WO2016185396A1 - Cleaning of process waters or surfaces from bacteria using nanobubbles - Google Patents

Cleaning of process waters or surfaces from bacteria using nanobubbles Download PDF

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Publication number
WO2016185396A1
WO2016185396A1 PCT/IB2016/052892 IB2016052892W WO2016185396A1 WO 2016185396 A1 WO2016185396 A1 WO 2016185396A1 IB 2016052892 W IB2016052892 W IB 2016052892W WO 2016185396 A1 WO2016185396 A1 WO 2016185396A1
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WO
WIPO (PCT)
Prior art keywords
gas bubbles
paper
gas
paper making
less
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PCT/IB2016/052892
Other languages
French (fr)
Inventor
Isto Heiskanen
Kaj Backfolk
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Stora Enso Oyj
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Publication date
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Publication of WO2016185396A1 publication Critical patent/WO2016185396A1/en

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Classifications

    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
    • D21H21/00—Non-fibrous material added to the pulp, characterised by its function, form or properties; Paper-impregnating or coating material, characterised by its function, form or properties
    • D21H21/14—Non-fibrous material added to the pulp, characterised by its function, form or properties; Paper-impregnating or coating material, characterised by its function, form or properties characterised by function or properties in or on the paper
    • D21H21/36—Biocidal agents, e.g. fungicidal, bactericidal, insecticidal agents
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
    • D21H21/00—Non-fibrous material added to the pulp, characterised by its function, form or properties; Paper-impregnating or coating material, characterised by its function, form or properties
    • D21H21/02—Agents for preventing deposition on the paper mill equipment, e.g. pitch or slime control
    • D21H21/04—Slime-control agents
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
    • B01F23/00—Mixing according to the phases to be mixed, e.g. dispersing or emulsifying
    • B01F23/20—Mixing gases with liquids
    • B01F23/23—Mixing gases with liquids by introducing gases into liquid media, e.g. for producing aerated liquids
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
    • B01F23/00—Mixing according to the phases to be mixed, e.g. dispersing or emulsifying
    • B01F23/20—Mixing gases with liquids
    • B01F23/23—Mixing gases with liquids by introducing gases into liquid media, e.g. for producing aerated liquids
    • B01F23/237—Mixing gases with liquids by introducing gases into liquid media, e.g. for producing aerated liquids characterised by the physical or chemical properties of gases or vapours introduced in the liquid media
    • B01F23/2373—Mixing gases with liquids by introducing gases into liquid media, e.g. for producing aerated liquids characterised by the physical or chemical properties of gases or vapours introduced in the liquid media for obtaining fine bubbles, i.e. bubbles with a size below 100 µm
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21B—FIBROUS RAW MATERIALS OR THEIR MECHANICAL TREATMENT
    • D21B1/00—Fibrous raw materials or their mechanical treatment
    • D21B1/04—Fibrous raw materials or their mechanical treatment by dividing raw materials into small particles, e.g. fibres
    • D21B1/12—Fibrous raw materials or their mechanical treatment by dividing raw materials into small particles, e.g. fibres by wet methods, by the use of steam
    • D21B1/30—Defibrating by other means
    • D21B1/32—Defibrating by other means of waste paper
    • D21B1/325—Defibrating by other means of waste paper de-inking devices
    • D21B1/327—Defibrating by other means of waste paper de-inking devices using flotation devices
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
    • D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
    • D21C9/10—Bleaching ; Apparatus therefor
    • D21C9/147—Bleaching ; Apparatus therefor with oxygen or its allotropic modifications
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
    • D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
    • D21C9/10—Bleaching ; Apparatus therefor
    • D21C9/147—Bleaching ; Apparatus therefor with oxygen or its allotropic modifications
    • D21C9/153—Bleaching ; Apparatus therefor with oxygen or its allotropic modifications with ozone
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
    • D21H21/00—Non-fibrous material added to the pulp, characterised by its function, form or properties; Paper-impregnating or coating material, characterised by its function, form or properties
    • D21H21/50—Non-fibrous material added to the pulp, characterised by its function, form or properties; Paper-impregnating or coating material, characterised by its function, form or properties characterised by form
    • D21H21/56—Foam
    • C—CHEMISTRY; METALLURGY
    • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
    • C12M—APPARATUS FOR ENZYMOLOGY OR MICROBIOLOGY; APPARATUS FOR CULTURING MICROORGANISMS FOR PRODUCING BIOMASS, FOR GROWING CELLS OR FOR OBTAINING FERMENTATION OR METABOLIC PRODUCTS, i.e. BIOREACTORS OR FERMENTERS
    • C12M39/00—Means for cleaning the apparatus or avoiding unwanted deposits of microorganisms
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
    • D21F1/00—Wet end of machines for making continuous webs of paper
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
    • Y02W30/00—Technologies for solid waste management
    • Y02W30/50—Reuse, recycling or recovery technologies
    • Y02W30/64—Paper recycling

Definitions

  • the present document relates to a method for reducing bacterial growth and bio-film formation in a paper making process by introducing gas bubbles having a diameter of less than 0.5 micrometers into the process.
  • microbial growth in make-up water streams, process waters, slurries, and on the paper sheet itself can all lead to significant product quality issues such as odors, contaminations, discoloration, and breaks.
  • product quality issues such as odors, contaminations, discoloration, and breaks.
  • the growth or deposits, i.e. a so called bio-film formation, on the paper or board machine can lead to severe product quality issues, but also to spoilage of raw materials such as starch, mineral suspensions, fibers or recycled broke.
  • One conventional way of removing or reducing bacterial growth in the process waters is to add chemicals, such as biocides.
  • Electrochemical methods are also often used to remove the deposits or bio- films.
  • the wet end of the paper machine i.e. the stock preparation, the broke system, the water circulation and the wire section can all be equipped with online cleaning units, for instance, spray shower nozzles, spraying water, for preventing an increase in microbial activity or formation of deposits.
  • online cleaning units for instance, spray shower nozzles, spraying water, for preventing an increase in microbial activity or formation of deposits.
  • the washing water used in the process can be a source of microbial growth, and this can thus cause serious problems if biocides are not used, or if the spray shower nozzles used for introducing the washing water are not cleaned regularly.
  • biocides are, however, undesirable from an environmental and cost point of view, and in addition, if the paper product is to be used for food packaging etc. the use of biocides may compromise the product safety, or the amount that can be used during manufacture may be very limited due to safety regulations in for instance the food packaging industry. There is thus a need for a new way of cleaning or sanitizing process waters, including the raw materials, and the papermaking machines in a more efficient and environmentally safe manner.
  • a method for removing or reducing bacterial growth or bio-film formation in a paper or paperboard making process comprising introducing gas bubbles, having a diameter of less than 0.5 micrometer, into the paper or paperboard making process.
  • the gas bubbles may be introduced into a process water stream of the papermaking process.
  • process water stream is meant any stream of water used in any part of the paper making process.
  • gas bubble may be introduced into the stock preparation system, the stock and water supply thereto, or the white water system or fiber recovery system, or any other process water stream.
  • nanobubbles may be introduced directly into the water where bacterial growth occurs and provides for an efficient cleaning in the process water.
  • gas bubbles may be introduced into a cleaning water stream of the paper making process.
  • cleaning water stream any stream of substantially fresh water used for cleaning or washing any part or surface of a paper making machine, e.g. washing felts or cleaning parts of the machine such as the wire.
  • cleaning water any stream of substantially fresh water used for cleaning or washing any part or surface of a paper making machine, e.g. washing felts or cleaning parts of the machine such as the wire.
  • the nanosized bubbles of gas may be introduced into the process by means of firstly being dissolved in the cleaning water, prior to its application in the process, thus creating a nanobubble water stream.
  • the water stream may be applied onto for instance a roll/cylinder or the wire to remove deposits such as bio-films.
  • the water stream comprising the nanosized bubbles may be used for removal of other deposits of process chemicals such as for instance alkyl ketene dimer (AKD), alkyl succinic anhydride (ASA) or other waxy components.
  • ALD alkyl ketene dimer
  • ASA alkyl succinic anhydride
  • PCC precipitated calcium carbonate
  • gas bubbles may be formed in-situ in the paper making machine.
  • in-situ is meant that the bubbles are generated within the paper making machine.
  • the gas bubbles may be injected into a wet end of a paper making machine.
  • the gas bubbles may be introduced continuously.
  • gas bubbles are supplied into the paper making process, such as a process water stream or into the cleaning water in a continuous manner.
  • the gas bubbles may be introduced in a batch operation.
  • the air bubbles may be introduced in a separate cleaning step or as a "shock treatment" of the system.
  • the diameter of the gas bubbles may be less than 400 nanometer, or less than 300 nanometers, or less than 200 nanometers.
  • the gas bubbles may comprise any one of atmospheric air, oxygen, nitrogen, carbon dioxide, ozone or a mixture of two or more of atmospheric air, oxygen, nitrogen, ozone or carbon dioxide.
  • the gas may be hot.
  • the gas may be cold.
  • the method may further comprise the introduction of additives for removing or reducing bacterial growth, wherein said additives includes biocides.
  • additives for removing or reducing bacterial growth
  • biocides for reducing bacterial growth
  • the combination of conventional additives and nanobubbles may further enhance the effect on bacterial removal or growth.
  • gas bubbles having a diameter of less than 0.5 micrometers for introduction into a paper making process and for removing or reducing bacterial growth or bio-film formation.
  • Fresh water may for instance used to form the stock solution, or for cleaning the machine or different parts of the machine.
  • White water is the process water that is removed from the furnish during formation of a paper sheet. The white water is usually recycled directly in the process to form the thick stock solution. A part of the white water may be cleaned and filtered, and the clear white water stream may be discharged to wastewater treatment, or it may be further filtered to make it suitable for use in cleaning showers on the paper machine.
  • gas bubbles are introduced into the paper making process.
  • the gas bubbles have a diameter which is less than 0.5 micrometers (pm).
  • the small size of these bubbles, or the so called micro- or even nanosized bubbles (i.e. a nanobubble) gives them physical stability such that they do not dissolve away, and they are highly persistent once formed.
  • Nanobubbles can be formed in a number of different ways described in the art, such as cavitations mechanisms with power ultrasound, or creating vapor from surrounding liquid, by using uniform nonporous membranes which can achieve sub-100 nm bubbles, or by using a fluidic oscillation technique (Towards energy efficient nanobubble generation with fluidic oscillation, Zimmerman B. W et al, Current Opinion in Colloid & Interface Science 16 (201 1 ) 350-356).
  • the gas is atmospheric air, i.e. a mixture of oxygen, nitrogen and other gases present in the earth's atmosphere.
  • the gas is oxygen (O2).
  • the gas is nitrogen (N2).
  • the gas is carbon dioxide (CO2).
  • the gas is ozone (O3).
  • the gas is a mixture of different gases, such as a mixture of air and N2, or air and CO2.
  • the gas may also be any other suitable gas or mixture of gases.
  • the gas is hot, or has been heated prior to the introduction into the process.
  • the gas is cold, or has been cooled prior to the introduction into the process.
  • the diameter of the nanobubble is in the range of from 0.1 pm to 10 pm. In one embodiment the diameter of the nanobubble is in the range of from 0.1 pm to 1 pm. In another embodiment the diameter of the nanobubble is in the range of from 0.1 pm to 0.8 pm. According to yet an embodiment the diameter of the nanobubble is in the range of from 0.1 pm to 0.6 pm. In one embodiment the diameter is less than 0.5 pm. According to another embodiment the diameter is less than 0.4 pm. According to yet another embodiment the diameter is less than 0.3 pm.
  • gas bubbles having different diameters.
  • the main part of the gas bubbles introduced into the paper making process, or formed within the paper making process are preferably nanosized, i.e. having a diameter of less than 0.5 micrometers.
  • the air bubbles i.e. the nanobubbles may, according to one
  • nanobubbles are bubbled into for instance the stock solution or into the white water.
  • the nanobubbles may be formed directly before being bubbled into the process water, or pre-formed and then transported or stored before being introduced into the process water.
  • the nanobubbles could also, alternatively, be formed in-situ, i.e. within the paper making machine itself.
  • the nanobubbles could, according to one embodiment, be supplied continuously into the process water in a so called in-line process.
  • nanobubbles could be introduced in a batch operation as a "shock treatment” or cleaning step in the process or of the machine.
  • the nanobubbles could be introduced into a stream of cleaning or washing water, i.e. introduced as a nanobubble stream into the process or machine. This could be advantageous when using the nanobubbles for cleaning or washing different parts and surfaces of the paper making machine such as the wire or the surface of cylinders.
  • the nanobubble water stream could be introduced continuously, e.g. in an in-line process, or according to an alternative embodiment in a batch operation, e.g. when spraying the wire or cylinders to clean them from deposits of formed bio-film or other types of deposits.
  • the introduction of the nanobubbles into the paper making process or machine could give synergistic effects with for instance existing biocide systems.
  • One theory is that more reactive free radicals can be formed and thus enhance the efficiency of the biocides or other types of additives used for removing or reducing bacterial growth or bio- film formation in the paper making process. It is thus possible to reduce the amount of biocides or additives used and still achieve the same effect. This is due to that the efficiency of the biocides is increased when nanobubbles are added.
  • Bioactive chemicals are also included in the meaning of biocides.
  • biocides examples include; chlorine gas, hypochlorite, ozone, peroxide, quaternary ammonium compounds, halogenated hydantoin, 2-Bromo-2-nitropropane-1 ,3-diol, 5-Chloro-2-methyl-4-isothiazolin-3-one, 2,2- Dibromo-2-cyanoacetamide (DBNPA), n-Octyl-isothiazolin-3-one, Methylene bisthiocyanate (MBT), Tetrakis(hydroxymethyl)phosphonium sulfate (THPS) and/or glutaraldehyde.
  • DBNPA 2,2- Dibromo-2-cyanoacetamide
  • Methylene bisthiocyanate Methylene bisthiocyanate
  • THPS Tetrakis(hydroxymethyl)phosphonium sulfate

Abstract

A method for removing or reducing bacterial growth or bio-film formation in a paper or paperboard making process, wherein the method comprises introducing gas bubbles, having a diameter of less than 0.5 micrometer, into the paper or paperboard making process.

Description

CLEANING OF PROCESS WATERS OR SURFACES FROM
BACTERIA USING NANOBUBBLES
Technical field
The present document relates to a method for reducing bacterial growth and bio-film formation in a paper making process by introducing gas bubbles having a diameter of less than 0.5 micrometers into the process.
Background
In the papermaking industry, including paperboard industry, microbial growth in make-up water streams, process waters, slurries, and on the paper sheet itself can all lead to significant product quality issues such as odors, contaminations, discoloration, and breaks. Further to the bacterial growth in the process water, the growth or deposits, i.e. a so called bio-film formation, on the paper or board machine can lead to severe product quality issues, but also to spoilage of raw materials such as starch, mineral suspensions, fibers or recycled broke. One conventional way of removing or reducing bacterial growth in the process waters is to add chemicals, such as biocides.
Electrochemical methods are also often used to remove the deposits or bio- films. The wet end of the paper machine, i.e. the stock preparation, the broke system, the water circulation and the wire section can all be equipped with online cleaning units, for instance, spray shower nozzles, spraying water, for preventing an increase in microbial activity or formation of deposits. However, even the washing water used in the process can be a source of microbial growth, and this can thus cause serious problems if biocides are not used, or if the spray shower nozzles used for introducing the washing water are not cleaned regularly.
The use of biocides is, however, undesirable from an environmental and cost point of view, and in addition, if the paper product is to be used for food packaging etc. the use of biocides may compromise the product safety, or the amount that can be used during manufacture may be very limited due to safety regulations in for instance the food packaging industry. There is thus a need for a new way of cleaning or sanitizing process waters, including the raw materials, and the papermaking machines in a more efficient and environmentally safe manner. Summary
It is an object of the present disclosure, to provide an improved process for cleaning process waters or a paper making machine, which eliminates or alleviates at least some of the disadvantages of the prior art cleaning techniques.
The object is wholly or partially achieved by a method according to the appended independent claims. Embodiments are set forth in the appended dependent claims, and in the following description.
According to a first aspect, there is provided a method for removing or reducing bacterial growth or bio-film formation in a paper or paperboard making process, wherein the method comprises introducing gas bubbles, having a diameter of less than 0.5 micrometer, into the paper or paperboard making process.
Conventionally the introduction of high amount of air in the furnish during production of paper or paper board is highly undesirable, due to the fact that air bubbles produces holes and other flaws in the produced paper or board. Surprisingly though, the introduction of these very fine so called micro or nanosized air bubbles (nanobubbles) does not impair the paper making process. It has been shown that the introduction of the nanobubbles of gas, such as for instance air, is very efficient for reducing bacterial growth or even completely inhibiting growth of bacteria in the paper making process. Through this method it is thus possible to efficiently prevent or reduce bacterial growth in the paper making process, without the, or with a reduced, need for using harmful chemicals such as for instance biocides.
According to one embodiment the gas bubbles may be introduced into a process water stream of the papermaking process.
By "process water stream" is meant any stream of water used in any part of the paper making process. This means that the gas bubble may be introduced into the stock preparation system, the stock and water supply thereto, or the white water system or fiber recovery system, or any other process water stream. This means that the nanobubbles may be introduced directly into the water where bacterial growth occurs and provides for an efficient cleaning in the process water.
According to another embodiment the gas bubbles may be introduced into a cleaning water stream of the paper making process.
By "cleaning water" stream is meant any stream of substantially fresh water used for cleaning or washing any part or surface of a paper making machine, e.g. washing felts or cleaning parts of the machine such as the wire. This means that the nanosized bubbles of gas may be introduced into the process by means of firstly being dissolved in the cleaning water, prior to its application in the process, thus creating a nanobubble water stream. The water stream may be applied onto for instance a roll/cylinder or the wire to remove deposits such as bio-films.
In addition to being efficient for the removal of bio-films the water stream comprising the nanosized bubbles may be used for removal of other deposits of process chemicals such as for instance alkyl ketene dimer (AKD), alkyl succinic anhydride (ASA) or other waxy components. Also other types of deposits can be removed for example, deposits originating from precipitated calcium carbonate (PCC).
According to an alternative embodiment the gas bubbles may be formed in-situ in the paper making machine.
By formed "in-situ" is meant that the bubbles are generated within the paper making machine.
According to one embodiment of the first aspect the gas bubbles may be injected into a wet end of a paper making machine.
According to one embodiment the gas bubbles may be introduced continuously.
This means that the gas bubbles are supplied into the paper making process, such as a process water stream or into the cleaning water in a continuous manner.
According to one alternative embodiment the gas bubbles may be introduced in a batch operation. By this method the air bubbles may be introduced in a separate cleaning step or as a "shock treatment" of the system.
According to one embodiment of the first aspect the diameter of the gas bubbles may be less than 400 nanometer, or less than 300 nanometers, or less than 200 nanometers.
There may also be a mixture of gas bubbles having different diameters.
The gas bubbles may comprise any one of atmospheric air, oxygen, nitrogen, carbon dioxide, ozone or a mixture of two or more of atmospheric air, oxygen, nitrogen, ozone or carbon dioxide.
According to one embodiment the gas may be hot.
This means that the air may have been heated prior to the introduction into the paper making machine, or heated when formed in the paper making machine.
According to an alternative embodiment the gas may be cold.
This means that the air may have been cooled prior to the introduction into the paper making machine, or cooled when formed in the paper making machine.
According to one embodiment the method may further comprise the introduction of additives for removing or reducing bacterial growth, wherein said additives includes biocides. The combination of conventional additives and nanobubbles may further enhance the effect on bacterial removal or growth.
According to a second aspect there is provided the use of gas bubbles having a diameter of less than 0.5 micrometers for introduction into a paper making process and for removing or reducing bacterial growth or bio-film formation.
Description of Embodiments
In a paper making process and a paper making machine, process water and different types of water streams are used for different purposes. Fresh water may for instance used to form the stock solution, or for cleaning the machine or different parts of the machine. White water is the process water that is removed from the furnish during formation of a paper sheet. The white water is usually recycled directly in the process to form the thick stock solution. A part of the white water may be cleaned and filtered, and the clear white water stream may be discharged to wastewater treatment, or it may be further filtered to make it suitable for use in cleaning showers on the paper machine.
Due to the fact that the process water contains a lot of nutrients there is a substantial problem with bacterial growth in the water, but also as deposits or bio-films that forms or grows onto the various parts of the paper making machine.
In one embodiment of the present invention gas bubbles are introduced into the paper making process. The gas bubbles have a diameter which is less than 0.5 micrometers (pm). The small size of these bubbles, or the so called micro- or even nanosized bubbles (i.e. a nanobubble) gives them physical stability such that they do not dissolve away, and they are highly persistent once formed. Nanobubbles can be formed in a number of different ways described in the art, such as cavitations mechanisms with power ultrasound, or creating vapor from surrounding liquid, by using uniform nonporous membranes which can achieve sub-100 nm bubbles, or by using a fluidic oscillation technique (Towards energy efficient nanobubble generation with fluidic oscillation, Zimmerman B. W et al, Current Opinion in Colloid & Interface Science 16 (201 1 ) 350-356).
In the description the term nanosized bubble or nanobubble will be used. According to one embodiment the gas is atmospheric air, i.e. a mixture of oxygen, nitrogen and other gases present in the earth's atmosphere.
According to another embodiment the gas is oxygen (O2). According to another embodiment the gas is nitrogen (N2). According to yet another embodiment the gas is carbon dioxide (CO2). According to yet another embodiment the gas is ozone (O3). According to one embodiment the gas is a mixture of different gases, such as a mixture of air and N2, or air and CO2. The gas may also be any other suitable gas or mixture of gases.
According to one embodiment the gas is hot, or has been heated prior to the introduction into the process. According to an alternative the gas is cold, or has been cooled prior to the introduction into the process. According to one embodiment the diameter of the nanobubble is in the range of from 0.1 pm to 10 pm. In one embodiment the diameter of the nanobubble is in the range of from 0.1 pm to 1 pm. In another embodiment the diameter of the nanobubble is in the range of from 0.1 pm to 0.8 pm. According to yet an embodiment the diameter of the nanobubble is in the range of from 0.1 pm to 0.6 pm. In one embodiment the diameter is less than 0.5 pm. According to another embodiment the diameter is less than 0.4 pm. According to yet another embodiment the diameter is less than 0.3 pm.
There may also be a mixture of gas bubbles having different diameters. However, the main part of the gas bubbles introduced into the paper making process, or formed within the paper making process are preferably nanosized, i.e. having a diameter of less than 0.5 micrometers.
The air bubbles, i.e. the nanobubbles may, according to one
embodiment be introduced into the process water or water streams of the papermaking process or machine. This means that the nanobubbles are bubbled into for instance the stock solution or into the white water. The nanobubbles may be formed directly before being bubbled into the process water, or pre-formed and then transported or stored before being introduced into the process water.
The nanobubbles could also, alternatively, be formed in-situ, i.e. within the paper making machine itself.
The nanobubbles could, according to one embodiment, be supplied continuously into the process water in a so called in-line process.
Alternatively the nanobubbles could be introduced in a batch operation as a "shock treatment" or cleaning step in the process or of the machine.
According to one embodiment the nanobubbles could be introduced into a stream of cleaning or washing water, i.e. introduced as a nanobubble stream into the process or machine. This could be advantageous when using the nanobubbles for cleaning or washing different parts and surfaces of the paper making machine such as the wire or the surface of cylinders.
According to one embodiment the nanobubble water stream could be introduced continuously, e.g. in an in-line process, or according to an alternative embodiment in a batch operation, e.g. when spraying the wire or cylinders to clean them from deposits of formed bio-film or other types of deposits.
It is further provided that the introduction of the nanobubbles into the paper making process or machine could give synergistic effects with for instance existing biocide systems. One theory is that more reactive free radicals can be formed and thus enhance the efficiency of the biocides or other types of additives used for removing or reducing bacterial growth or bio- film formation in the paper making process. It is thus possible to reduce the amount of biocides or additives used and still achieve the same effect. This is due to that the efficiency of the biocides is increased when nanobubbles are added. Bioactive chemicals are also included in the meaning of biocides. Examples of biocides that could be used are; chlorine gas, hypochlorite, ozone, peroxide, quaternary ammonium compounds, halogenated hydantoin, 2-Bromo-2-nitropropane-1 ,3-diol, 5-Chloro-2-methyl-4-isothiazolin-3-one, 2,2- Dibromo-2-cyanoacetamide (DBNPA), n-Octyl-isothiazolin-3-one, Methylene bisthiocyanate (MBT), Tetrakis(hydroxymethyl)phosphonium sulfate (THPS) and/or glutaraldehyde.
In view of the above detailed description of the present invention, other modifications and variations will become apparent to those skilled in the art. However, it should be apparent that such other modifications and variations may be effected without departing from the spirit and scope of the invention.

Claims

1 . A method for removing or reducing bacterial growth or bio-film formation in a paper or paperboard making process
c h a r a c t e r i z e d in that the method comprises introducing gas bubbles, having a diameter of less than 0.5 micrometer, into the paper or paperboard making process.
2. The method as claimed in claim 1 , wherein said gas bubbles are introduced into a process water stream of the papermaking process.
3. The method as claimed in claim 1 , wherein said gas bubbles are introduced into a cleaning water stream of the paper making process.
4. The method as claimed in claim 1 , wherein said gas bubbles are formed in-situ in the paper making machine.
5. The method as claimed in claim 1 , wherein the gas bubbles are injected into a wet end of a paper making machine.
6. The method as claimed in any one of the preceding claims, wherein the gas bubbles are introduced continuously.
7. The method as claimed in any one of the preceding claims, wherein the gas bubbles are introduced in a batch operation.
8. The method as claimed in any one of the preceding claims, wherein the diameter of the gas bubbles is less than 400 nanometer, or less than 300 nanometers, or less than 200 nanometers.
9. The method as claimed in any one of the preceding claims, wherein the gas bubbles comprise any one of atmospheric air, oxygen, nitrogen, carbon dioxide, ozone or a mixture of two or more of atmospheric air, oxygen, nitrogen, ozone or carbon dioxide.
10. The method as claimed in any one of the preceding claims wherein the gas is hot.
1 1 . The method as claimed in any one of claims 1 to 9, wherein the gas is cold.
12. The method as claimed in any one of the preceding claims, wherein the method further comprises an introduction of additives into the paper or papermaking process for removing or reducing bacterial growth, wherein said additives includes biocides .
13. A use of gas bubbles having a diameter of less than 0.5 micrometers for introduction into a paper making process for removing or reducing bacterial growth or bio-film formation.
PCT/IB2016/052892 2015-05-21 2016-05-18 Cleaning of process waters or surfaces from bacteria using nanobubbles WO2016185396A1 (en)

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