Xylanase-induced reduction of chlorine dioxide consumption during elemental chlorine-free bleaching of different pulp types

The potential of crude xylanase from Thermomyces lanuginosus and Xylanase P (a commercial xylanase) was evaluated in bleaching of various paper pulp types. Xylanases released chromophores and reducing sugars and decreased kappa number of pulps. Chlorine-bleached, alkali-extracted bagasse and post-oxygen kraft pulps, pretreated with enzymes, gained over 5 brightness points over controls. Biobleaching of soda-aq pulp with Xylanase P produced chlorine dioxide savings of up to 30% or 4.5 kg chlorine dioxide t^–1 pulp.     

Optimization of hydrogen peroxide in totally chlorine free bleaching of cellulose pulp from olive tree residues

The influence of the operating conditions used in the bleaching of olive wood trimmings pulp (viz. hydrogen peroxide concentration and time) on the yield, kappa index and viscosity of the resulting pulp and on strength-related properties of paper sheets was studied to determine the optimal bleaching conditions of this pulp. Hydrogen peroxide bleached pulps at different sequences (oxygen, ozone, chlorine dioxide and alkaline extractions) were compared. Hydrogen peroxide bleaching proved to be suitable for this pulp. Considerable improvements in viscosity were obtained with respect to other bleaching sequences such as oxygen, ozone and chlorine dioxide. Hydrogen peroxide bleaching decreased the kappa index 51.3% less than ozone bleaching, 25.0% less than chlorine dioxide (D) and 6.3% less combined chlorine dioxide-alkaline extraction (DE). To obtain kappa indices 50.9% and 37.9% lower than the index achieved by hydrogen peroxide, oxygen (LaO(p)) and ozone (LaO(LaZ)R) sequences respectively were needed. Lower-medium levels of hydrogen peroxide concentrations (1-3%) and high reaction times (210 min) proved to be suitable for bleaching of pulp olive trimming residues. This approach could be used on this residue to produce adequately bleached pulp.     

The performance of fungal xylan-degrading enzyme preparations in elemental chlorine-free bleaching for Eucalyptus pulp

Cellulase-free xylan-degrading enzyme preparations from Acrophialophora nainiana, Humicola grisea var. thermoidea and two Trichoderma harzianum strains were used as bleaching agents for Eucalyptus kraft pulp, prior to a chlorine dioxide and alkaline bleaching sequence. In comparison to the control sequence (performed without xylanase pretreatment), the sequence incorporating enzyme treatment was more effective. Removal of residual lignin was indicated by a reduction in kappa number. Overall, enzyme preparations from T. harzianum were marginally more effective in reducing pulp viscosity and chlorine chemical consumption and improving the brightness of the kraft pulp. However, the highest reduction in pulp viscosity was mediated by the xylanase preparation from A. nainiana. Xylanase pretreatment compares very favorably with that of chemical pulping. Journal of Industrial Microbiology & Biotechnology (2002) 28, 204–206 DOI: 10.1038/sj/jim/7000227 Received 27 April 2001/ Accepted in revised form 03 November 2001     

Laccase for biobleaching of eucalypt kraft pulp by means of a modified industrial bleaching sequence

Biobleaching of kraft pulp is a possible application of laccase, but it has not been described in detail for complete industrial bleaching sequences yet. Therefore, in this work, the biobleaching of Eucalyptus globulus kraft pulp was performed using a modified industrial totally chlorine‐free sequence. The modification consisted in the substitution of an enzymatic delignification stage, based on the application of laccase from Trametes villosa, for the first alkaline extraction one. The enzymatic stage was performed with several synthetic and natural mediators, namely 1‐hydroxybenzotriazole (HBT), violuric acid (VA), methyl syringate, and syringaldehyde. Several pulp properties were analyzed after each stage of the bleaching process—kappa number, ISO brightness, viscosity, and optical properties of CIEL*a*b* system. The new biobleaching sequence improved the pulp properties, in comparison to the conventional bleaching sequence, if HBT or VA was used as mediators. VA was selected as the best mediator of those tested and the effect of its concentration in the enzymatic stage was subsequently studied. Reducing the initial concentration by 30%, the same pulp quality was obtained, but if the reduction attained 60%, an important decrease in pulp integrity was detected. The modified bleaching sequence could improve the bleached pulp properties (kappa number 10%, ISO brightness 1%, and viscosity 5%) in comparison to the mill sequence. © 2012 American Institute of Chemical Engineers Biotechnol. Prog., 2012     

Xylanases in bleaching: From an idea to the industry

Abstract: The utilization of hemicellulases in bleaching of kraft (sulphate) pulp is considered as one of the most important new large-scale industrial applications of enzymes. This is partly due to the great potential of an environmentally safe method. This method has in a short period also proven to be economically realistic. The main enzymes needed in the enzyme-aided bleaching have been shown to belong to the group of endo-/gb-xylanases. Xylanases act mainly on the relocated, reprecipitated xylan on the surface of the pulp fibres. Enzymatic hydrolysis of this specific type of xylan renders the structure of the fibres more permeable. The hydrolysis of xylan or mannan in the inner fibre layers may also enhance the bleachability. In practical process conditions, properties of the enzymes such as substrate specificity and the pH and temperature optima are of utmost importance. The benefits obtained by enzymes are dependent on the chemical bleaching sequence used as well as on the residual lignin content of pulp. The main goals in the enzyme-aided bleaching of kraft pulps have been the reduction of consumption of chlorine chemicals in the bleaching process and consequently lowering the AOX of the effluents. Enzymes have been applied as a pretreatment both in conventional (C/D)EDED and in ECF (elementary chlorine-free) bleaching sequences. In the production of TCF (totally chlorine-free) pulps, enzymes have also been successfully used for increasing the brightness of pulp.     

Comparative study of paper sheets from olive tree wood pulp obtained by soda,sulphite or kraft pulping

Paper sheets from olive tree wood pulp obtained by soda, sulphite or kraft pulping were studied to examine the influence of pulp beating on properties of the paper sheets.Paper sheets from kraft and sulphite pulps exhibited the highest resistance, and sulphite pulp the highest brightness. Soda pulp required more intensive beating than did kraft or sulphite pulps; in fact, the PFI beater had be operated at a 40–50% higher number of beating revolutions to obtain soda pulp with 70–80° SR.The breaking length, stretch, burst index and tear index of paper sheets obtained from kraft pulp, beaten to a Shopper–Riegler index of 70–80° SR were 20–30%, 30–50%, 50–60% and 15–35% higher, respectively, than those of sheets obtained from soda pulp.     

Identification of mutagenic compounds formed during chlorination of humic acid

Humic acid chlorination products are being studied in an effort to identify the chemicals responsible for the mutagenicity formed during water chlorination. In the present report, 19 chlorinated organic compounds have been identified and quantified in ether extracts of chlorinated humic acid solutions. 10 of these compounds, including a number of chlorinated propanones and chlorinated propenals, are direct-acting mutagens in the Salmonella/microsome mutagenicity assay. The position of the chlorine substituent has been found to be an important factor in the mutagenic activity of these two classes of compounds. The total mutagenicity of the compounds identified thus far, when tested either individually or as a composite, accounts for only 7-8% of the total TA100 mutagenicity, and less than 2% of the TA98 mutagenicity formed during humic acid chlorination. The addition of bromide to the humic acid chlorination reaction results in up to a 2-fold increase in the level of mutagenicity formed.     

Production of thermostable pectinase and xylanase for their potential application in bleaching of kraft pulp

A very high level of alkalophilic and thermostable pectinase and xylanase has been produced from newly isolated strains of Bacillus subtilis and Bacillus pumilus respectively. Enzyme production for pectinase was carried out under SSF using combinations of cheap agricultural residues while xylanase was produced under submerged fermentation using wheat bran as substrate to minimize the cost of production of these enzymes Among the various substrates tested, the highest yield of pectinase production was observed by using combination of WB + CW (6592 U/g of dry substrate) supplemented with 4% yeast extract when incubated at 37 °C for 72 h using deionized water of pH 7.0 as moistening agent. The biobleaching effect of these cellulase free enzymes on kraft pulp was determined. Both xylanase and pectinase showed stability over a broad range of pH from 6 to 10 and temperature from 55 to 70 °C. The bleaching efficiency of the pectinase and xylanase on kraft pulp was maximum after 150 min at 60 °C using enzyme dosage of 5 IU/ml of each enzyme at 10% pulp consistency with about 16% reduction in kappa number and 84% reduction in permanganate number. Enzyme treated pulp when subjected to CDED₁D₂ steps, 25% reduction in chlorine consumption and upto 19% reduction in consumption of chlorine dioxide was observed for obtaining the same %ISO brightness. Also an increase of 22 and 84% in whiteness and fluorescence respectively and a decrease of approximately 19% in the yellowness of the biotreated pulp were observed by pretreatment of the pulp with our enzymatic mixture.     

Mutagenicity on chlorination of products formed by ozonation of naphthoresorcinol in water

The mutagenicity of products formed by chlorination after ozonation of naphthoresorcinol in aqueous solution was assayed with Salmonella typhimurium strains TA98 and TA100 in the presence and absence of S9 mix from phenobarbital- and 5,6-benzoflavone-induced rat liver. Ozonated and subsequently chlorinated naphthoresorcinol was directly mutagenic, as was ozonated naphthoresorcinol, in both strains tested. The mutagenic activity at chlorination with 8 equivalents of chlorine per mole of naphthoresorcinol after ozonation was markedly higher than that at only ozonation. Of the identified ozonation products of naphthoresorcinol, muconic acid, after chlorination with 2 or 4 equivalents of chlorine per mole of the compound, induced direct mutagenicity against TA98 and TA100. The chlorination of glyoxal with 0.5 and 1 chlorine equivalents per mole of the compound was shown to produce direct mutagenicity toward TA98. The identification of the chlorination products of these compounds is also discussed.     

Changes in the structural composition of hardwood kraft pulp during bleaching

The possibility of using xylanase preparations for hydrolyzing hemicelluloses in a non-bleached kraft pulp in order to facilitate its bleaching was studied. The effects of enzymatic preparations of fungal and bacterial origins were examined, and the optimal conditions for xylanase activity were determined. UV spectroscopy demonstrated that the treatment of kraft pulp with enzymatic preparations containing xylanase facilitated the subsequent removal of lignin and increased the brightness by 5%. The effect of enzymatic treatment was retained in the case of peroxide bleaching. The enzymatic preparations studied are promising for the development of chlorine-free pulp bleaching technologies.     

Investigation of hydroxamic acids as laccase-mediators for pulp bleaching

A number of hydroxamic acids have been synthesized and investigated as laccase-mediators for pulp bleaching. As compared with N-hydroxyacetanilide (NHA), one of the most effective laccase-mediators reported so far, N-(4-cyanophenyl)acetohydroxamic acid (NCPA), resulted in the highest brightness and lowest kappa number of hardwood kraft pulp of all the laccase-mediators studied. The bleaching efficacy of a laccase/7-cyano-4-hydroxy-2H-1,4-benzoxazin-3-one system was also comparable with that of a laccase/NHA system. A laccase/NCPA system was further studied for the bleaching of unbleached softwood kraft pulp. The effects of pulp consistency, laccase dosage, NCPA dosage, incubation time, and oxygen pressure on the bleaching efficacy of a laccase/NCPA system were studied.     

Arundo donax L. reed: new perspectives for pulping and bleaching. Part 4. Peroxide bleaching of organosolv pulps

A comparative study on TCF (totally chlorine-free) bleachability of organosolv pulps from the annual fibre crop Arundo donax L. (giant reed) was carried out using a simple three-stage peroxide bleaching sequence without oxygen pre-bleaching. ASAM (alkali-sulfite-anthraquinone-methanol), Organocell (alkali-anthraquinone-methanol) and ethanol-soda organosolv pulps were bleached and compared with kraft pulp, as a reference. The final brightness of 76-78% ISO was attained for all tested pulps. The chemical charge required to reach this level of brightness varied for different pulps (despite the equal initial content of the residual lignin) and directly related to starting brightness values. No direct correlation between brightness improvement and lignin removal during bleaching was found, indicating the influence of the specific pulp properties introduced by pulping process on bleaching chemistry. The general higher bleaching response of organosolv pulps from A. donax was noted in comparison with kraft.     

Change in composition of structural components of leaf cellulose sulfate during fermentation bleaching by xylanases

The possibility of the use of xylanase preparations for hydrolysing hemicelluloses in a non-bleached kraft pulp in order to facilitate its bleaching was studied. The effects of enzymatic preparations of the fungal and bacterial origins were examined, and the optimal conditions for xylanase activity were determined. UV spectroscopy demonstrated that the treatment of kraft pulp with the enzymatic preparations containing xylanase facilitated the subsequent removal of lignin and increased the brightness by 5%. The effect of enzymatic treatment was retained in the case of peroxide bleaching. The enzymatic preparations studied are promising for the development of chlorine-free pulp bleaching technologies.     

Trichoderma reesei cellulases in the bleaching of kraft pulp

In this work the effects of individual purified cellulases of Trichoderma reesei were studied in the enzyme-aided bleaching of kraft pulps. The cellobiohydrolases I and II, when used alone, had no positive effect on the bleachability of kraft pulps. The endoglucanase I (EG I), however, acted on pulp similarly to xylanases and with an enzyme dosage of 0.1 mg/g a clear increase in pulp brightness could be observed. Due to the unspecificity of this enzyme, the viscosity of the pulp was simultaneously decreased. Of the cellulases, EG II was clearly most detrimental in reducing the pulp viscosity. Hence, the action of purified cellulases of T. reesei on pulp as a substrate differs profoundly, and all cellulases are not detrimental to the pulp properties. Correspondence to: J. Buchert     

Comparative study on application of T.lanuginosus SSBP xylanase and commercial xylanase on biobleaching of non wood pulps

Biobleaching of three non wood kraft pulps (bagasse, rice straw and wheat straw) by Thermomyces lanuginosus SSBP xylanase and commercial xylanase (cartazyme sandoz), was studied in order to investigate their potential and effect on their various properties (reduction sugars, chlorine dioxide, kappa number, brightness and chromophores). In generally, xylanases released chromophores and reducing sugars and decreased kappa number of pulps. These samples gained over six brightness points over controls. Biobleaching of rice straw pulp with xylanase cartazyme (Sandoz) produced chlorine dioxide savings of up to 25% or 3.5-4 kg chlorine dioxide/ton pulp.     

New polyoxometalate–laccase integrated system for kraft pulp delignification

New polyoxometalate–laccase integrated system (PLIDS) employing polyoxometalate [SiW₁₁V^VO₄₀]⁵⁻ and laccase of Trametes versicolor for the continuous delignification of eucalypt kraft pulp has been developed. Pulp was delignified in a batch reactor containing catalytic amounts of [SiW₁₁V^VO₄₀]⁵⁻ at about 90 °C under atmospheric pressure. Re-oxidation of reduced polyoxometalate (POM) with laccase was carried out at 45 °C in a separate aerated bioreactor coupled with an ultrafiltration tubular ceramic membrane. This allowed the separation of laccase from re-oxidized POM, which was supplied in turn continuously to the delignification reactor.Proposed PLIDS allowed sustainable pulp delignification with minimal degradation of polysaccharides. The implementation of PLIDS, instead the fist chlorine dioxide stage (D) in conventional DEDED bleaching sequence, showed almost 60% of chlorine dioxide savings with strength properties of the bleached pulp (90% ISO) similar to those obtained after the conventional bleaching.     

Enzymatic bleaching of kraft pulp by xylanase from Aspergillus sydowii SBS 45

Crude xylanase from Aspergillus sydowii SBS 45 was tested for enzymatic bleaching of kraft (Decker) pulp. After optimization of three parameters, consistency of pulp, retention time and enzyme dose, considerable increase in the release of UV and visible absorbance spectra of materials and reducing sugars was observed, which clearly indicated the action of xylanase on pulp. Final brightness of pulp was increased from 29.42 to 70.42% and kappa number was reduced from 15.93 to 1.61, when 25 U of xylanase was given with a retention time of 5 h and at a consistency of 10%. When 10 U g⁻¹ xylanase was given, 14.3% elemental chlorine and 14.3% H₂O₂ could be reduced and when 25 U g⁻¹ xylanase was given 14.3% elemental chlorine and 28.6% H ₂O₂ could be reduced thereby retaining the brightness at control level.     

Arundo donax L. reed: new perspectives for pulping and bleaching. 5. Ozone-based TCF bleaching of organosolv pulps

Three selected alkali-based organosolv pulps (alkali-sulfite-anthraquinone-methanol (ASAM), alkali-anthraquinone-methanol (organocell) and ethanol-soda) from agrofibre crop giant reed (Arundo donax L.) were bleached by an ozone-based TCF (totally chlorine- free) bleaching sequence AZE(R)QP (where A is an acidic pulp pre-treatment, Z is an ozone stage, (E(R)) is an alkaline extraction in the presence of reducing agent, Q is a pulp chelating, P is a hydrogen peroxide stage) without oxygen pre-bleaching, and compared with a conventional kraft pulp used as a reference. The different response on bleaching conditions within each bleaching stage was noted for all tested pulps. The pulp bleachability, in terms of brightness improvement or lignin removal per unit of applied chemicals, was found higher for the organocell pulp. The ASAM and ethanol-soda pulps showed the highest bleaching selectivity, expressed by viscosity loss per unit of lignin removed or brightness improved. The overall bleaching results of organosolv pulps were superior to kraft.     

Effects of surfactants on the enzymatic bleaching of kraft pulp by xylanase

A xylanase was purified from a commercial crude xylanase, Pulpzyme HC, and used for the bleaching of kraft pulp in the absence or in the presence of nonionic surfactants, Tween 20, Tween 80, and Igepal C930. The purified xylanase has a molecular weight of 23,500 as determined by a reducing SDS-PAGE. Tween 20 was most effective to enhance the efficiency of the enzymatic bleaching of kraft pulp by xylanase.     

Assessment of various commercial enzymes in the bleaching of radiata pine kraft pulps

Four xylanase preparations that are commercially available, namely Cartazyme from Sandoz, Ecopulp from Alko-ICI, Irgazyme from Ciba-Genencor and Pulpzyme HB from Novo Nordisk, were tested in bleaching experiments of kraft pulps from Pinus radiata. The main objective of this study was to optimize a reduction in the consumption of chlorine dioxide in the bleaching sequences C₉₀/D₁₀E_oDED, C₇₀/D₃₀E_oDED and D₁₀₀EDED. Enzymatic treatments led to savings of ClO₂ between 3.5 and 3.9 kg per air-dried tons (ADT) in the three bleaching sequences, without affecting the target brightness of the pulps. In these assays, some minor although reproducible differences in the performance of the enzymes were observed. In most cases, xylanase treatment partially affected the beatability of the pulps, measured as the number of revolutions in the PFI mill required to reach the same tensile index as the respective controls.