The Optimization of Dilute Acid Hydrolysis of Cotton Stalk in Xylose Production

Principal factors affecting the yield of dilute acid pretreatment of lignocellulosic biomass: A critical review

This review provides a critical analysis of the state of the art of dilute acid pretreatment applied to lignocellulosic biomass. Data from 63 publications were extracted and analysed. The majority of the papers used residence times of<30 min, temperature ranges from 100 °C to 200 °C, and acid levels between 0 % and 2 %. Yields are quantified directly after pretreatment (xylose content) or after enzymatic hydrolysis (glucose content). Statistical analyses allowed the time-temperature equivalence to be quantified for three types of biomass: they were formulated by non-linear expressions. In further works, investigating less explored areas, for example moderate temperature levels with longer residence times, is recommended. Pretreatment material (time-temperature kinetics, reactor type) and analytical methods should be standardized and better described. It becomes mandatory to promote the development of an open, findable, accessible, interoperable, and reusable data approach for pretreatments research.

Ligninolytic characteristics of Pleurotus ostreatus cultivated in cotton stalk media

Biodelignification is widely regarded as a low-efficiency process because it is usually slow and difficult to control. To improve its efficiency and understand its mechanism, the present study analyzed the delignification characteristics of Pleurotus ostreatus grown on a cotton stalk medium. The results demonstrated that all strains of P. ostreatus can selectively degrade the cotton stalk lignin. When cultured in a cotton stalk medium for 60 days, P. ostreatus degraded lignin primarily during its mycelium growth with up to 54.04% lignin degradation and produced laccase and manganese dependent peroxidase with high activity levels at the peaks of 70.17 U/ml and 62.39 U/ml, respectively, but no detectable lignin peroxidase. The results of nuclear magnetic resonance spectroscopy and Fourier transform infrared spectroscopy analyses of significant changes in lignin structure revealed that syringyl (S) lignin units were more degraded than guaiacyl (G) lignin units, with a significantly elevated G/S ratio. The Gas Chromatography-Mass Spectrometer analysis of low-molecular-weight compounds revealed that the delignification resulted in the formation of alcohols, organic acids, benzodiazepines, and alkanes. Identified benzodiazepines implied the degradation of G and S units of lignin. These findings will help to improve the efficiency of biodelignification and expand our understanding of its mechanism.

Optimization of activated charcoal detoxification and concentration of chestnut shell hydrolysate for xylitol production

OBJECTIVES

To increase xylose concentration of the chestnut shell hemicellulosic hydrolysate with an acceptable phenolic compound level in order to enhance xylitol production by Candida tropicalis M43.

RESULTS

The xylose concentration and total phenolic compound concentration of the hydrolysate were obtained as 33.68 g/L and 77.38 mg gallic acid equivalent/L, respectively by optimization of detoxification parameters and concentration level (60 °C, 115 min contact time, 5.942% (w/v) dosage of activated charcoal, 120 strokes/min shaking rate and 0.2 volume ratio). Xylitol production was achieved in the hydrolysate by using Candida tropicalis M43. The maximum xylitol concentration was 6.30 g/L and productivity, yield and percentage of substrate conversion were calculated as 0.11 g/L h, 19.13% and 97.79%, respectively. In addition, the chestnut shell hydrolysate fortified with xylose and the maximum xylitol concentration increased to 18.08 g/L in the hydrolysate-based medium containing 80 g/L xylose.

CONCLUSIONS

Optimizing detoxification conditions with concentration level was found to be useful for enhancing xylitol production. In addition, fortification of the hydrolysate caused a three fold increase in maximum xylitol concentration.

Evaluation of some lignocellulosic byproducts of food industry for microbial xylitol production by Candida tropicalis

Some lignocellulosic food byproducts such as potato peels, wheat bran, barley bran and chestnut shells were evaluated as potential sources of xylose for microbial xylitol production by yeasts. Potential yeast strains were selected after screening xylitol production of some indigenous yeasts in a defined fermentation medium. Candida tropicalis strains gave the highest results with 83.28 and 54.07 g/L xylitol production from 100 g/L xylose. Lignocellulosic materials were exposed to acid hydrolysis at different conditions. Chestnut shells gave the highest xylose yield and the hydrolysate of chestnut shells was used in further experiments in which xylitol productions of two potential C. tropicalis strains were investigated. Combined detoxification method including evaporation, overliming and activated charcoal with the use of threefold concentration and also yeast extract supplementation suggested to be efficient for both growth and product formation in chestnut shell hydrolysate in which 40 % xylitol yield was obtained. It was concluded that detoxified and fortified chestnut shell hydrolysate could be a potential medium for xylitol production.

The Influence of Sugar Cane Bagasse Type and Its Particle Size on Xylose Production and Xylose-to-Xylitol Bioconversion with the Yeast Debaryomyces hansenii

In the present study, the effect of the type of sugar cane bagasse (non-depithed or depithed) and its particle size on the production of xylose and its subsequent fermentation to xylitol by Debaryomyces hansenii CBS767 was investigated using a full factorial experimental design. It was found that the particle size range and whether bagasse was depithed or not had a significant effect on the concentration and yield of xylose in the resulting hemicellulose hydrolysate. Depithed bagasse resulted in higher xylose concentrations compared to non-depithed bagasse. The corresponding detoxified hemicellulose hydrolysates were used as fermentation media for the production of xylitol. The hemicellulose hydrolysate prepared from depithed bagasse also yielded meaningfully higher xylitol fermentation rates compared to non-depithed bagasse. However, in the case of non-depithed bagasse, the hemicellulose hydrolysate prepared from larger particle size range resulted in higher xylitol fermentation rates, whereas the effect in the case of non-depithed bagasse was not pronounced. Therefore, depithing of bagasse is an advantageous pretreatment when it is to be employed in bioconversion processes.

Improved enzymatic saccharification of steam exploded cotton stalk using alkaline extraction and fermentation of cellulosic sugars into ethanol

Cotton stalk, a widely available and cheap agricultural residue lacking economic alternatives, was subjected to steam explosion in the range 170-200°C for 5min. Steam explosion at 200°C and 5min led to significant hemicellulose solubilization (71.90±0.10%). Alkaline extraction of steam exploded cotton stalk (SECOH) using 3% NaOH at room temperature for 6h led to 85.07±1.43% lignin removal with complete hemicellulose solubilization. Besides, this combined pretreatment allowed a high recovery of the cellulosic fraction from the biomass. Enzymatic saccharification was studied between steam exploded cotton stalk (SECS) and SECOH using different cellulase loadings. SECOH gave a maximum of 785.30±8.28mg/g reducing sugars with saccharification efficiency of 82.13±0.72%. Subsequently, fermentation of SECOH hydrolysate containing sugars (68.20±1.16g/L) with Saccharomyces cerevisiae produced 23.17±0.84g/L ethanol with 0.44g/g yield.

Evaluation of cotton stalk hydrolysate for xylitol production

Cotton stalk is a widely distributed and abundant lignocellulosic waste found in Turkey. Because of its rich xylose content, it can be a promising source for the production of xylitol. Xylitol can be produced by chemical or biotechnological methods. Because the biotechnological method is a simple process with great substrate specificity and low energy requirements, it is more of an economic alternative for the xylitol production. This study aimed to use cotton stalk for the production of xylitol with Candida tropicalis Kuen 1022. For this purpose, the combined effects of different oxygen concentration, inoculum level and substrate concentration were investigated to obtain high xylitol yield and volumetric xylitol production rate. Candida tropicalis Kuen 1022 afforded different concentrations of xylitol depending on xylose concentration, inoculum level, and oxygen concentration. The optimum xylose, yeast concentration, and airflow rate for cotton stalk hydrolysate were found as 10.41 g L(-1), 0.99 g L(-1), and 1.02 vvm, respectively, and under these conditions, xylitol yield and volumetric xylitol production rate were obtained as 36% and 0.06 g L(-1) hr(-1), respectively. The results of this study show that cotton stalk can serve as a potential renewable source for the production of xylitol.

Ethanol production from cotton gin trash using optimised dilute acid pretreatment and whole slurry fermentation processes

Cotton ginning trash (CGT) collected from Australian cotton gins was evaluated for bioethanol production. CGT composition varied between ginning operations and contained high levels of extractives (26-28%), acid-insoluble material (17-22%) and holocellulose (42-50%). Pretreatment conditions of time (4-20 min), temperature (160-220 °C) and sulfuric acid concentration (0-2%) were optimised using a central composite design. Response surface modelling revealed that CGT fibre pretreated at 180 °C in 0.8% H2SO4 for 12 min was optimal for maximising enzymatic glucose recoveries and achieved yields of 89% theoretical, whilst the total accumulated levels of furans and acetic acid remained relatively low at <1 and 2 g/L respectively. Response surface modelling also estimated maximum xylose recovery in pretreated liquors (87% theoretical) under the set conditions of 150 °C in 1.9% H2SO4 for 23.8 min. Yeast fermentations yielded high ethanol titres of 85%, 88% and 70% theoretical from glucose generated from: (a) enzymatic hydrolysis of washed pretreated fibres, (b) enzymatic hydrolysis of whole pretreated slurries and (c) simultaneous saccharification fermentations, respectively.

Hydrolysis of Hazelnut Shells as a Carbon Source for Bioprocessing Applications and Fermentation

Hazelnut shells are generated in large amounts from hazelnut processing. Currently, it is used as fuel. However, reuse in bioprocessing can release remarkable content of sugars, which can be used for production of additives such as enzymes widely used in the food industry. Thus, the present study was undertaken to determine the effect of single and combined chemical and enzymatic hydrolysis on the production of fermentable sugars from hazelnut shells. Batch hydrolysis was carried out under various conditions to select optimal conditions. The results revealed that an optimal sugar concentration of about 19.2 g/l was achieved after 3.42% (w/w) dilute acid pretreatment conducted at 130°C for 31.7 min and enzymatic load of 200 U/g for 24 h. The overall sugar yield was calculated as 72.4% (g reducing sugar/g total carbohydrate). Therefore, hazelnut shells can be considered a suitable feedstock to compete with synthetic sugars used in fermentations.

Evaluation of alkaline pretreatment temperature on a multi-product basis for the co-production of glucose and hemicellulose based films from lignocellulosic biomass

Cotton stalks were subjected to alkaline pretreatment for the co-production of glucose and hemicellulose based films with a multi-product approach. Three pretreatment temperatures (25, 60 and 90 °C) were evaluated for their effects both on the glucose yield and on the properties of hemicellulose based films. Compared to untreated cotton stalks, the glucose yields were enhanced 3.9, 4.1 and 4.2 times for pretreatments conducted at 25, 60 and 90 °C, respectively. The pretreatment temperature of 90 °C was detrimental in terms of film formation. Tensile energy to break values of the films obtained after pretreatments conducted at 25, 60 and 90 °C were 1.1, 0.8, and 0.4 MJ/m3, respectively. The hemicellulosic part of the process, which considers the production of hemicellulose based films, should govern the pretreatment temperature since it was more responsive to the changes in the pretreatment temperature compared to the cellulosic part that accounts for glucose production.