Research On Start-up?Operation And Microbial Community Structure Of Anammox Reactor For Low Strength Wastewater

Anammox process has the advantages of no aeration,no carbon source and low excess sludge production.If it is applied to the mainstream treatment of municipal wastewater,it will greatly reduce the operation cost.Therefore,it is of great significance to explore the stable operation of anammox process treating low substrate wastewater.In this paper,by starting granular sludge reactor,biofilm reactor and activated sludge reactor with different sludge aggregation forms,the nitrogen removal performance and stability of different reactors in treating low ammonia nitrogen wastewater during operation were studied;the surface characteristics of sludge with different aggregation forms were discussed;the effect of extracellular polymer substract?EPS?on sludge characteristics was studied;and the microbial community in the reactor was analyzed,structures and abundance changes of anammox bacteria were studied.In order to provide a theoretical basis for the promotion of anammox process treating low substrate wastewater,the aims of paper is to reveal the effect of different sludge aggregation forms on the nitrogen removal performance of anammox process,The main results of this paper are as follows:?1?Start-up and operation of anammox reactor in low substractGranular sludge treating high substract?NH₄⁺-N,NO₂^--N concentration is about200 mg/L?was used as inoculated sludge to treat low substract wastewater.There was no start-up process in the granular sludge reactor.The average conversion of NH₄⁺-N and NO₂^--N was 92.1%and 97.1%,and the average removal rate of TN was 82.2%.During the operation of the reactor,the biomass remained stable,thus achieving sustainable operation.During stable operation of biofilm reactor for 100 days,The average conversion of NH₄⁺-N and NO₂^--N was 92.1%and 97.1%,and the average removal rate of TN was 75.7%.The biomass of the biofilm reactor was kept in the range of 0.0225 g/carrier to 0.0298 g/carrier.The sludge concentration of activated sludge reactor decreased from 1541 mg/L to 149 mg/L in 60 days.The conversion rates of NH₄⁺-N and NO₂^--N decreased from 56.7%to 22.8%and from 68.6%and 24.5%respectively.The removal rate of TN decreased from 46.6%to 18.5%.Sludge loss seriously made the operation of activated sludge reactor unsustainable.?2?Sludge Characteristics of anammox reactor in low substractCompared with the inoculated granular sludge treating high substract,the particle size,settling rate and sludge strength of granular sludge decreased under low substract wastewater.The amount of sludge adhering to the packings in biofilm reactor exists in the form of attachment and aggregation.Compared with biofilm,the microorganisms on the surface of granular sludge were more closely arranged and aggregated.Higher hydrophobicity and less hydrophilic groups were the reasons why granular sludge had stronger aggregation ability and compact structure than biofilm,and also why granular sludge had stronger aggregation ability than inoculated sludge.The EPS content,PN/PS and TB-EPS ratio of granular sludge were higher than biofilm.The flocculating ability of SEPS,LB-EPS and TB-EPS showed that the flocculating ability of EPS in different layers of granular sludge was stronger than that of biofilm.Three-dimensional fluorescence analysis showed that there were mainly tryptophan and tyrosine fluorescence peaks,and the fluorescence intensity of TB-EPS was higher than that of LB-TPS and SEPS.The hydrophobicity and Zeta potential of granular sludge and biofilm decreased before and after EPS extraction.The former decreased more than the latter,indicating that hydrophobic and compressive double layers of EPS from granular sludge were stronger.?3?Microbial community structure of anammox reactor in low substractHigh-throughput sequencing results showed that species richness and diversity of granular sludge reactor decreased under low substrate conditions when granular sludge treating high substract was used as inoculated sludge.The main genus of anammox bacteria wereCandidatus Brocadia?Candidatus Jettenia?unclassified_fBrocadiaceae and Candidatus Kuenenia.Compared with the high substrate sludge,the anammox and denitrifying bacteria abundance of the low substrate granular sludge were higher.In granular reactor,the size of sludge in the upper and lower layers of sludge bed was different,the microbial community structure was different,and the abundance of anammox bacteria with large size was higher.Under low substrate conditions,the richness and diversity of biofilm microbial community increased with time.Candidatus Brocadia,Candidatus Jettenia and Candidatatus Kuenenia were the anammox bacteria during 180 days of operation.For low substrate anammox sludge,biofilm had higher microbial community richness and diversity than granular sludge,the abundance of anammox bacteria and denitrifying bacteria was lower than that of granular sludge.This difference could be attributed to different sludge aggregation patterns.At the same time,the presence of denitratisoma in biofilm and granular sludge indicated that nitrogen removal was carried out by the two reactors under the synergistic action of denitrification and anammox.