| In this experiment,a SBR reaction device was used as a basic device,and the artificially simulating wastewater was prepared as an object.Based on 16S rRNA high-throughput sequencing technology,ammonia oxidizing bacteria?AOB?was enriched and cultured under low free ammonia?FA?condition,and short-cut nitrification process was realized.Subsequently,the inhibitory effect of free nitrous acid?FNA?on AOB was investigated in activated sludge rich in AOB.The non-matrix inhibition kinetic model was used to fit the experimental data and the environmental factors were analyzed by Structural Equation Modeling?SEM?.This paper aims to provide theoretical support for the optimization of short-cut nitrification technology,so as to obtain an efficient,stable and economical biological nitrogen removal method for wastewater.During the AOB enrichment test under low FA conditions,it was found that the FA concentration was always less than 1.05 mg·L-11 throughout the medium range of the test,and the reaction DO concentration was controlled at 1.00-2.0 mg·L-1 at a temperature of 19-21?.By gradually increasing the concentration of NH4+-N,the AOB enrichment culture could be realized after 280 cycles.The average NH4+-N concentration of the SBR system was maintained at 2.6 mg·L-1,while the average of ARE was greater than 90%,and the cycle of 210-280 was stable to the average NiAR at 90%and NaAR at 10%,indicating the realization of short-cut nitrification.By controlling the stop aeration time at the"ammonia valley"of pH curve,the test can ensure the accumulation of NO2--N and limit the growth of nitrite-oxidizing bacteria?NOB?,so as to ensure the sustained and stable operation of the short-cut nitrification system in the reactor.The microbial diversity of three NiAR?39%,75%and 95%?activated sludge samples during AOB enrichment was investigated by 16S rRNA high-throughput sequencing.With the implementation of the short-cut nitrification process,the richness and diversity of sample bacteria showed a decreasing trend,and the samples showed a certain degree of proliferation of Proteobacteria,Acidobacteria,Spirochaetes,Caldiserica,Deinococcus-Thermus,Armatimonadetes and Patescibacteria.In this SBR system,Nitrosomonas coexisted with Nitrospira,and the variation trend of the relative abundance of the two genera in the three groups of samples was Nitrosomonas?5.12%?9.30%?13.47%?and Nitrospira?5.87%?3.13%?0.00%?.Under the low FA condition,AOB was well enriched and cultivated, while NOB was completely inhibited.Thauera eventually became the dominant denitrifying bacterium in short-cut nitrification systems.Based on the test of the inhibitory effect of FNA on AOB,it was found that when the concentration of NH4+-N was kept at 57.32 mg·L-1,and the concentration of FNA in the reactor was in the range of 5.12×10-4-1.00 mg·L-1,the concentration of NH4+-N fluctuated from 12.07-50.52 mg·L-1 at the end of nitrification.When the concentration of FNA?1.00 mg·L-1,the concentration of NH4+-N almost remained at 52.71 mg·L-1 at the end of nitrification,which reached the upper limit of AOB inhibition.Due to the high concentration of NO2--N in the inlet,the average standard deviation of NO2--N concentration in each cycle was 11.90 mg·L-1,which impacted the short-cut nitrification process in the reactor,and the concentration deviation of NO2--N at the end of nitrification was negative.The Vadivelu non-matrix inhibition model better fitted the inhibition kinetics of FNA on ARE and SAOR.SEM analysis showed that both ARE and SAOR were negatively correlated with FNA concentration and NO2--N concentration,and positively correlated with pH.Based on the analysis of 16S rRNA high-throughput sequencing technology,it was found that during the inhibition of AOB by FNA,the microbial diversity of the system changed significantly.When FNA concentration was 0-0.51 mg·L-1,the differences among microbial groups were small;when FNA concentration was 0.51-2.20 mg·L-1,the differences between microbial communities were significant.Meanwhile,with the increase of FNA concentration,the microbial flora richness decreased and the diversity increased.Proteobacteria,Bacteroidetes and Chloroflexi were the dominant phyla in the system,accounting for more than 95%of the relative abundance of all samples.With the increase of FNA concentration,Proteobacteria,Acidobacteria and Patescibacteria were significantly inhibited,while Bacteroidetes and Chloroflexi showed little changes.When the FNA concentration was greater than 1.0 mg·L-1,a relatively rare Thaumarchaeota was detected in this experimental system.When the concentration of FNA reached 0.26 mg·L-1,the inhibition of AOB was obvious.Nitrotoga activity was inhibited when FNA reached 0.26 mg·L-1 and Nitrospira activity was inhibited when FNA reached 0.51 mg·L-1. |
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