Comparative study on ethanol production from pretreated sugarcane bagasse using immobilized Saccharomyces cerevisiae on various matrices

Microwave alkali pretreated sugarcane bagasse was used as a substrate for production of cellulolytic enzymes, needed for biomass hydrolysis. The pretreated sugarcane bagasse was enzymatic hydrolyzed by crude unprocessed enzymes cellulase (Filter paper activity 9.4 FPU/g), endoglucanase (carboxymethylcellulase, 148 IU/g), β-glucosidase (116 IU/g) and xylanase (201 IU/g) produced by Aspergillus flavus using pretreated sugarcane bagasse as substrate under solid state fermentation. Concentrated enzymatic hydrolyzate was used for ethanol production using Saccharomyces cerevisiae immobilized on various matrices. The yield of ethanol was 0.44 g_p/g_s in case of yeast immobilized sugarcane bagasse, 0.38 g_p/g_s using Ca-alginate and 0.33 g_p/g_s using agar-agar as immobilization matrices. The immobilized yeast studied up to 10 cycles in case of immobilized sugarcane bagasse and up to 4 cycles in case of agar-agar and calcium alginate for ethanol production under repeated batch fermentation study.     

Effect of NaOH on pretreatment of Gossypium herbaceum

In present study, the substrate Gossypium herbaceum (cotton stalks) was treated with sodium hydroxide to investigate its greatest promising use as an economical substrate for bioethanol production. Initially, 2 mm mesh size cotton stalks were soaked in various concentrations of NaOH (1–3%) for different soaking intervals of 2, 4, 6, 12, 24, and 48 h. The results showed that the cellulose content and delignification increased with the increase in the concentration of alkali and soaking time. However, the maximum cellulose and delignification (60.6% and 51.5%) were observed with 2.5% NaOH after 24 h of soaking. In physiochemical pretreatment, the maximum cellulose content (73.19%) was achieved with 2.5% NaOH at 121°C after 60 min while delignification was found to be 77.7%. All these results of the present study indicate that a suitable concentration of alkali as well as an autoclaving period at specific temperature are very much crucial to expose the maximum cellulosic contents prior to employing cotton stalks as substrates for bio-fuel production.     

Batch-based enzymatic saccharification of sweet sorghum bagasse

To improve enzymatic digestibility and sugar concentration, sweet sorghum bagasse was pretreated with alkali and liquid hot water, and then subjected to fed-batch enzymatic hydrolysis. Scanning electron microscopy assay suggested that different pretreatment methods resulted in different composition and structure of residues; these changes had a significant influence on cellulose hydrolysis. Fresh substrate was pretreated and then added at different amounts during the first 48 h to yield a final dry matter content of 30% (w/v). For liquid hot water pretreatment, a maximal glucose concentration of 95.71 g/L, corresponding to 52.85% xylan removal, was obtained with the sweet sorghum bagasse pretreated at 184°C for 18 min. NaOH soaking at ambient conditions removed lignin up to 60%, and the subsequent hydrolysis with cellulase loading of less than 10 FPU/g DM, and substrate supplementation every few hours yield the high glucose and xylose concentrations of 114.89L and 29.93 g/L, respectively after 144 h.     

Assessment of sugarcane bagasse gasification in supercritical water for hydrogen production

Sugarcane bagasse is one of the major resources of agricultural biomass waste in the world. In this work, supercritical water gasification characteristics of sugarcane bagasse were investigated. The effect of temperature (600–750 °C), concentration (3–12 wt%), residence time (5–20 min) and catalysts (Raney-Ni, K₂CO₃ and Na₂CO₃) on bagasse gasification were studied. A kinetic study on the non-catalytic and Na₂CO₃ catalytic bagasse gasification was conducted to describe the kinetic information of the bagasse gasification reaction. The results showed that a higher reaction temperature, a lower bagasse concentration and a longer residence time could favor the gasification of bagasse, leading to a higher hydrogen yield. Bagasse was nearly completely gasified at 750 °C without using any catalyst and the carbon gasification efficiency could reach up to 96.28%. The addition of employed catalysts remarkably promoted the bagasse gasification reactivity. The maximum hydrogen yield (35.3 mol/kg) was achieved at 650 °C with the Na₂CO₃ loading of 20 wt%. The experimental data fitted well with a homogeneous model based on a Pseudo-first-order reaction hypothesis. The kinetic study showed that Na₂CO₃ catalyst could lower the activation energy E_a of bagasse gasification from 117.88 kJ/mol to 78.25 kJ/mol.     

Cellulase production using biomass feed stock and its application in lignocellulose saccharification for bio-ethanol production

A major constraint in the enzymatic saccharification of biomass for ethanol production is the cost of cellulase enzymes. Production cost of cellulases may be brought down by multifaceted approaches which include the use of cheap lignocellulosic substrates for fermentation production of the enzyme, and the use of cost efficient fermentation strategies like solid state fermentation (SSF). In the present study, cellulolytic enzymes for biomass hydrolysis were produced using solid state fermentation on wheat bran as substrate. Crude cellulase and a relatively glucose tolerant BGL were produced using fungi Trichoderma reesei RUT C30 and Aspergillus niger MTCC 7956, respectively. Saccharification of three different feed stock, i.e. sugar cane bagasse, rice straw and water hyacinth biomass was studied using the enzymes. Saccharification was performed with 50 FPU of cellulase and 10 U of β-glucosidase per gram of pretreated biomass. Highest yield of reducing sugars (26.3 g/L) was obtained from rice straw followed by sugar cane bagasse (17.79 g/L). The enzymatic hydrolysate of rice straw was used as substrate for ethanol production by Saccharomyces cerevisiae. The yield of ethanol was 0.093 g per gram of pretreated rice straw.     

Statistical modeling and optimization of pretreatment of Bombax ceiba with KOH through Box–​Behnken design of response surface methodology

Bioethanol is considered the cleanest liquid fuel used as a substitute for depleting fossil fuels. Various technologies have been introduced to form bioethanol from lignocellulosic biomass. Seed pods of Bombax ceiba, which are produced and wasted in large amount annually, were used as a source of cellulose. In this study, response surface methodology was used to explore the effects of KOH concentrations, substrate loading, and residence time on cellulose exposure and liberation of reducing sugars (RS), total sugars (TS), and total phenolic compounds from seed pods of B. ceiba. Box–Behnken design with three variables and three levels showed maximum release of total phenolic compounds (394.04 mg/ml) and RS (50.06 mg/ml) corresponding to 3% KOH concentration, 15% substrate level with residence time of 8 h at 121°C, and maximum cellulose exposure (64%), and TS (206.65 mg/ml) liberation was observed at 5% KOH concentration and 10% substrate level at same temperature for same soaking time. While at room temperature maximum cellulose exposed (46%), TS (146.1480 mg/ml), total phenol (300.3901 mg/ml), and RS (9.0075 mg/ml) were observed at 3% KOH, 15% substrate concentration, and 8-h residence time. These results suggested that thermochemical pretreatment is more effective than chemical pretreatment alone. The second-order polynomial equation using analysis of variance was employed for analyzing the results.     

Bioethanol production by Saccharomyces cerevisiae,Pichia stipitis and Zymomonas mobilis from delignified coconut fibre mature and lignin extraction according to biorefinery concept

In search to increase the offer of liquid, clean, renewable and sustainable energy in the world energy matrix, the use of lignocellulosic materials (LCMs) for bioethanol production arises as a valuable alternative. The objective of this work was to analyze and compare the performance of Saccharomyces cerevisiae, Pichia stipitis and Zymomonas mobilis in the production of bioethanol from coconut fibre mature (CFM) using different strategies: simultaneous saccharification and fermentation (SSF) and semi-simultaneous saccharification and fermentation (SSSF). The CFM was pretreated by hydrothermal pretreatment catalyzed with sodium hydroxide (HPCSH). The pretreated CFM was characterized by X-ray diffractometry and SEM, and the lignin recovered in the liquid phase by FTIR and TGA. After the HPCSH pretreatment (2.5% (v/v) sodium hydroxide at 180 °C for 30 min), the cellulose content was 56.44%, while the hemicellulose and lignin were reduced 69.04% and 89.13%, respectively. Following pretreatment, the obtained cellulosic fraction was submitted to SSF and SSSF. Pichia stipitis allowed for the highest ethanol yield – 90.18% – in SSSF, 91.17% and 91.03% were obtained with Saccharomyces cerevisiae and Zymomonas mobilis, respectively. It may be concluded that the selection of the most efficient microorganism for the obtention of high bioethanol production yields from cellulose pretreated by HPCSH depends on the operational strategy used and this pretreatment is an interesting alternative for add value of coconut fibre mature compounds (lignin, phenolics) being in accordance with the biorefinery concept.     

Physicochemical characterization of alkali pretreated sugarcane tops and optimization of enzymatic saccharification using response surface methodology

Alkali pretreatment of sugarcane tops was carried out with 3% NaOH for 60 min at 121 °C in a laboratory autoclave. The effect of solid loading, enzyme loading, incubation time and surfactant concentration on enzymatic saccharification was studied using a response surface method according to Box–Behnken design. Under optimized conditions 77.5% sugar was recovered from the pretreated biomass. This yield was seven times higher than that obtained with untreated sugarcane tops. A substantial amount of lignin (90%) was removed by this pretreatment method. Physicochemical characterization of native and alkali pretreated sugarcane tops were carried out by XRD, FTIR and SEM and the changes in the chemical composition were also monitored. The X-ray diffraction profile showed that the degree of crystallinity was higher for alkali pretreated biomass than that for native.     

Enhanced biohydrogen production from cornstalk through a two‐step fermentation: Dark fermentation and photofermentation

The pretreated cornstalk (CS) was employed for biohydrogen production through combining dark‐fermentative bacteria, cow dung, and photosynthetic bacteria, Rhodobacter capsulatus mutant in this work. In the first step, the cornstalk was pretreated with 0.75% NaOH, 12 IU/g‐CS cellulase, and 2400 IU/g‐CS hemicellulase under different hydrolysis time and temperature. The reducing sugar yields were very close under different conditions, and its maximum was 0.51 ± 0.01 g/g‐CS at hydrolysis 108°C for 2.0 hours. However, the H₂ yield of dark fermentation enhanced with the increasing hydrolysis time and temperature, and the maximum was 156.7 ± 8.6 mL/g‐CS at hydrolysis 126°C for 2.0 hours. The biogas was only H₂ and CO₂, and no methane was found. In the second step, R. capsulatus ZYHAB3 with the mutation on both hvrA and hupAB genes was obtained from wild type (R. capsulatus SB1003) and the inactivation of both hvrA and hupAB genes remarkably enhanced nitrogenase activity. When the dark‐fermentation effluent was employed as a substrate, the H₂ yield and maximum H₂ evolution rate of ZYHAB3 were 2827.5 ± 283.5 mL/L and 40.9 ± 2.3 mL/(Lh), which increased by 44.5 and 39.1% compared with those of wild type, respectively. The high H₂ yield of 439.4 mL/g‐CS was obtained from pretreated cornstalk through the 2‐step process, and the chemical oxygen demand removal rate achieved 90.6%. The results suggest that combining cow dung and R. capsulatus mutant (hvrA ^? hupAB ^?) could be a promising way to produce H₂ form agricultural wastes.     

Biohydrogen production from thermochemically pretreated corncob using a mixed culture bioaugmented with Clostridium acetobutylicum

Bovine ruminal fluid (BRF) bioaugmented with Clostridium acetobutylicum (Clac) was assessed for hydrolyzing cellulose and produce biohydrogen (BioH₂) simultaneously from pretreated corncob in a single step, without the use of external hydrolytic biocatalysts. The corncob was pretreated using three thermochemical methods: H₂SO₄ 2%, 160 °C; NaOH 2%, 140 °C; NaOCl 2%, 140 °C; autohydrolysis: H₂O, 190 °C. Subsequently, BioH₂ production was carried out using the pretreated material with the highest digestibility applying a Taguchi experimental array to identify the optimal operating conditions. The results showed a higher glucose released from pretreated corncob with H₂SO₄ (134.7 g/L) compared to pretreated materials by autohydrolysis, NaOH and NaOCl (123 g/L, 89.8 g/L and 52.9 g/L, respectively). The mixed culture was able to hydrolyze the pretreated corncob and produce 575 mL of H₂ (at 35 °C, pH 5.5, 1:2 ratio of BRF:Clac and 5% of solids loading) equivalent to 132 L H₂/Kg of biomass.     

甘蔗渣的不同预处理方法比较及其酶水解的类分形动力学

分别采用NaOH（0.45 mol/L aq.）、HCl（0.034 mol/L aq.）和高温液态水（LHW）三种方法对甘蔗渣进行预处理,并对其组分变化和酶解效果进行了比较。NaOH预处理方法获得最高的木质素去除率,达91.1%,糖损失率达23.5%;HCl和LHW预处理结果类似,木聚糖溶解率分别为85.2%和79.7%,糖损失率均约为15%,木质素去除率均小于16%。三种方法处理的甘蔗渣经纤维素酶水解后得到总单糖（葡萄糖 + 木糖）浓度分别为38.7 g/L（NaOH）、16.1 g/L（HCl）和15.6 g/L（LHW）。综合比较预处理和酶水解工艺,NaOH水溶液预处理法的糖回收率最高,其次为HCl水溶液预处理法,LHW预处理法的糖回收率最低。作为描述纤维素酶反应动力学的有力工具,类分形理论的研究表明,各种预处理后底物的不规则性依次为：HCl＞LHW＞NaOH,其与酶的有效吸附大小依次为：NaOH＞HCl＞LHW。     

Oxidative catalytic steam gasification of sugarcane bagasse for hydrogen rich syngas production

Reactive Flash Volatilization (RFV) is an emerging thermochemical method to produce tar free hydrogen rich syngas from waste biomass at relatively lower temperature (<900 °C) in a single stage catalytic reactor within a millisecond residence time. Here, we show catalytic RFV of bagasse using Ru, Rh, Pd, or Re promoted Ni/Al₂O₃ catalysts under steam rich and oxygen deficient environment. The optimum reaction conditions were found to be 800 °C, steam to carbon ratio = 1.7 and carbon to oxygen ratio = 0.6. Rh–Ni/Al₂O₃ performed the best, resulting in highest hydrogen concentration in the synthesis gas at 54.8%, with a corresponding yield of 106.4 g-H₂/kg bagasse. A carbon conversion efficiency of 99.96% was achieved using Rh–Ni, followed by Ru–Ni, Pd–Ni, Re–Ni and mono metallic Ni catalyst in that order. Alkali and Alkaline Earth Metal species present in the bagasse ash and char, that deposited on the catalyst, was found to enhance its activity and stability. The hydrogen yield from bagasse was higher than previously reported woody biomass and comparable to the microalgae.     

Investigation on performance of microbial fuel cells based on carbon sources and kinetic models

Substrate concentration has great influence on the electrical performance of a microbial fuel cell (MFC). In this study, date syrup with a high sugar content and diversified types of nutrients was used as a substrate in a dual‐chambered MFC. The results obtained were compared with glucose as a conventional substrate for power generation. A pure culture of Saccharomyces cerevisiae was used as a biocatalyst in the anode chamber and potassium ferricyanide as an oxidizing agent in the cathode side. Maximum power density of 65 mW/m² was obtained in an MFC operated with date syrup at an equivalent total carbohydrate content of 6 g/l. When the electron acceptor in the cathode side was replaced with potassium permanganate, power density was increased almost 2.5‐fold and reached 234 mW/m². The system was loaded with low to high concentrations of sugar (1–7, 10, 20 and 30 g/l). However, at high concentrations of substrates, an inverse relationship with the MFC electrical performance was observed, which was most probably due to substrate inhibition in the MFC. Substrate inhibition models were applied to investigate inhibition kinetic from an electrical point of view. Tessier, Aiba and Haldane as inhibition models were well fitted with experimental data (R² = 0.98–0.99). The tested models revealed that the inhibitory effect for the substrate can be described in terms of model parameters. In order to evaluate the effect of the concentration of substrates on electrical performance, different inhibition concentrations were suggested by the models with respect to electrical responses achieved in the MFC. Copyright © 2012 John Wiley & Sons, Ltd.     

Parametric gasification process of sugarcane bagasse for syngas production

This research focuses on parametric influence on product distribution and syngas production from conventional gasification. Three experimental parameters at three different levels of temperature (700, 800 and 900 °C), sugarcane bagasse loading (2, 3 and 4 g) and residence time (10, 20 and 30 min) were studied using horizontal axis tubular furnace. Response Surface Methodology supported by central composite design was adopted in order to investigate parameters impact on product distribution (i.e., gas, tar and char) and gaseous products (i.e., H₂, CO, CO₂ and CH₄). The highest H₂ fraction obtained was 42.88 mol% (36.91 g-H₂ kg-biomass⁻¹) at 3 g of sugarcane bagasse loading, 900 °C and 30 min reaction time. The temperature was identified as the most influential parameter followed by reaction time for H₂ production and diminishing the bio-tar and char yields. An increase in sugarcane bagasse loading, on other hand, favored the production of bio-tar, CO₂ and CH₄ production. The statistical analysis verified temperature as most significant (p-value 0.0008) amongst the parameters investigated for sugarcane bagasse biomass gasification.     

Ethanol production from agroindustrial biomass using a crude enzyme complex produced by Aspergillus niger

This study investigates ethanol production from simultaneous fermentation and saccharification (SFS) and separated hydrolysis and fermentation (SHS) using enzyme complexes produced by Aspergillus niger strains (ATCC 16404, ATCC 1057, ATCC 9029). The enzyme complexes were produced by solid-state fermentation (SSF) on inexpensive and readily available agroindustrial products: rice byproduct (composed of AFEX-treated rice rust and rice bran), whey and sugarcane bagasse. The ethanol was produced by Saccharomyces cerevisiae Y904 using whey and rice byproduct as the substrate and the enzyme complex produced by A. niger. The best result for solid-state fermentation (40 U/g of dry substrate, A. niger ATCC 16404) was obtained in a 0.5 L rotating drum bioreactor at 40 °C filled half filled with solid biomass composed of rice byproduct (86% wt/wt), whey (12% wt/wt) and CaCl₂ (2.0% wt/wt). The best result for ethanol fermentation (11.7 g/L of ethanol) was obtained after 12 h of SFS at pH 4.5 and 35 °C. A comparative study of ethanol production by Trichoderma reesei CCT 2768 and A. niger ATCC 16404 complexes under the same optimised SFS and SSF conditions was also performed, revealing that ethanol production by the A. niger enzyme complex was 2.25 times higher than that by T. reesei. These findings suggest that the ethanol production using crude enzymatic complexes produced by A. niger and agroindustrial biomass described in this paper is very promising in terms of disposal of the whey produced by cheese-making and other dairy food processing.     

Effect of Carbonization Temperature on Combustion Reactivity of Bagasse Char

Abstract

The combustion reactivity of bagasse chars was investigated under isothermal conditions at 400°C in air. The bagasse char samples were prepared by carbonizing bagasse in a fixed bed reactor at temperatures between 500°C and 800°C. It was observed that raising the carbonization temperature resulted in a significant decrease in reactivity of bagasse char. This was manifested by the decrease in the values of the maximum reaction rate, average rate based on 50% burnout and conversion achieved in 30 minutes with the increase in carbonization temperature. The decrease in reactivity of bagasse char with carbonization temperature was attributed to changes in the reactive components of bagasse.     

Production of ethanol from cassava pulp via fermentation with a surface-engineered yeast strain displaying glucoamylase

Cassava (Manihot esculenta Crantz) pulp, produced in large amounts as a by-product of starch manufacturing, is a major biomass resource in Southeast Asian countries. It contains abundant starch (approximately 60%) and cellulose fiber (approximately 20%). To effectively utilize the cassava pulp, an attempt was made to convert its components to ethanol using a sake-brewing yeast displaying glucoamylase on the cell surface. Saccharomyces cerevisiae Kyokai no. 7 (strain K7) displaying Rhizopus oryzae glucoamylase, designated strain K7G, was constructed using the C-terminal-half region of α-agglutinin. A sample of cassava pulp was pretreated with a hydrothermal reaction (140 °C for 1 h), followed by treatment with a Trichoderma reesei cellulase to hydrolyze the cellulose in the sample. The K7G strain fermented starch and glucose in pretreated samples without addition of amylolytic enzymes, and produced ethanol in 91% and 80% of theoretical yield from 5% and 10% cassava pulp, respectively.     

Steam explosion pretreatment and enzymatic saccharification of duckweed (Lemna minor) biomass

Our previous research has shown that duckweed is potentially an ideal feedstock for the production of biofuels because it can be effectively saccharified enzymatically. Here we report the results of experiments in which duckweed was pre-treated by steam explosion prior to enzyme digestion. A range of temperatures, from 130 to 230 °C with a fixed retention time of 10 min, were employed. The best pretreatment conditions were 210 °C for 10 min; these conditions produced the highest amount of water-soluble material (70%), the greatest levels of starch solubilisation (21%) and hemicellulose and pectic polysaccharides degradation (60%). The use of these steam explosion conditions enabled large reductions in the concentrations of enzymes required for effective saccharification. The amount of Celluclast required was reduced from 100 U (4.35 FPU) g⁻¹ substrate to 20 U g⁻¹ substrate, and additional beta-glucosidase was reduced from 100 to 2 U g⁻¹ substrate.     

Techno-economic evaluation of strategies based on two steps organosolv pretreatment and enzymatic hydrolysis of sugarcane bagasse for ethanol production

Several strategies based on a two steps organosolv pretreatment followed by enzymatic hydrolysis of sugarcane bagasse (SCB) were evaluated with the objective of selecting operational conditions suitable to promote an efficient and low cost production of ethanol. Initially, the influence of six variables used for the organosolv pretreatment was studied. The variables included the time of the first organosolv pretreatment step, the use of 45% ethanol as pulping solution, solid-to-liquid ratio of the ethanol solution used during the first pretreatment step, time of second organosolv pretreatment, concentration of ethanol and concentration of NaOH solution used in the second pretreatment step. Further assays of enzymatic hydrolysis were carried out to promote additional reduction in the costs of the process and improve the results of cellulose conversion to glucose. Eliminating the milling step of the pretreated SCB, using a commercial tensoactive (composed of esters and several surfactants), and recycling 50% of the slurry obtained during the second step of organosolv pretreatment as reaction medium proved to be feasible for use during the enzymatic hydrolysis. Fermentation of the glucose medium produced under the selected pretreatment conditions to ethanol by Saccharomyces cerevisiae occurred with 81% efficiency and a cost of 102.88 $/hL of ethanol.     

Screening of thermotolerant yeast by low-energy ion implantation for cellulosic ethanol fermentation

One thermotolerant mutant, ST-1559, was selected after mutagenizing with ion beam implantation. The results showed that ST-1559 could grow well under 45°C,and its ethanol yield reached 109.46 g/L when the glucose content was 250 g/L in the fermentation medium. When corn straw which was pretreated by NaOH was used as substrate in fermentation experiment under 45°C, it produced 13.48 g/L ethanol, and 82.17% of the cellulose was achieved. These results suggest that ST-1559 had advantage in simultaneous saccharification and fermentation.