IL153456A - Method of treating water containing an alkaline earth metal bromide or alkali metal bromide - Google Patents

Description

' 153456 'n I 453567 ΤΑΊΝ A METHOD OF TREATING WATER CONTAINING AN ALKALINE EARTH METAL BROMIDE OR ALKALI METAL BROMIDE 153456/3 BACKGROUND OF THE INVENTION This invention relates to the use of bromine (Br) for the treatment of water.

International Patent Publication No. WO 02/070404, the contents of which are incorporated herein by reference, relates to stabilised hypobromous aid solution for the treatment of water.

US Patent No. 5,422,126 teaches a method for producing well-defined aqueous hypobromous acid solutions from a mixture of hydrobromic acid and sodium hypochlorite and introducing an additive to suppress bromate formation. These solution are stated as being useful as biocides for water sanitation.

US Patent No. 5,946,126 teaches a method for producing stabilized aqueous alkali or alkaline earth metal hypobromite solutions.

EP 0 31 1 954 teaches the addition of a sulfamate to water to be treated with chlorine, in the form of hypochlorous acid or sodium hypochlorite together with NaBr, in order to prevent decomposition of phosphonates.

None of these documents teaches or suggests the utilization of bromide present in the water to be treated, nor do they relate to the benefits which can be obtained by the process of the present invention which is using bromide already contained in a water solution, while at the same time lowering the bromide concentration in the water.

It is an object of this invention to provide a new method for treating water, particularly water that has a bromide content.

SUMMARY OF THE INVENTION According to a first aspect of the invention there is provided a method of treating water containing an alkaline earth or alkali metal bromide, the method including the steps of: 1. determining the bromine demand of the water; 2. adding sufficient hypobromous acid solution to the water to satisfy or almost satisfy the bromine demand; and 3. adding sufficient alkali or alkaline earth metal hypochlorite solution, such as a sodium hypochlorite, potassium hypochlorite, lithium hypochlorite, magnesium hypochlorite or calcium hypochlorite to activate the alkaline earth or alkali metal bromide in the water and to provide residual bromine in the water.

Usually, the alkali or alkaline earth metal hypochlorite solution will have a pH of from 11 to 14.

The water may contain from 0.5mg/i to 80mg/£ bromide.

The alkali or alkaline earth metal bromide in the water may be as a result of naturally occurring sodium bromide, or it may be added by dissolving an alkali or alkaline earth metal, such as sodium bromide in the water, prior to adding the hypobromous acid solution.

Advantageously, the alkali or alkaline earth metal hypochlorite solution is added to the water at a ratio of alkali or alkaline earth metal bromide to alkali or alkaline earth metal hypochlorite of 1 :1.9-7.4.

Advantageously, the hypobromous acid solution is a stabilised hypobromous solution.

Preferred stabilised solutions according to the invention contain the following amounts of hypobromous acid and cyanuric acid: 1. A hypobromous acid concentration of 20% and 0,2 ppm cyanuric acid. 2. A hypobromous acid concentration of 10% and 0,3 ppm cyanuric acid; and 3. A hypobromous acid concentration of 5% and 0,4 ppm cyanuric acid.

The solution may be a sodium or potassium based hypobromous acid solution, but for the purposes of drinking water and particularly irrigation water, the solution is a potassium based hypobromous acid solution.

Typically, a potassium based hypobromous acid solution has a potassium concentration of less than 40%.

The preferred stabilised solutions according to the invention for treating irrigation water contain the following amounts of hypobromous acid, potassium, and cyanuric acid: 1. a hypobromous acid concentration of 20%, a potassium concentration of 35% and 0,2 ppm cyanuric acid; 2. a hypobromous acid concentration of 10%, a potassium concentration of 25% and 0,3 ppm cyanuric acid; and 3. a hypobromous acid concentration of 5%, a potassium concentration of 15% and 0,4 ppm cyanuric acid.

DESCRIPTION OF EMBODIMENTS Any sections of the specification that fall outside the scope of the claims are not part of the present invention.

This invention relates to a method for treating water such as drinking water, irrigation water, cooling tower water and sewerage effluent having an alkali or alkaline earth metal bromide content of from 0.5 to 1.5 mg/f, with a hypobromous acid solution. The alkali or alkaline earth metal bromide content may be as a result of naturally occurring bromides in the water, or an alkali or alkaline earth metal of a bromide, (such as sodium bromide), may be added to the water to provide the bromide content.

In a first step, the sodium bromide content of the water to be treated is tested to ascertain the sodium bromide content of the water, and secondly to ascertain the bromine demand. The bromine demand of the water is measured to determine the amount of hypobromous acid (HOBr) that must be applied to water to produce an available active bromine residue after a selected period of contact.

Thereafter, sufficient hypobromous acid solution is added to the water to satisfy or almost satisfy the bromine demand. Advantageously, the hypobromous acid solution is a stabilised acid solution containing from 5-20% hypobromous acid, at a pH of 8-9, preferably 8.8, and containing cyanuric acid as the stabiliser, the cyanuric acid not exceeding 1 ppm. In a typical scenario, where the bromine demand is found to be 1 ,2mg/f, the water is dosed with 1 mg/t active bromide i.e. 5mt of a hypobromous acid solution containing 20% hypobromous acid, at a pH of 8.8 and 0.2ppm cyanuric acid is added per litre of water to be treated. The hypobromous acid satisfies or almost satisfies the bromine demand and kills microorganisms such as bacteria in the water.

Thereafter, an alkali or alkaline earth metal hypochlorite solution having a pH of 11-14 is added to the water to activate the sodium bromide in the water, to provide active residual bromine in the water. Usually the hypochlorite will be sodium hypochlorite, which is added according to the amount of bromide in the water (calculated in the first step above), to provide a ratio of bromide to hypochlorite of 1 :1.89-7.4. For example, if there is 0.5mg/. sodium bromide in the water 0.9mg/f of a 10% sodium hypochlorite solution is added. Forty five minutes after the addition of the hypochlorite solution, the sodium bromide content of the water is reduced to less than 0.1 mg/t.

The process of the invention finds particular application for water, such as that found in Israel, which has inherent concentrations of sodium bromide of from 0.5mg/f to 80mg/i. The process not only activates the bromide ions from sodium bromide so that they can be used in water treatment, but also lowers the sodium bromide concentration in the water, after treatment.

The process of the invention finds particular application for water, such as that found in Israel, which has inherent concentrations of sodium bromide of from 0.5mg/i to 80mg/f. The process not only activates the bromide ions from sodium bromide so that they can be used in water treatment, but also lowers the sodium bromide concentration in the water, after treatment.

Claims (3)

6 153456/3 Claims 1. A method of treating water containing an alkaline earth metal bromide or alkali metal bromide, the method including the steps of: 1. determining the bromine demand of the water; 2. adding sufficient hypobromous acid solution to the water to satisfy or almost satisfy the bromine demand; and 3 adding sufficient alkali or alkaline earth metal hypochlorite solution to activate the alkali or alkaline earth metal bromide in the water and to provide residual bromine in the water. 2. The method according to claim 1 , wherein the alkali or alkaline earth metal hypochlorite solution is sodium hypochlorite, potassium hypochlorite, lithium hypochlorite, magnesium hypochlorite or calcium hypochlorite solution. 3. The method according to claim 2, wherein the alkali or alkaline earth metal hypochlorite solution is a sodium hypochlorite solution. 4. The method according to claim 1 , wherein the alkali or alkaline earth metal hypochlorite solution has a pH of from 11 to 14. 5. The method according to claim 1 , wherein water contains from 0.5mg/i to 80mg/i bromide. 6. The method according to claim 1 , wherein the alkali or alkaline earth metal hypochlorite solution is added to the water at a ratio of alkali or alkaline earth metal bromide to alkali or alkaline earth metal hypochlorite of 1 :1.9-7.4. 7. The method according to claim 1 , wherein the hypobromous acid solution is a stabilised hypobromous acid solution. 7 153456/3 The method according to claim 7, wherein the stabilised hypobromous acid solution contains the following amounts of hypobromous acid and cyanuric acid: 1. A hypobromous acid concentration of 20% and 0.2 ppm cyanuric acid; or 2. A hypobromous acid concentration of 10% and 0.3 ppm cyanuric acid; or 3. A hypobromous acid concentration of 5% and 0.4 ppm cyanuric acid. 9. The method according to claim 7, wherein said stabilised hypobromous acid solution is a sodium or potassium based hypobromous acid solution. 10. The method according to claim 9, for treating drinking or irrigation water. 11. The method according to claim 10, wherein the potassium based hypobromous acid solution has a potassium concentration of less than 40%. 12. The method according to claim 11 , for treating irrigation water, wherein the stabilised hypobromous acid solution contains:

1. A hypobromous acid concentration of 20%, a potassium concentration of 35% and 0.2 ppm cyanuric acid; or

2. A hypobromous acid concentration of 10%, a potassium concentration of 25% and 0.3 ppm cyanuric acid; or

3. A hypobromous acid concentration of 5%, a potassium concentration of 15% and 0.4 ppm cyanuric acid. MILB 90167/4.2