[Study on treatment of coking wastewater by A/O process of biological filter].

Coking wastewater was treated by A/O process of biological filter with a special kind of carrier. The wastewater contained much more phenolic compounds with about 2000 mg/L of COD and 260 mg/L of NH4+ -N. The A/O system could achieve average removal efficiencies of 87.0% and 91.6% for COD and NH4+ -N, respectively, when HRT was 60 h. The NH4+ -N in the effluent could meet the first level of National Discharge Standard at optimal operation condition. The phenolic compounds with low molecular weight could be fully biodegraded by A/O system. The organic compounds in the effluent were in the relative molecular weight range of 10,000-30,000 and contained --OH, C==O, C--O and phenyl group. Based on the support and protection of the carrier, a great number of microorganisms adhered and immobilized on the outer and inner surface of carrier, which contributed to a simultaneous removal of COD, NH4+ -N and TN. The A/O system biological filter showed a characteristic of steady performance and resistance ability during the operation period.