Spectral characteristics of dissolved organic matters in reject water from wastewater treatment plants

Reject water generated from sludge thickening, dewatering and stabilization process contains high-content and complex dissolved organic matters (DOM). The spectral characteristics of DOM in the reject water were investigated by three-dimensional excitation-emission matrix and Fourier transform infrared spectroscopy. Fluorescent DOM (FDOM) from reject water were decomposed into six components by parallel factor analysis, the protein-like C1 (275/355 nm), C4 (235/350 nm) and C6 (275/305 nm) and the humic-like C2 (250, 340/440 nm), C3 (320/380 nm) and C5 (250/465 nm). Soluble COD in the sludge thickening reject water was positively correlated with all the three humic-like substances at P<0.01 level, and was insignificantly influenced by protein-like substances. The tryptophan-like C1, C4 and humic-like C5 increased in the centrifugal dewatering reject water (CDRW). FDOM in the advanced dewatering reject water (ADRW) were significantly different from those of other reject water in fluorescence peak locations and intensities, and humic-like C3 and tyrosine-like C6 in the DOM were 15.63 and 7.30 times higher than those in CDRW. Compared to sludge thickening reject water, infrared peaks related to polysaccharide and humic substances in CDRW were enhanced, and massive proteins were released into ADRW. DOM structures in ADRW were changed owing to the complexation between metals and both humic substances and proteins.