WO2006061018A1

WO2006061018A1 - Use of carbohydrate oxidase for sediment control

Info

Publication number: WO2006061018A1
Application number: PCT/DK2005/000771
Authority: WO
Inventors: Hui Xu; Henrik Lund; Jing Luo; Greg Delozier
Original assignee: Novozymes A/S; Novozymes North America, Inc.
Priority date: 2004-12-06
Filing date: 2005-12-02
Publication date: 2006-06-15

Abstract

The invention relates to the use of at least one carbohydrate oxidase for control of sediment such as scale, in particular for the treatment of equipment such as paper machine felts and wires, process water, and/or wastewater of a pulp or paper mill. The carbohydrate oxidase oxi-dizes carbohydrates to the corresponding acids, which in turn are believed to chelate with the cationic part of inorganic salts such as scale. This enables better cleaning and/or control of sediments, and for water streams it leads to a turbidity reduction, to an improved settling behav-iour, as well as to a colour reduction, all of which makes cleaning and effluent control proce-dures easier and less expensive. Furthermore, the retention of sediment in the paper web is im-proved.

Description

Use of Carbohydrate Oxidase for Sediment Control

FIELD OF THE INVENTION

The present invention relates to the use of carbohydrate oxidase for sediment control. Sediment control is important in various industries, in particular in the pulp and paper industry.

BACKGROUND OF THE INVENTION

Sediment build-up on equipment surfaces is a serious problem. A most annoying example of sediment is inorganic sediment such as scale, the sediment formed on surfaces in contact with water when, e.g., the calcium hardness, pH or total alkalinity levels are too high. Scale may appear as grey, white or dark streaks or a hard crust on the surfaces of the equipment in contact with the water. Scale is for example a problem in chemically unbalanced pool and spa water, but also in many other industries, in particular in pulp and paper mills which very often have to slow down the processes for scale clean up, often with harsh chemicals and using mechanical force.

In pulp and paper mills, these problems are caused in particular by inorganic salts such as calcium salts, present in, e.g., carbonate fillers, and/or as calcium hardness in the water, these calcium ions forming various salts of low solubility, observed as deposits on equipment, and/or as sedimentation, and/or turbidity in process water and/or wastewater. But also other salts than calcium salts (e.g., calcium carbonate and calcium sulphate), may give rise to scale formation in pulp and paper mills, viz. for example barium sulphate, strontium sulphate, calcium fluoride, aluminium silicate, manganese salts, and various cationic flocculants.

During conventional papermaking operations, water is an invaluable means to saturate, suspend and transport fiber, fines, fillers, sizes, etc. In addition, water provides a medium in which specific reactions between the fiber and chemical additives can readily take place. This dependency upon water has propelled the paper industry into one of the largest water consumers on the planet. Prior to release of process water (e.g. into receiving bodies of water or as land application) or reuse of process water within the mill, it must undergo a "conditioning regime" in which contaminat- ing substances are removed. If allowed to remain within the mill effluent, these substances (e.g. fiber, fines, fillers, lignin, extractives, sizes, inks, strength agents, biomass, etc.) contribute to, La., turbidity and color. Should the process water be recycled back into mill operations, the presence of these interfering substances can have very detrimental results (e.g. sticky formation, slime and biofilm, anionic trash, etc.). Primary water treatment within the mill is comprised of one or two clarifiers in which the colloidally stable material, suspended within the process water, is allowed to settle under relatively quiescent conditions. In some instances, additives (i.e. coagulants and/or flocculants) are added to the process water to enhance the rate and degree of settling. In many instances, the inclusion of polymeric flocculants or multivalent coagulating cations (e.g. ferric sulphate, alum) may not effectively clarify the process water. In addition, the former tends to be expensive while both treatments can cause problems if returned with the process water (e.g. scaling, poor formation, deposits, volatile pH, etc.).

The present invention sets out to provide an alternative, less labour-intensive, and more environmentally friendly way of controlling sediments, be it for equipment cleaning purposes, and/or for conditioning of process water and/or wastewater, with particular emphasis on the pulp and paper industry.

SUMMARY OF THE INVENTION

According to the invention, control of sediment such as scale may be achieved by using one or more carbohydrate oxidases.

In a pulp and/or paper manufacturing process these enzymes may be used, for example, to treat process water, and/or wastewater; and/or for equipment cleaning or conditioning purposes. Important pieces of equipment are the paper machine felts (the fabric that presses the paper web against the drying cylinder on the paper machine) and wires.

Additional effects of treatment of water streams such as process water or wastewater with carbo- hydrate oxidases are: Turbidity reduction, improved settling behaviour, as well as colour reduction, all of which make cleaning and/or effluent control procedures easier and less expensive. Furthermore, the retention of sediments in the paper web is improved.

Although not limited to any one theory of operation, the carbohydrate oxidase treatment is be- lieved to convert carbohydrate materials (e.g., mono-, oligo- and polysaccharides) into their acidic counterparts, such as, gluconic acid, lactobionic acid, and/or cellobionic acid. These acids can facilitate precipitation, and/or improve the settling behaviour, of suspended light-scattering and/or coloured material. In addition, they can compete, as complexing or chelating agents, with carbonate or oxalate and the like inorganic anions, for the cationic calcium ions, thereby decreasing the concentration thereof. This, in turn, reduces the formation of, for example, calcium oxalate and calcium carbonate scale, and also reduces turbidity. Furthermore, enzymatic oxidation of coloured material suspended within the stream diminishes or destroys the ability of the material to absorb and possibly remit certain wavelengths within the visual spectrum.

DETAILED DESCRIPTION OF THE INVENTION

A carbohydrate oxidase (EC 1.1.3) refers to an enzyme which is able to oxidize carbohydrate substrates (e.g., glucose or other sugar or oligomer intermediate) into an organic acid, e.g., gluconic acid, lactobionic acid, and/or cellobionic acid. These enzymes are oxidoreductases acting on the CH-OH group of donors with oxygen as acceptor. Examples of carbohydrate oxidases include malate oxidase (EC 1.1.3.3), glucose oxidase (EC 1.1.3.4), hexose oxidase (EC 1.1.3.5), galactose oxidase (EC 1.1.3.9), pyranose oxidase (EC 1.1.3.10), catechol oxidase (EC 1.1.3.14), sorbose oxidase (EC 1.1.3.11), cellobiose oxidase (EC 1.1.3.25), and mannitol oxidase (EC 1.1.3.40). Preferred oxidases include monosaccharide oxidases, such as, glucose oxidase, hexose oxidase, galactose oxidase and pyranose oxidase.

The carbohydrate oxidase may be derived from any suitable source, e.g., a microorganism, such as, a bacterium, a fungus or a yeast. Examples of carbohydrate oxidases include the carbohydrate oxidases disclosed in WO 95/29996 (Novozymes A/S); WO 99/31990 (Novozymes A/S), WO 97/22257 (Novozymes A/S), WO 00/50606 (Novozymes Biotech), WO 96/40935 (Bioteknolo- gisk Institut), U.S. Patent No. 6,165,761 (Novozymes A/S), U.S. Patent No. 5,879,921 (Novozymes A/S), U.S. Patent No. 4,569,913 (Cetus Corp.), U.S. Patent No. 4,636,464 (Kyowa Hakko Kogyo Co., Ltd), U.S. Patent No. 6,498,026 (Hercules Inc.); EP 321811 (Suomen Sokeri); and EP 833563 (Danisco A/S).

The glucose oxidase may be derived from a strain of Aspergillus or Penicillium, preferably, A. ni- ger, P. notatum, P. amagasakiense or P. vitale. Preferably, the glucose oxidase is an Aspergillus niger glucose oxidase. Other glucose oxidases include the glucose oxidases described in "Methods in Enzymology", Biomass Part B Glucose Oxidase of Phanerochaete chrysosporium, R. L. KeI- ley and CA. Reddy (1988), 161, pp. 306-317 and the glucose oxidase Hyderase 15 (Amano Pharmaceutical Co., Ltd.).

Hexose oxidase can be isolated, for example, from marine algal species naturally producing that enzyme. Such species are found in the family Gigartinaceae which belong to the order Gigartina- les. Examples of hexose oxidase producing algal species belonging to Gigartinaceae are Chon- drus crispus and lridophycus flaccidum. Also algal species of the order Cryptomeniales are poten- tial sources of hexose oxidase. Hexose oxidases have been isolated from several red algal species such as Irido-phycus flaccidum (Bean and Hassid, 1956, J. Biol. Chem., 218:425-436) and Chondrus crispus (Ikawa 1982, Methods Enzymol., 89:145-149). Additionally, the algal species Euthora cristata (Sullivan et al. 1973, Biochemica et Biophysica Acta, 309:11-22) has been shown to produce hexose oxidase. Other potential sources of hexose oxidase include microbial species or land-growing plant species. An example of a plant source for a hexose oxidase is the source disclosed in Bean et al., Journal of Biological Chemistry (1961) 236: 1235-1240, which is capable of oxidizing a broad range of sugars including D-glucose, D-galactose, cellobiose, lactose, maltose, D-2-deoxyglucose, D-mannose, D-glucosamine and D-xylose. Another example of an en- zyme having hexose oxidase activity is the carbohydrate oxidase from Malleomyces mallei disclosed by Dowling et al., Journal of Bacteriology (1956) 72:555-560. Another example of a suitable hexose oxidase is the hexose oxidase described in EP 833563.

The pyranose oxidase may be derived, e.g., from a fungus, e.g., a filamentous fungus or a yeast, preferably, a Basidomycete fungus. The pyranose oxidase may be derived from genera belonging to Agaricales, such as Oudemansiella or Mycena, to Aphyllophorales, such as Trametes, e.g. T. hirsuta, T. versicolour T. gibbosa, T. suaveolens, T. ochracea, T. pubescens, or to Phanero- chaete, Lenzites or Peniophora. Pyranose oxidases are of widespread occurrence, but in particular, in Basidiomycete fungi. Pyranose oxidases have also been characterized or isolated, e.g., from the following sources: Peniophora gigantea (Huwig et al., 1994, Journal of Biotechnology 32, 309-315; Huwig et el., 1992, Med. Fac. Landbouww, Univ. Gent, 57/4a, 1749-1753; Danneel et al., 1993, Eur. J. Biochem. 214, 795-802), genera belonging to the Aphyllophorales (VoIc et al., 198S, Folia Microbiol. 30, 141-147), Phanerochaete chrysosporium (VoIc et al., 1991 , Arch. Miro- biol. 156, 297-301 , VoIc and Eriksson, 1988, Methods Enzymol 161 B, 316-322), Polyporus pinsi- tus (Ruelius et al., 1968, Biochim. Biophys. Acta, 167, 493-500) and Bierkandera adusta and Phebiopsis gigantea (Huwig et al., 1992, op. cit.) Another example of a pyranose oxidase is the pyranose oxidase described in WO 97/22257, e.g. derived from Trametes, particularly T. hirsuta.

Galactose oxidase enzymes are well-known in the art. An example of a galactose oxidase is the galactose oxidases described in WO 00/50606.

Commercially available carbohydrate oxidases include GLUZYME TM (Novozymes A/S) and GRINDAMYL TM (Danisco A/S), Glucose Oxidase HP S100 and Glucose Oxidase HP S120 (Genzyme); Glucose Oxidase- SPDP (Biomeda); Glucose Oxidase, G7141 , G 7016, G 6641, G 6125, G 2133, G 6766, G 6891 , G 9010, and G 7779 (Sigma-aldrich); and Galactose Oxidase, G 7907 and G 7400 (Sigma-aldrich).

The carbohydrate oxidase selected for use in the treatment process of the present invention pref- erably depends on the carbohydrate source present in the system, process or composition to be treated. Thus, in some preferred embodiments, a single type of carbohydrate oxidase may be preferred, e.g., a glucose oxidase, when a single carbohydrate source is involved. In other preferred embodiments, a combination of carbohydrate oxidases will be preferred, e.g., a glucose oxidase and a hexose oxidase. Preferably, the carbohydrate oxidase is derived from a fungus belonging to the genus Microdochium, preferably the fungus is Microdochium nivale, such as Microdochium nivale as deposited under the deposition no CBS 100236, as described in U.S. Patent No. 6,165,761 (Novozymes A/S.), which is hereby incorporated by reference. The Microdochium nivale carbohydrate oxidase has activity on a broad range of carbohydrate substrates.

The carbohydrate oxidase sample is preferably catalase-free to prevent degradation of hydrogen peroxidase used in subsequent processing steps.

The carbohydrate oxidase treatment may be used to control (i.e., reduce or prevent) formation of sediment such as scale in any desired environment, such as, in a factory (e.g., factory effluent), machine, process stream (e.g., white water in a mill), sludge treatment plant, wastewater treatment plant, lagoon, storage facility, waste or disposal container, and waste or disposal facility. In preferred embodiments, the carbohydrate oxidase treatment is applied to i) process water; ii) wastewater; iii) the paper machine felts and wires.

For treatment of water streams such as process water and wastewater, the carbohydrate oxidase treatment is preferably carried out by contacting process or wastewater with the carbohydrate oxidase.

For treatment of equipment, the carbohydrate oxidase treatment is preferably carried out by add- ing carbohydrate oxidase to the cleaning liquid.

In a pulp and paper mill, process water can be classified as that used during pulping operations (generating virgin or recovered furnishes) or that used at the wet-end of the paper machine (e.g. white water). Deposits formed on equipment such as the paper machine felts are partly of an organic, and partly of an inorganic nature. Therefore, it may be advantageous to combine the treatment according to the invention with other enzymes used to treat the organic part of the deposit, for example lipases, cutinases, amylases etc. Therefore, in other preferred embodiments, the carbohydrate oxidase is added in combination (such as, for example, sequentially or simultaneously) with a lipase, a cuti- nase, and/or a carbohydrate-degrading enzyme (e.g., a starch-degrading enzymes, such as an alpha-amylase or glucoamylase and/or a cellulose or hemicellulose degrading enzyme, e.g., cellu- lase or hemicellulase such as xylanase) to convert the carbohydrate material to substrates suitable for the carbohydrate oxidase.

The carbohydrate oxidase is added in an amount effective to reduce turbidity, prevent or reduce sedimentation, improve settlement behaviour, and/or decolourize, whichever of these effects are aimed at. Examples of effective amounts of carbohydrate oxidase include 0.01 mg - 1g enzyme protein /L, preferably, 0.1 mg - 500 mg enzyme protein /L, and more preferably, 0.5 mg - 100 mg enzyme protein/L.

The temperature and pH for the carbohydrate oxidase treatment is not critical, provided that the temperature and pH is suitable for the enzymatic activity of the carbohydrate oxidase. Generally, the temperature and pH will depend on the system, composition or process which is being treated. Suitable temperature and pH conditions include 5⁰C to 12O⁰C and pH 1 to 12, however, ambient temperatures and pH conditions are preferred. Although not limited, for pulp and paper processes, the temperature and pH will generally be 15⁰C to 65⁰C, and pH 3 to 9.

The treatment time will vary depending on, among other things, the extent of the sediment, turbid- ity or colour problem (e.g., the amount and kind of carbohydrate material and/or kind and amount of inorganic additives such as fillers present) and the type and amount of the carbohydrate oxidase employed. The carbohydrate oxidase may also be used in a preventive manner, such that the treatment time is continuous or carried out at a set point in the process.

In preferred embodiments, the present invention relates to the use of carbohydrate oxidase, preferably in a pulp and paper mill, i) to reduce or prevent sedimentation; ii) to reduce or prevent turbidity; iii) to improve settling behaviour, preferably during primary clarification; and/or iv) for de- colourization. In still further preferred embodiments, carbohydrate oxidase is added to industrial process water or wastewater; the process water recycling circuit; mill effluents prior to release, lagoon, and/or settling basin feed stream.

Sedimentation, turbidity and colour problems in pulp and paper mills, and other industrial processes, is becoming even more of a problem as such processes and facilities move to closed water system or loops (e.g., white water or wastewater) which lead to a build up of the sediments.

The invention also relates to: I. A method for controlling sedimentation, comprising contacting equipment, process water, and/or wastewater, with at least one carbohydrate oxidase.

II. The method of I, wherein the equipment, the process water, and/or the wastewater, comprises a carbohydrate material.

III. The method of I or II, wherein the equipment is paper machine felts and/or wires. IV. The method of I or II, wherein the process water, and/or wastewater, derives from a pulp or paper manufacturing process.

V. The method of I, Il or IV, wherein the process water, and/or wastewater, is in a closed loop system.

VI. The method of I-V for scale control. VII. The method of l-ll or IV-VI for turbidity reduction of process water and/or wastewater. HX. The method of any l-ll or IV-VII for colour reduction of process water and/or wastewater.

IX. The method of l-ll or IV-IIX for improvement of settling behaviour of process water and/or wastewater.

X. The method I-IX for increasing the retention of sediment in a paper web. Xl. The method of I-X, wherein the carbohydrate oxidase treatment results in an increase in the amount of carbohydrate acid, which in turn chelates the cationic part of inorganic salts. XII. The method of I-XI, wherein the carbohydrate oxidase is used in combination with at least one lipase, cutinase, and/or carbohydrate degrading enzyme.

The present invention furthermore relates to the use of organic acids, such as, for example, gluconic acid, lactobionic acid, and/or cellobionic acid as sediment control agents. In this aspect of the invention, the, organic acids function directly as sediment control agents, with or without the carbohydrate oxidase treatment. The organic acids may accordingly be added to compositions or processes in an amount effective to control (reduce or prevent) sediments. EXAMPLES

Example 1

Use of gluconic acid for reducing turbidity

Various amounts (see Table 1 below) of 10% (w/w) gluconic acid were added to containers containing 200 ml of calcium chloride (registered as 200 ppm water hardness), following which sodium oxalate was added to each container to reach a concentration of 200 ppm (w/w). Using a sample without added calcium chloride, sodium oxalate, and gluconic acid as a control, the turbidity was measured by passing focused light from a tungsten-filament lamp through the sample, having a 90-degree scatter detector receiving light scattered by particles, and transmitted and forward scatter detectors receiving light that passes through the sample. The turbidimeter was a Hach Ratio Turbidimeter and it was used in the ratio mode, and generally according to the manufacturer's instructions (Hach Company, P.O.Box 389, Loveland, CO 80539, US). The results are shown in Table 1 below.

Table 1

As shown in Table 1 , the liquid turbidity decreased as more gluconic acid was added to the container. This indicates that gluconic acid prevents the formation of calcium oxalate.

Example 2

Use of carbohydrate oxidase for sediment control

A newsprint pulp slurry at 3% consistency was treated for 24 hours with 2kg/t of Gluzyme 10000 BG, which is a carbohydrate oxidase (glucose oxidase), commercially available from Novozymes A/S, Krogshoejvej 36, DK-2880 Bagsvaerd, Denmark. As a control, a sample of the same pulp was mixed under identical conditions without the enzyme. The filtrates from each treatment were collected and mixed in a glass container at different ratios as shown in Table 2 below. Ca²⁺ (calcium chloride) and CO₃ ^2" were then added to reach a hardness of 250 ppm and a concentration of sodium carbonate of 200 ppm (w/w). The turbidity was measured as described in Example 1 , and the weight of precipitate determined after evaporation of the liquid. The results are shown in Table 2.

Table 2

As shown in Table 2, the liquid with higher fraction of filtrate from the enzyme-treatment resulted in a lower turbidity and a lower weight of CaCO₃ precipitate.

Example 3 Use of carbohydrate oxidase for improving settling behaviour and for colour reduction

100 oven dry grams (odg) of old corrugated container (OCC) and another 100 odg of mixed office waste (MOW) were separately diluted to 2000 ml total volume with de-ionized H₂O. The suspensions were then disintegrated for 15000 revolutions in a standard laboratory disintegrator to yield 5% consistency pulps. To these pulps, a mixture of cellulase (Celluclast 1.5 L), glucoamylase (Spirizyme Fuel), and amylase (Aquazyme 120), all commercially available from Novozymes A/S, Denmark, was added to obtain respective doses of 2, 2, and 4 kg/ oven dried ton (odt) of fiber. The pulps were incubated with the enzymes for 120 minutes at 45⁰C within a Launder-O-Meter, commercially available from Atlas Electric Devices Company, Chicago, IL, USA. This is a standard piece of equipment used in the textile industry that spins the beakers, end-over-end, within a pre- heated, water-filled chamber.

After this time, the pulps were filtered across a Whatman 41 filter paper and the resultant pulp pads discarded. The filtrates, representative of process water and wastewater, were then separated equally into four 1 L Launder-O-Meter beakers and Gluzyme 10000 BG (a carbohydrate oxi- dase, viz. glucose oxidase, commercially available from Novozymes A/S, Denmark), was applied according to table 3:

Table 3

The beakers were then sealed and returned to the Launder-O-Meter to incubate for another 60 minutes at 45°C. Afterwards, the beakers were placed, for 3 hours, in a 45°C water bath.

Following the bath incubation, 25 ml was transferred from each beaker (after ensuring that the beaker contents were thoroughly mixed) to a turbidity vial where the settling rate was predicted by recording turbidity over time with a Hach Ratio Turbidimeter as described in Example 1. The results of the turbidity measurements are shown in Table 4 below. The turbidity of the untreated MOW process water was initially higher than 200 units, the upper detectable threshold of the turbidity meter, and did not become lower for the duration of the observations.

Table 4

From Table 4 it is clear that application of carbohydrate oxidase to OCC and MOW process waters greatly increased the settling rate of suspended solids (seen as a significant reduction in sample turbidity over time).

To assess colour within the treated process water, 5 ml of the mixed liquor was filtered through a

0.45 mm pore-size syringe filter into a cuvette for UV-Spec analysis. Analyses were performed on a Hewlett-Packard 8453 Spectrophotometer. Absorbance spectra were recorded from 3 samples taken from each treated process water. Absorbance values were taken at 250, 280 and 480 nm (Table 5).

Table 5

From Table 5 it is clear that treating a MOW process water with 100 g/m³ carbohydrate oxidase reduced the absorbencies at 250, 280 and 480 nm, by 81%, 82% and 98%, respectively, relative to an untreated control. In the case of OCC process water, the reductions were 31%, 26% and 70%, respectively.

Claims

CLAIMS:

1. Use of at least one carbohydrate oxidase for sediment control.

2. The use of claim 1 , wherein the carbohydrate oxidase is used for equipment cleaning, and/or to treat process water and/or wastewater.

3. The use of any one of claims 1-2, wherein the equipment, the process water, and/or the wastewater, comprises a carbohydrate material.

4. The use of any one of claims 1-3, wherein the equipment is in a pulp and/or paper mill, and/or the process water, and/or wastewater, derives from a pulp or paper manufacturing process.

5. The use of claim 4, wherein the equipment is paper machine felts and/or wires.

6. The use of any one of claims 1-4, wherein the process water, and/or wastewater, is in a closed loop system.

7. The use of any one of claims 1-6, for scale control.

8. The use of any one of claims 1-4 and 6-7, for turbidity reduction of process water and/or wastewater.

9. The use of any one of claims 1-4 and 6-8, for colour reduction of process water and/or wastewater.

10. The use of any one of claims 1-4 and 6-9, for improvement of settling behaviour of process water and/or wastewater.

11. The use of any one of claims 4-10, for increasing the retention of sediment in a paper web.

12. The use of any one of claims 1-11 , wherein the carbohydrate oxidase treatment results in an increase in the amount of carbohydrate acid, which in turn chelates the cationic part of inorganic salts.

13. The use of any one of claims 1-12, wherein the carbohydrate oxidase is used in combination with at least one lipase, cutinase, and/or carbohydrate degrading enzyme.