Performance And Microbial Characteristics Of Completely Autotrophic Nitrogen Removal Over Nitrite (CANON) In Membrane Bioreactor

Completely autotrophic nitrogen removal over nitrite (CANON) process is considered as one of the most economical and efficient nitrogen removal technology. It could save60%oxygen and100%organic carbon consumption when compared with conventional nitrification-denitrification process. However, there are still some challenges in this process, such as the long start-up period and low nitrogen removal rate (NRR). Thus, membrane bioreactor (MBR) was adopted to this study at ambient temperature, to resolve the above problems in CANON process. The main contents of this study were as follows: rapid start-up of CANON process; influence factors of CANON process; feasibility for treating domestic sewage; corresponding microbial characteristics.Three MBR reactors with identical setup (named R1, R2and R3) were adopted into this study with a constant reaction temperature of25°C, all of which were seeded with conventional activated sludge taken from Gaobeidian municipal plant. Specifically, R1was successfully started-up in78days by gradually decreasing HRT, with a maximum nitrogen removal rate (NRR) of0.95kg/m3/d; R2was successfully started-up in50days by gradually increasing influent ammonia, with a NRR of0.70kg/m3/d；R3was started-up in36days using intermittent operation mode, with a NRR of0.61kg/m3/d. The three statagies were all effective for the start-up of CANON, during which the intermittent operation mode was the most rapid but with a lowest NRR.DGGE was used to study the microbial community dynamics during the start-up of CANON process. Results suggested the biodiversity decreasing of aerobic ammonia-oxidizing bacteria (AerAOB) with Nitrosomonas as dominant specie, and that of anaerobic ammonia-oxidizing bacteria (AnAOB) transformed to Candidatus Kuenenia stuttgartiensis from Candidatus Brocadia flugida with biodiversity increasing. Moreover, MBR was proved to be a beneficial set-up for the realization of CANON. Both biofilm (membrane surface) and activated sludge (in the mixed liquor) coexisted in the reactor. The proportion of AnAOB was higher in the biofilm while that of AerAOB was higher in the sludge, organisms in these two parts both contributed to the high-rate nitrogen removal.Ammonia concentration was an important influence factor of CANON, which could either affect the nitrogen removal or the organism species. To study the effect of ammonia on CANON process, performances and microbial characteristics of R1and R2were compared, together with batch experiments under different ammonia. Results suggested that in R2with higher ammonia, the biodiversity of AerAOB, and the bioactivity of AerAOB and AnAOB were higher, while those of NOB were both lower. The ammonia decreasing performed a more significant impact on AerAOB than AnAOB. Moreover,by studying the combined effects of ammonia loading rate (ALR) and aeration flow rate (AFR), a key parameter (AFR/ALR) was proposed. AFR/ALR should be limited below0.28(L/min)/(kg/m3/d) for stable CANON.Another substrate for CANON was alkalinity, which also acts as inorganic carbon. The effect of influent alkalinity on bioactivity, reactor performance and distribution were studied. Results suggested that CANON was significantly affected when the ratio of influent alkalinity to ammonia (A/a) was below4; NRR could not totally recover even A/a was improved to10; A long-term shortage of alkalinity would lead to the proportion decreasing of both AerAOB and AnAOB. A/a should be kept around8for high bioactivity of AerAOB and AnAOB, together with effective inhibition on NOB. Glucose was added into the influent to study the effect of COD. Results indicated that COD had no influence when C/N was lower than1; Dinitrification occurred in the reactor when C/N was higher than1, which improved the NRR to some extent.Domestic sewage was introduced to two MBR-CANON systems. In this phase, the biodiversity of AerAOB decreased with little change of AnAOB. The proportions of AerAOB and AnAOB both decreased, and the sludge showed a more incompact distribution. Results showed the feasibility of this system for simultaneous effective removal of COD, total nitogen and SS. The turbidity in effluent of the two reactors were both below1NTU. If coupled with a subsequent dosing of inorganic metal salt, this system could realize a simultaneous removal of phosphorus.Results in this thesis demonstrated that MBR was a suitable experimental setup for the operation of CANON seeding with conventional activated sludge at ambient temperature. Simultaneous removal of COD, TN and SS from domestic sewage could be achieved in the MBR-CANON system.