1. Background
Many municipal water treatment plants do not perform permanent disinfection of tap water, but instead implement an emergency chlorination process. This process is activated when needed, adding chlorine to the tap water as a disinfectant.
2. Measurement Requirements
The special feature of emergency chlorination is that it's rarely necessary, meaning the water flowing through water treatment plants is usually non-chlorinated. Traditional measurement techniques often face the problem of biofilm buildup on the membrane, which can eventually malfunction the sensor. Therefore, some operators periodically add extra chlorine to prevent this buildup, even though it's unnecessary from the perspective of tap water quality. If a larger dose of chlorine isn't added, the system must be inspected and mechanically cleaned regularly. In some cases, it may be necessary to replace the membrane and recalibrate the system.
If the gradual aging of the sensor goes unnoticed, and during emergency chlorination, the diaphragm is simply replaced when the measurement system fails to start normally, it can lead to very serious consequences.
• By measuring the chlorine content in tap water, the free chlorine levels during emergency chlorination at water treatment plants can be determined.
• High measurement accuracy can be achieved thanks to the easy-to-maintain thin-film-free sensor and automatic sensor cleaning function.
• Calibration without neutron emission tomography is performed by comparing the result with the expected DPD test value.
Once chlorine is added to water, the legal limits for chlorine levels in wastewater must be monitored (0.1 mg/L in Germany, according to the Drinking Water Ordinance). To monitor these limits and ensure accurate chlorine measurement, online measurement techniques are often used. Unlike traditional sampling and laboratory testing, this technique allows for continuous monitoring of values.
In addition, the conductivity, pH value, turbidity, and flow rate of the water at the waterworks outlet are measured along with the chlorine content.
Schematic diagram of typical measurement points at the outlet of a waterworks
In this example, only measurement point 2 is described. During monitoring, in addition to the chlorine level measurement system, a second measurement system (measurement point 1) is sometimes used to control the disinfectant ratio. To supplement this, a typical measurement point is marked at the waterworks outlet in the diagram.
3. Cologne Solutions
At the waterworks outlet, an OPTISYS CL1100 measurement system with an automatic sensor cleaning system and a membrane-free constant potential sensor is used to monitor chlorine levels during the process. Measurements are performed via a bypass measurement with an open outlet.
4. Customer benefits
Unlike other similar sensors, the constant potential sensor in the OPTISYS CL1100 measurement system is uncoated, so it will not be clogged by biofouling (which forms naturally in unchlorinated water).
The sensor used in the OPTISYS CL1100 has two external gold electrodes whose metal surfaces are resistant to biofouling. Furthermore, thanks to the sensor's automatic cleaning function, the electrodes are cleaned daily without the need for chemical reagents.
Therefore, OPTISYSCL1100 is a ready-to-use product that can function normally even without chlorine for a long time.
The OPTISYSCL1100 has been certified by the IWWRheinisch-WestfälischesInstitutfürWasser (Water Resources Management Agency) in Mühlheim, Germany, for its accuracy and applicability in measuring chlorine content in tap water.
5. Use the product
OPTISYSCL1100
• Free chlorine, chlorine dioxide, and ozone measurement system
• A ready-to-use measurement system that can measure free chlorine content, monitor flow rate, and provide automatic temperature compensation.
• Automatic sensor cleaning system
• For flow rates greater than 30 l/h, measurements are unaffected by flow rate.
• Simple calibration is performed based on the DPD by comparing it with the test value.
• pH compensation can be selected when the pH fluctuation is greater than 7.5.
