Chlorine Dioxide Consumption Research Articles

Effect of pipe corrosion scales on chlorine dioxide consumption in drinking water distribution systems

Previous studies showed that temperature and total organic carbon in drinking water would cause chlorine dioxide (ClO 2) loss in a water distribution system and affect the efficiency of ClO 2 for Legionella control. However, among the various causes of ClO 2 loss in a drinking water distribution system, the loss of disinfectant due to the reaction with corrosion scales has not been studied in detail. In this study, the corrosion scales from a galvanized iron pipe and a copper pipe that have been in service for more than 10 years were characterized by energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The impact of these corrosion scale materials on ClO 2 decay was investigated in de-ionized water at 25 and 45 °C in a batch reactor with floating glass cover. ClO 2 decay was also investigated in a specially designed reactor made from the iron and copper pipes to obtain more realistic reaction rate data. Goethite ( α-FeOOH) and magnetite (Fe 3O 4) were identified as the main components of iron corrosion scale. Cuprite (Cu 2O) was identified as the major component of copper corrosion scale. The reaction rate of ClO 2 with both iron and copper oxides followed a first-order kinetics. First-order decay rate constants for ClO 2 reactions with iron corrosion scales obtained from the used service pipe and in the iron pipe reactor itself ranged from 0.025 to 0.083 min −1. The decay rate constant for ClO 2 with Cu 2O powder and in the copper pipe reactor was much smaller and it ranged from 0.0052 to 0.0062 min −1. Based on these results, it can be concluded that the corrosion scale will cause much more significant ClO 2 loss in corroded iron pipes of the distribution system than the total organic carbon that may be present in finished water.

Enhanced production of cellulase-free thermostable xylanase by Bacillus pumilus ASH and its potential application in paper industry

A very high level of cellulase-free, thermostable xylanase has been produced from newly isolated strain of Bacillus pumilus under submerged fermentation in a basal medium supplemented with wheat bran (2%, w/v) pH 8.0 and at 37 °C. After optimization of various production parameters, an increase of nearly 13-fold in xylanase production (5407 IU/ml) was achieved. The produced xylanase is stable in neutral to alkaline pH region at 70 °C. The suitability of this xylanase for use in the bioleaching of eucalyptus Kraft pulp was investigated. A xylanase dose of 5 IU/g of oven dried pulp of 10% consistency exhibited the optimum bleach boosting of the pulp at pH 7.0 and 60 °C after 180 min of treatment. An increase of 5% in brightness along with an increase of 21% and 28% in whiteness and fluorescence respectively, whereas 18% decrease in the yellowness of the biotreated pulp was observed. Enzyme treated pulp when subjected to chemical bleaching, resulted in 20% reduction in chlorine consumption and up to 10% reduction in consumption of chlorine dioxide. Also a reduction of about 16% in kappa number and 83% in permanganate number, along with a reduction in COD value and significant improvement in various pulp properties, viz. viscosity, tensile strength, breaking length, burst factor, burstness, tear factor and tearness were observed in comparison to the conventional chemical bleaching.

The impact of kappa number composition on eucalyptus kraft pulp bleachability

Consumption of chemicals during ECF bleaching of kraft pulp correlates reasonably well with kappa number, which measures with KMnO4 the total amount of oxidizable material in the pulp. However, the method does not distinguish between the oxidizable material in residual lignin and other structures susceptible to oxidation, such as hexenuronic acids (HexAs), extractives and carbonyl groups in the pulp. In this study an attempt is made to separate the main contributors to the kappa number in oxygen - delignified eucalyptus Kraft pulps and evaluate how these fractions behave during ECF bleaching using chlorine dioxide as the sole oxidant (DEDD sequence). Residual lignin and HexAs proved to be the main fractions contributing to the kappa number and chlorine dioxide consumption in ECF bleaching. Pulp bleachability with chlorine dioxide increases with increasing HexAs content of the pulp but chlorine dioxide per se does not react with HexAs. Reduction of pulp with sodium borohydride under conditions for removing carbonyl groups has no impact on bleachability. No correlation was found between the pulp of the extractive content and pulp bleachability. The removal of HexAs prior to ECF bleaching significantly decreases the formation of chlorinated organics in the pulp (OX) and filtrates (AOX) as well as of oxalic acids in the filtrates.

Effluent Loads From Different ECF Bleaching Sequences Used In Hardwood Kraft Pulp Bleaching

Effluent loads from different traditional and emerging ECF bleaching sequences were investigated. Oxygen delignified Eucalyptus camaldulensis and Acacia mangium kraft pulps having similar kappa number, ca 12.0 were used in this study. Different ECF bleaching sequences were compared with reference sequence, D 0 EopD 1 in terms of effluent load, such as AOX, COD and TOC. Depending on the nature of sequences 6.0 to 63.0% chlorine dioxide consumption was reduced and as a result the amount of AOX formation was also reduced. The effluent from sequences (DZ)EopD 1, DHTEopD1, AhotD0EopD1, Ahot(DZ)EopD1 and ZEopD1 showed marginally higher COD and TOC in comparison with reference sequence, D 0 EopD 1 . Sequences like, D 0 EopQ(PO) and (DZ)EopQ(PO) having (PO) instead D 1 of reference sequence reduced AOX in effluent substantially; but COD and TOC loads were increased. In all cases acacia gave marginally higher effluent loads compared to eucalyptus.

Enzymes improve ECF bleaching of pulp

The delignification efficiency of different laccase enzymes was examined on the eucalyptus Kraft pulp. The laccase enzyme from Trametes versicolor showing the highest delignification efficiency was selected and used in the elemental chlorine-free bleaching sequence for improving the pulp bleachability. A n appreciable reduction in chlorine dioxide consumption was also obtained. Further reduction in chlorine dioxide consumption was obtained when the same laccase treated pulp was subjected to an acid treatment after the extraction stage followed by the DE P D sequence. Elemental-chlorine free bleaching was also performed using the xylanase-laccase treated pulp. Xylanase treatment was incorporated to the laccase mediator system in the elemental-chlorine free bleaching both sequentially and simultaneously. The bleaching sequence DE P D followed and in both the cases, the reduction in chlorine dioxide consumption was greater in comparison to the control. The chlorine dioxide consumption was reduced further when xylanase-laccase treated pulp was given an additional acid treatment. The final pulp properties of the treated pulps were comparable to the control pulp.

Effect of Structural Features of Wood Biopolymers on Hardwood Pulping and Bleaching Performance

Industrial hardwoods such as Eucalyptus species, Betula pendula, and Acacia mangium required different chemical charges during kraft pulping and presented distinct profiles of polysaccharides removal. The corresponding kraft pulps showed different chlorine dioxide consumption during bleaching. Woods and corresponding kraft pulps were characterized by chemical methods, 1 H and 13 C NMR spectroscopy, X-ray diffraction analysis, and gel permeation chromatography. The ease of lignin degradation and dissolution was essentially determined by differences in the proportion of syringyl and guaiacyl units and in the degree of condensation. The bleaching response was shown to be related also to the content of β-O-4 structures in the residual lignin. The relative stability of xylans during the pulping was suggested to be associated with differences in structure and molecular weight. The higher retention of Eucalyptus xylans was attributed essentially to their peculiar structure, including 0-2-substituted uronic acid groups linked to other cell wall polysaccharides.

Xylanase production by fungal strains on spent sulphite liquor

Xylanase production by seven fungal strains was investigated using concentrated spent sulphite liquor (SSLc), xylan and D: -xylose as carbon substrates. An SSLc-based medium induced xylanase production at varying levels in all of these strains, with Aspergillus oryzae NRRL 3485 and Aspergillus phoenicis ATCC 13157 yielding activities of 164 and 146 U ml(-1), respectively; these values were higher than those obtained on xylan or D: -xylose with the same fungal strains. The highest xylanase activity of 322 U ml(-1) was obtained with Aspergillus foetidus ATCC 14916 on xylan. Electrophoretic and zymogram analysis indicated three xylanases from A. oryzae with molecular weights of approximately 32, 22 and 19 kDa, whereas A. phoenicis produced two xylanases with molecular weights of about 25 and 21 kDa. Crude xylanase preparations from these A. oryzae and A. phoenicis strains exhibited optimal activities at pH 6.5 and 5.0 and at 65 and 55 degrees C, respectively. The A. oryzae xylanolytic activity was stable at 50 degrees C over the pH range 4.5-10. The crude xylanase preparations from these A. oryzae and A. phoenicis strains had negligible cellulase activity, and their application in the biobleaching of hardwood pulp reduced chlorine dioxide consumption by 20-30% without sacrificing brightness.

Polyoxometalate-Catalyzed Oxygen Delignification of Kraft Pulp: A Pilot-Plant Experience

The results of the first pilot-scale kraft pulp oxygen bleaching catalyzed by polyoxometalate are presented. A modified heptamolybdopentavanadophosphate heteropolyanion (HPA) was used as the catalyst. Scale-up experiments clearly revealed the dependency of the pulp delignification rate on the mass- and heat-transfer phenomena showing a rate constant on the pilot equipment assay twice that on the laboratory reactor. The selectivity of the oxygen-catalyzed bleaching stage (OHPA) was higher than that of the conventional oxygen alkaline bleaching (O). Pilot trials demonstrated similar consumption of chlorine dioxide and the strength properties of pulps bleached by OHPADED and ODED sequences. The chemical oxygen demand, absorbable organic halogens, and toxicity of the effluent streams were assessed for each bleaching stage. No catalyst retention on fully bleached pulp was detected. The practical aspects of the eventual industrial application of polyoxometalate-catalyzed oxygen bleaching are discussed.

Kinetics of the First Chlorine Dioxide Bleaching Stage (D1) of a Hardwood Kraft Pulp

In the present work, kinetic studies were performed to investigate the first chlorine dioxide bleaching stage of a Eucalyptus globulus kraft pulp. The bleaching reaction can be described by an initial short but very fast step, followed by a slower step. The proposed model for the D1 stage is based on both the light absorption coefficient and the chlorine dioxide concentration. A set of two depletion factors for the chlorine dioxide concentration and for the light absorption coefficient was described as a function of temperature for the fast and short steps of the reaction. The longer and slower periods were described by a homogeneous model. A nonlinear relationship between the chlorine dioxide consumption and the decrease in the light absorption coefficient, which is dependent on the extent of delignification but independent of temperature, was also established. Moreover, a linear relationship between the upper brightness limit and the temperature was observed. The fit of the experimental results obtained for different temperatures, initial chlorine dioxide concentrations, and initial light absorption coefficients is very good, revealing the ability of the model to predict typical mill operating conditions.

Effect of Pulping Conditions on the ECF Bleachability of Eucalyptus globulus Kraft Pulps

The effect of Eucalyptus globulus wood kraft pulping conditions on the chlorine dioxide consumption in elemental chlorine free bleaching of pulps was investigated. When the pulping is extended (kappa number decreases), the bleachability [as (OXE/ton)/kappa number] is reduced, suggesting that residual lignin and other oxidizable unsaturated structures in pulp become less reactive as their content in the pulp decreases. For the same unbleached pulp kappa number, the increase in active alkali and sulfidity used in pulping improves bleachability, whereas the pulping temperature (150-170°C) does not affect the bleaching response. The increase in liquor-to-wood ratio has a detrimental effect on the bleachability. No clear correlation could be established between unbleached pulp brightness and its bleaching response. Overall, the results obtained show a good correlation between the integral of the relative reaction rate constant (H factor) used in the pulping and pulp bleachability, with a low H factor being beneficial to the bleaching response of the pulp.

Bleach boosting effects of purified xylanase from Thermomyces lanuginosus SSBP on bagasse pulp

Unbleached bagasse soda pulp was pretreated with a purified xylanase from Thermomyces lanuginosus SSBP under optimum conditions using various enzyme charges. The xylanase exhibited direct brightening abilities on bagasse pulp improving brightness by 1.5 points, however, kappa number decreased by 0.5 points. The purified enzyme, used at 150 U/g, enhanced brightness of DED-bleached pulp by 4.5 points whereas pretreatment at a charge of 5 U/g pulp brightened pulp by 2.6 points over control, indicating the high enzyme efficiency at low doses. No correlation between kappa number and brightness was observed during biobleaching. Chlorine dioxide consumption was reduced by 18% with xylanase-pretreated pulps while still maintaining brightness at the control level. Examination of pulp strength properties revealed negligible differences between the enzyme treated and control samples. Scanning electron microscopy revealed significant surface modification of bagasse pulp fibres without marked fibre disruptions.

Development of chlorine dioxide-related by-product models for drinking water treatment

Factorial experiments were conducted using source waters from seven drinking water treatment plants in Ontario, Canada to develop statistically based model equations capable of predicting chlorine dioxide consumption and chlorite and chlorate formation upon chlorine dioxide application. The equations address raw water quality and operational parameters including pH, temperature, chlorine dioxide concentration, reaction time and water organic content (as described by non-purgeable organic carbon×ultraviolet absorbance measured at 254 nm, NPOC×UV 254). Terms describing two-factor interaction effects were also included, improving the accuracy of the predictive equations in fitting measured response concentrations as evaluated through internal and external validations. Nearly 80% of the predictions for chlorine dioxide consumption and chlorite formation were observed to be within 20% of the measured levels. Over 90% of the predicted chlorate levels were within ±0.1 mg/L of the measured levels. Chlorine dioxide concentration and NPOC×UV 254 were key parameters when developing the predictive models.

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.

Effect of a novel enzyme on fibre morphology during ECF bleaching of oxygen delignified Eucalyptus kraft pulps

The use of a novel “xylanase A” enzyme was found beneficial in the elemental chlorine free (ECF) bleaching of oxygen delignified Eucalyptus kraft pulps. The application of the enzyme made possible production of fully bleached pulps with high brightness (89% ISO) and viscosities (above 800 cm 3/g), without elemental chlorine (XD n EpD and D n EpD sequences) at low chlorine dioxide consumption. As a result of the enzyme treatment, morphological changes such as cracks, flakes, filaments and peeling of the fibre cell wall were observed by SEM (scanning electron microscopy). These modifications of the fibre surface facilitated the access to the fibre cell wall for the successive bleaching with less chemicals.

Mechanism and kinetics of chlorine dioxide reaction with hydrogen peroxide under acidic conditions

AbstractThe reaction of chlorine dioxide with hydrogen peroxide was studied in a well stirred batch reactor in a pH range of 3.60 to 5.07, which is of interest for commercial chlorine dioxide bleaching of chemical pulp. The reaction rate was determined by following the consumption of chlorine dioxide and hydrogen peroxide and the formation of chlorite. The rate equation was established. It was found that the concentration dependencies of chlorine dioxide, hydrogen peroxide and hydroxide ion were all first‐order. A reaction mechanism compatible with the rate equation was proposed. Since it was found in previous work that chlorite in chlorine dioxide solution by the addition of small amount of hydrogen peroxide potentially led to a decrease in the formation of organically bound chlorine during chlorine dioxide bleaching, two methods were suggested to implement this technique in a bleach plant.

Chlorine dioxide delignification kinetics and eop extraction of softwood kraft pulp

AbstractA kinetic model for 100% chlorine dioxide delignification based on experimental data is presented. From the unbleached kappa number, chlorine dioxide charge and reaction time, the model predicts kappa, brightness and residuals after the first bleaching stage. The model consists of two ordinary differential equations representing the slow and fast reactions of lignin with chlorine dioxide. In addition we found that the relationship between the chlorine dioxide consumption and the kappa number decrease was linear in the range studied and independent of the unbleached pulp kappa number.

Purification and properties of xylanase A from alkali-tolerant Bacillus sp. strain BP-23.

Xylanase A from the recently isolated Bacillus sp. strain BP-23 was purified to homogeneity. The enzyme shows a molecular mass of 32 kDa and an isoelectric point of 9.3. Optimum temperature and pH for xylanase activity were 50 degrees C and 5.5 respectively. Xylanase A was completely inhibited by N-bromosuccinimide. The main products of birchwood xylan hydrolysis were xylotetraose and xylobiose. The enzyme was shown to facilitate chemical bleaching of pulp, generating savings of 38% in terms of chlorine dioxide consumption. The amino-terminal sequence of xylanase A has a conserved sequence of five amino acids found in xylanases from family F.

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 C 90 D 10 E o DED , C 70 D 30 E o DED and D 100EDED. Enzymatic treatments led to savings of ClO 2 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.

Kinetics of reactions of chlorine dioxide (OClO) in water—I. Rate constants for inorganic and organic compounds

The kinetics of chlorine dioxide consumption by a wide range of inorganic and organic compounds, including a comprehensive series of phenols, have been determined using conventional batch-type and stopped-flow methods. In all cases, the rate law was first-order in chlorine dioxide and first-order in substrate. The methods allowed us to determine second-order rate constants over a range from 10 −5 to 10 5 M −1s −1. Measured rate constants were high for nitrite, hydrogen peroxide, ozone, iodide, iron (II), and, whenever the pH was not very low, for phenolic compounds, tertiary amines, and thiols. Bromide, ammonia, structures containing olefinic CC double bonds, aromatic hydrocarbons, primary and secondary amines, aldehydes, ketones and carbohydrates were unreactive under conditions of water treatment. For substrates that are weak acids, such as phenols, or weak bases, the effect of pH on the reaction rate showed that the rate constants for the deprotonated compounds are much higher than those for the protonated species.

Chlorine dioxide as a post-disinfectant for Dutch drinking water

Chlorine dioxide has some important advantages over chlorine with respect to water quality (no formation of trihalomethanes, no impairment of taste and no odor) and stability when used for oxidation/disinfection of drinking water. In this paper, results are presented of experiments into the consumption and reaction kinetics of chlorine dioxide in a number of (drinking) waters in The Netherlands. It was found that chlorine dioxide consumption is related to the dissolved oxygen content (DOC) of the water and the reaction time. Water samples from a plant that applied ozonation and activated carbon filtration had a very low chlorine dioxide consumption. Other water quality parameters, including pH and CO 3 2−, did not have any influence on consumption. The temporary advised Dutch guideline of 0.2 mg l −1 (dosage) is sufficient for activated carbon treated water. For other Dutch drinking waters, however, none of the 0.2 mg l −1 chlorine dioxide remained after a reaction time of 10 min, as was also found for the water of Dutch pumping stations where chlorine dioxide is at present used for disinfection.