WO2013012934A1

WO2013012934A1 - Methods of reducing biofilm in air scrubbers

Info

Publication number: WO2013012934A1
Application number: PCT/US2012/047224
Authority: WO
Inventors: Michael F. Coughlin
Original assignee: Diversey, Inc.
Priority date: 2011-07-18
Filing date: 2012-07-18
Publication date: 2013-01-24

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 introducing into a liquid flow stream of the wet air scrubber a composition comprising at least one phosphate co-precipitant or phosphate precipitant. In some embodiments, the compositions comprise ferric chloride. In some embodiments, the compositions comprise aluminum chlorhydrate.

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. 61/509,000, filed July 18, 201 1 , and U.S. Provisional Patent Application No. 61/531 ,972, filed September 7, 201 1 , each of which is incorporated herein by reference in its entirety.

FIELD OF INVENTION

[0002] The present disclosure relates to methods for operating air scrubbers and reducing biofilm.

INTRODUCTION

[0003] 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 ingredients used by pharmaceutical companies. The air surrounding rendering plant equipment may have a bad odor and may contain volatile organic compounds (VOCs).

[0004] 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.

[0005] 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.

[0006] Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings.

SUMMARY

[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 method including introducing into a liquid flow stream of the air scrubber a composition comprising an effective amount of at least one phosphate precipitant to at least one of reduce biofilm, control the formation of biofilm, or control the growth of biofilm in the air scrubber.

[0008] In certain aspects, provided are methods of reducing biofilm in an air scrubber having a liquid flow system, the methods including maintaining a level of at least one phosphate precipitant in the liquid flow system in an amount effective to reduce microbial growth in the air scrubber.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 is a schematic diagram of a wet air scrubber.

DETAILED DESCRIPTION

[0010] Before any embodiments of the disclosure are explained in detail, it is to be understood that the disclosure 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 disclosure is capable of other embodiments and of being practiced or of being carried out in various ways.

[0011] 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.

[0012] 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 disclosure 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 disclosure 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.

[0013] Biofilm is a mixture of organic compounds, including at least one of polysaccharide, nucleic acid, and protein, and inorganic salts, such as phosphate, magnesium, calcium, and sodium, in an aqueous medium. Wet air scrubbers are prone to biofouling due to the ideal conditions they present for microbial growth. The macronutrients commonly associated with microbial growth are a carbon source (for making carbohydrates), a nitrogen source (for making amino acids, nitrate, and ammonia), and phosphate (for making nucleic acid). In wet air scrubbers there may be ample carbon and nitrogen sources available to support microbial growth. Because phosphate is normally associated with non-volatile compounds, however, its presence in wet air scrubbers is necessarily low and limits microbial growth. Nevertheless, trace levels of phosphate may be found in wet air scrubbers and can be scavenged by bacterial communities to support further growth. Thus, microbial growth is at least partially dependent on the level of phosphate in the liquid flow of wet air scrubbers.

[0014] In certain aspects, provided are methods of reducing biofilm in a wet air scrubber. The methods may comprise removing soluble phosphate from the liquid flow of a wet air scrubber. Removal of soluble phosphate prevents the phosphate from being incorporated into bacterial biofilms and planktonic populations. In some embodiments, methods comprise adding a composition comprising a phosphate co-precipitant or phosphate precipitant, or combinations thereof, to the liquid flow of an air scrubber. A phosphate co-precipitant or phosphate precipitant may also be referred to as a coagulant.

[0015] Examples of a phosphate precipitant or co-precipitant include, but are not limited to, at least one of ferric ions, ferrous ions, calcium ions, magnesium ions, aluminum ions, lanthanum ions, as well as chloride salts, sulfate salts, oxide salts, and chlorhydrates thereof. Particularly suitable examples include ferric chloride, ferric sulfate, ferrous sulfate, ferric oxide, aluminum sulfate, lanthanum chloride, polyaluminum chlorides, and combinations thereof. Examples of polyaluminum chlorides, may include, but are not limited to, aluminum salts such as aluminum chlorhydrate. For example, aluminum chlorhydrate is commercially available as ULTRAPAC® 290 from GEO Specialty Chemicals (Lafayette, IN).

[0016] Compositions comprising an effective amount of a phosphate precipitant or co- precipitant may be added to an air scrubber in any suitable form, for example, in solution or in solid forms. In some embodiments, the compositions may comprise at least about 10% precipitant or co-precipitant, at least about 20% precipitant or co-precipitant, or at least about 30% precipitant or co-precipitant by w/v. Compositions may comprise less than about 100% precipitant or co-precipitant, less than about 90% precipitant or co-precipitant, less than about 80% precipitant or co-precipitant, or less than about 70% precipitant or co-precipitant by w/v. Compositions may comprise about 1 % to about 100% precipitant or co-precipitant, about 10% to about 90% precipitant or co-precipitant, about 20% to about 80% precipitant or co-precipitant, or about 30% to about 70% precipitant or co-precipitant. For example, a 100% solution of ferric chloride may be added to the air scrubber. As another example, a 30% solution of ferric chloride may be added to the air scrubber. As another example, an aluminum chlorhydrate solution may be added to the air scrubber. [0017] Phosphate precipitants or co-precipitants may be added to an air scrubber by any suitable means. For example, phosphate precipitants or co-precipitants may be added to the basin of an air scrubber.

[0018] An effective amount may be a dosage of a composition effective for eliciting a desired effect, commensurate with a reasonable benefit/risk ratio. An effective amount may also refer to an amount effective at bringing about a desired effect in an air scrubber, preferably, a reduction in biofilm, control in the formation of biofilm, or control of the growth of biofilm.

[0019] Phosphate precipitants or co-precipitants may be added to an air scrubber in an amount equal to or in excess of the phosphate concentration in the air scrubber. The phosphate precipitant or co-precipitant may be added at a ratio of at least about or about 1 :1 , of at least about or about 1 .5:1 , of at least about or about 2:1 , of at least about or about 2.5:1 , of at least about or about 3:1 , of at least about or about 3.5:1 , of at least about or about 4:1 , of at least about or about 4.5:1 , of at least about or about 5.0:1 , of at least about or about 5.5:1 , of at least about or about 6:1 , of at least about or about 6.5:1 , of at least about or about 7:1 , of at least about or about 7.5:1 , of at least about or about 8:1 , of at least about or about 8.5:1 , of at least about or about 9:1 , of at least about or about 9.5:1 , or of at least about or about 10:1 of precipitant or co-precipitant to soluble phosphate in the air scrubber. For example, a 100% solution of FeCI₃-6H₂0 may be added to an air scrubber in a ratio of about 3 parts FeCI₃-6H₂0 to about 1 part soluble phosphate in the air scrubber.

[0020] The amount of soluble phosphate present in the liquid flow of an air scrubber may be determined by any suitable means known in the art. For example, the Hach Method may be used. For example, a DR/890 Colorimeter (Hach Company, Loveland, CO) may be used, wherein a reagent is added to a sample of air scrubber water or fluid flow, and the blue color change is proportional to the phosphate concentration. For example, the amount of soluble phosphate in an air scrubber prior to addition of precipitant or co-precipitant may be at least about or about 0.1 ppm, at least about or about 0.2 ppm, at least about or about 0.3 ppm, at least about or about 0.4 ppm, at least about or about 0.5 ppm, at least about or about 0.6 ppm, at least about or about 0.7 ppm, at least about or about 0.8 ppm, at least about or about 0.9 ppm, at least about or about 1 .0 ppm, at least about or about 1 .5 ppm, at least about or about 2.0 ppm, at least about or about 2.5 ppm, at least about or about 3.0 ppm, at least about or about 3.5 ppm, at least about or about 4.0 ppm, at least about or about 4.5 ppm, or at least about or about 5.0 ppm, at least about or about 5.5 ppm, at least about or about 6.0 ppm, at least about or about 6.5 ppm, at least about or about 7.0 ppm, at least about or about 7.5 ppm at least about or about 8.0 ppm, at least about or about 8.5 ppm, at least about or about 9.0 ppm, at least about or about 9.5 ppm, at least about or about 10.0 ppm. For example, the amount of soluble phosphate in the air scrubber prior to addition of precipitant or co-precipitant may be about 0.1 pm to about 5 ppm, or about 0.1 ppm to about 1 ppm. The sample of air scrubber water or fluid flow may be filtered prior to determining phosphate concentration, to remove other contaminants that would obscure measurement.

[0021] The phosphate precipitant or co-precipitant may be added to the liquid flow stream of an air scrubber in an amount of at least about or about 0.1 ppm, at least about or about 0.2 ppm, at least about or about 0.3 ppm, at least about or about 0.4 ppm, at least about or about 0.5 ppm, at least about or about 0.6 ppm, at least about or about 0.7 ppm, at least about or about 0.8 ppm, at least about or about 0.9 ppm, at least about or about 1.0 ppm, at least about or about 1 .5 ppm, at least about or about 2.0 ppm, at least about or about 2.5 ppm, at least about or about 3.0 ppm, at least about or about 3.5 ppm, at least about or about 4.0 ppm, at least about or about 4.5 ppm, or at least about or about 5.0 ppm, at least about or about 5.5 ppm, at least about or about 6.0 ppm, at least about or about 6.5 ppm, at least about or about 7.0 ppm, at least about or about 7.5 ppm at least about or about 8.0 ppm, at least about or about 8.5 ppm, at least about or about 9.0 ppm, at least about or about 9.5 ppm, at least about or about 10.0 ppm. This may include amounts of about 0.1 ppm to about 10.0 ppm, about 0.5 ppm to about 5.0 ppm, or about 1.0 ppm to about 2.0 ppm.

[0022] The phosphate precipitant may be added to the liquid flow stream of the air scrubber at regular intervals, for example, every about 10 minutes, about 20 minutes, about 30 minutes, about 40 minutes, about 50 minutes, about 60 minutes, about 2 hours, about 3 hours, about 4 hours, about 5 hours, about 6 hours, about 12 hours, about 24 hours, about 48 hours, about 72 hours and so on.

[0023] Concentrations of phosphate less than 0.1 ppm may impede biofilm development in the air scrubber. The methods and compositions of the present disclosure may reduce the phosphate concentration in the liquid flow stream of the air scrubber to less than about or about 0.1 , less than about or about 0.09, less than about or about 0.08, less than about or about 0.07, less than about or about 0.06, less than about or about 0.05, less than about or about 0.04, less than about or about 0.03, less than about or about 0.02, or less than about or about 0.01 ppm. [0024] In some embodiments, the compositions may further comprise a surfactant. Surfactants may include, but are not limited to, cationic surfactants, anionic surfactants, and nonionic surfactants. Examples of surfactants are disclosed in International Patent Application No. PCT/US 10/47344, filed August 31 , 2010, which published as International Patent Application Publication No. WO 201 1/0261 14 on March 3, 201 1 , and is incorporated herein by reference in its entirety. Suitable surfactants include those in ReNew A and ReNew B (Diversey, Sturdevant, Wl).

[0025] In some embodiments, the compositions may be added to another composition for use in a wet air scrubber. For example, compositions as described herein may be added to compositions as described in International Patent Application No. PCT/US 10/47344, filed August 31 , 2010, which published as International Patent Application Publication No. WO 201 1/0261 14 on March 3, 201 1 , and is incorporated herein by reference in its entirety. For example, compositions as described herein may be added to ReNew A, ReNew B, or ReNew C (Diversey, Sturdevant, Wl).

[0026] In some embodiments, the pH of the fluid flow in the air scrubber may be monitored and controlled to remain in a range suitable for phosphate precipitation or co-precipitation. The pH may be at least about or about 4.0, at least about or about 4.5, at least about or about 5.0, or at least about or about 5.5. The pH may be less than about or about 7.0, less than about or about 6.5, or less than about or about 6.0. This includes ranges of about 4.0 to about 7.0, about 4.5 to about 6.5, or about 5.0 to about 6.0. The pH of the fluid flow of an air scrubber may be monitored and controlled by any suitable means, such as those originally part of the air scrubber machinery system. Additional pH monitoring and control systems may be found in International Patent Application No. PCT/US2012/045175, filed July 1 , 2012, which is hereby incorporated by reference in its entirety. The compositions of the present disclosure may also be used in conjunction with the desiccation methods set forth therein. For example, a biofilm may be desiccated by providing an air flow in the air scrubber. The air flow may be provided by an air flow source such as a fan, blower, bellow, compressed air, or other motive source. The air scrubber may be operated with at least one fan in the absence of water or liquid flow in the air scrubber to produce a desiccated biofilm. Fans, blowers, bellows, compressed air or other motive sources may include any suitable commercially available fan, bellow, compressed air or motive source known in the art including, but not limited to, fans or blowers of a commercial air scrubber. An air flow source (e.g., a fan) may operate with air flow of about 15,000 to about 100,000 cfm. The air flow source may be operated in the wet air scrubber for a period of time of about 6 h to about 30 h. The air flow source may be operated while the air scrubber is offline. The air flow source may be operated for multiple or repeated periods of time. The air flow source may be operated until the air scrubber is a suitable level of dryness.

EXAMPLES

[0027] Example 1. The concentration of phosphate in an air scrubber is determined by taking a 10 mL sample of the air scrubber fluid flow and testing it with a DR/890 Colorimeter (Hach Company, Loveland, CO). A 30% solution of FeCI₃-6H₂0 is added to the basin of the air scrubber in an amount such that the ratio of FeCI₃-6H₂0 to soluble phosphate in the air scrubber is about 3:1. Soluble phosphate is precipitated out of the air scrubber fluid flow. The formation of biofilm in the air scrubber is reduced or removed.

[0028] Example 2. The concentration of phosphate in an air scrubber is determined by taking a 10 mL sample of the air scrubber fluid flow and testing it with a DR/890 Colorimeter (Hach Company, Loveland, CO). A 100% solution of ULTRAPAC® 290 (GEO Specialty Chemicals, Lafayette, IN) is added to the basin of the air scrubber in an amount such that the final concentration of ULTRAPAC® 290 is about 10 ppm in the air scrubber. ULTRAPAC® 290 is added once an hour to maintain the about 10 ppm concentration. Alternatively, the final concentration of ULTRAPAC® 290 is added to the air scrubber and maintained at about 1 ppm to about 10 ppm. Soluble phosphate is precipitated out of the air scrubber fluid flow. The formation of biofilm in the air scrubber is reduced or removed.

Claims

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 introducing into a liquid flow stream of the air scrubber a composition comprising an effective amount of at least one phosphate co-precipitant or phosphate precipitant to at least one of reduce biofilm, control the formation of biofilm, or control the growth of biofilm in the air scrubber.

2. The method of claim 1 , wherein the phosphate co-precipitant or phosphate precipitant comprises at least one of ferric ions, ferrous ions, calcium ions, magnesium ions, aluminum ions, lanthanum ions, as well as chloride salts, sulfate salts, oxide salts, and chlorhydrates thereof.

3. The method of any one of the above claims, wherein the phosphate co-precipitant or phosphate precipitant comprises ferric chloride.

4. The method of claim 1 or claim 2, wherein the phosphate co-precipitant or phosphate precipitant comprises aluminum chlorhydrate.

5. The method of any one of the above claims, wherein the composition comprises the at least one phosphate co-precipitant or phosphate precipitant in an amount of about 10% to about 90% by weight.

6. The method of any one of the above claims, wherein the composition comprises the at least one phosphate co-precipitant or phosphate precipitant in an amount of about 20% to about 80% by weight.

7. The method of any one of the above claims, wherein the composition is added to the basin of the air scrubber.

8. The method of any one of the above claims, wherein the phosphate co-precipitant or phosphate precipitant is added to the liquid flow of the air scrubber to a concentration of about 1 ppm to about 10 ppm.

9. The method of any one of the above claims, wherein the phosphate co-precipitant or phosphate precipitant is added to the liquid flow of the air scrubber to a ratio of FeCI₃-6H₂0 of about 1 :3.

10. The method of any of the above claims, wherein the composition is a liquid.

1 1 . The method of any of the above claims, wherein the composition is a solid.

12. The method of any of the above claims, wherein the effective amount of the at least one phosphate precipitant in the liquid flow stream is at least about 0.1 ppm.

13. The method of any of the above claims, wherein the effective amount of the at least one phosphate precipitant in the liquid flow stream is at least about 1 .0 ppm.

14. The method of any of the above claims, wherein the effective amount of the at least one phosphate precipitant in the liquid flow stream is at least about 5.0 ppm.

15. The method of any of the above claims, wherein the composition further comprises a surfactant.

16. The method of any of the above claims, wherein the liquid flow stream has a pH, and the pH is maintained in a range of about 5.0 to about 6.0.

17. A method of reducing biofilm in an air scrubber having a liquid flow system, the method comprising maintaining a level of at least one phosphate co-precipitant or phosphate precipitant in the liquid flow system in an amount effective to reduce microbial growth in the air scrubber.

18. The method of claim 17, wherein the phosphate co-precipitant or phosphate precipitant comprises at least one of ferric ions, ferrous ions, calcium ions, magnesium ions, aluminum ions, lanthanum ions, as well as chloride salts, sulfate salts, oxide salts, and chlorhydrates thereof.

19. The method of any one of claims 17-18, wherein the phosphate co-precipitant or phosphate precipitant comprises ferric chloride.

20. The method of any one of claims 17-18, wherein the phosphate co-precipitant or phosphate precipitant comprises aluminum chlorhydrate.

21 . The method of any one of claims 17-20, wherein the composition comprises the at least one phosphate co-precipitant or phosphate precipitant in an amount of about 10% to about 90% by weight.

22. The method of any one of claims 17-21 , wherein the composition comprises the at least one phosphate co-precipitant or phosphate precipitant in an amount of about 20% to about 80% by weight.

23. The method of any one of claims 17-22, wherein the composition is added to the basin of the air scrubber.

24. The method of any one of claims 17-23, wherein the phosphate co-precipitant or phosphate precipitant is added to the liquid flow of the air scrubber to a concentration of about 1 ppm to about 10 ppm.

25. The method of any one of claims 17-24, wherein the phosphate co-precipitant or phosphate precipitant is added to the liquid flow of the air scrubber to a ratio of FeCI₃-6H₂0 of about 1 :3.

26. The method of any one of claims 17-25, wherein the effective amount of the at least one phosphate precipitant in the liquid flow system is at least about 0.1 ppm.

27. The method of any one of claims 17-26, wherein the effective amount of the at least one phosphate precipitant in the liquid flow system is at least about 1.0 ppm.

28. The method of any one of claims 17-27, wherein the effective amount of the at least one phosphate precipitant in the liquid flow system is at least about 5.0 ppm.

29. The method of any one of claims 17-28, wherein the liquid flow system has a pH, and the pH is maintained in a range of about 5.0 to about 6.0.

30. The method of any of the above claims, further comprising desiccating biofilm in the air scrubber.