Enrichment And Physiological Characteristics Of Complete Ammonia Oxidizers

In recent years,the discovery of complete ammonia oxidizers(comammox for short)broke people’s perception that nitrification must be accomplished by two nitrifying bacteria groups.The microorganism can perform the functions of ammonia oxidation and nitrite oxidation at the same time,and oxidize ammonia nitrogen to nitrate nitrogen in an aerobic state.Compared with traditional ammonia oxidizing microorganisms,it has high affinity for ammonia and high growth rate.The enrichment culture of comammox is the basis for its isolation and identification,microbial mechanism analysis and engineering application.However,due to its slow growth,it is difficult to separate from traditional ammonia oxidizing microorganisms.There is currently only one pure strain and a few enriched cultures.In this paper,the main research content is the enrichment culture of nitrifying bacteria in the whole process.Two different configuration reactors,the sequencing batch reactor(SBR)and the sequencing batch membrane bioreactor(SBBR)are used.The effects of different influent nitrogen loads and different inoculated sludges on the enrichment and denitrification performance of comammox were compared.The enrichment optimization strategy and denitrification mechanism of comammox of denitrification were analyzed.At the same time,molecular biology techniques such as qPCR and high-throughput sequencing are used to explore microbial community changes.In order to provide theoretical support for the promotion and application of comammox in the field of sewage biological treatment.Below are key research findings:(1)Change the operating load of the reactor by reducing the ammonia nitrogen concentration in the influent.Comammox was effectively enriched in both reactors R1 and R2.R2 has stronger anti-interference ability and more stable effluent quality due to the addition of fillers and internal circulation system.(2)The microbial community structure analysis showed that the relative abundance of Nitrospira in R2 reached 22.79%,which was 6.8 times that of R1.Secondly,Proteobacteria,Bacteroidetes,Acidobacteria,Chloroflexi and other species also showed differential changes in the R1 and R2 sludge samples.(3)During the experiment,the ammonia-oxidizing microorganisms in R1 and R2 were always dominated by comammox.At the end of the experiment,the copy number of comammox amoA in R2 reached 3.50E+08 copies/ng DNA,and its abundance was 27.9 times that of R1.And the ratio of comammox to total bacteria in R2 sludge is 16%,and R1 is only 2.4%,indicating that the SBBR reactor system(R2)is the optimal reactor configuration for enriching comammox in this experiment.(4)R3,R4,and R5 were inoculated with seaside sediment mud,freshwater lake bottom mud and flocculent sludge in aerobic pools of sewage treatment system,respectively.Different kinds of sludge can enrich comammox effectively.The addition of fillers in the system was beneficial to the formation of biofilm and the attachment of microbial community.(5)At the end of the experiment,the proportion of comammox in R3,R4,and R5 was 3.8%,27%,and 5%respectively.The amount of comammox in R4 reached 3.65E+08 copies/ng DNA,which dominated the nitrification process of the system.(6)The bacterial community structure of the samples after enrichment is obviously different.The microbial community richness and diversity in R3,R4,and R5 decreased continuously,and the relative abundances of Nitrospira were 7.9%,31.7%,and 7.3%,respectively.The results show that the high abundance of comammox can be achieved by using freshwater lake sediment.Using flocculent sludge in aerobic tank of sewage treatment system as inoculum can achieve low-abundance enrichment of comammox as the dominant ammoniaoxidizing microbial community.