| Anaerobic ammonium oxidation(anammox)is a novel biotechnology process.The corresponding anammox bacteria can directly transform ammonium(NH4+,electron donor)and nitrite(NO2-,electron acceptor)into nitrogen gas(N2).Compared to conventional nitrification-denitrification process,anammox process escapes the dependences of carbon sources and oxygen leading to a saving of 100%oxygen demand,100%organic carbon source,shorter process and less N2O production.But this process still has some shortcomings,such as:(1)the anammox bacteria has a long generation cycle,usually was more than 11 days,and leads to the longer start-up time;(2)the anammox bacteria is quite sensitive to the environment,pH,DO,temperature and free nitrous acid can influence the activity of bacteria and nitrogen removal performance;(3)total nitrogen removal rate needs to be improved.It was more than 20 years since anammox process was found,and researchers focus on shortening the start-up anammox process and starting up this process in extreme condition.They were trying to fast start up this process by choosing the type of reactor and inoculation sludge,adding the carrier and controlling the operating conditions.Researches have shown that zero-valent iron could reduce the residual DO in the reactor,provide a favorable environment,accelerate the bioaccumulation,and reduce nitrate.Magnetite could provide a weak magnetic field and iron ion for the microbe to enhance the activity of anammox bacteria.Meanwhile,magnetite could role as the carrier to promote the growth of microorganisms and the formation of granular sludge.In this paper,we will proceed from the view of adding the carrier to explore the effect of zero-valent iron and magnetite on the nitrogen removal performance and biological community distribution of the anammox start-up process.The main research results are as follows:(1)The 50 mg/L and 1000 mg/L concentration of zero-valent iron could shorten the startup time from 102 to 84 and 90 days,respectively.Nitrogen removal result and qPCR results revealed that 1000 mg/L concentration of zero-valent iron could inhibit the microbe at the initial reaction stage,but after 50 days,microbe could adapt the high zero-valent iron concentration,and the zero-valent iron could promote the activity and abundance of microbe.The qPCR results showed that,the copies number of anammox 16S rRNA for the reactor with 50 mg/L and the reactor with 1000 mg/L were 1.26×108 copies/ng and 1.34×108 copies/ng on day 120,while the result of control check was 8.73×107 copies/ng.(2)Compare with the control check(4.87 ?mol/L),production of N2O in the reactors with zero-valent iron are lower than that of control check(the production of reactor with 50 mg/L zero-valent iron was 3.76 ?mol/L and the production of reactor with 1000 mg/L zero-valent iron was 3.24 ?mol/L).At the same time,copy numbers of nosZ were 1.48×106 copies/ng(control check reactor),6.33×105 copies/ng(reactor with 50 mg/L zero-valent iron),and 1.09×106 copies/ng(reactor with 1000 mg/L zero-valent iron).Thus,zero-valent iron could inhibit the production of N2O.(3)High-throughput sequencing results revealed that zero-valent iron could influence the diversity of microorganisms and the distribution of Planctomycetes and Proteobacteria.And according to the result of taxonomic classification at the genus level,Candidatus Brocadia has strong adaptability and easy to enrichment.(4)Magnetite could shorten the endogenous denitrification phase,and could enhance the total nitrogen removal rate from 59.3%to 65.8%.When increase the nitrogen loading rate,the reactor with magnetite could show the capacity of resisting the loading.On day 150,the copy number of the reactor with magnetite was 2.59±0.009×108 copies/ng,and the proportion of anammox on whole bacteria was 58.88%.While the copy number of the control check reactor was 2.44 ±0.004 ×108 copies/ng copies/ng,and the proportion of anammox on whole bacteria was 57.35%.QPCR results showed that magnetite could accelerate the abundance of anammox bacteria.(5)The reduced N2O emission of the reactor with magnetite(25.06± 15.27?mol/L)combined with reduced nosZ qPCR results(2.26± 0.029×106 copies/ng)revealed that this magnetite-anammox reactor also can be served as an ideal alternative for N2O emission reduction in ammonium-rich wastewater treatment.(6)High-throughput sequencing results revealed that after a period of cultivation,microbial diversity reduced.The reactor with magnetite could enrich more Candidatus Jettenia,while the control check reactor could enrich more Candidatus Brocadia.That means environment have a greatly effect on microorganisms,and specific environment can select a specific microorganisms. |
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