Study On Formation And Factors Of Electroactive Ammonium Oxidation Biofilm

Anaerobic ammonia oxidation(Anammox)has been paid increasingly more attention in sewage treatment process over the years because of its low energy consumption and high nitrogen removal efficiency.Anammox is that the anaerobic ammonia oxidizing bacteria oxidize ammonium to nitrogen using nitrite as the electron acceptor.Compared with the traditional biological denitrification,Anammox path is short,and it does not need to add alkaline substance and organic carbon source,saving energy,material and other operating costs.However,the anaerobic oxidation bacteria is difficult to enrich and cultivation,which leads to limited application of Anammox in engineering.Recently,an electroactive ammonia oxidation biofilm(E-Anammox),which combines the characteristics of anaerobic ammonia oxidation and electroactive,has been well applied in sewage treatment reactor.But there was still a lack of depth understanding about the formation and electronic transfer mechanism of E-Anammox,especially the influence of C/N ratio and electrode potential.In this study,three-electrode system was established to explore the formation process of the E-Anammox biofilm and the redox activity of E-Anammox using a series of electrochemical techniques under different C/N ratio and potential.And our aims are to clarify how the C/N ratio and electrode potential impact on the performance of the E-Anammox and the inner microbial mediating mechanism.The main results were showed as below.(1)The system was domesticated with acetic acid as electron donor during the first 30 days,and afterwards ammonium chloride was replaced as electron donor(ACAM mode).The results showed that the ACAM incubation mode promoted the cultivation and domestication ammonia oxidizing bacteria and thus the formation of the E-Anammox.The startup time of the process was shortened from 120 days to 48 days.And the system was operated stably for more than 3 months.The ammonia nitrogen removal rate was up to 82±3%.(2)E-Anammox could be cultured and domesticated with the four different C/N ratio(C/N=5/5,5/10,5/15,5/20),but when the C/N ratio was high(C/N= 5/20),the domestication time was long and exceeded 15 days.The power density curve showed that the system power density when the C/N ratio was 5/20 was slightly lower than that of when the C/N ratio was 5/5,but higher than that of C/N ratio at 5/10 and 5/15.When the C/N ratio was low and high,the power of the system was mainly provided by the oxidation of the carbon source and the oxidation of nitrogen source,respectively.High-throughput sequencing results showed that the dominant population of the system was Geobacter genus under the low C/N ratio.However,as C/N ratio increased,Geobacter genus decreased,and the genus of Alicycliphil and Hylemonella were correspondingly increased.(3)Four different electrode potentials(0,0.2,0.4,0.6V)were used to test the potential influence on the E-Anammox.With the increasing of electrode potential,the peak of system current density decreased,indicating that the higher potential was not suitable for the growth of E-Anammox.The results of laser confocal microscope confirmed the conclusion that there were few live bacteria cell in the biofilm at the potential of 0.6 V.High-throughput sequencing results showed that the dominant population of the system was Geobacter genus under the different electrode potentials.However,with the increasing of the electrode potential,Geobacter genus decreased,Sphaerochaeta genus were almost unchanged,and Methanobacterium genus became more.In conclusion,the E-Anammox system can be started up quickly and maintained stable for long time by adopting the suitable ACAM domestication mode.The C/N ratio and electrode potential applied the system both had a great influence on the cultivation process of E-Anammox.At the high C/N ratio(5/20),the system started up slowly,but the output power density of the system was not affected.The higher electrode potential(>0.4 V)was unfavorable to the development of E-Anammox system.These results provided a theoretical basis and data support for the development of the Anammox process in the sewage treatment technology.