Characterizing Dissolved Organic Matter (DOM) in Wastewater from Scale Pig Farms Using Three-Dimensional Excitation-Emission Matrices (3DEEM)

The properties of material composition in swine wastewater are closely related to its potential environmental effects, and-it could provide theoretical bases for formulating scientific resource management measures to study the composition of organic matter in wastewater. In the present study, swine wastewater was directly collected from waste-retention basins in various scale pig farms with a different farming scale (based on the annual pig slaughter), namely Cheng Lin (CL, 5 000), Wu Yang-gao (WYG, 2 000), Wan Gu (WG, 20 000), and Zhang Bang (ZB, 24 000), located in Yujiang County of Jiangxi Province. The main purpose of this study was to characterize dissolved organic matter (DOM) in swine wastewater using threedimensional excitation-emission matrices (3DEEM) and parallel factor analysis (PARAFAC). Results of all samples examined showed, with respect to CL and WYG farm, chemical oxygen demand (COD), total nitrogen (TN), ammonium nitrogen (NH4), and dissolved organic carbon (DOC) concentration in swine wastewater was significantly higher than WG and ZB farm. Three DOM components, including two protein-like components (Cl, C2) and one humic-like component (C3), were identified in wastewater using 3DEEM and PARAFAC. Results of linear regression showed, the fluorescence intensity of Cl linked significantly with C2 (p<0. 001) and C3 (p<0. 001), respectively, suggesting a same source or similar variation trend existed possibly between different DOM components. Furthermore, consistent with the variation trend of nutrient concentration in wastewater, fluorescence intensity of each DOM component in CL and WYG farm was significantly higher than WG and ZB farm. The total contribution of Cl and C2 to DOM in swine wastewater was CL (89. 7%), WG (77. 5%), WYG (87. 9%), and ZB (72. 9%), respectively, and the percentage of C3 was CL (10. 3%), WG (22. 5%), WYG (12. 1%), and ZB (27. 1%), respectively. Thus, the percentage of two protein-like components was significantly higher than humic-like in swine wastewater. Meanwhile, the fluorescence indices FI370 and humification index (HIX) of WG and ZB farm were higher than CL and WYG. In addition, Pearson correlation analysis showed that the effects of environmental parameters on fluorescence indices were different, and COD and DOC concentrations were significantly correlated with the fluorescence intensities of DOM components in swine wastewater. In summary, to a certain degree, the nutrient levels affected formation of fluorescence characteristics and DOM compositions in swine wastewater between different scale pig farms.