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Study on nitrogen removal efficiency of different aeration modes in oxidation ditch

Under the same condition of aeration, two different aeration modes were operated to treat municipal sewage in oxidation ditch: point aeration and step aeration. The former ran in a way of mixing 6min and aerating 1min alternately that was repeated four times in a cycle. The latter contained mixing 24min and aerating 4min in a cycle. The results show that the oxygen is dissolved more efficiently with longer Aerobic region in point aeration than in step aeration, while the oxygen utilization rate(for nitrifying) is higher in step aeration than point aeration. The nitrifying bacteria activity under the two aeration modes is 4.55mgNH4+-N/gMLVSS.h and 4.56mgNH4+-N/gMLVSS.h respectively. NH4+-N concentration is below 5mg/L with equal nitrification effect. COD removal efficiency is respectively 91.01% and 92.19% with COD of the effluents below 30mg/L. But the elimination pathway of COD is unlike. COD is mainly used for denitrification in step aeration while only less organics is utilized for denitrification in point aeration where nitrogen removal efficiency is low and concentration of nitrate is high in the effluent.