The aim of this study was to demonstrate that the effectiveness of slaughterhouse wastewater treatment
by activated sludge could be enhanced through the use of optical techniques, such as UV–Visible absorbance
and fluorescence spectroscopy, to estimate the hydraulic retention time necessary to remove the
biodegradable chemical oxygen demand (COD). Two experiments were conducted. First, a batch aerobic
degradation was performed on four wastewater samples collected from four different cattle processing
sites in order to study the changes in the spectroscopic properties of wastewater during biodegradation.
Second, a sequencing batch reactor was used in order to confirm that the wastewater fluorescence could
be successfully used to monitor wastewater biodegradation in a pilot-scale experiment. Residual blood
was the main source of organic matter in the wastewater samples. The absorbance at 416 nm, related
to porphyrins, was correlated to the COD during wastewater biodegradation. The tryptophan-like/
fulvic-like fluorescence intensity ratio was related to the extent of biodegradation. The COD removal
efficiency ranged from 74% to 94% with an hydraulic retention time (HRT) of 23 h. A ratio of tryptophan-
like/fulvic-like fluorescence intensities higher than 1.2 indicated incomplete biodegradation of
the wastewater and the need to increase the HRT.