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ISE-ammonium Sensors in WRRFs: Field Assessment of Their Influencing Factors


Real-time quantification of the ammonium content in water resource recovery facilities (WRRFs) has raised attention in recent years for both monitoring and process control. Ion-selective-electrodes are a viable solution for online ammonium measurements with increasing number of installations worldwide. This paper describes a year-long field evaluation of ISE-ammonium sensors and discusses the sensor performance under different operating conditions during diurnal, and seasonal variations. Three ISE-ammonium sensors were installed in the aeration tank of an activated sludge process. Specifically, one probe was installed at the end of the aeration tank, to test the sensor in low range conditions (< 1 mg N-NH4+ L-1). Several factors that influenced the sensor in field applications are presented critically, such as fouling, interfering ions, disturbance from aeration bubbles, and various maintenance and operating procedures. The study highlights how the background ion content of the mixed liquor affects the performance of the low range application. We recorded a 40% error in NH4+-N concentration over the low range measurement (< 1.0 mg L-1) due to K+ and Na+ content (18 and 225 mg L-1 on average respectively). This 40% error exceeds the sensor precision by 1-log. Therefore, for low range installation, the background interference due to other cations represents the main bottleneck in the current state of this technology. On the other hand, for the high range application, the ion interference led to an error comparable in magnitude to the sensor precision of 5%. Sensor fouling was tracked over the time in operation: both reversible and irreversible fouling was observed, and it differed according to the application and, therefore, to the wastewater composition. Different operation and maintenance procedures were addressed and the study points out how overzealous maintenance or improper procedure can be counterproductive.

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Publication details

The article was received on 26 Oct 2018, accepted on 28 Jan 2019 and first published on 04 Feb 2019

Article type: Paper
DOI: 10.1039/C8EW00763B
Citation: Environ. Sci.: Water Res. Technol., 2019, Accepted Manuscript

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    ISE-ammonium Sensors in WRRFs: Field Assessment of Their Influencing Factors

    F. Cecconi, S. Reifsnyder, Y. Ito, M. Jimenez, R. Sobhani and D. Rosso, Environ. Sci.: Water Res. Technol., 2019, Accepted Manuscript , DOI: 10.1039/C8EW00763B

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