Start-up of granular-flocculate sludge CANON process based on side-flow FNA treatment

In order to evaluate the feasibility of the free nitrite (FNA) lateral flow treatment of flocculent sludge by initializing the autotrophic nitrogen removal (CANON) processing, this study was conducted to investigate effects of the FNA treatment on ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) activities and the operation efficiency of hydraulically screened flocculent sludge treatment in the granular-flocculation sludge SBR reactor. The results show that after 0.6mg/L FNA treatment of R1 for 30days, the removal rate of NH4+-N returned to the level before the treatment and the short-range nitrification was stable. The average total effluent nitrogen of the system was 13.84mg/L; and the ∆NO3--N/∆NH4+-N ratio was close to the theoretical one of the CANON reaction equation of 0.11, indicating successful start of the CANON process. However, R2, treated with 0mg/L FNA failed to start due to the massive proliferation of NOB. The batch test results confirm that after the treatment of 0.6mg/L FNA, the NOB activity was only 16.39% of the control group (FNA=0mg/L), and the recovery of NOB activity was not found in subsequent operation thus NOB was effectively inhibited. Additionally, the activity of AOB was affected because the removal rate of NH4+-N in the reactor was only 69.69% of that of before treatment and the activity of AOB recovered by only 68.06% after 6h. © 2022 Chinese Society for Environmental Sciences. All rights reserved.