Study On Nitrification Effect And Microbiologic Properties Of Nitrification System Under Different Operational Conditions

Nitrifying sludge system in continuous stirred tank reactor(CSTR)and sequencing batch reactor(SBR)achieve different nitrification effect and nitrifying bacteria have different possess characteristics by changing the operating parameters of reactors,such as influent ammonia nitrogen load and sludge retention time(SRT).In this study,the kinetic parameters of nitrifiers cultivated under different substrates availabilities were monitored,together with the identification of nitrifier species and sludge floc morphology characterization,which was in order to make clear the selection mechanism of nitrifying bacteria and influence factors of kinetic parameters.The results show that:(1)When the concentrations of influent NH4+-N was 70mgN/L,the shortcut nitrification was achieved by change SRT in CSTR,but couldn’t remain shortcut nitrification for a long time.And continue to lower SRT,shortcut nitrification couldn’t be achieved again.So this study concludes that in CSTR sewerage system,it is unrealistic to stabilize shortcut nitrification by control SRT alone.It is necessary to combine SRT and other factors to start and stabilize shortcut nitrification,(2)In SBR,by increasing the influent ammonia nitrogen load,the nitrifying sludge system could quickly start shortcut nitrification.And when reduced the influent ammonia nitrogen load,shortcut nitrification was destroyed,the inhibition on NOB was broken,full nitrification was achieved finally.In SBR,by changing the SRT,the nitrifying system could start shortcut nitrification.And the best SRT is 10d.In this working condition,NOB in nitrifying system can be elutriated using the difference of AOB and NOB,and the sludge and AOB won’t loss too much.(3)In the process of cultivation of activated sludge,the sludge floc morphology characterization changed in different conditions.The size and morphology can reflect the performance of the ability of absorbtion and degradation to contaminants.Under the condition of high influent ammonia nitrogen load,nitrifying bacteria can use a large number of substrate to reproduce.The reproduction and accumulation of bacteria cause the size of sludge floc to increase.The sludge floc become tight because bacteria reproduce and gather.The SRT is lower,the size of sludge floc is smaller.(4)The major AOB is Nitrosomonas and major NOB is Nitrospira in shortcut nitrification condition,and these two kind of bacteria are considered to be r-strategists which degradate substrate fast with rich substrate.And the major AOB is Nitrosomonas and major NOB is Candidatus Nitrotoga in full nitrification condition.For AOB,the lower the SRT is,the lower the percentage content of Nitrosomonas is,the higher the percentage content of Nitrosomonadaceae is.For NOB,the lower the SRT is,the lower the percentage content of Nitrospira is,the higher the percentage content of Candidatus Nitrotoga is.The difference of dominant bacteria has to do with the influent ammonia nitrogen load and SRT.Influent ammonia nitrogen load and SRT are important influence factors for bacteria’s reproduction.Microbial community characteristics changes continuously,the shorter the time interval is,the less significant the microbial community diversity is.The microbial community diversity is more significant under the condition of higher influent ammonia nitrogen load.Different SRT cause influence of microbial community diversity,the similar the SRT is,the less significant the microbial community diversity is.Microbial richness and microbial uniformity are both lower throughout the process.(5)The change of kinetic parameters is influenced by several factors,such as substrate conversion efficiency、forms of nitrogen and sludge floc morphology characterization.The μAOB max is higher under the condition of higher content of r-AOB.SRT affects the kinetic parameters indirectly.The μAOB max of Nitrosomonadaceae is higher than Nitrosomonas.The KNH4 increase with μAOB.The KO,AOB increase with the size of sludge floc.The μNOB,max is related to the type of bacteria.The μNOB.max of Nitrospira is higher than Candidatus Nitrotoga.The KO,NOB may increase with the size of sludge floc,or change with the transform of dominant bacteria.The KNO2 may increase with the size of sludge floc.(6)In the determination of kinetic parameters,the measured value seems to contradict the"intrinsic" value.It can be explained by the size of sludge floc.The high diffusion resistance in the high floc size condition could decrease the substrate concentration available to the nitrifying bacteria inside the flocs,and therefore lead to smaller measured values.So when analyze the kinetic parameters of nitrifying bacteria that have difference in size of sludge floc,diffusion resistance should be considered.The traditional classification of r-strategists and K-strategists nitrifiers should take the mass transfer due to variation of sludge morphology into account.