Fluorescence quotient of excitation–emission matrices as a potential indicator of organic matter behavior in membrane bioreactors

Abstract

The potential of using excitation–emission matrix (EEM) fluorescence spectroscopy in revealing organic matter properties has yet to be fully exploited. A fluorescence quotient (FQ) method was established to graphically compare different EEM spectra and hence, reflect the differential properties of organic matter in a wastewater treatment process on the basis of EEM. FQ is defined as a standardized element-wise quotient of two EEM spectra for organic matter in different states (e.g. before and after degradation) or in different forms (e.g. in sludge, in supernatant or on membranes as foulants). This method was applied to two full-scale membrane bioreactors, with multiple FQs calculated among the influent organics, sludge supernatant organics, extracellular polymeric substances and membrane foulants. Statistical analyses confirmed that the distribution of FQ as a function of the fluorescence excitation and emission wavelengths was significantly meaningful in highlighting the differential EEM characteristics, which enabled a clear depiction of the active regions of the different organics on an excitation–emission map. This might therefore indicate the differential propensity for a specific behavior of organic matter (such as biotransformation, sludge/water-phase distribution and membrane fouling) from the perspective of EEM. The FQ method provides a potential tool for EEM data exploitation to reflect organic matter behavior in wastewater treatment processes.