DK141657B - Process for disinfecting water and ion exchange resin for use in the process. - Google Patents

Description

(tt) FKHuntuimiiFT 141657 V53 / ¾ I BH * DENMARK mute *. · c 02 f mo «(21) Application No 6151/70 (28) indicated on 3 * Dec. 19? 0 (23) utodtf 3 · dee. 1970 (44) Aimuiiingan fromMteal eg 1 n On

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DIRECTORATE OF

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3 · dec. 1969 »881923, US

Nov 2 I97O # 86246, US

(TO KANSAS STATE UNIVERSITY RESEARCH FOUNDATION, Manhattan, Kaneae, US.

(72) Inventor: Jack Leeper Lambert, 800 Ratone Street, Manhattan, Kansas, US: Louis H _FIna, 18j? 3 ~ Alabama Lene, Manhattan, Kansas, US.

(74) FulchiTgdg unctar m «mm ΜμμΜ« ·:

Th. Ostenfeld Patentbureau A / s.

(94) Method of disinfecting water and ion exchange resin for use in the process.

The present invention relates to a method for treating bacterially contaminated water to obtain disinfected water which does not require further treatment to remove disinfectant residues, and a bactericide for carrying out the process.

There are relatively few ways to chemically treat water so that microorganisms are destroyed without leaving unwanted residues. The most widely used treatment method is with chlorine, but the treatment methods used today often leave excess chlorine at concentrations that irritate the eyes and mucous membranes. The other halogens, bromine and iodine, have been used to a much lesser extent and their utility has largely been limited to the treatment of swimming pools, often at physiologically unacceptable concentrations.

141657 2

To date, ion exchange resins, such as the quaternary ammonium resins, have not been considered to be of much value in disinfecting water. Certain quaternary ammonium compounds have bactericidal properties when used in aqueous solutions, but ordinary quaternary ammonium anion exchange resins exhibit only a very slight bactericidal effect. Thus, water contaminated with live bacteria can pass a layer of anion exchange resin without a noticeable reduction in the number of live bacteria.

Furthermore, it is well known that chloride, bromide and iodine ions have little or no bactericidal effect on water. Eg. it can be mentioned that bacteria are not killed when contacted with dilute aqueous solutions of e.g. sodium chloride and potassium chloride. Tri-iodide ions in solution have been referred to as having negligible germicidal properties compared to diatomic iodine or other halogens in elemental form. (See J. Bacteriol., 69-413-417 (1955) and Arch. Biochem., 6: 261-268 (1945)).

In the disclosure of U.S. Patent No. 3,316,173, a process for treating water with bromine is disclosed in which a highly basic anion exchange resin is used as a source of diatomic or elemental bromine, removing the bromine from the resin to form a relatively concentrated aqueous solution which then mixed with a larger volume of water, such as water in a swimming pool, to give a bactericidal concentration of bromine. The bromine is eluted from the resin at concentrations from 10 ppm to 10,000 ppm, which is well above physiologically acceptable bromine levels in water for human consumption.

The disclosure of U.S. Patent No. 3,462,363 discloses a further development of the process of the above-mentioned patent, in which a purifying resin is used in extension of a highly basic polyhalide anion exchange resin to reduce the excess halogen in the treated water to a physiologically acceptable level. In the first step of the process, the water containing microorganisms elementally elutes halogen from the resin to achieve a halogen concentration in the water above 5 ppm. Upon completion of the bactericidal treatment, the residual halogen is reduced to a value not exceeding 1.0 ppm by passing the solution through another anion exchange resin capable of absorbing the halogen.

U.S. Patent No. 3,436,345 discloses a polybromide-containing anion exchange resin for use in disinfecting water. The bromine content of this anion exchange resin is eluted, with the intention of using the resin a bactericidal concentration of bromine in the water is intended. The invention disclosed in the United States Patent is a further development of the invention disclosed in the above-mentioned United States Patent No. 3,316,173 and suffers from the same disadvantages of physiologically unacceptable bromine concentrations in the water.

Surprisingly, it has been found that for the disinfection of water, an ionic association can be used between a highly basic anion exchange resin and triiodide, which contains essentially no oxidizing iodine, thereby avoiding elution of iodine and preventing the disinfectant from being transferred to the water. that needs to be addressed. The process of the invention is based thereon and is characterized by the characterizing part of claim 1.

Further, a bactericide is provided for practicing the method of the invention, which bactericide is peculiar to the characterizing part of claim 4.

To prepare the bactericide of the invention, a highly basic anion exchange resin is reacted with triiodide ions to form a stable ion association compound with an extremely low dissociation in water. The association of the triiodide ions with the basic exchange positions (cationic groups) in the resin is such that the positions of ion exchange with the solution are blocked. The amount of iodine released (Cl2) or triiodide CI3D in the water is vanishing, being below the usual limits for its determination. The resin compound is nonetheless a potent bactericide. By some mechanism that is not yet fully understood, the thioiodide groups "react" to the resin with bacteria to achieve an almost instantaneous killing of the bacteria without forming a bactericidal concentration of iodine (or any oxidizing form thereof) in the water. The killed bacteria do not remain on the resin but will easily pass through the resin layer. Thus, complete bacterial sterilization of highly contaminated water can be achieved without introducing physiologically unacceptable amounts of iodine into the water. The amount of possibly iodine released in the reaction between the bacteria and the insolubilized triiodide is below the limits of analysis in studies that are sensitive to at least 100 parts per minute. billion iodine (or an oxidizing form thereof). The disinfected water is thereby ready for immediate use as drinking water or for other applications where bacterially sterile iodine-free water is desirable. No further treatment is usually required.

Any highly basic anion exchange resin can be used, but quaternary ammonium anion exchangers are preferred. The term "highly basic anion exchange resin" refers to a group of resins which either contain highly basic (cationic) groups such as quaternary ammonium groups, or which have highly basic properties which are essentially equivalent to quaternary pure ammonium anion exchange resins. The classification of "highly basic" resins contrasts with "weakly basic" resins, wherein the basic groups are amine nitrogen rather than quaternary ammonium groups. In addition to the quaternary ammonium resins which are commercially available from a number of companies, other highly basic resins are known, such as the tertiary sulfonium resins, the quaternary phosphonium resins and alkyl pyridine resins. Literature references showing · methods for making non-commercially available highly basic anion exchangers * are:

Tertiary sulfonium anion exchangers: G.J. deJong (to Stami-carbon NV), United States Patent No. 2,713,038, July 12, 1955, and - Staatmijnen in Limburg, Directie van de, Dutch Patents No. 72,245, April 15, 1953 and No. 75,968, 15. September 1954, and British Patent No. 737,924, October 15, 1955.

Quaternary phosphonium anion exchangers: Stamicarbon N.V., Dutch Patent No. 75,705, August 16, 1954.

Alkylpyridinium anion exchangers: U.S. Patent No. 2,739,948, March 27, 1956.

Commercially available quaternary ammonium anion exchange resins which may be used in the practice of the present invention include "Rexyn 201" (Fisher Scientific Co.), "Amberlite®IR 400" and "Amberlite®IR 401 S" (Mallinckrodt Chemical Works), "Ionac A 504 "(Matheson, Coleman & Bell) and" Dowex®1 "and" Dowex®2 "(Dow Chemical Co.). These resins are all characterized by having quaternary ammonium exchange groups in salt form, usually in the chloride or sulfate forms.

The terms "triiodide" or "triiodide ion" as used in this specification with claims refer to ions formed by iodine having the valence -1 but containing three iodine atoms. the lodion (I ~) unites with molecular iodine (^) to form the triiodide ion (I ^ -). If more of the elemental iodine ()) unites with the monovalent triiodide ion (I ^ -), higher polyiodide ions can be formed, e.g. the polyiodide ions 1 ^ and Ij ~.

The only polyiodide useful for the bactericide of the present invention is the triiodide. Higher polyiodide ions release molecular iodine (I2) to the solution, although they are united with the highly basic anion exchange resin. Trihalides other than triiodide also release halogen to the water, although absorbed on highly basic anion exchange resins. The triiodide is unique in that the iodine in this ion association compound is not eluted by contact with water at and below the 100-per-ml assay limits. billion.

Suitable methods for preparing solutions and salts of polyhalide ions, comprising polyiodides, are described in the literature. (See, for example, AI Popov and RE Buckles, "Polyhalogen Complex Salts", Preparation No. 46, and "Typical Polyhalogen Complex Salts", Preparation No. 47, in INORGANIC SYNTHESES vol. V, published by T. Moeller, McGraw —Hill Book Company, Inc., New York 1957, pp- 167-178). Following such methods for the purposes of the present invention, molecular iodine can be dissolved in an aqueous solution of the iodide salt. Eg. iodine is dissolved in a solution of sodium or potassium iodide. This solution will contain the monovalent ion I which will combine with the dissolved iodine I₂ to form the polyiodide ions. By essentially using one mole of I mol I, mainly only triiodide ions will be formed. If stoichiometric excess amounts of I 2 are used, some of the polyiodide ions may be formed, and particular steps may be desirable to remove the excess iodine from the resin. In an alternative method, the resin can first be converted to the iodide form (I) by contacting it with a solution of potassium or sodium iodide or another iodide salt, and a stirred aqueous slurry of the converted resin is contacted with elemental iodine (I2). to react with the absorbed I to form the bound. This process is less desirable as it is more difficult to ensure saturation of the column with triiodide.

The reaction between the triiodide ions and the strong basic anion exchange resin does not require any particular technique or reaction conditions. The aqueous solution of the triiodide ions can be contacted with a salt form of the resin at usual room temperatures (25-30 ° C) to obtain the association compound. The reaction can be carried out in batches, separating the resin from the solution by filtration or centrifugation. However, it is advisable to react the resin in a layer or column by allowing the triiodide solution to flow through the resin. The essential reaction can be illustrated as follows: 141657 6 +

C

C / = \ -N - CH3 C1 '+ K + Ii? CH

C J

i c c __, CH, I / ΓΛ I +.

- ^ c-Η: v-ch7 - n --- i “+ k ci i \ = / 2 / \ 3, CH, CH, C 0 5 In the above formulas, the quaternary ammonium anion exchange resin represented by three methyl groups is bonded to the basic nitrogen and the resin is shown to be originally in chloride form. However, it will be appreciated that other short chain aliphatic groups may be bonded to the nitrogen such as ethyl or hydroxyl groups. Certain commercial highly basic quaternary ammonium anion exchange resins, such as "Dowex®2n (Dow Chemical Company), contain alkyl and alkanol groups. It will also be appreciated that these resins may be delivered and used in salt forms different from the chloride form, such as the sulfate.

In the ion association compound, as shown, the triiodide is bound to the fixed quaternary ammonium group or other basic group and does not dissolve. The potassium and chloride ions can be easily washed out by the resin compound. If excess triiodide or iodine is present in the reaction solution, this can also be washed out by the resin compound by allowing water to pass through a column or layer or by batch washing followed by filtration or centrifugation. It is preferred that the resin compound be washed free of unreacted iodine and / or excess triiodide. Distilled or ion-free water can be used for the leaching.

Alternatively, the converted resin may first be washed out with an aqueous iodide salt solution before being washed out with water. This method of preparation is particularly desirable if the reaction solution may have contained higher polyhalide ions than I3. An iodide salt solution (I), e.g. Nauminum, potassium or ammonium iodide can be used. The iodide salt solution will convert all possible resin bound higher polyiodides (e.g.

Is "and I7") to the triiodide by removing the excess to form I3 ions in solution from the I ~ ions of the solution. Washing out with water, if continued long enough, will produce the same result, or caution may be shown by using exact stoichiometric ratios of I and Is that mainly only triiodide is bonded to the resin.

The triiodide ion association compound, prepared as described, can be used to disinfect water by a batch reaction with the contaminated water, but a continuous process is preferred. Water containing the viable bacteria to be killed is preferably passed through a layer of porous granular material consisting of the strong basic anion exchange resin which has previously reacted with triiodide ioners. The maximum permissible flow rates for total bacterial sterilization. will vary with the concentration of the triiodide groups in the resin and food concentrate in the onion of living bacteria in the water. However, sufficient Beam flow rates are possible so that the water to be disinfected can be pumped through columns of the resin compound while obtaining 1001 kills of the bacteria. The course of disinfection can be controlled by taking samples of the water after treatment. Drinkable, non-toxic water is readily prepared in practice, making the contaminated water bacterially sterile, without being rendered unaffected by the admixture of physiologically unacceptable free iodine.

The present invention is elucidated in the following Examples.

Example 1

A preferred method of preparing the bactericide of the present invention is as follows:

Slowly pass a solution consisting of 5 parts by weight of potassium iodide and 7.6 parts by weight of iodine dissolved in 100 parts by weight of water to 10 parts by weight of quaternary ammonium resin beads in a glass column. Wash thoroughly with distilled water until the wash water gives a negative reaction for iodine, polyiodide or other oxidant with a linear starch-cadmium iodide reagent (see Example 2), and negative for iodide ion with silver nitrate solution. Alternatively, the resin is washed with an aqueous solution of potassium iodide before leaching with distilled water to ensure the conversion of any excess of iodine 8 or higher polyiodide ions to Ij, thereby ensuring a saturation of the resin exchange positions with triiodide ions.

Similar resin polyiodide compounds made from "Ionac A-540" (Matheson, Coleman and Bell), "Rexyn 201" (Fisher Scientific Co.) or Amberlite ^ RA-400 "(Mallinckrodt Chemical Works), which are strong basic ion exchange resins on chloride or sulphate forms, all were effective in giving complete killing of bacteria at concentrations of 10 ^ per milliliter and higher (see Examples 3 and 6).

Example 2

The resin triiodide column, when prepared as described in Example 1, can be treated with distilled water or with solutions of up to 500 ppm of sulfate, bicarbonate, chloride, or nitrate ions without detectable concentrations of iodine, triiodide or other oxidant in eluent. The tests were performed with one linear starch cadmium iodide reagent (Lambert and Olguin Anal. Chem., 41, 838 (1969)), which can determine concentrations of iodine or its equivalent in the form of other oxidizing agents down to at least 0.1 ppm. The total concentration of iodine in any form (iodine, triiodide and iodide) in the eluent when distilled water passes through the column is less than 0.5 ppm when determined by neutron activation analysis. When distilled water passes through the column, iodide ion release gives no more than a slight cloudiness of silver iodide when tested with silver nitrate solution.

When solutions of the following anions pass through the column: 50 ppm sulfation or 100 ppm each of chloride, nitrate or bicarbonate ions, the iodide ion release is not greater than with distilled water.

Example 3 When 3.8 g of ionac A 540 quaternary ammonium ion exchange resin in triiodide form was used in an approximately 4 3/4 cm by 10 cm column at a flow rate of 20 milliliters per minute, typical bacterial killings were as follows: suspensions of Escherichia coli was reduced from 1.3 x 10 5 to zero viable spoken bacteria per ml; suspensions of Streptococcus faecalis were reduced from 1.1 x 10 6 to zero viable spoken bacteria per ml; and suspensions of Staphylococcus aureus were reduced from 1 , 8 x 10 5 to zero viable spoken bacteria per ml. The standard membrane filter method was used to count E. coli and S. faecalis. The standard agar plate count was used to determine the number of 9 141657 S. aureus. in chloride or sulphate form, suspensions of E. coli were reduced from 200 viable bacteria per milliliter to 120 per milliliter, indicating little or no killing or retention in the untreated column.

When 30g of Rexyn 201 'resin polyiodide compound was used in one column, suspensions of labeled E. coli with 3.0 x 10 5 ml. reduced to zero per day. ml.

Recovery of radioactivity in the eluent gave an average of 05.21 when samples were taken in 100 milliliter intervals up to 600 milliliters in total, indicating that virtually all of the killed bacteria passed through the column.

t *

Similar results were obtained with CC-labeled S. faecalis. In a targeted fatigue trial, a 4.0 g * s column of “lonac A-540 * resin triiodide dye decay killed 1.95 x 10 * ® E. coli in 15 liters with a slight loss in efficiency up to the time the test was discontinued . The column, when regenerated with triiodide ion solution, was found to be as effective a bactericide as it was freshly prepared. Standard sterile nutrient substrate with approx. 100 E. coli per milliliters were passed through the Enlanac A-540 * triiodide column, reducing the number of bacteria counted to zero; but the nutrient substrate nourished the growth of E. coli by subsequent inoculation. This indicates that organic matter in an aqueous medium, such as nutrient substrate, does not change significantly upon contact with the column.

Example 4

Laboratory scale preparations of quaternary ammonium ion exchange resins (highly basic) according to a procedure similar to that of Example 1 were prepared from Exyn 201 * (Fisher Scientific Co.) and Jb ^ erliti ^ RAMOD * (Mallinckredt Chemical Vorks), and Bacterial killing experiments were performed. 30 g * Rexyn 201 triiodide in a column measuring approx. 2.5 cm times approx. 20 cm reduced a suspension of 10 5 viable Escherichia coli per milliliters to zero numbered bacteria when a flow rate of 60 milliliters per milliliter was used. minute. The same resin without the bound triiodide reduced a suspension of 100 bacteria per milliliters to 30 viable spoken bacteria per ml, indicating little or no killing by the untreated resin column. The same * hexyn 201 * resin triiodide compound in a column weighing 4 g and measuring 4 3/4 cm times approx. 10 cm reduced at a rate of 20 ml./min. they counted viable bacteria in a suspension of 10 ^ Streptococcus faecalis per milliliters to zero. A similar column of "Amberlite®IRA-400" resin triiodide ion compound gave a total killing of a suspension of 1.3 x 10 6 E. coli by reducing the number of viable bacteria to zero.

Example 5

Other strong basic resins can be used to produce a resin triiodide ion bactericide similar to those made with quaternary ammonium exchange resins, including tertiary sulfonium resins, quaternary phosphonium resins and alkyl pyridinium resins. A sample of a tertiary sulfonium ion exchange resin was provided in sulfate form and a resin triiodide ion column was prepared in the same manner as described above for strong basic quaternary ammonium resins. The capacity of this particular resin was not found to be as great as that of the quaternary ammonium resin used; but by treating a suspension with 1.35 x 10 milliliters with one column of this compound, the viable bacteria count was reduced to zero. This shows that strong basic resins other than quaternary ammonium resins can be used to produce effective bacterioids with triiodide.

Example 6

Antibacterial experimental data are summarized below in Tables A and B: H U16B7

TABLE A

Antibacterial properties of specified resin-I, complexes

Resin mark Description Spoken viable E. coli per mlb Before After "Ionac A 540" Polystyrene Quater Review_ (Matheson, Coleman near alkyl type,, n · * m5 o & Bell) medium porosity * "Stamex S 44" Polystyrene ter-.

(Private source) for sulfonium 1.3 x 10 ** 0 type "Rexyn 201" Polystyrene alkyl 5 (Fisher Scienti quaternary amine 1.0 x f 50 fic Co.) type, medium porosity "Amberlite ^ IRA Polystyrene. quaternary 4,400M (Mallinck- near ammonium type, 1.4 x 10 4 0 root Chemical medium porosity

Works)

<D

"Amberiite IRA Polystyrene Quater-.

400 S "near ammonium type, 1.2 x 104 0 (Mallinckrodt high porosity

Chemical Works) 3.8 g of each resin were saturated with triiodide ion and tested for the ability to kill E. coli suspended in water at a flow rate of 20 ml. per. minute.

k) Standard Methods for the Study of Water and Wastewater, pp. 592-593, 12th ed. 1965, American Public Health Association,

New York.

12 141657

TABLE B

Counting of specified organisms before and after review of 5.8 g * s columns of “tonac A 540-lJ3 A r

Organism Counting per ml.

_ Before Review_After Review

Salmonella typhimurium 1.0 x 10 5

Escherichia coli 3.0 x 10 5

Pseudomonas aeruginosa 1.3 x 10 4

Staphylococcus aureus 1.8 x 10 0 4

Streptococcus faecalis 1.1 x 10 0 ^ Untreated and iodide-saturated columns had negligible effects on the number of live bacteria.

The cells were suspended in water and passed through the columns at a flow rate of 20 ml. per. minute.

Standard Methods for the Study of Water and Wastewater, pp. 592-593, 12th ed. 1965, American Public Health Association,

New York.

* ^ E. coli and S. faecalis are used as indicators of faecal contamination in the U.S-A, respectively. and Europe. Salmonella and Staphyl lococcus are pathogenic. Pseudomonas (species) is a source of water pollution. Escherichia. Salmonella and Pseudomonas (species) are gram negative, whereas S. faecalis and S. aureus are gram positive.

13 ΙΑ 1657

Example 7

Triiodide resin disinfectant was prepared as described above and washed at room temperature until no oxidizing iodine content was found in the wash water. The disinfectant was then subjected to temperature tests.

Boiling water at nearly 100 ° C was passed through three 30 g columns of the disinfectant. According to the cadmium iodide linear starch reagent sample, no iodine was eluted. The temperature remained above the 85 ° C that the wash water exhibited when collected in a flask. Traces of the halide ion, l ", were found in all the eluents after elution. It should be noted that the cadmium iodide linear starch test was performed after cooling the eluents to room temperature, since the reagent does not operate at temperatures as high as 85 ° C or 100 ° C.

Even when the three columns were placed in a bath at 80 ° C for 24 hours, according to the cadmium iodide-linear starch test, when the cooled solutions were examined at intervals of several hours, no iodine therefrom. One of the columns was still capable of effectively killing bacteria, even after 6 days in a bath at 80 ° C.

Example 8

An experiment to elucidate the effect of the stable triiodide resin-disinfectant was performed.

Three 0.25 inch diameter dialysis bags containing 3 ml each with 1.4 x 10 6 E. coli ml, was placed in a flask containing the triiodide resin disinfectant. The bags were securely tied at both ends. They were placed in a bath containing the disinfectant at 37 ° C and shaken. The bags were opened and examined as indicated in Table C.

Table C

Sack No. Time in hours Number of residual Dissolved iodine in viable E. coli sack solution _ _ in sack (per ml) 1 0 1.4 x 106 1 2 1.05 x 10 ^ nothing 2 4 1.93 x 10 ** nothing 3 25 0XX nothing Mortality probably roughly similar to normal degradation (however, the degradation cannot lead to completely sterilized water).

One plate exhibited an equivalent of 3.7 x 10 14 plates were absolutely sterile.

14 141,657

The conclusion must be that contact or close contact between bacteria and disinfectant is necessary. Dissolved iodine, eluted from the disinfectant alone, is unable to completely kill 10® E. coli per day. ml except after a longer period of time. However, if the usual disinfection method, where column passage for the water plus viable bacteria is used, killing of 10® E. coli per ml in seconds. This is proof that the disinfection is due to contact between the disinfectant and the bacteria-containing water. If contact between disinfectant and bacteria-containing water does not occur, 10® E. coli per kill is not killed. before sufficient iodine is removed from the triiodide resin to satisfy the static equilibrium conditions.

Example 9

An experiment was conducted which aimed to show that the killing mechanism does not depend on eluted iodine. Water passed through columns containing the disinfectant contains less than 200 parts of iodine, such as I billion parts of water, which can be detected by a cadmium iodide linear starch reagent.

When one bacterial protoplasm per One million parts of water (10® E. coli per ml) is suspended in this water, which has passed through the column containing the triiodide resin disinfectant, not all E. coli bacteria are killed, ml remains viable. By contrast, when a suspension of 7.4 x 10 5 E. coli is passed through a column, all the bacteria are killed. 7.4 x 10 bacteria make up 74 parts of bacterial protoplasm per million parts of water. Thus, the only way to obtain a 1001 disinfectant is to put the bacterial water in contact with the disinfectant. Solution of iodine to a concentration of 200 parts per One billion parts of water will not kill 10® live E. coli per day. ml of water.

Example 10

A further experiment to show that the triiodide resin disinfectant only works by direct contact and without elution of large concentrations of iodine or triiodide ions into the solution was performed as follows. Four columns were prepared and tested for disinfection. The disinfectant in two of the columns was 100¾ saturated and the disinfectant in the other two columns was 97¾ saturated for triiodide. 1.8 x 10 ml was suspended in distilled water and passed through the columns. The content of live E. coli in the water was thereby reduced to zero. Next, iodine solutions containing at least 0.2 parts of iodine per ml were prepared. million parts of water, which was measured with the cadmium iodide linear starch reagent. When these solutions were passed through each of the four columns, collected and immediately tested for iodine or other oxidizing iodine-containing constituents, it appeared that the contents were too small to be measured. This showed that the disinfectant removes iodine when present at concentrations greater than the minimum concentration required for determination. Lethal concentrations of iodine in the immediate vicinity of the disinfectant resin material are available as needed for killing bacteria, but the iodine concentrations in the water in contact with the disinfectant are kept at a size below the limit of determination.

The mechanism of the reaction of the insolubilized triiodide has not been scientifically proven. The antibacterial effect may be explained by assuming a charge distribution in the bound triiodide:

Resin N - - - “i" Λ 16 141657

If the Ij ion is polarized as shown, the partial positive charge on the end date could be effective in attracting negatively charged bacteria. Once the bacterium and the bound group have become sufficiently close together, it is possible that one or even two iodine atoms will react directly with -SH groups in the cell wall. It is known that the killing mechanism does not depend on the solution concentration of 1 ^, as evidenced by the fact that the disinfected solutions do not contain germicidal concentrations of As the disinfected solutions are also free of oxidizing iodine (e.g., , IOj, and it appears that the root of bound triiodide groups must directly react with the bacterial cells.

Generally, it is believed that concentrations of elemental halogen in water of less than 0.1 ppm do not produce an effective bactericidal effect. The process of the present invention differs substantially from previous use of iodine for disinfecting water, the amount of oxidizing iodine supplied to the water being below 0.1 ppm. The disinfectant resin triiodide agent contains the iodine in such a firmly bound form that there is no detectable release of iodine, as measured by analytical samples known to be sensitive to at least 100 parts per minute. billion oxidizing iodine.

The term "oxidizing iodine" as used herein means to iodine in any oxidizing form thereof, including e.g. Fully reduced iodine in the form of iodide ion (I) is not included.

Iodide ions are non-toxic at low concentrations in water. However, iodide ions can give the water a noticeably bitter taste at sufficient concentrations, and are thus organoleptically undesirable in drinking water. If very hard water or high ionic water passes through a column of the triiodide-resin bactericide, iodide ions may be present in the eluent at concentrations sufficient to affect organoleptic quality. In such cases, excess iodide can be removed by well known and established ion exchange methods. This is usually not necessary as the amount of iodide ions in the treated water is harmless, non-toxic and below the threshold of bitter taste in an average person.

According to well-known methods, the presence of iodide ion (I ~) in the treated water, if desired, can be detected by examining the water with silver nitrate. Usually, no more than a slight cloudiness will be observed in the water.

To determine the perfection of the leaching of the resin triiodide compound, the water can be tested with an analytical reagent which is sensitive to oxidizing iodine such as an iodine starch reagent. The reagent should preferably be sensitive to at least 100 parts per minute. billion oxidizing iodine. A suitable reagent of this type is the linear starch cadmium iodide reagent described in Lambert and Olguin, Anal. Chem., 41. 838 (1969). The same reagent can be used to determine the content of oxidizing iodine in water which has been treated with the resin triiodide compound to kill the bacteria therein. A suitable procedure for such studies is as follows: add one ml. linear starch-cadmium iodide reagent to a 20 ml. sample of the treated water and note if a blue color is present indicating oxidizing agents such as an oxidizing forums of iodine. The presence of a blue color will indicate that there are at least 100 parts per a billion or more oxidizing iodine present in the solution, while the absence of a blue color will indicate that the amount of iodine present, if at all, is less than 100 parts per minute. billion. Where it is desirable to test in advance a freshly prepared or just regenerated batch of the resin triiodide compound for use in a column, the sample may be 20 ml. water is obtained as follows: Place 3.8 g sample of the dry resin triiodide in an inner diameter glass tube of approx. 4,7cm.

Allow distilled water to pass through the resin layer thus formed at a rate of approx. 20 ml. per. minute. The water may have the usual room temperature (eg 25-30 ° C). Take a sample of 20 ml. eluent from the sample column, and investigate by the method described above using the linear starch-cadmium iodide reagent. A negative reaction (no blue color) indicates that the resin triiodide is in optimum form for use in treating bacterially contaminated water by the method of the present invention.