Nine NH4 automatic analysers or monitors were tested in June-July 1995 (among them 2 prototypes):

- 5 based on ion electrode; ABB, Applikon, Contronic, Hydro-Environnement, STIP,

- 4 based on colorimetry; Danfoss, Data Link (UV absorption), Meerestechnik, Skalar

Laboratory tests are aimed to determine response time, repeatability, response linearity, short-term stability, influence of various factors on the measurement. The field test relates to real conditions: all the sensors were installed in parallel at the discharge point of a Wastewater treatment plant (WWTP). Recorded outputs were compared with conventional laboratory analysis of average hourly samples.

Response time range from 2 to 21 minutes. Repeatability varies from 1 to 10%, stability from 1 to 17%. Linearity is always good and detection limits (about 0.2 mg/l) do not seem to be critical for use in a WWTP. Among factors of influence, power voltage has limited effect, sample temperature is affecting some monitors, chemical interferents have nearly no effect excepted for one monitor. Field tests have shown that NH4 monitors are still very sensitive and that installation is crucial. Each monitor suffered several failures, some of them required high maintenance and used costly reagents.

This content is only available as a PDF.
You do not currently have access to this content.