Pretreatment of rice straw using an extrusion/extraction process at bench-scale for producing cellulosic ethanol

Extraction, Biochemical Characterization, and Health Effects of Native and Degraded Fucoidans from Sargassum crispifolium

In the current investigation, a native crude fucoidan (Ex) was extracted from Sargassum crispifolium, pretreated by single-screw extrusion, and two degraded fucoidans, i.e., ExAh (degradation of Ex by ascorbic acid) and ExHp (degradation of Ex by hydrogen peroxide), were obtained. The extrusion pretreatment increased the extraction yield of fucoidan by approximately 1.73-fold as compared to the non-extruded sample. Among Ex, ExAh, and ExHp, their molecular weight and chemical compositions varied, but the structural features were similar. ExHp possessed the greatest antioxidant activities among the extracted fucoidans. According to the outcome, ExAh exhibited the maximum immune promoting effects via enhanced NO, TNF-α, IL-1β, IL-6, and IL-10 secretion. Thus, both ExHp and ExAh may potentially be used as an effective antioxidant and as immunostimulant agents, which could be of great value in the development of food and nutraceutical products.

An Overview of Extrusion as a Pretreatment Method of Lignocellulosic Biomass

Lignocellulosic biomass is both low cost and abundant, and unlike energy crops, can escape associated ethical dilemmas such as arable land use and food security issues. However, their usage as raw material in a biorefinery implies an inherent upstream pretreatment step to access compounds of interest derived from lignocellulosic biomass. Importantly, the efficiency of this step is determinant for the downstream processes, and while many pretreatment methods have been explored, extrusion is both a very flexible and promising technology. Extrusion is well-known in both the polymer and pharmaceutical industries and has been used since the 18th century. However, as a pretreatment method for lignocellulosic biomass, extrusion is relatively new. The first use for this purpose dates back to the 1990s. Extrusion enjoys a high degree of flexibility due to the many available parameters, but an understanding of extrusion requires a knowledge of these parameters and the different relationships between them. In this paper, we present a concise overview of lignocellulosic biomass extrusion by reviewing key extrusion parameters and their associated extruder design components and operating conditions.

Pretreatment of extruded Napier grass byhydrothermal process with dilute sulfuric acid and fermentation using a cellulose-hydrolyzing and xylose-assimilating yeast for ethanol production

One of the potential bioresources for bioethanol production is Napier grass, considering its high cellulose and hemicellulose content. However, the cost of pretreatment hinders the bioethanol produced from being economical. This study examines the effect of hydrothermal process with dilute acid on extruded Napier grass, followed by enzymatic saccharification prior to simultaneous saccharification and co-fermentation (SScF). Extrusion facilitated lignin removal by 30.2 % prior to dilute acid steam explosion. Optimum pretreatment condition was obtained by using 3% sulfuric acid, and 30-min retention time of steam explosion at 190 °C. Ethanol yield of 0.26 g ethanol/g biomass (60.5% fermentation efficiency) was attained by short-term liquefaction and fermentation using a cellulose-hydrolyzing and xylose-assimilating Saccharomyces cerevisiae NBRC1440/B-EC3-X ΔPHO13, despite the presence of inhibitors. This proposed method not only reduced over-degradation of cellulose and hemicellulose, but also eliminated detoxification process and reduced cellulase loading.

Acid-based lignocellulosic biomass biorefinery for bioenergy production: Advantages, application constraints, and perspectives

The production of chemicals and fuels from renewable biomass with the primary aim of reducing carbon footprints has recently become one of the central points of interest. The use of lignocellulosic biomass for energy production is believed to meet the main criteria of maximizing the available global energy source and minimizing pollutant emissions. However, before usage in bioenergy production, lignocellulosic biomass needs to undergo several processes, among which biomass pretreatment plays an important role in the yield, productivity, and quality of the products. Acid-based pretreatment, one of the existing methods applied for lignocellulosic biomass pretreatment, has several advantages, such as short operating time and high efficiency. A thorough analysis of the characteristics of acid-based biomass pretreatment is presented in this review. The environmental concerns and future challenges involved in using acid pretreatment methods are discussed in detail to achieve clean and sustainable bioenergy production. The application of acid to biomass pretreatment is considered an effective process for biorefineries that aim to optimize the production of desired products while minimizing the by-products.

Physicochemical and Antioxidant Properties of Gelatin and Gelatin Hydrolysates Obtained from Extrusion-Pretreated Fish (Oreochromis sp.) Scales

Fish gelatin and its hydrolysates exhibit a variety of biological characteristics, which include antihypertensive and antioxidant properties. In this study, fish gelatins were extracted from extrusion-pretreated tilapia scales, and then subjected to analyses to determine the physicochemical properties and antioxidant activity of the extracted gelatins. Our findings indicate that TSG2 (preconditioned with 1.26% citric acid) possessed the greatest extraction yield, as well as higher antioxidant activities compared with the other extracted gelatins. Hence, TSG2 was subjected to further hydrolyzation using different proteases and ultrafiltration conditions, which yielded four gelatin hydrolysates: TSGH1, TSGH2, TSGH3, and TSGH4. The results showed that TSGH4 (Pepsin + Pancreatin and ultrafiltration < 3000 Da) had a higher yield and greater antioxidant activity in comparison with the other gelatin hydrolysates. As such, TSGH4 was subjected to further fractionation using a Superdex peptide column and two-stage reverse-phase column HPLC chromatography, yielding a subfraction TSGH4-6-2-b, which possessed the highest 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging activity compared with the other fractions. Further LC-ESI/MS/MS analysis of TSGH4-6-2-b suggested two novel peptides (GYDEY and EPGKSGEQGAPGEAGAP), which could have potential as naturally-occurring peptides with antioxidant properties. These promising results suggest that these antioxidant peptides could have applications in food products, nutraceuticals, and cosmetics.

Valorization of Greenhouse Horticulture Waste from a Biorefinery Perspective

Greenhouse cultivation and harvesting generate considerable amounts of organic waste, including vegetal waste from plants and discarded products. This study evaluated the residues derived from tomato cultivation practices in Almería (Spain) as sugar-rich raw materials for biorefineries. First, lignocellulose-based residues were subjected to an alkali-catalyzed extrusion process in a twin-screw extruder (100 °C and 6–12% (w/w) NaOH) to assess maximum sugar recovery during the subsequent enzymatic hydrolysis step. A high saccharification yield was reached when using an alkali concentration of 12% (w/w), releasing up to 81% of the initial glucan. Second, the discarded tomato residue was crushed and centrifuged to collect both the juice and the pulp fractions. The juice contained 39.4 g of sugars per 100 g of dry culled tomato, while the pulp yielded an extra 9.1 g of sugars per 100 g of dry culled tomato after an enzymatic hydrolysis process. The results presented herein show the potential of using horticulture waste as an attractive sugar source for biorefineries, including lignocellulose-based residues when effective fractionation processes, such as reactive extrusion technology, are available.

Fish Collagen: Extraction, Characterization, and Applications for Biomaterials Engineering

The utilization of marine-based collagen is growing fast due to its unique properties in comparison with mammalian-based collagen such as no risk of transmitting diseases, a lack of religious constraints, a cost-effective process, low molecular weight, biocompatibility, and its easy absorption by the human body. This article presents an overview of the recent studies from 2014 to 2020 conducted on collagen extraction from marine-based materials, in particular fish by-products. The fish collagen structure, extraction methods, characterization, and biomedical applications are presented. More specifically, acetic acid and deep eutectic solvent (DES) extraction methods for marine collagen isolation are described and compared. In addition, the effect of the extraction parameters (temperature, acid concentration, extraction time, solid-to-liquid ratio) on the yield of collagen is investigated. Moreover, biomaterials engineering and therapeutic applications of marine collagen have been summarized.

Degradation of Sargassum crassifolium Fucoidan by Ascorbic Acid and Hydrogen Peroxide, and Compositional, Structural, and In Vitro Anti-Lung Cancer Analyses of the Degradation Products

Fucoidans possess multiple biological functions including anti-cancer activity. Moreover, low-molecular-weight fucoidans are reported to possess more bioactivities than native fucoidans. In the present study, a native fucoidan (SC) was extracted from Sargassum crassifolium pretreated by single-screw extrusion, and three degraded fucoidans, namely, SCA (degradation of SC by ascorbic acid), SCH (degradation of SC by hydrogen peroxide), and SCAH (degradation of SC by ascorbic acid + hydrogen peroxide), were produced. The extrusion pretreatment can increase the extraction yield of fucoidan by approximately 4.2-fold as compared to the non-extruded sample. Among SC, SCA, SCH, and SCAH, the chemical compositions varied but structural features were similar. SC, SCA, SCH, and SCAH showed apoptotic effects on human lung carcinoma A-549 cells, as illustrated by loss of mitochondrial membrane potential (MMP), decreased B-cell leukemia-2 (Bcl-2) expression, increased cytochrome c release, increased active caspase-9 and -3, and increased late apoptosis of A-549 cells. In general, SCA was found to exhibit high cytotoxicity to A-549 cells and a strong ability to suppress Bcl-2 expression. SCA also showed high efficacy to induce cytochrome c release, activate caspase-9 and -3, and promote late apoptosis of A-549 cells. Therefore, our data suggest that SCA could have an adjuvant therapeutic potential in the treatment of lung cancer. Additionally, we explored that the Akt/mammalian target of rapamycin (mTOR) signaling pathway is involved in SC-, SCA-, SCH-, and SCAH-induced apoptosis of A-549 cells.

Recent advances in the pretreatment of microalgal and lignocellulosic biomass: A comprehensive review

Microalgal and lignocellulosic biomass is the most sumptuous renewable bioresource raw material existing on earth. Recently, the bioconversion of biomass into biofuels have received significant attention replacing fossil fuels. Pretreatment of biomass is a critical process in the conversion due to the nature and structure of the biomass cell wall that is complex. Although green technologies for biofuel production are advancing, the productivity and yield from these techniques are low. Over the past years, various pretreatment techniques have been developed and successfully employed to improve the technology. This paper presents an in-depth review of the recent advancement of pretreatment methods focusing on microalgal and lignocellulosic biomass. The technological approaches involving physical, chemical, biological and other latest pretreatment methods are reviewed.

Disruption of lignocellulosic biomass along the length of the screws with different screw elements in a twin-screw extruder

Proper screw design is crucial for effectively pre-treating wood fibers, to assist in the downstream enzymatic conversion of the cellulose into fermentable sugars. Initially, the impact of extruder barrel temperature (50, 100, and 150 °C) and screw speed (25, 50, and 75 rpm) were studied to arrive at the optimum conditions for sugar yield. Lower temperatures and screw speeds resulted in increased sugar yields. To examine the influence of shear imparted by the screws, the residuals samples were recovered from different zones along the screws and evaluated. Sugar yield, crystallinity index, and the particle size distribution of the material collected at different zones were determined. Glucose yield and xylose/mannose yields of the material along the screws, ranged from 23.25 to 42.88% and from 11.95 to 20.54%, respectively. The importance of the screw design was highlighted.

Pretreatment with lower feed moisture and lower extrusion temperatures aids in the increase in the fermentable sugar yields from fine-milled Douglas-fir

The impact of independent variables of extrusion on dependent variables of pre-milled Douglas-fir forest residuals was studied to enhance the enzymatic hydrolysis for production of fermentable sugar without catalysts. Co-rotating twin screw extruder was operated with three different feedstock moisture contents (30, 40, and 50%) at four different barrel temperatures (25, 50, 100, and 150 °C) as a pretreatment. The specific mechanical energy input ranged from 0.07 and 0.30 kWh/kg and had a very strong positive correlation with torque (r = 0.96, p < 0.01), glucose (r = 0.92, p < 0.01) and xylose/mannose yields with (r = 0.84, p < 0.01). Douglas-fir residuals extruded at lowest moisture content (30%) and temperature (25 °C) had the highest sugar yield, requiring the highest SME. Higher barrel temperature increased the median particle size and had lower glucose and xylose/mannose yields. Recrystallization and agglomeration were observed under higher temperature conditions.

A Sequential Steam Explosion and Reactive Extrusion Pretreatment for Lignocellulosic Biomass Conversion within a Fermentation-Based Biorefinery Perspective

The present work evaluates a two-step pretreatment process based on steam explosion and extrusion technologies for the optimal fractionation of lignocellulosic biomass. Two-step pretreatment of barley straw resulted in overall glucan, hemicellulose and lignin recovery yields of 84%, 91% and 87%, respectively. Precipitation of the collected lignin-rich liquid fraction yielded a solid residue with high lignin content, offering possibilities for subsequent applications. Moreover, hydrolysability tests showed almost complete saccharification of the pretreated solid residue, which when combined with the low concentration of the generated inhibitory compounds, is representative of a good pretreatment approach. Scheffersomyces stipitis was capable of fermenting all of the glucose and xylose from the non-diluted hemicellulose fraction, resulting in an ethanol concentration of 17.5 g/L with 0.34 g/g yields. Similarly, Saccharomyces cerevisiae produced about 4% (v/v) ethanol concentration with 0.40 g/g yields, during simultaneous saccharification and fermentation (SSF) of the two-step pretreated solid residue at 10% (w/w) consistency. These results increased the overall conversion yields from a one-step steam explosion pretreatment by 1.4-fold, showing the effectiveness of including an extrusion step to enhance overall biomass fractionation and carbohydrates conversion via microbial fermentation processes.

Green methods of lignocellulose pretreatment for biorefinery development

Lignocellulosic biomass is the most abundant, low-cost, bio-renewable resource that holds enormous importance as alternative source for production of biofuels and other biochemicals that can be utilized as building blocks for production of new materials. Enzymatic hydrolysis is an essential step involved in the bioconversion of lignocellulose to produce fermentable monosaccharides. However, to allow the enzymatic hydrolysis, a pretreatment step is needed in order to remove the lignin barrier and break down the crystalline structure of cellulose. The present manuscript is dedicated to reviewing the most commonly applied "green" pretreatment processes used in bioconversion of lignocellulosic biomasses within the "biorefinery" concept. In this frame, the effects of different pretreatment methods on lignocellulosic biomass are described along with an in-depth discussion on the benefits and drawbacks of each method, including generation of potentially inhibitory compounds for enzymatic hydrolysis, effect on cellulose digestibility, and generation of compounds toxic for the environment, and energy and economic demand.

Silica distinctively affects cell wall features and lignocellulosic saccharification with large enhancement on biomass production in rice

Rice is a typical silicon-accumulating crop with enormous biomass residues for biofuels. Silica is a cell wall component, but its effect on the plant cell wall and biomass production remains largely unknown. In this study, a systems biology approach was performed using 42 distinct rice cell wall mutants. We found that silica levels are significantly positively correlated with three major wall polymers, indicating that silica is associated with the cell wall network. Silicon-supplied hydroculture analysis demonstrated that silica distinctively affects cell wall composition and major wall polymer features, including cellulose crystallinity (CrI), arabinose substitution degree (reverse Xyl/Ara) of xylans, and sinapyl alcohol (S) proportion in three typical rice mutants. Notably, the silicon supplement exhibited dual effects on biomass enzymatic digestibility in the mutant and wild type (NPB) after pre-treatments with 1% NaOH and 1% H2SO4. In addition, silicon supply largely enhanced plant height, mechanical strength and straw biomass production, suggesting that silica rescues mutant growth defects. Hence, this study provides potential approaches for silicon applications in biomass process and bioenergy rice breeding.

Continuous alkaline pretreatment of Miscanthus sacchariflorus using a bench-scale single screw reactor

Miscanthus sacchariflorus 'Goedae-Uksae 1' (GU) was developed as an energy crop of high productivity in Korea. For the practical use of GU for bioethanol production, a bench-scale continuous pretreatment system was developed. The reactor performed screw extrusion, soaking and thermochemical pretreatment at the following operating conditions: 3 mm particle size, 22% moisture content, 140 °C reaction temperature, 8 min residence time, 15 g/min biomass feeding and 120 mL/min NaOH input. As a result of minimizing NaOH concentration and enzyme dosage, 90.8±0.49% glucose yield was obtained from 0.5 M NaOH-pretreated GU containing 3% glucan with 10 FPU cellulase/g cellulose at 50 °C for 72 h. The separate hydrolysis and fermentation of 0.5 M NaOH-pretreated GU containing 10% glucan with 10-30 FPU for 102 h produced 43.0-49.6 g/L bioethanol (theoretical yield, 75.8-87.6%). Thus, this study demonstrated that continuous pretreatment using a single screw reactor is effective for bioethanol production from Miscanthus biomass.

Low temperature calcium hydroxide treatment enhances anaerobic methane production from (extruded) biomass

Ca(OH)2 treatment was applied to enhance methane yield. Different alkali concentration, incubation temperature and duration were evaluated for their effect on methane production and COD conversion efficiency from (non-)extruded biomass during mesophilic anaerobic digestion at lab-scale. An optimum Ca(OH)2 pretreatment for grass is found at 7.5% lime loading at 10°C for 20h (37.3% surplus), while mild (50°C) and high temperatures perform sub-optimal. Ca(OH)2 post-treatment after fast extrusion gives an additional surplus compared to extruded material of 15.2% (grass), 11.2% (maize straw) and 8.2% (sprout stem) regarding methane production. COD conversion improves accordingly, with additional improvements of 10.3% (grass), 9.0% (maize straw) and 6.8% (sprout stem) by Ca(OH)2 post-treatment. Therefore, Ca(OH)2 pretreatment and post-treatment at low temperature generate an additional effect regarding methane production and COD conversion efficiency. Fast extrusion gives a higher energy efficiency ratio compared to slow extrusion.

Reactors for High Solid Loading Pretreatment of Lignocellulosic Biomass

The review summarized the types, the geometry, and the design principle of pretreatment reactors at high solid loading of lignocellulose material. Among the reactors used, the explosion reactors and the helical stirring reactors are to be considered as the practical form for high solids loading pretreatment operation; the comminution reactors and the extruder reactors are difficult to be used as an independent unit, but possible to be used in the combined form with other types of reactors. The principles of the pretreatment reactor design at high solid loading were discussed and several basic principles for the design were proposed. This review provided useful information for choosing the reactor types and designing the geometry of pretreatment operation at the high solids loading.

Extrusion pretreatment of lignocellulosic biomass: a review

Bioconversion of lignocellulosic biomass to bioethanol has shown environmental, economic and energetic advantages in comparison to bioethanol produced from sugar or starch. However, the pretreatment process for increasing the enzymatic accessibility and improving the digestibility of cellulose is hindered by many physical-chemical, structural and compositional factors, which make these materials difficult to be used as feedstocks for ethanol production. A wide range of pretreatment methods has been developed to alter or remove structural and compositional impediments to (enzymatic) hydrolysis over the last few decades; however, only a few of them can be used at commercial scale due to economic feasibility. This paper will give an overview of extrusion pretreatment for bioethanol production with a special focus on twin-screw extruders. An economic assessment of this pretreatment is also discussed to determine its feasibility for future industrial cellulosic ethanol plant designs.

Screw extrude steam explosion: a promising pretreatment of corn stover to enhance enzymatic hydrolysis

A screw extrude steam explosion (SESE) apparatus was designed and introduced to pretreat corn stover continuously for its following enzymatic hydrolysis. SESE parameters temperature (100, 120, 150°C) and residence time (1, 2, 3min) were investigated. The enzymatic hydrolysis of corn stover pretreated by SESE and steam explosion (SE) process was carried out and analyzed systematically. A serial of analysis methods were established, and the corn stover before/after the pretreatment were characterized by scanning electron microscope (SEM), X-ray Diffraction (XRD) and Thermal Gravity/Derivative Thermal Gravity Analysis (TG/DTG). After treated by SESE pretreatment at the optimum condition (150°C, 2min), the pretreated corn stover exhibited highest enzymatic hydrolysis yield (89%), and rare fermentation inhibitors formed. Characterization results indicated that the highest yield could be attributed to the effective removal of lignin/hemicellulose and destruction of cellulose structure by SESE pretreatment.

Influence of twin-screw extrusion on soluble arabinoxylans and corn fiber gum from corn fiber

BACKGROUND

The effect of feed moisture content and screw speed in the extrusion process with and without chemical pretreatment of corn fiber was investigated. Different chemical pretreatment methods (NaOH and H2 SO4 solution) were compared. The improvement of reducing sugar, soluble arabinoxylans (SAX) content and the yield of corn fiber gum was measured.

RESULTS

A high reducing sugar content was obtained in the filtrate fraction from the extruded destarched corn fiber (EDCF) with H₂SO₄ pretreatment. Feed moisture content most effectively improved both reducing sugar and SAX content of filtrate. Increasing feed moisture content and screw speed resulted in a higher SAX content in the filtrate of the EDCF with NaOH pretreatment. The SAX content of the residual solid from the EDCF with NaOH pretreatment was higher compared to H₂SO₄ pretreated and unpretreated samples and significantly increased with decreasing feed moisture content. The screw speed did not have a major impact after enzyme hydrolysis. The yield of corn fiber gum was increased by 12% using NaOH pretreatment combined with extrusion process as compared to the destarched corn fiber.

CONCLUSION

The results show the great potential of the extrusion process as an effective pretreatment for disruption the lignocelluloses of corn fiber, leading to conversion of cellulose to glucose and hemicelluloses to SAX and isolation of corn fiber gum.

The influence of screw configuration on the pretreatment performance of a continuous twin screw-driven reactor (CTSR)

A combination of a continuous twin screw-driven reactor (CTSR) and a dilute acid pretreatment was used for the pretreatment of biomass with a high cellulose content and high monomeric xylose hydrolyzate. With the newly modified CTSR screw configuration (Config. 3), the influences of the screw rotational speed (30-60 rpm), of the pretreatment conditions such as acid concentration (1-5%) and reaction temperature (160-175 °C) at the operating condition of biomass feeding rate (1.0 g/min) and acid feeding rate (13.4 mL/min) on the pretreatment performance were investigated. The cellulose content in the pretreated rape straw was 67.1% at the following optimal conditions: barrel temperature of 165 °C, acid concentration of 3.0% (w/v), and screw rotational speed of 30 rpm. According to the three screw configurations, the glucose yields from enzymatic hydrolysis were 70.1%, 72.9%, and 78.7% for screw Configs. 1, 2, and 3, respectively.

Ethanogenic fermentation of co-cultures of Candida shehatae HM 52.2 and Saccharomyces cerevisiae ICV D254 in synthetic medium and rice hull hydrolysate

The ability of Candida shehatae, Saccharomyces cerevisiae, or the combination of these two yeasts in converting the mixed sugar composition of rice hull hydrolysate (RHH) as substrate for ethanol production is presented. In shake flask experiments, co-cultures showed ethanol yields (YP/S) of 0.42 and 0.51 in synthetic medium simulating the sugar composition of RHH and in RHH, respectively, with both glucose and xylose being completely depleted, while pure cultures of C. shehatae produced slightly lower ethanol yields (0.40). Experiments were scaled-up to bioreactors, in which anaerobiosis and oxygen limitation conditions were tested. Bioreactor co-cultures produced similar ethanol yields in both conditions (0.50-0.51) in synthetic medium, while in RHH, yields of 0.48 and 0.44 were obtained, respectively. The results showed near-theoretical yields of ethanol. Results suggest the feasibility of co-cultures of C. shehatae, a newly isolated strain, and S. cerevisiae in RHH as substrate for second-generation ethanol production.

Pilot-scale study on the acid-catalyzed steam explosion of rice straw using a continuous pretreatment system

A continuous acid-catalyzed steam explosion pretreatment process and system to produce cellulosic ethanol was developed at the pilot-scale. The effects of the following parameters on the pretreatment efficiency of rice straw feedstocks were investigated: the acid concentration, the reaction temperature, the residence time, the feedstock size, the explosion pressure and the screw speed. The optimal presteaming horizontal reactor conditions for the pretreatment process are as follows: 1.7 rpm and 100-110 °C with an acid concentration of 1.3% (w/w). An acid-catalyzed steam explosion is then performed in the vertical reactor at 185 °C for 2 min. Approximately 73% of the total saccharification yield was obtained after the rice straw was pretreated under optimal conditions and subsequent enzymatic hydrolysis at a combined severity factor of 0.4-0.7. Moreover, good long-term stability and durability of the pretreatment system under continuous operation was observed.

Pilot-scale ethanol production from rice straw hydrolysates using xylose-fermenting Pichia stipitis

Ethanol was produced at pilot scale from rice straw hydrolysates using a Pichia stipitis strain previously adapted to NaOH-neutralized hydrolysates. The highest ethanol yield was 0.44 ± 0.02 g(p)/g(s) at an aeration rate of 0.05 vvm using overliming-detoxified hydrolysates. The yield with hydrolysates conditioned by ammonia and NaOH was 0.39 ± 0.01 and 0.34 ± 0.01 g(p)/g(s), respectively, were achieved at the same aeration rate. The actual ethanol yield from hydrolysate fermentation with ammonia neutralization was similar to that with overliming hydrolysate after taking into account the xylose loss resulting from these conditioning processes. Moreover, the ethanol yield from ammonia-neutralized hydrolysates could be further enhanced by increasing the initial cell density by two-fold or reducing the combined concentration of furfural and 5-hydroxymethyl furfural to 0.6g/L by reducing the severity of operational conditions in pretreatment. This study demonstrated the potential for commercial ethanol production from rice straw via xylose fermentation.