Detoxification Of Hydrolysate Research Articles

Ethanol production from corn stover hemicellulosic hydrolysate using immobilized recombinant yeast cells

Ethanol production from corn stover hemicellulosic hydrolysate was investigated using immobilized recombinant Saccharomyces cerevisiae yeast cells. Detoxification of hemicellulosic hydrolysate by roto-evaporation and lime neutralization was carried out to remove volatile fermentation inhibitors. All furfural and more than 50% acetic acid in the hydrolysate were removed, meanwhile the xylose concentration was enhanced to 71.8 g/L. The fermentability of the detoxified hydrolysate was significantly improved using immobilized cells of recombinant S. cerevisiae by Ca-alginate. An ethanol concentration of 31.1 g/L and the corresponding ethanol yield on fermentable sugars of 0.406 g/g were obtained within 72 h in batch fermentation of the detoxified hydrolysate with immobilized cells. In addition, repeated batch fermentation of immobilized recombinant S. cerevisiae cells was attempted for ethanol production for 5 batches. The concentration of ethanol in each batch maintained above 30.1 g/L with the ethanol yield on fermentable sugars over 0.393 g/g. These results demonstrate the viability and significance of ethanol production from corn stover hemicellulosic hydrolysate.

Detoxification of biomass hydrolysates by reactive membrane extraction

Economical conversion of lignocellulosic biomass into biofuels is essential to reduce the world's dependence on fossil fuels. The typical biochemical process for biomass conversion includes a thermochemical pretreatment step to improve enzymatic cellulose hydrolysis and to release hemicellulosic sugars from the polymer matrix. However compounds that are toxic to microorganisms in subsequent fermentation steps may also be released. This work investigates the use of membrane extraction to detoxify or remove these toxic compounds from corn stover hydrolysates pretreated using dilute sulphuric acid. Extraction of sulphuric, acetic, formic and levulinic acid as well as 5-hydroxymethylfurfural and furfural has been investigated. Octanol and oelyl alcohol were used as organic phase solvents. Alamine 336 was used as the aliphatic amine extractant. Reactive extraction of sulphuric, acetic, formic and levulinc acid was observed while 5-hydroxymethylfurfural and furfural were extracted due to their distribution in the organic solvent. Significant removal of all toxic compounds investigated was obtained as well an increase in pH from 1.0 to 5.0. As small quantities of the organic phase transferred into the hydrolysate during extraction, the toxicity of the organic phase must be considered. As it is likely that detoxification will require the use of another unit operation in combination with membrane extraction, the economical viability of the combined process must be considered.

Detoxification of model phenolic compounds in lignocellulosic hydrolysates with peroxidase for butanol production from Clostridium beijerinckii

In the present study, we investigated the peroxidase-catalyzed detoxification of model phenolic compounds and evaluated the inhibitory effects of the detoxified solution on butanol production by Clostridium beijerinckii National Collection of Industrial and Marine Bacteria Ltd. 8052. The six phenolic compounds, p-coumaric acid, ferulic acid, 4-hydroxybenzoic acid, vanillic acid, syringaldehyde, and vanillin, were selected as model fermentation inhibitors generated during pretreatment and hydrolysis of lignocellulose. The enzyme reaction was optimized as a function of the reaction conditions of pH, peroxidase concentration, and hydrogen peroxide to substrate ratio. Most of the tested phenolics have a broad optimum pH range of 6.0 to 9. Removal efficiency increased with the molar ratio of H(2)O(2) to each compound up to 0.5-1.25. In the case of p-coumaric acid, ferulic acid, vanillic acid, and vanillin, the removal efficiency was almost 100% with only 0.01 microM of enzyme. The tested phenolic compounds (1 g/L) inhibited cell growth by 64-74%, while completely inhibiting the production of butanol. Although syringaldehyde and vanillin were less toxic on cell growth, the level of inhibition on the butanol production was quite different. The detoxified solution remarkably improved cell growth and surprisingly increased butanol production to the level of the control. Hence, our present study, using peroxidase for the removal of model phenolic compounds, could be applied towards the detoxification of lignocellulosic hydrolysates for butanol fermentation.

Xylitol production from wheat straw hemicellulosic hydrolysate: hydrolysate detoxification and carbon source used for inoculum preparation

Wheat straw hemicellulosic hydrolysate was used for xylitol bioproduction. The use of a xylose-containing medium to grow the inoculum did not favor the production of xylitol in the hydrolysate, which was submitted to a previous detoxification treatment with 2.5% activated charcoal for optimized removal of inhibitory compounds.

EFEITO DA DESTOXIFICAÇÃO DO HIDROLISADO DE BAGAÇO DE CANA SOBRE A REMOÇÃO DE FENÓIS, A PERDA DE AÇÚCARES E A BIOCONVERSÃO DE XILOSE EM XILITOL

RESUMO: O hidrolisado resultante do processo de hidrolise acida, metodologia comumente empregada para diferentes materiais lignocelulosicos, contem, alem dos acucares, compostos toxicos aos microrganismos. Dentre estes, os compostos fenolicos, tem sido mencionados como inibidores da bioconversao de xilose em xilitol, quer pela sua acao individual ou pela interacao sinergistica entre ele e outros compostos presentes nos hidrolisados como o furfural, hidroximetilfurfural e o acido acetico. Os compostos fenolicos conferem, ainda, ao hidrolisado uma coloracao escura, a qual interfere no processo de “downstrean” do xilitol. Este trabalho avaliou dois procedimentos de destoxificacao do hidrolisado de bagaco de cana-de-acucar: ajuste de pH combinado a adsorcao em carvao ativo e floculacao por polimero de origem vegetal. Os fenois totais e as concentracoes de xilose e glicose foram determinados pelo metodo de Folin-Ciocalteu e atraves de cromatografia liquida, respectivamente. Ambos os tratamentos resultaram em reducao da concentracao de fenois totais. Porem, o uso de carvao ativo resultou em maior perda deste composto (88.5% remocao), o que representa 17.8% de aumento em comparacao ao emprego do polimero. A perda de xilose foi minima (9%) para ambos os tratamentos empregados. O tratamento de ajuste de pH combinado a adsorcao em carvao ativo foi mais eficiente do que o procedimento de floculacao por polimero. Considerando estes ensaios preliminares e tambem o baixo custo e biodegradabilidade do polimero, pesquisas devem ser realizadas para que se estabelecam condicoes mais eficientes do uso deste composto, melhorando a fermentabilidade do hidrolisado e diminuindo a perda de xilose. Palavras-chave: Hidrolisado de bagaco de cana-de-acucar. Destoxificacao. Xilitol. Xilose. Compostos fenolicos. SUMMARY: The hydrolysate resulting from the acid hydrolysis process, a method usually employed for different lignocellulosic materials, contains, besides sugars, compounds that are toxic to the microorganisms. Among them, there are the phenolic compounds, that have inhibitory effect on the xylose-to-xylitol bioconversion, due to their individual action and also to their synergistic interaction with other compounds present in the hydrolysates, such as furfural, hydroxymethylfurfural and acetic acid. Furthermore, the phenolic compounds are responsible for the dark color of the hydrolysate, which interferes in the xilitol downstream process. This work evaluated two procedures of sugarcane bagasse hydrolysate detoxification: pH adjusting with active charcoal adsorption, and a vegetable-origin polymer flocculation technique. The total phenolics and the xylose and glycose concentrations were determined by Folin-Ciocalteu method and liquid chromatography, respectively. Both treatments resulted in reduction of total phenolics concentration. However, the use of active charcoal resulted in higher loss of this compound (88.5% removal), that represents 17.8% increase when comparised to the use of polymer. The xylose loss was minimum (8%) for both used treatments. The treatment using the combination of pH adjustment and active charcoal adsorption was more efficient than the procedure that used vegetable-origin polymer. Considering these preliminary assays and also the polymer low cost and its biodegradability, researches must be performed in order to establish conditions for the most effective use of this compound, improving the hydrolysate fermentability � Doutoranda/CAPES, DEBIQ, EEL-USP. Estrada Municipal do Campinho s/n, CEP �2602-8�0, Lorena

Aqueous two‐phase extraction using thermoseparating copolymer: a new system for phenolic compounds removal from hemicelullosic hydrolysate

AbstractBACKGROUND: The hydrolysis of hemicellulosic material can provide liquor with high xylose concentration (which can be used as a fermentation medium) and phenolic compounds (Phs), potentially immunostimulating compounds. However, these hydrolysates must be detoxified in order to remove the Phs that can act as inhibitors in bioconversions.RESULTS: Aqueous two‐phase systems composed of thermoseparating copolymers were used for rice straw hydrolysate detoxification. The hydrolysis process was able to promote chemical breakdown of 85% of the total hemicellulose content, 14% of the cellulose, and 2% of the lignin. The hydrolysate obtained contained 19.7 g L−1 of xylose and several phenolic compounds, such as vanillin, vanillic acid, ferullic acid, etc. The phenolics extraction was studied as a function of copolymer molar mass (1100 g mol−1, 2000 g mol−1 and 2800 g mol−1), their percentages (from 5% to 50%) and Phs initial concentration. Phenolic compounds extraction of around 80% was obtained under the following conditions: 20% (w/w) and 35% (w/w) copolymer 1100 g mol−1, 35% (w/w) copolymer 2000 g mol−1 and 35% (w/w) copolymer 2800 g mol−1 at 25 °C.CONCLUSIONS: The results demonstrated the viability of this method for the removal of Phs from rice straw hydrolysate, which has potential uses in bioconversion processes. Copyright © 2007 Society of Chemical Industry

Ethanolic fermentation of hydrolysates from ammonia fiber expansion (AFEX) treated corn stover and distillers grain without detoxification and external nutrient supplementation

External nutrient supplementation and detoxification of hydrolysate significantly increase the production cost of cellulosic ethanol. In this study, we investigated the feasibility of fermenting cellulosic hydrolysates without washing, detoxification or external nutrient supplementation using ethanologens Escherichia coli KO11 and the adapted strain ML01 at low initial cell density (16 mg dry weight/L). The cellulosic hydrolysates were derived from enzymatically digested ammonia fiber expansion (AFEX)-treated corn stover and dry distiller's grain and solubles (DDGS) at high solids loading (18% by weight). The adaptation was achieved through selective evolution of KO11 on hydrolysate from AFEX-treated corn stover. All cellulosic hydrolysates tested (36-52 g/L glucose) were fermentable. Regardless of strains, metabolic ethanol yields were near the theoretical limit (0.51 g ethanol/g consumed sugar). Volumetric ethanol productivity of 1.2 g/h/L was achieved in fermentation on DDGS hydrolysate and DDGS improved the fermentability of hydrolysate from corn stover. However, enzymatic hydrolysis and xylose utilization during fermentation were the bottlenecks for ethanol production from corn stover at these experimental conditions. In conclusion, fermentation under the baseline conditions was feasible. Utilization of nutrient-rich feedstocks such as DDGS in fermentation can replace expensive media supplementation.

Sugarcane bagasse hemicellulose hydrolysate for ethanol production by acid recovery process

In order to increase the reducing sugar concentration in the sugarcane bagasse hemicellulose acid hydrolysate and recover the acid, the acid hydrolysis was carried out in an acid recycle process and detoxification of hydrolysate was performed by electrodialysis. Two cycles of acidic treatments increased the reducing sugar concentration from 28 to 63.5 g l −1 and sulphuric acid consumption decreased to 0.056 g g −1 bagasse. After treatment by electrodialysis, 90% of acetic acid in hydrolysate was removed and the recovery ratio of sulphuric acid was 88%. The pretreated hydrolysates, supplemented with nutrient materials, were fermented to ethanol using Pachysolen tannophilus DW06. A batch culture with pretreated hydrolysate as substrate was developed giving 19 g ethanol l −1 with a yield of 0.34 g g −1 sugar and productivity of 0.57 g l −1 h −1.

Comparison of different procedures for the detoxification of eucalyptus hemicellulosic hydrolysate for use in fermentative processes

AbstractEucalyptus (Eucalyptus grandis) shavings were submitted to an acid hydrolysis process with the aim of obtaining a hemicellulosic hydrolysate rich in fermentable sugars. However, the hydrolysate obtained contained, in addition to sugars, several compounds that are toxic to microorganisms, namely furfural, hydroxymethylfurfural, acetic acid and phenolics. In order to produce a hydrolysate suitable for use in fermentative processes, several procedures were evaluated for hydrolysate detoxification, including concentration by vacuum evaporation and adsorption on activated charcoal, diatomaceous earths, ion‐exchange resin or adsorbent resin. Hydrolysate concentration was especially effective for furfural removal, whereas the adsorbent resin was efficient in removing hydroxymethylfurfural, phenolics and acetic acid. Combination of this resin with activated charcoal was better than with diatomaceous earths for removal of acetic acid and phenolics. The best detoxification procedure evaluated was based on hydrolysate concentration followed by adsorption on activated charcoal and adsorbent resin. By this treatment, removal rates of 82.5, 100, 100 and 94% were attained for acetic acid, furfural, hydroxymethylfurfural and phenolics, respectively. Copyright © 2005 Society of Chemical Industry

Sugarcane bagasse hydrolysis with phosphoric and sulfuric acids and hydrolysate detoxification for xylitol production

AbstractThe effectiveness of phosphoric acid to release xylose from sugarcane bagasse hemicellulose was assessed through a 23 full factorial design. The maximum xylose concentration in the hydrolysate (17.1 g dm−3) was attained when the bagasse was treated at 160 °C for 60 min, using 70 mg of phosphoric acid per gram of dry‐bagasse. Hydrolysis carried out with sulfuric acid, under optimum conditions previously determined, provided a hydrolysate with a similar xylose concentration (17.2 g dm−3). After vacuum concentration, these hydrolysates were detoxified and used for xylitol production with the yeast Candida guilliermondii. Two different detoxification strategies, which consisted of adjusting the pH of the hydrolysates to 5.5 with either calcium oxide or ammonium hydroxide, both followed by active charcoal adsorption, were tested. The best xylitol productions (18.1 and 19.2 g dm−3) were observed when calcium oxide was used to adjust the pH of both the phosphoric and the sulfuric acid hydrolysates, respectively. Copyright © 2004 Society of Chemical Industry

Detoxification of sugarcane bagasse hemicellulosic hydrolysate with ion‐exchange resins for xylitol production by calcium alginate‐entrapped cells

AbstractThis study describes the performance of four different resins, in sequence, to detoxify sugarcane bagasse hemicellulosic hydrolysate and to improve xylitol production by calcium alginate‐entrapped Candida guilliermondii FTI20037 cells under conditions of low oxygen concentration. The treatment resulted in a removal of 82.1% furfural, 66.5% hydroxymethylfurfural, 61.9% phenolic compounds derived from lignin degradation, 100% chromium, 46.1% zinc, 28.5% iron, 14.7% sodium and 3.5% nickel. On the other hand, the removal of acetic acid was not significant. A xylitol yield factor (YP/S) of 0.62 g g−1 and a volumetric productivity (Qp) of 0.24 g dm−3 h−1 were attained in the fermentation process for xylitol production from detoxified hydrolysate. Copyright © 2004 Society of Chemical Industry

Effect of pH and activated charcoal adsorption on hemicellulosic hydrolysate detoxification for xylitol production

AbstractBiotechnological conversion of xylose into xylitol using hydrolysates obtained from the hemicellulosic fraction of lignocellulosic materials is compromised by the presence of compounds released or formed during the hydrolysis process, some of them being toxic to microorganisms. In order to improve the bioconversion of these hydrolysates it is necessary to find methods to reduce their toxicity. In the present work, rice straw hemicellulosic hydrolysate was treated by six different procedures (all of them involving pH adjustment, with or without activated charcoal adsorption), before being used as a fermentation medium for xylitol production. The most effective method of treatment was to increase the initial pH (0.4) to 2.0 using solid NaOH, followed by the addition of activated charcoal (25 g kg−1) and increase in the pH to 6.5 using solid NaOH. Lignin degradation products were the most inhibitory compounds present in the hydrolysate; their removal was selective and strongly dependent on the pH employed in the treatment. The highest yield of xylitol was 0.72 g g−1 xylose, with a productivity of 0.55 g dm−3 h−1. Copyright © 2004 Society of Chemical Industry

Selection of anion exchangers for detoxification of dilute-acid hydrolysates from spruce.

Six anion-exchange resins with different properties were compared with respect to detoxification of a dilute-acid hydrolysate of spruce prior to ethanolic fermentation with Saccharomyces cerevisiae. The six resins encompassed strong and weak functional groups as well as styrene-, phenol-, and acrylic-based matrices. In an analytical experimental series, fractions from columns packed with the different resins were analyzed regarding pH, glucose, furfural, hydroxymethylfurfural, phenolic compounds, levulinic acid, acetic acid, formic acid, and sulfate. An initial adsorption of glucose occurred in the strong alkaline environment and led to glucose accumulation at a later stage. Acetic and levulinic acid passed through the column before formic acid, whereas sulfate had the strongest affinity. In a preparative experimental series, one fraction from each of six columns packed with the different resins was collected for assay of the fermentability and analysis of glucose, mannose, and fermentation inhibitors. The fractions collected from strong anion-exchange resins with styrene-based matrices displayed the best fermentability: a sevenfold enhancement of ethanol productivity compared with untreated hydrolysate. Fractions from a strong anion exchanger with acrylic-based matrix and a weak exchanger with phenol-based resin displayed an intermediate improvement in fermentability, a four- to fivefold increase in ethanol productivity. The fractions from two weak exchangers with styrene- and acrylic-based matrices displayed a twofold increase in ethanol productivity. Phenolic compounds were more efficiently removed by resins with styrene- and phenol-based matrices than by resins with acrylic-based matrices.

Eucalyptus hydrolysate detoxification with activated charcoal adsorption or ion-exchange resins for xylitol production

Eucalyptus hemicellulosic hydrolysate used for xylitol production by Candida guilliermondii FTI20037 was previously treated either with ion-exchange resins or with activated charcoal adsorption combined with pH adjustment, in order that acetic acid, furfural and hydroxymethylfurfural could be removed. The best results for xylitol yield factor (0.76 g/g) and volumetric productivity (0.68 g/(l h) were attained when a three-fold concentrated hydrolysate was treated with ion-exchange resins. Using activated charcoal combined with pH adjustment for treating a three-fold concentrated hydrolysate resulted in a xylitol yield factor of 0.40 g/g and a volumetric productivity of 0.30 g/(l h). This same treatment applied to a six-fold concentrated hydrolysate resulted in a xylitol yield factor of 0.66 g/g and a volumetric productivity of 0.50 g/(l h).

Detoxification of wood hydrolysates with wood charcoal for increasing the fermentability of hydrolysates

An effort was made to develop wood charcoals to remove inhibitors such as furan and phenolic compounds in wood hydrolysates for improving the fermentability of the wood hydrolysate. Wood charcoals prepared at various temperatures were found to selectively remove only the inhibitors without reducing the levels of fermentable sugars. It was also found that the wood charcoals prepared at higher temperature had enhanced ability to remove inhibitors, compared to wood charcoals prepared at lower temperature. The fermentability of the hydrolysates had been improved by the wood charcoal treatment. A closer investigation on the fermentability showed that hydrolysates treated with wood charcoals prepared at higher temperature could attain higher fermentability, compared to hydrolysates treated with wood charcoals prepared at lower temperature. This may be related to the mechanism of removal of inhibitors by the wood charcoals.

Hydrolysate detoxification with activated charcoal for xylitol production by Candida guilliermondii

A detoxification method using activated charcoal with concentrated rice straw hemicellulosic hydrolysate improved the conversion of xylose to xylitol by the yeast Candida guilliermondii by 22%. This was achieved when the hydrolysate:charcoal ratio was 40 g g−1, resulting in removal of 27% of phenolic compounds. Under this condition, the xylitol yield factor (0.72 g g−1) and volumetric productivity (0.61 g l−1 h−1) were close to those attained in a semi-defined medium simulating hydrolysate sugars.

Detoxification of wood hydrolysates with laccase and peroxidase from the white-rot fungus Trametes versicolor

Fermentation of wood hydrolysates to desirable products, such as fuel ethanol, is made difficult by the presence of inhibitory compounds in the hydrolysates. Here we present a novel method to increase the fermentability of lignocellulosic hydrolysates: enzymatic detoxification. Besides the detoxification effect, treatment with purified enzymes provides a new way to identify inhibitors by assaying the effect of enzymatic attack on specific compounds in the hydrolysate. Laccase, a phenol oxidase, and lignin peroxidase purified from the ligninolytic basidiomycete fungus Trametes versicolor were studied using a lignocellulosic hydrolysate from willow pretreated with steam and SO2. Saccharomyces cerevisiae was employed for ethanolic fermentation of the hydrolysates. The results show more rapid consumption of glucose and increased ethanol productivity for samples treated with laccase. Treatment of the hydrolysate with lignin peroxidase also resulted in improved fermentability. Analyses by GC-MS indicated that the mechanism of laccase detoxification involves removal of monoaromatic phenolic compounds present in the hydrolysate. The results support the suggestion that phenolic compounds are important inhibitors of the fermentation process.

Improved xylitol production with Debaryomyces hansenii Y-7426 from raw or detoxified wood hydrolysates

Xylose solutions obtained by acid prehydrolysis of raw or NaOH-treated Eucalyptus globulus wood samples were used for making fermentation media useful for xylitol production with Debaryomyces hansenii NRRL Y-7426. Several physicochemical treatments for detoxification of hydrolysates were tested including overliming, sulfite addition, adsorption in charcoal, and concentration by evaporation. Despite the relatively low xylose concentration of hydrolysates, high xylitol yields (up to 0.84 g xylitol g −1 consumed xylose) were obtained at good productivities (up to 0.53 g xylitol l −1h −1). The improvements obtained with the several strategies assayed are discussed in terms of overall productivities and product yield.