Simultaneous nitrification and denitrification in step feeding biological nitrogen removal process

Available online at www.sciencedirect.comJOURNAL OFENVIRONMENTALScienceDirectSCIENCESISSN 1001-0742CN1-26291XEEJoumal of Enviomnenlal Sciences 19(2007) 1043 -1048www.ec. ac.cnSimultaneous nitrifcation and denitrification in step feeding biologicalnitrogen removal processZHU Gui-bing2, PENG Yong .zhen13., WU Shu-yun' , WANG Shu-ying', XU Shi-wei41. School of Municipal and Emironrmental Engineering, Harbin Institute of Technology, Harbin 150090, China2. Research Center for Eco- Environmental Sciences, Chinese Academry of Sciences, Bejing 100085, China. E-mail: gbzhu@rees.ac.cn3. Key Laboratory of Bejing Water Quality Science and Water Environment Recovery Engineering,Bejing University of Technology, Bejing 10022, China4. Beijing Drainage Group Co. Lld, Beijing 100038, ChinaReceived 9 October 2006; revised 6 December 2006; accepted 4 April 2007AbstractThe simultaneous nitrification and denitrifcation in step-feeding biological nitrogen removal process were investigated underdifferent infuent substrate concentrations and acration flow rates. Biological occurence of simultaneous nitrification and denitrifcationwas verified in the aspect of nitogen mass balance and alkalinity. The experimental results also showed that there was a distinct linearrelationship between simultaneous nitrifcation and denitification and DO concentration under the conditions of low and high aerationflow rate. In each experimental run the floc sizes of activated sludge were also measured and the results sbowed that simultaneousnitrification and denitrification could occur with very small size of foc.Key words: biological nitrogen removal; dissolved oxygen; floc size; simultaneous nitrifcation and denitrification; step feeding processIntroductionmicrobial flocs or biofilms due to difusional limitations.The biological explanations for SND are in contrast to theBecause of the stringent nutrient levels being requiredtraditional“engineering" conception of nitrification andin the effluents to protect lakes and other natural waterdenitrification. Microbiologists have reported the existencefrom eutrophication, removal of nitrogen from dischargedof aerobic denitrifers as well as beterotrophic nitrifierswastewater has been required in many wastewater treat- (Kim et al, 2005; Zhu et al, 2007b).ment plants. The step-feeding anoxic/aerobic biologicalPrevious researches showed that three principle fac-nitrogen removal process is characterized by high totaltors, carbon supply, oxygen concentration and foc size,nitrogen removal efficiency and unecessary intermal re-predominantly infuenced SND (Zhu et al, 2007b). Butcycle. During the last decade, many researchers have putthere were still some unresolved problems. The largemuch attention to this process and drawn many valu-loc parameter was likely to promote the SND due toable conclusions (Larrea et al, 2001; Zhu et al, 2005).difusional limitation of oxygen in the floc, whether smallMoreover, nitrogen loss and simultaneous nitrification andsize parameter is adverse to SND was still not reported.denitrification in step feeding process were also reportedIn addition, it has not been reported in literature thatby researchers (Gorgun et al, 1996; Zhu et al, 2007a).denitrification reaction could be accomplished under highSimultaneous nitrification and denitrification (SND)DO concentration condition and the relationship of DOimplies that nitrification and denitification occur concur-concentration and SND. In the article, the SND in steprently in the same reaction vessel under identical overall feeding process was investigated. The main objective wasoperating conditions. SND is of particular interest in sav-to explain the relationship of DO concentration and SND.ing anoxic volume and in treatment wastewaters with lowC:N ratio (Zhu et al, 2007b). The mechanism and explana-1 Material and methodstion for SND can be divided into two broad categories. Thephysical and conventional explanation is that SND occurs1.1F中国煤化工as a consequence of DO concentration gradients withinA1:MHC N M H Gjical nitrogen removalProject supported by the Key Inlermational Cooperative Program ofprocess made of plexiglass with a working volume ofNSFC (No. 50521140075), the Hi-Tech Research and Devclopment80L(800mmx220mmx500mm)wasusedinthisProgram (863) of China (No. 2004AA601020) and the Attached Projectsof“863" Project of Beijing Municipal Science and Technology (No,MAAOstudy (Fig.1). The volume of four stages was the same20005186040421). *Corresponding author. E mail: pyz@bjut.edu.cn.and the volume ratio of anoxic to oxic in each stageZHU Gui-bing es al.Vol. 19CD也1本11Fig. 1 Schematic diagram of step feoding biological nitogen removal process. (1) infuent tank; (2) check value; (3) feeding pump: (4) mechanicalmixer; (5) difuser; (6) air flow mcter; (7) air compressor; (8) secondary clarifer, (9) efuent; (10) returm sludge pump; (1 I) waste slodge.Table 2 Experimental operating procedurewas maintained at 1:3.5. A mechanical mixer was usedin anoxic zone to provide liquid mixed well. A number LabInfuentAerationof outlets for sample analysis were emplaced with theTKN (mg/L)COD (mg/L)flowrate (m2/h)distance of 20 cm from reactor bottom in each anoxic and402680.6aerobic zone. An air compressor with micropore difuser E234was used for aeration. An air flow meter was used for!272contolling the airflow rate. The type of final clarifier was551.46upright clarifer with a working volume of 30 L.3634012374501.2 Experimental operating procedureThe reactor feeding consisted of synthetic wastewaterwas measured using Liquid Particle Counting Systemwith characteristics similar to those of domestic wastew-Model 9703 (HIAC Royco) with the sensor HRLD .400.ater (Watnabe et al, 1995). It was prepared by using tapAll analyses were performed according to the Standardwater, dechlorinated by the use of sodium thiosulfate, andMethods (APHA, 1995).the addition of dosages of chemicals, as indicated in Table1. During the experimental period, the solid retention time2 Results and discussion(SRT) was controlled at 18 d using hydraulic controllingapproach (Zhu et al, 2007c).The total influent flow rate was 240 L/d and each stage2.1 Simultaneous nitrification and denitrificationwas set at 60 L/d, respectively, which was controlled byThe original experimental observed mass of ammoniafour same peristaltic pumps (Model ESBN4, Iwaki Cop.loss and NOx-N formation in seven experiments are shownJapan). The sludge return ratio was set at 50% of influentin Table 3. It shows that the mass of NH3-N decayflow rate by a peristaltic pump. The experimental operatingwas obviously larger than the mass of NOx-N forma-procedure is shown in Table 2. During each experimenttion, especially in the former stage of the step feedingthe step feeding process was operated for more than twoprocess. But this phenomenon of nitrogen loss could notsludge ages (36 d).definitely be attributed to the simultaneous nitrification and13 Samples and analytical proceduresdenitrification. In step feeding process suspended solidsgradient along the reactors was formed because of infuentThe parameters measured included floc size, temper-step feeding. The large amounts of biomass in the formerature, DO, COD, NH4+-N, NO2-N, NOz-N, TN andstage grew and reproduced rapidly with abundant organicalkalinity. Samples were prepared by filtering with 0.45substrate. It is well known that nitrogen is also needed inm Whatman filter papers. The DO measurements werethe process of metabolisms of activated sludge microor-conducted using YSI Model 58 DO meter. The floc sizeganisms. So it is necessary to make certain that the nitrogenloss should be attributed to the assimilation of activatedTable 1 Compostion of syntbetic wastewatersludge microorganisms or simultaneous nitrification andCompoundConcentration (mg/L)denitrification.Breweny、wastewater1080In steady state of activated sludge process the mass ofBrewery1146sludge discharoed ic emal tn the mass of microorganismNaHCO3900.0grow中国煤化工consumption because1050KH2PO4105.0of cculated with the cellMgSO4-7H2O150.0NaCl110.0formYHCNM HCemy, 200),，in whichCaCl285.5N is accounted for about 12%. The calculated results ofZnSO490.0nitrogen loss for assimilation during different experimentalNo. 9Simultaneous nitrifcation and denitrification in step feeding biological nitrogen removal process1045Table 3 Observed mass of ammola loss and NO2-N formation during dferent experimental operating conditonsLabStagoNH3-N (mgL)Mass of NH3-NNOx-N (mg/L)Mass of NO2-NStart ofEnd ofdecay (g/d) (1)formation (g/d) (2)aerobic zoneEA14.24800.82202.41687.83301.410010.08300.0002.41990.00005.93001.42328.00102.40024.99506.16502.21954.1150B212. 90002.65001.84515.54200.99779.89001.8550 .1.92844.21901.01268.72001.3002.22604.35001.30516.09500.26502.09883.53101.271318.02006.36006.54201.177714.57503.18002.73486.84401.642613.25004.24002.70315.59501.678611.39504.77002.38514.37501.575114. 17506.00001.62143.37500.607412.00005. 500026020.9.20000.0000 .2.28000.68408.50003.07301.1064 .Es11.48002.26648.79201.482610.77009.04702.17138.77002.73117.41002.22317.240000002.69646.38502.19879.0200000001.8236 .6.58301.08496.89001.6536 .6.37501.2531.76865.40001.2625.03500.001.81274.40601.28620.79501.90806.79201.22267.95006.46901.55268.21502.46466.34501.90346.62505.10401.8374StageMass of N lossTotal N lossDischarge sludgeDischarge rateN loss forAverage MLSS(1)-(2) (g/d)in system (g/d)conc. (mg/L)(mg/d)assimilation (g/d)(mg/L)1.00683.6432735013.2301.587649000.996736800.901729600.73802450E20.84743.5116753013.5541.626549760.915837780.920929770.827525103.8479744013.3921.607049181.092237361.024629330.810024801.0143.4291768013.8241.678349950.905537900.63630500.873625900.78382.203751813.5321.656349470.413537720.50829950.497725560.73872.172414.0941.6731497747800.40060.506630025822.1496759613.6731.7107505039050.561131500.54772640operating conditions are shown in Table 3. From Tablev中国煤化工xrved ates of akaliniti3 it was obvious the mass of nitrogen loss in the systemlossC N M H Gferent experimental op-were larger than the mass of nitrogen loss for assimilation. erating Condiuons are snown 1n Table 4. From Table 4So it could reasonably be speculated that there must be the calculated results of alkalinity loss were all below thesimultaneous nitrification and denitrification in the reactor.theoretical value of 7.14 mg/L (Bruce and Perry, 2001),The occurrence of SND was also verified with alkalinity average of 6.247 mg/L, of al]kalinity as CaCO3 per mg1046ZHU Gui-bing et al.Vol. 19Table 4 Observed alkalinity consumption, rates of ammonia loss and NO,-N formation, DO concentration during diferent experimentaloperating conditionsLabStage AlkalinityNH 4NO.NAlkaliniryRate of NH4Rate of NO3Averagecoosumptionloss ratiodecay (kgNH4/formation (kgNO3/DO (mg/L)(mg/H)1)(2(1):(2)(kg MLSS-d))E675.006.703411.4898 .0.58340.03220.01880.58390.3900625.006.198610.53970.58810.04300.02530.58900.8500562.505.62439.00900.62430.05330.03330.62500.9700565.056.11039.15430.66750.05920.03950.66701.9700468.756.097611.27760.54070.02460.01330.53900.1670560.006.969513.27330.52510.03430.01800.52620.26306.738511.49420.58630.04950.02900.58500.5460525.006.00349.91220.60570.05600.03390.60500.8460581.256.646711.84660.56110.02800.01570.56000.3600675.015.92379.86270.60060.04860.02920.6000656.255.82699.38340.62100.06010.03730.62000.9360675.00.6.792510.28580.66040.06360.04200.66001.4800266255.749010. 51850.54660.01480.00810.54900.1670.290 006.444411. ,14520.57820.01920.01110.5780350007.00001228070. 57000.02670.01520.5710350.0012.28070550705280.02950.55800.76806.3636 .11.389505587ES431.255.00876.54000.76590.02760.02110.7660, 1630750.006.9638 .0.84000.046000386oeoo4 0005.7013202000.84490.04940.84403.9300449.994.14364.69850.88190.06130.88184.5630E6468.75 .0.72980.02160.01580.73262.4630092530.02940.92664.3800475.006.23467.03700,88600.88664.4700337.504.46875.10670.87510.04830.87504.1600E77.075511.04240.64080.02540.01630.64301.7830540.008.34760.8137.03390.81303.7400660.006.42738.32160.77240.05480.04230.77203.6800705.007.09439.20840.7704 .0.04900.77103.8260of ammonia oxidized. The low alkalinity consumption a comparison of the data shown in column 6th and col-rates could be attributed to the occurrence of simultaneous umn 9th of Table 4. The production of alkalinity due tonitrification and denitrification, because alkalinity would simultaneous nitrifcation and denitrification would havealso be affected by two processes occurring at the same the efect of decreasing the observed rate of alkalinity losstime.and NOx-N formation per mg of ammonia oxidized. TheThe theoretical rate of alkalinity production during ratio of NO-N formed to NH3-N consumed is expected todenitrification is 3.57 mg of alkalinity per mg of NOx- be near the theoretical value after accounting for NH3-NN reduced. Theoretically, the ratio of observed alkalinityconsumed in synthesis. This ratio would also be reflecteddestruction rates with respect to ammonia loss and NOx-Nin the kinetic rates ammonia consumption and NOx-Nformation is corresponded to the ratio of observed rates formation depicted in Table 4. From the figure the datafor NO,-N formation and ammonia loss. Fig2 presents were also consistently less than 1, which suggested thatnitrification and denitrification occurred simultaneously.1.02.2 Dissolved oxygen concentrationExperiments were performed under low and high aer-9tation flow rate condition to evaluate the influence of DOconcentration on the SND. The results are shown in Tableg0.84. With the experimental data in column of 9th and 10th ofTable 4, the dependency of the ratio of NOx-N formation0.7下rate to NH3-N decay rate on DO could be depicted in Fig.3.From Fig.3 the following equations were drawn:曼0.6-r= 0.89487* + 0.07732low DO concentration :ONO-N= 0.07502D0 + 0.53455(1)ANH3-N00.highAlkalinity destruction per ammonia loss/ alkaity中国煤化工destruction per nitate formationANGANHMHCNMHGFig 2 Comparison of the ratio of alkalinity loss with respect to NH3=Ndecay and NOr-N formation with the ratio of NOr-N formation to NHg-From the figure the dependency of the ratio on DO underN decay.low and high DO concentrations respectively was linearity.No.9Simultaneous nitrifcation and denitrification in step feeding biological nitrogen removal process10470.9|1.0p0.0.80729-533434g 0.0.75 0.Y= 0.07502X + 0.534555. 0.6R= 0.883782 o.: R-0.89144 ”0.1- t0.50 0.20.40.6 0.8 1.01.2 1.4 1.6 1.82.00 0.5 1.01.52.0 2.53.03.5 4.04.5 5.000.5 1.01.52.0 2.5 3.03.5 4.04.5 5.0DO concentation (mg/L)DO concentration (mg/L)DO conceotration (mg/L)Fig. 3 Relationship of DO concentration and the ratio of the NOr-N formation rate to tbe NH3-N decay rate. (a) low aeration fow rate; (6) high aerationflow rate; (C) over al.The DO concentration showed greatly efcts on SND. Thethe influent characteristic. Compared with the real munic-overall dependencies of the ratio on DO under both lowipal sewage the synthetic wastewater is more simplex inand high DO concentrations was drawn and expressed as:constitute and content. The large foc parameter is likely topromote the SND due to diffusional limitation of oxygenANO,-NANH3-N: 0.07727DO + 0.53346in the floc. But in such small floc size it is impracticableto produce DO concentration gradients within microbialEquation (3) shows that there is an obvious linearflocs leading to denitrification in this area (Hisashi et al,relationship between DO concentration and simultane-2003; Li and Bishop, 2004), which remarkably clarify theous nitrification and denitrifcation. The rate of NOx-Nincorrectness of physical explanation standpoint.formation was almost equal to that of ammonia decaywhen the DO concentration was 6.05 mg/L. At this DO3 Conclusionsconcentration simultaneous nitrifcation and denitrificationdid not happen in the reactor. When the DO concentrationThe laboratory pilot scale studies were conducted towas 0.5 mg/L the rate of NOx-N formation was 0.57 timesevaluate the simultaneous nitrification and dnitrifcationthan that of ammonia decay, which was corresponded wellin step feeding biological nitrogen removal process. Thewith the results of the Munch et al. (1996). In this researchresults demonstrated that the biological occurrence ofthe specific relationship of DO concentration and SND wassimultancous nitrifcation and denitrification was obviousproposed.in step feeding process, even under high DO concentration.2.3 Floc sizeThere was a distinct linear relationship between the ratio ofammonia decay rate to NOr-N formation rate and DO con-To test the hypotheses of physical explanation on SND,centration. The mathematical expression of SND with DOthe activated sludge foc sizes of different experimentalconcentration was proposed to be: ANO:N = 0.07727DO+ .conditions were measured and shown in Fig.4. The average0.53346. 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