Tracking changes in organic matter during nitrification using fluorescence excitation–emission matrix spectroscopy coupled with parallel factor analysis (FEEM/PARAFAC)

Abstract

Fluorescence excitation-emission matrix spectroscopy coupled with parallel factor analysis (FEEM/PARAFAC) was applied to characterise natural organic matter (NOM) present in nitrified and non-nitrified waters from different sampling sites in a drinking water distribution system in Australia. Each excitation-emission matrix (EEM) data set of nitrified and non-nitrified water samples were successfully decomposed into a three component PARAFAC model (C-1, C-2, and C-3). The spectral shapes of these components were compared with those identified earlier in other studies from the OpenFluor database. While C-1 and C-2 exhibited similar fluorescence spectra in both non-nitrified and nitrified sampling locations, there were some fluorescence peaks in C-3 for nitrified water samples that were not present in non-nitrified water samples. Both C-1 and C-2 in each PARAFAC model for nitrified and non-nitrified water samples showed striking similarities with components previously listed as humic-like compounds. While C-3 for non-nitrified water samples also consisted of terrestrial humic-like compounds, C-3 in PARAFAC model for nitrified water samples represented protein-like material produced as a result of microbiological activity. The fluorescence peaks that appeared only in nitrified sampling locations are related to the formation of microbial-like compounds associated with nitrification. These results indicate that PARAFAC modelling of EEM data can be used to investigate nitrification and water quality changes in chloraminated drinking water distribution systems.