Innovative Biological Process for Treatment of Coking Wastewater

Coking wastewater was treated by an A-O-1-O-2 biofilm system composed of an anoxic bioreactor and two aerobic ones. To improve removal efficiency of organic pollutants, the anoxic bioreactor was used to investigate organic removal via anoxic process with enhanced denitrification, and the first aerobic bioreactor was used to test the feasibility of nitrogen removal via nitrite in an attached growth system. Concentrations of ammonium nitrogen (NH4+-N), phenols, and chemical oxygen demand (COD) in the wastewater ranged between 200 and 500, 250 and 350, and 1,700 and 2,200mg L-1, respectively. Removal of organic pollutants through anoxic process was enhanced by raising NO3--N/COD ratio in the influent of anoxic bioreactor. Removal efficiencies for total organic compounds of 17.84%, 41.78%, 82.63%, and 88.73% were obtained at NO3--N/COD ratios of 1:10, 1:5, 1:3, and 1:2, respectively. Shortcut nitrification was obtained in the first aerobic bioreactor when dissolved oxygen was 2.0-3.0 mg L-1 at 35 degrees C +/- 1 degrees C. Both ammonia oxidation ratio and nitrite accumulation ratio were maintained above 85%, with ammonia load ranging from 0.22 to 0.30 g NH4+-N (L day)(-1) by adjusting the hydraulic retention time and influent NH4+-N concentration. Gas chromatography/mass spectrometry analysis demonstrated that most of organic compounds were decomposed at the enhanced denitrification stage and the high removal efficiency of total organic compounds was obtained through the A-O-1-O-2 process. This study was presumed to provide a better option for the treatment of coking wastewater.