Three-Stage Biological System for Treatment of Coke Oven Effluent

A three-stage continuous biological treatment system has been developed for removal of cyanide, phenol, organics, and ammonia from a coke oven effluent. Two stages of activated sludge treatment with completely mixed aeration tanks followed by a hybrid anoxic reactor, in series, were used. The hybrid anoxic reactor uses self-immobilized microbial biomass (granular sludge) under fluidized conditions. A $50\mathrm{L}/\text{day}$ pilot plant was evaluated for a period of over 6 months to monitor organics, ammonia, phenol, and cyanide removal. The activated sludge treatment systems were operated at a hydraulic retention time of 1 day and the hybrid reactor at 16 h. Major constituents of the effluent used in the study were cyanide ($9–33\mathrm{mg}/\mathrm{L}$), phenol ($21–235\mathrm{mg}/\mathrm{L}$), ammoniacal nitrogen ($400–\mathrm{1,600}\mathrm{mg}{\mathrm{NH}}_3\text{-}\mathrm{N}/\mathrm{L}$), organic load [400–1,500 mg chemical oxygen demand $(\mathrm{COD})/\mathrm{L}$], and nitrate nitrogen ($0–90\mathrm{mg}{\mathrm{NO}}_3\text{-}\mathrm{N}/\mathrm{L}$). Removal efficiencies were around 90% for organic load, 88% for ammoniacal nitrogen, 100% for nitrate nitrogen, and almost 99 and 100% for cyanide and phenol, respectively. The process is presently being scaled up to 1,000 L per day.