Measure NH₄: Wet-chemical analyzer or ion-selective sensor?

You want to monitor ammonium (NH₄ ) at a wastewater treatment plant or in a waterbody? And you wonder which measuring method is the better one? Then this article is the right one. Here you will learn the differences between an ion-selective sensor and a wet-chemical automatic analyzer and where they are used.

The right technology for your challenges in aeration tanks and at the outlet

Together with nitrate, ammonium is the two most important nitrogen parameters in wastewater treatment. Compliance with the limit values of these two parameters - in the citation forms NH₄-N and NO₃-N - and thus their monitoring are central tasks of a wastewater treatment plant. In addition to monitoring at the outlet of the plant, upstream control of biological treatment stages is the classic area of application. In the nitrification process, ammonium is oxidized via nitrite to nitrate. Here, measurement technology helps to display the process transparently so that it is possible to react quickly to changing concentrations. The same applies to deammonification, where the existing ammonium is only partially converted to nitrite in a first step. Details on the processes can be found here.

Outside of wastewater treatment, monitoring of NH₄ also takes place in surface waters (especially rivers). In addition to ammonium, the pH value must also be monitored, since ammonium is converted into ammonia, which is toxic to fish, at pH values of 7 and above. This is one of the reasons why the specified effluent values of wastewater treatment plants must be correspondingly low.

Xylem Analytics Germany develops, manufactures and distributes analytical measurement technology worldwide and has over two decades of experience and expertise in the water and wastewater industry. With our proven IQ Sensor Net technology, we offer sensors and instruments for the analysis of all important parameters.

Two methods exist for the continuous measurement of ammonium - sensors with ISE electrodes and wet-chemical ammonium analyzers. This report describes the differences and areas of application.

Product selection - Our recommendation

Automatic analyzer for monitoring of sewage algae outlets and water bodies

Due to its high accuracy even in the lower measuring range, the Alyza IQ NH₄ analyzer is particularly suitable for monitoring the outlet of sewage treatment plants or surface waters. Nevertheless, it can also be used in nitrification, provided that very accurate measurement is already required there and at the same time one can cope with a measurement interval of ten minutes or longer. Consumables and chemistry are easily replaceable by the end user. A maintenance contract is therefore not mandatory. On our product details page Alyza IQ NH4 you will find further information.

ISE sensor for process control in biological treatment

The ion-selective sensors AmmoLyt®^PLUS 700 IQ and VARiON®^PLUS 700 IQ, on the other hand, are ideal for controlling biological treatment thanks to their continuous measurement and high speed. With the help of this real-time data, processes such as nitrification or deammonification can be transparently displayed and optimized in an energy-efficient manner. You can find an application example here:

The good accuracy is completely sufficient for this application. The sensors are also convincing due to the long lifetime of the electrodes (12-18 months), which can also be replaced individually. The use in the outlet is possible depending on the required accuracy. On our product detail pages you will find further information for the sensors AmmoLyt® PLUS700 IQ and VARiON® PLUS700 IQ.

The products in comparison

Both measuring methods are established as standard procedures and provide reliable measurement values. The decisive question in product selection is the area of application or the resulting requirements:

• Biological treatment requires fast, continuous measurement in order to control the process without delays. ISE sensors with their good accuracy are the ideal choice for this.

• The monitoring of outlet or surface waters requires above all a very high accuracy, even at low concentrations. Here, the wet-chemical analyzer according to DIN 38 406 is the better choice.

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