From UV spectra to degradability of industrial wastewater/definition and use of a shape factor

The measurement of global parameters such as TOC or specific compounds as phenol is not sufficient for the characterization of high loaded industrial wastewater. A previous study dealing with a treatability test based on the use of a photochemical reactor and the UV spectrophotometric control of the experiment has shown the interest of this alternative procedure for the biodegradability estimation of samples. Starting from a simple typology of wastewater based on the structure of UV spectra, a factor called "Shape Factor", or SF, ratio of second derivative value at a maximal wavelength on the corresponding peak absorbance, is proposed for the characterization of UV spectra shape. The interest of the use of SF, related to the probable presence of a major absorbing pollutant, is shown after a short kinetic study of the photochemical test for chemical and petrochemical wastewater. The degradation rate constant of the pseudo first order photo-reaction (calculated for the degradation of a major pollutant) seems to be linked to the SF factor. For samples characterized by UV absorption peak(s) and thus a high SF value, the degradation rate constant is relatively important. For example, for effluents the UV spectra of which are very structured, the degradation rate constant is above 2.3 s super(-1). In conclusion, this simple procedure based on the UV spectroscopic typology of samples must be, on one hand, validated from several industrial effluents, and, on the other hand, improved with a more complete kinetic study.