Rapid and direct determination of wastewater BOD values using a fluorescence technique

The biodegradable constituents in wastewater are parameterized by the biochemical oxygen demand (BOD) values. The technology based on fluorescence detection for the real-time, non-invasive monitoring of the biodegradable constituents of various sewage samples is investigated and the advantages over current methods (BOD, TOC, COD and absorption at 254 nm) are discussed. Fluorescence properties of industrial and domestic sewage were examined. The spectral signatures (both absorption and fluorescence) of settled sewage samples collected as 24-h composites from three different treatment works were found to be similar, having an absorption band at around 280 nm and a fluorescence maximum at 340 nm (using 280 nm excitation). The UV-absorbance (ABS) and the peak fluorescence (FL) intensities were found to be much lower than those for corresponding samples of treated effluent, indicating the extent of biodegradation in the processing of raw sewage. To compensate for the attenuation of the incident excitation radiation caused by the sample, the fluorescence intensities were normalized to the water Raman signal. The fluorescence intensities were also corrected for the differential absorption/re-absorption of the fluorescence signals. The long-term and short-term variations in the fluorescence and absorption properties of the sewage samples were investigated and the results correlated with corresponding BOD values. Fluorescence was found to have reasonable correlations (regression 0.94) with the BOD values.