FI110533B - Method for controlling microbial growth - Google Patents

Abstract

The invention relates to a process for controlling microbial growth in a production line for cellulosic products with the aid of gases. The invention also relates to the use of gases such as carbon dioxide, nitrogen, argon and/or non-naturally occurring mixtures thereof for controlling microbial growth. In the process an aqueous material containing water and suspended pulp fibers and/or additives therefor is treated with the gaseous inhibitor to significantly retard or inhibit the growth of microorganisms therein. An oxygen rich gas may be introduced in addition to the inhibitor of the invention.

Description

> 110533

Method for controlling microbial growth

The invention relates to a method for controlling microbial growth in a production line of cellulose products by means of gases. The invention also relates to the use of gases, for example carbon dioxide, nitrogen, noble gas and / or non-naturally occurring mixtures thereof, for controlling microbial growth.

In the manufacture of cellulosic products such as pulp, paper and board (hereinafter referred to as paper), cellulose fibers are treated in aqueous slurries under various conditions. The amount of water in the production line is huge, and water is constantly circulated in smaller or larger loops. Production line conditions are often favorable for microbial growth. This is particularly true during storage of aqueous material.

All microbes require for their growth that the system contains sufficient nutrients and that pH, temperature, humidity, oxygen content, etc., are appropriate.

To grow, microbes need time to grow and multiply in the system. The residence time shall be sufficiently long; otherwise the cells will be leached from the system. In a papermaking system, microbes can easily find places where they can stay long enough, such as water storage tanks, pulp types, wreckage paper handling, and long pipelines.

Normal papermaking conditions are suitable for the growth of a variety of microbes. The short and long cycle circulating zero water contains enough carbohydrates and other essential ingredients ... such as inorganic substances and trace elements. Also used in papermaking * '! the chemicals themselves are ideal sources of nutrients, for example starch, or contain · ;;; quite a lot of nutrients such as kaolin as impurities. Incoming '· · ·' raw water can also contain significant amounts of nutrients.

• · · · ... The microbes found in the papermaking system can be divided into three main groups: bacteria, • fungi and algae. The bacteria are either spore-forming (anaerobic) or non-spore-forming (aerobic); fungi and molds and yeasts; and the predominant algae are bluish-green or green-green.

Microbial growth can cause many different problems, for example Air problems, runnability problems, corrosion problems, additive problems and product problems.

Unless antimicrobials are added to the papermaking system, overall microbial growth -: *: *. requirements are usually well met in papermaking systems. Modern microbial pesticides can be roughly divided into groups that act in the following ways: oxidative degradation of microbes 2 110533 (O2, CIO2, O3, peroxides); biocides that inhibit or kill microbes (organic, synthetic chemicals); and enzymes.

Oxygen is mainly used to prevent anaerobic conditions, while chlorine dioxide, ozone and peroxide act as biocides and disinfectants. They are quite effective, but they are considered expensive. Conventional biocides may be used alone or in combination with oxidative biocides. They are effective but toxic. They can also be hazardous to the environment and risky for the working environment. The use of the enzyme is a relatively new method of controlling mucus. Enzymes are active in the pH range of 3.5-10, which is an advantage over conventional biocides. However, enzymes have a limited effect on bacteria.

Oxygen and oxygen-rich gases have been used mainly to prevent the formation of hydrogen sulfide and other volatile gases produced by anaerobic bacteria in waste water. Robichaud, W.T., Tappi Journal, February, 1991, pp. 149-153, has described the use of aeration to control anaerobic bacteria to improve product quality and mill safety in papermaking systems.

The use of carbon dioxide in papermaking has previously been proposed for various reasons, mainly related to certain pH adjustment needs or to affecting carbonate or bicarbonate chemistry. Examples of patents relating to the use of carbon dioxide in papermaking systems are US 5,378,322 (Canadian Liquid Air); US 5,262,006 (Mo och Domsjo AB); EP 0 296 198 (AGA Aktiebolag); EP 0 281 273 (BOC Group); GB 2 008 562 (J.M. Voith GmbH); WO 99/24661 (AGA Aktiebolag); and WO 99/35333 (AGA Aktiebolag).

, .. None of these publications relate to the problem of microbial growth.

Mixtures of gas have been used in food packaging for the original taste of the food, ·; * ·; to maintain structure and appearance. Mixtures of gases usually consist of carbon dioxide, nitrogen and oxygen, but other gases such as nitric oxide, argon and hydrogen have also been used. Carbon dioxide inhibits microbial activity in food by lowering pH and penetrating biological membranes, causing changes in permeability and function. Nitrogen is mainly used to replace oxygen in packages. Oxygen helps maintain the oxidized form of myoglobin, which gives the meat its red color. Oxygen is also required for the breathing of fruits and vegetables.

L, .: In Amanatidou, A .; Smid, E. J.; Gorris, L. G.; J Appl. Microbiol., March 1999, p.

429-38, the effect of elevated oxygen and carbon dioxide levels on the surface growth of vegetable-associated microorganisms is described. Strong inhibition was consistently observed only when the two gases were used together.

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As mentioned above, microbial growth problems are common in papermaking systems, particularly in storage tanks and long pipelines. In addition, protecting the environment by shutting down zero-water cycles and increased recycling of process water, as well as increased use of waste paper, have resulted in a significant increase in microbial growth in papermaking systems.

As a result, there is a growing need in the paper industry for ways to reduce microbial growth in a technically feasible, inexpensive and environmentally friendly manner.

It has now been found that a gas inhibitor in the form of carbon dioxide, nitrogen, noble gas, or a gas mixture containing one or more of said gases can be used to control microbial growth in papermaking systems.

Therefore, the present invention provides a process for controlling microbial growth in a cellulosic product production line, which process comprises providing an aqueous material containing water as well as suspended pulp fibers and / or additives, said aqueous material being maintained under conditions susceptible to microbial growth, gaseous, a gas selected from the group consisting of nitrogen, noble gases or non-natural gas mixtures containing the same, and introducing said gas inhibitor into said aqueous material in an amount sufficient to significantly slow down or inhibit the growth of microorganisms therein.

Preferably, the gas inhibitor is added immediately prior to and / or during storage of said aqueous material, since storage provides sufficient time for microbes .. to multiply.

The gas inhibitor should preferably consist of or contain carbon dioxide, nitrogen and / or noble gas such as: helium, neon, argon, krypton, xenon and / or radon: '' ': a significant amount. Carbon dioxide is a preferred gas according to the invention. Argon is an inexpensive noble gas.

,> ··. If a gas mixture is used, said mixture must be non-natural. The gases of the mixture may be mixed together prior to being introduced into the aqueous material, or they may be added separately, simultaneously or sequentially. Although the gas mixture may contain oxygen, it should not be an air composition: · Because air is known to inhibit the growth of only anaerobic microbes.

; The gas inhibitor of the invention can be used in combination with oxygen, either by combining oxygen with a mixture of carbon dioxide, nitrogen and / or argon, or by adding oxygen separately from the other 4,105,333 gases. When oxygen is added to the gas mixture, the amount of oxygen may vary from 10 to 90% of the total gas volume. However, according to one embodiment of the invention, the oxygen-rich gas is introduced into the aqueous material separately from the gas inhibitor of the invention. Such an oxygen rich gas may be added either before or after the addition of the inhibitory gas mixture.

The invention will now be described in more detail with reference to papermaking systems. However, it is clear that the gaseous inhibition system of the invention can also be used in the manufacture of pulp, board, etc. As used in the invention, the production line for cellulosic products comprises pulp, paper, board and the like. The production line typically comprises at least a portion of the recycled paper and / or waste paper and includes circulating loops. The production line has a more or less closed water cycle, and one skilled in the art will recognize that problems associated with microbial growth tend to escalate in closed systems, thereby increasing the mass of microbes circulating in the system and accumulating.

The temperature of papermaking systems usually ranges from 30 ° C to 60 ° C. Due to recycling, the temperature of the zero water often exceeds 50 ° C. Fungi and yeasts generally do not tolerate temperatures above 40 ° C. In contrast, many bacteria thrive in a very high temperature range. The pH usually ranges from 3 to 10. The acidic conditions at pH 3-6 are very suitable for fungi and yeasts. The bacteria predominate under neutral and alkaline conditions, i.e. in the pH range of 7-10. Anaerobic conditions can be found in many locations throughout the production line, such as post-bleach storage, pulp types' ·; and in circulation tanks.

• ... 'Mucus helps germs to attach to surfaces and acts as a food store. Microbial growth causes usability problems by clogging filters and screens, lowering the age of the wire and felt, and lowering productivity due to breaks, washes, and the like. Microbial corrosion is: * _ _: due to vigorous microbial activity on surfaces.

·; ··· The most important microbial species in this field are sulphate-reducing bacteria, which are, ·· *, anaerobic in nature. However, there are many aerobic species that are harmful.

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Additives such as starch can be spoiled by microbial activity, not to mention:>; : The fact that a contaminated starch slurry can form a rich inoculum in the zero water cycle.

: 'When the microbial masses are removed from their actual places of growth, the result may be spots, holes or smudges on the final paper product. Spore-forming bacteria are very resistant to heat and usually survive the drying stage. Thus, they remain alive in the product and may subsequently be harmful.

110533 The use of the present invention must take into account the particular conditions of the papermaking system, which utilize enormous amounts of fluid that are in motion all the time and do not have clear surfaces on which microbes tend to occur. This is in sharp contrast to, for example, packaging food with shielding gases. Food does not move anywhere in the package, its surface is solid and the product is surrounded by a gas atmosphere. In a papermaking system, the surface of the aqueous material is constantly changing and cannot be surrounded by gas.

The term microbial or microorganism as used in the context of the present invention refers to bacteria, fungi and / or algae as described above. It will be appreciated that not all microorganisms present in the papermaking system will be affected by the gas inhibitor of the invention, and therefore the gas inhibitor of the invention may be used in combination with other inhibitors such as oxygen rich gases and various biocides.

According to the invention, the gas inhibitor reduces microbial growth in the papermaking system. The gas inhibitor of the invention is a gas or gas mixture capable of inhibiting, in whole or in part, the growth of microorganisms in a papermaking system. The preferred single gas is carbon dioxide. The gas inhibitor may also contain nitrogen and / or argon. Said gases can also be used alone, but more preferably they are used in combination with carbon dioxide. A suitable gas inhibitor consists of a mixture of carbon dioxide, nitrogen and argon. Preferably the mixture contains at least 10% carbon dioxide.

The gas inhibitor may additionally contain oxygen. Oxygen should not be used in air-like combinations because such a mixture is effective only against anaerobic microorganisms.

In the mixture of carbon dioxide and oxygen, the proportion of carbon dioxide should be between 90% and 10% and the proportion of oxygen should be between 10% and 90%. It should be noted that ordinary air contains about 21% oxygen and about 0.03% carbon dioxide.

In a preferred embodiment of the invention, a gas inhibitor consisting essentially of: carbon dioxide, nitrogen, argon, or a mixture thereof, is introduced into the liquid stream of the second material passing to the storage tanks of said liquid material, or directly to said storage tanks. a storage tank. The oxygen-free gas inhibitor is added: preferably in an amount sufficient to deplete the oxygen in said aqueous material, thereby inhibiting the growth of aerobic bacteria therein. Most aerobic bacteria are. sensitive to oxygen deficiency and with this action they will eventually die off while carbon dioxide. ·,: Contrary to many anaerobic species.

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In an improved embodiment, oxygen is used separately from the gas inhibitor of the invention. Then, after a suitable residence time of the gas inhibitor and / or prior to its use, an amount of oxygen-containing gas is introduced into said storage tank in an amount sufficient to kill the anaerobic bacteria from the aqueous material.

Conducting the gas inhibitor and conducting the oxygen may be repeated alternately during the storage of said aqueous material.

Preferably, the inhibitor is added to the site where the risk of microbial growth is greatest, i.e.. storage tanks for aqueous slurry or aqueous additives that are susceptible to microbial attack. However, the gas inhibitor may also be added to the liquid streams of the aqueous material, to the circulation water and to the raw water before it enters the system. The basic principle of the invention is to reduce microbial growth in any place where it would otherwise rise to harmful dimensions. It is not necessary to kill all microbes, but it is essential to reduce the microbial growth to a level that minimizes harmful accumulations in the production line and in the final product.

In a preferred embodiment of the invention, the gas inhibitor is introduced into the liquid stream of the aqueous material or into the liquid stream of the diluent or additive for said material just prior to storage. The gas inhibitor may also be introduced into any storage container containing said aqueous material by blowing gas into the aqueous material and / or filling the void above the liquid.

In a typical process according to the invention, the aqueous material contains pulp slurry. ·· In the papermaking system, and the slurry is treated with a gas inhibitor before it enters and / or stored in the pulp stockpile, pulp type, broke ': tower, or similar storage container.

In a preferred embodiment, the aqueous material to be treated contains paper machine zero water, preferably long-cycle zero water.

In one embodiment, the aqueous material contains a slurry of an additive chemical, such as starch, a coating agent, a pigment, a filler, or the like. Such additives are generally held in aqueous slurries ready for use in the papermaking process, and many additives contain nutrients, making them susceptible to microbial attack. Typically this is: the situation with starch, which is itself a nutrient for many microorganisms. Many other additives, although unresponsive themselves, contain sufficient amounts of impurities, which over time renders them susceptible to microbial attack. Treatment of such additive containers by occasionally introducing a gas inhibitor effectively reduces the amount of microbes entering the system.

In a preferred embodiment of the invention, the gas inhibitor is added at a late stage, preferably just before the point where the microbial attack is expected to be most severe, such as in a storage tomato. An additional gas inhibitor (carbon dioxide / nitrogen / argon) should be added to the top of the tower if necessary.

If oxygen is used in combination with a gas inhibitor, oxygen should preferably be added immediately after the aqueous material is pumped into the tank to utilize all the turbulence to effect effective mixing. If necessary, additional oxygen should be added to one of the turret's recirculation tubes to avoid creating anaerobic areas without tanks.

It should be noted that although gases such as carbon dioxide and oxygen have been previously used in papermaking, the gas inhibitor of the invention containing carbon dioxide, nitrogen or argon alone or in a non-native gas mixture has not previously been used in papermaking systems to control microbial growth.

The aqueous materials of the cellulose production line are processed into cellulose products, such as paper, board, dried pulp or the like, in a manner which is conventional in all other respects, except for the biocidal treatment of the invention.

* * · ..: The invention will now be described by the following examples.

'| · Example 1

A series of representative bacterial strains were isolated from a blank water sample from a Swedish recycled pulp mill. The sample initially produced 70 strains of bacteria, each representing a group of different .... bacteria growing under the same conditions. The strains were tested on various media and, ···. their oxygen requirements were examined. The results indicated the presence of eight main groups. Additional '·' studies showed that three of the eight main groups appeared to be almost identical.

:. These three groups were combined into one large group.

. *, ·. From this group of powers, one strain was selected for carbon dioxide tests. Two,,: other positions from another recycled pulp mill were included in the experiments.

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The glass vials were heated to 45 ° C and CO2 was added to create a carbon dioxide atmosphere. Bacteria from the three isolated strains were added to separate flasks with nutrient broth. The first sample, representing the "0 min" group, was immediately removed from each flask, and then several times over the next three hours. Each sample was diluted in a dilution series with 1/10 dilution in six steps (10'-106) and grown on agar plates. Plates were incubated at 45 ° C for two days, after which the number of colonies was counted and proportional to dilution.

Table 1 shows the percentage of surviving cells as a function of growth time in a CO2 atmosphere.

table 1

Time Strain 1 Strain 2 Strain 3 Average (min) (%) (%) (%) (%) 0 100 100 100 100 10 75 141 92 103 20 34 76 77 62 30 73 137 58 89 40 50 48 47 48 50 61 94 36 64 60 59 46 67 57 80 39 88 44 57 100 16 55 42 38 120 18 43 16 47 140 5 35 7 16 160 4 41 4 16 180 9 24 2 12

The results clearly show that after about 1 hour, about 60% of the bacteria had survived, after about 2 hours about 50% and after about 3 hours just over 10% (just over 100; * *:% values are due to small sampling or dilution) errors).

"; Example 2

The mill produced wood-free paper from chemical pulp. During the tests, the mill will store the pulp for long periods in the tank tomatoes before the pulp is manufactured. Storage caused problems in the form of bad odor and black spots in the pulp, believed to be due to the lively microbial activity during storage.

A full treatment assay with a gas inhibitor was performed. Thus, carbon dioxide gas was introduced. in quantities of 1 to 2 kg COV / tonne shortly before tank.

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Both the bad smell of the pulp and the number of black spots in the pulp decreased. No adverse effects were observed with the use of CC 1.

Example 3

The pulp storage tomato, which has the problem of excessive microbial growth at the end of production, is filled with a pump until the storage tomato is filled to about 80% of capacity.

Just before the pulp enters the tower, a gas inhibitor containing a 70/25/5 carbon dioxide / nitrogen / argon mixture is added. The gas is supplied to the feed line at a dose of 1.5 kg gas per tonne of pulp. The gas supply is continued for about 5 minutes after the feed pump has stopped supplying mass to the tower so that the gas inhibitor fills the upper space of the tower.

Two hours after feeding the gas inhibitor mixture, oxygen-rich gas (air) is added to the pulp in the tower via a gas manifold. The oxygen-rich gas addition is continued until a significant amount of oxygen is present in the air outlet of the tower.

The treatment is repeated the next day by first feeding the gas inhibitor of the invention to the gas manifold, and after a residence time of about 2 hours, oxygen-rich gas is fed through the tube. The microbicidal treatment is repeated daily at the end of production.

The tank-free microbial growth is reduced to an acceptable level, and at start-up no odor problems are detected. The paper web normally consists of stored pulp, and only a minimal amount of dirt spots are detected on the paper.

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Claims (23)

1. A process for preventing the proliferation of microbes in the cellulose product production line, characterized in that an aqueous material, consisting of the water, suspended pulp fibers and / or its additives, is prepared - the aqueous material is preserved in conditions favorable for microbial propagation - are provided from a group consisting of carbon dioxide, nitrogen, noble gases and mixtures thereof which are not found in nature - said inhibitor gas is introduced into the aqueous material in sufficient quantity to significantly inhibit or prevent the propagation of microorganisms therein. A process according to claim 1, characterized in that the aqueous material is stored in a storage vessel and said inhibitor gas is introduced before and / or during storage. 3. A process according to claim 1 or 2, characterized in that said gas consists mainly of carbon dioxide, nitrogen or one or more noble gases. A method according to claim 1 or 2, characterized in that said noble gas is selected from helium, neon, argon, krypton, xenon or radon. 5. A process according to claim 1 or 2, characterized in that said inhibitor gas is a mixture of carbon dioxide and nitrogen. probably in the ratio 10-90%, carbon dioxide and 90-10% nitrogen. 6. A method according to claim 1 or 2 characterized therein. the said "": inhibitor gas further contains oxygen. > <· T · 7. A process according to claim 5, characterized in that said inhibitor gas: contains a combination of carbon dioxide and oxygen, preferably in the ratio of 10-90% of carbon dioxide and 90-10% of oxygen. ; 8. A process according to claim 1, characterized in that said inhibitor gas contains a combination of carbon dioxide. nitrogen, noble gases and oxygen. consisting of at least 10 in carbon dioxide. 9. A method according to any one of claims 1-8, characterized in that said inhibitor gas is conducted in a liquid stream of said material prior to said storage. 10. A process according to any one of claims 1 to 8, characterized in that said inhibitor gas is conducted into a brewing container containing said aqueous material. 11. A process according to any one of claims 1 to 8, characterized in that said inhibitor gas is introduced into a diluent for said material. A method according to any of claims 1-11, characterized in that said microorganisms comprise bacteria, fungi and / or algae. 13. A process according to claim 1, characterized in that said inhibitor gas consisting mainly of carbon dioxide, nitrogen, argon gases or mixtures thereof, is passed into the container of said aqueous material through a liquid stream or into the container itself. 14. A method according to claim 13, characterized in that the said introduction of the inhibitor gas is followed and / or preceded by the introduction of an oxygen-containing gas into the reservoir container or into the liquid stream flowing into the container. 15. A process according to claim 14, characterized in that said introduction of the inhibitor gas and said introduction of the oxygen-containing gas is repeated in turn during said storage of the aqueous material. i I · I · 16. A process according to any one of claims 1 to 15, characterized in that said aqueous material is a pulp suspension stored in a pulp storage compartment, one or more. : pulp cases, a scrap paper tower, or equivalent trash container. A method according to any one of claims 1-15 characterized therein. that said aqueous material is pulp for the production of pulp in one,. paper production system. 18. A process according to any of claims 1 to 15, characterized in that said aqueous material is backwater in a paper machine, presumably backwater in ... | the backwater tank for the long cycle. 1 A method according to any of claims 1-15 characterized therein. that said aqueous material is sludge from a chemical additive such as starch. coating, pigment, filler or equivalent. 20. A method according to any of claims 1-19, characterized in that said production line for cellulose products comprises a production line for pulp, paper, paperboard or the like. 21. A method according to claim 20, characterized in that said production line comprises reworking of recovered paper and / or scrap paper. 22. A method according to claim 20 or 21, characterized in that said production line has a substantially closed rear water system. A process according to any one of claims 1 to 22, characterized in that said aqueous material treated with said inhibitor gas is processed into a cellulose product such as pulp, paper, paperboard or the like. Use of carbon dioxide, nitrogen or noble gas separately or in a non-natural gas mixture characterized in that it precedes inhibitor gas to prevent microbial propagation in an aqueous material containing water and suspended pulp fibers and / or its additives, and the material is treated and treated. / or stored in the production line for cellulose products. Use according to claim 24, characterized in that said inhibitor gas consists mainly of carbon dioxide. Use according to claim 25, characterized in that carbon dioxide and oxygen are used:>: together or alternately introduced into said material. ► · 3 Use according to any one of claims 24 - 26, characterized in that it precedes: production of paper in a production line with a substantially closed t, · ·, backwater system comprising reworking of recovered paper. > »» »· J ·» * a * I