| As an environment-friendly biological nitrogen removal process,the anaerobic ammonium oxidation(anammox)process has received increased attention.It is catalyzed by anammox bacterna,which oxidize ammonium into nitrogen gas with nitrite as an electron acceptor in the absence of oxygen.Although full-scale anammox plant have been established around the word,the applicability of anammox process to sewage treatment is limited due to its extremely long doubling time,the environmental sensitivity of anammox bacteria and the production of nitrate.In recent years,researchers have expended great effort to achieve the rapid start?up and stability of anammox reactors.An efficacious alternative was used to increase the activity of anammox bacteria by changing some physicochemical factors.Some studies have found that anammox bacteria possess iron-rich particles inside the anammoxosome,and almost all of the iron inside the anammoxosome act as a cofactor in Fe-S proteins and heme proteins which partake in electron transport including the transition of ammonium to dinitrogen gas.then promote anammox metabolism.This study was designed mainly to explore whether anammox process could be strengthened under the role of nanoscale zero-valent iron(nZVI)and magnetic field and under the influence of iron sulfide(FeS).The main reaearch results as follows:(1)Under the combined action of nZVI and magnetic field,the start-up time of anammox reactor was shortened from 60 to 50 days,and the efficiency was improved by 16.7%.Under the action of magnetic field,the start-up time of the reactor was shortened from 60 to 41 days,and the efficiency was improved by 31.7%.The addition of nZVI did not significantly shorten the start-up time of the reactor.When the nitrogen loading rate was increased,the reactor with combining nZVI and magnetic field had the best stability.(2)Both nZVI and magnetic field promoted the reproduction of anammox bacteria.Compared with the blank control group,the content of anammox bacteria was increased by 29.0%and 25.5%;the expression of functional gene Hzo was increased by 37.8%,62.2%,respectively.Under the combined action of nZVI and magnetic field,the content of anammox bacteria and the expression of functional gene Hzo were increased by 40.3%and 67.9%,respectively.The qPCR results showed that nZVI also promote the reproduction of ammonia-oxidizing bacteria(AOB)and denitrifying bacteria.And the magnetic field of this intensity(65±10 mT)had an inhibitory effect on denitrifying bacteria.(3)nZVI and magnetic fields have a certain impact on microbial communities.The relative abundance of anammox genus"Candiatus Brocadia"was increased under the action of nZVI and magnetic field.Under the combined action of nZVI and magnetic field,the relative abundance of the autotrophic denitrifying bacterium"Thaure"is significantly increased.(4)At the start-up period,the removal rate of nitrite and total nitrogen were significantly improved by FeS.The total nitrogen removal rate of reactor with FeS reached more than 80%on the 42nd day,while that of the control group reached more than 80%until the 51 st day.When the nitrogen load increased,the reactor with FeS had less fluctuation and was more stable.Compared with the control group,the content of anammox bacteria increased by 29%in the experimental group,indicating that FeS promoted the growth and reproduction of anammox bacteria.(5)The structural and components of FeS were changed due to redox reaction.It was observed by SEM that FeS formed many honeycomb voids which were favourable for microbial adhesion.FeS released a certain amount of iron ions in the reactor.On the one hand,iron ions and anammox bacteria could be agglomerated by salt bridge,which was conducive to the formation of granular sludge.On the other hand,Fe2+ promoted the synthesis of heme c.heme was involved in the formation of various enzymes such as hydroxylamine oxidoreductase,cd1 nitrite reductase and nitrite-reductase(ammonia-forming).qPCR results and PICRUSt functions forecast also showed that the expression of the nirS gene(encoding cd1 nitrite reductase)nearly doubled;the content of nitrite reductase(ammonia-forming)increased by 26.4%.The difference in functional bacteria and enzyme contents in the system resulted in a difference in nitrogen removal between the two reactors.(6)High-throughput results indicated that FeS increased the richness diversity of micrbial community and enhanced the metabolic function of the microbial community.The anammox bacteria with the highest content in the control group and the experimental group were"Ca.Kuenenia"the addition of FeS would not change its dominant position. |
