| At present,the complete denitrification process of activated sludge is NO3-NO2-NO N2O N2.The process of short-range denitrification is to reduce nitrate nitrogen?NO3--N?only to nitrite nitrogen?NO2--N?.There are many types of denitrifying bacteria.A reaction link,which may achieve the accumulation of NO2--N.Compared with traditional denitrification,short-range denitrification saves a lot of reduction steps in the process.Not only can the reaction rate be increased,the consumption of external carbon sources is reduced,but the sludge output will also be greatly reduced.But because NO2--N has certain biological toxicity,people have been trying to avoid its accumulation.However,in recent years,with the gradual application of anaerobic ammonia oxidation denitrification technology,people pay more and more attention to the short-range denitrification reaction,because its accumulated large amount of NO2--N is the electron acceptor needed for anaerobic ammonia oxidation reaction.And the NO3--N produced by anaerobic ammonia oxidation also provides electron acceptors for the denitrification process.This paper uses activated sludge in reactors with different operating modes to study the effects of different factors on the accumulation characteristics of nitrite nitrogen in the denitrification process,and in-depth analysis of high-throughput measurement of microbial abundance and diversity in different reactors Nitrogen removal efficiency of different activated sludge.Taking activated sludge from anoxic reactor as the test object,the effects of carbon-to-nitrogen ratio?C/N?,types of carbon source,NO3--N concentration and aeration time on the accumulation effect of NO2--N in short-term denitrification were studied The test results show that reducing the amount of carbon source added is beneficial to the accumulation of NO2--N.When C/N=2.5,the nitrite accumulation rate?NAR?reached the maximum,44.01%,NO2--N accumulation amount was 27.44 mg·L-1,and the accumulation time was longer.Under the same low C/N conditions,sodium acetate as a carbon source is more conducive to the accumulation of NO2--N.The conversion rate of NO3--N,nitrite accumulation rate,and nitrite conversion rate?NTR?when sodium acetate is used as the carbon source are higher than those of other carbon sources,and the maximum nitrite nitrogen accumulation is24.3 mg·L-1.With the increase of NO3--N concentration,NTR and NAR gradually increased,and the maximum accumulation of NO2--N gradually increased from 5.85 mg·L-1 to 29.98mg·L-1.Prolonging the aeration time before anoxic denitrification reaction is conducive to the accumulation of nitrite.As the aeration time increases,the longer the nitrate reduction lag time,NTR gradually increases from 34.96%to 48.05%,and NAR gradually increases from 30.89%As high as 40.44%,the maximum accumulation of NO2--N gradually increased from 19.5mg·L-1 to 25.7 mg·L-1.The experiment also used activated sludge in the SBR reactor operated by A/O,simulating the AAO operating mode of the sewage plant.The activated sludge was returned from the outside through the anaerobic tank to the anoxic tank,from the inside to the anoxic tank,and the The three conditions of the oxygen tank circulation and the state of the activated sludge after the sludge is mixed in different proportions under the three conditions.The characteristics of nitrite accumulation during denitrification of activated sludge in different states.The test results show that the NO2--N accumulation amount can be increased by adjusting the mixing ratio of sludge in different states,and the NO2--N accumulation effect of the activated sludge that repeatedly passes through anoxic-aerobic is the best,and the highest NO2--N accumulation The amount and NAR are 15 mg·L-1,37.5%;Proper reduction of C/N is conducive to NO2--N accumulation,and the accumulation of NO2--N is maintained at a higher concentration for a long period of time,but the serious shortage of carbon source will result in nitrate nitrogen cannot be fully reduced,resulting in NO2--N The accumulation effect is poor.In order to explore the characteristics of nitrite accumulation and their relationship with microbial communities during the denitrification of activated sludge in the above two different reactors,the experiment set the same initial NO3--N concentration,different carbon to nitrogen ratio conditions,and observed Nitrogen removal carbon characteristics.The test results show that the NO2--N accumulation rate of the activated sludge in the anoxic reactor is higher than that of the activated sludge in the A/O operation SBR reactor under the conditions of each carbon to nitrogen ratio,The NAR of the two reactors reached the maximum under the conditions of C/N=3 and C/N=4,respectively,36.26%and 26.67%.High-throughput sequencing results show that the abundance and diversity of microbial community of activated sludge in A/O SBR reactor is significantly higher than that of anoxic reactor.The predominant phylum of the two reactors is Proteobacteria,Bacteroidetes,Chloroflexi,and Acidobacteria.The genus of denitrifying bacteria that the two reactors have in common are Thauera and Dechloromonas,other denitrifying bacteria are different. |
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