FIELD OF THE INVENTION

[0001] The present invention relates to methods and compositions for improving chlorine dioxide treatment processes, such as, pulp delignification and bleaching processes.

BACKGROUND

[0002] Chlorine dioxide is one of the most widely used delignification/bleaching agents in the pulp and paper industry, providing a high-quality, low-cost delignification and bleaching process. Chlorine dioxide treatment is superior to chlorine bleaching processes in that it virtually eliminates all dioxin discharges into the environment, and has accordingly, helped pulp and paper manufactures to employ environmentally friendly processes and to meet environmental requirements. Accordingly, the use of chlorine dioxide treatment is increasing and most pulp and paper mills now have at least one chlorine dioxide delignification or bleaching stage. Chlorine dioxide treatment has also been used to treat wastewater, sludge and other process streams.

[0003] During the chlorine dioxide treatment processes some of the chlorine dioxide is converted to chlorate and chlorite, which decreases the efficiency of the chlorine dioxide treatment. Methods have been proposed to improve the efficiency of the chlorine dioxide treatment process by reducing chlorate and chlorite formation. Seger et al., Chiang, Tappi J., 1992, 75(7): 174-180, for example, discloses a two step high-pH and low-pH process, which is believed to reduce the formation of chlorate at the higher pH and chlorite becomes reactive in the low-pH step. Joncourt et al., International Symp. Wood Pulping Chemistry, Montreal, Jun. 9-12, 1997, discloses the use of iron to regenerate chlorine dioxide from chlorite. Jiang et al, U.S. Patent No. 6,235,154, discloses process for improving chlorine dioxide delignification or bleaching by regenerate chlorine dioxide from the chlorite using formaldehyde.

[0004] New compositions and methods are needed to improve the efficiency and effectiveness of chlorine dioxide treatment, including, chlorine dioxide delignification and bleaching processes.

SUMMARY OF THE INVENTION

[0005] The present invention relates to methods and compositions for chlorine dioxide delignification and/or bleaching processes by reacting pulp with chlorine dioxide and a peroxidase and/or a laccase. In accordance with the present invention, a peroxidase and/or a laccase is/are added to a chlorine dioxide delignification and/or bleaching step. Although

not limited to any one theory of operation, the addition of a peroxidase and/or a Iaccase to a chlorine dioxide treating composition is believed to result in the regeneration of chlorine dioxide from chlorite, resulting in improved delignification and/or brightening during bleaching of pulp.

[0006] The present invention relates to methods and compositions for chlorine dioxide treatment of wastewater, sludge or any other process stream. In accordance with the present invention, a peroxidase and/or a Iaccase is added to a chlorine dioxide treatment step to improve the chlorine dioxide treatment process.

DETAILED DESCRIPTION

[0007] A "peroxidase" means a peroxidase (E.C.1.11.1.7) and/or a haloperoxidase, such, as, preferably, a chloride peroxidase (E. C.1.11.1.10). Preferably, the peroxidase is an acid stable peroxidase.

[0008] Peroxidases may be obtained from any suitable source, such as, e.g., from plants (e.g., a soy bean or horseradish peroxidase) and from microorganisms (fungi and bacteria, such as, e.g., the peroxidase may be obtained from a strain of Coprinus, e.g., C. cinerius or C. macrorhizus, or of Bacillus, e.g. B. pumilu). Some preferred fungal sources include strains belonging to the subdivision Deuteromycotina, class Hyphomycetes, e.g., Fusarium, Humicola, Tricoderma, Myrothecium, Verticillum, Arthromyces, Caldariomyces, Ulocladium, Embellisia, Cladosporium or Dreschlera, in particular, Fusarium oxysporum (DSM 2672), Humicola insolens, Trichoderma resii, Myrothecium verrucana (IFO 6113), Verticillum alboatrum, Verticillum dahlie, Arthromyces ramosus (FERM P-7754), Caldariomyces fumago, Ulocladium chartarum, Embellisia alii or Dreschlera halodes. Other preferred fungal sources include strains belonging to the subdivision Basidiomycotina, class Basidiomycetes, e.g., Coprinus, Phanerochaete, Coriolus or Trametes, in particular Coprinus cinereus f. microsporus (IFO 8371), Coprinus macrorhizus, Phanerochaete chrysosporium (e.g., NA-12) or Coriolus versicolor (e.g., PR4 28-A). Further preferred fungal sources include strains belonging to the subdivision Zygomycotina, class Mycoraceae, e.g., Rhizopus or Mucor, in particular, Mucor hiemalis. [0009] Some preferred bacterial peroxidase sources include strains of the order Actinomycetales, e.g., Streptomyces spheroides (ATTC 23965), Streptomyces thermoviolaceus (IFO 12382) or Streptoverticillum verticillium ssp. verticillium. Other preferred bacterial sources include Bacillus pumillus (ATCC 12905), Bacillus stearothermophilus, Rhodobacter sphaeroides, Rhodomonas palustri, Streptococcus lactis, Pseudomonas purrocinia (ATCC 15958) or Pseudomonas fluorescens (NRRL B-11).

[00010] Haloperoxidases may be obtained form any suitable source. Haloperoxidases, for example, have been isolated from various organisms, including mammals, marine animals, plants, algae, a lichen, fungi and bacteria (for reference see Biochimica et Biophysica Acta 1161 , 1993, pp. 249-256). Suitable choloroperoxidases include the chloroperoxidase obtained from the fungus Curvularia inaequalis (see SWISS- PROT:P49053), the chloroperoxidase obtained from the fungus Curvularia verruculosa (see WO 97/04102) and the chloroperoxidases disclosed in Svendsen et al, U.S. Patent No. 6,372,465.

[00011] Laccases (EC 1.10.3.2) may be obtained from any suitable sources, such as, from a genus selected from the group consisting of Aspergillus, Botrytis, Collybia, Fomes, Lentinus, Myceliophthora, Neurospora, Pleurotus, Podospora, Polyporus, Scytalidium, Trametes, and Rhizoctonia. In a more preferred embodiment, the laccase is obtained from a species selected from the group consisting of Humicola brevis var. ihermoidea, Humicola brevispora, Humicola grisea var. thermoidea, Humicola insolens, and Humicola lanuginosa (also known as Thermomyces lanuginosus), Myceliophthora thermophila, Myceliophthora vellerea, Polyporus pinsitus, Scytalidium thermophila, Scytalidium indonesiacum, and Torula thermophila. The laccase may be obtained from other species of Scytalidium, such as Scytalidium acidophilum, Scytalidium album, Scytalidium aurantiacum, Scytalidium circinatum, Scytalidium flaveobrunneum, Scytalidium hyalinum, Scytalidium lignicola, and Scytalidium uredinicolum. Rhizoctonia solani and Coprinus cinereus. The laccase may be obtained from other species of Polyporus, such as Polyporus zonatus, Polyporus alveolaris, Polyporus arcularius, Polyporus australiensis, Polyporus badius, Polyporus biformis, Polyporus brumalis, Polyporus ciliatus, Polyporus colensoi, Polyporus eucalyptorum, Polyporus meridionalis, Polyporus varius, Polyporus palustris, Polyporus rhizophilus, Polyporus rugulosus, Polyporus squamosus, Polyporus tuberaster, and Polyporus tumulosus.

[00012] A "chlorine dioxide treatment" means any chloride dioxide treatment process, such as, for example, chlorine dioxide treatment stages used in pulp and paper mills and chlorine dioxide treatment of wastewater and/or sludge, for example, plant wastewater or ordinary household sewage or wastewater.

[00013] Typically chlorine dioxide treatment is applied in a pulp and paper mills in delignification and pulp bleaching processes. Any suitable pulp may be treated, although preferably, the pulp is a lingocellulosic pulp. The pulp may be treated with other delignification and/or bleaching agents prior to, during or following the chlorine dioxide treatment, such as, e.g., oxygen delignification, peroxide treatment, and enzyme treatment processes.

[00014] The chlorine dioxide used in the treatment process may be generated by any suitable method. However, because chlorine dioxide is unstable as a gas and can only stored as a solution, it is usually generated on-site, e.g., at the pulp mill. Once in solution, however, chlorine dioxide is fairly stable.

[00015] Chlorine dioxide is generally added in amounts effective to treat the pulp or process waters (e.g., waste water), as are known in the art.

[00016] Typically, chlorine dioxide treatment of pulp is carried out at a temperature from about 40 to 8O ⁰ C for a period of about 15 to 120 min. The effectiveness of the chlorine dioxide depends in part on pH, and is maximized at a pH of about 2 to 4. Because the pH of pulp streams and other process waters are typically more basic, acid may be added to the treatment water to reduce the pH. In some processes, the pH of the process water may be controlled by applying excess amounts of chlorine dioxide.

[00017] The peroxidase and/or laccase is/are applied directly to the chlorine dioxide process stream in an amount effective to improve the chlorine dioxide treatment process, as exemplified below. The peroxidase and/or laccase may be applied as part of the chlorine dioxide solution, a part of a filtrate used to prepare the process water (e.g. delignification or bleaching liquour), in the recycled process water, and/or by a separate addition. [00018] The peroxidase and/or laccase are applied in an amount effective to improve the chlorine dioxide treatment process, such as, as measured by improved pulp delignification and/or improved pulp bleaching. An example of an effective amount of a peroxidase is 0.005mg-10g/L of process water, more preferably 0.01-1000mg/L of process water, and most preferably 0.05-500mg/L of process water. In regard to pulp applications, such effective amount of a peroxidase will include 0.01g-20kg/ton of pulp, more preferably 0.1 g- 5kg/ton of pulp, and most preferably 1g-2kg/ton of pulp. An example of an effective amount of a laccase is 0.005mg-10g/L of process water, more preferably 0.01-1000mg/l_ of process water, and most preferably 0.05-500mg/L of process water. In regard to pulp applications, such effective amount of a laccase will include 0.01g-20kg/ton, more preferably 0.1 g- 5kg/ton, and most preferably 1g-2kg/ton. The peroxidases and laccases are preferably selected based their compatibility with the process conditions for the pulp treatment or waste water/sludge treatment, e.g., pH optimum, temperature optimum, acid stability. [00019] Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.

EXAMPLES

Example 1 :

160 mg of NaCIO ₂ was dissolved in 100 ml_ of Dl water. 1OmL aliquots of the NaCIO ₂ solution were added to different test tubes. 20 uL of acetic acid were added to each tube and the pH was adjusted to about 3.5. Then 100 uL of enzyme was added to the solution. After 30 min of incubation at ambient temperature, the solution was diluted 3 times by Dl water. CIO ₂ formation was detected by UV absorbency at 360 nm. It is evident that all of the enzymes can generate CIO ₂ to some extent under the conditions used in this experiment.

Table 1. Enzymatic Chlorine Dioxide Generation

Example 2:

5 g (o.d. dry) of unbleached kraft pulp was added to each beaker and diluted to about 5% consistency. The pulp was adjusted to various pH by 2N H ₂ SO ₄ . 10 mL of 11.3/L of NaCIO ₂ was added to each beaker. 500 ul of peroxidase (Coprinus cinereus peroxidase, NovozymesJ was added to the solution and the beaker was incubated at 6O ⁰ C for 1 hr. After bleaching, the pulp was rinsed with Dl water and handsheets were made and tested for brightness. Brightness was tested according to Tappi standard (T452). It is clear the peroxidase improved pulp brightness in all the pH range.