Testing free chlorine when superchlorinating

In some applications, such as fresh-cut product manufacturing, many regulations stipulate that free chlorine must be applied to the water at a concentration greater than 50 mg/L. Such levels are known as superchlorination.

What is superchlorination?

Superchlorination describes the process of adding chlorine in large quantities to overcome nitrogenous materials in water and achieve ‘breakpoint’.

In order to understand what ‘breakpoint’ is, we need to be able to differentiate between free and combined chlorine. Free chlorine usually exists in water as hypochlorous acid (HOCl) or the hypochlorite ion (^–OCl), with the proportion of each dependent on the pH of the sample. When nitrogenous material such as ammonia is present in solution, chloramines will form. There are three types of chloramines; monochloramine (NH₂Cl), dichloramine (NHCl₂) and trichloramine (NCl₃). The amount of free chlorine in a sample plus the amount of chloramines is equal to the total chlorine.

Free Chlorine + Combined Chlorine = Total Chlorine

Distinguishing between free and combined chlorine below the breakpoint is vital to ensure adequate disinfection.

Chloramines are weaker disinfectants than free chlorine so often a longer contact time or higher doses are required when used as a disinfectant.

ZONE 4

As more chlorine is added, the free chlorine begins to oxidise the chloramines. The point at which all the dichloramines and trichloramines are oxidised into nitrogen is the ‘breakpoint’ and is the point most superchlorination are seeking to achieve, as from this point, any additional chlorine added exists as free chlorine and therefore has more potent disinfectant properties.

Superchlorination of Fresh Produce

Superchlorination of fresh produce was historically the predominant method for treating fresh produce. This can be an effective way of reducing microbial load by 10 to 100 times. However, you need to ensure that the contact time is sufficient and carry out regular testing to check there is enough free chlorine present in the water. There has been a shift to alternative forms of disinfection recently due to concerns about chlorination by-products when superchlorinating.

Palintest sensor technology has been independently verified as the best test method for testing produce wash water. A study by CEBAS investigated 5 test methods, and our chronoamperometric sensor was found to be the best test method offering precise, real-time monitoring of wash water. Find out more about the study and why Kemio has been identified as the best method here.

Superchlorination of Pools and Spas

Superchlorination is not recommended for pools and spas as it can cause the production of unwanted by-products. However, there are a few occasions such as poor results from microbiological tests or a breakdown in usual treatment which may mean it is necessary to superchlorinate the water. To find out more about chlorine in the pool and spa sector click here.