation and the genomic information of Clostridium in Yunnan-Tibet hot springs.

Butanol production from lignocellulosic biomass: revisiting fermentation performance indicators with exploratory data analysis

After just more than 100 years of history of industrial acetone-butanol-ethanol (ABE) fermentation, patented by Weizmann in the UK in 1915, butanol is again today considered a promising biofuel alternative based on several advantages compared to the more established biofuels ethanol and methanol. Large-scale fermentative production of butanol, however, still suffers from high substrate cost and low product titers and selectivity. There have been great advances the last decades to tackle these problems. However, understanding the fermentation process variables and their interconnectedness with a holistic view of the current scientific state-of-the-art is lacking to a great extent. To illustrate the benefits of such a comprehensive approach, we have developed a dataset by collecting data from 175 fermentations of lignocellulosic biomass and mixed sugars to produce butanol that reported during the past three decades of scientific literature and performed an exploratory data analysis to map current trends and bottlenecks. This review presents the results of this exploratory data analysis as well as main features of fermentative butanol production from lignocellulosic biomass with a focus on performance indicators as a useful tool to guide further research and development in the field towards more profitable butanol manufacturing for biofuel applications in the future.

The significance of proline on lignocellulose-derived inhibitors tolerance in Clostridium acetobutylicum ATCC 824

When lignocellulosic biomass was used for acetone-butanol-ethanol (ABE) fermentation, several lignocellulose-derived inhibitors, which are toxic to Clostridium acetobutylicum, were generated during acid hydrolysis process and seriously hindered the industrialization of lignocellulosic butanol. In this study, an engineered strain 824(proABC) with significantly improved tolerance to multiple lignocellulose-derived inhibitors (formic acid and phenolic compounds) was constructed by strengthening the proline biosynthesis. The engineered strain exhibited more effective synthesis ability of proline and scavenging ability of reactive oxygen species (ROS). Consequently, the butanol produced by 824(proABC) was 1-, 2.4- or 3.4-fold higher than that of the wild type strain when using the undetoxified hydrolysate of soybean straw, rice straw or corn straw as the substrate, respectively. Therefore, enhancing the proline biosynthesis can be used as an effective strategy to improve the tolerance of C. acetobutylicum to multiple lignocellulose-derived inhibitors, and 824(proABC) has great potential to produce butanol from undetoxified lignocellulosic hydrolysates.

Nutrient modulation based process engineering strategy for improved butanol production from Clostridium acetobutylicum

The present study demonstrates a process engineering strategy to achieve high butanol titer and productivity from wild type Clostridium acetobutylicum MTCC 11274. In the first step, two different media were optimized with the objectives of maximizing the biomass and butanol productivity, respectively. In the next step, attributes of these two media compositions were integrated to design a two-stage fed-batch process which resulted in maximal butanol productivity of 0.55 g L^-1 h^-1 with titer of 13.1 g L^-1 . Further, two-stage fed-batch process along with combinatorial use of magnesium limitation and calcium supplementation resulted in the highest butanol titer and productivity of 16.5 g L^-1 and 0.59 g L^-1 h^-1 , respectively. Finally, integration of the process with gas stripping and modulation of feeding duration resulted in a cumulative butanol titer of 54.3 g L^-1 and productivity of 0.58 g L^-1 h^-1 . The strategy opens up possibility of developing a viable butanol bioprocess. © 2019 American Institute of Chemical Engineers Biotechnol. Prog., 35: e2771, 2019.

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.

Influence of size reduction treatments on sugar recovery from Norway spruce for butanol production

This study investigated whether the effectiveness of pretreatment is limited by a size reduction of Norway spruce wood in biobutanol production. The spruce was milled, chipped, and mashed for hydrogen peroxide-acetic acid (HPAC) and dilute acid (DA) pretreatment. Sugar recoveries from chipped and mashed spruce after enzymatic hydrolysis were higher than from milled spruce, and the recoveries were not correlated with the spruce fiber length. HPAC pretreatment resulted in almost 100% glucose and 88% total reducing sugars recoveries from chipped spruce, which were apparently higher than DA pretreatment, demonstrating greater effectiveness of HPAC pretreatment on sugar production. The butanol and ABE yield from chipped spruce were 126.5 and 201.2 g/kg pretreated spruce, respectively. The yields decreased with decreasing particle size due to biomass loss in the pretreatment. The results suggested that Norway spruce chipped to a 20 mm length is applicable to the production of platform sugars for butanol fermentation.

Recent trends in biobutanol production

Finite availability of conventional fossil carbonaceous fuels coupled with increasing pollution due to their overexploitation has necessitated the quest for renewable fuels. Consequently, biomass-derived fuels are gaining importance due to their economic viability and environment-friendly nature. Among various liquid biofuels, biobutanol is being considered as a suitable and sustainable alternative to gasoline. This paper reviews the present state of the preprocessing of the feedstock, biobutanol production through fermentation and separation processes. Low butanol yield and its toxicity are the major bottlenecks. The use of metabolic engineering and integrated fermentation and product recovery techniques has the potential to overcome these challenges. The application of different nanocatalysts to overcome the existing challenges in the biobutanol field is gaining much interest. For the sustainable production of biobutanol, algae, a third-generation feedstock has also been evaluated.

Waste-to-biofuel: production of biobutanol from sago waste residues

The main concern of extensive production of biobutanol has been associated with the high cost of the substrate and the relatively low tolerance of Clostridia to biobutanol production. In this study, the use of fermentable cassava waste residue (CWR) as substrate for biobutanol production was investigated using solvent-tolerant Clostridium sp. Four of obligatory, solvent-producing bacteria were isolated from sago industry waste sites. The NSW, PNAS1, SB5 and SBI4 strains showed identical profiles of 16S rRNA gene sequence similarity of Bacillus coagulans, Clostridium bifermentans and Clostridium sp. (97% similarity) and a wide range of carbohydrate substrate; however, the CWR was found to be suitable for the production of biobutanol considerably. Batch culture study was carried out using parameters such as time and temperature and carbon sources have been studied and optimized. Using pre-optimized CWR medium, significant amount of solvent production was observed in NSW, PNAS1, SB5 and SBI4 with 1.53, 3.36, 1.56 and 2.5 g L^-1of butanol yield and 6.84, 9.012, 8.32 and 8.22 g L^-1of total solvents, respectively. On the basis of these studies, NSW is proposed to represent the B. coagulans for butanol production directly from sago waste residues.

Substrate dependent modulation of butanol to ethanol ratio in non-acetone forming Clostridium sporogenes NCIM 2918

Present study reports a non-acetone producing Clostridium sporogenes strain as a potential producer of liquid biofuels. Alcohol production was positively regulated by sorbitol and instant dry yeast as carbon and nitrogen sources respectively. Media optimization resulted in maximum butanol and ethanol titer (gL^-1) of 12.1 and 7.9 respectively. Depending on the combination of carbon sources, the organism was found to manipulate its metabolism towards synthesis of either ethanol or butanol, thereby affecting the total alcohol titer. Among various dual substrate combinations, glucose-glycerol mixture in the ratio of 60:40 resulted in maximum butanol and ethanol titer (gL^-1) of 11.9 and 12.1 respectively with total alcohol productivity of 0.59gL^-1h^-1. In the mixture, when pure glycerol was replaced with crude glycerol, butanol and ethanol titer (gL^-1) of 11.2 and 11.7 was achieved. Hence, the strain shows immense potential for biofuels production using crude glycerol as cheap substrate.

Simultaneous saccharification and fermentation of hemicellulose to butanol by a non-sporulating Clostridium species

Production of lignocellulosic butanol has drawn increasing attention. However, currently few microorganisms can produce biofuels, particularly butanol, from lignocellulosic biomass via simultaneous saccharification and fermentation. Here we report discovery of a wild-type, mesophilic Clostridium sp. strain MF28 that ferments xylan to produce butanol (up to 3.2g/L) without the addition of saccharolytic enzymes and without any chemical pretreatments. Application of selective pressure from 2-deoxy-d-glucose facilitated isolation of strain MF28, which exhibits inactivation of genes (gid and ccp genes) responsible for carbon catabolite repression, thus allowing strain MF28 to simultaneously ferment a combination of glucose (30g/L), xylose (15g/L), and arabinose (15g/L) to produce 11.9g/L of butanol. Strain MF28 possesses several unique features: (i) non-sporulating, (ii) no acetone/ethanol, (iii) complete hemicellulose-binding enzymatic domain, and (iv) absence of carbon catabolite repression. These unique characteristics demonstrate the industrial potential of strain MF28 for cost-effective biofuel generation from lignocellulosic biomass.

Butanol production employing fed-batch fermentation by Clostridium acetobutylicum GX01 using alkali-pretreated sugarcane bagasse hydrolysed by enzymes from Thermoascus aurantiacus QS 7-2-4

Sugarcane bagasse (SB) is a potential feedstock for butanol production. However, biological production of butanol from SB is less economically viable. In this study, evaluation of eight pretreatments on SB showed that alkali pretreatment efficiently removed lignin from SB while retaining the intact native structure of the released microfibrils. In total, 99% of cellulose and 100% of hemicellulose in alkali-pretreated SB were hydrolysed by enzymes from Thermoascus aurantiacus. The hydrolysate was used to produce butanol in a fed-batch fermentation by Clostridium acetobutylicum. At 60h, 14.17 and 21.11gL(-1) of butanol and acetone-butanol-ethanol (ABE) were produced from 68.89gL(-1) of total sugars, respectively, yielding 0.22 and 0.33gg(-1) of sugars. The maximum yield of butanol and ABE reached 15.4g and 22.9g per 100g raw SB, respectively. This established process may have potential application for butanol production from SB.

Exploring the inhibitory characteristics of acid hydrolysates upon butanol fermentation: A toxicological assessment

This study aimed to quantitatively evaluate the inhibitor tolerance of butanol-producing bacterium Clostridium acetobutylicum. The inhibitory effect of the inhibitors generated by acid pretreatment of biomass feedstock on butanol fermentation decreased in the order of formic acid>oxalic acid>furfural>5-HMF>Na2SO4. C. acetobutylicum has a small tolerance range for furfural (1.06-2.6g/L) and 5-HMF (1.99-2.3g/L). However, the inhibitory effect of Na2SO4 appears to have a wide range, with a chronic toxicity for C. acetobutylicum. All the results could explain, in quantitative manner, the instability of butanol fermentation with C. acetobutylicum from various acid-pretreated feedstocks caused by the fermentation inhibitors.

Adsorption of butanol vapor on active carbons with nitric acid hydrothermal modification

Butanol can be produced from biomass via fermentation and used in vehicles. Unfortunately, butanol is toxic to the microbes, and this can slow fermentation rates and reduce butanol yields. Butanol can be efficiently removed from fermentation broth by gas stripping, thereby preventing its inhibitory effects. Original active carbon (AC) and AC samples modified by nitric acid hydrothermal modification were assessed for their ability to adsorb butanol vapor. The specific surface area and oxygen-containing functional groups of AC were tested before and after modification. The adsorption capacity of unmodified AC samples was the highest. Hydrothermal oxidation of AC with HNO3 increased the surface oxygen content, Brunauer-Emmett-Teller (BET) surface area, micropore, mesopore and total pore volume of AC. Although the pore structure and specific surface area were greatly improved after hydrothermal oxidization with 4M HNO3, the increased oxygen on the surface of AC decreased the dynamic adsorption capacity.

n-Butanol derived from biochemical and chemical routes: A review

Traditionally, bio-butanol is produced with the ABE (Acetone Butanol Ethanol) process using Clostridium species to ferment sugars from biomass. However, the route is associated with some disadvantages such as low butanol yield and by-product formation (acetone and ethanol). On the other hand, butanol can be directly produced from ethanol through aldol condensation over metal oxides/ hydroxyapatite catalysts. This paper suggests that the chemical conversion route is more preferable than the ABE process, because the reaction proceeds more quickly compared to the fermentation route and fewer steps are required to get to the product.

Biobutanol from cheese whey

At present, due to environmental and economic concerns, it is urgent to evolve efficient, clean and secure systems for the production of advanced biofuels from sustainable cheap sources. Biobutanol has proved better characteristics than the more widely used bioethanol, however the main disadvantage of biobutanol is that it is produced in low yield and titer by ABE (acetone-butanol-ethanol) fermentation, this process being not competitive from the economic point of view. In this review we summarize the natural metabolic pathways for biobutanol production by Clostridia and yeasts, together with the metabolic engineering efforts performed up to date with the aim of either enhancing the yield of the natural producer Clostridia or transferring the butanol production ability to other hosts with better attributes for industrial use and facilities for genetic manipulation. Molasses and starch-based feedstocks are main sources for biobutanol production at industrial scale hitherto. We also review herewith (and for the first time up to our knowledge) the research performed for the use of whey, the subproduct of cheese making, as another sustainable source for biobutanol production. This represents a promising alternative that still needs further research. The use of an abundant waste material like cheese whey, that would otherwise be considered an environmental pollutant, for biobutanol production, makes economy of the process more profitable.

Saccharification of rice straw by cellulase from a local Trichoderma harzianum SNRS3 for biobutanol production

BACKGROUND

Rice straw has shown to be a promising agricultural by-product in the bioconversion of biomass to value-added products. Hydrolysis of cellulose, a main constituent of lignocellulosic biomass, is a requirement for fermentable sugar production and its subsequent bioconversion to biofuels such as biobutanol. The high cost of commercial enzymes is a major impediment to the industrial application of cellulases. Therefore, the use of local microbial enzymes has been suggested. Trichoderma harzianum strains are potential CMCase and β-glucosidase producers. However, few researches have been reported on cellulase production by T. harzianum and the subsequent use of the crude cellulase for cellulose enzymatic hydrolysis. For cellulose hydrolysis to be efficiently performed, the presence of the whole set of cellulase components including exoglucanase, endoglucanase, and β-glucosidase at a considerable concentration is required. Biomass recalcitrance is also a bottleneck in the bioconversion of agricultural residues to value-added products. An effective pretreatment could be of central significance in the bioconversion of biomass to biofuels.

RESULTS

Rice straw pretreated using various concentrations of NaOH was subjected to enzymatic hydrolysis. The saccharification of rice straw pretreated with 2% (w/v) NaOH using crude cellulase from local T. harzianum SNRS3 resulted in the production of 29.87 g/L reducing sugar and a yield of 0.6 g/g substrate. The use of rice straw hydrolysate as carbon source for biobutanol fermentation by Clostridium acetobutylicum ATCC 824 resulted in an ABE yield, ABE productivity, and biobutanol yield of 0.27 g/g glucose, 0.04 g/L/h and 0.16 g/g glucose, respectively. As a potential β-glucosidase producer, T. harzianum SNRS3 used in this study was able to produce β-glucosidase at the activity of 173.71 U/g substrate. However, for cellulose hydrolysis to be efficient, Filter Paper Activity at a considerable concentration is also required to initiate the hydrolytic reaction. According to the results of our study, FPase is a major component of cellulose hydrolytic enzyme complex system and the reducing sugar rate-limiting enzyme.

CONCLUSION

Our study revealed that rice straw hydrolysate served as a potential substrate for biobutanol production and FPase is a rate-limiting enzyme in saccharification.

Acetone, butanol, and ethanol production from gelatinized cassava flour by a new isolates with high butanol tolerance

To obtain native strains resistant to butanol toxicity, a new isolating method and serial enrichment was used in this study. With this effort, mutant strain SE36 was obtained, which could withstand 35g/L (compared to 20g/L of the wild-type strain) butanol challenge. Based on 16s rDNA comparison, the mutant strain was identified as Clostridium acetobutylicum. Under the optimized condition, the phase shift was smoothly triggered and fermentation performances were consequently enhanced. The maximum total solvent and butanol concentration were 23.6% and 24.3%, respectively higher than that of the wild-type strain. Furthermore, the correlation between butanol produced and the butanol tolerance was investigated, suggesting that enhancing butanol tolerance could improve butanol production. These results indicate that the simple but effective isolation method and acclimatization process are a promising technique for isolation and improvement of butanol tolerance and production.

Composting of cow dung and crop residues using termite mounds as bulking agent

The present study reports the suitability of termite mounds as a bulking agent for composting with crop residues and cow dung in pit method. Use of 50 kg termite mound with the crop residues (stover of ground nut: 361.65 kg; soybean: 354.59 kg; potato: 357.67 kg and mustard: 373.19 kg) and cow dung (84.90 kg) formed a good quality compost within 70 days of composting having nitrogen, phosphorus and potassium as 20.19, 3.78 and 32.77 g kg(-1) respectively with a bulk density of 0.85 g cm(-3). Other physico-chemical and germination parameters of the compost were within Indian standard, which had been confirmed by the application of multivariate analysis of variance and multivariate contrast analysis. Principal component analysis was applied in order to gain insight into the characteristic variables. Four composting treatments formed two different groups when hierarchical cluster analysis was applied.

Production of butanol by Clostridium saccharoperbutylacetonicum N1-4 from palm kernel cake in acetone-butanol-ethanol fermentation using an empirical model

Palm kernel cake (PKC) was used for biobutanol production by Clostridium saccharoperbutylacetonicum N1-4 in acetone-butanol-ethanol (ABE) fermentation. PKC was subjected to acid hydrolysis pretreatment and hydrolysates released were detoxified by XAD-4 resin. The effect of pH, temperature and inoculum size on butanol production was evaluated using an empirical model. Twenty ABE fermentations were run according to an experimental design. Experimental results revealed that XAD-4 resin removed 50% furfural and 77.42% hydroxymethyl furfural. The analysis of the empirical model showed that linear effect of inoculums size with quadratic effect of pH and inoculum size influenced butanol production at 99% probability level (P<0.01). The optimum conditions for butanol production were pH 6.28, temperature of 28°C and inoculum size of 15.9%. ABE fermentation was carried out under optimum conditions which 0.1g/L butanol was obtained. Butanol production was enhanced by diluting PKC hydrolysate up to 70% in which 3.59g/L butanol was produced.

Recent advances on biobutanol production

Recent studies have shown that butanol is a potential gasoline replacement that can also be blended in significant quantities with conventional diesel fuel. However, biotechnological production of butanol has some challenges such as low butanol titer, high cost feedstocks and product inhibition. The present work reviewed the technical and economic feasibility of the main technologies available to produce biobutanol. The latest studies integrating continuous fermentation processes with efficient product recovery and the use of mathematical models as tools for process scale-up, optimization and control are presented.

Xylanase and cellulase systems of Clostridium sp.: an insight on molecular approaches for strain improvement

Bioethanol and biobutanol hold great promise as alternative biofuels, especially for transport sector, because they can be produced from lignocellulosic agro-industrial residues. From techno-economic point of view, the bioprocess for biofuels production should involve minimal processing steps. Consolidated bioprocessing (CBP), which combines various processing steps such as pretreatment, hydrolysis and fermentation in a single bioreactor, could be of great relevance for the production of bioethanol and biobutanol or solvents (acetone, butanol, ethanol), employing clostridia. For CBP, Clostridium holds best promise because it possesses multi-enzyme system involving cellulosome and xylanosome, which comprise several enzymes such as cellulases and xylanases. The aim of this article was to review the recent developments on enzyme systems of clostridia, especially xylanase and cellulase with an effort to analyse the information available on molecular approaches for the improvement of strains with ultimate aim to improve the efficiencies of hydrolysis and fermentation.

Process integration for simultaneous saccharification, fermentation, and recovery (SSFR): production of butanol from corn stover using Clostridium beijerinckii P260

A simultaneous saccharification, fermentation, and recovery (SSFR) process was developed for the production of acetone-butanol-ethanol (AB or ABE), of which butanol is the main product, from corn stover employing Clostridium beijerinckii P260. Of the 86 g L(-1) corn stover provided, over 97% of the sugars were released during hydrolysis and these were fermented completely with an ABE productivity of 0.34 g L(-1)h(-1) and yield of 0.39. This productivity is higher than 0.31 g L(-1)h(-1) when using glucose as a substrate demonstrating that AB could be produced efficiently from lignocellulosic biomass. Acetic acid that was released from the biomass during pretreatment and hydrolysis was also used by the culture to produce AB. An average rate of generation of sugars during corn stover hydrolysis was 0.98 g L(-1)h(-1). In this system AB was recovered using vacuum, and as a result of this (simultaneous product recovery), 100% sugars were used by the culture.

Organosolv pretreatment of rice straw for efficient acetone, butanol, and ethanol production

Acetone-butanol-ethanol (ABE) was produced from rice straw using a process containing ethanol organosolv pretreatment, enzymatic hydrolysis, and fermentation by Clostridium acetobutylicum bacterium. Pretreatment of the straw with 75% (v/v) aqueous ethanol containing 1% w/w sulfuric acid at 150 °C for 60 min resulted in the highest total sugar concentration of 31 g/L in the enzymatic hydrolysis. However, the highest ABE concentration and productivity (10.5 g/L and 0.20 g/Lh, respectively) were obtained from the straw pretreated at 180 °C for 30 min. Enzymatic hydrolysis of the straw pretreated at 180 °C for 30 min with 5% solid loading resulted in glucose yield of 46.2%, which was then fermented to 80.3 g butanol, 21.1 g acetone, and 22.5 g ethanol, the highest overall yield of ABE production. Thus, the organosolv pretreatment can be applied for efficient production of the solvents from rice straw.

Felled oil palm trunk as a renewable source for biobutanol production by Clostridium spp

This study aimed to convert felled oil palm trunk to biobutanol by Clostridium spp. For efficient utilization of oil palm trunk, it was separated into sap and trunk fiber. The sap was used directly while the trunk fiber was hydrolyzed to fermentable sugars before use. Among five clostridia strains screened, Clostridium acetobutylicum DSM 1731 was the most suitable strain for butanol production from the sap without any supplementation of nutrients. It produced the highest amount of butanol (14.4 g/L) from the sap (sugar concentration of 50 g/L) with butanol yield of 0.35 g/g. When hydrolysate from the trunk fiber was used as an alternative carbon source (sugar concentration of 30 g/L), of the strains tested Clostridium beijerinckii TISTR 1461 produced the highest amount of butanol (10.0 g/L) with butanol yield of 0.41 g/g. The results presented herein suggest that oil palm trunk is a promising renewable substrate for biobutanol production.