Increased digestibility of bagasses by pretreatment with alkalis and steam explosion

Alkali treatment and steam explosion of bagasse were investigated in order to develop economical and effective methods of increasing the digestibility of bagasse. The treated bagasse was to be used as a substrate for the production of volatile fatty acids by anaerobic acidogenic bacteria. The alkalis examined were NaOH, NH(3) (aqueous), NaOH + NH(3), Ca(OH)(2), and Ca(OH)(2) + Na(2)CO(3), at ambient temperature and in combination with steam explosion at 200 degrees C, 6.9 MPa, and 5 min cooking times. Digestibilities of up to 733 g organic matter (OM)/kg bagasse dry matter (DM) were obtained for bagasse treated with NaOH and Ca(OH)(2) + Na(2)CO(3); less than 430 g OM was obtained for bagasse treated with aqueous NH(3); and up to 724 g OM was obtained for bagasse treated with Ca(OH)(2). This digestibility was only achieved by using high concentrations of Ca(OH)(2), i.e., 180-300 g/kg bagasse. Steam explosion increased the digestibility of bagasse up to 740 g OM in the presence of alkali but only to 610 g OM in the absence of alkali. The digestibility of bagasse without pretreatment was 190 g OM/kg bagasse DM. More than one-half the hemicellulose present was solubilized by pretreatment. The composition of the liquid fraction of steam-exploded material was examined and contained mainly xylose monomers and oligomers (112 g/kg original bagasse DM) and acetic acid (33 g/kg original DM). The relative costs of the alkalis used were obtained for the United States, Australia, and Europe. Lime [Ca(OH)(2)] was the least expensive alkali per unit of additional digestible OM obtained. Ammonia was the most expensive alkali to use, except in the United States where the difference in its cost relative to other alkalis was smaller. However, ammonia provides organic nitrogen for microbial growth, and could be recycled. With acidogenic fermentations, alkali is able to double as a neutralizing agent during fermentation. Thus, concentrations of alkali equal to that required for neutralization may be used in pretreatment. Concentrations of Ca(OH)(2) as high as 300 g/kg bagasse were needed for neutralization and should, therefore, be considered for pretreatment. Steam explosion of bagasse resulted in digestible, sterilized substrates of small particle size with readily separable liquid and pulp streams.     

Enhancement of the enzymatic digestibility of sugarcane bagasse by alkali–peracetic acid pretreatment

The enzymatic digestibility of sugarcane bagasse was greatly increased by alkali (NaOH)–peracetic acid (PAA) pretreatment under mild conditions. The effects of several factors affecting the pretreatment were investigated. It was found that when bagasse was pre-pretreated by 10% (based on initial dry materials) NaOH with 3:1 liquid-to-solid ratio at 90 °C for 1.5 h and further delignified by 10% peracetic acid (based on initial dry materials) at 75 °C for 2.5 h, the yield of reducing sugars reached 92.04% by enzymatic hydrolysis for 120 h with cellulase loading of 15 FPU/g solid. Compared with acid and alkali pretreatment, alkali–PAA pretreatment could be conducted under milder conditions and was more effective for delignification with less carbohydrates being degraded in the pretreatment process. Alkaline stage played an important role for partial delignification, swelling fibers and subsequently reducing PAA loading. No loss of cellulase activity (FPA) was observed in the liquid phase for alkali–PAA pretreated bagasse after enzymatic hydrolysis for 120 h.     

Enhancement of the enzymatic digestibility of sugarcane bagasse by steam pretreatment impregnated with hydrogen peroxide

Sugarcane bagasse was subjected to steam pretreatment impregnated with hydrogen peroxide. Analyses were performed using 2³ factorial designs and enzymatic hydrolysis was performed at two different solid concentrations and with washed and unwashed material to evaluate the importance of this step for obtaining high cellulose conversion. Similar cellulose conversion were obtained at different conditions of pretreatment and hydrolysis. When the cellulose was hydrolyzed using the pretreated material in the most severe conditions of the experimental design (210°C, 15 min and 1.0% hydrogen peroxide), and using 2% (w/w) water‐insoluble solids (WIS), and 15 FPU/g WIS, the cellulose conversion was 86.9%. In contrast, at a milder pretreatment condition (190°C, 15 min and 0.2% hydrogen peroxide) and industrially more realistic conditions of hydrolysis (10% WIS and 10 FPU/g WIS), the cellulose conversion reached 82.2%. The step of washing the pretreated material was very important to obtain high concentrations of fermentable sugars. © 2012 American Institute of Chemical Engineers Biotechnol. Prog., 2012     

Effects of fungal pretreatment and steam explosion pretreatment on enzymatic saccharification of plant biomass

The effects of consecutive treatments by a lignin-degrading fungus Phanerochaete chrysosporium and by steam explosion for the enzymatic saccharification of plant biomass were studied experimentally, and the optimal operational conditions for obtaining the maximum saccharification were evaluated. Beech wood-meal was treated by the fungus for 98 days and then by high steam temperatures of 170-230 degrees C with steaming times of 0-10 min. The treatment of the wood-meal by fungus prior to steam explosion enhanced the saccharification of wood-meal. The treated wood-meal was separated into holo-cellulose, water soluble material, methanol soluble lignin, and Klason lignin. The saccharification decreased linearly with the increase in the amount of Klason lignin. It was estimated by the equation for the saccharification of exploded wood-meal expressed as a function of steam temperature and steaming time that the maximum saccharification of wood-meal was obtained by consecutive treatments such as fungal treatment for 28 days and then steam explosion at a steam temperature of 215 degrees C and a steaming time of 6.5 min. (c) 1995 John Wiley & Sons, Inc.     

Improved pretreatment of lignocellulosic biomass using enzymatically-generated peracetic acid

Release of sugars from lignocellulosic biomass is inefficient because lignin, an aromatic polymer, blocks access of enzymes to the sugar polymers. Pretreatments remove lignin and disrupt its structure, thereby enhancing sugar release. In previous work, enzymatically generated peracetic acid was used to pretreat aspen wood. This pretreatment removed 45% of the lignin and the subsequent saccharification released 97% of the sugars remaining after pretreatment. In this paper, the amount of enzyme needed is reduced tenfold using first, an improved enzyme variant that makes twice as much peracetic acid and second, a two-phase reaction to generate the peracetic acid, which allows enzyme reuse. In addition, the eight pretreatment cycles are reduced to only one by increasing the volume of peracetic acid solution and increasing the temperature to 60 °C and the reaction time to 6 h. For the pretreatment step, the weight ratio of peracetic acid to wood determines the amount of lignin removed.     

一株乳杆菌对蒸汽爆破处理纤维物料的乳酸发酵研究

用筛选得到的一株乳酸杆菌ZJU-1(Lactobacillus sp．)对蒸汽爆破预处理纤维物料的乳酸发酵进行了研究,结果表明该菌株能对蒸汽爆破处理的纤维物料酶解液进行乳酸发酵,在还原糖质量浓度为52．1mg/mL时,乳酸量为42．1mg/mL;与纤维素酶的酶解过程相耦合,对蒸汽爆破处理的物料进行同时糖化乳酸发酵。其发酵周期比分步糖化发酵的过程周期短,在底物质量分数为80mg/mL,接种量为10％,温度为45％时,乳酸量为45．3mg/mL。     

Processing cereal straws by steam explosion in a pilot plant to enhance digestibility in ruminants

Wheat, barley and oat straws were treated by steam explosion (SE) and then washed with 50g/l NaOH solution. The SE treatment was optimized at batch scale on the basis of carbohydrate recovery. Stocks of fodder (300kg) were produced at 198 degrees C for 2.5min by a continuous reactor and used for in vivo digestibility tests carried out on sheep. The flow-sheet and the mass balances were obtained for the entire process. For the three straws, the water consumption has been 7.3kg/kg of straw. To delignify and improve the digestibility of the straws, 20g of NaOH/kg straw was used. The yield of fodder, lignin and hemicellulose is dependant on the nature of the starting straw. Delignified fodder (insoluble fraction) can be produced with a yield of 0.64, 0.59, 0.55, respectively, from wheat, barley and oat straw. SE improved the digestibility of the straw by 25%; alkaline washing further increased it by 9%. Balanced rations containing, on a DM basis, 1/4 of treated straw, had digestibility coefficients similar to those of commercial rations based on alfalfa.     

Effect of steam explosion pretreatment on pore size and enzymatic hydrolysis of poplar

The purpose of this study was to determine the effect of batch steam explosion pretreatment on the rate of subsequent enzymatic hydrolysis of hybrid poplar wood. This pretreatment was found to be effective as indicated by the fact that for many of the pretreatment conditions studied the glucose yield obtained after 24 h of enzymatic hydrolysis using enzymes from Trichoderma reesei And Aspergillus niger is in excess of 90% of the potential, whereas the corresponding yield from unpretreated substrate is only 15%. The effect of pretreatment is believed to be primarily due to the increase in pore surface area accessible to enzyme molecules. Measurements show a considerable increase in pore volume available to 5–9 nm solute probes. Pretreated wood that was subsequently oven-dried hydrolysed poorly and showed a reduction in available pore volume after drying. Xylans are readily hydrolysed to xylose during pretreatment and owing to decomposition the amount of xylose in solution after steam pretreatment decreases as the severity of the reaction conditions increases; the converse is true for glucose. We conclude that steam explosion pretreatment can be effective on hybrid poplar and that the quantitative results obtained can be used for process design.     

Effect of treatment of wheat straw with ammonia and peracetic acid on digestibility in vitro and cell wall composition

Wheat straw was treated with four levels of ammonia (0, 35, 70 and 105 g kg^?1 straw dry matter), allowed to react for five days and then treated with four levels of peracetic acid (0, 40, 80 and 120 k kg^?1 straw dry matter) for five more days. There was a 1.24 percentage unit increase in dry matter digestibility in vitro (IVDMD) with each 10.0 g of ammonia added per kg of straw dry matter. The IVDMD increased 1.01 percentage unit for each 10.0 g of peracetic acid added per kg of straw dry matter. The lignin content of the straw decreased 0.39% with each 10.0 g of peracetic acid added per kg of straw dry matter. The hemicellulose content of the straw decreased 0.82% with the addition of 10.0 g of ammonia per kg of straw dry matter. Cellulose content was not affected by the addition of peracetic acid or ammonia.The development of more economical and safe procedures which combine swelling and delignification would be very beneficial for improving the nutritive value of low quality roughages.     

Mild pretreatment of yellow poplar biomass using sequential dilute acid and enzymatically-generated peracetic acid to enhance cellulase accessibility

Biomass contains cellulose, xylan and lignin in a complex interwoven structure that hinders enzymatic hydrolysis of the cellulose. To separate these components in yellow poplar biomass, we sequentially pretreated with dilute sulfuric acid and enzymatically-generated peracetic acid. In the first step, the dilute acid with microwave heating (140°C, 5 min) hydrolyzed 90% of xylan. The xylose yield in hydrolysate after dilute acid pretreatment was 83.1%. In the second step, peracetic acid (60°C, 6 h) removed up to 80% of lignin. This sequential pretreatment fractionated biomass into xylan and lignin, leaving a solid residue enriched in cellulose (~80%). The sequential pretreatment enhanced enzymatic digestibility of the cellulase by removal of the other components in biomass. The glucose yield after enzymatic hydrolysis was 90.5% at a low cellulase loading (5 FPU/g of glucan), which is 1.6 and 18 times higher than for dilute acid-pretreated biomass and raw biomass, respectively. This novel sequential pretreatment with dilute acid and peracetic acid efficiently separates the three major components of yellow poplar biomass, and reduces the amount of cellulase needed.     

Increased drought resistance induced by pretreatment with abscisic acid in germinating embryos of Haplopappus gracilis

Embryos of Haplopappus gracilis (Nutt.) Gray were prehydrated in water or under different conditions, all of them inhibiting or greatly reducing embryo elongation (abscisic acid, polyethylenglycol, cycloheximide, cordycepin, aminophylline, and at 4°C), dehydrated for 24 h and regerminated. All treatments resulted in improved drought resistance compared with water controls, but the best results were obtained with pretreatment with abscisic acid. In fact these embryos revealed in the rehydration phase, (a) the highest percentage of embryos able to resume germination, (b) the lowest leakage of ninhydrin reacting substances, and (c) the highest level of ¹⁴C-leucine incorporation. Lengthening of the prehydration phase in abscisic acid up to 24–48 h improved the conditions of the embryos in the rehydration phase, with less damage to the cells of the radicle tip. A protective action of abscisic acid, possibly at the level of the cell membrane system, is hypothesized.     

基于闪爆-超声波联合作用的红麻精干麻制备

针对红麻脱胶困难且传统脱胶方法污染严重的问题,提出一种新的脱胶方法,即闪爆-超声波联合脱胶。首先对红麻进行闪爆预处理,进而结合红麻超声波脱胶单因子试验和正交试验,以红麻精干麻纤维残胶率为考核指标,探讨了不同超声波频率、氢氧化钠介质浓度以及超声波处理时间对脱胶效果的影响。结果表明,在闪爆预处理后,采用频率为28 kHz的超声波在氢氧化钠浓度为2%的溶液中处理红麻试样60 min,可以使红麻精干麻纤维残胶率降低到9.72%,细度达到139.45 Nm。闪爆-超声波处理可有效去除红麻胶质成分,提高红麻精干麻的分散性,以利于后续纺织加工。     

Effect of peracetic acid, sodium hydroxide and phosphoric acid on cellulosic materials as a pretreatment for enzymatic hydrolysis

Crystalline cellulose and cellulosic wastes have been treated with various concentrations of peracetic acid and other reagents at 100°C for various times, washed with water, ethanol and air dried. For each treated cellulose, the degree of enzymatic solubilization was measured with Trichoderma viride cellulase [1,4-(1,3;1,4)-β-d-glucan 4-glucanohydrolase, EC 3.2.1.4]. Cellulosic wastes such as sunflower stalks, wheat straw and sugar-cane bagasse were solubilized effectively by the enzyme. Delignification of wheat straw with 1% sodium hydroxide and treatment of this straw with peracetic acid enhanced the degree of enzymatic solubilization. Infrared spectra of the untreated and treated cellulosic wastes were recorded.     

Removal of CCA from treated wood by oxalic acid extraction, steam explosion, and bacterial fermentation

Most preservative-treated wood produced and consumed in the United States is treated with toxic inorganic compounds containing copper, chromium, and arsenic. Because chromated copper arsenate (CCA) is fixed to the wood, CCA-treated wood has not been considered toxic or hazardous and it is currently disposed of in approved landfills. Growing public concern about environmental contamination from treated wood combined with the removal of greater quantities of CCA-treated wood from service have presented a disposal challenge for this fiber source. In this study, CCA-treated wood was processed by acid extraction, steam explosion, and bacterial fermentation and evaluated for removal of copper, chromium, and arsenic. Copper was the easiest to remove by these treatments and chromium the most resistant to removal. Exposing CCA-treated wood to steady-state bacterial growth by continuous culture with Bacillus licheniformis CC01 did not enhance removal of CCA components compared to standard mixed culture when acid extraction preceded bacterial fermentation. Nor did steam explosion, alone or in conjunction with acid extraction and bacterial fermentation, enhance removal of CCA components; the chromium and arsenic components resisted removal. Grinding CCA-treated wood chips into 20-mesh sawdust provided greater access to and removal of CCA components by all processes. However, grinding the chips was unnecessary if they were treated with acid prior to bacterial fermentation. Extraction with oxalic acid as a precursor to bacterial fermentation with B. licheniformis CC01 removed 90% copper (CuO), 80% chromium (CrO₃), and 100% arsenic (As₂O₅) from treated chips. The combination of acid extraction and bacterial fermentation removed 80–100% of these metals from CCA-treated wood. Received 15 December 1997/ Accepted in revised form 08 March 1998     

Unpolluted fractionation of wheat straw by steam explosion and ethanol extraction

An unpolluted process of wheat straw fractionation by steam explosion coupled with ethanol extraction was studied. The wheat straw was steam exploded for 4.5 min with moisture of 34.01%, a pressure of 1.5 MPa without acid or alkali. Hemicellulose sugars were recovered by water countercurrent extraction and decolored with chelating ion exchange resin D412. The gas chromatography (GC) and high-performance liquid chromatography (HPLC) analysis results indicated that there were organic acids in the hemicellulose sugars and the ratio of monosaccharides to oligosaccharides was 1:9 and the main component, xylose, was 85.9% in content. The total recovery rate of hemicellulose was 80%. Water washed materials were subsequently extracted with ethanol. The optimum extraction conditions in this work were 40% ethanol, fiber/liquor ratio 1:50 (w/v), severity log(R)=3.657 (180 degrees C for 20 min), 0.1% NaOH. The lignin yield was 75% by acid precipitation and 85% ethanol solvent was recovered. The lignin was purified using Bj?rkman method. Infrared spectrometry (IR) results indicated that the lignin belonged to GSH (guaiacyl (G) syringyl (S) and p-hydroxyphenyl (H)) lignin and its purity rate reached 85.3%. The cellulose recovery rate was 94% and the results of electron spectroscopy for chemical analysis (ESCA) and infrared spectrometry (IR) showed that hemicellulose and lignin content decreased after steam explosion and ethanol extraction.     

Study on the conversion of wool keratin by steam explosion

A wool fiber sample was submitted to chemical-free steam explosion in view of potential exploitation of keratin-based industrial and farm wastes. Fiber keratin was converted into a dark-yellow sludge that was submitted to phase separation by filtration, centrifugation, and precipitation of the soluble materials from the supernatant liquid. The resulting products, when compared with the original wool, showed the extent of disruption of the histology structure, reduction of the molecular weight to water-soluble peptides and free amino acids, and change of the structure of the remainder of the protein associated with breaking of disulfide bonds and decomposition of the high-sulfur-content protein fraction.     

Fractionation of Eucalyptus grandis chips by dilute acid-catalysed steam explosion

Steam explosion of Eucalyptus grandis has been carried out under various pretreatment conditions (200-210 degrees C, 2-5 min) after impregnation of the wood chips with 0.087 and 0.175% (w/w) H2SO4. This study, arranged as a 2(3) factorial design, indicated that pretreatment temperature is the most critical variable affecting the yield of steam-treated fractions. Pretreatment of 0.175% (w/w) H2SO4-impregnated chips at 210 degrees C for 2 min was the best condition for hemicellulose recovery (mostly as xylose) in the water soluble fraction, reaching almost 70% of the corresponding xylose theoretical yield. By contrast, lower pretreatment temperatures of 200 degrees C were enough to yield steam-treated substrates from which a 90% cellulose conversion was obtained in 48 h, using low enzyme loadings of a Celluclast 1.5 1 plus Novozym 188 mixture (Novo Nordisk). Release of water-soluble chromophores was monitored by UV spectroscopy and their concentration increased with pretreatment severity. The yield of alkali-soluble lignin increased at higher levels of acid impregnation and pretreatment temperatures. Thermoanalysis of these lignin fractions indicated a pattern of lignin fragmentation towards greater pretreatment severities but lignin condensation prevailed at the most drastic pretreatment conditions.     

Ozone pretreatment to increase digestibility of lignocellulose

Treatment of lignocellulose with ozone yielded products which included acids, sugars and a fibrous material rich in cellulose. Ozone attacks lignin and hemicelluloses in preference to cellulose, and is effective in disrupting the association between the various components so as to produce a substrate with enhanced reactivity to hydrolytic enzymes.