Wastewater Purification: Aerobic Granulation in Sequencing Batch Reactors - Chapter 5 potx

69
5
Roles of SBR Volume
Exchange Ratio and
Discharge Time in
Aerobic Granulation
Zhi-Wu Wang and Yu Liu
CONTENTS
5.1 Introduction 69
5.2 The Role of SBR Volume Exchange Ratio in Aerobic Granulation 70
5.3 Effect of Volume Exchange Ratio on Aerobic Granulation 71
5.4 Effect of Volume Exchange Ratio on Sludge Settleability 73
5.5 Effect of Volume Exchange Ratio on Production of Extracellular
Polysaccharides 75
5.6 Effect of Volume Exchange Ratio on Calcium Accumulation in
Aerobic Granules 75
5.7 VolumeExchangeRatioIsaSelectionPressureforAerobic
Granulation 76
5.8 Effect of Discharge Time on Formation of Aerobic Granules 78
5.9 Effect of Discharge Time on Settleability of Bioparticles 79
5.10 Effect of Discharge Time on Cell Surface Hydrophobicity 82
5.11 Effect of Discharge Time on Production of Extracellular
Polysaccharides 82
5.12 Conclusions 83
References 84
5.1 INTRODUCTION
It appears from the preceding chapters, among all the operation parameters that have
beendiscussedsofar,onlysettlingtimecanserveasaneffectiveselectionpressure
for aerobic granulation. However, a basic question to be addressed is if there are
still other parameters that can also play the roles of selection pressure in aerobic
granulation other than the identied settling time. The answer to such a question is

essential for developing the design and operation strategy for rapid and stable aerobic
granulation in both small- and large-scale sequencing batch reactors (SBRs). This
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70 Wastewater Purification
chapter looks into two other potential candidate parameters that may act as selection
pressuresinaerobicgranulationinSBR,namelySBRvolumeexchangeratioand
discharge time.
5.2 THE ROLE OF SBR VOLUME EXCHANGE RATIO IN
AEROBIC GRANULATION
According to gure 5.1, the mixed liquor volume exchange ratio, or volume exchange
ratio for short, is the volume of efuent that is withdrawn after a preset settling time
dividedbythetotalworkingvolumeofacolumnSBR:
Volume exchange ratio



R,
R(
,
(
2
2
(5.1)
in which r istheradiusofacolumnSBR,andH is the working height of the column
SBR. This equation clearly shows that the volume exchange ratio is proportionally
related to L.Tolookintothepotentialroleofvolumeexchangeratioinaerobic
granulation,Wang,Liu,andTay(2006)designedandranfouridenticalcolumn
SBRs at different volume exchange ratios of 20% to 80% (gure 5.1), while the other

operatingconditionswereallmaintainedatthesamelevels.
P
Feeding
pump
80%
Air
60%
40% 20%
Discharging
pump
P
P
P
Substrate
4°C
P
FIGURE 5.1 Schematics of four SBRs operated at the respective volume exchange ratios of
80%,60%,40%,and20%.(FromWang,Z W.2007.Ph.D.thesis,NanyangTechnological
University,Singapore.Withpermission.)
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Roles of SBR Volume Exchange Ratio and Discharge Time 71
5.3 EFFECT OF VOLUME EXCHANGE RATIO ON
AEROBIC GRANULATION
Wang,Liu,andTay(2006)investigatedtheeffectofvolumeexchangeratioonthe
formationofacetate-fedaerobicgranules.Theevolutionofsludgemorphologyinthe
course of SBR operation at different volume exchange ratios is shown in gure 5.2.
Morphologiesofaerobicgranulesformedinfourreactorsappearedtobecloselycorre
-

latedwiththeappliedvolumeexchangeratio;thatis,only8daysafterreactorstartup,
80%
60%
40%
20%
0d
8d 16d 24d 30d
FIGURE 5.2 Morphologies of sludge cultivated at different volume exchange ratios in the
course of aerobic granulation in SBRs; scale bar: 6 mm.
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72 Wastewater Purification
aerobicgranulesrstappearedintheSBRoperatedatthehighestvolumeexchange
ratioof80%,whileaerobicgranulesweresubsequentlyobservedatthevolume
exchangeratiosof60%,40%,and20%,respectively,6,12,and20dayslater.Itcan
be seen in gure 5.2 that the larger and more spherical aerobic granules were formed
atthehighervolumeexchangeratioof80%,whereasbioocswerecultivatedand
becamepredominantintheSBRoperatedatthelowervolumeexchangeratioof20%.
It is apparent from gure 5.2 that only a mixture of bioocs and aerobic granules
wascultivatedatsmallvolumeexchangeratios.Analysisofthefractionofaerobic
granules formed in each SBR reveals that nearly a pure aerobic granular sludge blanket
wasindeeddevelopedatthevolumeexchangeratioof80%(gure5.3).Incontrast,
almostnoaerobicgranulationwasfoundatthevolumeexchangeof20%,indicating
afailedgranulation(gure5.3).ItisthusreasonabletoconsiderthattheSBRvolume
exchange ratio can play an essential role in aerobic granulation, and a high SBR volume
exchange ratio facilitates rapid and successful aerobic granulation in SBR.
As presented in the preceding chapters, aerobic granules can be simply distin
-
guished from bioocs by their large particle size. The mean size of aerobic gran

-
ules cultivated at different volume exchange ratios are presented in gure 5.4. The
size of the aerobic granules tended to increase with the increase in the SBR volume
exchange ratio, for example, the size of aerobic granules developed at the volume
exchangeratioof20%wassmallerthan1mm,whereasaerobicgranulesaslargeas
about3.8mmwereobtainedatthevolumeexchangeratioof80%.
In the operation of nitrogen-removal SBRs, Kim et al. (2004) also manipulated
theSBRdischargeheightsoastoimposeonmicroorganismstwoslightlydifferent
selectionpressuresintermsofminimumsettlingvelocityof0.6and0.7mh
–1
.Even
such a marginal difference in the minimum settling velocity could also result in
distinctmorphologiesofcultivatedsludge.Forexample,largebioparticlesof1.0to
2.0 mm were harvested at the (
V
s
)
min
of 0.7 m h
–1
, while only small bioparticles of 0.1
to0.5mmwerecultivatedatthe(
V
s
)
min
of 0.6 m h
–1
(Kim et al. 2004). Microscopic
observation further revealed that the high volume exchange ratio SBR favored the

Volume Exchange Ratio (%)
0 20 40 60 80 100
Fraction of Aerobic Granule (%)
20
40
60
80
100
FIGURE 5.3 Fraction of aerobic granules in four SBRs run at volume exchange ratios of 20%
to80%.(DatafromWang,Z W.,Liu,Y.,andTay,J H.2006.Chemosphere 62: 767–771.)
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Roles of SBR Volume Exchange Ratio and Discharge Time 73
cultivation of spherical granular sludge (gure 5.5b), while only bioocs instead
ofgranularsludgeweredevelopedintheSBRrunatthelowvolumeexchange
(gure5.5a).SimilartothendingsbyWang,Liu,andTay(2006),thetimefor
formation of aerobic granules and to reach steady state was signicantly shortened
atahighvolumeexchangeratio(Kimetal.2004).
5.4 EFFECT OF VOLUME EXCHANGE RATIO ON
SLUDGE SETTLEABILITY
In the eld of biological wastewater treatment, sludge volume index (SVI) has been
used commonly as a good indicator of microbial sludge settleability. Figure 5.6
Volume Exchange Ratio (%)
0 20406080100
Mean Size (mm)
0
1
2
3

4
FIGURE 5.4 Comparison of mean size of aerobic granules developed at volume exchange
ratiosof20%to80%.(DatafromWang,Z W.,Liu,Y.,andTay,J H.2006.
Chemosphere
62: 767–771.)
115 µm
1.2 mm
A B
2 µm
FIGURE 5.5 Morphology of steady-state granules obtained at different minimum settling
velocities,(a):0.6mh
–1
and (b): 0.7 m h
–1
,respectively.(FromKim,S.M.etal.2004.Water
Sci Technol 50:157–162.Withpermission.)
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74 Wastewater Purification
shows comparison of the settleability of sludge cultivated at different volume
exchange ratios in SBRs. It can be seen that the sludge SVI was inversely correlated
to the volume exchange ratio, that is, a sludge with excellent settleability would be
developed at a high volume exchange ratio. For example, the settleability of sludge
cultivatedatthevolumeexchangeratioof80%isalmostthreetimessuperiorto
thatharvestedatthevolumeexchangeratioof20%.Kimetal.(2004)alsoreported
similar results showing that high volume exchange ratio SBR corresponding to a
high (
V
s

)
min
could promote the development of sludge with excellent settleability,
indicatedbyalowSVIof50mLg
–1
(gure 5.7).
FIGURE 5.6 Sludge volume index (SVI) versus volume exchange ratios in SBRs. (Data
fromWang,Z W.,Liu,Y.,andTay,J H.2006.Chemosphere 62: 767–771.)
FIGURE 5.7 Sludge volume index (SVI) versus minimum settling velocities (V
s
)
min
deter-
mined from the volume exchange ratios. (Data from Kim, S. M. et al. 2004. Water Sci Technol
50:157–162.)
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Volume Exchange Ratio (%)
0 20 40 60 80 100
SVI (mL g
–1
)
20
40
60
80
100
(V
s

)
min
(m h
–1
)
0.6 0.7
SVI (ml g
–1
)
40
50
60
70
80
90
Roles of SBR Volume Exchange Ratio and Discharge Time 75
5.5 EFFECT OF VOLUME EXCHANGE RATIO ON PRODUCTION OF
EXTRACELLULAR POLYSACCHARIDES
Extracellular polysaccharides (PS) are a kind of bioglue that interconnects individ-
ual cells into the three-dimensional structure of attached-growth microorganisms
(seechapter10).Ahighappliedvolumeexchangeratiowasfoundtostimulatecells
toproducemorePS(gure5.8).Asdiscussedinchapter10,PSindeedisnotan
essential cell component under normal living conditions, and its production is only
necessarywhenmicrobialcellsaresubjectedtostressfulconditions.Figure5.8
seemstoindicatethatthehighSBRvolumeexchangeratiocanimposeapressureon
microbialsludge,leadingtoanenhancedproductionofPS.
5.6 EFFECT OF VOLUME EXCHANGE RATIO ON
CALCIUM ACCUMULATION IN AEROBIC GRANULES
Calcium ion was accumulated signicantly in aerobic granules developed at high
volumeexchangeratio,forexample,thecalciumcontentingranulescultivatedat

thevolumeexchangeratioof80%wasalmostthreetimeshigherthanthatobtained
atthevolumeexchangeratioof20%(gure5.9).Figure5.10showsfurtherthat
themeansizeoftheaerobicgranulestendedtoincreasewiththecalciumcontent,
whileaninversetrendwasfoundforSVI.AccordingtoStokeslaw,theincreasein
particle size will improve the settling ability of particles, and this in turn results in a
lowered SVI (gure 5.10). The improved settleability of bioparticles can effectively
preventthemfrombeingwashedoutoftheSBRatahighvolumeexchangeratio
(gure 5.9). Thus, it is most likely that the selective accumulation of calcium would
be a defensive strategy of microbial aggregates to resist the hydraulic discharge from
the reactor through the calcium-promoted increases in their size and settleability in
termsofSVI(gure5.10).Infact,itisgenerallybelievedthatcalciummayfacilitate
Volume Exchange Ratio (%)
0 20 40 60 80 100
EPS Content (g g
–1
SS)
0.0
0.1
0.2
0.3
0.4
0.5
FIGURE 5.8 Extracellular polysaccharide production at different volume exchange ratios.
(DatafromWang,Z W.,Liu,Y.,andTay,J H.2006.Chemosphere 62: 767–771.)
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76 Wastewater Purification
anaerobic granulation (Schmidt and Ahring 1996; Yu, Tay, and Fang 2001), while
evidence also shows that the removal of calcium from the anaerobic granule matrix

results in lowered strength of upow anaerobic sludge blanket (UASB) granules
(Pereboom 1997). Consequently, a certain amount of calcium in biogranules would
improve their long-term stability.
5.7 VOLUME EXCHANGE RATIO IS A SELECTION PRESSURE FOR
AEROBIC GRANULATION
It appears from chapter 4 that the settling time of SBR can serve as a selection pres-
sureforaerobicgranulation,forexample,atashortsettlingtime,bioparticleswith
poorsettleabilitywouldbewashedoutaccordingtotheminimumsettlingvelocity:
()6
,
T
S
S
min

(5.2)
in which
t
s
is settling time and L is the traveling distance of the bioparticles above
the discharge port, which is proportionally correlated to the volume exchange ratio
of SBR (gure 5.11).
Atadesignedsettlingtimeanddischargeheight,bioparticleswithasettling
velocity less than (
V
s
)
min
arewashedoutofthereactor,whilethosewithasettling
velocity greater than (

V
s
)
min
areretained(gure5.11).Itisobviousthattheselection
pressure in terms of minimum settling velocity (
V
s
)
min
is not only a function of settling
time (
t), but also depends on the discharge height (L), which can be translated to the
volume exchange ratio as given in equation 5.2. This means that the volume exchange
ratio can be another essential selection pressure for successful aerobic granulation.
Volume Exchange Ratio (%)
0 20 40 60 80 100
Calcium Content (g g
–1
SS)
0.00
0.05
0.10
0.15
0.20
0.25
FIGURE 5.9 Calciumcontentofsludgecultivatedatdifferentvolumeexchangeratiosin
SBRs.(DatafromWang,Z W.,Liu,Y.,andTay,J H.2006.Chemosphere 62: 767–771.)
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Roles of SBR Volume Exchange Ratio and Discharge Time 77
Mean Bioparticle Size (mm)
15
30
45
60
75
90
105
Calcium Content (g g
–1
SS)
0.06 0.09 0.12 0.15 0.18 0.21 0.24
SVI (mL g
–1
)
0.5
1.0
1.5
2.0
2.5
3.0
3.5
FIGURE 5.10 Correlations among size of bioparticles (O), SVI (/), and calcium content.
(DatafromWang,Z W.,Liu,Y.,andTay,J H.2006.Chemosphere 62: 767–771.)
L
FIGURE 5.11 SchematicdiagramofacolumnSBR.
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78 Wastewater Purification
Accordingtoequation5.2,theminimumsettlingvelocityisthefunctionofsettling
timeanddischargeheightorvolumeexchangeratioforanSBRwithagivendiam
-
eter.Bycontrolling(
V
s
)
min
, bioparticles can be effectively selected according to their
respective settleability. This means that selection of bioparticles indeed can be realized
by manipulating settling time and volume exchange ratio. To examine the collective
effects of SBR volume exchange ratio and settling velocity on aerobic granulation,
gure5.12showsthecorrelationofthefractionsofaerobicgranulesinSBRsto(
V
s
)
min
calculatedfromvarioussettlingtimes(seechapter6)andvolumeexchangeratios.As
expected,thedegreeofaerobicgranulationinanSBRisdeterminedby(
V
s
)
min
.
Itappearsfromgure5.12thatata(
V
s
)

min
lessthan4mh
–1
,onlyapartialaerobic
granulation can be achieved in SBR, and the growth of suspended sludge seems to be
promotedinthiscase.Thetypicalsettlingvelocityofconventionalactivatedsludgeis
generallylessthan5mh
–1
(Giokasetal.2003).ThisimpliesthatforanSBRoperated
ata(
V
s
)
min
below the settling velocity of conventional activated sludge, suspended
sludge cannot be effectively withdrawn. In this case, suspended sludge will easily
outcompeteaerobicgranules,whichwillleadtotheinstabilityandevenfailureof
aerobicgranularsludgeSBRs.Nowitisclearthatsuspendedsludgewilltakeoverthe
entire reactor at low (
V
s
)
min
,asshowningure5.12.Toachieverapidandenhanced
aerobicgranulationinSBRs,theminimumsettlingvelocity(
V
s
)
min
must be controlled

atalevelhigherthanthesettlingvelocityofsuspendedsludge(seechapter6).
5.8 EFFECT OF DISCHARGE TIME ON FORMATION OF
AEROBIC GRANULES
Asillustratedingure5.13,dischargetimeofSBR(t
d
)isdenedasthetimepreset
to withdraw the volume of the mixed liquor above the discharge port of the SBR, and
(V
s
)
min
(m h
–1
)
0246810
Fraction of Granules (%)
0
20
40
60
80
100
FIGURE 5.12 Fractionofaerobicgranulesversus(V
s
)
min
, obtained from studies of volume
exchange ratio (D) and settling time ($).(DataonvolumeexchangeratiofromWang,Z W.,
Liu, Y., and Tay, J H. 2006. Chemosphere 62:767–771;dataonsettlingtimefromQin,L.,
Liu, Y., and Tay, J. H. 2004. Biochem. Eng. J. 21: 47–52.)

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Roles of SBR Volume Exchange Ratio and Discharge Time 79
it can be expressed as the ratio of the discharge volume of SBR (V
e)
to the discharge
owrateoftheSBR(
Q
e
):
T
6
1
D
D
D

(5.3)
Wang(2007)studiedthepotentialeffectofdischargetimeonaerobicgranulation
inSBRs.Forthispurpose,fouridenticalSBRswereoperatedatdifferentdischarge
timesof5to20minutes,whileallotheroperatingconditionswerekeptatthesame
levels. Figure 5.14 shows the morphologies of bioparticles developed at the various
discharge times. It can be seen that smooth, round aerobic granules were successfully
cultivatedatashortdischargetimeof5minutes,andonlyoc-likebioparticleswere
observedintheSBRoperatedatthelongestdischargetimeof20minutes.
Moreover,
gure5.15showsthatthemeansizeofthebioparticleswasinverselyrelatedtothe
applied discharge time. This seems to indicate that a prolonged discharge time would
delayorpreventtheformationofaerobicgranulesinSBReventhoughbothsettling

time and volume exchange ratio are properly controlled.
Asdiscussedinchapter4,thefractionofaerobicgranulesoverthewholesludge
blanketinanSBRrepresentsthedegreeofaerobicgranulationthatcanbeachieved
under given operating conditions. Figure 5.16 shows that the fraction of aerobic
granulesdecreasedastheapplieddischargetimewasprolongedfrom5to20minutes,
forexample,intheSBRrunatthedischargetimeof20minutes,almostnoaerobic
granules were formed. Similar to settling time and volume exchange ratio, the
observedfailureofaerobicgranulationatthelongdischargetimemayimplythatthis
parametercouldalsoserveasakindofselectionpressureforaerobicgranulation.
5.9 EFFECT OF DISCHARGE TIME ON
SETTLEABILITY OF BIOPARTICLES
As presented in the preceding chapters, settleability of bioparticles can be evalu-
atedbyasimpleparameter,namelytheSVI.Figure5.17showsacomparisonofthe
V
d
Q
d
FIGURE 5.13 Illustration of the discharge time.
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80 Wastewater Purification
5 min 10 min
15 min 20 min
FIGURE 5.14 Morphologyofthesteady-statesludgecultivatedatdifferentdischargetimes;
scalebar:3mm.(FromWang,Z W.2007.Ph.D.thesis,NanyangTechnologicalUniversity,
Singapore. With permission.)
FIGURE 5.15 Mean size of bioparticles versus different discharge times observed in SBRs.
(DatafromWang,Z W.2007.Ph.D.thesis,NanyangTechnologicalUniversity,Singapore.)
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Discharge Time (min)
0 5 10 15 20 25
Mean Size (mm)
0.0
0.5
1.0
1.5
2.0
2.5
Roles of SBR Volume Exchange Ratio and Discharge Time 81
SVIofbioparticlesharvestedinSBRsrunatdifferentdischargetimes.HighSVI
values were obtained at long discharge times. This implies that bioparticles with
poorersettleabilitywouldbecultivatedatthelongerdischargetime.Itshouldbe
realizedthattheSVIofbioparticlesobtainedfromanSBRwitha20-minutedis
-
chargetimewassimilartothatoftypicalactivatedsludgeocs.Thisobservationis
in line with the results presented in gure 5.15. Arrojo et al. (2004) also reported that
alongdischargetimewouldleadtoahighconcentrationoftotalsuspendedsolidsin
efuent, for example the concentration of total suspended solids in the efuent from
anSBRoperatedatadischargetimeof3minuteswasfourtimeshigherthanthat
at 0.5 minutes of discharge time, indicating that the sludge with poor settleability
FIGURE 5.16 Fraction of aerobic granules cultivated at different discharge times. (Data
fromWang,Z W.2007.Ph.D.thesis,NanyangTechnologicalUniversity,Singapore.)
Discharge Time (min)
0 5 10 15 20 25
SVI (mL g
–1
)

0
20
40
60
80
100
120
140
FIGURE 5.17 Sludge volume index (SVI) of sludge cultivated at different discharge times.
(DatafromWang,Z W.2007.Ph.D.thesis,NanyangTechnologicalUniversity,Singapore.)
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Discharge Time (min)
0 5 10 15 20 25
Fraction of Aerobic Granules (%)
0
20
40
60
80
100
82 Wastewater Purification
wascultivatedatlongdischargetime(gure5.17).Thepoorsettleabilitysludge
is actually a practical indicator of unsuccessful aerobic granulation in the SBR. It
seemscertainthataprolongedSBRdischargetimewouldpreventaerobicgranula
-
tion in the SBR.
5.10 EFFECT OF DISCHARGE TIME ON
CELL SURFACE HYDROPHOBICITY

Theeffectofdischargetimeoncellsurfacehydrophobicityisshowningure5.19.
Alowhydrophobicitywasobservedatalongdischargetime,forexample,thecell
surfacehydrophobicitywasincreasedfrom26%fortheseedsludgetoastablevalue
of71%,65%,52%,and39%inSBRsrunatdischargetimesof5to20minutes.
This implies that a microbial community developed at short discharge time would
exhibit a high cell surface hydrophobicity. As shown in gure 5.16, incomplete
aerobicgranulationwasobservedinSBRsrunatthedischargetimesof10,15,and
20 minutes, while successful aerobic granulation was only achieved at the discharge
time of 5 minutes. This may be partially attributed to the difference in cell surface
hydrophobicity,asdetailedinchapter9.
5.11 EFFECT OF DISCHARGE TIME ON PRODUCTION OF
EXTRACELLULAR POLYSACCHARIDES
As shown in the preceding chapters, the production of extracellular polysaccharides
(PS)iscloselyassociatedwiththeoperationconditionsintheSBR.Figure5.20
shows the effect of discharge time on the sludge PS content. An inverse correlation
ofthePSproductiontotheapplieddischargetimewasobserved,thatis,ashorter
discharge time would stimulate cells to produce more PS. Microscopic observation
Discharge Time (min)
0.5 1.0 3.0
Effluent TSS (gL
–1
)
0.0
0.1
0.2
0.3
0.4
0.5
FIGURE 5.18 Totalsuspendedsolids(TSS)intheefuentsfromSBRsoperatedatdifferent
dischargetimes.(DatafromArrojo,B.etal.2004.Water Res 38: 3389–3399.)

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Roles of SBR Volume Exchange Ratio and Discharge Time 83
further reveals that bacteria were tightly connected and embedded in the PS matrix of
aerobicgranulescultivatedattheshorterdischargetimeof5minutes(gure5.21).
5.12 CONCLUSIONS
This chapter provides experimental evidence showing that the volume exchange
ratioanddischargetimeoftheSBRaretwodecisiveparametersthathighlyinu-
enceaerobicgranulation,andcanserveaseffectiveselectionpressuresforaerobic
granulationinanSBR.Ahighvolumeexchangeratiofavorsaerobicgranulation,and
ashortdischargetimehasthesamefunction.
Discharge Time (min)
0 5 10 15 20 25
Hydrophobicity (%)
40
50
60
70
FIGURE 5.19 Cell surface hydrophobicity at different discharge times. (Data from
Wang,Z W.2007.Ph.D.thesis,NanyangTechnologicalUniversity,Singapore.)
FIGURE 5.20 Polysaccharide content of sludge cultivated at different discharge times.
(DatafromWang,Z W.2007.Ph.D.thesis,NanyangTechnologicalUniversity,Singapore.)
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Discharge Time (min)
0 5 10 15 20 25
PS Content (g g
–1

SS)
0.0
0.1
0.2
0.3
0.4
84 Wastewater Purification
TheessentialroleofvolumeexchangeratioinaerobicgranulationinSBRs
canbereasonablyinterpretedbytheconceptofminimumsettlingvelocity,while
the mechanism by which discharge time can inuence aerobic granulation will be
further discussed in chapter 6.
REFERENCES
Arrojo,B.,Mosquera-Corral,A.,Garrido,J.M.,andMendez,R.2004.Aerobicgranulation
with industrial wastewater in sequencing batch reactors.
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Comparison and evaluation of empirical zone settling velocity parameters based
on sludge volume index using a unied settling characteristics database.
Water Res
37: 3821–3836.
Kim,S.M.,Kim,S.H.,Choi,H.C.,andKim,I.S.2004.Enhancedaerobicoc-likegranula
-
tionandnitrogenremovalinasequencingbatchreactorbyselectionofsettlingvelocity.
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Pereboom,J.H.F.1997.Strengthcharacterisationofmicrobialgranules.
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FIGURE 5.21 FilamentousPSobservedinaerobicgranules,scalebar=3µm.
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© 2008 by Taylor & Francis Group, LLC
© 2008 by Taylor & Francis Group, LLC