Dissolved organic matter in digested piggery wastewater from combined treatment process

ABSTRACT

The temporal and spatial variation of dissolved organic matter in the processes of hydrolytic acidification and biological contact oxidation during post-treatment of digested piggery wastewater were characterized systematically by means of ion chromatography, fluorescence spectra, and ultraviolet spectra in this study. The highest removal efficiencies of chemical oxygen demand and nitrogen have been achieved when the 1/3 effluent of biological contact oxidation reactor was backflow into the reactor of hydrolytic acidification. It was found that the concentrations of total organic acids were 283.6 mg/L at the first 2 h of hydrolytic reaction and 305.5 mg/L at the beginning of recirculation between the two reactors and then decreased to around 200 mg/L and keep stable. The results of synchronous and three-dimensional excitation–emission matrix fluorescence spectroscopy revealed that the protein-like fluorescence peaks were identified in the hydrolytic acidification reactor and their intensities increased gradually along with hydrolytic time increasing. Moreover, the fulvic acid-like fluorescence peaks in biological contact oxidation reactor were observed, and the intensity increased gradually. The synchronous intensity of 277 nm wavelength was significantly correlated with the total organic acids concentration. Variation of SUVA₂₅₄ and E ₂₅₃/E ₂₀₃ during the hydrolytic acidification process indicated that concentrations of aromatic and unsaturated compounds slightly increase and those aromatic compounds are not stable. However, SUVA₂₅₄ and E ₂₅₃/E ₂₀₃ decreased rapidly in the biological contact oxidation reactor, which suggested that easily degradable organic matters had been consumed rapidly.

Keywords :

• Anaerobic digested wastewater
• Dissolved organic matter
• Ion chromatography
• Three-dimensional fluorescence spectroscopy
• Ultraviolet spectra

Acknowledgements

This study is supported by the National Natural Science Foundation of China (No. 40901248), the Mega-projects of Science Research for Water Environment Improvement (Program Nos. 2009ZX07106-001, 2012ZX07101-002) and the China Basic Research Program (Program No. 2008CB418206). We are grateful for the three anonymous reviewers for their constructive comments and suggestions on the manuscript.