Optimization of dilute-acid pretreatment of corn stover using a high-solids percolation reactor

We have previously demonstrated that pretreatment of corn stover with dilute sulfuric acid can achieve high digestibility and efficient recovery of hemicellulose sugars with high yield and concentration. Further improvement of this process was sought in this work. A modification was made in the operation of the percolation reactor that the reactor is preheated under atmospheric pressure to remove moisture that causes autohydrolysis. This eliminated sugar decomposition during the preheating stage and led to a considerable improvement in overall sugar yield. In addition, liquid throughput was minimized to the extent that only one reactor void volume of liquid was collected. This was done to attain a high xylose concentration in the hydrolyzate. The optimum reaction and operating conditions were identified wherein near quantitative enzymatic digestibilities are obtained with enzyme loading of 15 FPU/g glucan. With a reduced enzyme loading of 5 FPU/g glucan, the enzymatic digestibility was decreased, but still reached a level of 92%. Decomposition of carbohydrates was extremely low as indicated by the measured glucan and xylan mass closures (recovered sugar plus unreacted) which were 98% and 94%, respectively. The data obtained in this work indicate that the digestibility is related to the extent of xylan removal.     

Relatively High-Substrate Consistency Hydrolysis of Steam-Pretreated Sweet Sorghum Bagasse at Relatively Low Cellulase Loading

Sweet sorghum bagasse (SSB) was steam pretreated in the conditions of 190 °C for 5 min to assess its amenability to the pretreatment and enzymatic hydrolysis. Results showed that pretreatment conditions were robust enough to pretreat SSB with maximum of 87% glucan and 72% xylan recovery. Subsequent enzymatic hydrolysis showed that the pretreated SSB at 2% substrate consistency resulted in maximum of 70% glucan-glucose conversion. Increasing substrate consistency from 2% to 16% led to a significant reduction in glucan conversion. However, the decrease ratio of glucan-glucose conversion was the minimum when the consistency increased from 2% to 12%. When the pretreated SSB consistency of 12% was applied for hydrolysis, increase in cellulase loading from 7.5 up to 20 filter paper units (FPU)/g glucan resulted only in 14% increase in glucan-glucose conversion compared to 20% increase with cellulase loading varying from 2.5 to 7.5 FPU/g glucan. More than 10 cellobiase units (CBU)/g glucan β-glucosidase supplementation had no noticeable improvement on glucan-glucose conversion. Additionally, supplementation of xylanase was found to significantly increase glucan-glucose conversion from 50% to 80% with the substrate consistency of 12%, when the cellulase and β-glucosidase loadings were at relatively low enzyme loadings (7.5 FPU/g and 10 CBU/g glucan). It appeared that residual xylan played a critical role in hindering the ease of hydrolysis of SSB. A proper xylanase addition was suggested to achieve a high hydrolysis yield at relatively high substrate consistency with relatively low enzyme loadings.     

Enzymatic production of xylooligosaccharides from corn stover and corn cobs treated with aqueous ammonia

A novel method of producing food-grade xylooligosaccharides from corn stover and corn cobs was investigated. The process starts with pretreatment of feedstock in aqueous ammonia, which results delignified and xylan-rich substrate. The pretreated substrates are subjected to enzymatic hydrolysis of xylan using endoxylanase for production of xylooligosaccharides. The conventional enzyme-based method involves extraction of xylan with a strong alkaline solution to form a liquid intermediate containing soluble xylan. This intermediate is heavily contaminated with various extraneous components. A costly purification step is therefore required before enzymatic hydrolysis. In the present method, xylan is obtained in solid form after pretreatment. Water-washing is all that is required for enzymatic hydrolysis of this material. The complex step of purifying soluble xylan from contaminant is essentially eliminated. Refining of xylooligosaccharides to food-grade is accomplished by charcoal adsorption followed by ethanol elution. Xylanlytic hydrolysis of the pretreated corn stover yielded glucan-rich residue that is easily digestible by cellulase enzyme. The digestibility of the residue reached 86% with enzyme loading of 10 filter paper units/g-glucan. As a feedstock for xylooligosaccharides production, corn cobs are superior to corn stover because of high xylan content and high packing density. The high packing density of corn cobs reduces water input and eventually raises the product concentration.     

Pretreatment of corn stover by soaking in aqueous ammonia at moderate temperatures

Soaking in aqueous ammonia at moderate temperatures was investigated as a method of pretreatment for enzymatic hydrolysis as well as simultaneous saccharification and cofermentation (SSCF) of corn stover. The method involves batch treatment of the feedstock with aqueous ammonia (15-30 wt%) at 40-90 degrees C for 6-24 h. The optimum treatment conditions were found to be 15 wt% of NH(3), 60 degrees C, 1:6 of solid-to-liquid ratio, and 12 h of treatment time. The treated corn stover retained 100% glucan and 85% of xylan, but removed 62% of lignin. The enzymatic digestibility of the glucan content increased from 17 to 85% with 15 FPU/g-glucan enzyme loading, whereas the digestibility of the xylan content increased to 78%. The treated corn stover was also subjected to SSCF test using Spezyme-CP and recombinant Escherichia coli (KO11). The SSCF of the soaking in aqueous ammonia treated corn stover resulted in an ethanol concentration of 19.2 g/L from 3% (w/v) glucan loading, which corresponds to 77% of the maximum theoretical yield based on glucan and xylan.     

Hydrolysis of Ammonia-pretreated Sugar Cane Bagasse with Cellulase, β-Glucosidase, and Hemicellulase Preparations

Sugar cane bagasse consists of hemicellulose (24%) and cellulose (38%), and bioconversion of both fractions to ethanol should be considered for a viable process. We have evaluated the hydrolysis of pretreated bagasse with combinations of cellulase, β-glucosidase, and hemicellulase. Ground bagasse was pretreated either by the AFEX process (2NH₃: 1 biomass, 100 °C, 30 min) or with NH₄OH (0.5 g NH₄OH of a 28% [v/v] per gram dry biomass; 160 °C, 60 min), and composition analysis showed that the glucan and xylan fractions remained largely intact. The enzyme activities of four commercial xylanase preparations and supernatants of four laboratory-grown fungi were determined and evaluated for their ability to boost xylan hydrolysis when added to cellulase and β-glucosidase (10 filter paper units [FPU]: 20 cellobiase units [CBU]/g glucan). At 1% glucan loading, the commercial enzyme preparations (added at 10% or 50% levels of total protein in the enzyme preparations) boosted xylan and glucan hydrolysis in both pretreated bagasse samples. Xylanase addition at 10% protein level also improved hydrolysis of xylan and glucan fractions up to 10% glucan loading (28% solids loading). Significant xylanase activity in enzyme cocktails appears to be required for improving hydrolysis of both glucan and xylan fractions of ammonia pretreated sugar cane bagasse.     

Pretreatment of corn stover by low-liquid ammonia recycle percolation process

A pretreatment method using aqueous ammonia was investigated with the intent of minimizing the liquid throughput. This process uses a flow-through packed column reactor (or percolation reactor). In comparison to the ammonia recycle percolation (ARP) process developed previously in our laboratory, this process significantly reduces the liquid throughput to one reactor void volume in packed bed (2.0–4.7 mL of liquid/g of corn stover) and, thus, is termed low-liquid ARP (LLARP). In addition to attaining short residence time and reduced energy input, this process achieves 59–70% of lignin removal and 48–57% of xylan retention. With optimum operation of the LLARP to corn stover, enzymatic digestibilities of 95, 90 and 86% were achieved with 60, 15, and 7.5 filter paper units/g of glucan, respectively. In the simultaneous saccharification and fermentation test of the LLARP samples using Saccharomyces cerevisiae (NREL-D₅A), an ethanol yield of 84% of the theoretical maximum was achieved with 6% (w/v) glucan loading. In the simultaneous saccharification and cofermentation (SSCF) test using recombinant Escherichia coli (KO11), both the glucan and xylan in the solid were effectively utilized, giving an overall ethanol yield of 109% of the theoretical maximum based on glucan, a clear indication that the xylan content was converted into ethanol. The xylooligomers existing in the LLARP effluent were not effectively hydrolyzed by cellulase enzyme, achieving only 60% of digestibility. SSCF of the treated corn stover was severely hampered when the substrate was supplemented with the LLARP effluent, giving only 56% the overall yield of ethanol. The effluent appears to significantly inhibit cellulase and microbial activities.     

Oxidative Lime Pretreatment of Dacotah Switchgrass

Oxidative lime pretreatment increases the enzymatic digestibility of lignocellulosic biomass primarily by removing lignin. In this study, recommended pretreatment conditions (reaction temperature, oxygen pressure, lime loading, and time) were determined for Dacotah switchgrass. Glucan and xylan overall hydrolysis yields (72 h, 15 FPU/g raw glucan) were measured for 105 different reaction conditions involving three different reactor configurations (very short term, short term, and long term). The short-term reactor was the most productive. At the recommended pretreatment condition (120 °C, 6.89 bar O₂, 240 min), it achieved an overall glucan hydrolysis yield of 85.2 g glucan hydrolyzed/100 g raw glucan and an overall xylan yield of 50.1 g xylan hydrolyzed/100 g raw xylan. At this condition, glucan oligomers (1.80 g glucan recovered/100 g glucan in raw biomass) and xylan oligomers (25.20 g xylan recovered/100 g xylan in raw biomass) were recovered from the pretreatment liquor, which compensate for low pretreatment yields.     

Enhancement of the enzymatic digestibility of waste newspaper using tween

Methods of increasing the enzymatic digestibility of waste newspaper by adding Tween (TW)-20 and 80 surfactants were investigated. Tween-series surfactants were selected because these surfactants increase cellulase activity during enzymatic hydrolysis and do not inhibit cell growth in downstream fermentation processes. When surfactant was used in a pretreatment, a benefic effect was expected in the enzymatic hydrolysis stage owing to surfactant carry-over from the pretreatment stage immediately upstream of the hydrolysis. However, because it was necessary to wash the pretreated substrate with water to remove inhibitors produced during pretreatment, no added benefit was obtained. When surfactant was used in the pretreatment only, it was found that it had a marked effect on digestibility and that this effect was higher at lower enzyme loadings. Also, TW-80 was found to be more effective than TW-20, and the addition of enzyme and TW-80 to substrate at the beginning of enzyme reaction was found to most effectively increase digestibility. When TW-80 was added into either the pretreatment stage or the hydrolysis stage the digestibilities of untreated sample increased by approx 40%, whereas an increase of only 45% was observed when TW-80 was added to both stages. These results show that the addition of surfactant to either the pretreatment or the enzymatic hydrolysis stage is sufficient to increase digestibility.     

Impact of Pretreatment with Dilute Sulfuric Acid Under Moderate Temperature on Hydrolysis of Corn Stover with Two Enzyme Systems

Pretreatment of corn stover with dilute sulfuric acid at moderate temperature was investigated, and glucan digestibility by Cellic CTec2 and Celluclast on the pretreated biomass was compared. Pretreatments were carried out from 60 to 180 min at the temperature from 105 to 135 °C, with acid concentrations ranging from 0.5 to 2 % (w/v). Significant portion of xylan was removed during pretreatment, and the glucan digestibility by CTec2 was significantly better than that by Celluclast in all cases. Analysis showed that glucan digestibility by both two enzymes correlated directly with the extent of xylan removal in pretreatment. Confidence interval was built to give a more precise range of glucan conversion and to test the significant difference among pretreatment conditions. Response surface model was built to obtain the optimal pretreatment condition to achieve high glucan conversion after enzymatic hydrolysis. Considering the cost and energy savings, the optimal pretreatment condition of 1.75 % acid for 160 min at 135 °C was determined, and glucan conversion can achieve the range from 72.86 to 76.69 % at 95 % confidence level after enzymatic hydrolysis, making total glucan recovery up to the range from 89.42 to 93.25 %.     

Kinetic Studies on the Product Inhibition of Enzymatic Lignocellulose Hydrolysis

In order to understand the product inhibition of enzymatic lignocellulose hydrolysis, the enzymatic hydrolysis of pretreated rice straw was carried out over an enzyme loading range of 2 to 30 FPU/g substrate, and the inhibition of enzymatic hydrolysis was analyzed kinetically based on the reducing sugars produced. It was shown that glucose, xylose, and arabinose were the main reducing sugar components contained in the hydrolysate. The mass ratio of glucose, xylose, and arabinose to the total reducing sugars was almost constant at 52.0?%, 29.7?% and 18.8?%, respectively, in the enzyme loading range. The reducing sugars exerted competitive inhibitory interferences to the enzymatic hydrolysis. Glucose, xylose, and arabinose had a dissociation constant of 1.24, 0.54 and 0.33?g/l, respectively. The inhibitory interferences by reducing sugars were superimposed on the enzymatic hydrolysis. The enzymatic hydrolysis could be improved by the removal of the produced reducing sugars from hydrolysate.     

Enhancing enzymatic hydrolysis of crystalline cellulose and lignocellulose by adding long-chain fatty alcohols

The effects of long-chain fatty alcohols (LFAs) on the enzymatic hydrolysis of crystalline cellulose by two commercial Trichoderma reesei cellulase cocktails (CTec2 and Celluclast 1.5L) were studied. It was found that n-butanol inhibited the enzymatic hydrolysis, but n-octanol, n-decanol and n-dodecanol had strong enhancement on enzymatic hydrolysis of crystalline cellulose in the buffer pH range from 4.0 to 6.0. LFAs can increase the hydrolysis efficiency of crystalline cellulose from 37 to 57 % at Celluclast 1.5L loading of ten filter paper units (FPU)/g glucan. LFAs have similar enhancement on the enzymatic hydrolysis of crystalline cellulose mixed with lignin or xylan. The enhancement of LFAs increased with the decrease of the crystallinity index. LFAs not only enhanced the high-solid enzymatic hydrolysis of lignocellulose, but also improved the rheological properties of high-solid lignocellulosic slurries by decreasing the yield stress and complex viscosity. Meanwhile, LFAs can improve the enzymatic hydrolysis of cellobiose to glucose, especially at low cellulase loading.     

Two-Stage Fractionation of Corn Stover Using Aqueous Ammonia and Hot Water

Hot water and aqueous ammonia fractionation of corn stover were used to separate hemicellulose and lignin and improve enzymatic digestibility of cellulose. A two-stage approach was used: The first stage was designed to recover soluble lignin using aqueous ammonia at low temperature, while the second stage was designed to recover xylan using hot water at high temperature. Specifically, the first stage employed a batch reaction using 15 wt.% ammonia at 60 °C, in a 1:10 solid:liquid ratio for 8 h, while the second stage employed a percolation reaction using hot water, 190–210 °C, at a 20 ml/min flow rate for 10 min. After fractionation, the remaining solids were nearly pure cellulose. The two-stage fractionation process achieved 68% lignin purity with 47% lignin recovery in the first stage, and 78% xylan purity, with 65% xylan recovery in the second stage. Two-stage treatment enhanced the enzymatic hydrolysis of remaining cellulose to 96% with 15 FPU/g of glucan using commercial cellulase enzymes. Enzyme hydrolyses were nearly completed within 12–24 h with the remaining solids fraction.     

Study on the Decreased Sugar Yield in Enzymatic Hydrolysis of Cellulosic Substrate at High Solid Loading

Current technology for conversion of biomass to ethanol is an enzyme-based biochemical process. In bioethanol production, achieving high sugar yield at high solid loading in enzymatic hydrolysis step is important from both technical and economic viewpoints. Enzymatic hydrolysis of cellulosic substrates is affected by many parameters, including an unexplained behavior that the glucan digestibility of substrates by cellulase decreased under high solid loadings. A comprehensive study was conducted to investigate this phenomenon by using Spezyme CP and Avicel as model cellulase and cellulose substrate, respectively. The hydrolytic properties of the cellulase under different substrate concentrations at a fixed enzyme-to-substrate ratio were characterized. The results indicate that decreased sugar yield is neither due to the loss of enzyme activity at a high substrate concentration nor due to the higher end-product inhibition. The cellulase adsorption kinetics and isotherm studies indicated that a decline in the binding capacity of cellulase may explain the long-observed but little-understood phenomenon of a lower substrate digestibility with increased substrate concentration. The mechanism how the enzyme adsorption properties changed at high substrate concentration was also discussed in the context of exploring the improvement of the cellulase-binding capacity at high substrate loading.     

Understanding the Nonproductive Enzyme Adsorption and Physicochemical Properties of Residual Lignins in Moso Bamboo Pretreated with Sulfuric Acid and Kraft Pulping

In this work, to elucidate why the acid-pretreated bamboo shows disappointingly low enzymatic digestibility comparing to the alkali-pretreated bamboo, residual lignins in acid-pretreated and kraft pulped bamboo were isolated and analyzed by adsorption isotherm to evaluate their extents of nonproductive enzyme adsorption. Meanwhile, physicochemical properties of the isolated lignins were analyzed and a relationship was established with non-productive adsorption. Results showed that the adsorption affinity and binding strength of cellulase on acid-pretreated bamboo lignin (MWLa) was significantly higher than that on residual lignin in pulped bamboo (MWLp). The maximum adsorption capacity of cellulase on MWLp was 129.49 mg/g lignin, which was lower than that on MWLa (160.25 mg/g lignin). When isolated lignins were added into the Avicel hydrolysis solution, the inhibitory effect on enzymatic hydrolysis efficiency of MWLa was found to be considerably stronger than that with MWLp. The cellulase adsorption on isolated lignins was correlated positively with hydrophobicity, phenolic hydroxyl group, and degree of condensation but negatively with surface charges and aliphatic hydroxyl group. These results suggest that the higher nonproductive cellulase adsorption and physicochemical properties of residual lignin in acid-pretreated bamboo may be responsible for its disappointingly low enzymatic digestibility.     

Pretreatment and Fractionation of Corn Stover by Soaking In Ethanol and Aqueous Ammonia

A new process for pretreatment of lignocellulosic biomass, designated the soaking in ethanol and aqueous ammonia (SEAA) process, was developed to improve hemicellulose preservation in solid form. In the SEAA process, an aqueous ammonia solution containing ethanol is used. Corn stover was treated with 15 wt.% ammonia at 1:9 solid–liquid ratio (by weight) at 60 °C for 24 h with ethanol added at 1, 5, 20, and 49 wt.% (balance was water). The extents by which xylan was solubilized with no ethanol and with ethanol added at 1, 5, 20, and 49 wt.% of the total liquid were 17.2%, 16.7%, 14.5%, 10.4%, and 6.3% of the original xylan, respectively. Thus, at the highest ethanol concentration used the loss of hemicellulose to the liquid phase was reduced by 63%. The digestibility of glucan and xylan in the pretreated corn stover samples by cellulase was not affected by ethanol addition of up to 20 wt.%. The enzymatic digestibility of the corn stover treated with 49 wt.% ethanol added was lower than the digestibility of the sample treated with no ethanol addition. Thus, based on these results, 20 wt.% was found to be the optimum ethanol concentration for use in the SEAA process for pretreatment of corn stover.     

Influence of ionic-liquid incubation temperature on changes in cellulose structure,biomass composition,and enzymatic digestibility

Varying ionic liquid, 1-ethyl 3-methyl imidazolium acetate, pretreatment incubation temperature on lignocellulosic biomass substrates, corn stover, switchgrass and poplar, can have dramatic effects on the enzymatic digestibility of the resultant regenerated biomass. In order to delineate the chemical and physical changes resulting from the pretreatment process and correlate changes with enzymatic digestibility, X-ray powder and fiber diffraction, ¹³C cross polarization/magic angle spinning nuclear magnetic resonance spectroscopy, and compositional analysis was completed on poplar, corn stover and switchgrass samples. Optimal pretreatment incubation temperatures were most closely associated with the retention of amorphous substrates upon drying of regenerated biomass. Maximal glucan to glucose conversion for 24 h enzyme hydrolysis was observed for corn stover, switchgrass and poplar at ionic liquid incubation temperatures of 100, 110 and 120 °C, respectively. We hypothesize that effective pretreatment temperatures must attain lignin redistribution and retention of xylan for optimal enzyme digestibility.     

Pretreatment of corn stover by soaking in aqueous ammonia

Soaking in aqueous ammonia (SAA) was investigated as a pretreatment method for corn stover. In this method, the feedstock was soaked in aqueous ammonia over an extended period (10–60 d) at room temperature. It was done without agitation at atmospheric pressure. SAA treatment removed 55–74% of the lignin, but retained nearly 100% of the glucan and 85% of the xylan. The xylan remaining in the corn stover after SAA treatment was hydrolyzed along with the glucan by xylanase present in the Spezyme CP enzyme. In the simultaneous saccharification and fermentation (SSF) test of SAA-treated corn stover, using S. cerevisiae (D₅A), an ethanol yield of 73% of theoretical maximum was obtained on the basis of the glucan content in the treated corn stover. The accumulation of xylose in the SSF appears to inhibit the cellulase activity on glucan hydrolysis, which limits the yield of ethanol. In the simultaneous saccharification and co-fermentation (SSCF) test, using recombinant E. coli (KO11), both the glucan and xylose were effectively utilized, resulting in on overall ethanol yield of 77% based on the glucan and xylan content of the substrate. When the SSCF process is used, the fact that the xylan fraction is retained during pretreatment is a desirable feature since the overall bioconversion can be carried out in a single step without separate recovery of xylose from the pretreatment liquid.     

Potential of Agricultural Residues and Hay for Bioethanol Production

Production of bioethanol from agricultural residues and hays (wheat, barley, and triticale straws, and barley, triticale, pearl millet, and sweet sorghum hays) through a series of chemical pretreatment, enzymatic hydrolysis, and fermentation processes was investigated in this study. Composition analysis suggested that the agricultural straws and hays studied contained approximately 28.62-38.58% glucan, 11.19-20.78% xylan, and 22.01-27.57% lignin, making them good candidates for bioethanol production. Chemical pretreatment with sulfuric acid or sodium hydroxide at concentrations of 0.5, 1.0, and 2.0% indicated that concentration and treatment agent play a significant role during pretreatment. After 2.0% sulfuric acid pretreatment at 121 degrees C/15 psi for 60 min, 78.10-81.27% of the xylan in untreated feedstocks was solubilized, while 75.09-84.52% of the lignin was reduced after 2.0% sodium hydroxide pretreatment under similar conditions. Enzymatic hydrolysis of chemically pretreated (2.0% NaOH or H2SO4) solids with Celluclast 1.5 L-Novozym 188 (cellobiase) enzyme combination resulted in equal or higher glucan and xylan conversion than with Spezyme(R) CP- xylanase combination. The glucan and xylan conversions during hydrolysis with Celluclast 1.5 L-cellobiase at 40 FPU/g glucan were 78.09 to 100.36% and 74.03 to 84.89%, respectively. Increasing the enzyme loading from 40 to 60 FPU/g glucan did not significantly increase sugar yield. The ethanol yield after fermentation of the hydrolyzate from different feedstocks with Saccharomyces cerevisiae ranged from 0.27 to 0.34 g/g glucose or 52.00-65.82% of the theoretical maximum ethanol yield.     

Nonisothermal simultaneous saccharification and fermentation for direct conversion of lignocellulosic biomass to ethanol

The enzymatic reaction in the simultaneous saccharification and fermentation (SSF) is operated at a temperature much lower than its optimum level. This forces the enzyme activity to be far below its potential, consequently raising the enzyme requirement. To alleviate this problem, a nonisothermal simultaneous saccharification and fermentation process (NSSF) was investigated. The NSSF is devised so that saccharification and fermentation occur simultaneously, yet in two separate reactors that are maintained at different temperatures. Lignocellulosic biomass is retained inside a column reactor and hydrolyzed at the optimum temperature for the enzymatic reaction (50°C). The effluent from the column reactor is recirculated through a fermenter, which runs at its optimum temperature (20-30°C). The cellulase enzyme activity is increased by a factor of 2-3 when the hydrolysis temperature is raised from 30 to 50°C. The NSSF process has improved the enzymatic reaction in the SSF to the extent that it reduces the overall enzyme requirement by 30-40%. The effect of temperature on β-glucosidase activity was the most significant among the individual cellulase compounds. Both ethanol yield and productivity in the NSSF are substantially higher than those in the SSF at the enzyme loading of 5 IFPU/g glucan. With 10 IFPU/g glucan, improvement in productivity was more discernible for the NSSF. The terminal yield attainable in 4 d with the SSF was reachable in 40 h with the NSSF.     

Effect of pretreatment severity on the enzymatic hydrolysis of bamboo in hydrothermal deconstruction

Bamboo was subjected to hydrothermal deconstruction to release xylans for the enhancement of enzymatic hydrolysis. The de-waxed and de-starched bamboo culm was non-isothermally pretreated in a batch reactor at a solid to liquid ratio of 1:10 g/mL at 120–240 °C. With the increase of the maximum heating temperature from 120 to 240 °C, the pH value of the liquor decreased from 5.98 to 2.71. A maximum yield of the non-volatile components in the liquid was achieved at a pretreatment severity of 4.20. With the increase of the pretreatment severity from 1.18 to 4.82, the yield of the solid residue decreased from 99.52 to 59.91 %, accompanying a decrease of xylan content from 28.86 to 0 %, an increase of glucan content from 42.80 to 59.14 % and an increase of lignin content from 28.10 to 40.57 %. The solid residues after the hydrothermal pretreatment were comprehensively characterized by FT IR, XRD, and element analysis. Enzymatic hydrolysis of the solid residues was assayed by commercial cellulase. Under enzymatic hydrolysis for 96 h, the enzymatic hydrolysis of the pretreated bamboo at the pretreatment severity of 4.82 was 81.16 %, which equaled to 4.7 times of that of the untreated bamboo. This study provided an environmentally friendly process to pretreat biomass for the production of energy.