Simultaneous and on-line estimation of nitrates and nitrites by UV spectral identification in waste water treatment [Estimation simultanée et en ligne de nitrates et nitrites par identification spectrale UV en traitement des eaux usées]
Pham H.N.,University Of Technologique Of Complegne |
Mottelet S.,University Of Technologique Of Complegne |
Schoefs O.,University Of Technologique Of Complegne |
Pauss A.,University Of Technologique Of Complegne |
And 5 more authors.
Eau, l'INDUSTRIE, les Nuisances | Year: 2010
Pursuant to the EU Water Framework Directive, the member states must restore a good ecological and chemical status of the surface water bodies within 15 years. As regards the nitrogen compounds, the threshold values not to be exceeded in the natural environment have been set to 2 mg.L-1, 0.5mg.L-1, 0.3 mg.L-1 et 50 mg.L-1for Kjeldahl nitrogen (NK), ammonia nitrogen (NH4 +), nitrite nitrogen (NO2 -) and nitrate nitrogen (NO3 -) respectively. Achieving these quality objectives implies that the wastewater treatment plant operators can control and monitor the concentrations of both nitrate and nitrite nitrogen in discharged water. Now, whereas the UV-type measuring apparatuses in current use enable to record the values for both species, they are not suitable for discriminating them. Against that background, the scientists from the Université Technologique de Compiègne and the Syndicat Interdépartemental pour l'Assainissement de l'Agglomération Parisienne have launched a study for testing and improving the on-line measuring apparatuses for NO3 -/NO2+ - As a matter of fact, a prototype on-line spectrophotometer discriminating the specific concentrations of nitrates and nitrites was tested and validated under actual operating conditions in a SIAAP's treatment plant (Seine Centre - Colombes - 800000 equivalent inhabitants). As evidenced by the results, there were good correlations between the estimated and experimental values ranging from 0.5 to 18 mg-N.L-1 for nitrates and from 0.5 to 5 mg-N.L-1 for nitrites. The discrimination between the nitrate and nitrite contents stems from the mathematical treatment of the UV spectrum rather than the resolution of the spectrophotometer. The outcome of the optimization and improvement of the spectral identification software has been weighed against the globally similar results given by such identification methods as PCR (Principal Component Regression) and PLS (Partial Least Squares).