Study on the use of NADH fluorescence measurements for monitoring wastewater treatment systems

Fluorescence measurement of intracellular nicotinamide adenine dinucleotide (NADH) provides information about the physiological response of microbes towards changing conditions in their environment and has been suggested to be useful for the control of wastewater treatment plants. In this study, the practical usefulness of such measurements was evaluated from batch experiments with a commercially available NADH sensor in a bench scale reactor. The sensor was linear in the NADH concentration, robust, almost maintenance free, and hardly sensitive to floc size distribution. Measured fluorescence intensity proved to depend strongly on the concentration of active heterotrophic biomass. The NADH level was supposed to be dependent on the ratio of electron donor/electron acceptor availability inside the cells; however, neither acetate nor ammonium addition was reflected by the measurement signal. A jump wise NADH signal change was observed at complete oxygen or nitrate depletion as also reflected by bends in the redox curve. In the near zero concentration ranges of oxygen and nitrate (0.1–0.5 mg/l) the signal changes only slightly in the opposite direction to the redox trend.