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Keywords:

  • anaerobic/anoxic/oxic/oxic(A2/O2);
  • biofilm bioreactor;
  • coking wastewater;
  • removal efficiency;
  • hydraulic retention time(HRT)

Abstract

BACKGROUND: Biological treatment efficiency of coking wastewater is rather poor, especially for chemical oxygen demand (COD) and ammonia-nitrogen (NHequation image-N) removal due to its complex composition and high toxicity.

RESULTS: A pilot-scale anaerobic/anoxic/oxic/oxic (A2/O2) biofilm system has been developed to treat coking wastewater, focusing attention on the COD and NHequation image-N removal efficiencies. Operational results over 239 days showed that hydraulic retention time (HRT) of the system had a great impact on simultaneous removals of COD and NHequation image-N. At HRT of 116 h, total removal efficiencies of COD and NHequation image-N were 92.3% and 97.8%, respectively, reaching the First Grade discharge standard for coking wastewater in China. Adequate HRT, anoxic removal of refractory organics and two-step aerobic bioreactors were considered to be effective measures to obtain satisfactory coking effluent quality using the A2/O2 biofilm system. The correlation between removal characteristics of pollutants and spatial distributions of biomass along the height of upflow bioreactors was also revealed.

CONCLUSION: The study suggests that it is feasible to apply the A2/O2 biofilm process for coking wastewater treatment, achieving desirable effluent quality and steady process performance. © 2012 Society of Chemical Industry