WO1993004986A1

WO1993004986A1 - Antibacterial treatment of bulk water

Info

Publication number: WO1993004986A1
Application number: PCT/AU1992/000479
Authority: WO
Inventors: Bruno Anthony Gluck; Amir Guirguis Mattha
Original assignee: Novapharm Research (Australia) Pty. Limited
Priority date: 1991-09-09
Filing date: 1992-09-09
Publication date: 1993-03-18

Abstract

The invention relates to the control of microorganisms in bulk quantities of water and to a composition of matter comprising in combination a halogen complex and an oxidizing agent. The microorganisms are controlled by establishing a dynamic equilibrium between an iodophor and free iodine, allowing the free iodine to interact with the microorganisms and oxidizing any iodide formed to iodine. By using the method of the invention a marked unexpected reduction in the TBC count has been shown.

Description

Title: ANTIBACTERIAL TREATMENT OF BULK WATER

FIELD OF THE INVENTION

This invention relates to the control of micro-organisms in bulk quantities of water.

BACKGROUND OF THE INVENTION

The invention will be described with particular reference to the treatment of water in cooling towers, but is applicable for water treatment in swimming pools, holding tanks and other situations in which control of micro-organisms is required.

The problems associated with breeding of bacteria such as Legionella in cooling ^"towers and the consequent infection of associated condenser water and air-conditioning systems, are well-known. It is also important to control levels of slime and algae which reduce cooling tower efficiency and to control corrosion and scale formation in the cooling tower and associated plant.

In the case of relatively quiescent waters such as in swimming pools or storage tanks, bacterial control has been achieved by chlorination or ozonolysis.

It has also been proposed over the years to use iodination which is less likely to give rise to problems of eye irritation, odour, taste and corrosion than chlorination. It has been proposed to iodinate by dosing with controlled quantities of iodide salt. The iodide has no bacterial activity but, by maintaining a large excess of an oxidizing agent (e.g. chlorine, persulphate) , and by controlling pH, the iodide is oxidized to elemental diatomic iodine and hypoiodous acid producing a very effective bactericide.

The large excess of oxidant ensures that substantially all the iodine in the system is present in its oxidized diatomic form, pH control and oxidant selection being important to prevent the formation of the biologically inactive hypoiodite (01^~) and iodate (I0^~) ions.

Thus, U.S. Patent No. 2,443,429 describes treatment of swimming pools with a water soluble iodide in combination with hypochlorite salt or chloramine to provide a bank of available chlorine to oxidize the iodide. U.S. Patent No. 3,161,588 utilizes hypoiodous acid together with a chloramine bank. U.S. Patent No. 3,215,627 utilizes an iodide with a persulphate bank as oxidizer, while U.S. Patent No. 2,232,869 describes the use of that combination together with UV irradiation.

An advantage of these systems is that in the process of killing micro-organisms the active agent, iodine, is reduced to inactive iodide, which is then promptly reconverted by the oxidant bank to elemental iodine. However, the systems lose iodine to the atmosphere and to relatively inactive forms such as iodate and require replenishment of iodide as well as monitoring of other conditions. None of these systems has met with commercial acceptance even in quiescent water treatment, owing to the cost and/or corrosive effects of the bank of oxidant required, the cost of iodine losses, the difficulties of system control and in some cases, the discolouration caused by combination of iodine with organic impurities.

It has also been proposed (U.S. Patent No. 3,326,747) to dose a pool with an iodide salt, and to continuously treat a withdrawn stream with ozone whereby a portion of the iodide bank is oxidized to elemental iodine in an amount proportional to the salt concentration in the stream. Bacteria in the stream are killed by the iodine and the stream is returned to the bulk water as feed together with any un-reacted iodine and iodateε .

This system effectively treats only a portion of water at any time and, since it lacks a bank of oxidant, depends upon continuous addition of ozone to the side stream together with sufficient recirculation rate and a sufficiently high concentration of iodide to achieve control.

The system tends to lose iodine more rapidly than previously discussed systems due to turbulence in the recirculation stream and to over-oxidation. Importantly, the system provides no reserve of biocide capable of withstanding a failure in the ozone supply or an above average load of micro-organism reductant. For the above reasons, iodine systems have not been commercially successful. The most cost-effective and widely-accepted biocide currently available for microbiological control of quiescent waters is chlorine, despite its disadvantages.

The problems of treating cooling water are far greater than those of treating quiescent waters. Not only is chlorine an irritant of the eyes and ucosa but at levels of free chlorine in excess of 1 - 2 ppm it will progressively increase corrosion of mild steel and copper bearing alloys by destroying passive protection and initiating active corrosion. Chlorine tends to delignify timber.

When used to treat non-quiescent waters, the loss of halogen to the atmosphere is usually excessive. This is especially the case in cooling towers wherein the water is subjected to turbulent flow to provide a large air/water interface. Therefore chlorine has not found favour for use in cooling towers and it is more usual to treat cooling tower or non-potable water with a "soup" of non-volatile toxic chemicals including biocides, corrosion and scale inhibitors and the like which must periodically be drained and replaced. Examples of biocides which have been specifically developed for microbiological control in bulk, non-potable water include isothiazolone, biothiocyanate derivates and dibromonitrolopropionamide. Such biocides are highly toxic to operators and liable to cause serious environmental problems. The disposal of waste water treated with biocides in sewers interferes with sewerage treatment plants and is itself a major environmental problem. In addition, the chemical treatments employed are costly and are difficult to monitor and control.

It is an object of the present invention to provide a method for control of micro-organisms in bulk quantities of water which avoids at least some of the disadvantages of the prior art. It is an object of preferred embodiments of the invention to provide a method for the control of micro-organisms for use in cooling towers and other systems in which water is recirculated, as well as quiescent waters such as swimming pools. It is a further object of the invention to provide a process of antimicrobial control comprising a non-toxic biocide for safe handling by operating personnel and which does not present any danger to the environment .

DISCLOSURE OF THE INVENTION

According to one aspect, the invention consists in a method for control of microorganisms in a bulk quantity of water comprising the steps of:

(1) establishing in the water a dynamic equilibrium between (a) a concentration of an iodophor comprising a carrier and complexed iodine and (b) a concentration of free iodine such that available iodine is at least 0.2 ppm of the water;

(2) allowing the free iodine to interact with microorganisms, if any, in the water, whereby the free iodine is reduced to iodide; and

(3) continuously or repetitively oxidizing the iodide to iodine.

If desired, further amounts of iodophor or of a water-soluble iodine salt, or of an iodophor forming composition or solutions thereof may be added continuously or periodically and alone or in combination.

An iodophor is a loose complex of elemental iodine with a water-soluble carrier. The carriers are usually neutral polymers such as polyvinyl pyrrolidone, polyether glycols, polyvinyl alcohols, polyacrylic acid, polyamides and polyoxyalkylenes or a quaternary ammonium compound, in which the iodine is held as a complex. A concentration of free iodine dissolved in the water exists in equilibrium with the complexed iodine.

According to a second aspect the invention consists in a composition of matter comprising in combination a halogen complex and an oxidizing agent, said combination exhibiting a synergistic effectiveness for reduction of a bacterial population.

The halogen complex is preferably an iodophor and the oxidizing agent is desirably ozone or hydrogen peroxide.

PREFERRED EMBODIMENTS OF THE INVENTION

Preferred embodiments of the invention will now be described by way of example only.

In performing the method of the invention, one establishes a dynamic equilibrium (a) a concentration of an iodophor comprising a carrier and complexed iodine and (b) a concentration of free iodine such that available iodine is at least 0.2 ppm of the water. Typically the iodophor comprises a non-ionic surfactant as carrier. Use of a non-ionic carrier provides a low foaming composition which is particularly effective to penetrate microscopic crevices, pores and the like in which bacteria tend to breed and which tend to be inaccessible to many bactericides. Suitable non-ionic surfactants are those with low foam characteristics and meeting biodegradable requirements for environmental protection, such as the polyoxyethylene derivatives or polyoxypropylene block polymers or derivatives of linear fatty alcohols containing a low percentage of the polyoxypropylene group in the molecule, such as Pluriol PE 6800, Lutensol LF 304 both from BASF.

The most preferred oxidant is ozone which not only reconverts any iodide to iodine but also reconstitutes the iodine in a nascent monotomic state in which it is particularly effective.

Although all water-soluble oxidising substances such as the alkali salts of persulphates, perborates and periodates or chlorine dioxide are suitable, hydrogen peroxide or ozone are preferred as not leaving any residue, converting either to water or oxygen after oxidation.

Optionally a cyanuric acid carrier is present in the water.

The water may be shock treated with an iodophor to reduce the Total Bacterial Count ("TBC") to not more than log 3.0 and thereafter intermittently treating the water with an iodophor to provide not less than 0.2 pp of available iodine. Preferred embodiments of the invention have a number of advantages in comparison with systems which use continuous ozone injection alone for the control of microorganisms.

To obtain effective control, prior art ozone systems must operate continuously as they produce no residual effect when treatment ceases. In the event of disruption of the ozone supply, due for example to power or mechanical failure, the bacterial count can rise to above one million per millilitre in six hours. In contrast, the presence of the iodophor of the present invention ensures that the bulk water contains a reservoir of iodine and an appropriate free iodine concentration in such circumstances. While continuous ozonolysis is slow to reduce bacterial count and may require days to achieve a required count of below 10,000 per ml, depending on ozone strength and ambient temperatures, preferred embodiments of the present invention achieve in less than one hour rapid reduction in comparison with ozone.

Advantageously, in comparison with halogenation, preferred embodiments of the invention have minimal corrosive effect on metals. Although it is not essential to treat new or well-maintained cooling towers with anti-corrosive agents when treated according to the invention, it is advisable to include anti-corrosives in systems already showing a degree of rust formation. Suitable anti-corrosives are the phosphonate salts of zinc, chromium and iron as well as certain molybdenum salts.

It might also be advisable under certain climatic conditions favouring strong algae formation, to add copper salts to the water or incorporate the use of an ionizer chamber producing a slow stream of copper ion through the system to control their formation.

An important advantage of the invention is that there is a marked unexpected reduction in the TBC in time, using considerably less amounts of available iodine after regeneration, than when an iodophor is directly added. Ozone by itself does not show any appreciable reduction in TBC even after one hour while the method of the invention results in more than a thousandfold reduction in TBC within 15 minutes.

TBC Reduction

Av.I. From To Time

IODOPHOR 20 ppm 5.0 x 10' 2.0 x 10 30 min,

20 ppm 2.0 x 10 2.5 x 10' 30 min.

20 ppm 5.8 x 10' 2.0 x 10 30 min.

10 ppm 1.0 x 10' 1.0 x 10 30 min.

10 ppm 1.2 x 10" 6.0 x 10 30 min.

10 ppm 1.1 x 10' 5.2 x 10 30 min.

OZONE* 8.3 x 10' 6.2 x 10' 1 hour

2.6 x 10' 2.1 x 10' 1 hour

1.0 x 10 6.4 x 10 1 hour

IODOPHOR 2.2 ppm 3.6 x 10" 1.0 x 10' 15 min,

REGENERATED 2.9 ppm 4.1 x 10" 3.2 x 10^: 15 min.

WITH OZONE* 3.0 ppm 1.5 x 10' 1.0 x 10 15 min.

*0_ AT THE RATE OF 0.5 g/h per 200 L

The above table indicates unexpected synergism between the iodophor and ozone in achieving TBC reduction. The invention will now be more particularly described by way of example only with reference to various examples.

EXAMPLE 1

A cooling tower made by the Baltimore Air Coil Corporation U.S.A. was inoculated with flavo bacteria. The total bacterial count (TBC) was assayed as 6.8 x 10 . It was then dosed with an iodophor, made by adding 3.0 kg of finely divided iodine to a solution of 1.5 kg potassium iodide, 0.85 kg propylene glycol, 8.7 kg 81% phosphoric acid, and 26.0 kg Teric 12A6 (I.C.I.) . The mixture is slowly stirred at 35°C until all the iodine has dissolved and added to a sufficient amount of cooling tower water to yield an initial concentration of 20 ppm iodine.

2 After 30 minutes the TBC had fallen to 5.2 x 10 ; leaving the water in the cooling tower for 24 hours, the

TBC rose again 6.9 x 10 . The pH was checked and adjusted to a pH of approximately 7.2 to 7.4 to bring it within the range of normal industrial or public water and ozone injected for one hour at the rate of 3 - 4 g/hour every 24 hours.

The following table shows the results for 14 days treatment after initial dosing with the iodophor. TBC

Day

1

2

3

4

5

6

7

8

9

10

11

12

13

14

N.T. = not tested

The results clearly show that bacterial growth during this period due to the persistent antimicrobial activity of the iodophor remains below the internationally accepted limit of 5.5 x 10 5 for cooling tower water for 24 hours. After this period the tower was dosed with a follow up product made by dissolving 130 kg of potassium iodide in 35L of water and adding it to a mixture of 50 kg nonylphenol ethoxylate with 7.5 - 8 ml ethoxy and 2 kg propylene glycol to give a concentration of 20 ppm of iodide from which the iodine to form the iodophor was generated every 24 hours by use of ozone in the described manner. The ozone was supplied via a UV-ozone generator supplied by Ozonic P/L Sydney.

EXAMPLE 2

The microbicidal properties of the iodophor as in Example 1 were examined in accordance with the "Guide lines for testing of chemical disinfectants" Deutsche Gesellschaft for Microbiology and Hygiene (DGHM) 1972, using tap water with a pH of 6.8 and a pH of 8.0 and a hardness degree of 2. The test waters were mixed with the iodophor to achieve an iodine concentration of 0.4 ppm. The following test microorganisms were used. E. coli ATCC 11229 Ps. aeruginosa ATCC 15442 St. aureus ATCC 6538

Chlorella vulgaris (laboratory strain) The results are shown in the following table: PH = 6 . 8

Reaction Escherichia Pseudomonas- Staphylococ- Chlorella time coli aeruσinosa cus aureus vulσaris in mins. ϊ - (7) = 7

5 - - ++

10 - - - ++

15 - - ++

30 - - +

60 - - - +

120 -

PH = 8.0

Reaction Escherichia Pseudomonas- Staphylococ- Chlorella time coli aeruσinosa cus aureus vulσaris

_ _ __ _ _

5 - - ++

10 - - ++

15 - - ++

30 - - - +

60 - - - +

120 - Blank Values with non-treated water (growth control)

Symbols: - no growth + distinct growth

++ intensive growth Double determinations were made for all investigations.

The germ content of the test germ suspension was

7 approximately 10 reproducible germs per 1 ml.

EXAMPLE 3

Standard coupons of various metals were exposed two times for two months in the body of the cooling tower during the iodophor - ozone treatment as described in Example 1 to test the corrosive properties of the process. Average results of the tests are recorded in the following table:

* Anti-corrosion protective laquer. Trade Mark of Baltimore Air Coil Corporation, U.S.A. The results show clearly that the process only causes minimal, and for practical use, negligible corrosion, except for mild steel which is unsuitable for use in cooling towers and therefore rarely being found as part of them.

EXAMPLE 4

To a swimming pool containing 50,000 litres water at the beginning of the season an initial shock treatment of 800 ml of the iodophor as described in Example 1 is added in the evening.

Next day 20 ml of a 30% hydrogen peroxide solution is injected by an automatic dosing device. As a routine the regeneration of the iodine is to take place every day.

The time when all iodine to be generated is used up depends largely on the frequency and number of people bathing in it. This can be determined by a similar colour reaction as with chlorine.

The iodine content is then renewed by adding 400 ml of an iodophor producing solution to allow further generation of iodine by the hydrogen peroxide.

An amount of cyanuric acid or derivative might be added to avoid the destabilising effect of prolonged exposure to sunlight UV radiation.

EXAMPLE 5

To the cooling tower as described in Example 1, an iodophor forming composition made by dissolving 4.5 kg of potassium iodide in 50L of water, 0.80 kg propylene glycol, 8.7 kg 81% phosphoric acid and 26.0 kg Teric 12A6 are added. The mixture is slowly stirred until a clear homogeneous product is obtained and added in sufficient amounts to the cooling tower water to give an initial concentration of 40 ppm iodine. After the addition ozone is generated at a rate of 0.5 grams per hour for the first hour and repeated every 24 hours.

In order to keep the potassium iodide level up for generation of iodine losses due to bleeding, evaporation and air drift of the water during operation small doses can be injected or added to the make-up water to maintain the required level.

As will be appreciated by those skilled in the art from the teaching hereof, an iodophor may be used in combination with oxidants other than ozone or hydrogen peroxide with effect similar to that exemplified. Iodine complexes other than the exemplified iodophor may be used. Complexes of halogens other than iodine which are synergistically effective against bacteria in a manner analagous to those herein described are deemed to be within the inventive concept disclosed. The method may be carried out using automatic control equipment or by other means. The method of the invention may be embodied in other forms without departing from the scope hereof.

Claims

CLAIMS : -

1. A method for control of microorganisms in a bulk quantity of water comprising the steps of:

(2) allowing the free iodine to interact with micro-organisms, if any, in the water, whereby the free iodine is reduced to iodide; and

(3) continuously or repetitively oxidizing the iodide to iodine.

2. A method according to Claim 1 wherein the iodophor comprises a non-ionic surfactant.

3. A method according to Claim 1 or Claim 2 where the iodide is oxidized to iodine by using ozone.

4. A method according to any one of the preceding claims wherein a cyanuric acid carrier is present in the water.

5. A method according to any one of the preceding claims further comprising the step of shock treating the water with an iodophor to reduce the TBC to not more than log 3.0 and thereafter intermittently treating the water with an iodophor to provide not less than 0.2 ppm of available iodine.

6. A method according to any one of the preceding claims wherein the bulk water is recirculated.

7. A method according to any one of the preceding claims wherein further amounts of iodophor or of a water-soluble iodine salt, or of an iodophor forming composition or solutions thereof are added alone or in combination.

8. A method according to claim 7 wherein the further amounts are added continuously.

9. A composition of matter comprising in combination a halogen complex and an oxidizing agent, said combination exhibiting a synergistic effectiveness for reduction of a bacterial population.

10. A composition according to Claim 9 wherein the halogen complex is an iodophor.

11. A composition according to claim 9 or 10 wherein the oxidizing agent is ozone or hydrogen peroxide.