Parameter optimization of CANON granular-flocculate composite system with side-flow FNA suppression

In order to explore the best combination of process parameters related to the strategy of inhibiting nitrite oxidizing bacteria (NOB) by side flow free nitrous acid (FNA) treatment, in the completely autotrophic nitrogen removal over nitrite (CANON) process of granular-flocculate composite system, batch test was used to explore the effects of sludge sedimentation time, FNA treatment concentration and FNA processing and processing time to the related functional bacteria activity influence. The NOB activity was targeted inhibition and treatment time on the activity of relevant functional bacteria, so as to inhibit the activity of NOB and reduce the effect of FNA on the activity of functional bacteria. The result showed that the settling time affected the activity of functional bacteria in the treated sludge. With the prolongation of the settling time, the activity of anaerobic ammonium oxidizing bacteria (AnAOB) in the discharged sludge gradually decreased. After settling for 1min, most of the discharged sludge was NOB, and retained as much AnAOB as possible in the reactor. At this time, the relative activities of AnAOB, ammonia oxidizing bacteria (AOB) and NOB were 15.79%, 54.55% and 68.63%, respectively. Considering the effect of FNA on the activity of NOB and AOB, the activity of AOB was 38.71%, while the NOB activity was only 12.5% after inhibition with 0.6mg/L FNA for 12h. The results of response surface analysis showed that the treatment time and treatment concentration of FNA were the key factors affecting the activity of NOB and AOB. © 2022 Chinese Society for Environmental Sciences. All rights reserved.