Study On The Effect Of Inffluent C/N And FA On The Nitrification Characteristic Of Microbial Populations In The Biological Nitrogen Removal Of Sequencing Batch Reactor

Biological nitrogen removal is a sequence reaction，that ammonia is oxidized tonitrite by ammonia oxidizing bacteria （AOB）, and then nitrite is oxidized to nitrate bynitrite oxidizing bacteria （NOB）. Both AOB and NOB are mainly executor ofnitrification process and called nitrifying bacteria. If nutrients or environmentalconditions can not satisfy the requirement, they cannot metabolize and reproducenormally, even nitrification process cannot implement. C/N （carbon/nitrogen ratio）and FA （free ammonia） are the most important influcing factors of nitrification rateand process. From several of studies, the higher C/N value is, the more beneficial toheterotrophic bacteria in activated sludge cultivate, which have inhibitory effect onthe growth of nitrifying bacteria. But too much higher FA value will have inhibitoryeffect on the growth of nitrifying bacteria. Comparing with NOB, AOB has lesssusceptibility to toxicity of FA. In order to further study on C/N and FA effect onmicrobial nitrification characteristics, this study adopts sequencing batch reactor（SBR） based on different feed C/N and initial FA, nitrification and denitrificationcharacteristics of microbial population tamed with different C/N, FA long-term effecton microbial nitrification and short-term effect on nitrification characteristics ofdifferent activated sluges are evaluated.For studying the influence of C/N ratio on microbial nitrification characteristics,microbial population was tamed respectively in sequencing batch reactor （SBRs） withC/N ratios of0,5,10and15, and then, tamed microbial population was used totreating real municipal wastewater. The nitrification characteristic of tamed microbialpopulation was evaluated during the nitrification. Besides, the effects of differentelectron acceptor （nitrite, nitrate, nitrite+nitirate） on reduction capability of tamedmicrobial population were studied using batch tests. The study achieves mainlyconclusion as follows:（1）C/N ratio is the maily important factor that affects nitrificationprocess. Theammonium removal efficiency （ARE） was not affected by influent ammoniumconcentration when dissolved oxygen （DO） concentration and reaction time wereenough. But a slight increase trend from0.14at C/N ratio of0to0.18kgN/m3·d atC/N ratio of15was observed on nitrification rate. Furthermore, the relation betweenTN loss and C/N was described through a linear equation and the highest TN lossefficiency reached60.8%at C/N of15.（2）Nitrification characteristics of tamed microbial population have certaindifference. During the tamed microbial population treating municipal wastewater, above99.5%ammonium was oxidized to nitrate and nitrite when influent C/N ratiowas in the ranges of2.8-3.6. The average nitrification rates were5.82,5.40,5.26and5.63mgN/（L·h）, respectively, for microbial population tamed at four C/N ratios. TNloss efficiency was between12.6and19.6%likely due to the low influent C/N ratio.Moreover, simultaneous nitrification and denitrification may be used to explain theTN loss phenomenon in the nitrification process.（3）A significant difference of denitrification characteristic was observed fortamed microbial population. When nitrite was used as electron acceptor, the reductionrates of nitrite were0.67,1.10,1.66and0.24mgN/L·min, respectively, for tamedmicrobial population at four C/N ratios. The reduction rates of nitrate were0.31,0.61,0.82and1.01mgN/L·min, respectively, using nitrite as electron acceptor. As nitriteand nitrate co-existed in the system, nitrite reduction rate was higher than those ofnitrate for tamed microbial population at C/N ratios of0and5, while nitrite reductionrate was relatively lower for tamed microbial population at C/N ratios of10and15.（4）It was also found that the increased amount of pH value in single nitritereduction was higher than those in sole nitrate reduction. The high increased amountof pH value was obtained in co-existing system of nitrite and nitrate for tamedmicrobial population at C/N ratios of0and5.In order to investigate long-term effect of FA on microbial nitrificationcharacteristics, this study examines the variations of ammonia removing ratio, nitriteaccumulation and nitrifying bacteria activity in the SBR when initial FA concentrationincreased periodically from1.0mg/L to5.3,16.6,13.3mg/L, then periodicallydecreased to9.9,5.2,1.0mg/L. The mainly conclusions are as follows:（1）SBR systemachieves effective nitrogen removal during different FAstage.During the whole test period, influent NH4+-N concentration is in the range of31.7⁹7.6mg/L, effluent average NH4+-N concentration is0.6m/L, and ARE is99.1%.Influent TN concentration is in the range of32.5⁹8.0mg/L, effluent TNconcentration is less than5.0mg/L, and average removal rate is98.1%.（2）FA has obvious influence on NO₂--N accumulation and activity of AOBand NOB. FA increasing from1.00mg/L to13.3mg/L periodically, NO₂--Naccumulation phenomenon get obviously, nitrite accumulation rate can reach99.0%after stability AOB activity is effected and recovery to initial activity in short time,but NOB activity is restrained finally.. After that, FA reduced to1.0mg/l, nitriteaccumulation rate （NiAR） can keep on92.1%, NOB activity cannot be recovered..（3）Effect on FA long-term suppressed, supplemented real-time control modeon combination of pH and DO, SBR system can obtain high efficiency, lasting and stable shortcut nitrification. Excessive aeration has no effect on shortcut nitrificationperformance.In order to investigate the short-term effect of FA on microbial nitrificationcharacteristics, this research adopts the simulated domestic wastewater, respectivelyuse the complete nitrification activated sludge （CNAS） and the partial nitrificationactivated sludge （PNAS） as the research object, examines the nitrificationcharacteristics of CNAS when initial FA concentration increased gradually from2.4mg/L to197.2mg/L， the nitrification characteristics of PNAS system when initial FAconcentration increased from9.6mg/L to193.5mg/L, and the special ammoniaoxidation rate （SAOR） of two kinds of activated sludge.in the different FA conditionsthrough the batch test.Based on the study of short-term effect of FA on CNAS, mainly from thefollowing conclusions:（1） Influent NH4+-N concentration is in the range of31.7⁹7.6mg/L, effluentNH4+-N concentration remain is in the range of0⁸.7mg/L, ARE as high as99.1%..Influent TN concentration is in the range of65.3³37.9mg/L, Effluent TNconcentrations is in the range of64.5³19.0mg/L, TN loss was found in the system（2）The FA has obvious effects on ARE. ARE reduced on the conditions ofhigher FA concentrations （61.4¹97.2mg/L）. TN loss in the system is obvious whenthe FA in the range of2.4⁷.8mg/L and20.6¹97.2mg/L, especially on FA is137.6mg/l, TN loss efficiency is highest as21.1%.（3）With FA increased, nitrite accumulation rate changes at various stagesNitrite is hardly accumulated when the FA in the range of2.4～100.6mg/L. Nitriteaccumulation ratio increase from9.4%to58%, NOB activity is suppressed obviouslyduring FA in the range of137.6¹50.8mg/L. Nitrite accumulation ratio will beincreased during FA in the range of165.4¹97.2mg/L, and can reach97.6%when FAis197.2mg/L.（4）The FA has certain inhibitoryeffect on activity of AOB and NOB, and thiseffect presents the obvious segmentation phenomenon. AOB and NOB activity wasslightly decreased, and the inhibition effect of NOB is more apparent on FA in therange of2.4～7.7mg/L. AOB and NOB activity goes stably on FA in the range of8.3～16.3mg/L. AOB activity gradually increases, and NOB activity is not stable onFA in the range of20.6～100.6mg/L. NOB activity is suppressed obviously during FAin the range of137.6¹97.2mg/L.,and is almost completely suppressed in the FAconditions of197.2mg/L. Higher AOB activity is observed as a whole in this FA scope.（5）OnFAshort-term effect, SBR systemcan realize high efficiency and stableshortcut nitrification. When FA value are176.4mg/l and1.3mg/l, NO₂--N is nottransformed to NO3--N and shortcut nitrification cannot be damaged in the excessiveaeration process.Based on the study of short-term effect of FA on CNAS, mainly from thefollowing conclusions:（1）Influent NH4+-N concentration is in the range of89.6³11.2mg/L, effluentNH4+-N concentration is in the range of19.6¹62.6mg/L, ARE is in the range of78.1⁴7.7%and average value is67.1%. Influent TN concentration is slightly higherthan the NH4+-N concentrationin, effluent TN concentration is in the range of95.6³23.4mg/L, TN loss phenomenon is not obvious and TNLE always maintainedwithin16.2⁴.2%.（2）The FA has obvious effects onARE. Withthe increase ofconcentrations ofFA, ARE gradually increasing, and has a good linear relationship, both specific fittingequation is: y=82.21508-0.17373x，R2=0.93.（3）At the end of aeration, the concentration of NO₂--N increased from74.5mg/L to158.0mg/L as the initial system the concentration of FA gradua lly increasedfrom9.6mg/L to193.5mg/L. During the whole test, the accumulation rate of NO₂--Nhas remained in the range of97.6⁹9.1%, the result show that the concentration of FAhas no effect on SBR system within the concentration of FA in the range of9.6¹93.5mg/L, and the ability of the partial nitrification system is graduallyincreasing as the increase of the concentration of FA.（4）The concentration of FA is between9.6¹93.5mg/L, the SNaAR alwaysremain in the range of0.003⁰.005gN/（gVSS·d）. It is showed that the activity ofNOB is always in a suppressed state. However, the concentration of SNiPR increasefrom0.14gN/（gVSS·d） to0.31gN/（gVSS·d）, and SAOR increase from0.13gN/（gVSS·d） to0.29gN/（gVSS·d）, so the activity of AOB activity enhanced with theincrease of the concentration FA.Based on the comparison and analysis of short-term effect of FA on CNAS andPNAS, mainly from the following conclusions:（1）To CNAS in nitrificationperiod, SOAR will increase withFAconcentrationraised and different trend in different arrange of FA concentration. FA is in the rangeof2.4³0.2mg/L, SAOR value reduces from0.18gN/（gVSS·d） to0.14gN/（gVSS·d）;when FA increases from9.3mg/L to137.6mg/L, SAOR value increases from 0.13gN/（gVSS·d） to0.33gN/（gVSS·d） rapidly; when FA concentration in the range of137.6¹97.2mg/L, SAOR keeps in the range of0.27⁰.34gN/（gVSS·d）.（2）To PNAS in nitrification period, SAOR increases almost like exponentialgrowth trend when FA concentration in the range of9.6mg/L¹93.5mg/L, whichvalue increases from0.13gN/（gVSS·d） to0.30gN/（gVSS·d）, fitting equation is：y=-0.22811*exp（-x/102.7437）+0.34767, R2=0.98。（3）BetweenCNAS and PNAS sludge SAOR curves have increased trend withFA concentration increased. But both have difference in different FA concentration.When FA concentration is in the range of2.4¹9.3mg/L, SAOR curve of CNAS is alittle lower than that of PNAS, that means AOB activity in CNAS is better than that ofPNAS. When FA concentration is in the range of19.3¹43.3mg/L, SAOR curve ofCNAS is a higher than that of PNAS, that means AOB activity in CNAS is weakerthan that of PNAS. When FA concentration is in the range of150.8¹97.2mg/L,SAOR curve of PNAS is a higher than that of CNAS, that means AOB activity ofPNAS is better than that of CNAS.