Chlorination and chlorate formation

by B . Grochowski

Both in the municipal drinking water supply and in the food and beverage industry (for ingredient and process water), chlorination is regularly relied upon as the primary means of disinfection.  For the municipal water supply, residual disinfection is necessary to ensure adequate disinfection throughout the entire distribution network.  As a result of the chlorination process, disinfection by-products (DBPs) can be formed.  Many of these DBPs such as trihalomethanes (THMs) and haloacetic acids (HAAs) have been identified as potential carcinogens.

Among beverage manufacturers in particular, there is additional concern around the possibility of chlorate formation.  Chlorates are now part of the USEPA Unregulated Contaminant Monitoring Rule (UCMR 3) for Public Water Systems and it has been identified as an emerging contaminant.  Food and beverage facilities should be aware of the amount of chlorates in their incoming water.  In addition, it is important to consider how chlorates are formed if a food and beverage facility is relying on chlorination as their primary disinfection method in their process.  This is especially important for water used as an ingredient, but may also apply to process water that comes into direct contact with a food or beverage product.

The American Water Works Association (AWWA) and Water Research Foundation (WRF) published some excellent tips on control strategies to limit chlorate formation from on-site stored hypochlorite.  Some of these tips are quite reasonable and should be easy to implement including dilution of hypochlorite on-site, pH control, and just-in-time delivery.
https://www.awwa.org/Portals/0/files/legreg/documents/HypochloriteAssess.pdf

For the food and beverage industry, several tactics should be considered to ensure unwanted chlorates are not introduced into your product.  These would include…

• Regularly monitor incoming chlorate concentrations from your municipal water supply
• Implement control strategies (per AWWA recommendations) for any hypochlorite stored on-site
• Consider water treatment barriers to remove chlorate before water is used as an ingredient
• Consider alternate disinfection strategies (such as UV or ozone) as the primary means of disinfection
• Consider a dual disinfection strategy with complementary technologies such as UV and chlorine so chlorine concentrations (and chlorate formation) can be reduced

More information from the World Health Organization on chlorate exposure concerns can be found at the link below.
https://www.who.int/water_sanitation_health/dwq/chemicals/chlorateandchlorite0505.pdf

More information from the AWWA on the prevalence of chlorates in the municipal drinking water supply can be found at the link below.
https://www.awwa.org/Portals/0/files/legreg/documents/2014AWWAChlorateBriefingPaper.pdf