Effluents characterization using NIR and UV-Vis spectroscopy

Abstract

Nitrogen compounds (e.g. nitrates - NO3-) discharge into the environment can cause serious problems such as eutrophication and deterioration of water courses. The biological nitrate reduction, named denitrification, has been shown to be more useful, economical, and the most versatile approach among all methods to remove nitrate from wastewaters. To prevent imbalances of those biological processes, analytical methods with chemicals addition are routinely used for systems monitoring. The search for a rapid technique could be an alternative monitoring procedure to enhance the process performance. Over the last thirty years, the application of spectroscopy techniques for industrial process monitoring is achieving an increasing significance. This technology has been mostly applied in the food industry and in the pharmaceutical industry. Regarding environmental processes, the application of spectroscopy is still rarely applied. In this work, UV-Visible and Near-Infrared (NIR) spectroscopy techniques were used to monitor denitrifying processes using different carbon sources: acetate, propionate (volatile fatty acids - VFAs), glucose, and sucrose (sugars). Denitrifying rates were also found using four different biomass/chemical oxygen demand (VSS/COD) ratios. The main goal of this project was to test the ability of each spectroscopy technique to detect and monitor the denitrification process. For each assay, nitrate and each carbon source were also analyzed using standard analytical methods. Using spectral data and chemometrics tools, models for different parameters were developed: nitrate, VFAs, and sugars. After spectra pre-processing for removing the less relevant information and with application of partial least squares regression (PLS) the described parameters were modeled.