Novel insights into anoxic/aerobic1/aerobic2 biological fluidized-bed system for coke wastewater treatment by fluorescence excitation–emission matrix spectra coupled with parallel factor analysis

•We developed a novel anoxic/aerobic1/aerobic2 process to treat coke wastewater.•DOM in bio-treatment was characterized using EEM and PARAFAC.•Correlations between contaminants and EEM components were investigated.•EEM–PARAFAC can be used to monitor the performance of coke wastewater treatment.

Fluorescence spectroscopy coupled with parallel factor analysis (PARAFAC) was applied to investigate the contaminant removal efficiency and fluorescent characteristic variations in a full scale coke wastewater (CWW) treatment plant with a novel anoxic/aerobic1/aerobic2 (A/O1/O2) process, which combined with internal-loop fluidized-bed reactor. Routine monitoring results indicated that primary contaminants in CWW, such as phenols and free cyanide, were removed efficiently in A/O1/O2 process (removal efficiency reached 99% and 95%, respectively). Three-dimensional excitation–emission matrix fluorescence spectroscopy and PARAFAC identified three fluorescent components, including two humic-like fluorescence components (C1 and C3) and one protein-like component (C2). Principal component analysis revealed that C1 and C2 correlated with COD (correlation coefficient (r) = 0.782, p < 0.01 and r = 0.921, p < 0.01), respectively) and phenols (r = 0.796, p < 0.01 and r = 0.914, p < 0.01, respectively), suggesting that C1 and C2 might be associated with the predominating aromatic contaminants in CWW. C3 correlated with mixed liquor suspended solids (r = 0.863, p < 0.01) in fluidized-bed reactors, suggesting that it might represent the biological dissolved organic matter. In A/O1/O2 process, the fluorescence intensities of C1 and C2 consecutively decreased, indicating the degradation of aromatic contaminants. Correspondingly, the fluorescence intensity of C3 increased in aerobic1 stage, suggesting an increase of biological dissolved organic matter.

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