Abstract
This research has used fluorescence spectroscopy and parallel factor analysis (PARAFAC) in order to characterize dissolved organic matter in septic tank effluent, as it passes through the biomat/biozone, infiltrating into the unsaturated zone beneath domestic wastewater treatment systems (DWWTSs). Septic tank effluent and soil moisture samples from the percolation areas of two DWWTSs have been analyzed using fluorescence excitation–emission spectroscopy. Using PARAFAC analysis, a six-component model was obtained whereby individual model components could be assigned to humified organic matter, fluorescent whitening compounds (FWCs), and protein-like compounds. This has shown that fluorescent dissolved organic matter (FDOM) in domestic wastewater was dominated by protein-like compounds and FWCs and that, with treatment in the percolation area, protein-like compounds and FWCs are removed and contributions from terrestrially derived (soil) organic decomposition compounds increase, leading to a higher degree of humification and aromaticity. The results also suggest that the biomat is the most important element determining FDOM removal and consequently affecting DOM composition. Furthermore, no significant difference was found in the FDOM composition of samples from the percolation area irrespective of whether they received primary or secondary effluent. Overall, the tested fluorometric methods were shown to provide information about structural and functional properties of organic matter which can be useful for further studies concerning bacterial and/or virus transport from DWWTSs.
Highlights
In many countries (e.g., USA and Ireland), rural areas rely heavily on on-site domestic wastewater treatment systems (DWWTSs), which typically consist of a septic tank or packaged secondary treatment system followed by a percolation area [1,2]
Most studies have focused on studying the mechanism of soil clogging which has provided some information about the types of organic matter (OM) found in DWWTSs
Analysis has been shown with respect to the characterization of fluorescent dissolved organic matter (DOM) in septic tank effluent and its subsequent transformations as it passes through the biomat/biozone, infiltrating into the unsaturated zone beneath DWWTSs
Summary
In many countries (e.g., USA and Ireland), rural areas rely heavily on on-site domestic wastewater treatment systems (DWWTSs), which typically consist of a septic tank or packaged secondary treatment system followed by a percolation area [1,2]. Most studies have focused on studying the mechanism of soil clogging which has provided some information about the types of organic matter (OM) found in DWWTSs. In the biomat, the enhanced biological processes involve the production of microbial cells and organic by-products (e.g., extracellular polymeric substances) from stimulated microbial growth and decay [11,12]. Research has suggested that the cyclical aerobic–anaerobic conditions stimulated during subsurface infiltration may support microbial formation and accumulation of complex organic material within the biomat [8,13]. It should be noted that there is an ongoing debate as to what terms such as humic substances refer to, with the more traditional view of it representing large-molecular-size and persistent compounds left from the decomposition process being challenged and that, in reality, soil organic matter should be viewed more as a continuum of decomposition products [14]. Others prefer to retain the use of such terms but recognize the need for them to be defined more accurately [15]
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