Total Chlorine Free Bleaching Research Articles

Optimization of Cellulose Extraction and TCF Bleaching from Olive Tree Pruning Residues by Box–Behnken Design

ABSTRACT In this work, we successfully produced Totally Chlorine Free (TCF) Bleached pulp from olive tree pruning residues using the soda-anthraquinone pulping method. TCF pulp bleaching was carried out using a chelating–hydrogen peroxide bleaching sequence. Box–Behnken design (BBD), as an experimental design for response surface methodology (RSM), was used to study the effects of the different operating conditions on the cellulose extraction and bleaching pulp and to find an optimum for each process. After pulping under optimum conditions, we obtain a yield of 28.84% for leaves and 44.18% for stems, with a kappa number of 19.74 for leaves and 36.87 for stems. Soda-anthraquinone pulps from olive tree pruning residues were then bleached with a TCF sequence, reaching a value of brightness of about 82 and a kappa number of 10.13 for leaves and 13.69 for stems. A morphological study was investigated using scanning electron microscopy (SEM), showing the raw material structures and the fiber surfaces after delignification and bleaching processes. Isolated cellulose under optimum conditions was characterized using Fourier transform infrared spectroscopy (FTIR) confirmed that cellulose amolecules were not removed using several chemical treatments both of delignification and bleaching stages.

Formic Acid Pulping and TCF Bleaching of Cassava Stalks

The formic acid (FA) pulping process is well-known for its advantage to overcome the problems caused by the presence of high silica and fines content of agriculture residues during pulping. In this context a new and unconventional raw material, cassava stalk was pulped using formic acid followed by treatment withperoxyformic acid (PFA) treatment was applied to the formic acid treated pulps at 800C for two hours.It was found that the FA/PFA process lowered pulp yield of cassava stalks when FA concentration was increased. The PFA pulping decreased the kappa number of the pulps. After the FA/PFA treatment of cassava stalks, the pulp yield reached 37- 42% with kappa number of 21-34 at different formic acid concentrations. FA/PFA pulp from cassava stalks did not show promising result in total chlorine free bleaching and final brightness reached only up to 54%. DUJASE Vol. 6 (2) 1-6, 2021 (July)

Spectral analysis and kinetic studies of enzymatic delignification of kraft wood pulp by xylanase

The traditional bleaching methods used chlorine as bleaching agent which produced large amount of chlorinated organic compounds including dioxins which are persistent environmental pollutants. The alternate methods using peroxides and enzymes were developed to achieve total chlorine free bleaching. The xylanase enzyme was used as bleaching agent in this study. The delignification study was performed to evaluate the optimum conditions required for obtaining minimum kappa number of the pulp to remove maximum lignin from the wood fibres. The interactions of various factors such as pulp consistency, enzyme dosage and temperature were studied. The best conditions for enzymatic bleaching obtained were 10% consistency, 50 IU of enzyme dosage and 52oC in the range studied. The predicative mathematical models were developed for enzymatic bleaching. The activation energy for xylanase delignification of paper pulp was 13.989kJ/mol. The significant functional groups in bleached pulp samples were analysed using Fourier transform infrared spectroscopy and the surface morphology of pulp fibres was studied using Scanning electron microscopy images.

Utilization of sarkanda for making pulp and paper using elemental chlorine free and total chlorine free bleaching processes

A lignocellulosic non-wood material sarkanda available in abundance as waste, was evaluated for chemical constituents, pulping behavior, morphological properties, bleaching behavior and paper handsheet strength properties. Present study reveals that sarkanda contains cellulose 36.2 ± 0.5 %, hemicelluloses 35.2 ± 0.41 %, lignin 21.2 ± 0.22 % and ash 8.2 ± 0.3 %. Soda-anthraquinone pulping of sarkanda using 15 % active alkali resulted in unbleached pulp with 14.7 kappa number, 16.0 cP viscosity and 54.6 % pulp yield. With use of elemental chlorine free bleaching sequence, OD0EOPD, final bleached pulp achieved 85.7 % ISO brightness, whereas, using total chlorine free bleaching sequence, OZEOPPOPO, the brightness obtained was 81.9 % ISO. Elemental chlorine free bleached sarkanda pulp had tensile index of 39.4 N m/g, burst index of 3.4 kN/g and tear index of 5.7 mN m2/g. The study exhibits that sarkanda has potential to be utilized for papermaking. Such approach of using non-wood raw material with elemental chlorine free bleaching and total chlorine free bleaching sequences for papermaking can be a valuable approach for reducing pollutants generation, utilization of waste biomass and fulfillment of fibrous raw material requirement for paper industry.

Effects of Caustic Extraction on Properties of Viscose Grade Dissolving Pulp

Viscose, a cellulose-based commodity fibre, is produced by pulping and bleaching of wood, yielding a high quality “dissolving pulp” which is then spun. During pulping and bleaching, effective hemicellulose extraction is required to allow fibre production. We present a design of experiments (DoE) approach to optimise caustic extraction in a total chlorine free (TCF) bleaching sequence (O-CE-Z-P) of beech wood sulphite pulp. Temperature and sodium hydroxide concentration were varied to identify highest xylan extraction yield, and a maximum xylan removal of 83% was achieved at 20 °C and 120 g/L NaOH. Additionally, caustic extraction conditions were derived from the DoE model that led to pulps with high yield, high alpha cellulose content or uniform cellulose molecular weight distribution. Pulps from verification experiments exhibited good reactivity in viscose application tests. Hence, the presented O-CE-Z-P bleaching sequence can be considered as suitable for integrated viscose fibre production. We assume that the presented caustic extraction model will be useful for pulp and biorefinery researchers who work on caustic biorefinery processes involving hardwood feedstocks.

Antagonistic, synergistic and interaction effects of process parameters during oxygen delignification of Melia dubia kraft pulp

Melia dubia is a recently identified hardwood for papermaking. This study reports oxygen delignification of its kraft pulp. Modeling of O2 delignification was done implementing central composite design taking temperature, time and NaOH charge as process parameters while pulp yield, kappa number, intrinsic viscosity and brightness were the process outputs. The high precision quadratic models developed for O2 delignification revealed antagonistic, synergistic and significant interaction effects between temperature, time and NaOH charge. The optimum values of process parameters estimated were 90 °C, 90 min and 1.39% respectively which gave pulp yield 96.64%, total kappa number 10.52, intrinsic viscosity 628.54 cm3/g and brightness 42.52% which were very much comparable to other papermaking raw materials. On the whole, the optimization desirability obtained for O2 delignification was 0.621. The overall O2 delignification efficiency based on the total kappa number and the true lignin kappa number was found to be 30.33% and 38.23% respectively. The O2 delignification practiced in this investigation led to 10.42% increase in brightness and 19.93% reduction in viscosity which would prove advantageous for subsequent elemental and total chlorine free bleaching.

Modelling and optimization of the last two stages of an environmentally-compatible TCF bleaching sequence

A totally chlorine free (TCF) bleaching sequence was studied for an acid sulfite pulp mill that produces dissolving pulps. Laboratory analyses of the last two bleaching stages, an oxidant-reinforced alkaline extraction stage (EOP), and a subsequent pressurized peroxide with oxygen stage (PO), were performed on a eucalypt pulp that had been delignified by an ozone (Z) stage in the pulp mill. The goal was to predict the optimal costs and operational conditions for the (EOP)(PO) partial bleach sequence for three different specialty pulp products. Four independent variables affecting the pulp quality properties were examined for each stage (i.e., reaction temperature, reaction time, NaOH dosage and H2O2 dosage). The dependent variables were various pulp properties, such as intrinsic pulp viscosity, alpha-cellulose content, kappa number, and GE brightness. Three scenarios were considered to optimize the bleaching process, which related to a regenerated cellulose product (viscose) that is widely commercialized, and to two novel products (nanocrystalline cellulose (NCC) and nanofibrillated cellulose (NFC). Statistical response surface models indicated that the bleaching behavior of the ozone-treated pulp could be represented by second-order polynomial equations. These non-linear optimization models predict cost savings of 62.2%, 73.4%, and 63.3% for producing viscose, NCC, and NFC pulp grades, respectively.

A new era of straw-based pulping? Evidence from a carbon metabolism perspective

Abstract Straw pulping plays a vital role in virgin pulp supply and regional agricultural residue utilization. However, a significant decrease in its production has been observed. From an environmental perspective, why has there been a sharp decrease in straw pulping? Are there any innovations in straw pulp production that alleviate the heavy environmental burdens of straw pulping? In this study, factors contributing to the decrease in straw pulp are examined. An innovative technique to produce straw pulp is introduced and its environmental performance is analyzed and compared with conventional pulping. The results show that the main reasons contributing to the environmental burdens of straw pulping lie in the difficulties in black liquor extraction and alkaline recovery for the black liquor. Technical processes are changed in the innovative technique of straw pulping through using a rapid displacement cooking process, converting black liquor into fertilizers, utilizing total chlorine-free bleaching, etc. The new technique (Case B) achieves superior environmental performance than that of the conventional technique (Case A) from a carbon metabolism perspective. Specifically, 1022.90 kg and 857.80 kg of biogenic-carbon (bio-carbon), and 594.32 kg and 628.13 kg of fossil-carbon are needed to make 1 ton of bleached straw pulp for Case A and Case B, respectively. The carbon efficiencies for Case A, Case B (when pulp is the only desired product) and Case B (when including other products) are 39.10%, 46.63% and 92.21%, respectively. The carbon factors for Case A, Case B (when pulp is the only desired product) and Case B (when including other products) are 3.66, 3.60 and 1.86 kg CO2-eq, respectively. In addition, the corresponding E factors, which reflect the waste generation level, are 3.20, 2.69, and 1.39 kg, respectively. The new technique for straw pulping, which follows the principle of a circular economy by fully utilizing resources and reducing the generation of waste, achieves both economic and environmental benefits. It is a promising technique for straw pulping.

Assessment of physical properties of self-bonded composites made of cellulose nanofibrils and poly(lactic acid) microfibrils

Cellulose nanofibrils and poly(lactic acid) microfibrils, two bio-based polymers were used to elaborate composite films, and their properties were evaluated. Cellulose nanofibrils were obtained from organic pulping with total chlorine-free bleaching and were manufactured using high-pressure homogenization; while poly(lactic acid) microfibrils were obtained from a commercial partner. Morphological aspects of cellulose nanofibrils were assessed by atomic force microscopy showing traditional morphology for the elaborated nanofibrils, as well as the effects of sonication on the poly(lactic acid) microfibrils. Self-bonded composite films with different compositions were fabricated by hot pressing following methodologies previously reported. Uniaxial tensile stress was measured with a universal testing machine showing a decrease in most mechanical properties because of the low interactions between cellulose nanofibrils and polylactide microfibrils. Water vapor permeability was evaluated with a thermohygrometer and surface energy with the sessile-drop contact angle method these results showed good values for printing and gluing, with surface free energies ranging between 27 and 60 m Nm−1. Furthermore, industrial standards for paper-like materials and thermal properties of the composites were also analyzed of which it is to highlight the good bending strength as well as the concurrence of the results of Parker Print Surface tests with those of water contact angle.

Environmental Aspect of Using Chlorine Dioxide to Improve Effluent and Pulp Quality During Wheat Straw Bleaching

This paper illustrates the need of using the agro waste (wheat straw) as a substitute for forest products in paper industry. It aims on using the soda-AQ pulping process for converting waste to fibrous pulp. Further, it emphasizes on use of chlorine dioxide in place of elemental chlorine and hypochlorite during bleaching with aim of reducing the wastewater load and improving the pulp quality. Complete chemical characterization of wheat straw was performed. The soda-AQ (anthraquinone) method was opted for cooking and to make a pulp of kappa number 13. The pulp was bleached with elemental chlorine and calcium hypochlorite based sequences. To study the impact of adding chlorine dioxide on paper properties and effluent quality, elemental chlorine and hypochlorite were replaced with dioxide. The total elemental chlorine free bleaching sequence was also studied. The hand sheets were prepared to analyze the bleached and unbleached pulp properties using standard methodology. The effluent quality was studied by measuring the properties COD, BOD, TDS, TSS, TS, colour, lignin and adsorbable organic halides. Proximate chemical analysis of wheat straw showed that it contains holocellulose 67.3 ± 0.16%, hemicelluloses 39.2 ± 0.7%, cellulose 34.2 ± 0.9%, lignin content 14.9 ± 0.09% and ash 9.2% that mainly composed of silica (7.7%). With soda-AQ process a pulp with 53% yield and good strength properties was obtained. The bleached pulp of chlorine dioxide based sequences was having better strength properties in comparison to chlorine based sequences. Total replacement of elemental chlorine with chlorine dioxide reduced the BOD (52%), COD (49%), colour (43%), lignin (57%) and AOX (63%). Research concluded that wheat straw can be utilized by paper mills to combat the problem of waste management, air pollution due to its burning and issues of raw material for papermaking. Soda-AQ pulping method was found to be effective for preparing the wheat straw pulp. Use of elemental chlorine free bleaching may prove to be a reliable approach for better environmental management with high pulp characteristics.

Production of cellulose nanoparticles from blue agave waste treated with environmentally friendly processes

Tequila elaboration leaves two main byproducts that are undervalued (bagasse and leaves). Organosolv pulping and Total Chlorine Free bleaching were integrated to obtain cellulose fibers from agricultural waste which consisted of blue agave bagasse and leaf fibers; together they represent a green process which valorizes biomass waste. The obtained celluloses were characterized by FT-IR, colorimetry, and SEM and their extraction yields were evaluated. These celluloses were used to produce cellulose nanocrystals and cellulose nanofibers. First, an acid hydrolysis was performed in a sonication bath to induce cavitation during the reaction to produce cellulose nanocrystals. Then a high-pressure homogenization was selected to produce cellulose nanofibers. These nanocelluloses were characterized by powder XRD, Nanosizer, zeta potential, NMR, and electronic microscopy. Results showed that cellulose from organosolv pulps bleached with TCF bleaching is suitable for nanocellulose production. Moreover, the use of a new step to separate cellulose nanocrystals resulted in yields almost doubling traditional yields, while the rest of the properties remained within the expected.

Environmentally Friendly Bleaching on Bamboo (Neosinocalamus) Kraft Pulp Cooked by Displacement Digester System

The bleaching of pulp prepared by a displacement digester system (DDS) for displacement cooking of bamboo (Neosinocalamus) was established by comparing the results from elemental chlorine-free (ECF) bleaching and totally chlorine-free (TCF) bleaching. This process produced the optimal performance of obtained pulp via O-D0-EOP-D1 bleaching, where the Kappa number of DDS pulp was 18 to 22, and the Kappa number of oxygen delignified pulp was 10 to 12. The brightness of the obtained pulp was over 86% ISO, the yield was up to 46%, and the viscosity was approximately 800 mL·g-1. In contrast, O-Q-P1-P2 bleaching was advantageous for pulp with kappa number less than 5 after oxygen delignification. The brightness of obtained pulp was up to 81% ISO, the yield was over 40%, and the viscosity was about 650 mL·g-1. In TCF bleaching, the water consumption was 20 m3·t-1, the chemical oxygen demand (COD) content was 30 kg·t-1, and the absorbable organic halogen (AOX) content was zero. The water consumption of ECF bleaching was 4 times that of TCF bleaching, while the COD content was 16 kg·t-1 and the AOX content was 2 kg·t-1.

EFFECTS OF TOTAL CHLORINE FREE (TCF) BLEACHING ON THE CHARACTERISTICS OF CHEMI MECHANICAL (CMP) PULP AND PAPER FROM MALAYSIAN DURIAN (DURIO ZIBETHINUS MURR.) RIND

The effects of bleaching process on the characteristics of pulp and paper produced from durian rind under chemi‑mechanical pulping (CMP) method were investigated. All process and characteristic tests were conducted according to Malaysian International Organisation for Standardization (MS ISO) and Technical Association of the Pulp and Paper Industry (TAPPI). Three (3) stages of peroxide (P‑P‑P) bleaching sequence through the Total Chlorine Free (TCF) bleaching process were applied to the unbeaten and unbleached durian rind CMP pulp. Bleached CMP durian rind pulp drainage time (32s) decreased (faster) and CSF freeness level (172.50ml) increased as compared to a control pulp. It was obtained that overall optical (brightness (66.36 %)) and mechanical characteristics (tensile index (38.33 Nm/g), tearing index (7.56 mN.m2/g), bursting index (2.42 kPa.m2/g), and number of folds (43)) of durian rind CMP 60 gsm paper sheet improved as the TCF bleaching process was applied to the unbleached CMP durian rind pulp.

Lignin valorization from side-streams produced during agricultural waste pulping and total chlorine free bleaching

Blue agave biomass (bagasse and leave fibers) was subjected to an organosolv pulping process along with a total chlorine free bleaching sequence to obtain cellulose for nanocellulose production. In this work, black liquors were collected after each pulping and bleaching stages, isolating lignin by selective precipitation. Physico-chemical characterization of the different samples was accomplished. Higher yields in lignin extraction are achieved from bagasse than from leaves. High recovery lignin yields could be achieved (∼90% for bagasse and ∼75% for leaves. As it was expected, the lignin extraction yields were reduced as bleaching sequence went on. An exhaustive physico-chemical characterization of all the samples was accomplished. The purity of the lignins, referred to the acid insoluble and soluble lignins, were lower for the bleaching stages, but remained with a purity level higher than 75% for every sample, which is a good purity level compared to lignin from other feedstock, and higher than 85% for the lignin from organsolv stage regardless of its source and being always higher for organsolv lignin than leaves ones. The molecular sizes of lignin samples were also measured. Chemical analysis was effected through Fourier transform infrared spectroscopy, nuclear magnetic resonance and pyrolysis, establishing in this way the chemical structure of the different lignins. Thermal properties were evaluated demonstrating by this the potential of valorization of lignin as part of an integrated biorefinery process. Bagasse lignins presented higher yield, purity and even better conditions in some case to be use in an integrated biorefinery.

Preparation and Fundamental Characterization of Cellulose Nanocrystal from Oil Palm Fronds Biomass

The objective of this work was to isolate cellulose nanocrystal (CNC) from oil palm fronds (Elaeis guineensis) and its subsequent characterization. Isolation involves sodium hydroxide/anthraquinone pulping with mechanical refining followed by total chlorine free bleaching (includes oxygen delignification, hydrogen peroxide oxidation and peracetic acid treatment) before acid hydrolysis. Bleaching significantly decreased kappa number and increased α-cellulose percentage of fibers as confirmed by Technical Association of the Pulp and Paper Industry standards. Transmission electron microscopy (TEM), X-ray diffraction, Fourier transform infrared spectroscopy and thermogravimetric analysis revealed that acid hydrolysis along with bleaching improved crystallinity index and thermal stability of the extracted nanocrystals. It was observed that CNC maintained its cellulose 1 polymorph despite hydrolysis treatment. Mean diameter as observed by TEM and average fiber aspect ratio of obtained CNC was 7.44 ± 0.17 nm and 16.53 ± 3.52, respectively making it suitable as a reinforcing material for nanocomposite.

Preparation of dissolving pulp from oil palm empty fruit bunch by prehydrolysis soda-anthraquinone cooking method

This study aimed to investigate the production of dissolving pulp (DP) from empty fruit bunch (EFB) of oil palm (Elaeis guineensis) as a non-wood material using a combination of prehydrolysis, soda-anthraquinone (AQ) cooking, and elementary chlorine-free (ECF) or totally chlorine-free (TCF) bleaching. Prehydrolysis was performed for 90–180 min at 150 °C. Subsequently, the prehydrolyzed EFB was subjected to several soda-AQ cooking conditions with active alkali (AA) dosages of 19, 20, and 21 % at 160 °C. The obtained pulps were bleached following ECF and TCF sequences with oxygen (O), chlorine dioxide (D0), extraction with peroxide (Ep), chlorine dioxide (D1), and peroxymonosulfuric acid (Psa) stages. The results showed that the optimal duration of the prehydrolysis was 180 min, while the best AA dosage of the soda-AQ cooking was 20 %. The determination of pulp qualities showed that ECF bleaching with the Psa–D0–Ep–D1 sequence reached 90.7 % ISO brightness, 8.5 cP viscosity, 98.6 % α-cellulose, and that TCF bleaching with the O–Psa–Ep–Psa–E sequence attained 81.6 % ISO brightness, 9.6 cP viscosity, and 95.9 % α-cellulose. The results indicated a promising potential of EFB for DP production.

Total Chlorine-Free Bleaching ofPopulus deltoidesKraft Pulp by Oxone

Since the bleaching process is one of the most important environmental pollutant stages in the pulp and paper industry, here, the total chlorine-free (TCF) bleaching of poplar kraft pulp by applying Oxone and peroxide under alkaline conditions has been investigated. The pulp samples were bleached in two stages of Oxone (OX) treatment using an AOX1OX2sequence (A: acid pretreatment), and then the treated pulps were bleached by peroxide (P) to achieve target brightness (about 80%). The influence of various reaction parameters such as alkali charge, temperature, reaction time, and bleaching agent dosage was optimized. The final achieved brightness was more than 78%. Accelerated aging experiments showed more stability in brightness for the Oxone treated pulp, because alkali Oxone bleaching stops thermal degradation. Similarly, the AOX1OX2P bleaching sequence was found to be effective in regaining some strength that had been lost during acidification of the pulp. Improvement in pulp strength made with acid treatment was achieved along with significant amount of lignin removal and it demonstrates the feasibility of Oxone in TCF bleaching. Furthermore, other results indicated the feasibility of Oxone bleaching as an environmentally favorable alternative TCF bleaching sequence, compared with elemental chlorine-free bleaching approaches and also other TCF bleaching sequences.

Application of peroxymonosulfuric acid as a modification of the totally chlorine-free bleaching of acacia wood prehydrolysis-kraft pulp

The totally chlorine-free (TCF) bleaching process avoids the generation of organochlorine substances. In this study, the application of peroxymonosulfuric acid (H2SO5: Psa) to TCF bleaching was proposed as a modification of the bleaching process of hardwood prehydrolysis-kraft pulp. Acacia mearnsii pulps were treated by oxygen bleaching, followed by Psa treatment, ozone bleaching, alkali extraction, and finally, hydrogen peroxide bleaching. The Psa treatment was conducted with 10 % pulp consistency at pH 3 and 70 °C. The use of Psa increased the removal of hexenuronic acid from the pulp and improved pulp brightness. After the final hydrogen peroxide bleaching, pulp brightness increased to 86.0 % ISO with a 0.6 % Psa dosage. The Psa treatment showed better selectivity, i.e., kappa number decrement per unit of viscosity, compared with ozone bleaching. A dosage of 0.2 % Psa afforded a 3.4 kappa number decrement with a 10.9 cP viscosity loss, while ozone treatment with a dosage of 0.5 % resulted in a 2.6 kappa number decrement with a 12.5 cP viscosity loss. The results showed that the Psa treatment can enhance pulp quality in terms of brightness and reduce ozone consumption, which improves the TCF bleaching process.

Evolution of Lignocellulosic Macrocomponents in the Wastewater Streams of a Sulfite Pulp Mill: A Preliminary Biorefining Approach

The evolution of lignin, five- and six-carbon sugars, and other decomposition products derived from hemicelluloses and cellulose was monitored in a sulfite pulp mill. The wastewater streams were characterized and the mass balances throughout digestion and total chlorine free bleaching stages were determined. Summative analysis in conjunction with pulp parameters highlights some process guidelines and valorization alternatives towards the transformation of the traditional factory into a lignocellulosic biorefinery. The results showed a good separation of cellulose (99.64%) during wood digestion, with 87.23% of hemicellulose and 98.47% lignin dissolved into the waste streams. The following steps should be carried out to increase the sugar content into the waste streams: (i) optimization of the digestion conditions increasing hemicellulose depolymerization; (ii) improvement of the ozonation and peroxide bleaching stages, avoiding deconstruction of the cellulose chains but maintaining impurity removal; (iii) fractionation of the waste water streams, separating sugars from the rest of toxic inhibitors for 2nd generation biofuel production. A total of 0.173 L of second-generation ethanol can be obtained in the spent liquor per gram of dry wood. The proposed methodology can be usefully incorporated into other related industrial sectors.

Production practice of total chlorine free clean bleaching bagasse pulp

The experimental research, process design and production practice of total chlorine free OpQPo bleaching bagasse pulp were introduced in this paper. The results showed that Kappa number decreased from 14.0-15.0 to 7.0-7.3 with a 50%-51% removal of residual lignin, and pulp brightness increased from 42%-45%(ISO) to 58%-60%(ISO) after a strengthened oxygen delignification. The production practice showed a better performance than that in lab. After subsequent pretreatment and pressurized hydrogen peroxide bleaching, the final pulp brightness was beyond 80% and the viscosity was over 800 mL/g. The pulp quality was much better than traditional Chlorine-Alkali Extraction-Hypochlorite(CEH) bleached pulp. Moreover, adsorbable organic halides (AOX) was not generated any more in the bleaching process. The wastewater was only discharged in chelating pretreatment (Q) stage and easily treated to meet the critical discharge standard due to its lower chromaticity and lower pollution load. In contrast to the traditional bleaching, no additional investment was needed in this new technology. Besides, the production procedure was flexible and the operation was stable. The investment of main equipments was about ¥13.55 million yuan.