Partial Least Squares local calibration of a UV-visible spectrometer used for in situ measurements of COD and TSS concentrations in urban drainage systems

Recent UV-visible spectrometers deliver on line and in situ absorbance spectra in wastewater or stormwater transported in urban drainage systems. After calibration with local data sets, spectra can be used to estimate pollutant concentrations. Calibration methods are usually based on PLS (Partial Le...

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Bibliographic Details
Published in:Water science and technology 2008-01, Vol.57 (4), p.581-588
Main Authors: Torres, A, Bertrand-Krajewski, J-L
Format: Article
Language:English
Subjects:
Calibration
Chemical oxygen demand
Data
Data processing
Drainage systems
Drainage, Sanitary
In situ measurement
Independent variables
Inlets (waterways)
Least squares method
Least-Squares Analysis
Measuring instruments
Nephelometry and Turbidimetry
Online Systems
Oxygen
Separated sewers
Sewage - analysis
Sewer systems
Spectra
Spectrometers
Spectrophotometry, Ultraviolet
Storage
Stormwater
Suspended particulate matter
Total suspended solids
Turbidity
Ultraviolet radiation
Urban drainage
Vectors
Wastewater
Water Pollutants - analysis
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Description
Summary:Recent UV-visible spectrometers deliver on line and in situ absorbance spectra in wastewater or stormwater transported in urban drainage systems. After calibration with local data sets, spectra can be used to estimate pollutant concentrations. Calibration methods are usually based on PLS (Partial Least Squares) regression. Their most important difficulty lies in the identification of the number of both i) the latent vectors and ii) the independent variables. A method is proposed to identify these variables, based on an exhaustive tests procedure (Jackknife cross validation and matrix of prediction indicator). It was applied to estimate TSS (total suspended solids) or COD (chemical oxygen demand) concentrations at the inlet of a storage-settling tank in a stormwater separate sewer system, and compared to three other calibration methods used either for turbidity meters or UV-visible spectrometers. With the available calibration data set: i) the spectrometer gives results with better prediction quality than the turbidity meter, ii) for the spectrometer, local calibration gives better results than global calibration, iii) the proposed PLS method gives results with a similar order of magnitude in uncertainties as the manufacturer local calibration method, but is more open and transparent for the user. Similar results were obtained for a second data set.
ISSN:0273-1223
1996-9732
DOI:10.2166/wst.2008.131