Abstract:
A flow of oxygen containing gas is irradiated with UV light to convert oxygen molecules to ozone molecules and produce an ozonated gas. Water to be treated is augmented with silver prior to entraining the ozonated gas in the water. The ozone enriched water containing silver is irradiated with UV light to produce hydroxyl radicals. Whereby, microorganisms are killed by the UV radiation, organic matter is oxidized by the ozone and the combination of silver and hydroxyl radicals prevent downstream growth of bio-film contamination.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application discloses subject matter common to and claims priority of a provisional patent application entitled “Apparatus and Process for Preventing Biological Regrowth” filed Aug. 1, 2006 and assigned Ser. No. 60/821,080 describing an invention made by the present inventors and assigned to the present assignee. 
     
    
     GOVERNMENT LICENSE RIGHTS 
       [0002]    The U.S. Government has a paid-up license in this invention and the right in limited circumstances to require the patent owner to license others on reasonable terms as provided by the terms of Contract No. NBCHC060008 awarded by the Department of Homeland Security. 
     
    
     BACKGROUND OF THE INVENTION 
       [0003]    1. Field of the Invention 
         [0004]    The present invention relates to the treatment of water for killing microorganisms and preventing bacterial regrowth. 
         [0005]    2. Description of Related Prior Art 
         [0006]    Most water treatment processes, particularly municipal drinking water treatment, seek to accomplish two major microbiological objectives. The first objective is to significantly reduce, inactivate or kill microorganisms such as bacteria, viruses and protozoa from the water. The second objective is to prevent regrowth of the microorganisms downstream of the treatment system. In the specific instance of drinking water treatment (see EPA Guidance Manual, “Alternative Disinfectants and Oxidants”, U.S. EPA 815-R-99-014, April 1999) the first objective is typically accomplished with so called primary disinfectants such as chlorine, chlorine dioxide, ultraviolet (UV) light or ozone. Bacterial regrowth is typically prevented with so called secondary disinfectants (secondary residuals) such as chloramines, chlorine or chlorine dioxide. Technologies such as UV light and ozone, which do not remain in the water for an extended period of time, are not useful as secondary residuals. Metal ions or salts of various metals, such as silver, copper and zinc can also be used as secondary residuals. The use of silver and/or copper has found utility in controlling bacterial regrowth in drinking water, cooling tower water, and medical and dental applications (Lin et al, 1998, Klueh et al, 2000, Armon et al, 200, Sabria and Yu, 2002, Abe et al, 2004, Samuel and Guggenbichler, 2004, Stout and Yu, 2003). 
         [0007]    UV irradiation has been extensively used to inactivate microorganisms. The use of UV light is gaining popularity in drinking water treatment as it does not form Disinfection-by-Products (DBPs) such as trihalomethanes (THMs) and haloacetics acids (HAAs) and there is no need to store or handle chemicals. UV light disinfection is very effective against bacteria, protozoan parasites ( Giardia, Cryptosporidium ), and most enteric viruses. However, very large doses are required to inactivate the double-stranded DNA adenoviruses. 
         [0008]    Microbial inactivation is proportional to the UV dose, which is expressed in microwatts-seconds per square centimeter (μwatt-s/cm 2 ) or in units of millijoules per square centimeter (mJ/cm 2 ). UV radiation at a wavelength of approximately 260 nm damages microbial DNA or RNA. At this wavelength it causes thymine dimerization which blocks nucleic acid replication and effectively inactivates microorganisms. The initial site of UV damage in viruses is the genome, followed by structural damage to the virus protein coat. Photo reactivation (i.e. repair of the UV damage) occurs in some UV light-damaged microorganisms. In these instances, repair is accomplished by a photo activating enzyme, which binds and then splits the thymine dimers. To prevent photo reactivation, sufficient doses must be applied. 
         [0009]    A minimum dose of 16,000 watt-s/cm 2  (16 mJ/cm 2 ) has been recommended for drinking water as this results in 99.9% inactivation of coliforms. Higher doses are required for inactivation of enteric viruses and protozoan cysts. Table 1 lists the UV dose required to kill 90% of a number of different enteric viruses. 
         [0000]                                      TABLE 1                   UV Dose to Kill 90% Enteric Microorganisms       (from Maier et al, 2000)                UV Dose       UV Dose       Organism   (watt-s/cm 2 )   Organism   (watt-s/cm 2 )                 E. Coli     1,300-3,000     Y. Enterocolitica      1,100         K. Terrigena     3,900     L. Pneumophila       920-2,500         S. Typhi     2,100-2,500     S. Dysenteriae       890-2,200         V. Cholera       650-3,400   Adenovirus   23,600-30,000       Coxackievirus   11,900-15,600   Echovirus   10,800-12,100       Poliovirus    5,000-12,000   Hepatitis A   3,700-7,300       Rotavirus SA11   8,000-9,900   Coliphage MS-2   18,600                    
Recently, Butkus et al (2004) have demonstrated an unexpected synergy for MS-2 virus inactivation when silver ions were utilized in combination with UV light. The combined effect, as shown by the bar graph in  FIG. 1 , achieves significantly greater bacterial reduction than the individual components alone. Column (1) depicts the use of silver alone. Column (2) depicts the use of UV alone. Column (3) depicts the MATHEMATICAL PREDICTED PERFORMANCE when the effect of column (1) is added to column (2). Column 4 illustrates the ACTUAL combined silver/UV performance. Column (5) is similar to column (4) except the test time was extended (from Butkus, et al, 2004).
 
         [0010]    Silver, in its own right, is an effective, albeit slowly acting, broad spectrum antimicrobial. Metallic silver and silver ions have been used for centuries to control pathogen exposure from water. More contemporaneously, silver has been used successfully in hospital drinking water systems for over a decade to control  Legionella  (Stout and Yu, 2003) and is currently used in millions of home water treatment products to control bacterial growth on carbon filters. Both the EPA and the World Health Organization recognize silver as safe for drinking water. 
         [0011]    Silver will bind with various species in water (e.g. chloride, phosphate, sulfides) and its overall contribution to disinfection may be hindered. Recently, Butkus et al (2005) discovered that the synergistic action that had been observed between UV and silver was reduced in the presence of chloride concentrations greater than 30 mg/L and high phosphate concentrations (above 5 nM). 
         [0012]    Ozone is a powerful oxidizing agent that does not produce THMs or other chlorinated by-products. However, aldehydes and bromates may be produced by ozonation and may have adverse health effects. Because ozone does not leave a lasting residual in the water, ozonation needs to be followed by a secondary disinfectant such as chlorine, chloramine or silver ions. The effectiveness of ozone is not influenced by pH or ammonia content of the water being treated. 
         [0013]    Ozone is a much more powerful oxidant than chlorine and its Concentration*Time (CT) values for enteric bacteria and enteric viruses are generally an order of magnitude or more lower than those of chlorine. Ozone appears to inactivate bacteria by mechanisms similar to that of chlorine: nucleic acid denaturization, impairment of enzyme function and/or protein integrity by oxidation of sulfhydral groups, and disruption of membrane permeability (Steward and Olson, 1996). 
         [0014]    Ozone can be produced from air or oxygen using corona discharge methods or by the exposure of air or oxygen to UV light. UV light of a 185 nm wavelength readily converts oxygen to ozone. 
         [0015]    Ozone consumption in natural waters has been observed to occur in two phases (Buffle, 2005). In the first phase, which spans only the 20 seconds or so, ozone depletion is very rapid. This phase is referred to as “Instantaneous Ozone Demand” (IOD). Since very little disinfection is achieved in this phase, it is presumed that the ozone demand arises from organics, meaning that the ozone is consumed for oxidation and not disinfection. During the second phase, ozone accomplishes disinfection and to a lesser extent oxidation. The first and second phases are illustrated in  FIG. 2 . 
         [0016]    The combination of UV light and ozone creates a potent oxidizer called hydroxyl radicals that destroy any organic matter (including pesticides, microorganisms) in its path. The US EPA (1980) found that combined UV/ozone treatment was 4-50 times faster at oxidation than UV or ozone alone, depending on the specific water contaminants and water conditions. 
         [0017]    The UV/ozone reaction can be described as, 
         [0000]      UV+O 3 →OH* 
         [0018]    where OH* represents a hydroxyl radical. 
         [0019]    The oxidation potential of hydroxyl radicals is 2.07 volts and is second only to fluorine in its oxidizing power. For this reason, processes that generate and use hydroxyl radicals have been termed Advanced Oxidation Processes. Hydroxyl radicals are generally utilized for oxidation as opposed to disinfection. Their non-selective oxidizing ability, compared to the selective oxidizing behavior of ozone, may cause even greater microorganism inactivation. For example, Magbanua et al (2006) recently demonstrated a synergistic effect between UV and ozone in the inactivation of  E. coli . They found that when ozone is used with UV, they could lower the UV dose by up to a factor of 10 to achieve the same result as using UV alone. Moreover, they found that when using UV with ozone, they could lower the ozone dose by a factor of 4 to achieve the same result as using ozone alone. 
         [0020]    DBPs (Disinfection-by-Products) arise when disinfectants such as chlorine interact with natural organic matter. The resulting by-products include Trihalomethanes (THMs) and Haloacetic acids (HAAs), chemical families that have been associated with adverse health effects. It is suspected that long-term exposure to THMs may statistically increase the rates of some cancers. Because of this finding, the EPA began, in 1979, to regulate the maximum contaminant level (MCL) for THMs and HAAs. These regulations are becoming more stringent with time. The Stage 1 D/DBP standard is 0.08 mg/L THMs and 0.06 mg/L HAAs. The proposed Stage 2 D/DBP standard will require no greater than 0.04 mg/L of THMs and no greater than 0.02 mg/L of HAAs. 
         [0021]    The use of UV and ozone are well known to improve the reduction of DBP formation. This has been shown not only for THMs but also for HAAs (Chin and Berube, 2005). 
         [0022]    Once drinking water is treated, it must travel through many miles of plumbing (i.e. pipe) or be held in storage tanks before it reaches the end user. The presence of dissolved organic compounds such as humates can cause bacterial colonization of water distribution systems (Bitton, 1994). Bio-films of microorganisms in the distribution system are of concern because of the potential for the protection of pathogens from the action of the secondary disinfectant. 
         [0023]    Bio-films may consist of a monolayer of cells in a microcolony or can be as thick as 10-40 mm as algal mats at the bottom of a water reservoir (Geldreich, 1996). Bio-films are held together by extracellular polymeric matrix called a glycocalyx that protects microorganisms from the effects of the residual disinfectant in the water system. The occurrence of even low levels of dissolved organics, such as humates, allow for the growth of bio-film. Secondary residuals that are also strong oxidizers (e.g. chlorine, chloramines and chlorine dioxide) will combine (i.e. oxidize) with the humates. In fact, an abundance of humates will deplete the entire secondary residual leaving the system vulnerable to bio-film growth. Because silver does not act through an oxidative mechanism, it can be expected not to suffer this disadvantage (Armon et al 2000). 
         [0024]    Only Engelhard and Kasten (U.S. Pat. No. 6,267,895) have brought together the combination of silver, ozone and UV for water treatment and control of bio-film. In their work, specific to the control of bio-film and organism development in dental lines, they placed the silver after the UV and ozone and did not recognize or anticipate the benefits of introducing silver upstream of the UV and ozone. 
       SUMMARY OF THE INVENTION 
       [0025]    In the present invention, silver, ozone and UV are combined to create a chlorine free water treatment system to inactivate microorganisms, lower DBP formation and prevent biological regrowth in the water distribution system. Silver is introduced in advance of the UV radiation and ozone to take advantage of a previously unknown synergistic effect between silver and ozone. By having the injected ozone in the water stream immediately converted to hydroxyl radicals (through photolysis with UV254), there appears to be no loss in disinfection efficacy over ozone. In other words, hydroxyl radicals perform as well as ozone for disinfection. This result is surprising given that ozone is generally regarded by the water treatment industry as a disinfectant (and oxidant) whereas hydroxyl radicals are generally considered for oxidation purposes only. Collectively, when the ozone/silver is followed by application of UV, an unexpected level of inactivation of microorganisms is achieved. The mechanism of action to bring about this result is not entirely understood. 
         [0026]    It is therefore a primary object of the present invention to provide for introduction of silver prior to entrainment of ozone in water subsequently irradiated with UV light in a water treatment apparatus. 
         [0027]    Another object of the present invention is to provide primary disinfectants and secondary residuals to purify and maintain pure drinking water. 
         [0028]    Yet another object of the present invention is to provide apparatus for preventing growth of bio-film in conduits and water tanks that ultimately provide water to an end user. 
         [0029]    Still another object of the present invention is to provide apparatus for disinfecting and preventing growth of bio-film in water used in conjunction with cooling towers, agricultural water dispensing apparatus, water coolers, food and beverage processing equipment and municipal drinking water systems. 
         [0030]    A further object of the present invention is to provide apparatus which does not rely upon chlorine for short term and long term disinfection of water thereby preventing DBP formation. 
         [0031]    A still further object of the present invention is to provide a method for introducing silver in water to be purified prior to entrainment of ozone and UV irradiation. 
         [0032]    A yet further object of the present invention is to provide a method for inactivating microorganisms and preventing biological regrowth in water systems. 
         [0033]    These and other objects of the present invention will become apparent to those skilled in the art as the description thereof proceeds. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0034]    The present invention will be described with greater specificity and clarity with reference to the following drawings, in which: 
           [0035]      FIG. 1  is a prior art bar graph illustrating inactivation of MS-2 by silver, UV and an combination of silver and UV; 
           [0036]      FIG. 2  is a prior art graph illustrating ozone concentration versus time and showing the first and second phases of depletion; 
           [0037]      FIG. 3  is a representative cross sectional view of apparatus for purifying water and for preventing bio-film formation; and 
           [0038]      FIG. 4  is a representative cross sectional view of a variant apparatus for purifying water and for preventing bio-film formation. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0039]    It can be theorized that the high level of oxidizing power hydroxyl radicals present throughout the water purification apparatus of the present invention maintains the silver in a chemical state conducive for interaction of the silver with UV. It is noted that Butkus et al (2005) observed a lowering of the effect of silver with UV when chloride or phosphate was present. In the present invention, an unexpected result was observed to the effect that no such lowering of the efficacy occurred despite the presence of chloride and/or phosphate. Another theory for the observed efficacy of the present invention could be that ozone, when used alone, is rapidly depleted from oxidation demands in the water (note the instantaneous ozone demand above) whereas when hydroxyl radicals are used, their non selective behavior is directed to all organisms in the water, including those that are microbial in nature. Somewhat similarly, Elovitz et al (2000) demonstrated that under varying water quality conditions (e.g. pH, temperature, dissolved organic matter) hydroxyl radical exposure (i.e. concentration integrated over time) remained almost unchanged whereas the ozone exposure varied by several orders of magnitude. Hence, water quality parameters have a major effect on ozonation for oxidation and disinfection whereas hydroxyl radical effectiveness is effectively invariant. A yet further theory relates to the unique behavior of UV light and ozone for advanced oxidation. While the combined catalytic oxidants can be used to generate hydroxyl radicals (e.g. UV-H 2 O 2 , O 3 —H 2 O 2  and UV-TiO 2 , UV-O 3 ), Gottschalk et al (2000) showed that the O 3  UV process provides a maximum yield of hydroxyl radicals. 
         [0040]    Referring to  FIG. 3 , there is representatively shown a water purifier  10 . Water to be purified, represented by arrow  12 , enters through inlet  14  into conduit  16 . The conduit conveys the water to and through a silver media cartridge  18  of one of many types presently available from various commercial sources. The silver media cartridge releases silver (silver ions) into the water to achieve a desired concentration of silver. A further conduit  20  conveys the water containing silver to and through a venturi  22 . A pipe  24  is connected to low pressure section  26  of the venturi. As is well known, the low pressure section of a venturi will draw a fluid into the venturi for entrainment with the further fluid flowing through the venturi. Thus, the fluid, in this case ozone, in pipe  24  will be drawn into the water (further fluid) flowing through the venturi and become entrained therein. The water with entrained ozone and silver flows from venturi  22  into a yet further conduit  28 , which is in fluid communication with tank  30 . As depicted by arrows  32 , the water flowing into tank  30  through inlet  34 , will tend to swirl within the tank. 
         [0041]    Tank  30  includes a hollow threaded boss  40  extending from the top of the tank for threaded engagement by a cap  42 . A sleeve  44  of UV transmissive material, such as quartz, extends into boss  40  and is retained in place by an O-ring  46  compressed by cap  42  against boss  40  to provide a sealing function and a retention function for the sleeve. It is to be understood that other apparatus may be employed to secure the sleeve in place. An inlet  48  in cap  24  provides for an inflow of air or other oxygen containing gas, as represented by arrow  50 . It is to be understood that piping or other gas conveying structures may be employed to channel the gas into cap  42  under ambient or greater than ambient pressure. An ultraviolet (UV) lamp  60  capable of producing germicidal UV254 and ozone generating UV 185 is disposed within sleeve  44 . Base  62  of the UV lamp may be secured within sleeve  44 , as depicted, or by retention elements attendant cap  42 . Electrical conductors  64  interconnect the UV lamp with a source of electrical power. 
         [0042]    A further hollow threaded boss  70  extends from the bottom of tank  30  to receive therein sleeve  44 . Moreover, UV lamp  60  may extend within the sleeve into proximity of boss  70 , as illustrated. A further cap  72  is in threaded engagement with boss  70 . An O-ring  74 , or the like, may be disposed intermediate sleeve  44 , boss  70  and cap  72  to provide a retaining function for the lower end of the sleeve and to provide a seal between the sleeve, the UV lamp and the interior surface of the boss. Other means for retaining the lower end of the sleeve and to provide a sealing function may be employed. Cap  72  includes an outlet  76 . Outlet  76  is connected to and in fluid communication with pipe  24  terminating at venturi  22 , as described above. 
         [0043]    As depicted by arrows  78  in annular space  80  between UV lamp  60  and the interior surface of sleeve  44 , air (or oxygen containing gas) will flow through the annular space and become irradiated by radiation from the UV lamp. The wavelength of the ultraviolet light is preferably 185 nm (UV185) as irradiation of the oxygen molecules present in the air/gas flowing through annular space  80  are particularly susceptible to conversion to ozone molecules at this wavelength. Thus, ozone molecules are created and will flow with the air/gas into venturi  22  to ultimately become entrained in the water flowing into tank  30 . 
         [0044]    Water containing entrained ozone and silver enters tank  30  through inlet  34 . The flow of the water is generally in a swirling motion about sleeve  44 , as represented by arrows  32 . Upon energization of UV lamp  60 , the water within tank  30  will be irradiated with ultraviolet light. Such irradiation will have a virucidal and bactericidal effect upon microorganisms that may be present. The UV radiation will also convert entrained oxygen molecules in the water to ozone molecules. The presence of ozone in the water will result in oxidation of organic matter. Additionally, the combination of ozone and UV radiation will produce hydroxyl radicals in the water. The ozonated, irradiated water containing silver will flow from tank  30  through outlet  36  into a conduit  38  to the ultimate user, as represented by arrow  39 . 
         [0045]    In summary, the water discharged from tank  30  into conduit  38  and to ultimate user  39  will have entrained therein a certain amount of ozone, silver and hydroxyl radicals. As discussed above, not only does this combination purify the water within tank  30  but the formation and regrowth of bio-film and other contaminants is severely restrained or prevented. 
         [0046]    If the radiation from UV lamp  60  is also at a wavelength of 254 nm (UV 254), the UV radiation will have a strong germicidal and virucidal effect upon any microorganisms present in the air flowing through annular space  80  or within the water swirling about sleeve  44 . Additionally, irradiation of the ozone with UV 254 will convert the ozone to hydroxyl radicals through a photolysis process. 
         [0047]    A variant water purifier  90  is representatively illustrated in  FIG. 4 . As tank  30  is duplicative of the tank shown in  FIG. 3 , the same nomenclature and reference numerals will be used for common elements and a detailed description thereof need not be repeated. 
         [0048]    It is well known that irradiating air or an oxygen containing gas at a pressure greater than ambient will result in more conversion of oxygen molecules to ozone molecules than if the air or gas is at ambient pressure. To increase the production of ozone molecules within annular space  80  in response to radiation of ultraviolet light from UV lamp  60 , a compressor  92  is used to compress the gas flowing into cap  42  through conduit  94 . To control the pressure of the gas within cap  42  and annular space  80  within sleeve  44 , a regulator  96  may be used in conjunction with the conduit. As described above, the gas flowing through annular space  80  is subjected to ultraviolet radiation from UV lamp  60  and such radiation will convert some of the oxygen molecules to ozone molecules. The gas with the ozone molecules, which may be referred to as ozonated gas, is discharged through outlet  76  into conduit  98 . A pressure regulator  100  is disposed in conduit  98  to maintain the gas and ozone molecules flowing through annular space  80  at a pre-determined pressure. The ozonated gas discharged from regulator  100  flows through a further conduit  102  into a chamber  104 . 
         [0049]    The water to be purified, represented by arrow  106 , flows through a conduit  108  into a silver media cartridge  110 , which cartridge may be any one of several commercially available cartridges. The purpose of the silver media cartridge is to introduce silver into the inflowing water. The water discharged from the silver media cartridge flows into chamber  104  via a conduit  112 . The flow of ozonated air or gas through conduit  102  into chamber  104  is discharged through a diffuser, such as a sparger  114 , to entrain bubbles of ozonated air or gas in the water within the chamber. It is to be understood that various other devices may be used in place of the sparger to cause entrainment of bubbles of ozonated air or gas in the water within chamber  104 . The water within chamber  104  now containing silver and entrained ozonated air or gas is discharged into tank  30 , as represented by arrow  116  through a conduit  118 . The water inflowing through inlet  34  will swirl about sleeve  44 , as represented by arrows  32 . During such swirling, the water will be irradiated by UV lamp  60  to convert some of the oxygen molecules present into ozone molecules. Moreover, the UV254 radiation will have a germicidal and virucidal effect upon microorganisms that may be present. Additionally, hydroxyl radicals will be formed, as discussed in further detail above. The UV irradiated water containing silver, ozone molecules and hydroxyl radicals is discharged through outlet  36  for use by an end user, as represented by arrow  39 . 
         [0050]    The silver media in the cartridge can be any type of media that releases silver. Examples of such silver media include: silver metal deposited on carbon, alumina, titania, zeolite, or other inorganic or organic substrate. The prior art describes processes for making such a media (see, for example, U.S. Pat. No. 6,383,273). The concentration of silver on the substrate can be several weight percent (e.g. 30%) or less than 1 weight percent (1%) provided that the silver is released into the water in the desired concentration range. The concentration of silver to be delivered to the water is preferably less than 400 ppb and more preferably less than 125 ppb. Some examples of silver compounds that can be used to prepare the media include, but are not limited to, silver nitrate, silver carbonate, silver acetate and silver chloride. Alternatively, a solution of silver salts can be injected into the water. An example would be a solution of silver nitrate that is connected to a volumetric pump, which delivers the silver nitrate solution at a rate commensurate with the water flow to achieve the desired silver concentration. 
         [0051]    To confirm the efficacy of the present invention, a number of experiments were conducted. These experiments (examples) and the results obtained are set forth below. 
       Examples 1-8 
       [0052]    In examples 1-8, the biocidal efficacy against E. Coli of both silver and chlorine in the presence of three different concentrations of Total Organic Carbon (TOC) (i.e. 0 mg/L, 3 mg/L and 10 mg/L) were compared. In all cases, the starting water was de-chlorinated tap water. The TOC was generated by addition of humic acid. These tests measure the ability of these two secondary disinfectants to remain biocidal in water for extended periods of time should the water be ladened with natural organic matter. As can be seen from examples 1-4, silver is not affected by the presence of humates whereas chlorine (examples 5-8) readily loses its biocidal efficacy presumably due to oxidation of the humate by the chlorine. The controls had neither chlorine, silver nor TOC added. 
         [0000]    Log 10  Reduction a  of  E. coli  (Initial Inoculum=4.50×10 6  CFU/ml) after Exposure to Silver in the presence of Total Organic Carbon. 
         [0000]                                                                                        Log 10  Reduction a  of  E. coli  (initial inoculum = 4.50 × 10 6  CFU/ml)       after exposure to silver in the presence of Total Organic Carbon.            Exam-                               ple   Test System   1 hour   2 hours   3 hours   4 hours   7 hours                    1   Control (0   0.01   0.03   0.05   0.07   0.09           μg/L Ag and           0 mg/L TOC)       2   100 μg/L Ag   2.51   4.40   5.55   &gt;5.65   &gt;5.65           and 0 mg/L           TOC       3   100 μg/L Ag   2.51   4.40   5.55   &gt;5.65   &gt;5.65           and 3 mg/L           TOC       4   100 μg/L Ag   2.39   4.40   5.55   &gt;5.65   &gt;5.65           and 10 mg/L           TOC                 a Average Log 10  reduction of triplicate tests            
Log 10  Reduction a  of  E. coli  (Initial Inoculum=5.00×10 6  CFU/ml) after Exposure to Chlorine in the Presence of Total Organic Carbon
 
         [0000]    
       
         
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                   
               
               
                 Log 10  Reduction a  of  E. coli  (initial inoculum = 5.00 × 10 6   
               
               
                 CFU/ml) after exposure to chlorine in the presence 
               
               
                 of Total Organic Carbon. 
               
             
          
           
               
                 Exam- 
                   
                   
                   
                   
                   
                   
               
               
                 ple 
                 Test System 
                 1 hour 
                 2 hours 
                 3 hours 
                 4 hours 
                 7 hours 
               
               
                   
               
             
          
           
               
                 5 
                 Control (0 
                 0.00 
                 0.01 
                 0.03 
                 0.05 
                 0.07 
               
               
                   
                 mg/L Cl and 
               
               
                   
                 0 mg/L TOC) 
               
               
                 6 
                 0.2 mg/L Cl 
                 &gt;5.70 
                 &gt;5.70 
                 &gt;5.70 
                 &gt;5.70 
                 &gt;5.70 
               
               
                   
                 and 0 mg/L 
               
               
                   
                 TOC 
               
               
                 7 
                 0.2 mg/L Cl 
                 0.13 
                 0.15 
                 0.15 
                 0.17 
                 0.19 
               
               
                   
                 and 3 mg/L 
               
               
                   
                 TOC 
               
               
                 8 
                 0.2 mg/L Cl 
                 0.14 
                 0.16 
                 0.17 
                 0.17 
                 0.18 
               
               
                   
                 and 10 mg/L 
               
               
                   
                 TOC 
               
               
                   
               
               
                   a Average Log 10  reduction of triplicate tests 
               
             
          
         
       
     
       Examples 9-20 
       [0053]    In examples 9-20, the biocidal efficacy of UV, ozone and silver were assessed by observing the Log 10  reduction of MS-2 bacteriophage. In all cases, the starting water was de-chlorinated tap water. A flow-through 2-liter per minute water treatment device providing a dosage of 50 mJ/cm 2  UV was used. The UV lamp was allowed to warm up for three minutes prior to each experiment. The ozone being generated by the UV lamp was injected into the water stream immediately in front of the UV chamber. The ozone dose was approximately 0.08 mg/l. In the experiments using silver (Ag), the silver (as silver nitrate) was added either five (5) minutes prior to simultaneous UV/Ozone exposure, or was added afterwards (with a five (5) minute incubation prior to addition of the neutralizer). The concentration of silver used was 100 ppb. From the data, it can be concluded that employing silver prior to the UV and ozone is advantageous. 
         [0000]    
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
               
               
                 Log 10  reduction of MS-2 after exposure to various 
               
               
                 combinations of UV, ozone and silver 
               
             
          
           
               
                   
                   
                 Initial virus 
                 Virus 
                   
               
               
                   
                   
                 inoculum 
                 (Pfu-ml) 
                 Log 10   
               
               
                 Example 
                 Test System 
                 (pfu/ml) 
                 Recovered 
                 Reduction 
               
               
                   
               
             
          
           
               
                 9 
                 UV only 
                 2.88 × 10 6   
                 3.17 × 10 3   
                 2.96 
               
               
                 10 
                 UV only 
                 1.93 × 10 7   
                  8.6 × 10 3   
                 3.36 
               
               
                 11 
                 Ozone only 
                 1.93 × 10 7   
                 1.88 × 10 6   
                 1.01 
               
               
                 12 
                 Ozone only 
                 2.88 × 10 6   
                 3.88 × 10 5   
                 0.87 
               
               
                 13 
                 UV/Ozone 
                 2.88 × 10 6   
                 2.80 × 10 2   
                 4.01 
               
               
                 14 
                 UV/Ozone 
                 1.16 × 10 8   
                 1.53 × 10 4   
                 3.88 
               
               
                 15 
                 UV/Ozone 
                 1.93 × 10 7   
                     4.88 × 102 
                 4.45 
               
               
                 16 
                 UV/Ozone followed 
                 1.16 × 10 8   
                 2.95 × 10 4   
                 3.61 
               
               
                   
                 by silver 
               
               
                 17 
                 Silver followed by 
                 1.93 × 10 7   
                   2 × 10 1   
                 5.98 
               
               
                   
                 UV/Ozone 
               
               
                 18 
                 Silver followed by 
                 1.16 × 10 8   
                 5.35 × 10 2   
                 5.33 
               
               
                   
                 UV/Ozone 
               
               
                 19 
                 Silver followed by 
                 2.88 × 1O 6   
                 &lt;5 
                 &gt;5.76 
               
               
                   
                 UV/Ozone 
               
               
                 20 
                 Silver only (5- 
                 1.16 × 10 8   
                 1.16 × 10 8   
                 0 
               
               
                   
                 minute exposure, 
               
               
                   
                 no UV or Ozone) 
               
               
                   
               
               
                   a Average Log 10  reduction of triplicate measurements 
               
             
          
         
       
     
       Examples 21-25 
       [0054]    In examples 21-25, the biocidal efficacy of UV, ozone and silver were assessed by observing the Log 10  reduction of Adenovirus type 2. In all cases, the starting water was de-chlorinated tap water. A flow-through 2-liter per minute water treatment device providing a dosage of 50 mJ/cm 2  UV was used. The UV lamp was allowed to warm up for three minutes prior to each experiment. The ozone, being generated by the UV lamp, was injected into the water stream immediately in front of the UV chamber. The ozone dose was approximately 0.05 mg/L. In the experiment using sliver (Ag), the silver (as silver nitrate) was added three (3) minutes prior to simultaneous UV/Ozone exposure. The concentration of silver used was 100 ppb. From the data, it can be concluded that employing silver prior to the UV and ozone is advantageous. 
         [0000]    
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
               
               
                 Log 10  Reduction of Adenovirus 2 after exposure 
               
               
                 to various combinations of UV, ozone and silver 
               
             
          
           
               
                   
                   
                 Initial virus 
                 Virus 
                   
               
               
                   
                   
                 inoculum 
                 (TCID 50 /ml) 
                 Log 10   
               
               
                 Example 
                 Test System 
                 (TCID 50 /ml) 
                 Recovered 
                 Reduction 
               
               
                   
               
             
          
           
               
                 21 
                 UV only 
                 1.33 × 10 6   
                 4.50 × 10 3   
                 2.47 
               
               
                 22 
                 Ozone only 
                 1.33 × 10 6   
                 2.08 × 10 5   
                 0.81 
               
               
                 23 
                 UV/Ozone 
                 1.33 × 10 6   
                 5.02 × 10 1   
                 4.42 
               
               
                 24 
                 UV/Ozone/Ag 
                 1.33 × 10 6   
                 &lt;3.73 × 10 0   
                 &gt;5.55 
               
               
                 25 
                 Ag only 
                 1.33 × 10 6   
                 1.33 × 10 6   
                 0