title: Influence of local calibration on the quality of online wet weather discharge monitoring: feedback from five international case studies.
abstract: This paper reports about experiences gathered from five online monitoring campaigns in the sewer systems of Berlin (Germany), Graz (Austria), Lyon (France) and Bogota (Colombia) using ultraviolet-visible (UV-VIS) spectrometers and turbidimeters. Online probes are useful for the measurement of highly dynamic processes, e.g. combined sewer overflows (CSO), storm events, and river impacts. The influence of local calibration on the quality of online chemical oxygen demand (COD) measurements of wet weather discharges has been assessed. Results underline the need to establish local calibration functions for both UV-VIS spectrometers and turbidimeters. It is suggested that practitioners calibrate locally their probes using at least 15-20 samples. However, these samples should be collected over several events and cover most of the natural variability of the measured concentration. For this reason, the use of automatic peristaltic samplers in parallel to online monitoring is recommended with short representative sampling campaigns during wet weather discharges. Using reliable calibration functions, COD loads of CSO and storm events can be estimated with a relative uncertainty of approximately 20%. If no local calibration is established, concentrations and loads are estimated with a high error rate, questioning the reliability and meaning of the online measurement. Similar results have been obtained for total suspended solids measurements.
authors.affiliation: Kompetenzzentrum Wasser Berlin gGmbH, Cicerostraße 24, Berlin D-10709, Germany E-mail: nicolas.caradot@kompetenz-wasser.de.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Caradot
authors.affiliation: Kompetenzzentrum Wasser Berlin gGmbH, Cicerostraße 24, Berlin D-10709, Germany E-mail: nicolas.caradot@kompetenz-wasser.de.
authors.forename: Hauke
authors.initials: H
authors.lastname: Sonnenberg
authors.affiliation: Kompetenzzentrum Wasser Berlin gGmbH, Cicerostraße 24, Berlin D-10709, Germany E-mail: nicolas.caradot@kompetenz-wasser.de.
authors.forename: Pascale
authors.initials: P
authors.lastname: Rouault
authors.affiliation: Institute of Urban Water Management and Landscape Water Engineering, Graz University of Technology, Stremayrgasse 10/I, Graz A-8010, Austria.
authors.forename: Günter
authors.initials: G
authors.lastname: Gruber
authors.affiliation: Institute of Urban Water Management and Landscape Water Engineering, Graz University of Technology, Stremayrgasse 10/I, Graz A-8010, Austria.
authors.forename: Thomas
authors.initials: T
authors.lastname: Hofer
authors.affiliation: Department of Civil Engineering, Research Group Ciencia e Ingeniería del Agua y el Ambiente, Pontificia Universidad Javeriana, Edificio J.G. Maldonado, S.J., Carrera 7 No. 40-62, Bogotá, D.C., Colombia.
authors.forename: Andres
authors.initials: A
authors.lastname: Torres
authors.affiliation: Université de Lyon, INSA Lyon, LGCIE, 34 avenue des Arts, Villeurbanne F-69621, France.
authors.forename: Maria
authors.initials: M
authors.lastname: Pesci
authors.affiliation: Université de Lyon, INSA Lyon, LGCIE, 34 avenue des Arts, Villeurbanne F-69621, France.
authors.forename: Jean-Luc
authors.initials: JL
authors.lastname: Bertrand-Krajewski
mesh_terms: D057919:Biological Oxygen Demand Analysis; D002138:Calibration; D003105:Colombia; D004784:Environmental Monitoring / Q000379:methods*; D005060:Europe; D055904:Meteorology / Q000379:methods; D009391:Nephelometry and Turbidimetry / Q000379:methods*; D011891:Rain; D015203:Reproducibility of Results; D013056:Spectrophotometry, Ultraviolet / Q000379:methods*