Analytical Instrumentation & Environmental Monitoring

A quick guide to disinfection

October 2023 Analytical Instrumentation & Environmental Monitoring

Disinfection in drinking water

The distribution system in a drinking water network provides a reliable supply of high-quality water to consumers. Endress+Hauser’s range of robust, low-maintenance sensors are ideal for monitoring disinfectant levels in the water. For example, to prevent any recontamination of the treated water as it leaves the waterworks, a small quantity of free chlorine or chlorine dioxide is added. This level of disinfection is often in the trace range. To keep track of these very low levels, Endress+Hauser’s Memosens CCS51D sensor for free chlorine or the Memosens CCS50D sensor for chlorine dioxide can be used. Both these sensors provide high-precision measurement with

long-term stability, and ensure consistent disinfection monitoring even at low water volumes. They feature an extremely fast response time, enabling prompt reaction to process changes and efficient process control.

Free chlorine and chlorine dioxide are residual disinfectants. They retain their disinfectant properties during distribution, and are therefore ideally suited to protecting the distribution network. Ozone, on the other hand, is a highly reactive oxidant but it does not form a residual. This makes it suitable for the disinfection of water during the actual treatment process but not for long-term disinfection in the distribution network. Endress+Hauser’s CCS58D sensor measures ozone. The robust sensor membrane with its high surfactant resistance provides high-precision measurement with an almost exclusive specificity for ozone, ensuring reliable disinfection monitoring.

Total chlorine is a combination of free and bound chlorine, and is a good indicator of residual disinfectants in discharge water. The Memosense CCS120D provides reliable monitoring of total chlorine in the water treatment plant’s outlet. It resists corrosion and moisture, enables laboratory calibration, and facilitates predictive maintenance. Maintenance effort is reduced due to the easy replacement of the electrolyte and membrane cap.

Breaking down pathogens

All three disinfectants inactivate pathogens by breaking down their cell walls. Chlorine is particularly effective in the case of certain bacteria, while chlorine dioxide also acts on viruses and single-celled organisms, and ozone oxidises almost everything due to its reactivity.

Disinfection in seawater

In many arid regions of the world, drinking water is generated from desalinated seawater. It is also used as process and cooling water in a wide range of industrial applications. The seawater is often disinfected before the desalination process. The purpose is to minimise its biological activity, thus maximising the service life of the downstream filters and the desalination system.

Seawater contains bromine. Hypobromous acid can be generated through the addition of hypochlorous acid. This too has powerful disinfectant properties and can be measured using Endress+Hauser’s CCS55D free bromine sensor, which also features a fast response time. It is suitable for a wide range of water qualities and provides high precision, stable measurement in seawater.

Disinfection in effluent from wastewater treatment plants

Once the wastewater treatment process is complete, the effluent is usually discharged into natural surface waters. Particularly in the dry season, these may consist primarily of effluent from the treatment plant − a case for disinfection.

This effluent typically contains low levels of ammonium ions, and this leads to the formation of chloramines when free chlorine is present. This can be reliably detected at the outlet, again using Endress+Hauser’s CCS120D total chlorine sensor. However, this sensor is sensitive to almost all oxidising components and is therefore no longer selective. If legislation makes it necessary to measure free chlorine separately, free chlorine is added until all chloramines are re-oxidised. This method is referred to as breakpoint chlorination.

Disinfection in cooling applications

Water is used as a cooling medium in industries ranging from power generation to food production. Cooling capacity can be maximised by minimising the buildup of any biofilm. Disinfectant is added to cooling water to prevent the formation of a layer of bacteria in the cooler pipes. Chlorine dioxide has proven to be effective here, as it acts across a wide pH range and retains its effectiveness even when pH-elevating corrosion inhibitors are added.

The choice depends on the application

Thanks to Memosens digital technology, all Endress+Hauser sensors combine maximum process and data integrity with simple operation, and provide the perfect basis for predictive maintenance. The choice of disinfection method depends on the application. Ozone treatment and UV irradiation are both highly energy-intensive processes. While chlorine-based methods of disinfection do not require any energy input, they have the potential to change the chemical composition of the finished product. Future use of disinfection methods will be determined by the value we assign to the finished product and the energy consumption involved.


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