Estimating DOC regime in a wastewater treatment plant by UV deconvolution

A UV-deconvolution method was modified, and applied to estimation of dissolved organic carbon (DOC) along a municipal wastewater treatment plant (WWTP) in Catalonia, Spain. One grab sample was taken every 2h at four sampling points, for 1 week (336 samples), in order to characterise day/night and weekday/weekend DOC regimes along the plant. Samples were centrifuged before DOC determination or estimation. Four components were selected for describing wastewater composition and spectra. Reference spectra for these components were taken from the literature and proved to correctly explain the sample spectra. A two-step deconvolution method was developed, which avoided negative nitrate coefficients while keeping deconvolution error low. The calibration file for DOC estimation was determined by analysing DOC and acquiring UV spectra from 48 samples. DOC values were correlated to UV spectra by multiple linear regression. Determination coefficient and standard error were comparable to the values found in the literature. In raw or diluted samples with an absorbance between 2.0 and 2.5, DOC was probably underestimated by the method. This points to some nonlinearity for absorbances above 2.0, rather than the 2.5 limit suggested by the original method. DOC calculation through UV deconvolution allowed for the estimation of DOC regime along the WWTP. Time bands for higher and lower DOC concentrations were determined and characterised at each sampling point, for weekdays and the weekend. Except for the plant effluent, clear time bands were found. In effluent, DOC was always low, and very small oscillations were detected, due to DOC removal and intense mixing in the biological process. DOC profiles at each point are discussed in this paper. The modified deconvolution method has proved to be an accurate and efficient technique for estimating DOC of a large number of raw and diluted samples.