Novel multistep physical/chemical and biological integrated system for coking wastewater treatment: Technical and economic feasibility

Harmless disposal of coking wastewater (CWW) has become a tough issue due to its complexity, heterogeneity and toxicity. In order to improve contaminant removal efficiency, a novel treatment system, taking into accounts the compositions and toxic characteristics of CWW, was deliberately developed and applied in a full-scale coking wastewater treatment plant. This system integrated a physical/chemical pre-treatment, a biological treatment and a physical/chemical advanced treatment. The pre-treatment, including the degreasing and air floatation, contributed to a significant reduction of oil (removal efficiency > 85%). The bio-treatment was a pre-aeration/aerobic1/hydrolysis/aerobic2 fluidized bed process, which removed 84.1% free cyanide, 93.5% thiocyanate and 86.2% total phenols, indicating an efficient biological detoxification. The successful degreasing and detoxification was conductive to the high removal efficiencies of COD (98.6%) and NH3-N (95.4%). The removal efficiency of total nitrogen reached 90%. Furthermore, the removal efficiencies of 18 polycyclic aromatic hydrocarbons were in the range of 80–99%, while the removal efficiencies of 5 benzene derivatives were in the range of 88–96%. The total concentrations of these trace toxic contaminants were maintained lower than 50 μg L−1 in the final effluent. The overall cost of this system was equal to 9.67 RMB m−3 (<2 US dollars) of CWW. The satisfactory performance of contaminants removal and the low cost implied that this integrated system was a feasible and reliable option for CWW treatment.