Cellulosic butanol production from alkali-pretreated switchgrass (Panicum virgatum) and phragmites (Phragmites australis)

Current progress on engineering microbial strains and consortia for production of cellulosic butanol through consolidated bioprocessing

In the last decades, fermentative production of n-butanol has regained substantial interest mainly owing to its use as drop-in-fuel. The use of lignocellulose as an alternative to traditional acetone-butanol-ethanol fermentation feedstocks (starchy biomass and molasses) can significantly increase the economic competitiveness of biobutanol over production from non-renewable sources (petroleum). However, the low cost of lignocellulose is offset by its high recalcitrance to biodegradation which generally requires chemical-physical pre-treatment and multiple bioreactor-based processes. The development of consolidated processing (i.e., single-pot fermentation) can dramatically reduce lignocellulose fermentation costs and promote its industrial application. Here, strategies for developing microbial strains and consortia that feature both efficient (hemi)cellulose depolymerization and butanol production will be depicted, that is, rational metabolic engineering of native (hemi)cellulolytic or native butanol-producing or other suitable microorganisms; protoplast fusion of (hemi)cellulolytic and butanol-producing strains; and co-culture of (hemi)cellulolytic and butanol-producing microbes. Irrespective of the fermentation feedstock, biobutanol production is inherently limited by the severe toxicity of this solvent that challenges process economic viability. Hence, an overview of strategies for developing butanol hypertolerant strains will be provided.

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.

Investigating the Processing Potential of Ethiopian Agricultural Residue Enset/Ensete ventricosum for Biobutanol Production

The Enset plant is a potential food source for about 20 million Ethiopians. A massive amount of residual byproduct is discarded from traditional Ethiopian Enset food processing. This study shows a compositional analysis of Enset biomass and its use for biobutanol production. The Enset biomass was pretreated with 2% (w/v) NaOH or 2% (v/v) H₂SO₄ and subjected to enzymatic hydrolysis. The enzymatic hydrolysates were then fermented anaerobically by C. saccharoperbutylacetonicum DSM 14923. The majority of Enset biomass waste samples contained 36–67% cellulose, 16–20% hemicelluloses, and less than 6.8% lignin. In all alkali-pretreated Enset biomass samples, the enzyme converted 80–90% of the biomass to glucose within 24 h, while it took 60 h to convert 48–80% of the acid-pretreated Enset biomass. In addition, the alkali pretreatment method released more glucose than the acid pretreatment in all Enset biomass samples. After 72 h of ABE fermentation, 2.8 g/L acetone, 9.9 g/L butanol, and 1.6 g/L ethanol were produced from mixed Enset waste hydrolysate pretreated with alkali, achieving an ABE yield of 0.32 g/g and productivity of 0.2 g × L⁻¹ × h⁻¹, showing the first value of butanol produced from Enset biomass in the literature.

Anaerobic biobutanol production from black strap molasses using Clostridium acetobutylicum MTCC11274: Media engineering and kinetic analysis

Microbial reduction of black strap molasses (BSM) by Clostridium acetobutylicum MTCC 11,274 was performed for the production of biobutanol. The optimum fermentation conditions were predicted using one factor at a time (OFAT) method. The identification of significant parameters was performed using Plackett-Burman Design (PBD). Furthermore the fermentation conditions were optimized using central composite design (CCD). The kinetics of substrate utilization and product formation were investigated. Initial pH, yeast extract concentration (g/L) and total reducing sugar concentration (g/L) were found as significant parameters affecting butanol production using C. acetobutylicum MTCC11274. The maximum butanol production under optimal condition was 10.27 + 0.82 g/L after 24 h. The waste black strap molasses obtained from sugar industry could be used as promising substrate for the production of next generation biofuel.

Viable strategies for enhancing acetone-butanol-ethanol production from non-detoxified switchgrass hydrolysates

A process engineering strategy was investigated towards developing a viable scheme for effective conversion of hydrothermolysis pretreated non-detoxified switchgrass hydrolysates (SH) to acetone butanol ethanol (ABE) using a metabolically engineered strain of Clostridium beijerinckii NCIMB 8052, C. beijerinckii_AKR. The engineered strain was modified by homologous integration into the chromosome and constitutive expression of Cbei_3974, which encodes an aldo-keto reductase. Intermittent feeding strategy was employed in which fermentation was initiated with 30% of the SH and the remaining 70% SH was added when the optical density (OD_600nm) of C. beijerinckii attained 0.5. The ABE (14.9 g/L) produced from non-detoxified SH by the inhibitor-tolerant C. beijerinckii_AKR was comparable to the P2-glucose control medium (14.7 g/L). Using intermittent feeding, wildtype and C. beijerinckii_AKR produced similar amounts of ABE (about 17.5 g/L). This shows that intermittent feeding strategy and C. beijerinckii_AKR enhanced ABE fermentation and eliminated the need for SH detoxification prior to fermentation.

Well-to-wake analysis of switchgrass to jet fuel via a novel co-fermentation of sugars and CO2

Lignocellulosic biomass such as switchgrass can be converted to n-butanol using fermentation, which can be further processed into jet fuel. Traditional acetone-butanol-ethanol (ABE) fermentation only converts sugars derived from switchgrass to ABE. Novel co-fermentation processes convert sugars and gas (CO₂/H₂) produced during fermentation into butanol, thus increasing ABE yields by 15.5% compared to traditional ABE fermentation. Herein, the environmental impact of a Switchgrass to Jet Fuel (STJ) pathway was assessed using life cycle assessment (LCA) from well-to-wake. LCAs were performed for greenhouse gas (GHG) emissions from jet fuel production via co-fermentation of sugars and gas for ideal and practical cases of ABE fermentation and seven other jet fuel pathways. The ideal case assumes 100% sugar recovery and 95% ABE yield. The practical case assumes 90% sugar recovery and an 80% ABE yield. Results are presented based on 100-year global warming potential (GWP) per MJ of jet fuel. Co-products were allocated using various methods. The increase in butanol yield via the co-fermentation technology reduced GWP-100 for the STJ pathway by 6.5% compared to traditional ABE fermentation. Similarly, the STJ pathway for the practical case with co-fermentation had 14.2%, 47.5%, 73.8%, and 44.4% less GWP-100 compared to HRJ, Fischer-Tropsch jet fuel from switchgrass, Fischer-Tropsch jet fuel from coal, and conventional petroleum jet fuel. The results demonstrate that the STJ pathway via co-fermentation has the potential to increase product yield while reducing GHG emissions compared to other jet fuel production pathways.

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

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

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

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

Comparative Study on Pretreatment Processes for Different Utilization Purposes of Switchgrass

Switchgrass (Panicum virgatum, L., Poaceae) with the advantages of high cellulose yield, and high growth even under low input and poor soil quality, has been identified as a promising candidate for production of low-cost biofuels, papermaking, and nanocellulose. In this study, 12 chemical pretreatments on a laboratory scale were compared for different utilization purposes of switchgrass. It was found that the pretreated switchgrass with sodium hydroxide showed considerable potential for providing mixed sugars for fermentation with 11.10% of residual lignin, 53.85% of residual cellulose, and 22.06% of residual hemicellulose. The pretreatment with 2.00% (v/v) nitric acid was the best method to remove 78.37% of hemicellulose and 39.82% of lignin under a low temperature (125 °C, 30 min), which can be used in the production of nanocellulose. Besides, a completely randomized design analysis of switchgrass pretreatments provided the alternative ethanol organosolv delignification of switchgrass for the papermaking industry with a high residual cellulose of 58.56%. Finally, scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FT-IR) were carried out to confirm the changes in functional groups, crystallinity, and thermal behavior of the three materials, respectively, from the optimal pretreatments.

Metabolic Engineering and Adaptive Evolution of Clostridium beijerinckii To Increase Solvent Production from Corn Stover Hydrolysate

The production of acetone-butanol-ethanol by solventogenic Clostridium using lignocellulosic biomass can be a potential alternative to petroleum-based butanol. However, previous studies on nondetoxified lignocellulose hydrolysate could not provide better results when compared to those in synthetic medium. In this study, we engineered the pentose pathway of Clostridium beijerinckii NCIMB 8052, which was then subjected to adaptive laboratory evolution in the gradient mixture of synthetic medium and pretreated corn stover enzymatic hydrolysate (CSH) prepared according to the National Renewable Energy Laboratory (NREL) standard. The final resultant strain CIBTS1274A produced 20.7 g/L of total solvents in NREL CSH diluted to 6% initial total sugars, supplemented with ammonium acetate. This performance was comparable with that of corn-based butanol. In addition, this strain was successfully used in the scale-up operation using nondetoxified corn stover and corncob hydrolysate at Lignicell Refining Biotechnologies Ltd., which once was the only commercial biobutanol industry in the world.

Feasibility of using biochar as buffer and mineral nutrients replacement for acetone-butanol-ethanol production from non-detoxified switchgrass hydrolysate

Biochar can be an inexpensive pH buffer and source of mineral and trace metal nutrients in acetone-butanol-ethanol (ABE) fermentation. This study evaluated the feasibility of replacing expensive 4-morpholineethanesulfonic acid (MES) P2 buffer and mineral nutrients with biochar made from switchgrass (SGBC), forage sorghum (FSBC), redcedar (RCBC) and poultry litter (PLBC) for ABE fermentation. Fermentations using Clostridium beijerinckii ATCC 51743 in glucose and non-detoxified switchgrass hydrolysate media were performed at 35 °C in 250 mL bottles for 72 h. Medium containing buffer and minerals without biochar was the control. Similar ABE production (about 18.0 g/L) in glucose media with SGBC, FSBC and RCBC and control was measured. However in non-detoxified switchgrass hydrolysate medium, SGBC, RCBC and PLBC produced more ABE (about 18.5 g/L) than the control (10.1 g/L). This demonstrates that biochar is an effective buffer and mineral supplement for ABE production from lignocellulosic biomass without costly detoxification process.

Phytoremediation of Heavy Metal-Contaminated Sites: Eco-environmental Concerns, Field Studies, Sustainability Issues, and Future Prospects

Environmental contamination due to heavy metals (HMs) is of serious ecotoxicological concern worldwide because of their increasing use at industries. Due to non-biodegradable and persistent nature, HMs cause serious soil/water pollution and severe health hazards in living beings upon exposure. HMs can be genotoxic, carcinogenic, mutagenic, and teratogenic in nature even at low concentration. They may also act as endocrine disruptors and induce developmental as well as neurological disorders, and thus, their removal from our natural environment is crucial for the rehabilitation of contaminated sites. To cope with HM pollution, phytoremediation has emerged as a low-cost and eco-sustainable solution to conventional physicochemical cleanup methods that require high capital investment and labor alter soil properties and disturb soil microflora. Phytoremediation is a green technology wherein plants and associated microbes are used to remediate HM-contaminated sites to safeguard the environment and protect public health. Hence, in view of the above, the present paper aims to examine the feasibility of phytoremediation as a sustainable remediation technology for the management of metal-contaminated sites. Therefore, this paper provides an in-depth review on both the conventional and novel phytoremediation approaches; evaluates their efficacy to remove toxic metals from our natural environment; explores current scientific progresses, field experiences, and sustainability issues; and revises world over trends in phytoremediation research for its wider recognition and public acceptance as a sustainable remediation technology for the management of contaminated sites in the twenty-first century.

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

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

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.

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

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

Clostridial conversion of corn syrup to Acetone-Butanol-Ethanol (ABE) via batch and fed-batch fermentation

Corn syrup - a commercial product derived from saccharification of corn starch - was used to produce acetone-butanol-ethanol (ABE) by Clostridium spp. Screening of commercial Clostridium spp., substrate inhibition tests and fed-batch experiments were carried out to improve ABE production using corn syrup as only carbon source. The screening tests carried out in batch mode using a production media containing 50 g/L corn syrup revealed that C. saccharobutylicum was the best performer in terms of total solvent concentration (12.46 g/L), yield (0.30 g/g) and productivity (0.19 g/L/h) and it was selected for successive experiments. Concentration of corn syrup higher than 50 g/L resulted in no solvents production. Fed-batch fermentation improved ABE production with respect to batch fermentation: the butanol and solvent concentration increased up to 8.70 and 16.68 g/L, respectively. The study demonstrated the feasibility of producing solvents via ABE fermentation using corn syrup as a model substrate of concentrated sugar mixtures.

Phytoremediation potential and control of Phragmites australis as a green phytomass: an overview

Phragmites australis (common reed) is one of the most extensively distributed emergent plant species in the world. This plant has been used for phytoremediation of different types of wastewater, soil, and sediments since the 1970s. Published research confirms that P. australis is a great accumulator for different types of nutrients and heavy metals than other aquatic plants. Therefore, a comprehensive review is needed to have a better understanding of the suitability of this plant for removal of different types of nutrients and heavy metals. This review investigates the existing literature on the removal of nutrients and heavy metals from wastewater, soil, and sediment using P. australis. In addition, after phytoremediation, P. australis has the potential to be used for additional benefits such as the production of bioenergy and animal feedstock due to its specific characteristics. Determination of adaptive strategies is vital to reduce the invasive growth of P. australis in the environment and its economic effects. Future research is suggested to better understand the plant's physiology and biochemistry for increasing its pollutant removal efficiency.

A Process Study of Lactic Acid Production from Phragmites australis Straw by a Thermophilic Bacillus coagulans Strain under Non-Sterilized Conditions

Phragmites australis straw (PAS) is an abundant and renewable wetland lignocellulose. Bacillus coagulans IPE22 is a robust thermophilic strain with pentose-utilizing capability and excellent resistance to growth inhibitors. This work is focused on the process study of lactic acid (LA) production from P. australis lignocellulose which has not been attempted previously. By virtue of thermophilic feature of strain IPE22, two fermentation processes (i.e., separated process and integrated process), were developed and compared under non-sterilized conditions. The integrated process combined dilute-acid pretreatment, hemicellulosic hydrolysates fermentation, and cellulose utilization. Sugars derived from hemicellulosic hydrolysates and cellulose enzymatic hydrolysis were efficiently fermented to LA in a single vessel. Using the integrated process, 41.06 g LA was produced from 100 g dry PAS. The established integrated process results in great savings in terms of time and labor, and the fermentation process under non-sterilized conditions is easy to scale up for economical production of lactic acid from PAS.

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

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

Industrial potato peel as a feedstock for biobutanol production

Potato peel from a snack factory was assessed as possible feedstock for biobutanol production. This lignocellulosic biomass was subjected to various physicochemical pretreatments (autohydrolysis and hydrolysis with dilute acids, alkalis, organic solvents or surfactants) under different conditions of time, temperature and reagent concentrations, in order to favour the release of sugars and reduce the generation of fermentation inhibitors. Thereafter, the pretreated potato peel was treated enzymatically to complete the hydrolysis. Autohydrolysis at 140 °C and 56 min was the most effective pretreatment, releasing 37.9 ± 2.99 g/L sugars from an aqueous mixture containing 10% (w/w) potato peel (sugar recovery efficiency 55 ± 13%). The fermentability of the hydrolysates was checked with six strains of Clostridium beijerinckii, C. acetobutylicum, C. saccharobutylicum and C. saccaroperbutylacetonicum. C. saccharobutylicum DSM 13864 produced 2.1 g/L acetone, 7.6 g/L butanol and 0.6 g/L ethanol in 96 h (0.186 g_B/g_S), whereas C. saccharoperbutylacetonicum DSM 2152 generated 1.8 g/L acetone, 8.1 g/L butanol and 1.0 g/L ethanol in 120 h (0.203 g_B/g_S). Detoxification steps of the hydrolysate before fermentation were not necessary. Potato peel may be an interesting feedstock for biorefineries focused on butanol production.

Diauxic growth of Clostridium acetobutylicum ATCC 824 when grown on mixtures of glucose and cellobiose

Clostridium acetobutylicum, a promising organism for biomass transformation, has the capacity to utilize a wide variety of carbon sources. During pre-treatments of (ligno) cellulose through thermic and/or enzymatic processes, complex mixtures of oligo saccharides with beta 1,4-glycosidic bonds can be produced. In this paper, the capability of C. acetobutylicum to ferment glucose and cellobiose, alone and in mixtures was studied. Kinetic studies indicated that a diauxic growth occurs when both glucose and cellobiose are present in the medium. In mixtures, D-glucose is the preferred substrate even if cells were pre grown with cellobiose as the substrate. After the complete consumption of glucose, the growth kinetics exhibits an adaptation time, of few hours, before to be able to use cellobiose. Because of this diauxic phenomenon, the nature of the carbon source deriving from a cellulose hydrolysis pre-treatment could strongly influence the kinetic performances of a fermentation process with C. acetobutylicum.

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.

Evaluation of efficient glucose release using sodium hydroxide and phosphoric acid as pretreating agents from the biomass of Sesbania grandiflora (L.) Pers.: A fast growing tree legume

Sesbania grandiflora (L.) Pers. is one of the fast growing tree legumes having the efficiency to produce around 50tha^-1 above ground dry matters in a year. In this study, biomass of 2years old S. grandiflora was selected for the chemical composition, pretreatments and enzymatic hydrolysis studies. The stem biomass with a wood density of 3.89±0.01gmcm^-3 contains about 38% cellulose, 12% hemicellulose and 28% lignin. Enzymatic hydrolysis of pretreated biomass revealed that phosphoric acid (H₃PO₄) pretreated samples even at lower cellulase loadings [1 Filter Paper Units (FPU)], could efficiently convert about 86% glucose, while, even at higher cellulase loadings (60FPU) alkali pretreated biomass could convert only about 58% glucose. The effectiveness of phosphoric acid pretreatment was also supported by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and Fourier transform infrared spectroscopy (FTIR) analysis.

Comparison of ethanol production from corn cobs and switchgrass following a pyrolysis-based biorefinery approach

BACKGROUND

One of the main obstacles in lignocellulosic ethanol production is the necessity of pretreatment and fractionation of the biomass feedstocks to produce sufficiently pure fermentable carbohydrates. In addition, the by-products (hemicellulose and lignin fraction) are of low value, when compared to dried distillers grains (DDG), the main by-product of corn ethanol. Fast pyrolysis is an alternative thermal conversion technology for processing biomass. It has recently been optimized to produce a stream rich in levoglucosan, a fermentable glucose precursor for biofuel production. Additional product streams might be of value to the petrochemical industry. However, biomass heterogeneity is known to impact the composition of pyrolytic product streams, as a complex mixture of aromatic compounds is recovered with the sugars, interfering with subsequent fermentation. The present study investigates the feasibility of fast pyrolysis to produce fermentable pyrolytic glucose from two abundant lignocellulosic biomass sources in Ontario, switchgrass (potential energy crop) and corn cobs (by-product of corn industry).

RESULTS

Demineralization of biomass removes catalytic centers and increases the levoglucosan yield during pyrolysis. The ash content of biomass was significantly decreased by 82-90% in corn cobs when demineralized with acetic or nitric acid, respectively. In switchgrass, a reduction of only 50% for both acids could be achieved. Conversely, levoglucosan production increased 9- and 14-fold in corn cobs when rinsed with acetic and nitric acid, respectively, and increased 11-fold in switchgrass regardless of the acid used. After pyrolysis, different configurations for upgrading the pyrolytic sugars were assessed and the presence of potentially inhibitory compounds was approximated at each step as double integral of the UV spectrum signal of an HPLC assay. The results showed that water extraction followed by acid hydrolysis and solvent extraction was the best upgrading strategy. Ethanol yields achieved based on initial cellulose fraction were 27.8% in switchgrass and 27.0% in corn cobs.

CONCLUSIONS

This study demonstrates that ethanol production from switchgrass and corn cobs is possible following a combined thermochemical and fermentative biorefinery approach, with ethanol yields comparable to results in conventional pretreatments and fermentation processes. The feedstock-independent fermentation ability can easily be assessed with a simple assay.

Combined Detoxification and In-situ Product Removal by a Single Resin During Lignocellulosic Butanol Production

Phragmites australis (an invasive plant in North America) was used as feedstock for ABE (acetone-butanol-ethanol) fermentation by Clostridium saccharobutylicum. Sulphuric acid pretreated phragmites hydrolysate (SAEH) without detoxification inhibited butanol production (0.73 g/L butanol from 30 g/L sugars). The treatment of SAEH with resin L-493 prior the fermentation resulted in no inhibitory effects and an ABE titer of 14.44 g/L, including 5.49 g/L butanol was obtained, corresponding to an ABE yield and productivity of 0.49 g/g and 0.60 g/L/h, respectively. Dual functionality of the resin was realized by also using it as an in-situ product removal agent. Integrating in-situ product removal allowed for the use of high substrate concentrations without the typical product inhibition. Resin-detoxified SAEH was supplemented with neat glucose and an effective ABE titer of 33 g/L (including 13.7 g/L acetone, 16.4 g/L butanol and 1.9 g/L ethanol) was achieved with resin-based in-situ product removal, corresponding to an ABE yield and productivity of 0.41 g/g and 0.69 g/L/h, respectively. Both detoxification of the substrate and the products was achieved by the same resin, which was added prior the fermentation. Integrating hydrolysate detoxification and in-situ butanol removal in a batch process through single resin can potentially simplify cellulosic butanol production.

Optimization of fermentation condition favoring butanol production from glycerol by Clostridium pasteurianum DSM 525

Butanol is a promising biofuel and valuable platform chemical that can be produced through fermentative conversion of glycerol. The initial fermentation conditions for butanol production from pure glycerol by Clostridium pasteurianum DSM 525 were optimized via a central composite design. The effect of inoculum age, initial cell density, initial pH of medium and temperature were quantified and a quadratic model was able to predict butanol yield as a function of all four investigated factors. The model was confirmed through additional experiments and via analysis of variance (ANOVA). Subsequently, numerical optimization was used to maximize the butanol yield within the experimental range. Based on these results, batch fermentations in a 7 L bioreactor were performed using pure and crude (residue from biodiesel production) glycerol as substrates at optimized conditions. A butanol yield of 0.34 mole(butanol) mole(-1)(glycerol) was obtained indicating the suitability of this feedstock for fermentative butanol production.

Chemical composition, pretreatments and saccharification of Senna siamea (Lam.) H.S. Irwin & Barneby: An efficient biomass producing tree legume

Protocols were developed for efficient release of glucose from the biomass of Senna siamea, one of the highly efficient biomass producing tree legumes. Composition of mature, 1year and 2years coppice biomass were analysed. For the hydrolysis of the glucan, two pretreatments, cellulose solvent- and organic solvent-based lignocellulose fractionation (COSLIF) and alkali (sodium hydroxide) were used; COSLIF (85% phosphoric acid, 45min incubation at 50°C) pretreated mature biomass exhibited best result in which 88.90% glucose released after 72h of incubation with the use of 5 filter paper units (FPU) of cellulase and 10 international units (IU) of β-glucosidase per gram of glucan. Of the biomass of different particle sizes (40-200mesh) used for saccharification, 40-60mesh shown the maximum glucose release. COSLIF pretreated mature, 1year and 2years coppice biomass showed equivalent glucose release profiles.

Butanol fermentation from microalgae-derived carbohydrates after ionic liquid extraction

Lipid extracted algae (LEA) is an attractive feedstock for alcohol fuel production as it is a non-food crop which is largely composed of readily fermented carbohydrates like starch rather than the more recalcitrant lignocellulosic materials currently under intense development. This study compares the suitability of ionic liquid extracted algae (ILEA) and hexane extracted algae (HEA) for acetone, butanol, and ethanol (ABE) fermentation. The highest butanol titers (8.05 g L(-1)) were achieved with the fermentation of the acid hydrolysates of HEA, however, they required detoxification to support product formation after acid hydrolysis while ILEA did not. Direct ABE fermentation of ILEA and HEA (without detoxification) starches resulted in a butanol titer of 4.99 and 6.63 g L(-1), respectively, which significantly simplified the LEA to butanol process. The study demonstrated the compatibility of producing biodiesel and butanol from a single feedstock which may help reduce the feedstock costs of each individual process.

Acetone-butanol-ethanol production from Kraft paper mill sludge by simultaneous saccharification and fermentation

Paper mill sludge (PS), a solid waste from pulp and paper industry, was investigated as a feedstock for acetone-butanol-ethanol (ABE) production by simultaneous saccharification and fermentation (SSF). ABE fermentation of paper sludge by Clostridium acetobutylicum required partial removal of ash in PS to enhance its enzymatic digestibility. Enzymatic hydrolysis was found to be a rate-limiting step in the SSF. A total of 16.4-18.0g/L of ABE solvents were produced in the SSF of de-ashed PS with solid loading of 6.3-7.4% and enzyme loading of 10-15FPU/g-glucan, and the final solvent yield reached 0.27g/g sugars. No pretreatment and pH control were needed in ABE fermentation of paper sludge, which makes it an attractive feedstock for butanol production. The results suggested utilization of paper sludge should not only consider the benefits of buffering effect of CaCO3 in fermentation, but also take into account its inhibitory effect on enzymatic hydrolysis.

Impact of butyric acid on butanol formation by Clostridium pasteurianum

The butanol yield of the classic fermentative acetone-butanol-ethanol (ABE) process has been enhanced in the past decades through the development of better strains and advanced process design. Nevertheless, by-product formation and the incomplete conversion of intermediates still decrease the butanol yield. This study demonstrates the potential of increasing the butanol yield from glycerol though the addition of small amounts of butyric acid. The impact of butyric acid was investigated in a 7L stirred tank reactor. The results of this study show the positive impact of butyric acid on butanol yield under pH controlled conditions and the metabolic stages were monitored via online measurement of carbon dioxide formation, pH value and redox potential. Butyric acid could significantly increase the butanol yield at low pH values if sufficient quantities of primary carbon source (glycerol) were present.

Butanol production from hydrothermolysis-pretreated switchgrass: Quantification of inhibitors and detoxification of hydrolyzate

The present study evaluated butanol production from switchgrass based on hydrothermolysis pretreatment. The inhibitors present in the hydrolyzates were measured. Results showed poor butanol production (1g/L) with non-detoxified hydrolyzate. However, adjusting the pH of the non-detoxified hydrolyzate to 6 and adding 4 g/L CaCO3 increased butanol formation to about 6g/L. There was about 1g/L soluble lignin content (SLC), and various levels of furanic and phenolic compounds found in the non-detoxified hydrolyzate. Detoxification of hydrolyzates with activated carbon increased the butanol titer to 11 g/L with a total acetone, butanol and ethanol (ABE) concentration of 17 g/L. These results show the potential of butanol production from hydrothermolysis pretreated switchgrass.

Butanol production from food waste: a novel process for producing sustainable energy and reducing environmental pollution

BACKGROUND

Waste is currently a major problem in the world, both in the developing and the developed countries. Efficient utilization of food waste for fuel and chemical production can positively influence both the energy and environmental sustainability. This study investigated using food waste to produce acetone, butanol, and ethanol (ABE) by Clostridium beijerinckii P260.

RESULTS

In control fermentation, 40.5 g/L of glucose (initial glucose 56.7 g/L) was used to produce 14.2 g/L of ABE with a fermentation productivity and a yield of 0.22 g/L/h and 0.35 g/g, respectively. In a similar fermentation 81 g/L of food waste (containing equivalent glucose of 60.1 g/L) was used as substrate, and the culture produced 18.9 g/L ABE with a high ABE productivity of 0.46 g/L/h and a yield of 0.38 g/g. Fermentation of food waste at higher concentrations (129, 181 and 228 g/L) did not remarkably increase ABE production but resulted in high residual glucose due to the culture butanol inhibition. An integrated vacuum stripping system was designed and applied to recover butanol from the fermentation broth simultaneously to relieve the culture butanol inhibition, thereby allowing the fermentation of food waste at high concentrations. ABE fermentation integrated with vacuum stripping successfully recovered the ABE from the fermentation broth and controlled the ABE concentrations below 10 g/L during fermentation when 129 g/L food waste was used. The ABE productivity with vacuum fermentation was 0.49 g/L/h, which was 109 % higher than the control fermentation (glucose based). More importantly, ABE vacuum recovery and fermentation allowed near-complete utilization of the sugars (~98 %) in the broth.

CONCLUSIONS

In these studies it was demonstrated that food waste is a superior feedstock for producing butanol using Clostridium beijerinckii. Compared to costly glucose, ABE fermentation of food waste has several advantages including lower feedstock cost, higher productivity, and less residual sugars.