Microbial Changes in the Fluorescence Character of Natural Organic Matter from a Wastewater Source

Abstract

Natural Organic Matter (NOM) is a mixture of aromatic and aliphatic organic compounds of natural origin in any type of aquatic system. Human activities impact the constituents of NOM, from its production to its fate, particularly in the treatment of domestic waste waters. In this work, the impact of microorganisms isolated from a Waste Water Treatment Plant (WWTP) was investigated to determine the fate of NOM fractions in raw sewage, using fluorescence spectroscopy. Wastewater samples were taken at three different times from a WWTP, and incubated for 4 days under two treatments: 1) "raw sewage", and 2) "spiked", i.e., the same raw sewage, spiked with bacteria previously isolated from the WWTP. The incubated waters were analyzed by fluorescence spectroscopy, digitally resolved into NOM components: humic-and fulvic-like, and two types of proteinlike, i.e., tryptophan-and tyrosine-like, using a Parallel Factor Analysis routine (PARAFAC). The results demonstrate that the "spiked" samples showed the largest changes with incubation time. The signals of the tryptophan-and tyrosine-like components decreased, suggesting a net microbial digestion of proteinaceous material. In contrast, the fulvic-like signals, and to some extent, the humic-like signals increased, suggesting the production of the associated molecular materials during the incubation period. This study provides direct evidence of human impact on the makeup of NOM: the cultures of microbes found at a WWTP consume the proteinaceous material, whereas humic-like and fulvic-like materials are produced.

Characterisation of Organic Matter and Its Transformation Processes in On-Site Wastewater Effluent Percolating through Soil Using Fluorescence Spectroscopic Methods and Parallel Factor Analysis (PARAFAC)

“…However, the non-humified component that was found by Yao et al [44] does not correspond to the FWC component (C2) in this study. Equally, Riopel et al [45] used PARAFAC analysis to characterize NOM in raw sewage and effluent of a large-scale wastewater treatment plant (WWTP) applying a three component model which picked up higher-MW humified and protein-like components, consistent with those found in this study, but failed to isolate FWCs as an important fluorescence component [44][45][46]. Our study not only identifies FWCs as one of the fluorophores (C2) but further highlights its major contribution in primary and secondary effluent as the second highest (33%) and highest contributor (52%) to the fluorescence signal respectively (Table 2).…”

“…Here, the removal of protein-like compounds and FWC resulted in a relative shift in contributions and increase in the higher-MW fractions that could be measured by the HI which increased consistently with higher degrees of treatment (Table 2). An alternative explanation, however, can be found in other studies that directly link the consumption of protein-like material with the concurrent production of DOM with more decomposed, humified characteristics [45,51,52]. Parlanti et al [52], for example, studied the change in fluorescence spectra (EEMs) for macro-algae degradation in water and observed a characteristic sequential appearance and disappearance of different peaks at longer wavelength which suggested that the proteinlike compounds (possibly from macro-algae cells and/or exudates) may be used to produce the other fluorophores and/or are undergoing a transformation/humification process.…”

“…Riopel et al [45] found that signals of the FDOM components in the raw sewage had protein-like characteristics, followed by more humified decomposition characteristics. Conversely, after treatment, the FDOM signals were dominated by lower-MW aromatic compounds components derived predominantly from microbial activities, followed by approximately equal signals of more humified, higher-MW and protein-like components.…”

“…Riopel et al [45] as well as Parlanti et al [52] performed their experiments in a closed system so they could draw conclusions regarding OM transformation processes. Here, however, there is a net removal of FDOM and, hence, an increase in the relative contribution of one component does not necessarily result from an increase in that compound's concentration.…”