Treatment of coke-plant wastewater by biofilm systems for removal of organic compounds and nitrogen

Coke-plant wastewater was treated by an anaerobic–anoxic–aerobic (A1–A2–O) biofilm system and an anoxic–aerobic (A/O) biofilm system, respectively. At same or similar levels of hydraulic retention time (HRT), the two systems had almost identical chemical oxygen demand (COD) and NH3 removals, but a different organic-N removal. Set-up of an acidogenic stage benefited for the removal of organic-N and the A1–A2–O system was more useful for total nitrogen removal than the A–O system. HRT did not have a substantial effect on the COD and NH3–N removal efficiencies, but considerably influenced the organic-N removal and distribution of oxidized nitrogen in the final effluent. The GC/MS analysis demonstrated that some refractory compounds were decomposed at the acidogenic stage and resulted in the production of some intermediates, which were more readily degraded in the subsequent aerobic stage. Hence, the A1–A2–O system had better effluent quality than the A–O system in terms of effluent composition.