the free halogen - generating biocide can be any known in the art , such as those described in u . s . pat . no . 5 , 565 , 109 , which is hereby incorporated by reference . according to one preferred embodiment , the free halogen - generating biocide is a slimicide . suitable free halogen - generating biocides include , but are not limited to , hypochliorites , hypobromites , chlorine gas , bromine , bromine chloride , halogenated cyanurates , dihalogenated hydantoins , and mixtures thereof . suitable hypochlorites include , but are not limited to , alkali metal hypochlorites ( such as sodium hypochlorite ), alkaline earth metal hypochlorites , and mixtures thereof . a bromide source may also be added to the aqueous solution . bromide compounds are significantly more stable than bromines . the bromide source can be any bromide containing material , such as sodium bromide , potassium bromide , ammonium bromide , hydrobromic acid , and the like . upon mixing , the free halogen - generating biocide oxidizes the bromide source to form a bromine ( which is also a free halogen - generating biocide ). preferred free halogen - generating biocides include , but are not limited to , sodium hypochlorite and mixtures of sodium hypochlorite and sodium bromide . the halogen stabilizer can be any known in the art , such as those described in u . s . pat . no . 5 , 565 , 109 . for example , the halogen stabilizer can be an n - hydrogen compound . suitable n - hydrogen compounds include , but are not limited to , 5 , 5 - dimethylhydantoin ( dmh ), glycouril , sulfamide , trisulfamide , p - toluene - sulfonamide , melamine , sodium triamidometaphosphate , 5 , 5 - alkylhydantoins ( such as 5 - methyl - 5 - ethyl hydantoin ( meh )), methanesulfonamide , barbituric acid , 5 - methyluracil , imidazoline , pyrrolidone , acetanilide , acetamide , n - ethylacetamide , phthalimide , benzamide , succinimide , cyanamide , urea , n - methylolurea , n - methylurea , acetylurea , biuret , methyl allophanate , methyl carbamate , phthalohydrazide , pyrrole , indole , formamide , n - methylformamide , dicyandiamide , ethyl carbamate , 1 , 3 - dimethylbiuret , methyl phenyl biuret , 4 , 4 - dimethyl - 2 - oxazolidinone , 6 - methyluracil , 2 - imidoazolidone , ethylene urea , 2 - pyrimidone , n - ethylacetamide , azetidin - 2 - one , 2 - pyrrolidone , caprolactam , phenyl sulfinimide , phenyl sulfinimidylamide , diphenyl sulfonimide , dimethyl sulfinimine , isothiazolene - 1 , 1 - dioxide , orthophosphoryl triamide , pyrophosphoryl triamide , phenyl phosphoryl - bis dimethyl amide , boric acid amide , hydantoin , pyrrole , sulfamic acid , ammonia , ammonium bromide , and mixtures thereof . preferred halogen stabilizers include , but are not limited to , 5 , 5 - dimethylhydantoin ( dmh ), 5 - methyl - 5 - ethyl hydantoin ( meh ), and mixtures thereof . the quaternary ammonium biocide can have the formula n + r 1 r 2 r 3 r 4 x − where r 1 and r 2 are independently unsubstituted or hydroxy substituted linear or branched c 1 - c 4 alkyl , —( ch 2 ch 2 o ) m ch 2 ch 2 oh , or —( ch 2 chch 3 o ) m ch 2 chch 3 oh where m is 1 to 10 ; r 3 is a substituted or unsubstituted benzyl , ethylbenzyl , methylnaphthyl , or linear or branched c 1 - c 22 alkyl ; r 4 is — r 5 ( o ) n ( c 6 h 5 ) r 6 where n is 0 or 1 ; r 5 is a substituted or unsubstituted c 1 - c 8 alkyl or c 1 - c 8 alkoxyalkyl ; r 6 is hydrogen or a substituted or unsubstituted , linear or branched c 1 - c 12 alkyl ; and x − is an anoin , such as chloride , bromide , propionate , sulfate , bicarbonate , or carbonate . according to one preferred embodiment , r 5 is preferably — ch 2 ch 2 och 2 ch 2 —. more preferably , r 4 is [ 2 -[ 2 -( 4 - diisobutylphenoxy ) ethoxy - ethyl ]. according to another preferred embodiment , r 4 is benzyl . preferred quaternary ammonium biocides include , but are not limited to , salts of benzethonium ([ 2 -[ 2 -( 4 - diisobutylphenoxy ) ethoxy ] ethyl ] dimethylbenzyl ammonium ), such as benzethonium chloride ( available as hyamine 1622 ® from lonza inc . of fair lawn , n . j . ); and salts of benzalkonium ( benzyl alkyl dimethyl ammonium ), such as benzalkonium chloride ( available as barquat ® mb - 50 and barquat ® mb - 80 from lonza inc . of fair lawn , n . j .). preferred benzalkonium salts include , but are not limited to , ( c 12 - c 18 ) alkyl benzyl dimethyl ammonium salts , such as ( c 12 - c 18 ) alkyl - benzyl dimethyl ammonium chloride . according to yet another preferred embodiment , the anion x − is carbonate : another suitable quaternary ammonium biocide has the formula r 19 r 20 r 21 r 22 n + x − , where r 19 , r 20 , r 21 , and r 22 independent are linear , branched , cyclic or any combination thereof saturated or unsaturated groups and x is an anion . the sum of the number of carbon atoms in r 19 , r 20 , r 21 , and r 22 broadly ranges from about 10 to about 50 . r 19 , r 20 , r 21 , and r 22 may be alkyl , alkenyl , alkynyl , cycloalkyl , aryl , or any combination of any of the foregoing . x may be chloride , carbonate , bicarbonate , nitrile , bromide , iodide , acetate , dehydroacetate , laurate , stearate , carboxylate , or borate . suitable carboxylate and borate anions include , but are not limited to , those disclosed in u . s . pat . no . 5 , 641 , 726 , which is hereby incorporated by reference . a preferred quaternary ammonium compound has the formula r 19 ( ch 3 ) 3 n + x —, where r 19 is a linear or branched c 10 - c 20 saturated or unsaturated group , such as alkyl , alkenyl , or alkynyl group and x is defined as above . more preferably r 19 is a linear c 16 - c 18 saturated or unsaturated group and x is chloride , carbonate , or acetate . an example of such a compound is n - octadecyl - n , n , n - trimethylammonium chloride . another preferred quaternary ammonium compound has the formula r 19 r 20 ( ch 3 ) 2 n + x —, where r 19 is a linear or branched c 6 - c 20 saturated or unsaturated group or c 6 - c 20 substituted or unsubstituted aryl group , r 20 is a linear or branched c 1 - c 20 saturated or unsaturated group or c 6 - c 20 substituted or unsubstituted aryl group , and x is defined as above . the term “ substituted ” as used herein includes , but is not limited to , substitution with any one or any combination of the following substituents : c 1 - c 4 alkyl . preferably , r 19 and r 20 independently are linear or branched c 8 - c 15 saturated or unsaturated groups . in a more preferred embodiment , r 19 and r 20 independently are linear or branched c 8 - c 12 saturated or unsaturated groups and x is chloride , carbonate , or acetate . special mention is made of didecyldimethylammonium chloride , which is available as bardac ® 2280 available from lonza inc . of fair lawn , n . j . ; didecyldimethylammonium bicarbonate ; and didecyldimethylammonium carbonate ; and n , n - di ( tetradecyl / pentadecyl )- n , n - dimethylammonium chloride , which is available as carsoquat ® 457 from lonza inc . ( carsoquat ® 457 is a mixture of n - tetradecyl - n - pentadecyl - n , n - dimethylammonium chloride , n , n - di ( tetradecyl )- n , n - dimethylammonium chloride , and n , n - di ( pentadecyl )- n , n - dimethylammonium chloride ). another suitable quaternary ammonium compound has the formula r 19 r 20 ( ch 3 ) 2 n + x − , where r 19 is a substituted or unsubstituted benzyl group , r 20 is linear c 10 to c 20 saturated or unsaturated group , and x is defined as above . according to a preferred embodiment , r 19 is benzyl , r 20 is a linear c 12 - c 18 saturated or unsaturated group , and x is chloride . examples of such compounds include , but are not limited to , a mixture of n —( c 12 - c 16 ) alkyl - n - benzyl - n , n - dimethylammonium chloride , which is available as barquat ® mb from lonza , inc . of fair lawn , n . j . ; and n - octadecyl - n - benzyl - n , n - dimethylammonium chloride , which is available as carsoquat ® sdq from lonza inc . another quaternary ammonium compound contemplated for use in the present invention has the formula r 19 r 20 n + ( ch 3 )( ch 2 ch 2 o ) n h x − where r 19 is a c 6 - c 20 linear or branched , substituted or unsubstituted alkyl group or a c 6 - c 20 substituted or unsubstituted aryl group , r 20 is a c 1 - c 20 linear or branched , substituted or unsubstituted alkyl group or a c 6 - c 20 substituted or unsubstituted aryl group , n is an integer from 1 to 2 , and x is defined as above . preferably , r 19 and r 20 are linear or branched c 8 - c 10 substituted or unsubstituted groups and more preferably are decyl . x is preferably propionate . an example of such a compound is n , n - didecyl - n - methyl - n - hydroxyethylammonium proprionate , available as bardap ® 26 from lonza , inc . of fair lawn , n . j . yet another suitable quaternary ammonium compound has the formula r 19 r 20 r 21 ( ch 3 ) n + x − , where r 19 , r 20 , and r 21 independently are linear or branched c 6 - c 22 saturated or unsaturated groups . more preferably r 19 , r 20 , and r 21 independently are linear or branched c 8 - c 10 saturated or unsaturated groups . x is preferably chloride . examples of such compounds include , but are not limited to , n , n , n - tri ( octyl / decyl )- n - methylammonium chloride , which is available as aliquat ® 336 from aldrich chemical company of milwaukee , wis . ( aliquat ® 336 is a mixture of n , n , n - tri ( octyl )- n - methylammonium chloride , n , n - di ( octyl )- n - decyl - n - methylammonium chloride , n - octyl - n , n - di ( decyl )- n - methylammonium chloride , and n , n , n - tri ( decyl )- n - methylammonium chloride . the polymeric quaternary ammonium biocide may be any known in the art . suitable polymeric quaternary ammonium biocides include , but are not limited to , poly [ oxyethylene ( dimethyliminio ) ethylene -( dimethylimino ) ethylene dichloride ]; reaction products of epichlorohydrin and dimethylamine ; and mixtures thereof . more preferred quaternary ammonium biocides include , but are not limited to , benzalkonium chloride and didecyl dimethyl ammonium chloride . the biocidal amine or salt thereof may be any known in the art . suitable amines include , but are not limited to , those having the formula nr 7 r 8 r 9 where r 7 , r 8 , and r 9 are independently hydrogen , alkyl ( such as c 1 - c 30 alkyl ), or aryl and r 7 , r 8 , and r 9 are optionally substituted with an amino group (— nh 2 ). according to one preferred embodiment , r 7 is a c 1 - c 18 alkyl and r 8 and r 9 are methyl ( e . g ., dodecyldimethyl amine ). according to another preferred embodiment , r 7 is a c 1 - c 18 alkyl and r 8 and r 9 are —( ch 2 ) 3 nh 2 ( e . g ., bis ( 3 - aminopropyl ) dodecylamine , which is available as lonzabac ® 12 from lonza inc . of fair lawn , n . j .). suitable salts of these amines include , but are not limited to , hydrochloric , hydrobromic , and sulfuric salts . the free halogen - generating biocide , halogen stabilizer , and quaternary ammonium biocide and / or biocidal amine may be directly added to the aqueous solution in any order or simultaneously . two or more of the free halogen - generating biocide , halogen stabilizer , and quaternary ammonium biocide may be mixed prior to addition to the aqueous solution . for example , the free halogen - generating biocide and a mixture of the halogen stabilizer and quaternary ammonium biocide and / or biocidal amine may be separately added to the aqueous solution . the halogen stabilizer / biocide mixture preferably is a single phase solution . if phase separation occurs , the halogen stabilizer and / or biocide are no longer uniformly distributed throughout the mixture . in systems where the halogen stabilizer / biocide mixture is stored in a container and pumped from the top or bottom of the container into an aqueous solution , this may result in an undesirable ratio of halogen stabilizer to biocide being added to the aqueous solution . the single phase solution is preferably phase stable at 4 ° c . for at least 3 or 5 days and / or phase stable at 50 ° c . for at least 30 days . the phase stability of a halogen stabilizer / quaternary ammonium biocide mixture may be improved by the addition of an amine oxide , such as a ( c 8 - c 22 alkyl ) dimethyl amine oxide . according to one preferred embodiment , a mixture of the halogen stabilizer and quaternary ammonium biocide and / or biocidal amine is provided and mixed with the free halogen - generating biocide prior to being added to the aqueous solution . preferably , the free halogen - generating biocide is mixed with the halogen stabilizer / biocide mixture just prior to being added to the aqueous solution . the mixture of halogen stabilizer and quaternary ammonium biocide and / or biocidal amine generally contains from about 1 to about 50 % or 99 % by weight of halogen stabilizer and from about 1 to about 99 % of quaternary ammonium biocide and / or biocidal amine , based upon 100 % weight of total mixture . according to one embodiment where the halogen stabilizer is dmh , the mixture in concentrated form contains broadly from about 1 to about 50 %, preferably from about 2 to about 25 %, and more preferably from about 5 to about 10 % by weight of dmh and from about 1 to about 99 %, preferably from about 2 to about 50 %, and more preferably from about 5 to about 25 % by weight of quaternary ammonium biocide and / or biocidal amine , based upon 100 % weight of total mixture . according to another preferred embodiment , a mixture of the halogen stabilizer , quaternary ammonium biocide and / or biocidal amine , and a bromide source is provided . the mixture is either applied directly to the aqueous solution together with the free halogen - generating biocide or mixed with the free halogen - generating biocide prior to being added to the aqueous solution . preferably the mixture contains from about 1 to about 50 % by weight of the bromide source . any of the free halogen - generating biocides , halogen stabilizers , and quaternary ammonium biocides maybe mixed with non - aqueous solvents and other adjuvants known in the art , prior to their addition to the aqueous solution . any mixtures can be prepared by mixing the appropriate ingredients . the mixtures may be heated and / or stirred to expedite mixing . the molar ratio of free halogen - generating biocide to halogen stabilizer maintained in the aqueous solution broadly ranges from about 20 : 1 to about 0 . 2 : 1 and preferably ranges from about 10 : 1 to about 0 . 9 : 1 . the molar ratio of halogen stabilizer to quaternary ammonium biocide and / or biocidal amine maintained in the aqueous solution broadly ranges from about 50 : 1 to about 0 . 02 : 1 and preferably ranges from about 10 : 1 to about 0 . 1 : 1 . when the halogen stabilizer is dmh , the weight ratio of dmh to quaternary ammonium biocide and / or biocidal amine maintained in the aqueous solution broadly ranges from about 100 : 1 to about 1 : 100 and preferably from about 50 : 1 to about 1 : 50 . for example , when the quaternary ammonium biocide is benzalkonium chloride , the weight ratio of dmh to benzalkonium chloride maintained in the aqueous solution broadly ranges from about 100 : 1 to about 1 : 100 and preferably from about 50 : 1 to about 1 : 50 . when the quaternary ammonium biocide is didecyl dimethyl ammonium chloride , the weight ratio of dmh to didecyl dimethyl ammonium chloride maintained in the aqueous solution broadly from about 100 : 1 to about 1 : 100 and preferably from about 50 : 1 to about 1 : 50 . the concentration of free halogen - generating biocide , halogen stabilizer , and quaternary ammonium biocide and / or biocidal amine maintained in the aqueous solution generally is a biocidally , algicidally , fungicidally , or bactericidally effective amount . according to one embodiment , the concentration of total oxidizing halogen biocidal species broadly is from about 0 . 05 to about 10 ppm , the concentration of halogen stabilizer broadly is from about 0 . 01 to about 100 ppm , and the concentration of quaternary ammonium biocide and / or biocidal amine broadly is from about 0 . 01 to about 100 ppm . according to one preferred embodiment , the concentration of total oxidizing halogen biocidal species is from about 0 . 1 to about 5 ppm , the concentration of halogen stabilizer is from about 0 . 1 to about ppm , and the concentration of quaternary ammonium biocide is from about 0 . 1 to about 5 ppm . the aqueous solution may be , for example , water in a swimming pool or spa , a water treatment facility , a toilet , a pulp slurry , a papermaking slurry , a mineral slurry or white water . white water is generally separated liquid that is re - circulated to a preceding stage of a papermaking process , especially to the first disintegration stage , where paper , water and chemicals are mixed . typical pulp slurries in paper applications contain from about 0 . 2 to about 18 % by weight of organic matter , based upon 100 % total weight of slurry . the organic matter is typically comprised of wood fiber ( or pulp ) and adjuvants , such as sizing and starch . generally , the organic matter comprises from about 90 to about 99 % by weight of wood fiber ( or pulp ), based upon 100 % total weight of organic matter . according to a preferred embodiment , the wood fiber is at least partially derived from recycled paper . the aqueous solution ( e . g ., pulp slurry ) may also contain other adjuvants known in the art . examples of such adjuvants include , but are not limited to , other biocides and / or slimicides ; sodium hydroxide ( or other caustic ); peroxide stabilizers , such as sodium silicate , magnesium sulfate , and polyphosphates ; chelating agents , such as edta ; fatty acids ; and combinations thereof . the following examples illustrate the invention without limitation . all parts and percentages are given by weight unless otherwise indicated . the ingredients in table 1 below were added to a 25 ml flask and monitored for phase and color stability . as shown by table 1 , dmh produces phase and color stable solutions with bardac ® 1552 and poly [ oxyethylene ( dimethyliminio ) ethylene -( dimethyliminio ) ethylene dichloride ]. the low and moderate temperature phase stability and high temperature compositional stability of the n - hydrogen compound / quaternary ammonium aqueous compositions shown in table 2 was determined as follows . the n - hydrogen compounds were hydantoins . some of the compositions also include an amine oxide . low temperature phase stability was determined by placing prepared formulations in 4 ° c . storage for 3 - 5 days followed by visual observation . acceptable formulations remained as single - phase solutions with no phase separation or crystallization . moderate temperature phase stability was defined as the ability to prepare a single - phase solution at room temperature with the composition . high temperature compositional stability was determined by placing prepared formulations in storage at 50 ° c . for approximately 30 days followed by hydantoin analysis by hplc . acceptable formulations remained as single - phase solutions with hydantoin recovery of greater than 90 %. the slimicidal efficacy of the barquat 1552 ®/ dmh / naocl compositions recited in table 3 below was evaluated with white water obtained from a u . s . northeastern tissue mill . the ph of the white water was about 7 . 5 . the test organisms were those native to the white water . bardac ® 1552 master biocide solutions were prepared such that the addition volume of quaternary stock solution was between 0 . 1 and 2 . 0 mls to the 50 ml test volume . master solutions of dmh were prepared in combination with naocl at a 1 : 1 molar ratio such that the addition volume of stock solution was between 0 . 1 and 2 . 0 mls to the 50 ml test volume . the appropriate volumes of these stock solutions were utilized to generate the active concentrations recited in table 3 below . a sufficient amount of the barquat 1522 ® master biocide solution and dmh master solution were added to the white water to obtain the concentrations of barquat 1522 ® , dmh , and naocl in the white water indicated in table 3 . the white water was then incubated for 3 hours at 37 ° c . the test conditions were based on astm e 1839 - 96 . microbiological counts were performed using tryptone glucose extract agar by known pour plate techniques . difco d / e neutralizing broth was used as the first serial dilution tube for biocide neutralization . under the conditions of astm e 1839 - 96 , slimicidal efficacy is demonstrated upon the achievement of a bacterial reduction of 99 % ( 2 logs ). many variations of the present invention will suggest themselves to those skilled in the art in light of the above detailed description . such obvious variations are within the full intended scope of the appended claims .
the present invention is a method for controlling the growth of microorganisms or killing microorganisms in an aqueous solution , such as that found in a water treatment facility or papermaking facility . the method includes adding an effective amount of a free halogen - generating biocide , a halogen stabilizer , and a quaternary ammonium compound , a biocidal amine or salt thereof , or mixture thereof to the aqueous solution . the aqueous solution may be water in a recreational facility , an industrial cooling system , a water treatment facility or a water slurry , such as a circulating water slurry , in a papermaking facility . the mixture of the present invention is useful as a slimicide . the quaternary ammonium biocide and / or biocidal amine increase the efficacy of the free halogen - generating biocidal system .