[Nitrite Accumulation Characteristics of Partial Denitrification in Different Sludge Sources Using Sodium Acetate as...

In order to explore the characteristics of nitrite accumulation during the operational period of partial denitrification in different sludge sources using sodium acetate as a carbon source, No.1 SBR and No.2 SBR were used to inoculate with surplus sludge taken separately from a secondary sedimentation tank of a sewage treatment plant and simultaneous nitrification and denitrifying phosphorus removal system. By reasonably controlling the initial nitrate concentration and anoxic time, partial denitrification was realized. The carbon and nitrogen removal characteristics under different initial COD and NO₃^--N concentrations were investigated. The results showed that, using sodium acetate as the carbon source, the partial denitrification process in No.1 SBR and No.2 SBR sludge successfully began in 21 d and 20 d, respectively. The accumulation of NO₂^--N and nitrite accumulation rate (NAR) in reactors were maintained at high levels (12.61 mg·L^-1, 79.76% and 13.85 mg·L^-1, 87.60%, respectively). When the initial NO₃^--N concentration of No.2 SBR was 20 mg·L^-1 and the initial COD concentration increased from 60 mg·L^-1 to 140 mg·L^-1, the operation time for achieving the highest NO₂^--N accumulation in the system was shortened from 160 min to 6 min. The NO₃^--N ratio of the denitrification rate (in VSS) increased from 3.84 mg·(g·h)^-1 to 7.35 mg·(g·h)^-1. Increased initial COD concentration was beneficial to the accumulation of NO₂^--N during partial denitrification. When the initial COD concentration of No.2 SBR was 100 mg·L^-1 and the initial NO₃^--N concentration increased from 20 mg·L^-1 to 30 mg·L^-1, NAR was maintained above 90% and up to 100% (the initial NO₃^--N concentration was 25 mg·L^-1). When the initial NO₃^--N concentration was ≥ 35 mg·L^-1, insufficient COD caused NO₃^--N to be completely reduced to NO₂^--N. Under different initial COD concentrations (80, 100, or 120 mg·L^-1) and different initial NO₃^--N concentrations (20, 25, 30, or 40 mg·L^-1), the nitrogen and carbon removal and partial denitrification performance of the No.2 SBR was better than that of No.1 SBR.