Injection of air into the headspace improves fermentation of phosphoric acid pretreated sugarcane bagasse by Escherichia coli MM170

Microaeration (injecting air into the headspace) improved the fermentation of hemicellulose hydrolysates obtained from the phosphoric acid pretreatment of sugarcane bagasse at 170 °C for 10 min. In addition, with 10% slurries of phosphoric acid pretreated bagasse (180 °C, 10 min), air injection into the headspace promoted xylose utilization and increased ethanol yields from 0.16 to 0.20 g ethanol/g bagasse dry weight using a liquefaction plus simultaneous saccharification and co-fermentation process (L+SScF). This process was scaled up to 80 L using slurries of acid pretreated bagasse (96 h incubation; 0.6 L of air/min into the headspace) with ethanol yields of 312-347 L (82-92 gal) per tonne (dry matter), corresponding to 0.25 and 0.27 g/g bagasse (dry weight). Injection of small amounts of air into the headspace may provide a convenient alternative to subsurface sparging that avoids problems of foaming, sparger hygiene, flotation of particulates, and phase separation.     

Effect of reduced sulfur compounds on the fermentation of phosphoric acid pretreated sugarcane bagasse by ethanologenic Escherichia coli

The addition of reduced sulfur compounds (thiosulfate, cysteine, sodium hydrosulfite, and sodium metabisulfite) increased growth and fermentation of dilute acid hydrolysate of sugarcane bagasse by ethanologenic Escherichia coli (strains LY180, EMFR9, and MM160). With sodium metabisulfite (0.5 mM), toxicity was sufficiently reduced that slurries of pretreated biomass (10% dry weight including fiber and solubles) could be fermented by E. coli strain MM160 without solid-liquid separation or cleanup of sugars. A 6-h liquefaction step was added to improve mixing. Sodium metabisulfite also caused spectral changes at wavelengths corresponding to furfural and soluble products from lignin. Glucose and cellobiose were rapidly metabolized. Xylose utilization was improved by sodium metabisulfite but remained incomplete after 144 h. The overall ethanol yield for this liquefaction plus simultaneous saccharification and co-fermentation process was 0.20 g ethanol/g bagasse dry weight, 250 L/tonne (61 gal/US ton).     

Simultaneous saccharification and fermentation of lignocellulosic residues pretreated with phosphoric acid–acetone for bioethanol production

Bermudagrass, reed and rapeseed were pretreated with phosphoric acid–acetone and used for ethanol production by means of simultaneous saccharification and fermentation (SSF) with a batch and fed-batch mode. When the batch SSF experiments were conducted in a 3% low effective cellulose, about 16 g/L of ethanol were obtained after 96 h of fermentation. When batch SSF experiments were conducted with a higher cellulose content (10% effective cellulose for reed and bermudagrass and 5% for rapeseed), higher ethanol concentrations and yields (of more than 93%) were obtained. The fed-batch SSF strategy was adopted to increase the ethanol concentration further. When a higher water-insoluble solid (up to 36%) was applied, the ethanol concentration reached 56 g/L of an inhibitory concentration of the yeast strain used in this study at 38 °C. The results show that the pretreated materials can be used as good feedstocks for bioethanol production, and that the phosphoric acid–acetone pretreatment can effectively yield a higher ethanol concentration.     

Production of bioethanol from sugarcane bagasse using NH<Subscript>4</Subscript>OH-H<Subscript>2</Subscript>O<Subscript>2</Subscript> pretreatment and simultaneous saccharification and co-fermentation

In this study, we investigated the production of bioethanol from sugarcane bagasse (SCB) using an NH₄OH-H₂O₂ pretreatment and simultaneous saccharification and co-fermentation (SScF). Response surface methodology and a 2³ Box-Behnken design were used to evaluate the effect of different liquid mixture concentrations, liquid-to-solid ratios (LSRs) and pretreatment temperatures on the production of ethanol. The liquid mixture concentration and LSR significantly influenced the fermentation efficiency. Based on ridge max analysis, the following pretreatment conditions resulted in a fermentation efficiency of 95.79 ± 0.01%: liquid mixture concentration 53%, LSR 28, and a temperature of 63°C. A morphological analysis performed using scanning electron microscopy (SEM) and chemical characterization revealed that these pretreatment conditions were effective in disrupting the sugarcane fibers and removing lignin. Ethanol fermentation with the pretreated SCB using SScF in yeast SHY 07-1 resulted in an ethanol concentration of 14.65 ± 0.17 g/L, an ethanol yield of 0.48 ± 0.01 g/g, and an ethanol productivity of 0.12 ± 0.01 g/(L/h), which represents increases of 106.02, 89.98, and 107.02%, respectively, over the values obtained from SScF with untreated SCB.     

Enzyme hydrolysis and ethanol fermentation of dilute ammonia pretreated energy cane

This study is the first one ever to report on the use of high fiber sugarcane (a.k.a. energy cane) bagasse as feedstock for the production of cellulosic ethanol. Energy cane bagasse was pretreated with ammonium hydroxide (28% v/v solution), and water at a ratio of 1:0.5:8 at 160 °C for 1 h under 0.9-1.1 MPa. Approximately, 55% lignin, 30% hemicellulose, 9% cellulose, and 6% other (e.g., ash, proteins) were removed during the process. The maximum glucan conversion of dilute ammonia treated energy cane bagasse by cellulases was 87% with an ethanol yield (glucose only) of 23 g ethanol/100 g dry biomass. The enzymatic digestibility was related to the removal of lignin and hemicellulose, perhaps due to increased surface area and porosity resulting in the deformation and swelling of exposed fibers as shown in the SEM pictures.     

Saccharification and fermentation of Sugar Cane bagasse by Klebsiella oxytoca P2 containing chromosomally integrated genes encoding the Zymomonas mobilis ethanol pathway

Pretreatment of sugar cane bagasse is essential for a simultaneous saccharification and fermentation (SSF) process which uses recombinant Klebsiella oxytoca strain P2 and Genencor Spezyme CE. Strain P2 has been genetically engineered to express Zymomonas mobilis genes encoding the ethanol pathway and retains the native ability to transport and metabolize cellobiose (minimizing the need for extracellular cellobiase). In SSF studies with this organism, both the rate of ethanol production and ethanol yield were limited by saccharification at 10 and 20 filter papaer units (FPU) g(-1) acid-treated bagasse. Dilute slurries of biomass were converted to ethanol more efficiently (over 72% of theoretical yield) in simple batch fermentations than slurries containing high solids albeit with the production of lower levels of ethanol. With high solids (i.e., 160 g acid-treated bagasse L(-1)), a combination of 20 FPU cellulase g(-1) bagasse, preincubation under saccharification conditions, and additional grinding (to reduce particle size) were required to produce ca. 40 g ethanol L(-1). Alternatively, almost 40 g ethanol L(-1) was produced with 10 FPU cellulase g(-1) bagasse by incorporating a second saccharification step (no further enzyme addition) followed by a second inoculation and short fermentation. In this way, a theoretical ethanol yield of over 70% was achieved with the production of 20 g ethanol 800 FPU(-1) of commercial cellulase. (c) 1994 John Wiley & Sons, Inc.     

Preparation of levoglucosenone through sulfuric acid promoted pyrolysis of bagasse at low temperature

Fast pyrolysis of bagasse pretreated by sulfuric acid was conducted in a fixed bed reactor to prepare levoglucosenone (LGO), a very important anhydrosugar for organic synthesis. The liquid yield and LGO yield were studied at temperatures from 240 to 350 °C and sulfuric acid loadings from 0.92 to 7.10 wt.%. An optimal LGO yield of 7.58 wt.% was obtained at 270 °C with a sulfuric acid pretreatment concentration of 0.05 M (corresponding to 4.28 wt.% sulfuric acid loading). For comparison, microcrystalline cellulose pretreated by 0.05 M sulfuric acid solution was pyrolyzed at temperature from 270 °C to 320 °C, and bagasse loaded with 3-5 wt.% phosphoric acid was pyrolyzed at temperature from 270 °C to 350 °C. The highest yield of LGO from bagasse was 30% higher than that from microcrystalline cellulose, and treatment with sulfuric acid allowed a 21% higher yield than treatment with phosphoric acid.     

Pretreatment and enzymic saccharification of water hyacinth cellulose

Water hyacinth was pretreated, under variable conditions, with NaOH, alkaline H₂O₂, peracetic acid and sodium chlorite. Combined pretreatments included sodium chlorite with each of NaOH, alkaline H₂O₂ and peracetic acid. Combined pretreatment with 0.1% NaClO₂ for 1 h at 100 °C and peracetic acid at 100 °C for 15 min afforded the most promising sample. The recovered lignin, cellulose and hemicellulose of this sample was 2.56%, 96.69%, and 81.38%, respectively. The same sample, by cellulase hydrolysis showed the highest cellulose conversion (80.8%) and 90% saccharification using 200 FPU/g substrate. Some ambient factors affecting saccharification of pretreated water hyacinth were investigated. Enzymic saccharification after 6 h was about 50% of that at 48 h, indicating a slow hydrolysis rate by time. Addition of 8% glucose at the beginning of the enzymic hydrolysis decreased the saccharification to about its half while addition of 8% ethanol brought about complete inhibition of the enzyme. Addition of cellobiase to the reaction mixture increased cellulose conversion and saccharification by 10%.     

The effects of phosphoric acid pretreatment on conversion of cellulose to ethanol at 45°C using the thermotolerant yeast Kluyveromyces marxianus IMB3

Summary Here we report on the effects of phosphoric acid pretreated cellulose as a substrate for ethanol production by K. marxianus IMB3 using simultaneous saccharification and fermentation systems at 45°C. With untreated, milled filter paper as substrate the maximum amount of ethanol produced was 25% of the maximum theoretical yield. After pre-treatment with 100% phosphoric acid, the yield increased to 42% of the maximum theoretical yield. When untreated microcrystalline cellulose was used as the fermentation substrate, yields of ethanol as 45°C amounted to 16% of the maximum theoretical yield whereas pretreatment of the substrate with phosphoric acid resulted in an increase in ethanol production to 69% of the maximum theoretical yield. This suggests that pretreatment of substrate with phosphoric acid would contribute to a reduction in the amount of exogenous enzyme needed.     

The effect of biomass moisture content on bioethanol yields from steam pretreated switchgrass and sugarcane bagasse

This study aimed to determine the effect of moisture content of three different feedstocks on overall ethanol yield. Switchgrass and sugarcane bagasse from two sources were either soaked in water (∼80% moisture) or left dry (∼12% moisture), and half each of these were impregnated with 3% w/w SO₂ and all were steam pretreated. The twelve resulting substrates were compared based on overall sugar recovery after pretreatment, cellulose conversion following enzymatic hydrolysis, and ethanol yield following simultaneous saccharification and fermentation. The overall ethanol yield after simultaneous saccharification and fermentation of hexoses was 18-28% higher in samples that were soaked prior to SO₂ addition than in SO₂-catalyzed samples that were not soaked. In samples that were uncatalyzed, soaking made little difference, indicating that the positive effect of increased moisture content may be related to increased permeability of the biomass to SO₂.     

Liquid hot water and alkaline pretreatment of soybean straw for improving cellulose digestibility

Soybean straw was pretreated with either liquid hot water (LHW) (170-210 °C for 3-10 min) or alkaline soaking (4-40 g NaOH/100 g dry straw) at room temperature to evaluate the effects on cellulose digestibility. Nearly 100% cellulose was recovered in pretreated solids for both pretreatment methods. For LHW pretreatment, xylan dissolution from the raw material increased with pretreatment temperature and time. Cellulose digestibility was correlated with xylan dissolution. A maximal glucose yield of 70.76%, corresponding to 80% xylan removal, was obtained with soybean straw pretreated at 210 °C for 10 min. NaOH soaking at ambient conditions removed xylan up to 46.37% and the subsequent glucose yield of pretreated solids reached up to 64.55%. Our results indicated LHW pretreatment was more effective than NaOH soaking for improving cellulose digestibility of soybean straw.     

An evaluation of the potential of Acacia dealbata as raw material for bioethanol production

In this work, the potential of Acacia dealbata as raw material for ethanol production was evaluated, as well as its composition with regard to cellulose, hemicelluloses, lignin, extractives and ash. The tree samples were subjected to several dilute acid pretreatments using a combined severity parameter ranging from 0.7 to 3.7. The highest ethanol concentration obtained was 10.31 g ethanol/L within 24 h by using a separate hydrolysis and fermentation of the water insoluble fraction after pretreatment at 180 °C with 0.8% of sulfuric acid for 15 min. With simultaneous saccharification and fermentation, results obtained for the washed solids of water insoluble fraction were better than those obtained with the whole slurry.     

Sweet Sorghum Juice and Bagasse as Feedstocks for the Production of Optically Pure Lactic Acid by Native and Engineered <Emphasis Type="Italic">Bacillus coagulans</Emphasis> Strains

Sweet sorghum is a bioenergy crop that produces large amounts of soluble sugars in its stems (3–7 Mg ha^?1) and generates significant amounts of bagasse (15–20 Mg ha^?1) as a lignocellulosic feedstock. These sugars can be fermented not only to biofuels but also to bio-based chemicals. The market potential of the latter may be higher given the current prices of petroleum and natural gas. The yield and rate of production of optically pure d-(?)- and l-(+)-lactic acid as precursors for the biodegradable plastic polylactide was optimized for two thermotolerant Bacillus coagulans strains. Strain 36D1 fermented the sugars in unsterilized sweet sorghum juice at 50 °C to l-(+)-lactic acid (～150 g L^?1; productivity, 7.2 g L^?1 h^?1). B. coagulans strain QZ19-2 was used to ferment sorghum juice to d-(?)-lactic acid (～125 g L^?1; productivity, 5 g L^?1 h^?1). Carbohydrates in the sorghum bagasse were also fermented after pretreatment with 0.5 % phosphoric acid at 190 °C for 5 min. Simultaneous saccharification and co-fermentation of all the sugars (SScF) by B. coagulans resulted in a conversion of 80 % of available carbohydrates to optically pure lactic acid depending on the B. coagulans strain used as the microbial biocatalyst. Liquefaction of pretreated bagasse with cellulases before SScF (L + SScF) increased the productivity of lactic acid. These results show that B. coagulans is an effective biocatalyst for fermentation of all the sugars present in sweet sorghum juice and bagasse to optically pure lactic acid at high titer and productivity as feedstock for bio-based plastics.     

Production of bioethanol, methane and heat from sugarcane bagasse in a biorefinery concept

The potential of biogas production from the residues of second generation bioethanol production was investigated taking into consideration two types of pretreatment: lime or alkaline hydrogen peroxide. Bagasse was pretreated, enzymatically hydrolyzed and the wastes from pretreatment and hydrolysis were used to produce biogas. Results have shown that if pretreatment is carried out at a bagasse concentration of 4% DM, the highest global methane production is obtained with the peroxide pretreatment: 72.1 L methane/kg bagasse. The recovery of lignin from the peroxide pretreatment liquor was also the highest, 112.7 ± 0.01 g/kg of bagasse. Evaluation of four different biofuel production scenarios has shown that 63-65% of the energy that would be produced by bagasse incineration can be recovered by combining ethanol production with the combustion of lignin and hydrolysis residues, along with the anaerobic digestion of pretreatment liquors, while only 32-33% of the energy is recovered by bioethanol production alone.     

Low-liquid pretreatment of corn stover with aqueous ammonia

A low-liquid pretreatment method of corn stover using aqueous ammonia was studied to reduce the severity and liquid throughput associated with the pretreatment step for ethanol production. Corn stover was treated at 0.5-50.0 wt.% of ammonia loading, 1:0.2-5.0 (w/w) of solid-to-liquid ratio, 30 °C for 4-12 weeks. The effects of these conditions on the composition and enzyme digestibility of pretreated corn stover were investigated. Pretreatment of corn stover at 30 °C for four weeks using 50 wt.% of ammonia loading and 1:5 solid-to-liquid ratio resulted in 55% delignification and 86.5% glucan digestibility with 15 FPU cellulase + 30 CBU β-glucosidase/g-glucan.Simultaneous saccharification and fermentation of corn stover treated at 30 °C for four weeks using 50 wt.% ammonia loading and 1:2 solid-to-liquid ratio gave an ethanol yield of 73% of the theoretical maximum based on total carbohydrates (glucan + xylan) present in the untreated material.     

Surface carbohydrate analysis and bioethanol production of sugarcane bagasse pretreated with the white rot fungus, Ceriporiopsis subvermispora and microwave hydrothermolysis

Effects of pretreatments with a white rot fungus, Ceriporiopsis subvermispora, and microwave hydrothermolysis of bagasse on enzymatic saccharification and fermentation were evaluated. The best sugar yield, 44.9 g per 100 g of bagasse was obtained by fungal treatments followed by microwave hydrothermolysis at 180 °C for 20 min. Fluorescent-labeled carbohydrate-binding modules which recognize crystalline cellulose (CjCBM3-GFP), non-crystalline cellulose (CjCBM28-GFP) and xylan (CtCBM22-GFP) were applied to characterize the exposed polysaccharides. The microwave pretreatments with and without the fungal cultivation resulted in similar levels of cellulose exposure, but the combined treatment caused more defibration and thinning of the plant tissues. Simultaneous saccharification and fermentation of the pulp fractions obtained by microwave hydrothermolysis with and without fungal treatment, gave ethanol yields of 35.8% and 27.0%, respectively, based on the holocellulose content in the pulp. These results suggest that C. subvermispora pretreatment could be beneficial part of the process to produce ethanol from bagasse.     

Enhanced enzymatic saccharification of kenaf powder after ultrasonic pretreatment in ionic liquids at room temperature

This study demonstrates for the first time that the enzymatic hydrolysis of cellulose is drastically enhanced following ultrasonic pretreatment of lignocellulosic material in ionic liquids (ILs) when compared to conventional thermal pretreatment. Five types of ILs, 1-buthyl-3-methylimidazolium chloride (BmimCl), 1-allyl-3-methylimidazolium chloride (AmimCl), 1-ethyl-3-methylimidazolium chloride (EmimCl), 1-ethyl-3-methylimidazolium diethyl phosphate (EmimDep), and 1-ethyl-3-methylimidazolium acetate (EmimOAc) were tested. Cellulose saccharification ratio was about 20% for kenaf powders pretreated in BmimCl, AmimCl, EmimCl, and EmimDep by conventional heating at 110 °C for 120 min. Conversely, 60-95% of cellulose was hydrolyzed to glucose, subsequent to ultrasonic pretreatment in the same ILs for 120 min at 25 °C. The cellulose saccharification ratio of kenaf powder in EmimOAc was 86% after only 15 min of the ultrasonic pretreatment at 25 °C, compared to only 47% in that case of thermal pretreatment in the IL.     

STEP ENZYMATIC HYDROLYSIS OF SODIUM HYDROXIDE-PRETREATED CHINESE LIQUOR DISTILLERS' GRAINS FOR ETHANOL PRODUCTION

Distillers' grains are a co-product of ethanol production. In China, only a small portion of distillers' grains have been used to feed the livestock because the amount was so huge. Nowadays, it has been reported that the distillers' grains have the potential for fuel ethanol production because they are composed of lignocelluloses and residual starch. In order to effectively convert distillers' grains to fuel ethanol and other valuable production, sodium hydroxide pretreatment, step-by-step enzymatic hydrolysis, and simultaneous saccharification and fermentation (SSF) were investigated. The residual starch was first recycled from wet distillers' grains (WDG) with glucoamylase to obtain glucose-rich liquid. The total sugar concentration was 21.3 g/L, and 111.9% theoretical starch was hydrolyzed. Then the removed-starch dry distillers' grains (RDDG) were pretreated with NaOH under optimal conditions and the pretreated dry distillers' grains (PDDG) were used for xylanase hydrolysis. The xylose concentration was 19.4 g/L and 68.6% theoretical xylose was hydrolyzed. The cellulose-enriched dry distillers' grains (CDDG) obtained from xylanase hydrolysis were used in SSF for ethanol production. The ethanol concentration was 42.1 g/L and the ethanol productivity was 28.7 g/100 g CDDG. After the experiment, approximately 80.6% of the fermentable sugars in WDG was converted to ethanol.     

Scale-up study of oxalic acid pretreatment of agricultural lignocellulosic biomass for the production of bioethanol

Building on our laboratory-scale optimization, oxalic acid was used to pretreat corncobs on the pilot-scale. The hydrolysate obtained after washing the pretreated biomass contained 32.55 g/l of xylose, 2.74 g/l of glucose and low concentrations of inhibitors. Ethanol production, using Scheffersomyces stipitis, from this hydrolysate was 10.3 g/l, which approached the predicted value of 11.9 g/l. Diafiltration using a membrane system effectively reduced acetic acid in the hydrolysate, which increased the fermentation rate. The hemicellulose content of the recovered solids decreased from 27.86% before pretreatment to only 6.76% after pretreatment. Most of the cellulose remained in the pretreated biomass. The highest ethanol production after simultaneous saccharification and fermentation (SSF) of washed biomass with S. stipitis was 21.1 g/l.     

Improving enzymatic hydrolysis of wheat straw using ionic liquid 1-ethyl-3-methyl imidazolium diethyl phosphate pretreatment

This study aims to establish a cellulose pretreatment process using ionic liquids (ILs) for efficient enzymatic hydrolysis. The IL 1-ethyl-3-methyl imidazolium diethyl phosphate ([EMIM]DEP) was selected in view of its low viscous and the potential of accelerating enzymatic hydrolysis, and it could be recyclable. The yield of reducing sugars from wheat straw pretreated with this IL at 130 °C for 30 min reached 54.8% after being enzymatically hydrolyzed for 12 h. Wheat straw regenerated were hydrolyzed more easily than that treated with water. The fermentability of the hydrolyzates, obtained after enzymatic saccharification of the regenerated wheat straw, was evaluated using Saccharomyces cerevisiae. This microbe could ferment glucose efficiently, and the ethanol production was 0.43 g/g glucose within 26 h. In conclusion, the IL [EMIM]DEP shows promise as pretreatment solvent for wheat straw, although its cost should be reduced and in-depth exploration of this subject is needed.