Characterizing treated wastewaters of different industries using clustered fluorescence EEM–PARAFAC and FT-IR spectroscopy: Implications for downstream impact and source identification
Introduction
Many industrial wastewaters, even after extensive treatment, contain notably higher organic matter loading and undesirable inorganic and organic pollutants than natural aquatic environments (e.g., Baker, 2002, Janhom et al., 2009, Lee et al., 2014). The discharge of such industrial wastewaters may exert detrimental effects on the receiving waterbodies such as odor, eutrophication, hypoxia, and toxicity (Eckenfelder, 2000). To effectively detect, monitor, and control the pollution to ensure the downstream water quality and safety, it is of great importance to collect information on the characteristics of various industrial wastewaters. Such efforts are also valuable for identifying the responsible facilities when the effluent levels exceed the regulatory criteria (e.g., total maximum daily loads) of a watershed, which is affected by multiple point sources.
Dissolved organic matter (DOM), a complex mixture of many organic compounds, is ubiquitous in wastewaters as well as in natural aquatic environments. The chemical composition of DOM may provide valuable fingerprints for different types of industrial wastewaters possibly present in watersheds. Fluorescence spectroscopy is a fast, simple and non-destructive tool for characterizing DOM, which can be easily developed into an in-situ monitoring technique (Henderson et al., 2009, Janhom et al., 2009, Chong et al., 2013). Fluorescence excitation–emission matrix (EEM) provides profound information about the DOM quality, revealing the distribution of all fluorescent components in a range of excitation and emission (Ex/Em) wavelengths. Previous studies demonstrated that some fluorescent peaks in EEM could be used for tracing industrial effluents (Santos et al., 2001, Baker, 2002, Li et al., 2014). In the recent decade, parallel factor analysis (PARAFAC) is becoming a popular tool for identifying and characterizing individual components from EEMs and for tracking their variability in both natural and engineered systems (Stedmon et al., 2003, Stedmon and Bro, 2008, Murphy et al., 2011, Murphy et al., 2014, Ishii and Boyer, 2012, Hur et al., 2014a, Yang et al., 2014a). Few studies have applied EEM–PARAFAC to characterize DOM in industrial wastewater treatment plants (Ou et al., 2014, Cohen et al., 2014), and in receiving waterbodies (Borisover et al., 2011, Cawley et al., 2012, Phong et al., 2014). Another valuable tool for characterizing organic matter is Fourier transform infrared (FT-IR) spectroscopy, which provides information on the relative distributions of functional groups or compounds in DOM (Mayo et al., 2004, Smidt et al., 2005, Kaiser and Ellerbrock, 2005, Lee et al., 2013, Hur et al., 2014b). To our knowledge, there are limited studies utilizing the FT-IR features to characterize industrial wastewater DOM (Karthikeyan et al., 2011, Navalon et al., 2011, Zhu et al., 2011, Jain et al., 2014).
While most previous studies of industrial wastewater DOM using fluorescence EEM–PARAFAC or FT-IR spectroscopy investigated only one industrial facility or category, the features of wastewater DOM from many industrial categories are still unexplored. In reality, a variety of facilities are usually present in industrial complexes and their effluents mix in downstream waterbodies. Therefore, a comprehensive comparison of a series of industrial wastewaters is critical to test the feasibility of these spectroscopic techniques in discriminating effluents from different facilities. This is particularly important because even for a similar industrial category (e.g., pulp mill industry), fluorescence features can be very different (Santos et al., 2001, Baker, 2002, Ciputra et al., 2010, Cawley et al., 2012). Furthermore, acquiring the chemical composition of DOM is essential in assessing its responses to biogeochemical processes (e.g., Stedmon and Markager, 2005, Hur et al., 2009, Ishii and Boyer, 2012, Chen and Jaffé, 2014, Shutova et al., 2014, Yang et al., 2014a, Yang et al., 2014b). Thus, the knowledge of industrial wastewater DOM quality has another important implication in understanding the fate of DOM and its effects on downstream ecosystem functions. Therefore, the objectives of this study were threefold: (1) to investigate the quantity and spectroscopic features of DOM in wastewaters from up to 57 facilities across 12 industrial categories using multiple DOM characterizing tools including dissolved organic carbon (DOC), specific UV absorbance (SUVA), fluorescence EEM–PARAFAC, and FT-IR spectroscopy; (2) to infer the biogeochemical reactivity of DOM and the influences on downstream waterbodies; and (3) to evaluate the feasibility of spectroscopically measured DOM features in the identification of the wastewater source. EEM–PARAFAC and FT-IR results were subject to cluster analysis to reveal the similarity (within cluster) and difference (among clusters) of all industrial wastewaters.
Section snippets
Sampling and measurements of TOC, DOC, and absorbance
Treated effluents were sampled nationwide in South Korea from 57 facilities belonging to 12 industrial categories, which produce or process non-alcoholic drink (D), electronic device (E), food (F), leather and fur (L), meat (M), organic chemical (O), pulp and paper (Pa), petrochemical (Pe), resin and plastic (R), steel (S), steam-power (SP), and textile dying (T) (Table S1). One final effluent sample was taken from the releasing pipe of each facility under normal operations, which showed
Organic carbon concentration and absorbance feature of industrial effluents
The TOC and DOC were 1.78–122 and 0.15–108 mg L−1 for all treated industrial wastewaters, respectively (Figs. 1 and S3a). The DOC was closely correlated with TOC (r = 0.92, p < 0.001) with a slope of 0.76 (Fig. S3b), indicating an overall major contribution of DOC to TOC. There were statistically significant differences for TOC and DOC among the 12 industrial categories (ANOVA, p < 0.001). Both TOC and DOC were highest in the wastewaters from organic chemical-producing facilities (84.8 ± 15.0 and 73.4 ±
Conclusions
The large variations in DOC, SUVA, EEM–PARAFAC and FT-IR features for the treated wastewaters from 57 facilities indicated notable variability in both quantity and chemical composition of DOM in industrial effluents. The notable variations in the chemical composition of DOM further suggested probable variability in its reactivity and impact on downstream ecosystem. Cluster analysis based on PARAFAC or FT-IR results identified different types of effluents which were dominated by specific PARAFAC
Acknowledgment
This work was supported by a National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP) (No. 2014R1A2A2A09049496). Additional support was provided by the Korea Environment Institute project (No. 2013-061).
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