Preliminary exploration on pretreatment with metal chlorides and enzymatic hydrolysis of bagasse

Converting biomass to fermentable sugar is the critical step in the biomass refinery. Moreover, pretreatment of biomass plays an important role in improving the conversion of biomass to sugar. In this study, sugarcane bagasse was pretreated by metal chloride Lewis acids (0.1 mol L⁻³ CrCl₃, FeCl₃, FeCl₂, ZnCl₂ and AlCl₃ solution) for cellulase hydrolysis. The effects of pretreatments on the yield, chemical components, and sequential cellulase hydrolysis of pretreated bagasse were investigated. The results indicated that metal chlorides with different pKa values could efficiently remove the hemicellulose in bagasse during pretreatment. Furthermore, an inhibition factor (IF) quantitatively reflecting difficulty of cellulase hydrolysis was proposed. The low IF means the facile cellulase hydrolysis. The IF of Fe (III)-pretreated bagasse could decrease to 1.35. In this case, the enzymatic digestibility of bagasse approached to 100%.     

Optimization of dilute acid and hot water pretreatment of different lignocellulosic biomass: A comparative study

Pretreatment of biomass to alter their recalcitrant structures is an essential step to obtain high yield of products via bioconversion processes. In this study, main emphasis was to compare the results evaluated in terms of total reducing sugars (TRS) yield after acid and hot water pre-treatment process performed with laboratory scale equipment using different lignocellulosic biomass. The biomass chosen for this purpose i.e. sugarcane bagasse and bamboo were collected from Guwahati, Assam and their physico-chemical characteristics were examined using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and thermo gravimetric analysis (TGA) including proximate and ultimate analysis. Crystalinity of the biomass used was observed to be 33.15% and 31.29% for sugarcane bagasse and bamboo respectively. Hot water and dilute acid pretreatment allows selective solubility of hemicellulose which improves the accessibility of enzymes for cellulose hydrolysis. The highest yield of TRS was observed at run order 8 for both acid and hot water pretreatment (23.49 and 26.50 gL⁻¹) with respect to sugarcane bagasse. But, the pretreatment results obtained for bamboo was slightly different to that of sugarcane bagasse. The highest yield of TRS was obtained at run order 8 for acid (15.6 gL⁻¹) and run order 10 for hot water (17.98 gL⁻¹) pretreatment respectively. Irrespective of biomass type, hot water pretreatment process produced more TRS than acid pretreatment process.     

Ethanol production from enzymatic hydrolysis of sugarcane bagasse pretreated with lime and alkaline hydrogen peroxide

In this work we evaluated ethanol production from enzymatic hydrolysis of sugarcane bagasse. Two pretreatments agents, lime and alkaline hydrogen peroxide, were compared in their performance to improve the susceptibility of bagasse to enzymatic action. Mild conditions of temperature, pressure and absence of acids were chosen to diminish costs and to avoid sugars degradation and consequent inhibitors formation. The bagasse was used as it comes from the sugar/ethanol industries, without grinding or sieving, and hydrolysis was performed with low enzymes loading (3.50 FPU g⁻¹ dry pretreated biomass of cellulase and 1.00 CBU g⁻¹ dry pretreated biomass of ??-glucosidase). The pretreatment with alkaline hydrogen peroxide led to the higher glucose yield: 691 mg g⁻¹ of glucose for pretreated bagasse after hydrolysis of bagasse pretreated for 1 h at 25 °C with 7.35% (v/v) of peroxide. Fermentation of the hydrolyzates from the two pretreatments were carried out and compared with fermentation of a glucose solution. Ethanol yields from the hydrolyzates were similar to that obtained by fermentation of the glucose solution. Although the preliminary results obtained in this work are promising for both pretreatments considered, reflecting their potential for application, further studies, considering higher biomass concentrations and economic aspects should be performed before extending the conclusions to an industrial process.     

Pyrolysis of sugarcane bagasse pretreated with sulfuric acid

Pyrolysis is a promising technique for the recovery of useful gas, tar, and solid products from biomass waste. However, the low tar yields obtained from lignocellulosic biomass are a significant drawback. To enhance tar yields, sugarcane bagasse, which is the most abundant agricultural waste in Fiji, was pretreated at ambient temperature and atmospheric pressure using various sulfuric acid (H₂SO₄) concentrations. Here, the ether bonds of cellulose, hemicellulose, and lignin were partially hydrolyzed. The pretreated samples were then pyrolyzed at 500 °C, and it was confirmed that H₂SO₄-pretreatment disrupted the bagasse cell structure, with the thermogravimetry and differential thermogravimetry results confirming that decomposition occurred at lower temperatures after pretreatment. In addition, tar yields were significantly enhanced from 5.6 wt% to 13.4 wt% for the untreated and 3 M H₂SO₄-pretreated samples respectively. The main components detected in this tar product were levoglucosan, andcellulose-and hemicellulose-derived products, whose proportions were increased following pretreatment. Thus, our work demonstrates that dilute acid pretreatment enhances tar production from sugarcane bagasse due to the production of shorter chain components via the partial hydrolysis of ether bonds.     

Influence of impregnation with lactic acid on sugar yields from steam pretreatment of sugarcane bagasse and spruce, for bioethanol production

Lignocellulosic biomass can be utilized to produce ethanol, a promising alternative energy source produced through fermentation of sugars. However, in order to achieve high sugar and ethanol yields, the lignocellulosic material must be pretreated before the enzymatic hydrolysis and fermentation. Dilute acid pretreatment, using SO₂, is one of the most promising methods of pretreatment for softwood and agricultural residues. However, handling the high acidity of the slurry obtained from pretreatment and difficulty in recycling/degradation of the impregnating agent are some of the drawbacks of the dilute acid processes. In the present study the influence of utilization of a weak organic acid (lactic acid), as impregnating agent, on the sugar yield from pretreatment, with and without addition of SO₂, was investigated. The efficiency of pretreatment was assessed by enzymatic hydrolysis of the slurry obtained by pretreatment, using sugarcane bagasse and spruce, stored for one and two months in the presence of lactic acid separately, as feedstocks. Pretreatment of bagasse after storage with 0.5% lactic acid resulted in an overall glucose yield, i.e. after enzymatic hydrolysis, of 79% of theoretical based on the amount available in the raw material. This was as good as pretreatment using SO₂ as impregnating agent. However, storage of spruce with lactic acid before pretreatment, with and without addition of SO₂, was not efficient and resulted in lower sugar yields than pretreatment using SO₂ only.     

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.     

Utilization of pineapple stem juice to enhance enzyme-hydrolytic efficiency for sugarcane bagasse after an optimized pre-treatment with alkaline peroxide

The enzymatic hydrolysis of sugarcane bagasse was investigated by treating a peroxide–alkaline bagasse with a pineapple stem juice, xylanase and cellulase. Pre-treatment procedures of sugarcane bagasse with alkaline hydrogen peroxide were evaluated and compared. Analyses were performed using 2⁴ factorial designs, with pre-treatment time, temperature, magnesium sulfate and hydrogen peroxide concentration as factors. The responses evaluated were the yield of cellobiose and glucose released from pretreated bagasse after enzymatic hydrolysis. The results show that the highest enzymatic conversion was obtained for bagasse using 2% hydrogen peroxide at 60 °C for 16 h in the presence of 0.5% magnesium sulfate. Bagasse (5%) was treated with pineapple stem extract, which contains mixtures of protease and esterase, in combination with xylanase and cellulase. It was observed that the amount of glucose and cellobiose released from bagasse increased with the mixture of enzymes. It is believed that the enzymes present in pineapple extracts are capable of hydrolyze specific linkages that would facilitate the action of digesting plant cell walls enzymes. This increases the amount of glucose and other hexoses that are released during the enzymatic treatment and also reduces the amount of cellulase necessary in a typical hydrolysis.     

Efficient sugar production from sugarcane bagasse by microwave assisted acid and alkali pretreatment

Sugarcane bagasse represents one of the best potential feedstocks for the production of second generation bioethanol. The most efficient method to produce fermentable sugars is by enzymatic hydrolysis, assisted by thermochemical pretreatments. Previous research was focused on conventional heating pretreatment and the pretreated biomass residue characteristics. In this work, microwave energy is applied to facilitate sodium hydroxide (NaOH) and sulphuric acid (H₂SO₄) pretreatments on sugarcane bagasse and the efficiency of sugar production was evaluated on the soluble sugars released during pretreatment. The results show that microwave assisted pretreatment was more efficient than conventional heating pretreatment and it gave rise to 4 times higher reducing sugar release by using 5.7 times less pretreatment time. It is highlighted that enrichment of xylose and glucose can be tuned by changing pretreatment media (NaOH/H₂SO₄) and holding time. SEM study shows significant delignification effect of NaOH pretreatment, suggesting a possible improved enzymatic hydrolysis process. However, severe acid conditions should be avoided (long holding time or high acid concentration) under microwave heating conditions. It led to biomass carbonization, reducing sugar production and forming ‘humins’. Overall, in comparison with conventional pretreatment, microwave assisted pretreatment removed significant amount of hemicellulose and lignin and led to high amount of sugar production during pretreatment process, suggesting microwave heating pretreatment is an effective and efficient pretreatment method.     

Fractional pretreatment of raw and calcium oxalate-extracted agave bagasse using ionic liquid and alkaline hydrogen peroxide

Occurrence of calcium oxalate (CaC₂O₄ – CaOX) crystals has been observed in more than 215 plant families. However, very little is known about the effects of calcium oxalate on biomass pretreatment and saccharification. Agave bagasse (AGB) was used as a model material due to its natural high levels of CaOX. To understand the physicochemical changes in function of biomass pretreatment, both raw AGB and CaOX-extracted agave bagasse (EAB) were subjected to ionic liquid (IL) with 1-Butyl-3-methylimidazolium chloride [C₄C₁Im][Cl] and alkaline hydrogen peroxide (AHP) pretreatments. Physicochemical changes were monitored by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and wet chemistry methods. Results show that free CaOX crystals affected negatively (by ca 39%) the saccharification of AHP-pretreated EAB compared to AGB. On the other hand, IL pretreatment achieved higher sugar yield (7.8 g dm⁻³) and lower crystallinity (14%) with EAB than for AHP (5.4 g dm⁻³ and 29%, respectively).     

机械活化预处理对蔗渣酶解产糖影响的研究

采用机械活化方法对蔗渣进行预处理,研究其对蔗渣酶解产糖的影响。用红外光谱、X-射线衍射和扫描电镜测定预处理前后蔗渣结构及表面形态的变化,并分析其作用机理。研究结果表明,机械活化用于蔗渣预处理,可明显提高预处理后蔗渣的酶解产糖率。酶解时间为48 h时,蔗渣酶解产糖率从未处理时的19.86%提高到59.34%。蔗渣酶解产糖率的提高是由于机械活化处理使得蔗渣纤维素分子间部分氢键发生断裂、结晶度下降、表面有序结构被破坏的所致。     

Screening and optimization of pretreatments in the preparation of sugarcane bagasse feedstock for biohydrogen production and process optimization

This work evaluated the effects of individual alkaline, sodium carbonate (Na₂CO₃ denoted as; NaC), sodium sulfide (Na₂SO₃ denoted as; NaS) and combination of NaC + NaS pretreatment for the saccharification of sugarcane bagasse (SCB). The effects of different pretreatments on chemical composition and structural complexity of SCB in relation with its saccharification were investigated. For enzymatic hydrolysis of pretreated SCB we have utilized the produced crude enzymes by Streptomyces sp. MDS to make the process more cost effective. A enzyme dose of 30 filter paperase (FPU) produced a maximum reducing sugar (RS) 592 mg/g with 80.2% hydrolysis yield from NaC + NaS pretreated SCB under optimized conditions. The resulted enzymatic hydrolysates of each pretreated SCB were applied for hydrogen production using Clostridium beijerinckii KCTC1785. NaC + NaS pretreated SCB hydrolysates exhibited maximum H₂ production relative to other pretreatment methods. Effects of temperature, initial pH of culture media and increasing NaC + NaS pretreated SCB enzymatic hydrolysates concentration (2.5–15 g/L) on bioH₂ production were investigated. Under the optimized conditions, the cumulative H₂ production, H₂ production rate, and H₂ yield were 1485 mL/L, 61.87 mL/L/h and 1.24 mmol H₂/mol of RS (0.733 mmol H₂/g of SCB), respectively. The efficient conversion of the SCB hydrolysate to H₂ without detoxification proves the viability of process for cost-effective hydrogen production.     

Biohydrogen production from pure and natural lignocellulosic feedstock with chemical pretreatment and bacterial hydrolysis

Pretreatment and saccharification of lignocellulosic materials is the key technology affecting the efficiency of cellulosic biohydrogen production. In this work, two pure cellulosic materials (i.e., carboxymethyl-cellulose (CMC) and xylan) were directly hydrolyzed (without pretreatment) by a cellulolytic isolate Cellulomonas uda E3-01 able to release extracellular cellulolytic enzymes. Natural cellulosic feedstock (i.e., sugarcane bagasse) was chemically pretreated prior to the bacterial hydrolysis.A temperature-shift strategy (35 °C for cellulolytic enzymes production and 45 °C for hydrolysis reaction) was used to increase the production of reducing sugars during the bacterial hydrolysis. The hydrolysates of CMC, xylan, and bagasse were efficiently converted to H₂ via dark fermentation with Clostridium butyricum CGS5. The maximum hydrogen yield was 8.80 mmol H₂/g reducing sugar (i.e., 1.58 mol H₂/mol hexose) for CMC, 6.03 mmol H₂/g reducing sugar (i.e., 0.91 mol H₂/mol pentose) for xylan, and 6.01 mmol H₂/g reducing sugar for bagasse.     

Production of bioethanol from sugarcane bagasse using yeast strains: A kinetic study

In this study, sugarcane bagasse (2 mm) was pretreated with 2.5% NaOH followed by steaming at 121°C for various time periods. Maximum cellulose content of 81% and delignification of 68.5% were achieved by soaking bagasse in 2.5% NaOH with a residence time of 1 h at room temperature followed by steaming at 121°C for 30 min residence time. The pretreated substrate was analyzed by SEM and FTIR to study the structural modification and functional group of the untreated and pretreated substrates. The pretreated substrate was saccharified by commercial cellulase enzyme depicting 106 µm mesh size of substrate yields maximum saccharification rate. The saccharified material was fermented by Saccharomyces cerevisiae and Pichia stipitis in mono- and co-culture modes. Maximum product yield (Y_p/s) was observed by monoculture using Saccharomyces cerevisiae after 96 h of fermentation period.     

Thermophilic biohydrogen production from energy plants by Caldicellulosiruptor saccharolyticus and comparison with related studies

Air-dried samples of sweet sorghum, sugarcane bagasse, wheat straw, maize leaves and silphium were utilized without chemical pretreatment as sole energy and carbon sources for H₂ production by the extreme thermophilic bacterium Caldicellulosiruptor saccharolyticus. The specific H₂ production rates and yields were determined in the batch fermentation process. The best substrate was wheat straw, with H₂ production capacity of 44.7 L H₂ (kg dry biomass)^?1 and H₂ yield of 3.8 mol H₂ (mol glucose)^?1. Enzymatically pretreated maize leaves exhibited H₂ production of 38 L H₂ (kg dry biomass)^?1. Slightly less H₂ was obtained from homogenized whole plants of sweet sorghum. Sweet sorghum juice was an excellent H₂ source. Silphium trifoliatum was also fermented though with a moderate production. The results showed that drying is a good storage method and raw plant biomass can be utilized efficiently for thermophilic H₂ production. The data were critically compared with recently published observations.     

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.     

Comparative study on combustion and oxy-fuel combustion environments using mixtures of coal with sugarcane bagasse and biomass sorghum bagasse by the thermogravimetric analysis

Biomass and coal have different physicochemical properties and thermal behavior. During the co-combustion of coal-biomass mixtures, their thermal behavior varies according to the percentage of each fuel in the mixture. Thereby, this research aims to characterize the thermal behavior of mixtures of coal, sugarcane bagasse, and biomass sorghum bagasse as biomass in simulated combustion (O₂/N₂) and oxy-fuel combustion (O₂/CO₂) environments. Experiments have been performed in duplicate on a thermogravimetric analyzer at heating rate of 10 °C/min. A uniform granulometry was considered for all materials (63 μm) in order to ensure a homogeneous mixture. Four biomass percentages in the mixture (10, 25, 50 and 75%) have been studied. Based on thermogravimetric (TG) and thermogravimetric (DTG) analyses, parameters such as combustion index, synergism, and activation energy have been determined, as well as the combustion environment influence on these parameters. The results indicate that, although sugarcane bagasse has the lowest activation energy, the thermal behavior of both types of biomass is similar. Thus, biomass sorghum bagasse can be used as an alternative biomass to supply the power required during sugarcane off-season. For both mixtures, optimal results were obtained at 25% of biomass. By analyzing the environment influence on combustion behavior, the results indicate that when N₂ is replaced with CO₂, it is observed an increase in reaction reactivity, a higher oxidation rate of materials and an improvement in evaluated parameters.     

The addition of hydrolyzed rice straw in xylose fermentation by Pichia stipitis to increase bioethanol production at the pilot-scale

The pretreatment of agricultural biomass by diluted acid is often employed to facilitate the release of monosaccharide for the subsequent enzyme hydrolysis for lignocellulosic ethanol production. However, furfural and hydroxymethylfurfural are usually generated and markedly decrease the yield of pentose fermentation during this pretreatment. In the present study, the enhancement of lignocellulosic ethanol production was successfully demonstrated at pilot scale with extra addition of hydrolyzed rice straw into pentose fermentation by Pichia stiptis. This way has resulted into the increase of P. stiptis cell mass was shown to play a positive role. The ethanol yield, 0.45 g_p/g_s, with the addition of hydrolyzed rice straw in hemicellulosic hydrolysate from plywood, bagasse and bamboo were increase 20–51% to demonstrate the applicability of this technology in a variety of lignocellulosic ethanol processes due to the efficient conversion of xylose.     

Fermentative hydrogen production by Clostridium butyricum CGS5 using carbohydrate-rich microalgal biomass as feedstock

In this work, a carbohydrate-rich microalga, Chlorella vulgaris ESP6, was grown photoautotrophically to fix the CO₂. The resulting microalgal biomass was hydrolyzed by acid or alkaline/enzymatic treatment and was then used for biohydrogen production with Clostridium butyricum CGS5. The C. vulgaris biomass could be effectively hydrolyzed by acid pretreatment while similar hydrolysis efficiency was achieved by combination of alkaline pretreatment and enzymatic hydrolysis. The biomass of C. vulgaris ESP6 containing a carbohydrate content of 57% (dry weight basis) was efficiently hydrolyzed by acid treatment with 1.5% HCl, giving a reducing sugars (RS) yield of nearly 100%. C. butyricum CGS5 could utilize RS from C. vulgaris ESP6 biomass to produce hydrogen without any additional organic carbon sources. The optimal conditions for hydrogen production were 37 °C and a microalgal hydrolysate loading of 9 g RS/L with pH-controlled at 5.5. Under the optimal conditions, the cumulative H₂ production, H₂ production rate, and H₂ yield were 1476 ml/L, 246 ml/L/h, and 1.15 mol/mol RS, respectively. The results demonstrate that the C. vulgaris biomass has the potential to serve as effective feedstock for dark fermentative H₂ production.     

Alkaline treatment for detoxification of acetic acid-rich pyrolytic bio-oil for microalgae fermentation: Effects of alkaline species and the detoxification mechanisms

Bio-oil derived from Pyrolysis of lignocellulosic biomass contains appreciable amounts acetic acid, which can be used as substrate for growing microalgae Chlamydomonas reinhardtii. However, the toxic compounds in the bio-oil inhibit the cell growth. This work is to develop alkaline treatment methods to reduce the toxicity and improve fermentability of acetic acid rich bio-oil. When growing in raw bio-oil without any detoxification treatment, the algae can only tolerate up to 0.1 wt% of bio-oil. Treatment with KOH, NaOH and Ca(OH)₂ significantly reduced the toxicity and consequently improved the fermentability of bio-oil. The bio-oil tolerant level by microalgae depended on the alkali species used. Among the three alkali species, Ca(OH)₂ proved the most effective detoxification reagent. Inhibitory compounds such as furans, phenols, ketones, aldehydes, ethers, esters, alcohols were removed by Ca(OH)₂ treatment through precipitation. The detoxification mechanisms by the Ca(OH)₂ -based treatment were also explored. The synergistic effect of alkaline pH, high temperature, and presence of Ca²⁺ played an important role for the precipitation of those compounds, and the consequent detoxification. Collectively, the results shows alkali, particularly Ca(OH)₂-based, treatment is an effective for reducing the toxicity of the pyrolysis derived bio-oil as fermentative substrate for microalgae growth. The microalgae can tolerant Ca(OH) ₂-treated bio-oil up to 5.5 wt%, which was 55 times higher than algal tolerance level of untreated bio-oil.     

Biological saccharification by Clostridium thermocellum and two-stage hydrogen and methane production from hydrogen peroxide-acetic acid pretreated sugarcane bagasse

The present work aimed at establishing an efficient degradation and energy recovery system form sugarcane bagasse (SCB) through hydrogen peroxide-acetic acid (HPAC) pretreatment, thermophilic hydrogen production and mesophilic methane production. The degradation ratio of HPAC pretreated SCB (HPAC-SCB, 2%, w/v) exceeded 90% under the biological hydrolysis of C. thermocellum without enzyme addition. The hydrogen yield in the co-culture fermentation of T. thermosaccharolyticum and C. thermocellum from HPAC-SCB (2%, w/v) reached 226 mL/g substrate. The long-term hydrogen fermentation was successfully established with 1.59 L/(L·d), 0.159 L/g substrate for average hydrogen productivity and yield, respectively. Methane production of 0.341 L/g COD (chemical oxygen demand)_added was recovered by semi-continuous methane fermentation from hydrogen-producing effluent at 12 days of hydraulic retention time (HRT). Average energy recovery of 8.79 MJ/kg SCB was obtained under the optimal conditions. The present work indicated the promising application of the established process in valorization of lignocellulosic bio-waste.