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Abstract
The impact of sludge deposition on nitrogen removal was studied in order to provide basic research data for alleviating the sludge deposition problem. The site was an emptied oxidation ditch at a wastewater treatment plant in Chongqing City (China). Actual tests and numerical simulations were used to analyze the distribution of deposited sludge. Organic substances and the X-ray fluorescence spectra and particle sizes of deposited sludge were also analyzed. The height of deposited sludge was 0.2–1.2 m, and the total volume of deposited sludge accounted for about 19% of the effective volume of the oxidation ditch. The sludge was mainly deposited in the anoxic zone, reducing the hydraulic retention time, and nitrogen removal rate by 57 and 20%, respectively. The volatile suspended solids (VSS)/suspended solids (SS) value of the deposited sludge ranged from 0.05 to 0.27, and the sludge's main component was sand. The median particle size (D50) range was 67.14–251.87 μm, and this had an obvious correlation with VSS/SS. Inorganic substances from influent precipitated in the bottom of the oxidation ditch together with sludge through attachment, capture, and entrapment.
Acknowledgements
The authors are grateful for the financial support of “Major Science and Technology Program for Water Pollution Control and Treatment” (2012ZX07307-001).