Chlorine Dioxide Substitution Research Articles

Applicability of Microbial Xylanases in Paper Pulp Bleaching: A Review

The pulp and paper industries are attempting to bring changes to the bleaching process to minimize the use of chlorine to satisfy regulatory and market demands. Xylanases offer a cost-effective way for mills to realize a variety of benefits in bleaching. One main benefit is reducing Adsorbable Organic Halides (AOX) discharge. This is achieved primarily by decreasing chlorine gas usage. Other benefits include eliminating chlorine gas usage in mills with high chlorine dioxide substitution levels and increasing the brightness ceiling (particularly for mills contemplating Elemental Chlorine Free (ECF) and Totally Chlorine Free (TCF) bleaching sequences and in mills using large amounts of peroxide or chlorine dioxide). These benefits are achieved in the long term when the enzymes are properly selected and integrated into the process. This review summarizes the application of xylanases in the bleaching of pulp, with emphasis on the mechanism and effects of xylanase treatment on pulp and paper and the factors affecting the bleaching process and its efficiency. Brightness gains of up to 1.4 to 2.1 units have been achieved with xylanase treatment with the reduction of chlorine consumption by 15.0%. Xylanase treatment can lower the AOX amount in filtrate by 25.0% as compared to references. The Chemical Oxygen Demand (COD) can be reduced by 85%.

Kraft ECF pulp bleaching: A review of the development and use of techno-economic models to optimize cost, performance, and justify capital expenditures

This work evaluates the findings of various research efforts and describes the development, use, and benefits of applying techno-economic models of different types to various production and bleach plant scenarios. During the late 1980s and early 1990s, researchers determined that bleach plants were releasing potentially significant quantities of chlorinated organics into receiving waters. This led to extensive research to develop bleaching chemicals to eliminate chlorine and hypochlorite from the bleaching sequence. Over time, 100% chlorine dioxide substitution for chlorine became the industry standard (today’s elemental chlorine free [ECF] bleaching), and research efforts shifted toward chemical optimization of the ECF bleaching sequence. Several delignification stage and brightening stage models were developed and refined for use in bleach plant simulations to optimize chemical performance. Advances in computing power and the availability of packaged spreadsheet and simulation programs likewise led to the development of detailed material and energy balance models of the bleach plants. These simulations are used to minimize bleaching and pulp production costs, and to assist engineers in the development of justifications for capital expenditures. These models have been used to predict operating conditions that could lead to or reduce scale formation. They have also been extensively used to predict environmental performance of both new and modified bleach plants.

Rapid Determination of HAAs Formation Potential of the Reaction of Humic Acid with Chlorine or Chlorine Dioxide

On the basis of gas chromatography (GC) coupled with a short capillary column and an electron capture detector (ECD), a simple and rapid method for the determination of five haloacetic acids(HAAs) in drinking water was developed by the optimization of derivation conditions and the modification of gas chromatographic program. HAAs formation potential (HAAFP) of the reaction of humic acid with chlorine was determined via this method. The major advantages of the method are the simplicity of chromatographic temperature program and the short run time of GC. Dichloroacetic acid(DCAA) and Trichloroacetic acid(TCAA), which were detected in the determination of HAAFP, were rapidly formed in the first 72 h of the reaction of humic acid with chlorine. HAAFP of the reaction of humic acid with chlorine increased with the increase in the concentrations of humic acid and chlorine. The average HAAFP of the reaction of humic acid with chlorine was 39.9 μg/mg TOC under the experimental conditions. When the concentration of humic acid was 4 mg/L, the concentration of HAAs, which were produced in the reaction of humic acid with chorine, may exceed MCL of 60 μg/L HAAs as the water quality standards for urban water supply of China and the first stage of US EPA disinfection/disinfection by-products (D/DBP) rule; when the concentration of humic acid was 2 mg/L, the concentration of HAAs may exceed MCL of 30 μg/L HAAs for the second stage of US EPA D/DBP rule. When humic acid was reacted with chlorine dioxide, only DCAA was detected with a maximum concentration of 3.3 μg/L at a humic acid content of 6 mg/L. It was demonstrated that the substitution of chlorine dioxide for chorine may entirely or partly control the formation of HAAs and effectively reduce the health risk associated with disinfected drinking water.

Waste minimization in a bleach plant

In this study a steady-state model was developed for a six stage bleaching system in a pulp and paper industry. A fortran source code was written to simulate the whole bleach plant. Different case studies were performed with the aim of decreasing the total amount of dissolved solids coming out from the six washers. Each stage of the sequence is composed of chemical additions and mixing, reaction in a retention tower, and washing. Unit operation models were formulated using mass balances on liquor, fibres, chromophores, chemicals and dissolved solids. In order to compare the simulation results with the mill data, Dalaman SEKA Pulp and Paper Mill bleaching unit was chosen. A good agreement between the simulation results and the mill data was achieved. In the case studies, the optimization of the process variables were performed in which the effects of retention tower operating temperature, residence time, consistency, bleaching liquor flow rate and the wash water flow rates in the washers were studied. Also, the effect of 100% chlorine dioxide substitution in the chlorination stage was analyzed. It was concluded that 100% chlorine dioxide substitution was the best way to decrease the amount of dissolved solids.

Elemental Chlorine Free Bleaching Impact on Metal Management

With the implementation of the Cluster Rule in the United States, all bleached grade kraft pulpmills required to meet stringent levels of absorbable organic halides in the effluent. The method most used to meet the absorbable organic halide levels was to convert to 100% substitution of chlorine dioxide in the predominately C or CD first stage. As mills substituted chlorine dioxide in the first stage the bleachplant, thereby converting to elemental chlorine free (ECF) bleaching, several key parameters were impacted. Two of these were that delignification in ECF was less than partial substitution of chlorine dioxide in the chlorine stage and secondly the increase in pH in the first stage did not give the level of metals solubility as compared to chlorine or CD bleaching. Metals management has become a significant issue in ECF bleaching as metals that previously had a minor influence in bleaching create issues with inorganic deposition and efficiency reduction of peroxide bleaching. Several operating conditions have been identified that when optimized, reduced the issues associated with scale development in various stages of the bleachplant.

Enhanced biological treatment of bleached kraft mill effluents — II. Reduction of mixed function oxygenase (MFO) induction in fish

Biological treatment studies with bleached kraft mill effluents (BKME) assessed the removal of hepatic MFO induction potency towards fish. Bench-scale activated sludge, facultative stabilization basin, and aerated stabilization basin processes were compared under conservative conditions of elevated sludge age and hydraulic retention times as well as moderate temperatures for the treatment of bleachery effluents from a modernized bleached kraft mill using oxygen delignification and 60% chlorine dioxide substitution. Optimized treatment for the removal of hard-to-degrade organics also consistently removed more than 85–90% of effluent-induced MFO activity of fish, based on laboratory bioassays. Follow-up mill-site pilot scale testing with an activated sludge treatment process in extended-aeration mode also demonstrated >90% reductions in the MFO induction potential of whole mill effluent. Characterization of various in-plant process waters sampled at the mill indicated that the softwood-line bleach plant was a major contributor (>70%) to the MFO induction potential of untreated and biologically-treated BKME.

Enhanced biological treatment of bleached kraft mill effluents — I. Removal of chlorinated organic compounds and toxicity

Laboratory-scale biological treatment studies with bleached kraft mill effluents assessed and optimized the removal of chlorinated organic compounds as well as aquatic and microbial toxicity. Three conventional biological processes, namely activated sludge and two stabilization basin treatment systems, were compared under conservative conditions of elevated sludge age (i.e. 15–25 days) and hydraulic retention times (i.e. 0.5–1 day and 15 days for the respective systems) as well as moderate temperatures for the treatment of softwood kraft bleachery effluents from a modernized mill using oxygen delignification and 60% chlorine dioxide substitution. Enhanced treatment performance was achieved with the optimized activated sludge, facultative stabilization basin and aerated stabilization basin processes as indicated by consistently high removals of conventional organic contaminants, polychlorinated phenolics (i.e. 85–93%), adsorbable organic halogen (i.e. 43–58%) and toxicity. The high level of polychlorinated phenolics removal was considered representative of an enhanced treatment capability for hard-to-degrade organics. The ultimate degree of biotreatability of various in-plant bleaching and non-bleaching process effluents from the kraft mill was also tested.

Evaluation of the extent of the oxidation reaction during chlorine bleaching of pulp

A modified method was developed to evaluate how much chlorine is consumed by the oxidation reaction during the chlorine bleaching process. This evaluation is, in principle, based on the sum of chloride produced during the chlorination stage (C-stage) and produced during alkali treatment of both the C-stage effluent and the chlorinated pulp. Results obtained by this method proved that about 50%–75% of chlorine was consumed by the oxidation reaction during chlorine bleaching, depending on the reaction condition of chlorination. Even under a reaction condition that is not favorable to an oxidation reaction (low pH), approximately three electrons were abstracted from one lignin structural unit by chlorine bleaching. This result provides additional evidence for our recent observation that lignin is extensively oxidized during chlorine bleaching even when pure chlorine without any chlorine dioxide substitution was used.

クロロホルム発生量に及ぼす漂白条件の影響

To estimate the amount of chloroform generation at kraft pulp bleaching plant, an evaluation method was developed. The effect of bleaching conditions on chloroform generation in the C-E-H -D sequence was investigated experimentally in our laboratory by the method. As for the amount of generation in chlorination, the influence of the pH was large, and it from alkaline pulp extraction, was ten times more than that from acidic pulp extraction. The proportion of chloroform generation at each bleaching stage was about 60% at hypochlorite stage, about 40% at chlorine stage, and trace amount at final chlorine dioxide stage. When several pulps were treated with chlorination and alkali extraction, a good relationship between chemical charge and chloroform generation was observed with some exception. Furthermore, on hypochlorite treatment, a good relationship was observed, too. These results introduced two equations between chemical charge and chloroform generation. Chloroform generation values at several bleach plants were estimated by these relative equations, and compared with measured values at these plants. In result, these were about equal or estimated values were higher with some exception. Thus, we think that the estimation of chloroform generation at bleach plant by these equations is possible. The reduction of carry over and chlorine dioxide substitution were effective on reduction of chloroform generation. We think these methods could be effective to reduce the chloroform production.

The Effect of Ambient Concentrations of Chlorate on Survival of Freshwater Aquatic Invertebrates

Abstract Chlorate (ClO3-) is present in some pulp and paper mill wastewater as a byproduct of the use of chlorine dioxide in the bleaching processes. Chlorate is harmful to some species of algae and consequently research was undertaken to determine its impact on survival of freshwater aquatic invertebrates. Five species representing four orders of Insecta (Plecoptera: Isoperla transmarina (Newman); Ephemeroptera: Baetis tricaudatus Dodds and Tricorythodes minutus Traver; Hemiptera: Dasycorixa hybrida (Hungerford); and Coleoptera: Haliplus sp.) were exposed to 5.0, 50.0 and 100.0 mg L-1 chlorate for 10 days. The plecopteran Isoperla longiseta Banks was exposed to 0.5, 5.0 and 50.0 mg L-1 chlorate for 10 days. Survival of specimens exposed to chlorate did not differ significantly from that of the controls. The LC50 for Daphnia magna Straus, determined using the 48 h acute lethality test, was estimated at 3,162 mg L-1. Chlorate levels from a bleached kraft pulp mill in northwestern Alberta that employs 100% chlorine dioxide substitution in its bleaching process ranged from nondetectable. (<0.002 mg L-1) to approximately 75 mg L-1 in effluent at the point of entry to the river system. At 25 and 127 km downstream from the mill, highest levels of chlorate in water samples were 3.25 and 1.00 mg L-1, respectively. Comparisons of laboratory results with field measurements suggest that chlorate discharges from this pulp mill would have no adverse effect on the survival of the aquatic insect species evaluated here.

Characterization of effluents from chlorine dioxide substitution bleaching and oxygen-reinforced extraction

The effects of chlorine dioxide substitution for elemental chlorine in the chlorination stage, aimed at the minimization of chlorinated organics and subsequent oxygen reinforcement in the proceeding extraction stage on the characteristics of bleaching effluents have been examined. The characteristics of the effluents were assessed in terms of molecular weight distribution by gel filtration, so that alternatives for the treatment of these effluents can be proposed. The analysis of chlorination and extraction stage effluents with different chlorine dioxide substitution levels and varying available chlorine charges by using a Sephadex G-50 column have indicated that indeed a marked change in the molecular weight distribution of chlorinated organic compounds have occurred. The molecular size of chlorinated organic compounds in the chlorination stage has increased with the chlorine dioxide substitution, while that in the extraction stage has decreased when compared with the molecular size of these compounds in original bleaching effluents with only elemental chlorine used in the chlorination stage and followed by extraction stage. Molecular size of the chlorinated organic compounds in the chlorination stage effluents was not seriously affected by the chlorine dioxide substitution level; while it was increased greatly by the increased total chlorine dosage. In the extraction stage effluents, chlorine dioxide substitution level has not appeared to be an important parameter influencing the molecular size distribution.

Environmental impacts of pulp and paper wastewater: evidence for a reduction in environmental effects at north American pulp mills since 1992

In the early 1990s, a variety of responses were reported in fish populations living downstream of bleached kraft pulp mills. This included delayed sexual maturity, smaller gonads, changes in fecundity, and a depression in secondary sexual characteristics. The changes in fish reproductive development were also associated with alterations in the endocrine mechanisms controlling the production of the sex steroid hormones. The early studies were conducted predominantly at large bleached kraft pulp mills with primitive pulping processes and little effluent treatment. Subsequent studies documented several of the changes at some sites with effluent treatment and without chlorine use, and the dominant reproductive changes (delayed maturity, reduced egg production, changes in secondary sexual characteristics) were replicated in laboratory fish exposed to secondary-treated effluent. Studies have continued to follow the responses of wild fish as these mills underwent process modifications and installed secondary treatment. Improvements in the performance of wild fish have been recorded at five North American sites after the mills modernized their waste treatment and pulping processes. However, the improvements are not complete and are not universal and the process changes resulting in the improvement in environmental conditions have not been defined and their identification remains a priority. Reductions in gonad size and depressions of sex hormones are still seen at one mill with 100% chlorine dioxide substitution and secondary treatment.

Characterization of effluents from chlorine dioxide substitution bleaching and oxygen-reinforced extraction

The effects of chlorine dioxide substitution for elemental chlorine in the chlorination stage, aimed at the minimization of chlorinated organics and subsequent oxygen reinforcement in the proceeding extraction stage on the characteristics of bleaching effluents have been examined. The characteristics of the effluents were assessed in terms of molecular weight distribution by gel filtration, so that alternatives for the treatment of these effluents can be proposed. The analysis of chlorination and extraction stage effluents with different chlorine dioxide substitution levels and varying available chlorine charges by using a Sephadex G-50 column have indicated that indeed a marked change in the molecular weight distribution of chlorinated organic compounds have occurred. The molecular size of chlorinated organic compounds in the chlorination stage has increased with the chlorine dioxide substitution, while that in the extraction stage has decreased when compared with the molecular size of these compounds in original bleaching effluents with only elemental chlorine used in the chlorination stage and followed by extraction stage. Molecular size of the chlorinated organic compounds in the chlorination stage effluents was not seriously affected by the chlorine dioxide substitution level; while it was increased greatly by the increased total chlorine dosage. In the extraction stage effluents, chlorine dioxide substitution level has not appeared to be an important parameter influencing the molecular size distribution.

オゾン漂白 グバナオゾン漂白システム

During the last several years, environmental aspects and market requirements to pulp and paper industry have had a great impact on technology development in pulping system.Ozone as an efficient delignification agent is being used for substitution of chlorine and chlorine dioxide in bleaching system and also ozone has been widely utilized for ECF and TCF in the world, especially in Scandinavia and Brazil. Bleaching effluent load is reduced by adopting ozone stage in bleaching plant and consequently partial closed or full closed system in bleaching effluent has been realized step by step.Kvaerner Pulping plays the important role of reader in this area and also involving in the development of ozone system. Kvaerner has got 10 orders of ozone bleaching until now and 8 units of these are operating. This paper introduces our ozone bleaching system in such a standpoint.

Environmental impacts of pulp and paper wastewater: Evidence for a reduction in environmental effects at North American pulp mills since 1992

In the early 1990s, a variety of responses were reported in fish populations living downstream of bleached kraft pulp mills. This included delayed sexual maturity, smaller gonads, changes in fecundity, and a depression in secondary sexual characteristics. The changes in fish reproductive development were also associated with alterations in the endocrine mechanisms controlling the production of the sex steroid hormones. The early studies were conducted predominantly at large bleached kraft pulp mills with primitive pulping processes and little effluent treatment. Subsequent studies documented several of the changes at some sites with effluent treatment and without chlorine use, and the dominant reproductive changes (delayed maturity, reduced egg production, changes in secondary sexual characteristics) were replicated in laboratory fish exposed to secondary-treated effluent. Studies have continued to follow the responses of wild fish as these mills underwent process modifications and installed secondary treatment. Improvements in the performance of wild fish have been recorded at five North American sites after the mills modernized their waste treatment and pulping processes. However, the improvements are not complete and are not universal and the process changes resulting in the improvement in environmental conditions have not been defined and their identification remains a priority. Reductions in gonad size and depressions of sex hormones are still seen at one mill with 100% chlorine dioxide substitution and secondary treatment.

The effects of oxygen delignification, complete chlorine dioxide substitution, and biological treatment on bleached kraft mill effluent quality

The effects of bleaching modifications on the biotreatability of the resulting Adsorbable Organic Halides (AOX) were studied using laboratory-scale bioreactors and mill-scale bleach plant filtrates. Under conventional pulping/bleaching conditions, biological removal of AOX averaged 40 percent. After modification to oxygen delignification and complete C102 substitution, the removal efficiency increased to 47 percent. Under the treatment conditions employed, the eight percent increase was found to be statistically significant at a 95 percent confidence level. These results indicate that AOX biotreatability efficiencies following bleaching sequence modifications to oxygen delignification and complete C102 substitution remain at least as high as those observed prior to such modifications.

Reducing chlorinated organics, AOX, in the bleachery effluents of a Turkish pulp and paper plant

The possibility for reducing the chlorinated organic compounds in the bleacheary effluents of the Turkish pulp and paper industry has been studied. Within the experimental work of this study, three different chlorine dioxide substitutions and three different total chlorine application rates were examined and nine experiments were performed. The AOX formation has been shown to be proportional to the amount of molecular chlorine consumed during delignification, regardless of whether it is from chlorine or chlorine dioxide. However, molecular chlorine contributes to AOX formation to a much greater extent. The lowest AOX concentrations were achieved when the total available chlorine dosage was lowest (10 kg/ton) and ClO2 substitution level was highest. An increase in the percentage of chlorine dioxide leads to a substantial reduction in the AOX concentration in the bleachery effluents. A chlorine dioxide substitution of 90%, when the chlorine charge was 40 kg/ton, causes a 77% decrease in the DC-AOX, and a 82% decrease in the EO-AOX. However, as the chlorine dioxide substitution reduced to 10%, the decrease in the the AOX concentration became less and only 51% and 41% reductions in DC-AOX and EO-AOX could have been achieved respectively.

Leeches as in situ biomonitors of chlorinated phenolic compounds. Part 2: Pulp mill investigations

Leeches ( Nephelopsis obscura Verrill) were evaluated as in situ biomonitors of chlorinated phenolic compounds in the Fraser River at Prince George, BC, downstream from three bleached kraft pulp mills practising chlorine dioxide (ClO 2) substitution. Five biomonitoring periods, of 7 days duration, were selected to cover a full range of seasonal river conditions. Leeches bioconcentrated tri- and tetrachlorinated phenolics (bioconcentration factors: 465–6000) in proportions similar to those present in both mill effluent and river water. Leeches showed 3,4,5-trichloroguaiacol (3,4,5-TCG) to be the most consistent tracer of bleached kraft mill discharge. Leeches provided direct evidence that increasing ClO 2 substitution reduces amounts of chlorinated phenolics accumulated by aquatic organisms, with sharp decreases observed at ClO 2 levels greater than 90%. This study suggests that leeches could be applied as routine biomonitors for environmental impact monitoring.

The role of dibenzo-p-dioxin and dibenzofuran precursors in the formation of tetrachlorinated dibenzo-p-dioxins/-furans during bleaching

The position of the theoretical line describing dioxins control technology is dependent upon the concentration of dioxins precursors in brownstock. The tolerance of the bleaching process to precursor contamination increases as chlorine dioxide substitution increases to the extent that when 100% substitution is used, at the highest levels of precursor contamination studied, 2378-tetrachlorodibenzo-p-dioxin is non-detectable in pulp, and 2378-tetrachlorodibenzofuran is detectable but only at background laboratory levels.

Reducing chlorinated organics, AOX, in the bleachery effluents of a Turkish pulp and paper plant

The possibility for reducing the chlorinated organic compounds in the bleacheary effluents of the Turkish pulp and paper industry has been studied. Within the experimental work of this study, three different chlorine dioxide substitutions and three different total chlorine application rates were examined and nine experiments were performed. The AOX formation has been shown to be proportional to the amount of molecular chlorine consumed during delignification, regardless of whether it is from chlorine or chlorine dioxide. However, molecular chlorine contributes to AOX formation to a much greater extent. The lowest AOX concentrations were achieved when the total available chlorine dosage was lowest (10 kg/ton) and ClO2 substitution level was highest. An increase in the percentage of chlorine dioxide leads to a substantial reduction in the AOX concentration in the bleachery effluents. A chlorine dioxide substitution of 90%, when the chlorine charge was 40 kg/ton, causes a 77% decrease in the DC-AOX, and a 82% decrease in the EO-AOX. However, as the chlorine dioxide substitution reduced to 10%, the decrease in the the AOX concentration became less and only 51% and 41% reductions in DC-AOX and EO-AOX could have been achieved respectively.