Comparison between anaerobic-anoxic-oxic and anoxic-oxic systems for coke plant wastewater treatment

Coke plant wastewater produces severe pollution throughout china because coal is the main energy resource. The anoxic-oxic (A(2)-O) system can be used to treat this type of wastewater for simultaneous removal of NH3-N and GOD. A comparative study between an anaerobic-anoxic-oxic (A(1)-A(2)-O) system and an A(2)-O system for coke plant wastewater treatment under the same operational conditions was undertaken to examine removal efficiencies of COD and NH3-N, denitrification performance, and transformation of organic pollutants in each system. The experimental results showed that the A(1)-A(2)-O system was comparatively more effective not only in nitrification but also in denitrification performance, The total NH3-N removal efficiency and the anoxic NOx-N removal rate of the A(1)-A(2)-O system were about 20% higher and more than twice that of the A(2)-O system, respectively. Coke plant wastewater subjected to anaerobic treatment resulted in less inhibitory effect on the subsequent nitrification process, and provided a more biodegradable and suitable carbon substrate far denitrifying bacteria. The anaerobic stage played an important role in nitrogen reduction in coke plant wastewater treatment.