ORIGINAL RESEARCH
Treatment of Mixed Chemical Wastewater by a Two-Stage A/O Process for Elimination of COD Nitrogen and Toxic Matters
Ping Du1, 2, Wenhong Li1, 3, Zhiwei Liang1, Yingxu Chen1, 3, Shangyuan Yang1, Fuping Yan1
 
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1Institute of Environmental Science and Technology, Zhejiang University, Hangzhou 310029, P. R. China
2Changye Environmental Protection Group Co., Ltd.
3Zhejiang Province Key Laboratory for Water Pollution Control and Environmental Safety,
Hangzhou 310029, P. R. China
 
Pol. J. Environ. Stud. 2013;22(1):85–91
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ABSTRACT
In our work a two-stage A/O system consisting of two independent A/O subsystems was used to remove high concentrations of COD, nitrogen, and toxic matter from mixed wastewater discharged by a comprehensive chemical group. The mixed liquid return was not adopted, and the sludge return ratio was kept at a high value of 100-200% to maintain high usable activated sludge concentration. Adequate NaHCO3 was added to keep the influent alkalinity/KN ratio around 7.14 to 1. The system was running stably during the whole experimental period. Subsystem one obtained high COD and organic nitrogen removal capability without being influenced by the increasing COD loading. 87.6% COD was removed and 75.7% org-N was transformed to NH4 +-N. Due to the low COD/KN ratio created by subsystem one, the nitrification efficiency of subsystem two reached a high value of 92.1%. Besides, aerobic biological oxidation of oxic tank one showed excellent ability on toxic matter elimination. The acute toxicity of the whole system dropped from 0.165 to 0.042 mg HgCl2/L. It has been proven by this study that, using the two-stage A/O system with sludge return only to treat COD nitrogen and toxic matters, laden mixed wastewater from comprehensive chemical groups may be feasible.
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ISSN:1230-1485