Sensor prototypes for measurement of ammonium, nitrate and phosphate in wastewater treatment plants are described together with the results obtained in laboratory and pilot scale wastewater treatment plants. A functional description of the sensor principles is presented together with the installation and operation procedures. Basically the measurements are done using membrane technology in combination with semi-micro Continuous Flow Analysis (μCFA) with classic colorimetry. Because of this the sensors can be installed directly in the aeration tanks without any need for sampling, filtration, etc. Furthermore, the semi-micro scale is used in such a way, that handling of chemicals and waste is a closed loop in a package to be changed once a month. The sensors have been tested thoroughly in a pilot scale waste water treatment plant (recirculation) using real raw wastewater as well as artificial wastewater. The sensors have been placed directly in the aeration tank or in the anoxic tank of the pilot plant. The tests show very little, if any, fouling problems due to the membrane material used. The test results show a good reproducibility and most important, compared to other available sensors/analyzers on the market, very low response times, less than 5 minutes. Owing to these low response times, experiments with direct measurement of nitrification and denitrification rates were carried out.
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