The removal of nitrate-nitrogen from groundwater was investigated using two rotating biological contactors (RBC) in series. The first pilot plant RBC reactor was operated under anoxic condition to remove nitrate-nitrogen. A fraction of effluent of the anoxic RBC was fed to a bench scale aerobic RBC to study the degradation of residual organic carbon and oxidation of nitrite-nitrogen. The first reactor achieved a nitrate removal efficiency of 90 percent for a loading rate of 76 mg/m2.h. The corresponding effluent nitrate, nitrite and residual carbon sources concentrations amounted to 3.3, 0.34 and 3.9 mg/l, respectively. The optimum ethanol to nitrate-nitrogen (E/N) ratio was found to be 2.35. No residual ethanol and nitrite-nitrogen were observed in the final effluent under optimum conditions. Dissolved oxygen in the final effluent was found to be greater than 7 mg/l. The results of the study suggest that using a continuous anoxic-aerobic RBC is a convenient and reliable process for removal of nitrate, residual organic carbon and nitrite.

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