Study On The Relationship Of Apparent And Intrinsic Specific Growth Rates Of Nitrifying Bacteria

In recent years,with the increasing attention of the community to the ecological environment,more stringent sewage discharge standards have been promulgated.Efficient and economical biological nitrogen removal technology has become the focus of many experts and scholars.Partial nitrification is a new biological nitrogen removal technology and the ammonium oxidation was controlled at nitrite step,without being further oxidized into nitrate.The key to partial nitrification is to inhibit the growth of NOB and promote the propagation of AOB.As a result,it's necessary to study the growth characteristics of AOB and NOB.Dissolved oxygen affinity of nitrifying bacteria has been studied,but the growth rate of nitrifying bacteria has not been studied yet.Therefore,the study will make a research on the relationship of granular sludge size and maximum specific growth rate between AOB and NOB.In this study,the CSTR and SBR will be used to cultivate ammonia oxidizing bacteria(AOB)and nitrite oxidizing bacteria(NOB),respectively.The water quality of CSTR and SBR will be analyzed with increasing the volume load.The particle morphology and size of nitrifying bacteria at different stages will be observed by optical microscope.The relationship between the maximum specific growth rate and the sludge particle size will be studied by a kinetic device.The results show that:(1)By gradually increasing the volume load of the two reactors,a large amount of nitrifying bacteria can be proliferated and the granulation process of nitrifying bacteria can be accelerated.Increasing volume load will reduce the initial treatment efficiency of the two reactors and microorganisms need some time to cope with the change of volume load.(2)With the increasing of volume load,the accumulation rate of NO2--N in the CSTR is also increasing,which indicates that the high ammonium volume load will inhibit the growth of NOB.It will take longer time for AOB and NOB to recover to the original removal efficiency with increasing the volume load.Faced with the sudden increase of volume load,NOB has the better ability to resist impact load than AOB.(3)At the initial stage of reaction,the sludge is mainly flocculent.At the later stage of reaction,the shape of granular sludge is round and elliptical.Granular sludge has obvious boundary,clear outline,compact structure and full shape.Dissolved oxygen and substrate entering the granules will have the greater resistance with the increase of granular size.Because the growth rate of NOB is lower than that of AOB,the granular size of NOB is smaller than that of AOB at the same reaction time.(4)During the operation of CSTR and SBR,the size of AOB and NOB increases to 445?m and 359?m respectively with the volume load increasing.As dissolved oxygen and substrates in the mixed solution entering the granules need to overcome diffusion resistance,the maximum specific growth rate of nitrifying bacteria will decrease with the size of granular sludge increasing.The maximum specific growth rate of AOB decreases from 1.12d-1 to 0.20d-1 and that of NOB decreases from 0.83d-1 to 0.10d-1.(5)When the size of granular sludge is small,the OUR curve increases exponentially.When the size of granular sludge is large,the OUR curve increases linearly.(6)When the particle size of AOB is in the range of 21-278 ?m,the maximum specific growth rate of AOB decreases slowly with the increase of particle size.When the particle size of AOB is in the range of 278-445 ?m,the maximum specific growth rate of AOB decreases rapidly with the increase of particle size.There is a linear decreasing relationship between the maximum specific growth rate of NOB and sludge particle size.When the granular sludge size is about 232?m.the difference between the maximum specific growth rate of AOB and NOB is the largest.On the basis of this,making the granular sludge size to 232?m can achieve the purpose of washing NOB and starting partial nitrification rapidly.