Study On Technologies And Mechanisms Of Bioactivity Promotion And Coupling Optimization Of Nitrogen Cycle Bacteria Based On Anammox

Sustainable development goal 6 of the United Nations emphasizes the efficient management of water resources,wastewater treatment,and reuse of treated wastewater.Among water pollutants,nutrients such as carbon,nitrogen,and phosphorus damage the aquatic environment by reducing the water quality.The main agenda of this endeavor was the removal of nitrogen from wastewater.Removing nitrogen from wastewater is an economically expensive and energy-consuming wastewater treatment process.However,discovering the anaerobic ammonium oxidation(anammox)process changes the wastewater treatment paradigm.Anammox is a slow-growing guild of bacteria,and the sole anammox process cannot be applied in main-stream and side-stream wastewater treatment processes.Nevertheless,coupling anammox with partial nitrification(PN-anammox)has been an immensely rewarding and scientifically supported side-stream wastewater treatment process.However,the PN-anammox process is inherited with severe issues of higher effluent nitrate and lower nitrogen removal efficiency at a lower temperature.Thus,it is evident that PN-anammox cannot meet the desired target without the involvement of other nitrogen cycle bacteria.This PhD dissertation studied shortening the anammox start-up period and coupling of anammox with the partial denitrification(PD)process.The quantitative polymerase chain reaction was performed for functional gene analysis.Advance omics techniques such as high-throughput sequencing and metagenomic and meta-transcriptomic analysis were performed to understand the microbial community’s diversity,compositions,and succession.The functional prediction of the nitrogen removal process was disclosed on the base of the KEGG,eggNOG,and COG databases.The main results of this endeavor are summarized as follows:1.First,the start-up of anammox by reducing the activity of non-objective bacteria was investigated in this study.The Fe(Ⅵ)supplement effectively shortened the start-up period of anammox from 52 to 32 days by reducing the pressure of non-objective bacteria.The anammox 16S rRNA gene copy counts were 2.86×107 copies/ng of DNA in R2,higher than 1.84 ×107 copies/ng of DNA in R1.The proportion of Planctomycetes increased from 0.025%to 4.3%in R2 and 0.41%to 3.8%in R1 at the end of the start-up period.Similarly,the relative abundance of Candidatus Brocadia in R2(0.011%)overpassed R1(0.003%)at the end of the start-up phase.Further,the network analysis showed modularity index values of 0.512(R1)and 0.713(R2),with a more positive correlation and a higher degree of average connectivity among nodes 12.3(R2)and 11.09(R1).However,in the nitrogen loading enhanced period,the application of Fe(VI)exhibited a negative influence.Thus,this study proposed that Fe(Ⅵ)effectively reduced the startup period of anammox by anaerobic sludge treatment with a recommended dose of 200mg/L.2.Second,coupling anammox with a partial denitrification process was developed,and the impacts of nano zero-valent iron(nZVI)were investigated.The nitrogen removal efficiency(83.12%)was improved at an nZVI concentration of 10 mg/L of reactor working volume compared with 79.15%without nZVI addition and 74%at higher nZVI concentration.The Candidatus Kuenenia dominated anammox genera with a relative abundance of 1.51%at lower nZVI concentration,which then decreased to 0.5%at higher nZV1 dose and again increased to 2.23%at the end of the recovery phase.The relative abundance of potential PD bacteria Thauera and Zoogloea was first decreased at a lower nZVI concentration and then increased at a higher nZVI dose,showing that PD bacteria are more resilient to adopt the higher nZVI concentration than anammox.Moreover,a lower amount of nZVI selectively enriched nitrate reductases and inhibited nitric and nitrous oxide reductases,showing a stable partial denitrification process for coupling with anammox.Likewise,KEGG pathways representing bacterial secretion,two-component system,and flagellar assembly were all improved under low-dose nZVI.The pathways representing ABC transporter(2.11%)and quorum sensing(1.88%)showed higher abundance at an nZVI dose of 50 mg/L,showing the resilience of microbial cells to resist the unfavored environment.In conclusion,this research elucidates that applying low-dose nZVI daily is more convenient for a stable PD-anammox process.3.Third,this study established the first stable connection of anaerobic ammonium oxidation with constant nitrite generation by PD bacteria under a low-strength(1.3 mT)magnetic field(MF).Under increased loading rates,the nitrogen removal efficiency achieved in the control reactor(R1)was 75%lower than that of the experimental reactor(R2),which was 85%.According to a metatranscriptomic analysis,Thauera and Zoogloea,potential PD bacteria were expressed at substantially lower levels in R1(5.75%and 1.21%,respectively)than in R2(10.25 and 6.61%,respectively).Metagenomic analysis showed that six functional modules related to nitrogen were all higher in R2 compared with R1.Carbon metabolism,pyruvate metabolism,carbon fixation pathways in prokaryotes,and citrate cycle were higher and more active pathways under lowstrength MF.The citrate cycle produced reducing power for nitrate reduction.which appeared to be a feasible explanation for the selective enrichment of PD bacteria.In contrast to the control reactor,which was dominated by a hydroxylamine-dependent anammox process as revealed by metagenomic and meta-transcriptomic,the reactor under the effect of low strength MF enhanced nitric-oxide-dependent anammox process.Overall,this study showed that low-strength MF is a valuable technique to lock the nitrate reduction until nitrite for successful anammox-centered nitrogen removal from wastewater.