US5098582A

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United States Patent 15 {11] Patent Number: 5,098,582
;
Antelman [45] Date of Patent: Mar. 24, 1992
[54] DIVALENT SILVER OXIDE BACTERICIDES parete 1/1985 Eder reer one
4,749, 6/1988 . 1
[75] Inventor: Marvin S, Antelman, Rehovot, Israel mischi et
. . Primary Examiner—Thomas Wyse
ee Assignee: N. Jonas & Co., Inc., Bensalem, Pa. Attorney, Agent, or Firm—Salter & Michaelson
21] Appl. No.: 697,782
5 ABSTRACT
[22] Filed: May 9, 1991 t 7 . . : ,
Divalent silver oxide provides a source for divalent
[51] Int, C15 C02F 1/50 bactericidal silver ions in the presence of persulfate.
[52] U.S. Cl. S175 eae a9e/908 This oxide is especially effective when applied to water
[58] Field of 210/757 758, 759, 764-766. used in industrial cooling towers, hot tubs and swim-
Searet 668 501: 432/98, 505: 424/618 ming pools and conforms to stringent EPA require-
oo oo ments of 100% kills of 100K/cc Streptococcus faecalis
[56] References Cited within 10 minutes. The oxide also can be used in water
U.S. PATENT DOCUMENTS with exceptionally high salt content without halide
curdy precipitate formation and will not stain the skin
pease ares Bechhold . aaened of users who may inadvertently be exposed to it.
2,521,713 9/1950 Goetz 210/764
4,092,245 5/1978 Franks et al. 424/618 4 Claims, No Drawings

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5,098,582

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DIVALENT SILVER OXIDE BACTERICIDES

BACKGROUND OF THE INVENTION

The bactericidal properties of divalent silver for
water treatment is the subject of U.S. Pat. No. 5,017,285
of the present inventor. In said patent the inventor has
claimed a method for controlling the growth of bacteria
in swimming pool and industrial cooling tower waters
utilizing soluble divalent silver complexes with inor-
ganic ligands which exhibit distinct advantages over
monovalent silver in terms of cost, efficacy, concentra-
tion and stability. It was found that water sources hav-
ing sodium chloride present at concentrations as high as
100 PPM would not precipitate insoluble chloride in
contradistinction to monovalent silver at the same con-
centration of parts per million of available silver. While
said divalent silver compounds are effective in brackish
waters and swimming pools having these concentra-
tions of salt, a major problem arises under conditions of 20
higher salt concentrations and in special situations
where higher halide concentrations are likely to prevail.

The situations where higher halide concentrations are
likely to occur are manifold. Among the more prevalent
cases are when sea water is used in swimming pools,
which is a common occurrence at sea resorts, when
brackish water is employed in cooling towers, and
when swimming pools are maintained with calcium
chloride in order to mineralize them. Another case is
hot tubs with mineral salts.

When the aforementioned divalent silver compounds
are added to said high halide concentration waters, a
white curdy precipitate occurs which clouds the water
to which it is added and makes it aesthetically unaccept-
able, even though the divalent silver performs its bacte-
ricidal action under these conditions of use. Acccrd-
ingly, it was desirable to explore and test divalent silver
compounds which would not produce a curdy halide
precipitate in water containing high concentrations of
salt or other halide salts.

Another problem associated with the divalent silver
solutions is that care must be taken that they not contact
the skin as they leave unsightly and difficult to remove
silver stains. Although this problem was ancillary to the
halide curdy precipitation problem, it was preferable
that the divalent silver compound selected be more
amenable to customer handling and remove the risk of,
or minimize, silver staining.

OBJECT OF THE INVENTION

The main object of this invention is to provide for a
bactericidal divalent silver agent which will not form
non-aesthetic curdy precipitates in high halide contain-
ing waters utilized for industrial cooling, swimming
pools and hot tubs. Still another object of this invention
is to provide for a divalent silver bactericidal medium
which will not leave persistent stains on the user’s skin
through accidental contact, or minimize said risk.

SUMMARY OF THE INVENTION

This invention relates to methods for keeping the
water in swimming pools, hot tubs and industrial cool-
ing installations free from bacteria. Said methods relate
to bactericidal agent additions of the compound AgO,
ie, divalent silver oxide, in contradistinction to the
monovalent oxide of silver, Ag2O.

Divalent silver oxide, prepared in the laboratory, and
purchased commercial materials were evaluated in the

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presence of persulfates to see whether they were effec-
tive at various concentrations in inhibiting bacterial
growth. It was found that they inhibited growth of
mixed coliforms at concentrations as low as 0.5 PPM of
AgO within 5 minutes. The addition of persulfates to
swimming pools is standard practice, and silver(II)
oxide exhibits its bactericidal action in their presence at
persulfate levels of 10 PPM. In the absence of persul-
fate, 100% kills do not occur.

A plausible explanation for this is based on a plethora
of references in the chemical literature as to the nature
and stability of silver ions so that the reaction mecha-
nism of this invention may be represented as follows:

AgO+ H20= Ag?+ +20

In the absence of oxidizing agents such as the persul-
fates silver(I), oxide’s dissociation into divalent silver
ions is unlikely to occur (J.A. McMillan, “Higher Oxi-
dation States of Silver”, Chemical Reviews, 1962, 62
p.67).

Silver(II) oxide was added at concentrations between
110 PPM to water containing 5000 PPM sodium chlo-
tide. No curdy precipitate occurred. The oxide sunk to
the bottom of the container and gradually formed a
white surface layer of chloride on the surface. The
chloride did not in any way interfere with the efficacy
of the oxide and was evaluated at said level of salt at a
pH of 7.5, killing 100% of the bacterium Streptococcus
faecalis (100,000 colonies/cc.) within 10 minutes.

A solution of divalent silver phosphate containing
5% silver by weight was prepared and tested for skin
reaction on the human hand by exposing it to a drop of
this solution 1 mm in diameter for 2 seconds, after
which the skin was washed. Upon exposure to sunlight,
the skin developed a lasting brown stain which lasted
about 2 weeks. The procedure was repeated with solid
AgoO and failed to produce any stain.

The action of the divalent silver oxide is unique in its
bactericidal action, for while it is known that monova-
lent silver salts exhibit said action, EPA protocols for
swimming pools, which require killing 100K/cc cul-
tures of bacterial within 10 minutes to levels of 100%,
are not achievable at the same concentrations of silver.
Indeed this was tested with silver lactate adjusted to
basic pH’s where only monovalent silver oxide can
exist, and even at silver concentrations of 10.0 PPM in
the presence of 10 PPM potassium monopersulfate the
resulting bacterial colonies remaining were designated
TNTC (too numerous to count).

Other objects and features of the present invention
will become apparent to those skilled in the art when
the present invention is considered in view of the ac-
companying examples. It should, of course, be recog-
nized that the accompanying examples illustrate pre-
ferred embodiments of the present invention and are not
intended as a means for defining the limits and scope of
the present invention. .

DESCRIPTION OF THE PREFERRED
EMBODIMENTS

As illustrative of the compositions of this invention in
their preferred embodiments is the following:

EXAMPLE I

Silver(II) oxide was prepared by modifying the pro-
cedure described by Hammer and Kleinberg in Ino-

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5,098,582

3

roanic Syntheses (IV) 12. A stock solution was made
containing 24.0 grams each of potassium peroxydisul-
fate and sodium hydroxide in 500 cc. distilled water.
Into 20 ml. vials were weighed quantities of silver ni-
trate containing 1.0 gram of silver. Now 50 ml. of the 5
aforementioned stock solution were heated in a 100 ml.
beaker, and the contents of one of the vials was added to
the solution after it had attained the temperature of 85
C. The beaker was then maintained at 90 C. for 15 min-
utes. The subsequent Ag(II) oxide which formed as a
deep black precipitate was washed and decanted 4 times
with distilled water and then dried to remove all mois-
ture.

The resulting product was submitted to a bactericidal
evaluation prescreening following “good laboratory
practice” regulations as set forth in Federal Regulations
(FIFRA and fidca/40 CFR 160, May 2, 1984). The
protocol consisted of exposures to (treptococcus faeca-
lis utilizing AOAC (15th) 1990:965:13 at two exposure
times, 5 and 10 minutes. The water solution tested was
adjusted to pH=7.5 and 10 mg./L of potassium monop-
ersulfate. Oxone (registered trademark of duPont
Chemicals) was added to the water, and 100% kills
were obtained at 5 and 10 minutes at Ag(II) oxide con-
centrations of 5.0 and 10.0 PPM. At a concentration of 25
1.0 PPM, 99+ % kills were obtained at 5 minutes, and
100.0% kills at 10 minutes.

EXAMPLE I

The aforementioned procedure described in Example
I was repeated excepting that the bactericidal evalua-
tion was performed with E. Coli coliforms at 100,000
colonies per cc. in water containing sodium chloride at
5000 PPM utilizing Ag(II)O at a concentration of 2.0
PPM. 100% kills were obtained within 5 minutes.

EXAMPLE III

The procedure described in Example II was repeated
except that the source of Ag(II) oxide utilized was com-
mercial material obtained from Whittaker Power Stor-

a

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age Systems, Denver, Colorado, and utilizing sodium
peroxydisulfate as well as Oxone at 10 mg./L. without
a pH adjustment of the distilled water used. In each
case, 100.0% kills were obtained at concentrations of
0.5 and 1.0 PPM of Ag(II) oxide at 5 and 10 minute
exposures and at 0.3 PPM Ag(II) oxide at the 10 minute
exposure. When the water was neutralized to a pH of 7,
100.0% kills were obtained at 1.0 PPM Ag(II) oxide at
both the 5 and 10 minute exposures. In all the tests
utilized in this example, two plates were used for confir-
mation, and blanks were run on both the dilution water
and persulfate.

As this invention may be embodied in several forms
without departing from the spirit or essential character-
istics thereof, the present embodiment is therefore illus-
trative and not restrictive, since the scope of the inven-
tion is defined by the appended claims rather than by
the description preceding them, and all changes that fall
within the metes and bounds of the claims or that form
their functional as well as conjointly cooperative equiv-
alents, are therefore intended to be embraced by these
claims.

What is claimed is:

1. A method for controlling the growth of bacteria in
the water of swimming pools, hot tubs and industrial
cooling towers which comprises adding to the water
divalent silver oxide in the presence of an oxidizing
agent so as to provide a source of divalent silver ions.

2. A method as claimed in claim 1 where the oxidiz-
ing agent is a persulfate.

3. A method according to claim 1 which can be uti-
lized in said waters where they contain sodium chloride
concentrations as high as 5,000 parts per million or an
aggregate amount of halide salts equivalent to the chlo-
ride concentration of said salt.

4. A method according to claim 1 which will not
leave silver stains on the user’s unprotected skin due to

inadvertent exposure.
ee