| Nitrifiers were present and active in municipal wastewaters,and natural continuous seeding the activated sludge system.However,it was necessary to further study the performance and community structure of the nitrifiers as well as the long-term effect on activated sludge system.In this study,the nitrification performance and nitrifier community in the raw sewage(June 2017 to March 2019)and acticated sludge(October2017 to March 2019)of the 2nd water resource recovery facilities(WRRFs)were investigated,and the relationship between the raw sewage and activated sludge were analysed.The main conclusions are as follows:(1)During the investigation,the influent water qualities of the WRRFs were relatively stable.The coefficients of variation of the water qualities(NH4+-N,TN,PO43--P,TP,COD,SS and VSS)ranged from 17.8%to 40.2%.The coefficient of variation of TN(17.8%)was the smallest and that of PO43--P(40.2%)was the largest.The average daily flow was 150,000?170,000 m3,and it was higher in summer than in winter.(2)During the investigation,as for the nitrifiers in raw sewage,the specific ammonia utilization rate(SAUR)and the specific nitrite utilization rate(SNUR)were 0.48?3.02mg N/(g VSS·h)and 0.94?3.12 mg N/(g VSS·h),respectively.And both were lowest in summer and highest in winter,SAUR was lower than SNUR except May and June.As for the activated sludge,SAUR and SNUR were 0.68?2.25 mg N/(g VSS·h)and1.07?3.6 mg N/(g VSS·h),respectively.SAUR was lower than SNUR except winter.(3)The SAUR and SNUR of influent nitrifiers were higher than those of activated sludge in winter.The correlation coefficient was 0.860 between SAUR of influent nitrifiers and SAUR of the next month in activated sludge,and the correlation was significant(0.000?0.05).Lagged effects of the SAUR in raw sewage on the SAUR of activated sludge.(4)The seeding intensity of Ammonia Oxidizing Bacteria(AOB)and Nitrite Oxidizing Bacteria(NOB)were 0.21?0.92 g/(g·d)and 0.17?0.78 g/(g·d),respectively.Both were significant in autumn and winter.The average seeding intensities of AOB and NOB in autumn and winter were 1.3 times and 2.6 times than the seeding intensity in summer,respectively.(5)Quantitative Real-Time Polymerase Chain Reaction(q PCR)results indicated that,as for the samples of the raw seage,the abundance of Nitrotoga in raw sewage was the lowest(4.86×105?3.78×106cells/g MLSS).The abundance of AOB and Nitrospira were 1.32×108?2.36×109cells/g MLSS and 1.64×109?5.18×109cells/g MLSS,respectively.As for the samples of activated sludge,the abundance of AOB,Nitrospira and Nitrotoga were 1.12×1010?1.19×1010cells/g MLSS,3.63×109?1.57×1010cells/g MLSS and 9.28×106?1.64×108cells/g MLSS,respectively.(6)The Illumina MiSeq high-throughput sequencing results showed that OTUs(Operational Taxonomic Units),community richness and diversity of AOB(amo A)and NOB(nxr B)in influent nitrifiers were higher than in activated sludge.The shared dominant genera of AOB was Nitrosomonas,and shared dominant species were Nitrosomonas?sp.?Nm58,Nitrosomonas?sp.?JL21 and bacterium?CYCU-0253 in raw sewage and activated sludge.Among them,Nitrosomonas?sp.?Nm58 and bacterium?CYCU-0253 were related to SAUR of nitrifiers in raw sewage and activated sludge.The shared dominant genera of NOB was Nitrospira,and shared dominant species were Nitrospira?defluvii and Nitrospira?calida in raw sewage and activated sludge.When nitrifiers of raw sewage entered the activated sludge system,some of the nitrifiers including those related to nitrification performance were retained,while others,such as Nitrosococcus?sp.?LT-3 and ammonia-oxidizing?enrichment?culture,were not detected in activated sludge.The difference of community structure of nitrifiers in activated sludge was smaller than that in raw sewage.The community structure of nitrifiers in the influent and activated sludge was similar,but this similarity was lower than that of the community structure of nitrifiers in raw sewage or in activated sludge at different time.The influent nitrifiers had certain effect on the community assembly in activated sludge,and the activated sludge system had certain selectivity to the influent nitrifiers. |
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