The measurement principle is based on the UV-light-absorption spectrum of ammoniac gas NH3 in equilibrium with dissolved ammonia (ammonium or NH4+) in the water sample.

A small quantity of sodium hydroxide (NaOH) is added to the sample to increase the pH for transforming NH4+ to NH3. A Fast Fourier Transform (FFT) is applied on the spectrum to extract the absorption signal typical to ammoniac gas. This method is very selective and no interference is known on river or waste water.

Moreover, turbidity or color of the water has no influence as the measurement is performed in the gaseous phase.

Wastewater with suspended solids (as activated sludge) can be admitted without filtering.

This method has been known since 1956* but requires advanced signal processing that only powerful-microprocessor-based instruments can provide.

*”Quantitative Microdetermination of Gaseous Ammonia by Its Absorption at 204.3 nm” by Gunther, Barkley, Kolbezen, Blinn, Staggs - University of California, Vol28, no12, 1956.

Measurement stability minimizes the need for costly standard solutions (as opposed to the ISE method). An auto-zero is performed at each measuring cycle.

The detection system is in a separate enclosure for better accessibility.

Once a day, a low-cost cleaning solution (5% sulphuric acid) automatically cleans the stripping pot. The 5-litre tank lasts about two weeks.

An alarm is generated when the cleaning solution tank becomes empty.

The operating cost is limited to the refilling of the 2-litre tank of cleaning solution every week with 5% sulphuric acid on distilled water. We estimate it to be about US$200 per year including labour.

The concentration of ammonia in river water is an important parameter for drinking water treatment plants.  

Stability, reliability and low maintenance are the major concerns for these applications that only UV spectroscopy method can achieve. The graph below shows typical measurements on river water.

Waste water treatments plants need a fast and reliable ammonia measurement to control the nitrogen removal process that only UV spectroscopy method can really achieve.

The measurement on the gaseous phase avoids any interference with turbidity or suspended solid and the use of large bore tubing make possible the measurement on activated sludge.

The automatic cleaning system maintains the tubing clean.

Measurement time	5 minutes
Interference with color or turbidity	no
Standard solution	no need
Expensive or specific reagents	no
Periodic change of electrode or lamp or parts	no
Maintenance	low
Filtering	no need
Automatic cleaning system	yes
Operating cost	low
Size	compact
Weight	15-25 kg approx.
Transportable by car or passenger plane	yes
Installation time	few minutes

home | products | notice | contact us