[Using a two-stage SBR process for removal of organics and nitrification-denitrification via nitrite]

High efficiency removal of organics and nitrogen by using a two-stage SBR process was introduced in this paper. Most of organics was removed in the first stage SBR reactor(SBR1) under the aerobic condition. Subsequently the second stage SBR reactor(SBR2) firstly operated under the aerabic condition for simultaneous nitrification and removal of a small amount of residual organics. Nitrification was controlled to the nitrite-type nitrification. Then denitrification happened in SBR2 under the anoxic condition. The petrochemical industry wastewater was used as external carbon sources in the denitrification. The experimental results indicated that in a two-stage SBR system, two kinds of biomass with the different function existed in the different reactors, which was beneficial to improve the treatment efficiency. The effluent COD reduced again because SBR2 removed COD which was left in SBR1 effluent. It resisted the disturbance of the high organic loading to nitrification. Consequently, as compared to a single SBR process, a two-stage SBR not only improved the treatment efficiency, but also saved the energy cost.