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This study proposes a strategy to inhibit nitrite-oxidizing bacteria (NOB) in the completely autotrophic nitrogen removal over nitrite (CANON) process by alternating long and short operational cycles. During long cycles, in-situ free ammonia (FA) was used to suppress NOB, while in short cycles, substrate inhibition was employed to continuously suppress NOB activity when FA concentrations fall below the inhibitory threshold for NOB. Two sets of SBR, R1 and R2, were operated with different long-short cycle alternation patterns. The results show that both R1 and R2 achieved good nitrogen removal efficiencies (NRE), with R2 slightly outperforming R1. The NRE for R1 and R2 were 78.73% and 85.41%, respectively, while the effluent NO3--N concentrations were 14.02mg/L and 7.21mg/L, respectively. At day 64, the specific nitrate production rates (SNPR) of R1 and R2 decreased to 2.88 and 1.95mgN/(gMLVSS·h), respectively, indicating effective suppression of NOB activity. Analysis of extracellular polymeric substances (EPS) revealed that the alternating long and short cycle strategy promoted microbial EPS secretion. The EPS content in R1 and R2 increased from 40.22mg/gVSS at inoculation to 86.41mg/gVSS and 97.79mg/gVSS, respectively. High-throughput sequencing results indicated that the dominant bacterial phyla in the system were Proteobacteria, Bacteroidota, and Planctomycetota. The growth of NOB, represented by Nitrospira and Nitrobacter, was inhibited in both R1 and R2. The relative abundance of Nitrospira decreased from 2.05% in the inoculated sludge to 0.18% in R1 and 0.11% in R2, while Nitrobacter abundance dropped from 1.97% to 0.06% in R1 and 0.05% in R2. Meanwhile, the abundance of AnAOB, (Candidatus_Brocadia) reached 8.92% (R1) and 9.14% (R2), and AOB, (Nitrosomonas) achieved abundances of 4.28% (R1) and 6.56% (R2), establishing a well-coordinated synergy.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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