Ammonia (Ammonium) Measurement in Water: Process Analyzers
Ammonia/ammonium measurement in wastewater, process water and sour water lines: ion-selective electrode online analyzers and NH₄-N analysis systems.
Measurement methods: Ion-Selective Electrode
What are ammonia and ammonium in water, and why are they measured?
Ammonia (NH₃) and ammonium (NH₄⁺) are the main forms of nitrogen compounds in water, and they convert into one another depending on pH. In wastewater treatment plants, ammonium nitrogen is the main monitoring parameter for nitrification and denitrification processes; it is measured continuously for aeration control and discharge quality. In aquatic environments, ammonia is toxic to living organisms and leads to oxygen consumption in receiving waters. In refineries, NH₄-N monitoring on sour water and stripped water lines is used for stripper unit performance.
Where is ammonia measured?
- Wastewater treatment plants: At aeration basins and outlet points.
- Refinery sour water and stripped water lines: At the stripper outlet.
- Cooling and process water: In tracking contamination and leakage.
How is ammonia measured?
Online ammonia analyzers use an ammonia-sensitive ion-selective electrode (ISE). The sample's pH is raised with a base to convert ammonium to ammonia; an electrode with a gas-permeable membrane forms a potential dependent on the amount of ammonia in the sample, and this value is converted to concentration. The analyzer is calibrated with standard solutions; reagent consumption and electrode life should be included in the maintenance plan. Versions with a protective enclosure make field installation easier.
Choosing an ammonia analyzer
- Expected ammonium range and sample matrix
- Sample filtration (wastewaters with a high suspended solids load)
- Reagent and electrode maintenance interval
- Need to monitor NH₄-N, pH and conductivity in one panel
Ammonia (water) measurement with Tetra
Tetra supplies the Thermo Orion 2110XP ammonia analyzer in Türkiye and provides installation, supply of reagents and consumables, commissioning, calibration and service. Tetra pH and conductivity analyzer systems (ATEX) are also associated with this measurement.
Frequently asked questions
What is the difference between NH₃, NH₄⁺ and NH₄-N?
NH₃ is free (un-ionized) ammonia and NH₄⁺ is the ammonium ion; their ratio depends on pH and temperature, and the NH₃ share rises at high pH. NH₄-N expresses the amount of nitrogen in ammonium and ammonia in terms of nitrogen, and it is the most common form of reporting in wastewater legislation and process control. When comparing results, check which form is used, because a value given as NH₄⁺ is approximately 29% higher than the NH₄-N value.
What methods are used for ammonia measurement?
In online measurement, ammonia electrodes (ISE) with a gas-permeable membrane and indophenol/salicylate-based colorimetric analyzers are common. Ammonium ISE probes immersed directly in the aeration basin are also used; these work without reagent but can be affected by ions such as potassium and need more frequent verification. Laboratory verification is generally carried out with photometric test methods.
What factors disturb an ammonia analyzer's measurement?
Buildup of oil, biofilm or deposits on the membrane surface slows the electrode response and causes drift. If the sample's pH is not raised enough, not all the ammonium converts to ammonia and a low reading results. Compounds that can pass through the membrane, such as volatile amines, can also interfere.
How are calibration and electrode maintenance planned for an ammonia analyzer?
The analyzer is calibrated with standard solutions of known concentration; calibration frequency is determined by the sample matrix and the manufacturer's recommendation. Periodic replacement of the membrane and internal filling solution, tracking of the base reagent and cleaning of the sample filter should be part of the maintenance plan. In dirty wastewaters, maintenance intervals are kept shorter than in clean process waters.
Products measuring this parameter
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