37 3 Aerobic Granulation at Different SBR Cycle Times Zhi-Wu Wang and Yu Liu CONTENTS 3.1 Introduction 37 3.2 Effect of Cycle Time on Aerobic Granulation 37 3.3 Effect of Cycle Time on Properties of Aerobic Granules 41 3.4 Conclusions 49 References 49 3.1 INTRODUCTION Itappearsfromtheprecedingchaptersthatanumberofoperatingparametersofa sequencing batch reactor (SBR) can inuence aerobic granulation. This chapter looks intoanotherSBRoperatingparameter,cycletimeanditseffectonaerobicgranula- tion,aswellasonthecharacteristicsofaerobicgranules.Cycletimeisassociated withthewashoutfrequencyofSBR,whichcanberegardedasakindofhydraulic selection pressure. In fact, hydraulic selection pressure has been shown to be impor- tantfortheformationofanaerobicgranulesinananaerobicSBR(HulshoffPoletal. 1982; Shizas and Bagley 2002). Denitely, a sound understanding of the role of SBR cycletimeinaerobicgranulationwouldbehelpfulfortheoptimizationanddesignof large-scale aerobic granular sludge SBR. 3.2 EFFECT OF CYCLE TIME ON AEROBIC GRANULATION Tay,Yang,andLiu(2002)investigatedtheformationofnitrifyinggranulesatdif- ferentcyclestimesof3to24hoursinSBRs.Acompletewashoutofthesludge occurredandledtoafailureofnitrifyinggranulationintheSBRrunattheshortest cycletimeof3hours,whileonlytypicalbioocswerecultivatedinSBRoperated nitrifyinggranuleswithmeandiametersof0.22and0.24mmappearedinSBRsrun atthecycletimesof12and6hours,respectively.Incomparisonwiththeseedsludge that had a very loose and irregular structure, nitrifying granules developed showed acompactstructurewithaclearoutershape;moreover,thenitrifyinggranules formedatthecycletimeof6hourswerefoundtobesmootheranddenserthanthose developedatacycletimeof12hours(gures3.1bandc). 53671_C003.indd 37 10/29/07 7:12:37 AM © 2008 by Taylor & Francis Group, LLC © 2008 by Taylor & Francis Group, LLC atthelongestcycletimeof24hours(gure3.1a).After2weeksofoperation,tiny 38 Wastewater Purification One outstanding characteristic of aerobic granules compared to bioocs is theirrelativelylargeparticlesize.Figure3.2showsthatashortcycletimeofSBR favors the development of large nitrifying granules. A similar phenomenon was also observed in an upow anaerobic sludge blanket (UASB) reactor, that is, when theHydraulicRetentionTime(HRT)wasdecreasedfrom10daysto1.5days,the diameteroftheUASBgranulesincreasedfrom0.56mmto0.89mm(Lin,Chang, and Chang 2001). The basis of aerobic and anaerobic granulation is the continuous selection of sludge particles, that is, light and dispersed sludge is washed out, while heavier components A B C FIGURE 3.1 MorphologiesofbioparticlescultivatedinSBRsrunatthecycletimesof 24(a),12(b),and6(c)hours;scalebar:1mm.(FromTay,J.H.,Yang,S.F.,andLiu,Y.2002. Appl Microbiol Biotechnol 59:332–337.Withpermission.) 53671_C003.indd 38 10/29/07 7:12:41 AM © 2008 by Taylor & Francis Group, LLC © 2008 by Taylor & Francis Group, LLC Aerobic Granulation at Different SBR Cycle Times 39 areretainedinthesystem.InanSBR,hydraulicselectionpressuremayresultfrom thecycletime(ShizasandBagley2002).ThisisduetothefactthattheSBRcycle timerepresentsthefrequencyofsoliddischargethroughefuentwithdrawal,and itisrelatedtotheHRT.Thisimpliesthatthelongestcycletimewouldresultinthe lowest selection pressure. As a result, no nitrifying granulation was observed in the SBRrunatthecycletimeof24hours.Infact,theabsenceofanaerobicgranula - tionwasobservedwhenthehydraulicselectionpressurewasveryweak(Alphenaar, Visser,andLettinga1993;OFlahertyetal.1997).Nitrifyinggranulesdevelopedwell inSBRswithcycletimesof12and6hours.Itisevidentthatarelativelyshortcycle time should suppress the growth of suspended sludge because of frequent washout of thepoorlysettleablesludge.However,iftheSBRisrunatanextremelyshortcycle time,forexample,3hours,thesludgelossduetohydraulicwashoutfromthesystem cannot be compensated for by the growth of nitrifying bacteria. In this case, biomass cannotberetainedinthesystem,andacompletewashoutofsludgeblanketoccurs andeventuallyleadstoafailureofnitrifyinggranulation.Asimilarphenomenonwas alsoreportedinaUASBreactor(Alphenaar,VisserandLettinga1993). TheeffectofthecycletimeofSBRontheformationofheterotrophicaerobic granuleswasalsoreportedintheliterature.Wangetal.(2005)usedsucroseasthe solecarbonsourcetocultivateaerobicgranulesatthecycletimesof3and12hours. Round aerobic granules rst appeared in the SBR run at the cycle time of 3 hours after30cyclesofoperation,whileirregularsmallgranuleswereobservedinthe the evidence points to the fact that in order to achieve a rapid aerobic granulation in SBR, SBR cycle time needs to be controlled at a relatively low level. Panetal.(2004)initiatedvecolumnSBRsusingprecultivatedglucose-fedaero - bicgranuleswithameansizeof0.88mmasseed,andoperatedthematthecycletimes of1,2,6,12,and24hours,respectively.ItwasfoundthatbiomassintheSBRrunata cycletimeof1hourwasentirelywashedoutsoonafterthereactorstart-up,andthisin Cycle Time (hours) 61224 Sludge Mean Size (mm) 0.09 0.12 0.15 0.18 0.21 0.24 0.27 FIGURE 3.2 Mean size of bioparticles cultivated in SBRs run at different cycle times. (Data fromTay,J.H.,Yang,S.F.,andLiu,Y.2002.Appl Microbiol Biotechnol 59: 332–337.) 53671_C003.indd 39 10/29/07 7:12:42 AM © 2008 by Taylor & Francis Group, LLC © 2008 by Taylor & Francis Group, LLC SBRoperatedatthecycletimeof12hoursafter120cycles(gure3.3).Sofar,all 40 Wastewater Purification turnresultedinreactorfailure.IntheSBRwithcycletimesof2to24hours,theseed granuleswerenallystabilizedafter10to20daysofoperation(gure3.4).Figure3.4a tocshowsthatattheshortcycletime,aerobicgranulestendedtogrowintolargegran - uleswithfewerbioocsinthebulksolution,whileintheSBRrunatthelongestcycle timeof24hours,amixtureofirregulargranulesandabundantsuspendedbioocs 1.0 mm 1.0 mm FIGURE 3.3 Morphologies of sucrose-fed aerobic granules cultivated in SBRs run at cycle timesof3hours(left)and12hours(right),respectively.(FromWang,F.etal.2005.World J Microbiol Biotechnol 21:1379–1384.Withpermission.) 5 mm B FIGURE 3.4 MorphologiesofsludgecultivatedinSBRsrunatcycletimesof2(a),6(b),12(c), and24(d)hours.(FromPan,S.etal.2004.Lett Appl Microbiol 38: 158–163. With permission.) 5 mm A 53671_C003.indd 40 10/29/07 7:12:44 AM © 2008 by Taylor & Francis Group, LLC © 2008 by Taylor & Francis Group, LLC Aerobic Granulation at Different SBR Cycle Times 41 wascultivated(gure3.4d).Itcanbefurtherseeningure3.5thatthesizeofstable granulesturnedouttobeinverselyrelatedtotheappliedcycletime. 3.3 EFFECT OF CYCLE TIME ON PROPERTIES OF AEROBIC GRANULES Panetal.(2004)reportedthatalongcycletimedoesnotfavorimprovementin sludge settleability. For instance, very poor settleability sludge with a high sludge volumeindex(SVI)of110mLg –1 wascultivatedintheSBRoperatedatthecycle timeof24hours.Incontrast,excellentsludgewiththelowerSVIof50mLg –1 were Itseemscertainthatashortcycletimecanselectivelyretainbioparticleswithgood settleability. By virtue of those excellent settleability sludge retained in SBR, high volatile suspended solids concentrations (VSS), up to 13 g VSS L –1 ,wereachieved inSBRsrunatshortcycletimes(gure3.7).However,only4gVSSL –1 was nally achievedintheSBRrunatthecycletimeof24hours.Inaddition,thequalityof efuent from SBR run at short cycle times was found to be much better than that fromthoseoperatedatlongcycletimes(gure3.8). Comparedtobioocswithloosestructure,aerobicgranulesalwayshavearela - tively high biomass density. The specic gravity of sludge reects the compactness ofthesludgestructure.Figure3.9showsthespecicgravityofnitrifyingsludge 5 mm C 5 mm D FIGURE 3.4 (continued) 53671_C003.indd 41 10/29/07 7:12:46 AM © 2008 by Taylor & Francis Group, LLC © 2008 by Taylor & Francis Group, LLC harvested in the SBRs operated at the cycle times of 2, 6, and 12 hours (gure 3.6). 42 Wastewater Purification cultivatedinSBRsrunatdifferentcycletimes.Aspointedoutearlier,poorlysettling sludgewouldbewashedout,andonlybioparticleswithgoodsettleabilitywould be retained in SBRs run at short cycle times. According to the well-known Stokes law,amorecompactparticlewouldhaveabettersettleability.Thismayexplainthe phenomenon shown in gure 3.9, that is, the specic gravity of nitrifying granules cultivatedatashortcycletimeisindeedmuchhigherthanthosecultivatedatlong cycletimes.Panetal.(2004)alsoreportedresultssimilartogure3.9,thatis,ashort cycletimefavorsthedevelopmentofaerobicgranuleswithhighspecicgravity (gure 3.10). In addition, a high sludge integrity coefcient was obtained at short cycle times, indicating that aerobic granules with high mechanical strength can be cultivatedatshortcycletimes(gure3.10andgure3.11). Cycle Time (hours) 0 5 10 15 2520 Mean Size (mm) 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 FIGURE 3.5 SludgemeansizeinSBRsrunatdifferentcycletimes.(DatafromPan,S. et al. 2004. Lett Appl Microbiol 38: 158–163.) Cycle Time (hours) 0 5 10 15 20 25 SVI (mL g –1 ) 0 20 40 60 80 100 120 FIGURE 3.6 Effect of cycle time on sludge settleability. (Data from Pan, S. et al. 2004. Lett Appl Microbiol 38: 158–163.) 53671_C003.indd 42 10/29/07 7:12:48 AM © 2008 by Taylor & Francis Group, LLC © 2008 by Taylor & Francis Group, LLC Aerobic Granulation at Different SBR Cycle Times 43 As discussed in chapter 9, cell surface hydrophobicity plays an important role inmicrobialaggregation.Theeffectofcycletimeoncellsurfacehydrophobicityis showningure3.12.Ascanbeseen,thecellsurfacehydrophobicitywasimproved as the cycle time was shortened. Higher cell surface hydrophobicity was developed in SBRsrunatcycletimesof6and12hoursascomparedtothatfoundintheSBRrun atthecycletimeof24hours.Figure3.1andgure3.12togetherseemtosuggestthat the formation of nitrifying granules is associated with the cell surface hydrophobicity inducedbytheshortcycletimeofSBR.Infact,theimportanceofcellsurfacehydro - phobicity in biolm and biogranulation processes is demonstrated in chapter 9. Similarresultstogure3.12werealsoreportedbyPanetal.(2004).Itwas observedthataerobicgranuleswithhighcellsurfacehydrophobicitywereobtainedat Cycle Time (hours) 0 5 10 15 20 25 Retained VSS (g L –1 ) 0 2 4 6 8 10 12 14 FIGURE 3.7 Effect of cycle time on suspended solids concentration retained in SBRs. (DatafromPan,S.etal.2004.Lett Appl Microbiol 38: 158–163.) Cycle Time (hours) 0 5 10 15 20 25 Effluent VSS (g L –1 ) 0.08 0.12 0.16 0.20 0.24 0.28 FIGURE 3.8 Effect of cycle time on efuent suspended solids concentrations from SBRs. (DatafromPan,S.etal.2004.Lett Appl Microbiol 38: 158–163.) 53671_C003.indd 43 10/29/07 7:12:49 AM © 2008 by Taylor & Francis Group, LLC © 2008 by Taylor & Francis Group, LLC 44 Wastewater Purification shortcycletimes,forexample,thecellsurfacehydrophobicityatacycletimeof2hours wasnearlytwotimeshigherthanthatatthecycletimeof24hours(gure3.13). Itseemscertainthatashortcycletimewouldenhancecellsurfacehydro- phobicity. Wilschut and Hoekstra (1984) proposed that the strong repulsive hydration interaction was the main force keeping the cells apart, and when bacterial surfaces were strongly hydrophobic, irreversible adhesion would occur. According to the thermodynamicstheory,anincreaseincellsurfacehydrophobicitywouldcausea corresponding decrease in the excess Gibbs energy of the cell surface, which pro - motes cell-to-cell interaction and further serves as a driving force for bacteria to Cycle Time (hours) 61224 Specific Gravity 1.005 1.010 1.015 FIGURE 3.9 Specic gravity of sludge developed at different cycle times. (Data from Tay,J.H.,Yang,S.F.,andLiu,Y.2002.Appl Microbiol Biotechnol 59: 332–337.) Cycle Time (hours) 0 5 10 15 20 25 Specific Gravity 1.03 1.04 1.05 1.06 1.07 1.08 Integrity Coefficient (%) 60 70 80 90 100 110 FIGURE 3.10 Specic gravity (D)andintegritycoefcient($)ofsludgecultivatedin SBRsrunatdifferentcycletimes.(DatafromPan,S.etal.2004.Lett Appl Microbiol 38: 158–163.) 53671_C003.indd 44 10/29/07 7:12:51 AM © 2008 by Taylor & Francis Group, LLC © 2008 by Taylor & Francis Group, LLC Aerobic Granulation at Different SBR Cycle Times 45 self-aggregate out of liquid phase, that is, a high cell surface hydrophobicity would result in a strengthened cell-to-cell interaction, leading to the formation of dense and stable aerobic granule structures (see chapter 9). Extracellular polysaccharides can mediate both cohesion and adhesion of cells and play a crucial role in building and further maintaining structure integrity in a communityofimmobilizedcells(seechapter10).Figure3.14displaystheeffect of cycle time on the ratio of cell polysaccharides (PS) to proteins (PN) of nitrify - ing granules. It is apparent that a short cycle time would stimulate the production Cycle Time (hours) 123 Integrity Coefficient (%) 80 82 84 86 88 90 92 FIGURE 3.11 IntegritycoefcientofsludgecultivatedinSBRsrunatdifferentcycletimes. (DatafromWang,F.etal.2005.World J Microbiol Biotechnol 21: 1379–1384.) Cycle Time (hours) 61224 Cell Surface Hydrophobicity (%) 60 65 70 75 80 85 FIGURE 3.12 Effect of cycle time of SBR on cell surface hydrophobicity of nitrifying bacteria. (Data from Tay, J. H., Yang, S. F., and Liu, Y. 2002. Appl Microbiol Biotechnol 59: 332–337.) 53671_C003.indd 45 10/29/07 7:12:52 AM © 2008 by Taylor & Francis Group, LLC © 2008 by Taylor & Francis Group, LLC 46 Wastewater Purification of cell polysaccharides over proteins in nitrifying granules. In fact, heterotrophic addition,thePS/PNratioinheterotrophicgranulescultivatedatthesamecycletime was nearly two times higher than that produced by nitrifying granules (gure 3.14). This is mainly due to the fact that nitrifying bacteria cannot utilize organic carbon fortheirgrowth,andonly11%to27%oftheenergygeneratedgoestobiosynthesis (Laudelout,Simonart,andvanDroogenbroeck1968),whiletheheterotrophic bacteria is able to convert up to 70% of the substrate energy into biosynthesis as well FIGURE 3.13 Effect of cycle time of SBR on cell surface hydrophobicity of glucose-fed aerobicgranules.(DatafromPan,S.etal.2004. Lett Appl Microbiol 38: 158–163.) Cycle Time (hours) 61224 PS/PN Ratio (mg mg –1 ) 2.0 2.4 2.8 3.2 3.6 4.0 FIGURE 3.14 Effect of cycle time on ratio of extracellular polysaccharide (PS) to protein (PN)ofthesludgefedbyammonia.(DatafromTay,J.H.,Yang,S.F.,andLiu,Y.2002.Appl Microbiol Biotechnol 59: 332–337.) 53671_C003.indd 46 10/29/07 7:12:54 AM © 2008 by Taylor & Francis Group, LLC © 2008 by Taylor & Francis Group, LLC Cycle Time (hours) 0 5 10 15 20 25 Cell Surface Hydrophobicity (%) 30 40 50 60 70 80 bacteriawerealsofoundtooverproducePSatshortcycletimes(gure3.15).In [...]... F., and Liu, Y 2002 Hydraulic selection pressure-induced nitrifying granulation in sequencing batch reactors Appl Microbiol Biotechnol 59: 33 2 33 7 Wang, F., Yang, F L., Zhang, X W., Liu, Y H., Zhang, H M., and Zhou, J 2005 Effects of cycle time on properties of aerobic granules in sequencing batch airlift reactors World J Microbiol Biotechnol 21: 137 9– 138 4 Wilschut, J and Hoekstra, D 1984 Membrane fusion:... formation by Pseudomonas aeruginosa in continuous culture Biotechnol Bioeng 26: 1409–1417 Schmidt, J E and Ahring, B K 1996 Granular sludge formation in upflow anaerobic sludge blanket (UASB) reactors Biotechnol Bioeng 49: 229–246 Shizas, L and Bagley, D M 2002 Improving anaerobic sequencing batch reactor performance by modifying operational parameters Water Res 36 : 36 3 36 7 Tay, J H., Yang, S F., and... Wastewater Purification 48 35 0 SNOUR (mg O2 g–1 SS h–1) 30 0 250 200 150 100 50 0 6 12 24 Cycle Time (hours) FIGURE 3. 16 Specific nitrification oxygen utilization rate (SNOUR) of sludge cultivated in different cycle SBRs (Data from Tay, J H., Yang, S F., and Liu, Y 2002 Appl Microbiol Biotechnol 59: 33 2 33 7.) 4.0 PS/PN (mg mg–1) 3. 6 3. 2 2.8 2.4 2.0 107 211 30 3 SNOUR (mg O2 g–1 SS h–1) FIGURE 3. 17 The relationship... and Liu, Y 2002 Appl Microbiol Biotechnol 59: 33 2 33 7.) It is very likely that at a high hydraulic selection pressure, in order to avoid being washed out from the system, the nitrifying community has to regulate its metabolic pathway so as to maintain a balance with the external pressure via consuming nongrowth-associated energy for polysaccharide production In fact, a decreased biomass yield at shortened... can be seen in figure 3. 16, the SNOUR was proportionally related to the cycle time of the SBR A higher selection pressure or a short cycle time results in an increased SNOUR This may imply that the nitrifying community can respond metabolically to changes in the hydraulic selection pressure Figure 3. 17 further shows that the PS/PN ratio increases with the increase in SNOUR The SNOUR is in fact correlated... velocity and hydraulic retention time on granulation in UASB reactors treating wastewater with a high sulphate content Bioresource Technol 43: 249–258 Calleja, G B 1984 Microbial aggregation Boca Raton, FL: CRC Press Hulshoff Pol, L W., de Zeeuw, W J., Velzeboer, C T M., and Lettinga, G 1982 Granulation in UASB -reactors Water Sci Technol 15: 291 30 4 Laudelout, H., Simonart, P C., and van Droogenbroeck,... of cellular polysaccharides, leading to improved bacterial attachment to solid surfaces (Schmidt and Ahring 1996) In fact, extracellular polysaccharides are the key bounding material that interconnects individual cells into attached growth and are further responsible for the structural integrity of the granular matrix (see chapter 10) The microbial activity of nitrifying bacteria can be quantified by... From liposome to biological membrane Trends Biochem Sci 9: 479–4 83 Wuertz, S., Pfleiderer, P., Kriebitzsch, K., Spath, R., Griebe, T., Coello-Oviedo, D., Wilderer, P A., and Flemming, H C 1998 Extracellular redox activity in activated sludge Water Sci Technol 37 : 37 9 38 4 © 2008 by Taylor & Francis Group, LLC © 2008 by Taylor 50 536 71_C0 03. indd & Francis Group, LLC 10/29/07 7:12:57 AM ... (2004) Figure 3. 18 shows that the biomass yield obtained at a cycle time of 2 hours was only half of that observed at the cycle time of 24 hours Robinson, Trulear, and Characklis (1984) thought that most of the nongrowth-associated energy was attributable to polysaccharide © 2008 by Taylor & Francis Group, LLC © 2008 by Taylor 48 536 71_C0 03. indd & Francis Group, LLC 10/29/07 7:12:56 AM Aerobic Granulation. .. utilization by Nitrosomonas and Nitrobacter Arch Mikrobiol 63: 256–277 © 2008 by Taylor & Francis Group, LLC © 2008 by Taylor 49 536 71_C0 03. indd & Francis Group, LLC 10/29/07 7:12:57 AM 50 Wastewater Purification Lin, C Y., Chang, F Y., and Chang, C H 2001 Treatment of septage using an upflow anaerobic sludge blanket reactor Water Environ Res 73: 404408 OFlaherty, V., Lens, P N L., deBeer, D., and Colleran, . 37 3 Aerobic Granulation at Different SBR Cycle Times Zhi-Wu Wang and Yu Liu CONTENTS 3. 1 Introduction 37 3. 2 Effect of Cycle Time on Aerobic Granulation 37 3. 3 Effect of Cycle. Improving anaerobic sequencing batch reactor perfor - mance by modifying operational parameters. Water Res 36 : 36 3 36 7. Tay, J. H., Yang, S. F., and Liu, Y. 2002. Hydraulic selection pressure-induced. Properties of Aerobic Granules 41 3. 4 Conclusions 49 References 49 3. 1 INTRODUCTION Itappearsfromtheprecedingchaptersthatanumberofoperatingparametersofa sequencing batch reactor (SBR) can in uence aerobic