BREAKPOINT CHLORINATION PDF

Where water already contains ammonia the production of chloramine is unavoidable when chlorine is added. To ensure the production of free chlorine to enhance bacterial kill, substantially more chlorine may have to be added because the additional chlorine at first only causes a reduction of the chloramines by oxidation. Only when this reaction is completed does the addition of further chlorine produce free chlorine. Stoichiometrically the breakdown of ammonia to nitrogen commences at a chlorine:ammonia as N ratio of and completes at a ratio of 7.

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Oxidation-reduction potential Continual breakpoint chlorination Continual breakpoint chlorination uses the continual addition of chlorine after bathers have left the pool to oxidise combined chlorine so that all of the total chlorine exists as free chlorine. Last updated: 09 April Content 1 Graphical representation of breakpoint chlorination The above graph demonstrates the theory of continuous breakpoint chlorination. On the right vertical axis is the ammonia-nitrogen i. The bottom horizontal axis represents the ratio of chlorine Cl2 to ammonia NH2 by weight which is zero on the left and increases to the right.

The bottom horizontal axis also represents time and increases from left to right. The breakpoint curve is a graphical representation of chemical relationship that exists with constant addition of chlorine to swimming pool water containing a small amount of ammonia-nitrogen.

This graph represents a swimming pool where bathing has ceased and no further ammonia-nitrogen is introduced into the pool. During an overnight period sodium hypochlorite is added at a constant rate. This curve has three zones. Chlorine is then added at a constant rate. The principal reaction in Zone 1 is the reaction between chlorine and the ammonium ion.

This reaction results in a Measured Total Chlorine of only monochloramine to the hump in the curve. The hump occurs, theoretically, at chlorine to ammonia-nitrogen weight ratio of This ratio indicates the point where the reacting chlorine and ammonia-nitrogen molecules are present in solution in equal numbers.

Monochloramine does not readily degrade. Zone 2 The breakpoint phenomenon occurs in this zone which is also known as the chloramine destruction zone. As the weight ratio exceeds , some of the monochloramine starts reacting with further addition of chlorine to form dichloramine, which is about twice as germicidal as monochloramine.

A pure dichloramine residual has a noticeable disagreeable taste and odour, while monochloramine does not. Total Chlorine Applied is still increasing and both the Concentration of ammonia-nitrogen and Measured Chlorine Residual decrease rapidly. This rapid decrease occurs because the dichloramine is reacting immediately with additional hypochlorous acid in a series of destruction reactions to form volatile compounds and other by-products such as nitrogen gas, nitrate and chloride.

Therefore, ammonia and chlorine are consumed in the reactions and lost from the pool. Thus, additional chlorine is required to destroy ammonia and chloramines. The breakpoint Point A is the point of the lowest concentration of Measured Chlorine Residual where nuisance chlorine residuals remain and where ammonia-nitrogen is not detected. The nuisance chlorine residuals are mainly organic chloramines which cannot be oxidised any further by reacting with hypochlorous acid.

Zone 3 Zone 3 is to the right of the breakpoint Point A and is where a free chlorine residual will appear. The total residual consists of the nuisance residuals plus free chlorine. If trichloramine is formed, it will appear in this zone. In reality, ammonia-nitrogen does not stay static but is continually added while the pool is open to the public. To achieve breakpoint chlorination, chlorination must continue after the pool has been closed to the public to ensure oxidation of the additional chloramines every night.

The shape of the breakpoint curve is affected by contact time, temperature, concentration of chlorine and ammonia, and pH.

Higher concentrations of the chemicals increase the speed of the reactions. Further information Public Swimming Pool and Spa Pool Document provides detailed explanations and information on disinfection, pool chemistry, risk assessment and other issues relevant to swimming pool operation.

Appendix A provides more detail on the other processes to achieve breakpoint chlorination. Public swimming pool issues may be discussed with an environmental health officer at a local Public Health Unit, or at your local council. Content 2 Contact page owner: Environmental Health Patients and public.

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What is breakpoint chlorination?

Oxidation-reduction potential Continual breakpoint chlorination Continual breakpoint chlorination uses the continual addition of chlorine after bathers have left the pool to oxidise combined chlorine so that all of the total chlorine exists as free chlorine. Last updated: 09 April Content 1 Graphical representation of breakpoint chlorination The above graph demonstrates the theory of continuous breakpoint chlorination. On the right vertical axis is the ammonia-nitrogen i. The bottom horizontal axis represents the ratio of chlorine Cl2 to ammonia NH2 by weight which is zero on the left and increases to the right. The bottom horizontal axis also represents time and increases from left to right. The breakpoint curve is a graphical representation of chemical relationship that exists with constant addition of chlorine to swimming pool water containing a small amount of ammonia-nitrogen.

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NSW Health

It is these pollutants which can cause stinging eyes and mal odours. These are primarily measured as ammoniacal nitrogen The effectiveness of the disinfection process is related to the pH of the water and the lower the pH the greater the efficiency of disinfection. The process of water treatment used in the UK is known as breakpoint chlorination. What does breakpoint chlorination mean? Breakpoint chlorination is the point where the demand for chlorine has been fully satisfied in terms of chlorine addition to the water. In other words, the chlorine has completely reacted with the bather pollutants leaving a zero chlorine residual.

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