biocidal methods and compositions for recirculating water systems.docx

7/24/2019 Biocidal methods and compositions for recirculating water systems.docx

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Biocidal methods and compositions for recirculating watersystemsWO 1990015780 A1R!"#

Improved biocidal composition and method for controlling biofouling and microorganism population

levels in recirculating water systems such as coolingtowers, swimming pools or spas is disclosed and

claimed. The composition comprises a hypochlorite donor and a bromide ion donor in proportions

selected to maintain a mole ratio of the sum of all bromine containing species to the sum of all

hypohalite species in the recirculating water of about 0.2 to about 20. The method comprises

introducing into the recirculating water a mixture or combination of a hypochlorite donor and a bromide

ion donor in an amount sufficient to maintain a ratio of the sum of all bromine containing species to the

sum of all species in the recirculating water in the range of about 0.2 to about 20. In addition, a

bromine volatilization suppressant may be introduced into the recirculating water to inhibit loss of

bromide ion through volatilization of bromine containing species formed by reaction of

the hypochlorite donor and the bromide ion donor. One or more scale inhibitors and compacting aids

may also be added.


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$%!&R'()'O* !e texte O"# peut contenir des erreurs.$

%IO"I&'! ()T*O&+ '& "O(-O+ITIO+ O# #)"I#"/!'TI 1'T)# ++T)(+

%'"3#O/& O T*) I4)TIO

5. ield of the Invention

6 This invention relates to the disinfection of water and to the control of biofouling in recirculating water

systems such as cooling towers, evaporative condensers, air washers, swimming pools, hot tubs, and

spas.

0 The invention more especially concerns methods and compositions for controlling biofouling and

microorganism population levels in such systems wherein water soluble hypochlorite donors and

bromide ion donors are added to the systems so as to improve biocidal effectiveness with 6 reducedcosts.

's used herein, the term 7hypochlorite donor7 means any compound that will

generate hypochlorite species when dissolved in water. 0

The term 7bromide ion donor7 means any compound that will generate bromide ions when dissolved in

water.

The term 7available halogen7 means the standard form for expressing the strengths or capacities of

halogenating chemicals as well as for the doses in which they are applied and for the hypohalite

species *O"5, O"l7, *O%r, O%r8$ which remain in the water.

The term 7available chlorine7 means the same as

7available halogen7, but refers specifically to chlorine compounds.

The term 7available bromine7 means the same as 7available halogen7, but refers specifically to

bromine compounds. The term 7hypohalite species7 means hypochlorous acid, hypochlorite ion,

hypobromous acid and hypobromite ion.

The term 7hypochlorite species7 means hypochlorous acid and hypochlorite ion.

The term 7hypobromite species7 means hypobromous acid and hypobromite ion.

The term 7bromine species7 means hypobromous acid, hypobromite ion, and bromide ion.

The terms 7free halogen7 and 7free available halogen7 are used interchangeably and are defined as

the concentration of halogen existing in the water as hypohalous acid, *O9, and hypohalite ion, 098,

where 9 is "l or %r.


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The terms 7free chlorine7 and 7free available chlorine7 are used interchangeably and are defined as

the concentration of chlorine existing in the water as hypochlorous acid, *O"5, and hypochlorite ion,

O"l7.

The terms 7free bromine7 and 7free available bromine7 are used interchangeably and are defined asthe concentration of bromine existing in the water as hypobromous acid, *O%r, and hypobromite ion,

O%r8.

The terms 7combined halogen7 and 7combined available halogen7 are used interchangeably and are

defined as the concentration of halogen existing in the water in chemical combination with ammonia or

organic nitrogen compounds.

The terms 7combined chlorine7 and 7combined available chlorine7 are used interchangeably and are

defined as the concentration of chlorine existing in the water in chemical combination with ammonia or


The terms 7combined bromine7 and 7combined available bromine7 are used interchangeably and are

defined as the concentration of bromine existing in the water in chemical combination with ammonia or


The terms 7total halogen7 and 7total available halogen7 are used interchangeably and are defined as

the sum of 7free halogen7 or 7free available halogen7$ and 7combined halogen7 or 7combined

available halogen7$.

The terms 7total chlorine7 and 7total available chlorine7 are used interchangeably and mean the same

as 7total halogen7 and 7total available halogen7 but specifically refer to chlorine.

The terms 7total bromine or 7total available bromine7 are used interchangeably and mean the same as

7total halogen7 and 7total available halogen7 but specifically refer to bromine.

The symbol 7'v"7 represents 7free chlorine7 and 7free available chlorine7 concentrations in the water.

The symbol 7'v"7 represents the available chlorine content of the hypochloritedonor.

The term 7halogen demand7 is defined as the amount of halogen which must be adde to the water

over a specific period of time to maintain the 7free halogen7 and:or 7free available halogen7 at a

specific concentration in the water. The term 7chlorine demand7 means the same as the 7halogen

demand7 but specifically refers to 7free chlorine7 and:or 7free available chlorine7 concentrations.

The term 7chlorinated isocyanuric acid derivative7 means chlorinated isocyanuric acid including

dichlorinated and trichlorinated isocyanuric acid, al;ali metal and al;aline earth metal salts of

chlorinated isocyanuric acid, and hydrates, complexes and mixtures thereof.

The term 7hydantoin derivative7 means an unsubstituted, halogenated i.e. chlorinated or brominated$,

or al;ylated hydantoin.


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The term 7sulfamic acid derivative7 means unsubstituted, halogenated, or al;ylated sulfamic acid.

The term 7sulfonamide derivative7 means halogenated, al;ylated, or arylated sulfonamide.

The term 7glycoluril derivative7 means unsubstituted, halogenated, or al;ylated glycoluril.

The term 7succinimide derivative7 means unsubstituted, halogenated, or al;ylated succinimide.

uilibrium shift from hypochlorous acid tohypochlorite ion.

*O"5 EFG O"l

7

H *

H

5$

-3 E loJ KO"I7/* 5 D.6 at 20L"$ O"lM

The hypochlorite ion canno IErocN8/*H

* t easily penetrate microorganism cell membranes, while the uncharged hypochlorous acid car

passively diffuse into cells to cause damage.

1ater in recirculating water systems is also fre>uently contaminated with ammonia due to the

decomposition of nitrogenous impurities in the water or to the lea;age of ammonia from refrigerationunits into the cooling water. 'mmonia or chloramines are also commonly introduced into the

recirculating water system by the ma;eup water. *ypochlorite species react with ammonia to form

chloramines. +ince chlorine is bound very strongly by nitrogen, the chlorine is not readily released by

chloramines to the water as hypochlorite species, and the biocidal activity of the chlorineEbased

biocide is, therefore, greatly reduced. The fact that the chloramines are relatively stable chlorine

compounds also ma;es it more difficult for some cooling tower systems to comply with the )-' total

halogen free halogen H combined halogen$ discharge limit of 0.2 ppm. In some cases,

these cooling tower systems fre>uently have to dechlorinate the discharge water in order to be in

compliance. (oreover, chloramines have a disagreeable and irritating odor. They can be converted toodorless nitrogen gas by maintaining the appropriate free chlorine concentration in the recirculating


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water, but some chloramines are still volatilized into the air. )ven though the amounts are negligible,

chloramine odors are still noticeable.

"hloramine odor is an important issue with indoor pools and spas because the air containing the

volatilized chloramines is retained in the buildings long enough for the chloramine concentration toaccumulate to levels that are ob=ectionable to the consumer. Thus, the formation of chloramines in

recirculating water can present a serious obstacle to the use of chlorineEbased biocides.

*ypobromous acid *O%r$, which can be generated from a number of compounds including li>uid

bromine and Ebromo organic compounds or by reacting a bromide salt with a solution of

hypochlorous acid or other oxidizing agents, is a more effective biocide on a molar basis than

hypochlorous acid. /nder some conditions, this superiority is >uite dramatic. In particular,

hypobromous acid is ;nown to react with ammonia to produce bromamines. %romamines, unli;e

chloramines, have very good biocidal activity and have a more acceptable odor. %romamines also

have a distinct advantage over chloramines because they dissipate more readily, thereby ma;ing it

easier to operate cooling towers in compliance with the )-' limits for total halogen. In addition,

hypobromite species are more effective than hypochlorite species at p* values above D.6 due to the

higher p3 value for the e>uilibrium shift from hypobromous acid to hypobromite ion. *O%r EG O%r H *

2$

p3 Elog rO%r7lull B.6 at 20P"$

*O%rM

In most cases where hypobromous acid is used as a biocidal agent, the hypobromous acid generating

composition contains a large weight percentage of bromine. !i>uid bromine, for example, is 500Q

bromine by weight and lEbromoE@EchloroE6,6Edimethylhydantoin %"&(*$ is @2.BQ bromine by weight.

This practice leads to higher costs for the bromineEbased biocides since the cost of bromine is about

three times the cost of chlorine per pound. +ince 2.26 pounds of bromine contain the same number of

moles of available halogen as only 5.0 pound of chlorine, bromine is over seven times more expensive

than chlorine on a per mole basis. )ven though hypobromous acid is generally superior to

hypochlorous acid, the higher cost of bromine has limited the use of bromineEbased biocides.

evertheless, in the past few years several products have been introduced into

thecooling tower mar;etplace which ta;e advantage of the bromine chemistry. In 5CB2, alco

introduced a bromineEbased product tradename

'ctibrom$ for use in large scale cooling towers. These towers already had chlorinators in=ecting

gaseous chlorine for disinfection. 'ctibroiri is simply an a>ueous solution of sodium bromide, and is

typically added in proportion to the chlorine gas using a separate feeder. +ee /.+. -atent o.

A,A65,@DR. 'nother bromineEbased biocide, lEbromoE@E chloroE6,6Edimethylhydantoin %"&(*$ was

introduced into the cooling tower mar;etplace by reat !a;es "hemical. +ee /.+. -atent o.

A,2CD,22A.


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%romine sanitizers have also gained some measure of popularity for indoor pool and spa applications,

because the odor of the bromamines, formed by reaction of hypobromite species with nitrogenous

wastes, is less ob=ectionable to the consumer. %romine sanitizers, however, have not been popular for

outdoor pools because the hypobromite species are rapidly dissipated in sunlight and the sanitizer

costs are considerably higher than chlorine sanitizers with cyanuric acid.

-otassium onopersulfate and sodium bromide have been mar;eted together as a bromine sanitizer

system for spa applications. The recommended practice is to dose the spa water with sodium bromide

usually as a solution$ and then add the recommended dosages of potassium monopersulfate as

needed. *ypobromous acid is generated by oxidation of the bromide ion with persulfate ions as shown

by the following e>uationS

3*+06.3*+0AH a%r G *O%r H 3*+OAH a3+0A@$

"urrently available dry sources of hypobromous acid suffer from a number of disadvantages in

addition to their higher cost. The hydantoin products such as %"&(*, 5,@E dichloroE6,6E

dimethylhydantoin ""&(*$, l,@EdibromoE6,6E dimethylhydantoin %%&(*$, l,@EdichloroE6EethylE6E

methylhydantoin "")(*$ , and lEbromoE@EchloroE6EethylE6E methylhydantoin %")(*$ have very low

dissolution rates which necessitates the use of large feeder systems and high water flow rates.

(oreover, in some cases it is desirable to add a large amount of available halogen at one time to

rapidly clean up a recirculating water system. This is ;nown as a 7shoc; treatment7. +uch a treatment

would be desired whenever a system has experienced a large amount of contamination or when

microorganism growth has gotten out of control. *owever, the hydantoin products are generally

unsuited for this application due to their low dissolution rates. In addition, the hydantoin products arenot as effective biocides as might be expected based on the amount of hypobromous acid formed,

because these products also release large amounts of 6,6Edimethylhydantoin &(*$ or 6EethylE6E

methylhydantoin )(*$ into the water, eventually leading to the buildup of high concentrations of &(*

or )(* in the water. *igh concentrations of &(* or )(* inhibit the biocidal activity of the

hypobromous acid by virtue of the following e>uilibriaS

*O%r H &(* G *20 H %&(* A$

*O%r H .)(* G *20 H %)(* 6$

where %&(* is bromoE&(* and %)(* is bromoE)(*. This effect has previously been noted in /.+.

-atent A,RCB,5R6.

's an alternative to the hydantoins, hypobromous acid may be prepared by reacting a bromide salt

with a source ofhypochlorite species according to the following e>uationS

*O"5 H %r G *O%r H "l Ra$

O"l7H %r7G O%r7H "l7Rb$

as previously taught, for example, in %ritish -atent


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5,@2D,6@5 and /.+. -atents 2,B56,@55 @,CD6,2D5 and A,55C,6@6. The hypobromous acid formed by

the above e>uation is the active biocide. *owever, in the process of ;illing microorganisms or oxidizing

organic material, the hypobromous acid is reduced to form bromide ion,as shown by the following

e>uationS D$ *O%r H microorganisms G dead microorganisms H %r7H *E0

Thus, the bromide ion can be reused to generate more hypobromous acid by reaction

with hypochlorite species as shown above in e>uations Ra and Rb. %ecause the bromide ion is

continuously reused, only small amounts of bromide ion are necessary to ma;e a chlorineEbased

biocide in combination with bromide salts perform as a bromine biocide.

+ome prior art teaches that, when using mixtures of chlorineEbased biocides in combination with

bromide salts large excesses of bromide ion should be maintained in the recirculating water. or

example, %ritish -atent o.

5,@2D,6@5 describes a process for sanitizing swimming pool water wherein the concentration of

bromide is maintained at 20 to 60 mg per liter expressed as sodium bromide$ and the concentration of

the hypobromite species is maintained at 0.A mg:!. Other prior art, e.g.G /.+. -atent o. @,CD6,2D5,

suggests that when hypobromous acid is generated by reacting a bromide salt with a source of

hypochlorous acid, the optimum mole ratio of chlorine to bromide is near 5. *owever, no information is

provided as to how to maintain the ratio near the optimum in the recirculating water while Uhlorine and

bromide salts are being fed simultaneously to the system as well as being lost from the system.

+/(('# O T*) I4)TIO

This invention is broadly concerned with compositions and methods for controlling biofouling and

microorganism population levels in recirculating water systems using compositions or combinations

of hypochlorite donors and bromide ion donors. The proportion of hypochlorite donor and bromide ion

donor in the composition or combination added to the system is selected to maintain an optimum ratio

of all bromine containing species to the sum of all hypohalite species in the recirculating water. It has

now been found that significant amounts of bromide ion are lost from recirculating water systems

through the pathways of volatilization of hypobromous acid and bromamines and of formation of stable

organobromine compounds. (oreover,hypochlorite species, hypobromite species, and bromide ion

are lost from the recirculating water at different rates. These loss rates must be ;nown in order to

prescribe at what rates to feed the hypochlorite donor and bromide ion donor to the water to

compensate for the losses and maintain the desired steady state concentrations.

It is very important, therefore, to control the chemistries of the reactions of the hypochlorite species

with the bromide ion e>uations Ra and Rb$ in a dynamic system. (ore specifically, it is critical to

control the mole ratio of the sum of all bromineEcontaining species *O%r, O%r7and %r7$ to the sum of

all hypohalite species *O%r, O%r7*O"5 and O"l7$ present in the water. or the purposes of this

discussion, this mole ratio will be referred to herein as the 7chlorineEtoEbromine conversion ratio7 or

7"onversion #atio7 7"#7$ and will be written

V asS


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"# moles of *O%r H O%r7H %r7l moles of *O%r H O%r7H *O"5 H O"l7$

This ratio will be used hereafter because it is a convenient way to express the instantaneous measure

of the extent of conversion of the hypochlorite species to hypobromite species. It is also a convenient

way to establish if the hypochloritedonor:bromide ion donor compositions are actually performing as abromine biocide, a mixture of bromine and chlorine biocides, or as a chlorine biocide only. or

example, consider the following four scenarios.

In the first scenario, the recirculating water does not contain any bromide ion. It follows then that there

will be no hypobromite species present. +ince the %r8M 0.0 and the *O%rM O%r8M 0.0,

then hypochlorite species will have some finite values e.g., 0.6 mole of

*O"5 and 0.6 mole of O"l7. 'lso, "# 0.0 as shown by the following calculationS

"# 0.0 H 0.0 H 0.05 O=W$ 0.0 0.0 H 0.0 H 0.6 H 0.6$ 5.0

/nder these conditions, the biocide will perform as a chlorine biocide.

'ssume in the second scenario that the recirculating water contains 0.6 mole of bromide ion, 0.6 mole

of *O"5 and 0.6 mole of O"l7before the hypochlorite species:bromide ion reactions occur. /nder

these conditions, there is only enough bromide ion to satisfy oneEhalf of the stoichiometric

re>uirements of the reactions outlined in e>uations Ra and Rb. Therefore, essentially all of the bromide

ions will be converted to hypobromite species, but only oneEhalf the hypochlorite species will be

converted to hypobromite species. 'lso, oneEhalf the hypochlorite species will still be present. Thus,

the hypohalite species in the water will be a 60:60 mixture of hypochlorite species and hypobromite

species and the "# will be 0.6 as shown by the following calculationS *O%rM H O%r7M 0.6 mole

*O"5M H O"l7M 0.6 mole

%r7M 0.0

"# 0.6 H 0.05 O= . 0.6 0.6 H 0.6$ 5.0

+ince the hypochlorite donor:bromide ion donor composition is capable of only maintaining a 0.6"onversion #atio, it will exhibit biocidal properties intermediate between that of a chlorine biocide and

a bromine biocide. It follows then that anyhypochlorite donor:bromide ion donor composition that

maintains a "onversion #atio between 0.0 and 5.0, will exhibit the same properties.

In the third scenario, assume that there are 5.0 mole of bromide ion and 5.0 mole

of hypochlorite species 0.6 mole of *O"5 and 0.6 mole O"l 7$ before the *O"l:%r7and 0"58:%r8

reactions occur. /nder these circumstances, essentially all of thehypochlorite species will be

converted to hypobromite species. +imilarly, essentially all of the bromide ions will be converted to

hypobromite species. *ence, there will .be essentially no hypochlorite species and bromide ions left.

's a conse>uence, after the reactions, the "onversion #atio will be 5.0 as shown by the following

calculationS


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%r7M 0.0 *0"5M O"l8M 0.0

*O%rM H O%rEM 5.0

"# 5.0 H 0.05 l=?0 5.0 0.0 H 5.0$ 5.0

'nd, the hypochlorite donor:bromide ion donor composition will perform as a bromide biocide.

inally, in the fourth scenario, assume that the recirculating water contains 5.2 moles of bromide ion

and 5.0 mole ofhypochlorite species before the hypochlorite species react with the bromide ion. /pon

completion of these instantaneous reactions, the recirculating water will contain essentially

no hypochlorite species, 5.0 mole of hypobromite species and 0.2 mole of bromide ion. 'ccordingly,

after the reactions, the "onversion #atio will be 5.2 as shown belowS

*O"5M O"l7

M 0.0

*O%rM H O%r7M 5.0

%r7M 0.2

Thus,

5.0 H 0.0$ 5.0

's a conse>uence, the hypochlorite donor:bromide ion donor composition will perform as a bromine

biocide.

Thus, it is desirable to maintain the "onversion #atio preferably at or slightly above 5.0. *owever, as

will be shown later, there are circumstances where other "onversion #atios are desirable. *ence, it is

preferable to maintain the "onversion #atio between about 0.2 and 20.0 and most preferably between

0.6 and A.0.

In order to control the "onversion #atio to maintain a small excess of bromide ion, enough bromide

ion must be fed to the water to compensate for any significant losses of bromine containing species.

%romide ion is, of course, lost from recirculating water systems through blowdown or turnover. These

terms refer to water that is bled from the system, a practice necessary to ;eep dissolved solids from

building up to the point where scaling occurs. *owever, there has been no recognition in the literature

that bromide ion is lost by volatilization of hypobromous


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comprising hypochlorite donors and bromide ion donors that are capable of simultaneously

compensating for the bromide ion losses and satisfying the chlorine demand of the recirculating water.

1ithout ;nowledge of bromide ion loss pathways, as will be shown in the detailed description of this

invention, it is virtually impossible to develop commercial products that will perform li;e bromineEbased

biocides without using a large excess of bromide ion. Thus, all significant pathways of bromide ion lossmust be accounted for in order to maintain an optimum "onversion #atio in the recirculating water.

The failure of the prior art to ade>uately compensate for bromide ion loss is evident in the prior artXs

use of either large excesses of bromide ion or of insufficient amounts to maintain maximum biocidal

activity. 'ny large excess of bromide ion is wasted since it is eventually discarded, for example, in

the cooling tower blowdown or pool water turnover. 'lso, as will be shown in the detailed description of

the present invention, a large excess of bromide ion is unnecessary because the physical and

chemical dynamics of the recirculating water system will force the bromide ion concentration to a

steady state condition. In many cases, this will result in considerable loss of bromide ion. 's a

conse>uence, it is preferable and more economical to supply only sufficient bromide ion to the

recirculating water to maintain the "onversion #atio at, or slightly above, 5.0 to ensure maximum

biocidal effectiveness.

In one aspect, the present invention provides a biocide composition containing a hypochlorite donor

and a bromide ion donor in amounts sufficient to satisfy the chlorine demand of the system and

maintain an optimum "onversion #atio.

In another aspect, the present invention provides a method of treating recirculating water which

comprises the steps of ascertaining the rates of bromide ion loss from the system due to blowdown,volatilization, and formation of stable organobromine compounds and adding a hypochlorite donor and

a bromide ion donor in amounts sufficient to compensate for the bromide ion losses and maintain an

optimum "onversion #atio. +uitable hypochlorite donors include gaseous chlorine, al;ali metal and

al;aline earth metal hypochlorites, chlorinated hydantoins, chlorinated oxazolidinones, chlorinated

imidazolidinones, and chlorinated isocyanuric acid derivatives.

+uitable bromide ion donors include li>uid bromine, bromine chloride, al;ali metal and al;aline earth

metal bromides, >uaternary ammonium bromides, bromamines, brominated hydantoins, brominated

sulfonamides, brominated succinimides, brominated oxazolidinones, brominated imidazolidinones,

brominated isocyanurates, and salts of trihalide or mixed trihalide ions containing bromine.

In a preferred embodiment the hypochlorite donor and bromide ion donor are dry solids having a

higher dissolution rate and a higher water solubility than hydantoins. -referred dry solids include

trichloroisocyanuric acid or sodium or potassium dichloroisocyanurate and sodium or potassium

bromide. 1hen these compounds are used, it has been found that proportions of about B6 to about CC

parts by weight hypochlorite donor and about 5 to about 56 parts by weight bromide ion donor are

capable of maintaining the "onversion #atio in the optimum range for most water systems. In other

instances


12/41

about CC parts by weight hypochlorite donor and about 5 to about 60 parts by weight bromide ion

donor are capable of maintaining an optimum "onversion #atio.

It has now also been found that certain compounds can be added to the recirculating water system to

suppress the loss of bromide ions through volatilization of hypobromous acid and bromamine. Thebromine volatilization suppressants may be included in the hypochlorite donor:bromide ion donor

biocide composition or combination thereof or may be added separately to the recirculating water.

+uitable bromine volatilization suppressants include hydantoin derivatives, sulfonamide derivatives,

sulfamic acid derivatives, glycoluril derivatives, oxazolidinone derivatives, imidazolidinone derivatives

and succinimide derivatives.

Other features and advantages of the present invention will become apparent from the following

detailed description, which is given by way of illustration only.

%#I) &)+"#I-TIO O T*) '1I+

I/#) 5 illustrates the effect of the "onversion #atio on ;illing efficiency.

I/#)+ 2ER illustrate the effect of the hypochlorite donor:bromide ion donor composition on the

"onversion #atio in the recirculating water and the ability of the biocide to perform as a bromine

biocide. a%r:'"!C0 -!/+ and a%r:'"!R0 compositions are used to illustrate the effects. a

I/#) .D illustrates the effect of &(* on the *enryXs !aw constant for a bromine biocide.

&)T'I!)& &)+"#I-TIO O T*) I4)TIO

' hypochlorite donor compound according to the present invention may be any chlorine containing

compound capable of providing a sufficient amount of hypochlorite species in a>ueous solution,

including but not limited to gaseous chlorine,hypochlorite salts such as

lithium hypochlorite, sodium hypochlorite, or calcium hypochlorite, chlorinated hydantoins such as

dichlorodimethylhydantoin, or bromochlorodimethylE hydantoin, chlorinated oxazolidinones such as @E

chloroE A,AEdimethylE2Eoxazolidinone, chlorinated imidazolidinones such as l,@EdichloroEA,A,6,6E

tetramethylE2E imidazolidinone, or chlorinated isocyanuric acid or its derivatives including its salts,

hydrates, complexes, or mixtures thereof.

+ome disadvantages may occur with the use of certain of these hypochlorite donor compounds. or

example, addition of calcium is not desirable since repeated use could increase the calcium ion

concentration in the water to the level where calcium scaling problems could occur. +ince chlorine gas

is a hazardous material, its use is generally limited to the larger, more sophisticated recirculating water

systems. inally, many of the chlorinated organic compounds are less useful than the chlorinated

isocyanuric acid derivatives due to higher costs, lower dissolution rates, lower halogen content, and:or

the buildup of species which inhibit biocidal activity.

-referred hypochlorite donor compounds include chlorinated isocyanuric acid derivatives chosen from

the following group of compoundsS sodium dichloroEsE triazinetrione also


13/41

called sodium dichloroisocyanurate, available from (onsanto "o. under the tradename '"!R0$,

potassium dichloroEsEtriazinetrione available from

(onsanto "o. under the tradename '"!6C$, the hydrate of sodium dichloroEsEtriazinetrione available

from (onsanto "o. under the tradename '"!6R$, dichloroisocyanuric acid, trichloroEsEtriazinetrionealso called trichloroisocyanuric acid, available from (onsanto under the tradename '"!C0 -!/+$,

mixtures thereof such as monotrichloro$Etetramonopotassium dichloro$ MEpentaEsE triazinetrione and

monotrichloro$Emonomonopotassium dichloro$ MEdiEsEtriazinetrione. These compounds are disclosed,

for example, in /.+. -atents @,0@6,06R @,0@6,06D @,560,5@2 @,26R,5CC @,2CA,DCD and @,6RA,5AR.

The bromide ion donor according to the present invention may be any compound capable of providing

a sufficient amount of bromide ion in a>ueous solution including, but not limited to, li>uid bromine,

bromine chloride, al;ali metal bromides, al;aline earth metal bromides, # AEammonium bromide where

# is an al;yl or aryl group, bromamines, Ebrominated organic compounds, such as Ebrominated

hydantoins, Ebrominated sulfonamides, E brominated oxazolidinones, Ebrominated

imidazolidinones,AEbrominated imides such as Ebromosuccinimide or E brominated isocyanurates

which can release hypobromite species or salts of trihalide or mixed trihalide ions such as %r?E or

"l%rE as described in /.+. -atent @,562,0D@.

The hypochlorite donor compound and the bromide ion donor compound may be added either

separately or as a single composition. or some combinations, the two components must be added

separately, for example, chlorine gas and sodiumbromide. In many cases, however, it is advantageous

to premix the two components and add the compositions to the recirculating water system. This

reduces the number of materials to be handled and thus the number of controls re>uired. Thus, it ispossible to introduce the biocide of the present invention into the recirculating water system by any of

the following meansS an erosion feeder, a floater, porous bags, perforated buc;ets or by hand dosing.

' preferred product is a solid dry mixture of a chlorinated isocyanuric acid derivative and a bromide ion

donor, most preferably compacted in the form of a tablet, stic; or puc;. One or more compacting aids

such as boric acid, sodium stearate, potassium stearate, aluminum hydroxide or monoglycerol

stearate may optionally be used. To eliminate any possible interaction between the two components of

the mixture it is necessary to eliminate any free water, as taught in /.+. -atent 2,B56,@55. If free water

is present, the two components may react to form bromine gas, which can corrode metallic containers

or pose a health hazard to persons handling the material. In addition to optional compacting aids, the

biocide of the present invention may also optionally include one or more scale inhibitor compounds

such as polymaleic acid, polyacrylic acid, a phosphonate, a polyphosphate, or mixtures thereof.

1hen the product used is a mixture of a solid hypochlorite donor and a bromide ion donor, the

appropriate composition depends on the operating characteristics of the individual recirculating water

system. Therefore a range of compositions is re>uired since there are a number of differences

between systems. These differences include variation in the >uality of the water used for ma;eup,

variation in local air >uality, variation in the blowdown or turnover rate, and other system variables. or

a composition of trichloroisocyanuric acid and7 sodium bromide, the weight percent of sodium bromide

in the composition re>uired to provide the optimum "onversion #atio in the recirculating water typically


14/41

ranges from about @Q a%r to about 56Q a%r, depending on how the recirculating water system is

operated.

To maintain the "onversion #atio in solution at the desired optimum, it is necessary to control both the

sum of the concentrations of the hypohalite species *O"5, 0"5 , *O%r, and O%r

7

$ and the sum of theconcentrations of all bromine containing species *O%r, O%r7, and %r7$ .

"ontrol of the free halogen concentration is straightforward and is normally achieved for most

systems, either with automated analyzer:control e>uipment or manually with the use of analytical test

;its. Test ;its and analytical control e>uipment determine free halogen concentrations by measuring

the oxidizing potential of the species dissolved in the water. *owever, these devices are incapable of

distinguishing whether the oxidizing potential was due to hypochlorite or hypobromite species.

"onse>uently, the free halogen concentrations measured in the recirculating water systems are the

sum of the free chlorine and the free bromine, and will usually be expressed in terms of free chlorine,

since chlorine test ;its are more widely used. The free halogen concentrations may also be expressed

in terms of free bromine byS 5$ multiplying the free chlorine reading by 2.26, which is the ratio of the

molecular weights of molecular bromine to molecular chlorine 5R0:D5 2.26$ or 2$ using a bromine

test ;it. *owever, when the "onversion #atio in the recirculating water is one or greater, all of the free

halogen species will be present as free bromine species, even though the free bromine may be

expressed in terms of free chlorine.

Initially, it was believed that bromide ion would be a conserved specie in recirculating water systems,

that is, that blowdown or turnover would be the only significant pathway for bromide ion loss.

%lowdown or turnover loss, %r!%&$, may be calculated using the following e>uation, assumingconstant bromide ion concentrationS %r! %&$ Y. x "? x @ . DC C $

P aZ5000 whereS %r!%&$ V bromide ion loss due to blowdown, gm:day

Y, blowdown or turnover rate, gal:day

"? total concentration of all bromine species, mg:liter

@.DC conversion factor, gallons to liters 5000 conversion factor, grams to milligrams

)xampleS a system contains 5.0 mg %r:liter distributed between bromide ion and hypobromite species,

and has a blowdown rate of 5000 gal:day. The calculated bromide ion loss due to blowdown would

then be @.DC gm %r:day.

(easurement of the bromide ion concentration during initial experiments has unexpectedly revealed

the existence of other significant pathways of bromide ion loss. urther investigation has now

demonstrated that in order to maintain an optimum "onversion #atio, it is necessary to compensate

for bromide ion losses by three additional pathwaysS 5$ volatilization of hypobromous acid, 2$

volatilization of bromamines and @$ formation of organobromine compounds. !oss of bromide ion by

the volatilization of hypobromous acid occurs as a result of the reaction described in e>uation Ra$.


15/41

%romide ion losses via volatilization of bromamines occurs as a conse>uence of the reaction between

hypobromous acid and nitrogenous contaminants expressed in terms of ammonia$. *O%r H *@[H

%r*2H *=O 50$

Organobromine compound formation occurs due to the reaction of hypobromous acid with organicmatter in the water to form compounds with carbonEbromine bonds, for exampleS

*O%r H #E"*@[< #E"*=%r H *=O 55$

The organobromine compounds include the trihalomethanes or other brominated al;anes, brominated

carboxylic acids, and the li;e. The carbonEbromine bonds are very stable and not readily hydrolyzed.

*ence, the bromine specie is no longer available as bromide ion for regeneration to hypobromous acid

by hypochlorous acid. Therefore, the bromide ion has been effectively removed from this chemical

recycle loop.

It is necessary to establish the magnitude of the bromide ion losses by these pathways in order to

determine the appropriate proportions of bromide ion donor and hypochlorite donor to feed to the

recirculating water system. This can be accomplished by two methodsS 5$ analytical determination of

the decrease in bromide ion concentration 7the bromide ion analytical method7$ and 2$ calculation of

losses by the. different pathways.

The determination of the appropriate amounts of bromide ion donor and hypochlorite donor can be

achieved by the bromide ion analytical method as outlined in the followingS

5. Ta;e samples of the recirculating water at regular intervals and note the sample times. 2. &etermine

the bromide ion concentration of the water samples with '+T( &E52AREB2a, (ethod & E Ion +elective

)lectrode or %romide. ote, in this case, the hypohalite species *O%r, O%r7, *O"5, O"l7$ must be

converted to halide species "l7and %r7$ prior to the determination of bromide ion. This is achieved by

adding sodium sulfite to the solutions in amounts of 5.26 times the stoichiometric amount re>uired to

satisfy the following e>uationS

O9 H a2+0@\


16/41

7%r

whereS %r& amount of bromide ion donor re>uired to compensate for losses and maintain the

bromide ion concentration at the desired level, gm:day (? & mole weight of bromide ion donor, gm

(] mole weight of bromide ion, gm

T%r! total daily bromide ion losses, gm:day

6. &etermine the daily chlorine demand, "&, of the system.

R. &etermine the amount of hypochlorite donor compound re>uired to satisfy the daily chlorine

demand with the following e>uationS

*"& "&? x 500Q 5A$ 'v" whereS *"& amount of hypochlorite donor compound re>uired tosatisfy the chlorine demand, gm:day

"& chlorine demand of the system, gm "l2:day

'v" available chlorine content of chlorine donor wt Q$

D. or hypochlorite donor:bromide ion donor combinations where it is more practical to feed the two

donors separately, the results of steps A and R indicate what the feed rates must be for the

corresponding donors in order to satisfy the chlorine demand and bromide ion donor re>uirements and

to ma;e the combinations perform as bromine biocides.

B. or a hypochlorite donor:bromide ion donor combination that will be contained in a single

composition or product, a composition is determined by the following calculationsS

a. *ypochlorite &onor:%romide Ion &onor "omposition #e>uirements

%" *"& H %r& 56$

whereS %" amount of hypochlorite donor:bromide ion donor composition re>uired to satisfy the

chlorine demand and bromide ion re>uirements simultaneously, gm:day

b. *ypochlorite &onor:%romide Ion &onor "omposition.

5R$

Q hypochlorite donor *"& x 500Q %"

5D$

Q bromide ion donor %r& x 500Q

%"


17/41

'lthough it is an alternative to calculating the appropriate amounts of bromide ion donor

and hypochlorite donor to feed to the system, the bromide ion analytical approach is generally beyond

the sophistication of most cooling tower, swimming pool and spa operations or would re>uire a

considerable expense for added instrumentation.

The present invention obviates the need for this costly instrumentation, since the appropriate amounts

of hypochlorite donor and bromide ion donor may also be established by the second method, that is,

by calculating bromide ion losses. Investigations relating to the present invention demonstrate that the

bromide ion can be lost by pathways other than blowdown. 't the optimum "onversion #atio, the

losses incurred by these pathways can be several times larger than the blowdown loss, ma;ing it

virtually impossible to maintain the desired "onversion #atio without ;nowledge of these pathways.

The magnitudes of the losses by the various pathways are totally surprising. 't "onversion #atios

much higher than optimum, the percentage of the total bromide ion lost by these pathways is much

lower, because the ionic bromide form is not volatile. In such cases, the volatilization losses are not

readily apparent. Thus, since prior art use of bromideEbased biocides was not at the optimum

"onversion #atio, the loss of bromide ion by these pathways was not recognized. %ecause bromide

ion was usually present in excess, the prior art did not perceive the importance of these additional

bromide ion loss pathways.

The amount of bromide ion lost by flashoff of *O%r, %r!!$, may be calculated using either e>uation

5B$ or 5C$.

f x *. 7 7%r @.DC %r!!$ x # x "wn? x F x x 5B$ !:1(a(*0%r5000 or

7w 7%r 2B.@5R

%r!!$ f*;Ya&a"*0%rx x x x 5AA0 5C$

(a7*O%r 5000

whereS %r!!$ amount of bromide ion lost by flashoff of hypobromous acid, gm %r:day

# the recirculation rate of the recirculating water system, gal:day f flashoff e>uilibrium coefficient

for the recirculating water system. ote, f has a value between 0 and 5.$

*. *enryXs !aw "onstant for hypobromous acid at the p* and temperature of the recirculating water

system

Y the flow rate of air through the 50 tower, ft @:min.

& density of air, gm:!

!:1Y ratio of the mass flow rate of the 56 recirculating water to the mass flow rate of air through the

system


18/41

(g0? mole weight of hypobromous acid, gm

20 "*O%r thLconcentration Pf hypobromite species as hypobromous acid, mg *O%r:!

(w mole weight of water, gm

26 ( "! mole weight of air, gm

V

(? mole weight of bromide ion, gm

@.DC conversion factor, gallons to liters @0

5000 conversion factor, grams to milligrams 2B.@5R conversion factor, cubic feet to liters

5AA0 conversion factor, days to minutes

It is important to point out that the value of " ^_&the concentration of hypobromite species, is not the

same as "n], the sum of concentrations of all bromineE containing species, since some of the bromine

species present can be in the form of bromide ion.

*enryXs !aw constant is defined by the following e>uationS

" solute gas$ 2d$

* F " ; solute li>uid

whereS *. *enryXs !aw "onstant cs?,o`lNu.,t


19/41

's an example, a cooling tower has .:1E, 5.@, f 0.6, # A00,000 gallons:day, and

the tower operates at p* B.0 and @0L". or the conditions in this particular example, *enryXs !aw

constant is 0.26. The concentration of free halogen is 0.6 mg:! 0.6 ppm, free chlorine basis$. The

bromide ion concentration is maintained at 0.B mg:! 0.B ppm$ to give a "onversion #atio of 5.06,

slightly greater than the optimum value of 5. Thus, all of the free halogen species are essentially freebromine species *O%r and O%r7$. 's a result, the free bromine concentration in terms of

hypobromous acid is 0.RB6 mg:!< "*0%r 'v" x (*0%r:(cl 0.6 x CR.C:D5 0.RB6M. /nder these

conditions, tne flashoff loss of bromide ion via the volatilization of hypobromous acid is 65.5 grams of

bromide ion per day. This loss is considerably larger than that due to blowdown cf. blowdown loss

calculation above$, demonstrating that volatilization of hypobromous acid can be a ma=or factor

contributing to the loss of bromide ion from recirculating water systems.

The *enryXs !aw constant for hypobromous acid used in the above example was determined as

follows, using a pilot scalecooling tower since there is no literature data for hypobromous acid or any

of the bromamines. The pilot cooling tower was a counterflow type with a capacity of B0 liters of water,

which was circulated through the tower at 5.2 gal:min. The air flow rate was 2B00 !:min. 'n electrical

heater, placed in the recirculation line, provided a constant heat source. In each experiment, the

pilot tower was filled with chlorineEdemandEfree water and an appropriate amount of biocide was

added to give A.0 mg:! as chlorine$. &uring the test, the biocide concentration was continuously

monitored using a *ach "!5D chlorine analyzer. The water was initially recirculated with no air flow for

@0 minutes to establish a baseline free halogen concentration. The air flow was then started and the

free halogen concentration was monitored for four hours. The drop in the halogen concentration during

this period, which is due to volatilization of any volatile species, can be used to calculate the *enryXs

!aw constant using the following e>uationS

log " E E log "5. $ 2.@0@ 4w &w (

*; x

whereS *. *enryXs !aw constant at temperature and p* of the experiment

4w volume of recirculatingawater, liters

& density of water,E gm:ml

& density of air, gm:ral

( Lmole weight of water, gm

(cl mole weight of air, gm

Ycl volumetric air flow, !:min


20/41

"E final halogen concentration, mg:! ". initial halogen concentration, mg:!

t length of time of experiment, min

This procedure assumes that the hypobromous acid has reached e>uilibrium between the gas and

li>uid phases. 1ith this method, *enryXs !aw constants were determined for hypobromous acid as a

function of p*, temperature, and the concentration of additional chemical species.

's stated previously, the presence of ammonia in the recirculating water has also been found to

increase the loss of bromide ion. This is due to the formation of various bromamine compounds,

especially monobromamine, which is more volatile than hypobromous acid. The effect of ammonia on

the volatility of hypobromous acid is reflected in an increase in the *enryXs !aw constant. This change

in the *enryXs !aw constant is dependent on the ratio of ammonia to free bromine, the p*, and the

temperature. There are no literature values for the *enryXs !aw constants for bromamines. The results

of our measurements indicate the *enryXs !aw constant for bromamines is considerably larger than

the *enryXs !aw constant for hypobromous acid under the same conditions. The simple bromamines

are, therefore, very volatile and do not build up to significant levels because they are flashed off very

rapidly.

/nder steady state conditions, the loss of the simple bromamines by flashoff will be approximately

e>ual to the rate of formation of monobromamine. The bromamine formation rate is determined by the

rate of introduction of ammonia into the recirculating water. In most cases, the ma=or source of

ammonia is the ma;eup water. Thus, the flashoff loss due to formation of bromamines, %r!%'$, can

simply be estimated by the following e>uationS

%r!%'$ "

whereS %r!%'$ amount of bromide ion lost by flashoff of bromamines, gm:day

"==g concentration of ammonia in ma;eup water, mg:!

Y ma;eup water rate, gal:day

`%i mole weight of bromide ion, gm

( mole weight of ammonia, gm

@.DC conversion factor, gallons to liters

5000 conversion factor, grams to milligrams

ote, e>uation 25$ applies only to relatively small ammonia concentrations.


21/41

'nother significant pathway for bromide ion loss is the formation of organobromine compounds as a

result of the reaction of hypobromous acid with organic molecules dissolved or suspended in the

water. "arbonEbromine covalent bonds are usually stable to hydrolysis so that the bromine is not

released bac; into the water and is not available for regeneration to hypobromite species. The amount

of bromide ion loss can vary widely depending on the organic content of the water, which can be>uantified as TO". TO", or total organic carbon in mg:!$, measures the total amount of organic

material dissolved or suspended in the water, without distinguishing the chemical form. +everal

commercial analyzers are available which perform this analysis. !ab experiments with both tap water

and untreated surface water have shown that about 0.2 mg:! of bromide ion is combined as

organobromine compounds for every mg:! of TO" introduced into the water. This number varies

somewhat depending on the individual water source, but 0.2 is a reasonable estimate for most cases.

The amount of bromide ion loss caused by the formation of organobromine compounds, %r!O%r$ can

be calculated with the following e>uation, which accounts for the total organic carbon introduced with

the ma;eup waterS

%r!O%r$ Y]m x 0.2 x TO" x @.DC 22$

5000

whereS %r!O%r$ amount of bromide ion lost due to the formation of organobromine compounds,

gm:day

Y ma;eup water rate, gal:day

TO" E total organic content of ma;eup water, mg:!

0.2 amount of bromide ion lost per mg:! of TO" in recirculating water, mg:! @.DC conversion factor,

gallons to liters

5000 conversion factor, grams to milligrams

ote, e>uation 22$ applies only to relatively small TO" concentrations. This calculation does not

account for any

TO" added from sources other than ma;eup, for instance, organic or biological contamination

absorbed from the air blown through the tower or contamination from process lea;s. If such

contamination is severe, the additional loss of bromide ion by reaction with these sources of TO"

should also be accounted for.

It is necessary to >uantify the ma=or pathways of bromide ion loss, blowdown, flashoff, and

organobromine formation in order to determine the appropriate proportions of bromide ion donor

and hypochlorite donor to feed to the recirculating water system. Once each of the bromide ion

pathway losses are >uantified, the optimum proportions of bromide ion donor andhypochlorite donor to

be fed to the system may be calculated according to the following stepsS


22/41

5$ &efine the desiredE free halogen concentration available chlorine basis$, 'v", and the desired

"onversion #atio, "#. "# may range from about 0.2 to about 20.0, more preferably from about 0.2 to

about 50.0, and most preferably from about 0.6 to about A.0. If excess bromide ion is desired "#

should be greater than 5.0 if not, then "# can be less than 5.0.

2$ "onvert the desired free halogen concentration to the concentration of hypobromous acid, "E

gn%rX b multiplying the free chlorine concentration, 'v", by 5.@D x "# if "# is less than 5.0 or by

5.@D if "# is greater than 5.0. The factor 5.@D is e>ual to CR.C5R:D0.C0R molecular weight of

*O%r:molecular weight of chlorine$.

@$ "alculate the desired total concentration of all bromine containing species, "E , in terms of bromide

ion, using the following e>uationS

"&, 'v" x "# x (?%rE+!

A$ "alculate the daily bromide ion loss caused by blowdown, %r!%&$, with e>uation C$.

6$ "alculate the daily bromide ion loss incurred by the flashoff of hypobromous acid, %r!!$, using

either e>uation 5B$ or 5C$.

R$ "alculate the daily bromide ion loss caused by bromamine flashoff, %r!%'$, with e>uation 25$.

D$ "alculate the daily bromide ion loss caused by the formation of organobromine compounds,

%r!O%r$, using e>uation 22$.

B$ "alculate the total daily bromide ion loss, T%r!, by combining the results of the calculations in steps

A, 6, R, and D. T%r! %r!%&$ H%r!!$ H%r! %'$ H%r!O%r $ 2@ $

C$ &etermine the daily >uantity of bromide ion donor re>uired to compensate for bromide ion losses

with e>uation 5@$.

50$ &etermine the amount of hypochlorite donor re>uired to satisfy the daily chlorine demand with

e>uation 5A$.

55$ or hypochlorite donor:bromide ion donor combinations where it is more practical to feed the two

donors separately, the results of steps C and 50 indicate what the feed rates must be for the

corresponding donors in order to satisfy the chlorine demand and bromide donor re>uirements

simultaneously and ma;e the combination perform as a bromine biocide.

52$ or products containing both the hypochlorite donor and bromide ion donor as a single

composition or mixture, determine the appropriate composition with e>uations 56$, 5R$ and 5D$.


23/41

The effectiveness of the hypochlorite donor:bromide ion donor biocides and the bromine volatilization

suppressants disclosed herein is demonstrated in the following examples, including ;illing efficiency

experiments, cooling tower and spa tests, and calculations in which compositions representative of the

present invention, such as '"!R0:a%r and '"!C0 -!/+:a%r, are compared with chlorine '"!R0$

and competitive bromine %"&(*$ biocides. )xample 5 E )ffectiveness of *ypochlorite&onor:%romideIon &onor "ompositions In "ooling Towers

' small crossflow, induced draft cooling tower, used to cool a 260 ton air conditioning system, was

used to test the relative effectiveness of the current invention versus chlorine and %"&(* biocides

over a period of five months. The p* of the towerwater was controlled at B.6 and the free halogen

concentration was controlled at 0.6 mg:! available chlorine base$ with an automated chlorine

analyzer:controller. +cale and corrosion inhibitors were also added as part of the normal operation of

thecooling tower. The effectiveness of each biocide was =udged on the ability of the biocide to control

the biofouling microorganism population as measured by a standard plate count method.

(icroorganism populations were reported as colony forming units per milliliter "/:ml$. +amples for

the determination of microorganism populations and bromide ion concentration were ta;en from the

same location in the cooling tower basin away from the point of chemical addition. Two to three

samples were ta;en per day. Immediately after sampling, any hypohalite species were reduced to

halide species withsodium thiosulfate. The bromide ion concentration was measured by ion

chromatography. The results of the test are shown below in Table 5S

T'%!) 5

#esults of "ooling Tower %iofouling "ontrol Tests "omparing %iocidal )ffectivenessof *ypochlorite &onor:%romide Ion &onor %iocide "ompositions to "hlorine and %romine %iocides.

Total -late

%iocide %r "one "ount "onversion Tested mg:!$ "/:ml$ #atio

'"!R0 0.0 5A,200 0.0

'"!R0:a%r 0.5A 6,R00 0.26

'"!C0 -!/+:a%r 5.B A,200 @.2

%"&(* [email protected] 2A,R00 A5.5

'"!R0:a%r 5B. 5,R00 @5.C

'"!C0 -!/+:a%r R.6 5,200 55.6

otesS


24/41

5. #esults are the average values observed during the test periods. 2. Test "onditionsS p* B.6 free

halogen 0.6 mg:!, available chlorine basis.

In these tests, '"!R0 sodium dichloroisocyanurate$ was used to demonstrate the biocidal

effectiveness of chlorine biocides under these conditions. "ombinations of sodium bromide with'"!R0 and sodium bromide with '"!C0 -!/+ trichloroisocyanurate$ were employed to illustrate the

effect of the "onversion #atio on the biocidal effectiveness of thehypochlorite donor:bromide ion donor

compositions, which are representative of the present invention, and their ability to perform as bromine

biocides. %"&(* was also included to compare the effectiveness of this bromine biocide to the ones

representative of the present invention. The results of these tests show that

the hypochlorite donor:bromide ion donor compositions of a%r:'"!R0 and '"!C0 -!/+:a%r, were

not only superior to the chlorine biocide, '"!R0, but were also superior to the bromine biocide,

%"&(*, in controlling the population of the biofouling microorganisms. The most effective

a%r:'"!R0 and a%r:'"!C0 -!/+ biocide compositions were those which maintained the

"onversion #atio in the recirculating water above 5.

The biocide compositions that were less effective were those which produced "onversion #atios of

less than one. *owever, all of the a%r:'"! compositions were more effective than the chlorine

'"!R0$ and %"&(* biocides, as evidenced by the fact that they controlled the biofouling

microorganism population at or below R000 "/:ml, whereas the chlorine and %"&(* biocides were

not capable of reducing the biofouling populations below 5A,000 and 2A,000 "/:ml, respectively, at

the same free halogen concentration.

)xample 2 E )ffectiveness of *ypochlorite &onor:%romide Ion &onor %iocide "ompositions in%iofouling "ontrol )xperiments.

The ;illing efficiencies of the biocides evaluated in )xample 5 were also determined in laboratory

experiments designed to simulate cooling tower conditions. In these experiments, a culture of

microorganisms from the cooling water in )xample 5 were cultured in a wellEstirred vessel by metering

nutrient solution into the solution containing the culture. The vessel contents were maintained at @DP"

and p* of B.0. )ach experiment consisted of shoc;ing the microorganisms with the biociie to be

tested. utrient solution was also fed continuously to the vessel to encourage growth of the

microorganisms and biocide solution was fed to the vessel to control the free halogen concentration at

0.6 mg:! available chlorine basis$ and the microorganism population. The microorganism population

was determined periodically by an *(%EII apparatus 34( )ngineering$ until the microorganism

population had ceased to decline and remained constant for several hours. This usually occurred in

about four hours after the start of the experiment. 't this point, the microorganism growth rate and the

microorganism death rate due to the biocidal activity of the biocide were considered to be in dynamic

e>uilibrium, or at steady state. The effectiveness of biocide was then =udged on the basis of ;illing

efficiency as defined by the following expression.

3) f-5E -5 x 500Q 2A$

-i


25/41

whereS 3) ;illing efficiency of the biocide, Q

-. microorganism population at the start of the experiment, "/:ml

-E [ microorganism population at steady state conditions, "/:ml

The results of the biocide ;illing efficiency experiments are summarized in Table 2. T'%!) D

#esults of %iocide 3illing )fficiency )xperiments

%iocide a%r:'"! R0 -.

Tested t. #atio "# "/:ml$ "/:ml$ 3)

%"&(* 2,5A0,000 5,2R0,000 A5

'"!R0 0.0 0.0 5,6R0,000 BB0,000 AA

'"!R0:a%r 0.5 0.5@ 5,CR0,000 B@0,000 6B

'"!R0:a%r 0.5C 0.22 5,A50,000 @60,000 D6

'"!R0:a%r 5.0 5.20 5,AR0,000 5R6,000 BC

"onditionsS p* B.6, temperature @DP ", free halogen 0.6 mg:! available chlorine basis$.

The results in Table 2 show that the a%r:'"!R0 compositions hypobromous acid generating

compositions$ have superior biocidal activity relative to the chlorine biocide, '"!R0, and the bromine

biocide, %"&(*, under the conditions of the experiments. The results also support the validity of the

results obtained in the cooling tower tests )xample 5$. The above results also show that the best

;illing efficiency was obtained at a "onversion #atio of 5.20. This represents the condition where the

amount of a%r is sufficient to ma;Xe the bromide ion concentration in the water slightly in excess of

the stoichiometric amount re>uired to satisfy the reactions shown in e>uations Ra$ and Rb$. Thus, the

best ;illing efficiency was obtained with the composition that performed as a true bromine biocide.

*owever, the results of the experiments indicate that the ;illing efficiencies of a%r:'"!R0

compositions which yield "onversion #atios of less than 5 are still better than the chlorine '"!R0$ or

%"&(* biocides. The effect of the "onversion #atio can be understood more clearly by referring to

the graph shown in igure 5. igure 5 is a plot of the ;illing efficiency of each '"!R0:a%r composition

tested as a function of the "onversion #atio. The results show that ;illing efficiencies increase as the

"onversion #atios increase until the maximum ;illing efficiency is attained near a "onversion #atio of

5.0. 't this point, all of the free halogen species are free bromine species. igure 5 also shows that

most of the improvement in ;illing efficiency from A2Q to D6Q$ occurred between "onversion #atios

of 0.0 and 0.2. This indicates that the "onversion #atio in the recirculating water system does not

have to be controlled tightly in order for the bromine based biocide to be significantly better than

chlorine biocides at p* levels of B or higher.


26/41

)ven though the performance of the hypochlorite donor:bromide ion donor biocide will be very good at

these low ratios, it is desirable to use these biocides at "onversion #atios of 5.0 or more, because the

biocides will control the microorganisms more effectively, thereby reducing biocide usage, and

because the formation of chloramines will be minimized. igure 5 shows at what levels the "onversion

#atio should be maintained to obtain maximum biocidal activity. 7*owever, it would not be economical,in most instances, to use products with proportions of bromide ion donor and hypochlorite donor

e>uivalent to the desired "onversion #atio in the recirculating water. Therefore, it is important to

understand how to develop compositions and methods that allow hypochlorite donor:bromide ion

donor compositions with low bromide ion donor contents to maintain the desired "onversion #atio in

the recirculating water. )xample @ E &iscovery of %romide Ion !oss -henomenon

&uring tests run on the cooling tower system described in )xample 5, '"!C0 -!/+

trichloroisocyanurate$ was fed to the recirculating water system at a rate sufficient to maintain a free

halogen concentration of 0.6 mg:! 0.6 ppm, free chlorine basis$. The chlorine demand of the

recirculating water system was determined to be about 2B2 grams of available chlorine per day. +ince

'"!C0 -!/+, which has an available chlorine content of

C0.DQ, was used as the hypochlorite donor, the '"!C0 -!/+ re>uirement was @50.A grams:day 2B2

< 0.C0D$ x 500QM.+odium bromide was fed to the system at a rate of 2.R gm a%r:day, a rate

calculated to account for blowdown loss and maintain a bromide ion concentration of 0.6R mg:!, a

concentration sufficient to maintain a "onversion #atio of one. 'nalyses of water samples ta;en from

the system revealed, however, that the bromide ion was consistently as low as about 0.06 mg:!,

considerably below the desired bromide ion concentration of 0.6R mg:!. Therefore, the bromide ion

was lost at a rate much higher than expected.

)xample A E &emonstration of the %romide Ion !oss -henomenon

Tests were conducted in the following manner. The blowdown value for the recirculating water system

of the cooling towercited in )xample 5 was closed to prevent the loss of water by this pathway. The

recirculating water system was then dosed with enough sodium bromide to obtain a concentration of

about 0.6 mg:! 0.6 ppm$ of bromide ion. The free halogen was maintained at 0.6 mg:! 0.6 ppm, free

chlorine basis$. The water was then recirculated for about one hour to obtain a uniform concentration

of bromide ion throughout the system. 1ater samples were then ta;en periodically over a 2A hour

period and analyzed for bromide ion. The results of the analyses in Table @ show that about D0Q of the

bromide ions were lost during this 2A hour period. !oss rates for the first few hours were actually even

higher. or instance, the loss rate for the first B.6 hours is over RQ per hour or 562Q per day.

T'%!) @

%romide !oss &ata for ero %lowdcswn

1ater Time %romide Ion %romide Ion !ithium "one +ample hr$ "one ppm$ !osses Q$ ppm$

5 0.0 0.60 0.0 0.A2 2 B.6 0.20 6A.0 0.A0 @ 2A.0 0.5@ RC.0 0.A5


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To prove that the bromide ion losses were not due to lea;s in the recirculating water system, the water

was also spi;ed with lithium chloride at the start of this test. !ithium is not commonly found in water,

can be easily analyzed for, and is not volatilized from the water system. The water samples ta;en for

bromide analyses were also analyzed for lithium. The results shown in Table @ demonstrate that

lithium was not lost from the system during the test, thereby demonstrating that the bromide ion losseswere not due to lea;s, but, instead were due to other phenomena.

This example also demonstrates that the bromide ion losses can be significant in recirculating water

systems, a fact not recognized by the prior art. In addition, it shows that many of the compositions

described in the prior art for mixtures ofhypochlorite donors and bromide ion donors actually

performed as chlorine biocides instead of performing as bromine biocides li;e the claimed

compositions. urthermore, the results clearly indicate that without the ;nowledge of these losses, it

would be impossible to ma;e hypochlorite donor:bromide ion donor compositions which would perform

efficiently and economically as bromine biocides.

)xample 6 E "ompensation for %romide Ion !oss

This example demonstrates that with ;nowledge of the existence of the bromide ion loss phenomena,

bromide ion losses can be ade>uately compensated for to produce the desired results F performance

of hypochlorite donor:bromide ion donor composition as bromine biocides. 's shown in )xample @,

prior to the discovery of the bromide ion loss phenomena, thesodium bromide was fed to

the cooling water system at the rate of 2.R grams:day, an


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perform as a bromine biocide. Thehypochlorite donor:bromine ion donor composition re>uirement,

%", for this particular combination was @2D.A grams:day @50.A H 5D.0$. Therefore, the appropriate

composition was CA.BQ '"!C0 -!/+ @50.A T @2D.A$ x 500Q$M and 6.2Q 5D.0 < @2D.A$ x

500QM sodium bromide.

If it is desired to add these two donors as a single product, the '"!C0 -!/+ and sodium bromide may

be blended together, compacted into tablets, placed in an appropriate erosion feeder, and used to

satisfy the chlorine demand and bromide ion re>uirements.of the system. The composition would

perform in the above described system as a bromine biocide. If it is desired to add the '"!C0 -!/+

and sodium bromide separately, the feed rates would be @50.A and 5D.0 gm:day respectively. )xa ple

D E %romide Ion !oss and "omposition "alculations for "ooling Towers.

'n example of the procedure outlined above for calculating the total bromide ion loss and

the hypochlorite donor:bromide ion donor composition re>uired to maintain the optimum "onversion

#ation is given below. Three cooling towers, having the characteristics given in Table A', will be used.

The three towers are various sizes and have somewhat different operating characteristics. ' ma=or

difference between the three towers is the >uality of the ma;eup water, which has a significant impact

on the amount of bromide ion loss.

T'#K.% __ "haracteristics of (odel "ooling Towers "haracteristic Tower ' Tower % Tower "

%lowdown #ate, Y gal:day$ 5,000 2 ,000 !2 ,000 #ecirculation #ate, # gal:day$ 200,000 R00 ,000

5.6SxlOD

(a;eup #ate, Y gal:day$ tn 6,000 50 ,000 R@ ,000

&esired ree *alogen "one, 'v" mg:!, as chlorine$ 0.@ 0.2 0.5

&esired "onversion #atio, "# 5.5 0.C 5.2

lashoff )>uilibrium "oefficient, f 0.6 0.6 0.6

TowerETop Temperature P"$ @0 @0 @0 p* B.0 B.0 B.0

'mmonia."oncentration in (a;eup 1ater mg * :!$ 0.0 0.5 0.5 TO" "oncentration in (a;eup 1ater

mg TO":!$ 2.0 5.0 5.0

%iocide /sage A00 D00 @,@00

grams '"!C0 -!/+:day$

rom the characteristics in Table A', the following parameters can be found for the three example

towers. +odium bromide mol.wt. 502.C0 gm:mole$ is used as the bromide ion donor and '"!C0


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-!/+ is the hypochlorite donor. T'#K.S W# "alculated -arameters of (odel "ooling Towers

"alculated -arameter Tower ' Tower % Tower "

*O%r "oncentration, " mg:!$ 0 .A50 0 .2AR 0 .5@D Total %r "one, " mg:!$ 0 . @D2 0 . 20@ 0 . 5@6

*enryXs !aw "onstant, *. 0 .260 ; 0.260 0 .260

%lowdown !oss, %r!%&$ 5 . A5 5. 6A R . 56 grams %r:day

*O%r lashoff !oss, %r!!$, 56.@0 2D.6A 5R6.D6 grams %r:day %romamine lashoff !oss, %r!%'$,

grams %r:day 0.0 5D.DB 552.05

Organobromine "ompound

ormation !oss, %r!O%r$, D.6B D.6B AD.D6 grams %r:day

Total %romide Ion !oss, T%r!, 2A.2C 6A.AA @@5.RD grams %r:day Total a%r eeded, grams:day @5.2B

D0.50 A2D.0C

Q a%r eeded in '"!C0 -!/+: D.26 C.50 55.AR a%r "omposition

The above calculations show .that the flashoff losses can be much larger than the blowdown loss,

especially when ammonia is present. iven the values above, the appropriate composition of a

trichloroisocyanuric acid:a%r mixture is calculated to be D.26Q a%r for Tower ', C.50Q a%r

for Tower % and 55.ARQ a%r for Tower ". If the flashoff losses and the loss due to formation of

organobromine species are not accounted for, the appropriate composition would mista;enly be

calculated as only 0.@6Q a%r for Tower ', 0.22Q a%r for Tower % and 0.5CQ for Tower ". If

chlorine gas is being used as thehypochlorite donor, then the second to last line in Table A% gives the

amount of sodium bromide that must be added separately to maintain the optimum "onversion #atio

in the recirculating water.

)xample B E &etermination of an 'ppropriate *ypochlorite &onor:%romide Ion &onor %iocide

"omposition.

This example demonstrates why understanding of bromide ion loss phenomena is critical to

development of commercial biocides containing both hypochlorite donors and bromide ion donors.

In this example, a cooling tower system with a recirculating water capacity of 500,000 gallons is

treated with '"!C0 -!/+ to maintain a free available chlorine concentration of 0.6 mg:! 0.6 ppm$ in

the water. The daily available chlorine demand is satisfied with 55.0 pounds of '"!C0 -!/+. +ince the

available chlorine content of '"!C0 -!/+ is C0.DQ, 55.0 pounds of '"!C0 -!/+ tablets per day are

e>uivalent to 50.0 pounds of available chlorine 55.0 x 0.C0D 50.0$.

The '"!C0 -!/+ chlorine7 biocide can be made to perform as a bromine biocide by adding

sufficient sodium bromide to the water to maintain a "onversion #atio of at least 5.0. This re>uires


30/41

maintenance of a bromide ion concentration in the coolingwater sufficient to satisfy the stoichiometric

re>uirements of e>uations Ra$ and

Rb$. *ence, the bromide ion concentration must be 0.6R ppm 0.6 ppm of "l 2x (%r:(cl 0.6 x

DC.C0C:D0.C0R 0.6R$. +ince the recirculating water in the example cooling tower weighs B@A,000pounds 500,000 gallons x B.@A pounds:gallon$, it must contain at least 0.AD pounds of bromide ion

0.6R x 50 x B@A,000 pounds 0.AD pounds$. This re>uires that the water contain a minimum of 0.R06

pound of sodium bromide 0.AD pound x f , ? :(? 0.AD x 502.C0:DC.C0C 0.R06$.

To ma;e an '"!C0 -!/+:a%r composition perform as a bromine biocide, the composition must

contain sufficient sodiumbromide to build the bromide ion concentration up to and maintain it at the

level re>uired to satisfy the optimum "onversion #atio. This can be achieved by ;nowing the bromide

ion loss rates for the recirculating water system. If the '"!C0 -!/+:a%r product contains the exact

amount of sodium bromide to compensate for the losses and maintain the "onversion #atio at exactly

one, then the sodium bromide concentration will automatically change with time until the desired

concentration is reached. This occurs as followsS

1hen feeding a a%r:'"! composition to a tower which initially contains no bromide ion, the bromide

ion concentration will increase. The bromide ion loss rate depends on the concentration, so that the

loss rate at low concentrations is very small, but slowly increases as the concentration of bromide ion

increases. Thus, the initial bromide ion addition rate is larger than the bromide ion loss rate and the

bromide ion concentration increases.

This continues until the bromide ion loss rate matches the rate at which bromide ion is added to thesystem. 't this point, a dynamic e>uilibrium condition, commonly referred to as a steady state, has

been reached. /nder these conditions, the bromide ion loss rate is e>ual to the rate at which bromide

ion is being added and no further change in the bromide ion content occurs. If

the hypochlorite donor:bromide ion donor composition contained the exact amount of bromide ion to

compensate for bromide ion losses at the desired steady state, that is the steady state which is

eventually attained. On the other hand, if the tower initially contains an excess of a%r over the

amount re>uired for a "onversion #atio of 5.0 and a a%r:'"! mixture is used that corresponds to the

desired steady state concentration, the bromide ion loss rate will be higher than the bromide addition

rate. In this case, the bromide ion concentration will decrease until the loss rate and addition rate are

e>ual and a steady state at "onversion #atio 5.0 is reached. 'gain, this steady state is determined

by the bromide ion addition rate, and, if the correct composition is used, the "onversion #atio will be

one at steady state.

This concept can best be visualized by considering the following information. irst, in the preceding

)xample, 55.0 pounds of '"!C0 -!/+ are re>uired to satisfy the daily chlorine demand of

the cooling water. +econd, 0.R06 lb of sodium bromide are re>uired to maintain the desired

"onversion #atio of 5.0. It follows that the total daily re>uirements for the hypochlorite donor:bromide

ion donor composition, '"! C0 -!/+:a%r$ are 55.R06 pounds 55.0 H 0.R06$. The appropriatecomposition of the hypochlorite donor:bromide ion donor composition re>uired to maintain the desired


31/41

"onversion #atio is, therefore, CA.BQ E55.0:55.R06 x 500Q CA.BQ$ '"!C0 -!/+ and 6.2Q

0.R06:55.R06 x 500Q 6.2Q$ a%r.

To understand how this composition can build up the bromide ion concentration to the desired level, it

is necessary to consider the bromide ion addition rate and total bromide ion loss rate on an hourlybasis. 'gain, as shown above, the total weight of bromide ion, 1? , re>uired to maintain the

"onversion #atio at 5.0 was established to be 0.AD lb at steady state. or the purpose of this

)xample, it is assumed that this will be the total amount of bromide ion that is lost daily. Then the total

hourly bromide ion loss rate all pathways$, *T%r!, is simply 1? divided by 2A hours. This

corresponds to a rate of 0.05C6B lb:hr 0.AD lb i 2A hr 0.05C6B$. 1ith respect to 1? , the percent

total hourly bromide ion loss rate, -*T%r! is, as determined by e>uation 26$, A.2Q 0.05C6B:0.AD x

500Q A.2Q$.

*T%r! -*T%r! x 500Q 26$ 1%r

This percent total hourly loss rate corresponds to a percent total daily loss rate of 500Q. It is important

to remember that it is entirely possible for percent total daily loss rate to be greater than 500Q.

1ith regards to the bromide ion addition rate, it was established previously that 0.R06 lb

of sodium bromide are re>uired to satisfy the "onversion #atio conditions specified. The

hourly sodium bromide addition rate is thus 0.02625 lb:hr 0.R06 lb < 2A hr$. In terms of bromide ion,

the total hourly addition rate is 0.05C6B lb:hr 0.02625 lb a%r:hr x ( %r:(a%r 0.02625 x B0:50@

0.05C6B$.

It follows that at the end of the first hour of use of the '"!C0 -!/+:a%r composition the bromide ion

content of the water will be 0.05C6B pounds minus the amount of bromide ion losses. +ince the total

hourly loss rate is A.2Q:hr, the amount of bromide ion lost in the first hour is only 0.000B2 lb 0.0A2 x

0.05C6B$. The bromide ion content at the end of the first hour is thus 0.05BDR lb 0.05C6B E 0.000B2$.

't the end of the second hour, another 0.05C6B lb of bromide will have been added bringing the gross

amount to 0.0@B@A 0.05BDR H 0.05C6B$ lb. *owever, the bromide ion loss is slightly higher and

amounts to approximately 0.005R5 lb 0.0@B@A x 0.0A20$. The net amount of bromide ion remaining

has now increased to 0.0@RD@ lb 0.0@B@A E 0.005R5$. Thus, with each successive addition

of sodium bromide, the bromide ion concentration will continue to increase, but at the same time, the

bromide ion loss rate will increase.

)ventually, the loss rate will catch up with the addition rate and the two rates will be essentially

e>uivalent thereafter. 't this point, steady state conditions have been attained and subse>uent '"!C0

-!/+:a%r additions merely maintain the "onversion #atio at the desired level, in this case, 5.0

' further refinement of these calculations is to determine the hourly bromide ion losses by the various

pathways, since blowdown losses apply to all bromine species but losses by flashoff of hypobromous

acid and bromamines and the formation of organobromine compounds apply only to the hypobromite

species. This is achieved with e>uations 2R$ and 2D$. The percent hourly bromide ion loss rate byblowdown, -*%r!%&$, is calculated by e>uation 2R$.


32/41

-*%r!%&$ %r!%&$ 5000 "]? x 4.. x2A x Nu< 2R$

X%r w whereS -*%r!%&$ the percent of bromide ion lost by blowdown, Q:hr

%r!%&$ as defined in e>uation C$

"%r as defined in step @$ of

7calculation of losses method7

4w volume of recirculating water, ! 5000 conversion factor, grams to milligrams

2A conversion factor, days to hours

The percent hourly loss of bromide ion by the other pathways flashoff of hypobromous acid and

bromamines and formation of organobromine compounds$ is specifically proportional to the amount of

hypobromite species in the recirculating water. The percent hourly loss of hypobromite species by

these pathways, -*O%r!, is calculated with e>uation 2D$.

2D$

-*O%r! ? .T%r! E %r!.%&.5 O%l 5000 500Q

"*O%r x 4w 7%r 2A whereS -*O%r! percent of hypobromite species lost by pathways other than

blowdown, Q:hr

T%r! as defined in e>uation 2@$ %r!%&$ as defined in e>uation C$

"*O%r as defined in step 2$ of 7calculation of losses method7

X1 volume of recirculating water, !

7% O%r E mole weight of hypobromous acid, gm

(%r mole weight of bromide ion, gm 5000 conversion factor, grams to milligrams

2A conversion factor, days to hours

-*O%r! is essentially the weight of hypobromite species lost per hour divided by the weight of

hypobromite species contained in the recirculating water. 1ith e>uation 26$, the percent total hourly

bromide ion loss rate, -*T%r!, was calculated to be A.2Q:hr. These refinements account for what

fraction of bromide ion losses are due to blowdown and the other pathways. To illustrate the

refinements of the calculations, the losses due to blowdown, -*%r!%&$, and the losses by other

pathways, -*O%r!, are ta;en to be 0.B@Q:hr and @.@@Q:hr, respectively, for igures 2E6. These

calculations can be used to illustrate the interrelationship between the concentration of the bromide ion


33/41

in the recirculating water and the composition of the hypochlorite donor:bromide ion donor

compositions. They were utilized to generate the graphs shown in igures 2E6 which illustrate the

effect of the biocide composition on the buildup of bromide ion with time and the ability of the

composition to attain the optimum "onversion #atio at steady state conditions. +ince these

calculations simulate the dynamics of the bromide ion content of water recirculation systems, they canbe used to determine the composition re>uired to produce the desired "onversion #atio once the

-*%r!%&$ and -*O%r! have been determined. igure R illustrates the effect of bromide ion loss rate

on the composition re>uired for the preferred range of "onversion #atios. Therefore, it illustrates, in

con=unction with the following examples, how the various compositions are able to perform as bromine

biocides.

)xample C E %uildup of %romide Ion to +teady +tate "oncentration with a 2Q a%r:CBQ '"!C0 -!/+

"omposition.

The cooling tower in )xample B is initially treated with 55.0 pounds of '"!C0 7-!/+ per day to

maintain a free chlorine concentration of 0.6 mg:!, thus the tower initially contains no bromine

containing species. The biocide is then switched to a composition of 2Q a%r and CBQ '"!C0 -!/+.

igure 2 presents the calculated bromide ion content in terms of sodiumbromide of the tower versus

the time elapsed since starting the a%r:'"!C0 -!/+ composition, given that -*O%r! @.@@Q:hour

B0Q:day$ and that -*%r!%&$ 0.B@Q:hour 20Q:day$. It shows how the total amount of bromine

containing species given as pounds of a%r$ contained in the recirculating water system builds up

with time during the initial few days of use of the 2.0Q a%r:CBQ '"!C0 -!/+ composition until a

steady state concentration is reached after about three days. 't steady state, the tower in igure 2

contains about 0.2 pounds of a%r, which is considerably below the 0.R06 pounds of a%r re>uired fora "onversion #atio of 5.0, as shown by the line labeled 7"# 5.07. In this case, the free halogen is a

mixture of hypochlorite species and hypobromite species and the ;illing efficiency is less than ideal.

)xample 50 E %uildup of %romide Ion to +teady +tate "oncentration with a CQ a%r:C5Q '"!C0

-!/+ composition.

igure @ shows the case where a a%r:trichloroisocyanuric acid '"!C0 -!/+$ composition with a

much higher percentage of a%r C.0Q$ is fed into the tower described in )xample B. 's in )xample C,

the bromide ion content of the tower builds up smoothly until a steady state is reached. In this case,

however, steady state is reached in about 20 days. The steady state a%r content is @.0 pounds and

the steady state "onversion #atio is 6.0. In this case, all of the free halogen is present as hypobromite

species and the ;illing efficiency is very high, but a considerable excess of bromide ion is present

which is wasted.

)xample 55 E %uildup of %romide Ion to +teady +tate "oncentration with the Optimum 6.2Q

a%r:CA.BQ '"!C0 -!/+ "omposition.

igure A shows the ideal case for the tower described in )xample B, where -*%r!%&$ is 0.B@Q:hour

20Q:day$ and -*O%r! is @.@@Q:hour B0Q:day$. ' "onversion #atio of 5.0 is achieved after aboutthree days and then maintained at steady state conditions by feeding a composition of 6.2Q


34/41

a%r:CA.BQ trichloroisocyanuric acid. This composition therefore performs as a bromine biocide in

this tower with very little excess bromide ion being re>uired.

)xample 52 E %uildup of %romide Ion to +teady +tate "oncentration with %"&(*

igure 6 shows the case for %"&(*, which has a bromide and available halogen content e&

biocidal methods and compositions for recirculating water systems.docx

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