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.     

Hydrogen Peroxide and Sodium Perborate Bleaching of Pulp from Olive Tree Residues

This paper will consider the influence of the operating conditions used in the hydrogen peroxide bleaching (concentration 1–5 % and process time 30–210 min) and sodium perborate bleaching (sodium perborate concentration 1–5 %, hydrogen peroxide 0–2% and process time 60–180 min) of olive wood trimmings pulp on the yield, kappa index and viscosity of the resulting pulp, and on strength related properties of paper sheets (stretch index and burst index) in order to determine the best bleaching conditions of this pulp. Medium to low hydrogen peroxide concentrations (1–3 %) and a high operation time (210 min) were desired in the bleaching of pulp. A high sodium perborate concentration and hydrogen peroxide concentration (5 % and 2 % respectively) and medium to low operation time (60–120 min) were desired for the sodium perborate bleaching. A comparison of both bleaching agents, under similar or under optimum operating conditions, revealed that sodium perborate bleaching results in lower brightness, a higher kappa index and also higher viscosity than hydrogen peroxide bleaching. Moreover, both provided similar stretch index and burst index values for sodium perborate bleaching with respect to hydrogen peroxide bleaching.     

Role of various enzymes for deinking paper: a review

Paper manufacturing industries depend mainly on forests for wood, which is the basic raw material. Forest plays an important role in balancing the ecosystem to protect forest deinking and bleaching (recycling) of waste paper had gained a lot of importance. Conventional chemical deinking processes require large amount of chemicals which are toxic and hazardous to the environment, hence other effective deinking methods are needed. Enzymatic deinking (cellulolytic, hemicellulolytic and ligninolytic) has attracted enormous attention because of high efficacy and minimum environmental impact. For bleaching, enzymatic action (individual as well as in combination), along with physical treatment, makes the pulp more accessible to the chemicals and also to the amount of chemicals required to obtain similar levels of brightness. Strength properties and brightness of the pulp are improved by these treatment methods. With minimum impact on the environment, this review gives comprehensive information about the various methods used for the recycling of waste paper.     

TCF mill trial on softwood pulp with Korsäs thermostable and alkaline stable xylanase T6

Abstract: Use of hemicellulases, including xylanases, for delignification in the paper industry has been slowed down by the lack of large-scale availability of enzymes which are active at a high pH (above 8) and a high temperature (above 60°C), conditions prevailing in many bleaching processes. During the past years, acidic or neutral hemicellulases, working at temperatures below 60°C, were used in most mill experiments. The Korsäs T6 xylanase from Bacillus stearothermophilus , which is active at a pH above 9.0 and at a temperature above 65°C, was produced on a large scale in collaboration with Gist-brocades and was employed on a full scale mill trial to produce a Total Chlorine chemical-Free (TCF) pulp from softwood. The bleaching sequence used was (OO)BQQPP. where O stands for oxygen delignification. B for the enzymatic treatment, Q for the chelating agent step and P for the hydrogen peroxide step. The enzyme bleaching step was performed during a period of 4 h at 63 ± 1°C and pH 8.7 ± 0.1. The results of the mill trial show that the TCF pulp produced had a brightness of 78% ISO and, at the same time, it preserved the same strength properties as chlorine dioxide-bleached pulp. The saving of hydrogen peroxide was 20%. The results on brightness, strength and chemical saving of this first full scale trial with T6 xylanase indicate that, after optimization, a TCF bleaching sequence including an enzymatic step with a xylanase working at a high pH and a high temperature, such as T6 xylanase, can be used to produce a high-strength bleached pulp. The advantages of a high pH and a high temperature enzymatic bleaching step are discussed.     

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.     

Biobleaching of wheat straw pulp with recombinant laccase from the hyperthermophilic <Emphasis Type="Italic">Thermus thermophilus</Emphasis>

The recombinant laccase from Thermus thermophilus was applied to the biobleaching of wheat straw pulp. The best bleaching effect was when the pulp was treated with 3 U laccase g⁻¹ dry pulp at 90°C, pH 4.5, 8% consistency for 1.5 h. Under these conditions, the pulp brightness was increased by 3.3% ISO, and the pulp kappa number was decreased by 5.6 U. Enzymatic treatment improved the bleachability of wheat straw pulp but caused no damage to the pulp fibers. The use of enzyme-treated pulp saved 25% H₂O₂ consumption in subsequent peroxide bleaching without decreasing the final brightness. Pulp biobleaching in the presence of 5 mM ABTS further increased the pulp brightness by 1.5% ISO. This is the first report on the application of laccase from T. thermophilus in the pulp and paper sector.     

Potential of xylanase from thermophilic Bacillus sp. XTR-10 in biobleaching of wood kraft pulp

An extracellular xylanase produced under optimal conditions by a thermophilic strain of Bacillus sp. XTR-10 was evaluated for its potential application in biobleaching of wood kraft pulp. Spectrophotometric analysis showed considerable release of lignin derived compounds and chromophoric material by the xylanase treated pulp samples. Xylanase was found to be effective in the liberation of reducing sugars in the pulp filtrates with increment in enzyme dose and reaction time. Eight hours pretreatment with 40 IU of xylanase/g of dry pulp resulted in 16.2% reduction of kappa number with 25.94% ISO increase in brightness as compared to the control. The same treatment slightly lowered the tensile strength and burst index, however. Enzyme pretreatment of the pulp saved 15% active chlorine charges in single step and 18.7% in multiple steps chemical bleaching with attainment of brightness at the level of the control. These results indicate the potential of enzymatic pretreatment of pulp for reduction in environmental discharge of hazardous waste from the pulp and paper industry.     

模拟水生态系统及其在环境研究中的应用

随着70年代污染生态毒理学的发展,微宇宙作为评价化学品的环境影响的有力工具日益受到重视。由于从点源和非点源释放的化学物质可经直接或间接途径进入水生态系统,水生微宇宙在环境研究中的应用发展很快。早期的研究工作侧重于化学污染物在水环境的归宿。自70年代末以来,研究注意力逐渐集中于有毒物质在水生态系统内不同生物学组织水平上的生态学效应。本文分下列4个方面进行述评:(1)关于模拟生态系统的若干基本概念;(2)应用于环境研究的不同类型水生微宇宙;(3)尚有争议的若干问题;(4)水生微宇宙技术应用的新动向和展望。     

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.     

TCF bleaching of soda-anthraquinone and diethanolamine pulp from oil palm empty fruit bunches

The AOpAZRP bleaching sequence (A is an acid treatment, Op an oxygen and peroxide stage, Z an ozone stage, R a reductive treatment and P a peroxide stage) have been applied to oil palm empty fruit bunches (EFB) soda-anthraquinone and diethanolamine pulp. On similar Kappa numbers for the two types of pulp (14.2 and 17.3), paper from unbleached soda-anthraquinone pulp exhibited increased tensile index (25.8 Nm/g), stretch (2.35%), burst index (1.69 kN/g), tear index (0.50 mN m(2)/g) and brightness (60.6%) relative to paper for unbleached diethanolamine pulp; but the latter type of pulp exhibited higher viscosity (659 mL/g) than the former. Upon bleaching with the AOpAZRP sequence, diethanolamine pulp exhibited higher viscosity (783 mL/g), and the properties of the paper sheets were close to or even better to those from soda-anthraquinone pulp, namely: 22.2 vs 20.4 Nm/g tensile index, 1.30 vs 1.42 kN/g burst index, 0.71 vs 0.70 mN m(2)/g tear index and 71.3% vs 77.5% brightness. Therefore, the properties of paper from diethanolamine pulp evolved more favourably during bleaching than did those of paper from soda-anthraquinone pulp.     

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.     

Comparison of different fungal enzymes for bleaching high-quality paper pulps

Wild and recombinant hydrolases and oxidoreductases with a potential interest for environmentally sound bleaching of high-quality paper pulp (from flax) were incorporated into a totally chlorine free (TCF) sequence that also included a peroxide stage. The ability of feruloyl esterase (from Aspergillus niger) and Mn2+-oxidizing peroxidases (from Phanerochaete chrysosporium and Pleurotus eryngii) to decrease the final lignin content of flax pulp was shown. Laccase from Pycnoporus cinnabarinus (without mediator) also caused a slight improvement of pulp brightness that was increased in the presence of aryl-alcohol oxidase. However, the best results were obtained when the laccase treatment was performed in the presence of a mediator, 1-hydroxybenzotriazol (HBT), enabling strong delignification of pulps. The enzymatic removal of lignin resulted in high-final brightness values that are difficult to attain by chemical bleaching of this type of pulp. A partial inactivation of laccase by HBT was observed but this negative effect was strongly reduced in the presence of pulp. The good results obtained with the same laccase expressed in A. niger at bioreactor scale, revealed the feasibility of using recombinant laccase for bleaching high-quality non-wood pulps in the presence of a mediator.     

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.     

Effect of xylanases on peroxide bleachability of eucalypt (E. globulus) kraft pulp

Industrial eucalypt (E. globulus L.) kraft pulp was treated with two commercial xylanase preparations Ecopulp^® TX-200A and Pulpzyme^® HC (endo-1,4-β-xylanase activity; EC 3.2.1.8) and bleached by totally chlorine-free (TCF) three-stage hydrogen peroxide bleaching sequence, without oxygen pre-delignification. The effect of enzymatic stage on pulp properties and bleachability has been studied and compared with reference (control) pulps, processed without enzyme addition. The similar mode of enzymatic action was noted for both xylanase preparations. Final brightness of 86% ISO was achieved after complete bleaching. Direct bleaching effect caused pulp brightening (by 1.2–1.5% ISO) and delignification (by 7–10%) immediately after the enzymatic stage. The maximal bleach boosting was shown after the first peroxide stage and then diminished, despite the progressive increase in delignification over the control. The loss in efficiency of xylanase treatment by the end of peroxide bleaching was associated with specific behavior of xylan-derived chromophores, i.e., hexenuronic acids.     

Effect of oxygen, ozone and hydrogen peroxide bleaching stages on the contents and composition of extractives of Eucalyptus globulus kraft pulps

The effects of oxygen (O), ozone (Z) and hydrogen peroxide (P) bleaching stages on the composition and total amount of Eucalyptus globulus kraft pulp lipophilic extractives was studied. These bleaching stages led to the partial removal and to several oxidative transformations of fatty acids and sterols, the main lipophilic extractives found in the unbleached pulp. Unsaturated extractives were found to be partially degraded while saturated ones were, in general, stable. The oxygen and hydrogen peroxide bleaching stages were more effective than ozone in removing fatty acids from pulp, by dissolution in the liquid phase. On the other hand, the ozone stage was more effective in the oxidative degradation of sterols. Oxygen and hydrogen peroxide bleaching stages were also effective in sterols removal, but led to the formation of sterol oxidation derivatives, previously shown to be involved in the formation of pitch that accumulates in the bleaching filtrates.     

重组极耐热木聚糖酶和重组极耐热漆酶协同漂白麦草浆

利用来自海栖热袍茵的重组极耐热木聚糖酶XynB和来自嗜热栖热菌Thermus thermophilus HB27的重组极耐热漆酶Tth-laccase对麦草浆进行协同漂白。结果表明,当未漂浆经XL漂序处理(X:重组木聚糖酶用量20 U/g绝干浆,pH 5.8,温度90℃,浆浓8%,处理时间2 h;L:重组漆酶用量3 U/g绝干浆,pH 4.5,温度90℃,浆浓8%,处理时间1.5 h),可获得最佳漂白效果。与对照浆比较,XL处理使浆料白度提升11.5%ISO,卡伯值降低6.9。双酶协同处理在改善浆料可漂性的同时,对纸浆纤维强度无负面影响。在后续过氧化氢漂白段中,当漂终白度相近时,XL预处理浆可节省约50%H_2O_2消耗量。     

An Index of the Ecological Impacts of Water Toxics Emitted to Freshwater Ecosystems

We describe a composite freshwater Aquatic Toxicity Index (ATI) for chronic toxicity conditions that can be easily computed for a broad range of chemicals. The ATI expresses the potential toxic impact of chemicals on the ecosystem, scaling the potency of each chemical with respect to a reference compound (1,4 dichlorobenzene). It is based on a simple stochastic process model and a few inherent properties of each chemical, such as chronic toxicity, adsorption coefficient to sediments, and Henry's Law constant. Our goal is to provide a simple compartmental model for obtaining a rough quantitative assessment of the life-cycle environmental impact of life-cycle emissions inventory data.

To illustrate the potential of our approach we compare the ATI index, for a small set of chemicals, with comparable measures of freshwater aquatic ecotoxicity potential and freshwater sediment ecotoxicity potential obtained by others using the European-based impact assessment tool USES-LCA, which is based on a more elaborate fate and transport model. The rank correlation between the ATI and USES-LCA indices is greater than 0.85, showing surprisingly good agreement given the simple nature of our model. More analysis of the differences between ATI and the results of other models is needed, but these results suggest that our model may be useful for priority setting and meta-modeling applications.     

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.     

Differential and synergistic effects of xylanase and laccase mediator system (LMS) in bleaching of soda and waste pulps

AIMS: Investigation of waste pulps and soda pulp bleaching with xylanase (X) and laccase mediator system (LMS) alone and in conjunction (one after the other) (XLMS). METHODS AND RESULTS: Soda and different grades of waste pulp fibres [used for making three-layered duplex sheets - top layer (TL), protective layer (PL) and bottom layer (BL)] when pretreated with either xylanase (40.0 IU g(-1)) or LMS (up to 200.0 U g(-1)) alone and in combination (one after the other) (XLMS) exhibited an increase in release of reducing sugars [up to 881.0% soda pulp; up to 736.6% (TL), up to 215.7% (PL) and up to 198.0% (BL) waste pulp], reduction in kappa number [up to 17.6% soda pulp; up to 14.0% (TL), up to 25.3% (PL) and up to 10.9% (BL), waste pulp], improvement in brightness [up to 20.4% soda pulp; up to 23.6% (TL), up to 8.6% (PL) and up to 5.0% (BL), waste pulp] when compared with the respective controls. The usage of XLMS along with 15% reduced level of hypochlorite at CEHHXLMS/EHHXLMS bleaching stage reduced kappa number [5.5% soda pulp; 11.4% (TL), 7.9% (PL), waste pulp] and improved brightness [1.0% soda pulp; 0.9% (TL), 1.4% (PL) waste pulp] when compared with the controls. Scanning electron microscopic studies revealed development of cracks, flakes, pores and peeling off the fibres in the enzyme-treated pulp samples. These modifications of the fibre surface during enzymatic bleaching in turn indicated the removal of lignin and derived compounds from the fibre cell wall. CONCLUSIONS: The work describes synergistic action of xylanase with LMS for bleaching of waste and nonwood pulps for eco-friendly production of paper and thus reveals a new unexploited arena for enzyme-based pulp bleaching. SIGNIFICANCE AND IMPACT OF THE STUDY: The drastic improvement in pulp properties obtained after xylanase and LMS treatment would improve the competitiveness of enzyme-based, environmentally benign processes over chemicals both economically and environmentally.     

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