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S. Winkler, L. Rieger, M. Thomann, H. Siegrist, C. Bornemann:
"In-Line Monitoring Of COD And COD-Fractionation: Improving Dynamic Simulation Data Quality";
Talk: Enviro 2002 Convention & Exhibition and IWA World Water Congress, Melbourne, Australia (invited); 2002-04-07 - 2002-04-12; in: "Proceeding auf CD", paper no.: e21604a (2002), 1 - 9.

Continuous monitoring of the COD and its fractionation in wastewater is by far no trivial issue, because of the many influences on the measurement quality. Especially in raw wastewater or primary clarifier effluent effects like failure of the probe, sampling and
preparation system, unrepresentative sampling or sensor fouling can lead to substantial errors in the measurement results. A new submersible spectrometer is presented, which utilises the UV-VIS-range (200-750 nm) for simultaneous measurement of COD, COD
fractionation, turbidity and nitrate with just a single instrument. The miniaturised spectrometer allows easy installation even in 2" boreholes for groundwater monitoring. It is a sensor installed directly in the process, thus requires no sampling, sample preparation, no reagents and is equipped with an auto-cleaning system. The spectrometer was tested at three different WWTP´s in Austria, Germany and Switzerland, it proved to work extremely reliably even in raw wastewater upstream the screening station and over long periods. The instrument can be calibrated to the measurement location specific wastewater matrices and therefore opens new possibilities with respect to data quality. A longterm validation showed that the instrument delivers results with a very good
repeatability (mean stddev. = 2.08 mgCOD/l) and trueness. The mean of the residuals was calculated to zero with a 95%-confidence interval of 13.7 mgCOD/l. The test results clearly indicate that continuous monitoring of COD and its fractionation delivers an improved quality of dynamic data compared to discontinuous laboratory analysis. Such data is valuable for dynamic simulation of wastewater treatment plants - especially in case processes are simulated - like excess biological phosphorous uptake - which are strongly influenced by dynamic changes of the concentration of the COD fractions.