WO2013006466A2

WO2013006466A2 - Methods of reducing biofilm in air scrubbers

Info

Publication number: WO2013006466A2
Application number: PCT/US2012/045028
Authority: WO
Inventors: Michael F. Coughlin
Original assignee: Diversey Inc
Current assignee: Diversey Inc
Priority date: 2011-07-01
Filing date: 2012-06-29
Publication date: 2013-01-10
Anticipated expiration: 2014-01-01
Also published as: WO2013006521A2; WO2013006521A3

Abstract

Provided are methods of reducing biofilm, controlling the formation of biofilm, or controlling the growth of biofilm in an air scrubber. The methods may comprise desiccating the biofilm to produce a desiccated biofilm. Further provided are methods for reducing biofilm, controlling the formation of biofilm, or controlling the growth of biofilm in an air scrubber, the methods comprising introducing a composition into a liquid flow stream of the air scrubber to produce an acidic pH of the liquid flow, and adjusting the pH of the liquid flow to an alkaline pH.

Description

METHODS OF REDUCING BIOFILM IN AIR SCRUBBERS

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Patent Application No. 61/503,995, filed July 1 , 201 1 , which is incorporated herein by reference in its entirety.

FIELD OF INVENTION

[0001] The present disclosyre relates to methods for operating air scrubbers and reducing biofilm.

INTRODUCTION

[0002] Wet air scrubbers may be used with rendering plants. Rendering plants process unwanted and unused animal parts and tissue, for example, from meat-processing houses and slaughter houses, and convert them into useful finished goods including animal feed, fuel oil, and Pharma Cos ingredients. The air surrounding rendering plant equipment may have a bad odor and may contain volatile organic compounds (VOCs).

[0003] Air scrubbers may be used to reduce or eliminate malodor at rendering plants, for example, by removing volatile organic compounds from the air. A wet air scrubber operates on the principle that VOCs in the air diffuse into water and consequently are prevented from entering the atmosphere. Air scrubbers may, for example, comprise a tower with water flowing from the top of the tower to the bottom of the tower, with water then recycled to the top of the tower again. As air from a rendering plant is flowed through the air scrubber, VOCs may be removed from the air. While some air scrubbers rely on sprayed water to create an air/water interface for purification, some air scrubbers use plastic or stainless steel media to increase air/water surface area and to decrease water flow as the air flows upwards through the scrubber. If the water in the air scrubber is being treated with an oxidizer or other conventional treatment solution including acidified bleach, chlorine dioxide, ozone and/or permanganates, this media is often fouled with insoluble high molecular weight proteins, oils, greases, and other organic debris.

[0004] This fouling may cause several problems. First, as the media is fouled, the cross section available for air flow decreases, and the removal efficiency of volatile organic compounds is diminished. Second, the organic debris may act as a source of odor, especially after downtime when the water is not recirculating, if the recirculating water temperature temporarily increases during operation due to process temperature changes, and/or when treatment chemical is not being fed. The air scrubber at rest may allow hydrogen sulfide generating anaerobic bacteria under the deposits to flourish.

[0005] Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings.

SUMMARY

[0006] In certain aspects, provided are methods for at least one of reducing biofilm, controlling the formation of biofilm, or controlling the growth of biofilm in an air scrubber, the methods comprising desiccating the biofilm to produce a desiccated biofilm. In some embodiments, desiccating comprises operating at least one fan in the absence of water flow in the air scrubber.

[0007] In certain aspects, provided are methods for at least one of reducing biofilm, controlling the formation of biofilm, or controlling the growth of biofilm in an air scrubber, the methods comprising, (a) introducing a composition into a liquid flow stream of the air scrubber to produce an acidic pH of the liquid flow, and (b) adjusting the pH of the liquid flow to an alkaline pH.

[0008] In certain aspects, provided are methods of reducing biofilm in an air scrubber having a liquid flow system, the methods comprising (a) maintaining an acidic pH in the liquid flow system of the air scrubber, and (b) maintaining an alkaline pH in the liquid flow system. Step (b) may be performed after step (a).

[0009] In certain aspects, provided are methods of reducing biofilm in an air scrubber having a liquid flow system, the method comprising, (a) maintaining a first pH in the liquid flow system of the air scrubber; and (b) maintaining a second pH in the liquid flow system,

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 is a schematic diagram of a wet air scrubber. DETAILED DESCRIPTION

[0011] Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways.

[0012] Wet air scrubbers are prone to biofilm formation, as many operate at a pH and temperature conducive to biofilm growth. The gases sent to a wet air scrubber and particulate matter entrained therein can provide ample nutrients to support microbial growth, such as phosphate, amines, and organic carbon. Wet air scrubbers that are treated with oxidizers such as chlorine and chlorine dioxide are not encumbered with biological control issues because the oxidizers not only remove the odiferous compounds but also curtail microbial growth. If microbial growth is not controlled, slime will form within and on the wet air scrubber media. The formation of biofilm on the media may hinder the exchange of gas into the water phase and in doing so, allow the odiferous gases to leave the wet air scrubber and enter the environment essentially untreated. The end result is the release of odiferous and sometimes noxious compound into the surrounding community.

[0013] In certain embodiments, provided are methods for operating a wet air scrubber, for example, an air scrubber at a rendering plant as depicted schematically in Figure 1. Wet air scrubbers may include, for example, a packed tower scrubber, a spray tower scrubber, an orifice scrubber, a venturi scrubber, a fiber-bed scrubber, an impingement-plate scrubber, a spray nozzle scrubber, a fluidized-bed scrubber, a packed-bed scrubber, multiple-stage scrubbers, baffle spray scrubber, a counter-flow scrubber, a crossflow scrubber, and combinations thereof. Wet air scrubbers can be custom designed by, for example, an independent designer, or competent staff at a rendering facility. Wet air scrubbers are commercially available, for example, from Verantis, AC Corporation, Sep Control Inc., and Millpoint Industries Inc. Compositions and methods according to the invention may also be used with packed media wet air scrubbers at factories or plants including, but not limited to, municipal wastewater plants, pet food plants, flavor and fragrance plants, rendering plants, breweries, and grain operations such as corn processing. The compositions and methods according to the invention may control, reduce, or eliminate the formation and/or growth of biofilm in wet air scrubbers. The methods of maintaining biological control in wet air scrubbers and cooling towers may be less hazardous than alternative methods, such as those using chlorine dioxide or bleach.

[0014] Biofilm is a mixture of organic compounds, including polysaccharides, nucleic acids, and proteins, and inorganic salts, such as phosphate, magnesium, calcium, and sodium, in an aqueous medium. Without adequate amounts of water, most microbial cells with either die or transition to a dormant state. A biofilm may be desiccated, and a desiccation kills the biofilm and also reduces it to a fraction of the original volume.

[0015] In certain embodiments, provided are methods of reducing biofilm in a wet air scrubber. The methods may comprise desiccating the biofilm by providing an air flow in the air scrubber in the absence of water or liquid flow. The air flow may be provided by a fan, blower, bellow, compressed air, or other motive source. The methods may comprise operating the air scrubber with at least one fan in the absence of water or liquid flow in the air scrubber to produce a desiccated biofilm. Fans may include any suitable commercially available fan known in the art including, but not limited to, fans or blowers of the air scrubber. For example, a fan may be located at the top of the air scrubber tower. Fans may operate with air flow that is the same as during normal operation of the air scrubber, i.e., air flow into the air scrubber and air flow out of the air scrubber. At least one fan may be used. In other embodiments, at least two fans may be used, and may be positioned throughout the air scrubber in a manner that is productive in reducing biofilm. When at least two fans are used, the fans may operate with the same air flow direction to each other through the air scrubber. A fan may operate with air flow of about 15,000 to about 100,000 cfm.

[0016] The fan may be operated in the wet air scrubber for a period of time, which may be at least about 1 h, about 2h, about 3 h, at least about 4 h, at least about 5 h, at least about 6 h, at least about 7 h, at least about 8 h, at least about 9 h, at least about 10 h, at least about 1 1 h, or at least about 12 h. The fan may be operated in the wet air scrubber for a period of time that is less than about 30 h, less than about 24 h, less than about 22 h, less than about 20 h, less than about 18 h, or less than about 16 h. The fan may be operated in the wet air scrubber for a period of time of about 6 h to about 30 h, about 8 h to about 24 h, about 10 h to about 20 h, about 6 h to about 18 h, about 4 h to about 18 h, about 6 h to about 10 h, or about 12 h to about 18 h. The fan may be operated while the air scrubber is offline. The fan may be operated for multiple or repeated periods of time. The fan may be operated until the air scrubber is a suitable level of dryness. [0017] Reduction in biofilm may be determined visually, or by determining whether or not a biofilm is present in the air scrubber. Reduction in biofilm may be determined by measuring a change in pressure during operation of the wet air scrubber. An increase in pressure (ΔΡ) during normal operation of an air scrubber may indicate the presence or increase of biofilm in the air scrubber. A reduction in pressure (ΔΡ) during normal operation of the air scrubber may indicate the reduction of biofilm in the air scrubber. ΔΡ is a measure of the air pressure of the air going into the air scrubber compared to the pressure of the air as it leaves the air scrubber.

[0018] The air scrubber fan may further operate with heat flow in the absence of water or liquid flow. Heat flow may come from the normal intake air of the air scrubber, e.g., from a cooker, a dryer, or a press.

[0019] The methods may further comprise operating the wet air scrubber with a composition comprising a surfactant to remove at least a portion of the desiccated biofilm. Surfactants may include, but are not limited to, cationic surfactants, anionic surfactants, and nonionic surfactants. Examples of surfactants and systems that may be used in conjunction with the present application include, but are not limited to, those disclosed in International Patent Application No. PCT/US 10/47344, filed August 31 , 2010 and published as WO201 1/0261 14; U.S. Patent Application No. 13/392995, filed May 16, 2012; and International Patent Application No. PCT/US2012/023504, filed February 1 , 2012, which are incorporated herein by reference in their entireties. Suitable surfactants include those in ReNew A and ReNew B (Diversey, Sturdevant, Wl).

[0020] All microorganisms grow within a defined pH range. No single species can grow at a wide pH range. A biofilm community may operate within a narrow pH range to survive and grow. In certain embodiments, provided are methods of reducing biofilm in a wet air scrubber, the methods comprising operating an air scrubber with a composition having a pH. The pH may be maintained at a first pH for a first period of time, and subsequently maintained at a second pH for a second period of time. The second pH may be greater or less than the first pH. For example, the pH may be maintained at first pH for a first time period, and subsequently maintained at a second pH for a second time period. The difference between the first pH and the second pH may be at least about 3.0, at least about 3.5, at least about 4.0, at least about 4.5, at least about 5.0, or at least about 5.5. The first pH may be an acidic pH or an alkaline pH, as defined below. The second pH may be an acidic pH or an alkaline pH, as defined below. For example, the pH may be maintained at an acidic pH for a first time period, and subsequently maintained at an alkaline pH for a second time period. In another example, the pH may be maintained at an alkaline pH for a first period of time, and subsequently maintained at an acidic pH for a second period of time. By alternating the pH, a community of biofilm may never manage to establish itself.

[0021] The acidic pH may be at least about pH 3.0, at least about pH 3.1 , at least about pH 3.2, at least about pH 3.3, at least about pH 3.4, at least about pH 3.5, at least about pH 3.6, at least about pH 3.7, at least about pH 3.8, at least about pH 3.9, or at least about pH 4.0. The acidic pH may be less than about pH 5.0, less than about pH 4.9, less than about pH 4.8, less than about pH 4.7, less than about pH 4.6, less than about pH 4.5, less than about pH 4.4, less than about pH 4.3, less than about pH 4.2, less than about pH 4.1 , or less than about pH 4.0. In some embodiments, the acidic pH is about 3.5 to about 4.5.

[0022] The alkaline pH may be at least about pH 7.0, at least about pH 7.1 , at least about pH 7.2, at least about pH 7.3, at least about pH 7.4, at least about pH 7.5, at least about pH 7.6, at least about pH 7.7, at least about pH 7.8, at least about pH 7.9, or at least about pH 8.0. The acidic pH may be less than about pH 10.0, less than about pH 10.9, less than about pH 10.8, less than about pH 10.7, less than about pH 10.6, less than about pH 10.5, less than about pH 10.4, less than about pH 10.3, less than about pH 10.2, less than about pH 10.1 , less than about pH 10.0, less than about pH 9.9, less than about pH 9.8, less than about pH 9.7, less than about pH 9.6, less than about pH 9.5, less than about pH 9.4, less than about pH 9.3, less than about pH 9.2, less than about pH 9.1 , or less than about pH 9.0. In some embodiments, the alkaline pH is about 7.5 to about 9.5.

[0023] The first and second time periods may each individually be at least about about 1 h, about 2 h, about 3 h, about 4 h, about 5 h, about 6 h, about 7 h, about 8 h, about 9 h, about 10 h, about 1 1 h, about 12 h, about 18 h, about 24 h, about 36 h, about 48 h, about 60 h, about 72 h, about 84 h, about 96 h, about a week, about 2 weeks, or at least about 3 weeks. The first and second time periods may each individually be less than about 3 weeks, less than about 2 weeks, or less than about 1 week.

[0024] Acid may be continually added to the recirculating water in the air scrubber to maintain the acidic pH, and then not continually added to the recirculating water such that the pH naturally rises to an alkaline pH. The acid may be an organic acid. Examples of organic acids include, but are not limited to, caproic acid, caprylic acid, capric acid, lauric acid, stearic acid, isostearic acid, behenic acid, erucic acid, oleic acid, and linoleic acid. Organic (fatty) acids may include palmitic acid, stearic acid, oleic acid, erucic acid, behenic acid, isostearic acid, 12- hydroxystearic acid. The acid may be an acid salt. Acid salts may include, but are not limited to, sodium bicarbonate, sodium hydrosulfide, sodium bisulfate, monosodium phosphate, and disodium phosphate. The acid may be an inorganic acid (also referred to as a mineral acid). Inorganic acids may include, but are not limited to, hydrochloric acid, nitric acid, phosphoric acid, sulfuric acid, boric acid, hydrofluoric acid, hydrobromic acid, perchloric acid, and sodium acid sulfate. The inorganic acid may be sodium acid sulfate.

EXAMPLES

[0025] Example 1. While the air scrubber is offline in the absence of water or fluid flow, the fan of an air scrubber is run. The flow of air from the fan dries the biofilm in the air scrubber. The fan is operated for about 6 hours to about 24 hours. Then the wet air scrubber is put back into normal operation with water or fluid flow. The normal operation of the air scrubber removes the dried biofilm from the air scrubber. The formation of biofilm in the air scrubber is reduced or removed.

[0026] Example 2. While the air scrubber was offline in the absence of water or fluid flow, the fan of an air scrubber was run. The flow of air from the fan dried the biofilm in the air scrubber. The fan was operated in the absence of water or fluid flow for about 7 hours to about 18 hours total over 2 days every week. The period of fan operation was occasionally split into 2 periods totaling 7 hours. Then the wet air scrubber was put back into normal operation with water or fluid flow. The normal operation of the air scrubber removed the dried biofilm from the air scrubber. The formation of biofilm in the air scrubber was reduced.

[0027] Example 3. While the air scrubber is online with flow of water or fluid, sodium acid sulfate is added to the liquid stream in an amount sufficient to reduce the pH to an acidic pH of about 3.5 to about 4.5. The pH is maintained at about 3.5 to about 4.5 for about 8-12 hours. The addition of sodium acid sulfate is stopped, and the pH returns to a neutral pH of about 6.5 to about 8. The pH is maintained at about 6.5 to about 8 for about 8-12 hours. The formation of biofilm in the air scrubber is reduced or removed.

Claims

CLAIMS We claim:

1. A method for at least one of reducing biofilm, controlling the formation of biofilm, or controlling the growth of biofilm in an air scrubber, the method comprising desiccating the biofilm to produce a desiccated biofilm.

2. The method of claim 1 , wherein desiccating comprises providing an air flow in the air scrubber in the absence of water flow in the air scrubber.

3. The method of claim 1 , wherein desiccating comprises operating at least one fan in the absence of water flow in the air scrubber.

4. The method of claim 3, wherein the fan is operated for about 4 h to about 24 h.

5. The method of any one of claims 1-4, the method further comprising introducing into the wet air scrubber a composition comprising a surfactant to remove at least a portion of the desiccated biofilm.

6. A method for at least one of reducing biofilm, controlling the formation of biofilm, or controlling the growth of biofilm in an air scrubber, the method comprising:

(a) introducing a composition into a liquid flow stream of the air scrubber to produce an acidic pH of the liquid flow stream; and

(b) adjusting the pH of the liquid flow stream to an alkaline pH.

7. The method of claim 6, wherein step (b) is performed after step (a).

8. The method of claim 6, wherein step (b) comprises terminating step (a).

9. The method of any one of claims 6-8, wherein the acidic pH is about 3.5 to about 4.5, and wherein the alkaline pH is about 7.5 to about 9.5.

10. The method of any one of claims 6-8, wherein the acidic pH is maintained at about 3.5 to about 4.5 for a first time period, and wherein the alkaline pH is maintained at about 7.5 to about 9.5 for a second time period.

1 1 . The method of claim 10, wherein the first and second time periods each are about one week.

12. The method of claim 10, wherein the first and second time periods each are at least about 72 hours.

13. The method of claim 10 wherein the first and second time periods each are at least about 48 hours.

14. The method of claim 10, wherein the first and second time periods each are at least about 24 hours.

15. The method of any one of claims 6-14, wherein the acidic pH of about 3.5 to about 4.5 is maintained with an inorganic acid.

16. The method of claim 15, wherein the inorganic acid comprises sodium acid sulfate.

17. A method of reducing biofilm in an air scrubber having a liquid flow system, the method comprising:

(a) maintaining an acidic pH in the liquid flow system of the air scrubber; and

(b) maintaining an alkaline pH in the liquid flow system.

18. The method of claim 17, wherein step (b) is performed after step (a).

19. A method of reducing biofilm in an air scrubber having a liquid flow system, the method comprising:

(a) maintaining a first pH in the liquid flow system of the air scrubber for a period of time; and

(b) maintaining a second pH in the liquid flow system for a period of time, the first pH and the second pH having a numerical difference of at least about 3.0.

20. The method of claim 19, wherein the difference between the first pH and the second pH is at least about 3.5.

21 . The method of claim 20, wherein the difference is at least about 4.0.

22. The method of claim 20, wherein the difference is at least about 4.5.

23. The method of claim 20, wherein the difference is at least about 5.0.

24. The method of claim 20, wherein the difference is at least about 5.5.

25. A method for at least one of reducing biofilm, controlling the formation of biofilm, or controlling the growth of biofilm in an air scrubber, the method comprising:

(a) introducing a composition into a liquid flow stream of the air scrubber to produce a first pH of the liquid flow; and

(b) adjusting the pH of the liquid flow to a second pH.

26. The method of claim 25, wherein the difference between the first pH and the second pH is at least about 3.0.

27. The method of claim 25, wherein the difference between the first pH and the second pH is at least about 3.5.

28. The method of claim 25, wherein the difference between the first pH and the second pH is at least about 4.0.

29. The method of claim 25, wherein the difference between the first pH and the second pH is at least about 4.5.

30. The method of claim 25, wherein the difference between the first pH and the second pH is at least about 5.0.

31 . The method of claim 25, wherein the difference between the first pH and the second pH is at least about 5.5.