Systematic disinfection is an essential step in water treatment and is legally required to protect people and systems in many areas. However, high doses of disinfectants can be toxic. Free chlorine sensors detect chlorine dioxide in drinking water, process and reuse water, pool water or seawater to ensure proper disinfection.
The choice of bromine and chlorine sensors and transmitters depends on their application:
Free chlorine is the most important disinfectant in water treatment due to its easy control and important disinfectant effect. Free chlorine sensors are used in the following cases:
- Drinking water – to ensure adequate disinfection
- Food – for the preparation of bottles and hygienic packaging
- Pool water – for an effective disinfectant dose
Chlorine dioxide is chosen more and more as a disinfectant because it has less corrosion and is not independent of pH. Chlorine dioxide sensors are used in the following cases:
- Cooling systems or towers
- Drinking water
- Rinse the packaged vegetable juice
- Desalination program to prevent reverse osmosis ClO2
Total chlorine is a good indicator of disinfectants remaining in the drain water. Sensors used in WWTP networks:
- To measure the status of wastewater disinfection.
- To control water reuse
Due to the unique chemical properties of this environment, free bromine is often used in seawater. Free bromine sensors apply in the following cases:
- Seawater re-uses and processes water
- Desalination program
- Fish farming – to ensure adequate disinfection of wastewater
- Cooling systems characterized by high pH values
Principle of ammetric measurement
Chlorine dioxide sensors have a working electrode that is separated from the environment by a thin membrane. Chlorine dioxide coming from the environment is diffused through this membrane and reduced at the working electrode. The circuit is completed using a counter electrode and an electrolyte. The reduction of electrons in the working electrode is proportional to the concentration of chlorine dioxide in the medium. This process works in a wide range of pH and temperature.
Measurements of available free chlorine are similar . Here, hypochlorous acid diffuses through the membrane and causes a reaction. The presence of hypochlorous acid in the medium depends on the pH value. This dependence is compensated for by measuring the pH in the current set and balancing in the transmitter.
The measurement of free bromine is very similar to the measurement of free chlorine but is possible in a more alkaline range.
To measure total chlorine, hypochlorous acid plus chloramines are involved in a complex reaction system.
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