Chemical and Biomolecular Engineering Faculty Research


Monitoring Aerobic Sludge Digestion by Online Scanning Fluorometry

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Publication Date

Fall 2005


With sludge samples from two wastewater treatment plants, batch experiments of aerobic sludge digestion were conducted under different dissolved oxygen (DO) and solids concentrations. A fluorometer capable of online excitation and emission scanning was used to monitor the digestion process. Three major fluorescence peaks were observed. The peak at excitation/emission maxima of 290/350 nm was attributed to the fluorescence of proteinaceous materials in the sludge, with tryptophan residues being the primary contributor. The sources for the other two peaks (at 370/430 nm and 430/510 nm) remain unknown. The well-known biological fluorescence from reduced nicotinamide adenine dinucleotides (NADH and NADPH), at excitation/emission maxima of 340/460 nm, was found very weak in the aerobic digestion systems studied. It was buried under the broad peak at 370/430 nm and was detectable only in the early stage of the experiment that had the highest solids loading (at 4.8%) and was operated under low DO (0.2–1.0 mg/L) conditions. On the other hand, the profile of the protein fluorescence (PF) correlated well with that of the volatile solids (VS) reduction in all the experiments. A semi-empirical exponential decay function was developed, which described well the profiles of both normalized VS and normalized PF. The feasibility of following the real-time performance of aerobic sludge digestion by monitoring PF was clearly demonstrated.





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