Denitrification Performance For Treating Digested Piggery Wastewater In Continuous-flow SNAD System

The start-up of SNAD(simultaneous partial nitrification,anaerobic ammonium oxidization and denitrification)process trough little aeration and gradually increasing ammonia concentration was investigated to treat low C/N high ammonia nitrogen by inoculating mixed sludges of partial nitrification and anaerobic ammonia oxidation in Continuous-Flow reactor.And then,high-throughput sequencing and qPCR were utilized to analyze the evolution of bacteria and functional species related with removal of nitrogen and carbon from the perspective of biotic population,in order to reveal the micro mechanism of decontamination.Besides,by adjusting the HRT(hydraulic retention time),the diffent effects of various HRT were gained,together with optimization of system and further denitrification mechanism as well as pollutant degradation in circle.The main contents and conclusions are summarized as follows:(1)By inoculating mixed sludges of partial nitrification and anaerobic ammonia oxidation,the process of continuous-flow SNAD for treatment of digested piggery wastewater was realized in 180 d under the condition of little aeration and gradually increasing ammonia concentration.The reactor had good decontamination performance,the removal rate of NH4+-N,TN and COD were65.86%,55.39%,75.21% respectively,and effluent reached163.93mg·L-1,188.46mg·L-1,96.68mg·L-1;with average accumulations of NO3--N and NO2--N being 10mg·L-1,0.84 mg·L-1,and the ratio of effluent(NO3--N+ NO2--N)/?NH4+-Nwas lower than theoretical value of autotrophic nitrogen removal process0.11.Besides,the biomass in the reactor raised gradually during the period of start-up,the biomass on the filler surface rised from3.19mg/unit to78.93mg/unit and the MLSS of effluent reduce from 15.69mg·L-1to 46.28 mg·L-1.The sludge was in compact structure and complete forms,with color being bright reddish brown.From the demonstration of SEM,the sludge was in abundant in various species,consisting ofspherical,rod-shaped and filamentous fungus,as well as fine pores which are beneficial for transfering nutrients and dissolved oxygen.(2)High throughput sequencing technology was applied to analyze the DNA sequence of the sludge samples in the stage of inoculation and successfulstart-up,great changes have taken place in the composition of microbial categories.The abundance ofDeinococcus-Thermus,Proteobacteria,Bacteroidetes,Firmicutes,Gemmatimonadetes and Actinobacteria reduced gradually;the Synergistetes was washed out enventually;by contrast,the content of Chloroflexi,Armatimonadetes,Bacteria,Planctomycetes,and Chlorobi enriched little by little.The microbe were mainly Anaerolineae(26.95%),Planctomycetacia(15.26%),chlorobia(6.86%),Armatimonadetes(4.25%),Proteobacteri a(8.05%),Sphingobacteriia(8.21%)during the phase of successful start-up.The main denitrifierwere as follow:the AOB was Nitrosomonas(2.08%);NOB was Nitrospira(1.01%);the dominant of anammox were Candidatus-Kuenenia and Candidatus-Brocadia,with relative abundance being 4.69% and3.96%;fied-Aeromonas(0.41%),Thauera(0.17%),Denitratisoma(1.38%)were major denitrification.(3)Quantitative PCR analysis of specific functional bacteria in sludge samples demonstrated that,the contents of AOB,AnAOB and denitrification reached1.34×1013(copies/mgDNA),4.41×1013(copies/mgDNA),4.12×108(copies/mgDNA)respectively.Anammox involving both AOB and AnAOB is the main means for the TN removal,and the denitrification efficiency of denitrifying bacteria was further enhanced by denitrification,toghther with the COD degradation.Different functions and proportion of different bacteria ensure the efficient removal of nitrogen and carbon in SNAD system.(4)When the HRT ranged from 1d to 0.8d and 0.6d,the average removal rate of NH4+-N were 69.16%,81.24%,64.58% respectively,the average effluent concentration reached 139.28 mg·L-1,85.62 mg·L-1,158.89 mg·L-1;and the TN average removal efficiency fell in 61.24%,74.78%,64.51%,with mean concentration of effluent being177.99 mg·L-1,116.67 mg·L-1and 164.87 mg·L-1;and for the removal rate and average effluent concentration of COD,they were 74.24% and 74.24%,84.42% and 52.87mg·L-1,70.63% and 93.09 mg·L-1respectively when the HRT being 1d,0.8d and0.6d.In addition,the SNAD system remained stable and was in good performance.(5)Analysis on variation of decontamination in one circle under the condition of optimal HRT being 0.8d indicated that,the removal efficiency and the degradation rate of NH4+-N,TN,COD were 81.86% and 22.46(mg/(L·h)),81.99% and 23.50(mg/(L·h)),78.65% and 10.71(mg/(L·h)),showing superior efficiency of TN and COD obviously.Denitrification contributed 17.2% to the removal of TN,and the contribution of anaerobic ammonium oxidation was 82.8%,significantly,autotrophic nitrogen removal played a dominant role in the system.