Methods for Determining Chlorine Dioxide and Chorite in Water
Chlorine dioxide is used as a disinfectant in water treatment due to its effectiveness against various microorganisms without forming disinfection byproducts like trihalomethanes. In the disinfection process, chlorite is formed as a byproduct, and its levels are carefully regulated to comply with health and safety standards. Proper dosage and monitoring ensure that chlorine dioxide effectively treats water while maintaining water quality and minimizing potential adverse health effects associated with chlorite.
The analysis of chlorine dioxide and chlorite in water can sometimes be difficult as chlorine dioxide is a volatile molecule, and standard test methods for measuring chlorine dioxide and chlorite can suffer interferences from other species.
Common Test Methods
There are a variety of methods available for testing chlorine dioxide and chlorite in water. Many are laboratory based, however there portable colorimetric and electrochemical methods are also available.
Ion chromatography is a laboratory-based method which works by separating out ions in solution. This method is used for measuring both chlorine dioxide and chlorite, and it is the standard method for measuring chlorite (4110 Determination of Oxyhalides using Ion Chromatography).
Colorimetric methods include DPD and Lissamine Green. Traditionally, the most used colorimetric method for testing chlorine dioxide was the DPD method. This method has been removed as a standard method due to concerns over chlorite interference, however it is still an EPA (Environmental Protection Agency) approved method. Lissamine Green is another indicator used to measure chlorine dioxide and chlorite. This is not a standard method, but it is an EPA approved method for measuring chlorine dioxide.
Amperometric methods are also used. Standard method 4500–ClO2 C and 4500–ClO2 E are both amperometric methods used for the measurement of ClO2 in water. Both methods are electrochemical methods which work by measuring current flow when a fixed voltage is applied to the electrode. This is the method Kemio Disinfection is based on.
More information on these and other standard methods for measuring chlorine dioxide and chlorite can be found in APHA AWWA WEF Standard Methods for the Examination of Water and Wastewater.
Advantages of Kemio
The sensor technology employed by Kemio can reliably speciate between chlorine dioxide and chlorite making it a useful tool to monitor chlorine dioxide disinfection process. It comes in portable and rugged kit to be used in field to monitor residuals and gives results in a few minutes. The readings are not impacted by coloured particles or turbid water. With its ease of use and stepwise onscreen instructions it becomes the choice of operator in the field.
The method to determine chlorine dioxide and chlorite by amperometry using disposable sensor technology (Palintest 2020c). has been approved by EPA under the method ChlordioX Plus, Rev. 1.1, as discussed in Adams 2020d on the Federal Register.
US EPA Regulations
The US EPA require that both chlorine dioxide (ClO2) and chlorite (ClO2–) are monitored daily at the start of a distribution network. They also specify that chlorite is measured less frequently at various points throughout a network.
The following are methods that have been approved by the USEPA for chlorine dioxide monitoring:
- Amperometric titration (Standard Method 4500 – ClO2 E)
- Colorimetric DPD (Standard Method 4500–ClO2 D – Reserved)
- Colorimetric Lissamine Green (USEPA Method 327.0 v1.1)
DPD has been removed as a standard method for determining ClO2 by the AWWA Standard Methods committee.
ChlordioX Plus, Rev. 1.0 (Palintest 2013) was approved as being equally effective, relative to the approved Standard Method 4500–ClO2 E (APHA 1998) for the analysis of chlorine dioxide and chlorite in drinking water, in the June 19, 2014, expedited methods approval action (USEPA 2014). EPA reviewed the changes that were made and has determined that ChlordioX Plus, Rev. 1.1 is equally as effective relative to the approved ChlordioX Plus, Rev. 1.0. The basis for this determination is discussed in Adams 2020d. Therefore, EPA has approved ChlordioX Plus, Rev. 1.1 for the analysis of chlorine dioxide and daily monitoring of chlorite in drinking water.
