ISE or spectrometer for measuring ammonium NH4 in wastewater treatment plants

Measuring ammonium (NH₄⁺) in a wastewater treatment plant is necessary because it directly affects treatment efficiency, compliance, and operating cost.

Briefly

• Process control – NH₄⁺ shows how well nitrification is working in the biological tanks.
• Regulatory compliance – High ammonium in the effluent can violate discharge limits and lead to fines.
• Aeration optimization – NH₄⁺ control prevents over-aeration, saving energy (biggest WWTP cost).
• Early warning – Sudden NH₄⁺ peaks indicate toxic inflow or process upset before failure occurs.
• Environmental protection – Ammonium is toxic to aquatic life and increases oxygen demand in rivers.

Standard solution 

• An NH₄⁺ ISE measures ammonium ions electrochemically, not optically or by color reagents.
• The electrode has a selective membrane that only responds to ammonium ions (NH₄⁺).
• When NH₄⁺ in the water contacts the membrane, it creates a potential difference (voltage).
• This voltage follows the Nernst equation, meaning it changes logarithmically with ammonium concentration.
• The transmitter converts this signal into a concentration value (mg/L NH₄-N or mg/L NH₄⁺).

In practice, most NH₄ ISEs

• Include automatic temperature compensation
• Require periodic calibration (typically 2-point)
• Are often paired with pH or K⁺ compensation to reduce interference
• Needs regular calibration for best accuracy
• Best accuracy at stable pH  is >10 or even much worse
• Replacement of ISE NH4 sensor twice year
• Expensive ISE electrode and service costs

New standard for NH4 measurement spectrometer with precise measurement based on calibration on site

• Accuracy 3-10% depending on the composition of the water matrix
• No reagents
• Easy maintenance
• Analyzes changes in the water matrix
• Can be expanded to 20 different measurements or more... depending on water matrix
• Calibration and adaptation at the installation site with real data

Customised calibration 

For the calibration 57 reference samples were determined by the laboratory of the wastewater treatment plant. These data were sent to controller as a table with the respective point in time. The controller remotely read out the associated 57 absorption spectra and performed the modelling.

Real example in the effluent of WWTP

Real trends

Are you looking for a reliable ammonium (NH₄) measurement solution for your wastewater treatment plant?

Terma Electric will help you select and install NH₄ measurement solutions – from ISE electrodes to spectrometric analyzers, with integration into PLC/SCADA systems.

If you want a stable process, lower energy costs, and guaranteed compliance, let's talk!