Sepa a ion and Pu i ica ion Technology 281 (2022) 119830
A ailable online 30 Sep embe 2021
1383-5866/© 2021 The Au ho (s). Published by Else ie B.V. This is an open access a icle unde he CC BY-NC-ND license
(h p://c ea i ecommons.o g/licenses/by-nc-nd/4.0/).
Op imiza ion o mul i-s age hickening o biomass in a demons a i e
ull–scale mic oalgae-based was ewa e ea men sys em
An onio O iz, Joan Ga cía, En ica Ugge i , Rub´
en Díez-Mon e o
*
GEMMA-G oup o En i onmen al Enginee ing and Mic obiology, Depa men o Ci il and En i onmen al Enginee ing, Uni e si a Poli `
ecnica de Ca alunya-
Ba celonaTech, c/ Jo di Gi ona 1-3, Building D1, Ba celona E-08034, Spain
ARTICLE INFO
Keywo ds:
Ha es ing
Dewa e ing
Lamella se ling ank
Cyanobac e ia
Field scale
ABSTRACT
This s udy ga he s he esul s o he ope a ion and op imiza ion o he hickening o mic oalgal biomass p oduced
a demons a i e scale in pho obio eac o s ed wi h ag icul u al uno and domes ic was ewa e . The op imi-
za ion was conduc ed du ing wo mon hs. The sys em consis ed in wo g a i y hickene s connec ed in se ies in a
mul i-s age app oach. The objec i e o hickening was o concen a e he mic oalgae g own in pho obio eac o s
( o al solids (TS) concen a ion o 0.1–1 g/L) in o a biomass wi h 20 g/L o TS, which was conside ed op imal o
he subsequen anae obic diges ion p ocess. Fi s , he u iliza ion o one single hickene alone allowed o achie e
a concen a ion ac o (CF) o 1.9 and eco e y e iciency (RE) o 28%. Howe e , he inal concen a ion o TS in
he hickened biomass (6.4 g/L) was s ill much lowe han he a ge concen a ion. The ins alla ion o he second
hickene connec ed in se ies wi h he i s one signi ican ly imp o ed he o e all pe o mance. Indeed, a TS
concen a ion o 26.5 g/L was inally achie ed, wi h an o e all CF o 3.6. The esul s o he s udy sugges ha he
mul i-s age hickening p ocess is a sui able s a egy and i is highly ad isable o achie e a success ul mic oalgal
biomass hickening a ull-scale. In addi ion, o he h ee poin s ha e been iden i ied as key ac o s o be aken
in o accoun o biomass ickening: p ope adjus men o he pu ge low a e, coo dina ion be ween pu ges imes
and olumes in he di e en s ages, and p ope adjus men o he ope a ion o he sc ape s.
1. In oduc ion
The ha es ing and eco e y o mic oalgal biomass a e essen ial
componen s o any mic oalgae-based biop ocess. The ypical concen-
a ion o mic oalgae in he cul u e medium is ela i ely low om a
downs eaming poin o iew, usually anging om 0.1 o 2 g/L o o al
solids (TS). This concen a ion mus be necessa ily inc eased one o
mo e o de s o magni ude o ensu e subsequen biomass alo iza ion
easibili y. Whe he he aim o he mic oalgae cul u e is he ea men o
was ewa e o he p oduc ion o aluable biop oduc s and bioene gy,
he cul u ed biomass should be subsequen ly ans o med in o a
concen a ed slu y, pas e o d ied solid.
A high cos is linked o ha es ing, hickening and dewa e ing o
mic oalgae biomass [1–5]. This is mainly due o he na u e and speci ic
cha ac e is ics o mic oalgae cells, which a e ex emely di icul o
sepa a e om wa e , and he e o e o eco e om he liquid cul u e
media. These cha ac e is ics include small size (gene ally be ween 5 and
20
μ
m), low ela i e densi y (gene ally be ween 1.05 and 1.1) and
nega i e elec ical su ace cha ge [6,7]. Se e al ha es ing echniques
ha e been success ully de eloped, bu mos o hem a e ene gy-
in ensi e, equi ing be ween 0.1 and 15 kWh pe m
3
o ea ed wa e ,
depending on he echniques [8]. Fo he comme cial applica ion o
mic oalgae biop ocesses, he ha es ing s ep should ha e low in es -
men and ope a ional cos s, while being e ec i e and eliable a ull-
scale [9,10].
In o de o op imize he ha es ing and eco e y o mic oalgae,
exis ing echniques a e usually combined and implemen ed in se e al
sequen ial s eps in a mul i-s age app oach. O cou se, hese echniques
can be used in isola ion, bu he mul i-s age app oach has ad an ages. In
each s age he mos sui able me hod is applied, so ha each p e ious
s age educes he biomass olume (wi h inc eased biomass concen a-
ion) o be p ocessed in each subsequen s age [9]. The eade should be
awa e ha in he nex lines we use a e minology analogous o he one
used in was ewa e enginee ing. The ypical s ages can s a wi h ha -
es ing (o p ima y concen a ion), which inc eases he TS concen a-
ion abou 10 imes. Then, a hickening s ep o he p ima y concen a e
can be pe o med, inc easing he TS concen a ion up o 10 imes and
p oducing a biomass concen a e wi h slu y-like consis ency. I
* Co esponding au ho .
E-mail add ess: [email p o ec ed] (R. Díez-Mon e o).
Con en s lis s a ailable a ScienceDi ec
Sepa a ion and Pu i ica ion Technology
jou nal homepage: www.else ie .com/loca e/seppu
h ps://doi.o g/10.1016/j.seppu .2021.119830
Recei ed 4 Augus 2021; Recei ed in e ised o m 10 Sep embe 2021; Accep ed 26 Sep embe 2021
Sepa a ion and Pu i ica ion Technology 281 (2022) 119830
2
equi ed, subsequen dewa e ing and d ying o he hickened biomass
can p oduce a we pas e o d y solid, espec i ely [10]. Fo many ap-
plica ions, he concen a ion o TS achie ed by hickening can be
enough. Fo ins ance, i he biomass is used o biogas p oduc ion by
means o anae obic diges ion, he slu y-like consis ency is sui able o
eeding he anae obic diges e . Indeed, he ull-scale implemen a ion o
anae obic diges ion o mic oalgae is inc easing [11,12].
A lo o esea ch e o has been done ega ding he s udy, selec ion
and op imiza ion o p ima y concen a ion ha es ing echniques
[13,1,2,14,3,4,15]. O e all, he au ho s epo ed concen a ions o he
ha es ed biomass be ween 5 and 15 g/L. Ne e heless, no s udies ha e
been speci ically epo ed ega ding he subsequen hickening s ep
nei he a lab-scale no a pilo -scale, and his opic has been only
men ioned in e y ew a icles wi h o he objec i es [9,16]. The hy-
po hesis o his s udy is ha a p ope mul i-s age hickening p ocess can
achie e concen a ions o 20 g/L o mo e wi hou signi ican ly
inc easing he land and ene gy equi emen s.
Thickening is he p ocess by which he suspended solids o an
al eady concen a ed biop ocess a e u he condensed o p oduce a
much mo e concen a ed biomass p oduc and a ela i ely solids- ee
supe na an . Se e al di e en me hods and echnologies can be used
o hickening suspended solids om a biop ocess, including dissol ed
ai lo a ion (DAF), cen i ugal hickening, g a i y bel hickening, and
g a i y hickening [17]. These echnologies di e in se e al pe o -
mance c i e ia, among hem he solids concen a ion ha can be ach-
ie ed and he ene gy demand equi ed o he hickening p ocess.
The e o e, he selec ion o one me hod o e he o he s should be ca ied
ou in acco dance wi h he speci ic condi ions and objec i es o each
biop ocess. In pa icula , g a i y hickening is he simples me hod,
based on he na u al endency o highe -densi y pa icles o se le ou o
he liquid o concen a e he solids [9]. Consequen ly, g a i y hickening
has much lowe ope a ing and main enance cos s han o he hickening
me hods [17]. The TS concen a ion achie ed by g a i y hickening is
20–30 g/L, which is lowe han ha o DAF, cen i ugal hickening o
g a i y bel [17,9], bu sui able o eeding an anae obic diges ion
p ocess. Fo hese easons, g a i y hickening is widely used in p ac ice
o concen a e biosolids in was ewa e ea men plan s p io o anae -
obic diges ion [18]. Howe e , he applica ion o g a i y hickening in
ull-scale mic oalgae-based plan s has been sca cely epo ed [19].
G a i y hickening is usually pe o med in ci cula anks wi h a sloped
shape conical bo om and sc ape s o assis se led solids anspo and
collec ion a he bo om o he ank. Thickened solids a e emo ed om
he ank a egula in e als, pumping hem om he ank bo om. The
main ope a ional challenges o di icul ies in g a i y hickene s include
he o ma ion o gas bubbles which cling o solid pa icles, he e o e
inc easing he solids’ buoyancy and educing hei se ling. This can be
a oided o educed using sc ape s o picke s a ached o he hickene
a m, which aid in eleasing gas om he sludge blanke . To educe
signi ican u bulence and esuspension o pa icles, hese de ices mo e
a a e y low speed. Ano he phenomenon ha should be a oided is
‘ a holing’, which consis s in he sho -ci cui ing o he d aw-o and
esul s in poo ly consolida ed biomass being emo ed, while a high
concen a ion o solids emains in he ank. Ra holing usually occu s i
hickened biomass is d awn-o oo quickly o oo slowly, esul ing in a
cone o dep ession a he d aw-o poin . To a oid a holing, he
pumping speed o solids emo al should be ca e ully adjus ed [17].
This pape p esen s he esul s o he op imiza ion o a hickening
p ocess o mic oalgae concen a ion and collec ion in a demons a i e
ull-scale mic oalgae bio e ine y, aimed a was ewa e ea men and
esou ce eco e y [20]. In his sys em, h ee pa allel pho obio eac o s
(PBRs) wi h a o al olume o 35 m
3
we e ed wi h ag icul u al uno
mixed wi h domes ic was ewa e [21]. The biomass he e p oduced un-
de wen o he ha es ing and hickening sys em, consis ing in a coag-
ula ion and loccula ion se ling ank ollowed by wo hickene s [15].
The ha es ed and hickened biomass was hen used o eed an anae -
obic diges e o biogas and biome hane p oduc ion.
Conside ing ha he hickening p ocess is a key s ep o biomass
ha es ing in mic oalgae-based ea men sys ems and mic oalgae bio-
e ine ies, he main mo i a ion o his s udy was o e i y he echnical
easibili y o g a i y hickening in o de o achie e he desi ed con-
cen a ion o he subsequen anae obic diges ion p ocess. The esul s
p esen ed in his s udy, ca ied ou a demons a i e scale, p o ide an
insigh o he success ul p oposal, design and ope a ion o ull-scale and
indus ial applica ions o low-cos mic oalgae cul u e in was ewa e .
Ou main echnical goal was o achie e a ela i ely cons an concen-
a ion o o al solids o 20 g/L o highe , which was conside ed op imal
o he subsequen anae obic diges ion. The concen a ion o he
biomass collec ed in he se ling ank was a ound 5 g/L o TS [15]. The
speci ic objec i es we e: 1) o assess he pe o mance o a mul i-s age
hickening p ocess, 2) o analyze and educe he hyd odynamic
impac o he in luen biomass s eam, con eyed om he se ling ank,
and 3) o inc ease he eco e y o biomass a oiding o educing he
a achmen o solids o he in e nal walls o he hickene s. This s udy is
no el because o he i s ime i speci ically add esses owa ds
mic oalgae biomass hickening. Mo eo e , expe imen s we e conduc ed
a a pilo demons a i e scale.
2. Ma e ials and me hods
2.1. Expe imen al se up
2.1.1. Was ewa e ea men and biomass p oduc ion sys em
The expe imen al se up consis ed in wo g a i y hickene s which
we e pa o a mic oalgae-based was ewa e ea men and esou ce
eco e y plan a demons a i e scale. The plan was designed, con-
s uc ed and ope a ed in he amewo k o he esea ch p ojec
INCOVER (Inno a i e Eco- echnologies o Resou ce Reco e y om
Was ewa e , GA 689242, h ps://inco e -p ojec .eu/). The plan was
loca ed ou doo s in he Ag `
opolis expe imen al campus o Uni e si a
Poli `
ecnica de Ca alunya (UPC) in Viladecans, nea he ci y o Ba celona
(Ca alonia, Spain; 41.29◦N, 2.04◦E). The mic oalgal biomass g ew in a
se o h ee semi–closed ubula ho izon al PBRs (11.7 m
3
olume each),
which we e ed wi h a mix o ag icul u al uno and pa ially ea ed
domes ic was ewa e . The ag icul u al uno , collec ed om a d ainage
channel beside he campus, was he majo componen o he in luen ,
wi h a a io o abou 10 pa s o ag icul u al uno o 1 pa o domes ic
was ewa e . The domes ic was ewa e was collec ed om a sep ic ank
which ecei ed he sewage om a building loca ed inside he campus.
The plan was ope a ed o 20 mon hs, om May 2017 un il
Decembe 2018. A de ailed desc ip ion o he PBRs and esul s ega ding
was ewa e ea men and biomass p oduc ion a e epo ed by [21] and
[22]. The PBRs we e ope a ed in o de o selec p oka yo ic mic oalgae
(Cyanobac e ia) and accumula e polyhyd oxybu y a e (PHB), as
desc ibed by [23]. The plan p oduced up o 2 kg o biomass (TS) pe day
(mos ly domina ed by Cyanobac e ia, bu also wi h p esence o
euka yo ic mic oalgae), which was ha es ed in a lamella se ling ank
coupled wi h a coagula ion and loccula ion sys em. The ha es ing
p ocess was op imized and low doses o aluminum polychlo ide (1–6
mg/L) we e used as coagulan o enhance he se ling and collec ion o
biomass in he se ling ank [15]. The ha es ed biomass was subse-
quen ly hickened in wo g a i y hickene s, p io o diges ion in an
anae obic diges e o biogas p oduc ion and upg ade o biome hane
[24]. The diges a e was u he s abilized and dewa e ed in a sludge
ea men we land o ob ain a bio e ilize .
The e luen wa e , cla i ied in he lamella se le , was pos ea ed in a
sola d i en ul a il a ion-disin ec ion uni and in adso p ion columns
o nu ien s emo al and eco e y, and e en ually eused o i iga ion
o apeseed and sun lowe c ops by means o a sma i iga ion sys em.
Howe e , all hese sys ems a e ou o he scope o he objec i es o he
p esen s udy. The eade may ind de ails abou he en i e expe imen al
si e in [20].
A. O iz e al.
Sepa a ion and Pu i ica ion Technology 281 (2022) 119830
3
2.1.2. G a i y hickene s
Each o he wo iden ical hickene s used in his s udy consis ed o
200 L polyp opylene cylind ical anks wi h a cone-shaped bo om. The
diame e o each ank was 58 cm and he heigh 94 cm (70 cm he cy-
lind ical pa and 24 cm he hoppe ). The hickene s we e pain ed wi h
wo coa s o ixa i e ollowed by se e al coa s o black pain and wo
whi e pain coa s. The wo anks we e black in o de o a oid any
glimme o ligh inside he hickene , hus c ea ing a o ally obscu e
en i onmen a oiding any pho osyn he ic ac i i y which could p oduce
gas bubbles making he se ling p ocess mo e di icul . The whi e in-
ishing was gi en wi h he objec i e o e lec ing he sunligh in o de o
a oid an excessi e inc ease o empe a u e wi hin he anks. A pic u e
and scheme o he hickene s is shown in Fig. 1.
The ha es ed biomass was pumped om he lamella se ling ank o
he hickene s h ough a pe is al ic pump (Damo a MP-811.16) wi h a
low a e o 0.4 m
3
/h and a subsequen hyd aulic loading a e o 1.5 m/h.
No e ha in he i s expe imen only one hickene was used, while in
o he s, he wo hickene s we e used connec ed in se ies (see desc ip ion
in Sec ion 2.2). The inle o he hickene s was loca ed 1 cm below he
op o he ank. The inle pipe en e ed he ank and discha ged he
in luen downwa ds h ough an L-shaped bend which was subme ged
10 cm below he ou le o e low le el. As men ioned abo e, in some
expe imen s he pu ge om he i s hickene was discha ged o he
second using a pe is al ic Damo a MP-811.16 pump. The hickened
biomass om he bo om o he second hickene was collec ed by an
iden ical pe is al ic pump which ed he anae obic diges e . The supe -
na an o each hickene o e lowed h ough a pipe loca ed in on o
he inle a he opposi e side o he hickene .
Du ing he expe imen al pe iod, a low eloci y sc ape was ins alled
in he hickene s in o de o a oid o educe mic oalgae a achmen o
he inne walls o he anks, hus inc easing biomass collec ion du ing
he pu ge. The sc ape consis ed o a one-me e long pliable i on ba
wi h a diame e o 5 mm, which was molded in o he shape o he ank.
The sc ape is shown in he scheme in Fig. 1B. The use o malleable i on
made i possible o ob ain he desi ed shape. The small diame e o he
ba was selec ed in o de o occupy a small a ea and educe he in luence
o he sc ape because o u bulence on he se ling and comp ession o
he biomass inside he hickene . The sc ape only wo ked du ing he
ope a ion o he pu ge pump. While wo king, he i on ba sc aped he
in e io wall o he cylind ical and he conical pa s o he ank. The op
o he i on ba was connec ed o a small mo o (0.73 W) loca ed on he
cen e o he lid o he ank, wi h a plas ic co e o p o ec i om ain
e en s. The mo o d o e he ba , o a ing a low speed (10 pm) du ing
he ope a ion o he pu ge pump.
2.2. Expe imen al p ocedu e
Du ing his s udy, an op imiza ion p ocedu e was ca ied ou in
consecu i e pe iods in o de o imp o e he hickening pe o mance.
This was ca ied ou by adding a second hickene connec ed in se ies,
adjus ing he imes and olumes o he pu ges and e alua ing he use o
sc ape s. The hickening p ocess was ope a ed ecei ing he biomass
ha es ed in he lamella se ling ank du ing he whole ope a ion o he
plan (20 mon hs). Howe e , he expe imen s conduc ed o he p esen
s udy las ed 3 mon hs (because once he p ocess was op imized, he
hickening was ope a ed in s eady condi ions). The se ling ank ope -
a ed du ing abou 18 h e e y day, ecei ing he o al daily olume o
mixed liquo collec ed om he PBRs (7 m
3
/d) [15]. The pu ge o
mic oalgal biomass om he se le was pe o med in e mi en ly, nine
pulses pe day. The du a ion o he pulses was adjus ed acco ding o he
amoun o mic oalgal biomass p oduced in he PBRs and he esul s o
ha es ing es s in he se le . This was mainly con olled by he V
30
es
o biomass om he se le (a de ailed desc ip ion o his p ocedu e can
be ound in [15]).
The biomass was di ec ly pumped om he se le o a i s hickene .
In some o he op imiza ion expe imen s he pu ge om he i s
hickene was conduc ed o he second wi h he same low a e and
equency as he pump con eying he ha es ed biomass om he se le
o he i s hickene , bu wi h sho e du a ion. This pu ge om he i s
hickene was ca ied ou jus be o e s a ing he eeding om he
se le , in o de o pe o m he pu ge wi h he maximum possible con-
cen a ion o TS and o educe biomass escape h ough he o e low o
he i s hickene . The hickened biomass was pu ged om he second
hickene once a day, en minu es be o e s a ing he eeding om he
i s hickene , and i was con eyed o he anae obic diges ion uni .
The expe imen s o he p esen s udy we e conduc ed in an in ensi e
op imiza ion campaign in win e -sp ing ( om Feb ua y o Ap il). The
expe imen s we e di ided in o ou di e en pe iods as desc ibed in he
Fig. 1. (A) Pho og aphy o he wo hickene s, (B) scheme o one o he hickene s. (1) Inle ; (2) Subme ged inle pipe; (3) O e low o supe na an ou le ; (4)
Sc ape ; (5) Thickened biomass ou le , (6) Sc ape mo o . All measu es in cen ime e s.
A. O iz e al.
Sepa a ion and Pu i ica ion Technology 281 (2022) 119830
4
ollowings and summa ized in Table 1. Pe iods I and II las ed 1 week
each and Pe iods III and IV las ed 2 weeks each. In ensi e measu emen s
o TS in he pu ge and TSS in he o e low we e pe o med du ing each
pe iod. No e ha he hyd aulic e en ion imes (HRTs) epo ed in
Table 1 e e s o he daily olume o biomass ed o each hickene and
he ime he biomass s ays in o he hickene , including he ime be-
ween eeding e en s.
Pe iod I was designed o assess he pe o mance o a single hickene
equipped wi h a low eloci y sc ape (Fig. 2A). Since he objec i e o a
concen a ion o 20 g/L o TS in he hickened biomass was no achie ed
wi h his con igu a ion, a second hickene was ins alled and connec ed
in se ies wi h he i s one in Pe iod II (Fig. 2B). In his pe iod, he second
hickene had no sc ape . The objec i e o his pe iod was o analyze he
e ec i eness and e iciency o a mul i-s age hickening.
Due o he unsuccess ul esul s wi h such con igu a ion, in Pe iod III
(Fig. 2C) a sc ape was ins alled in he second hickene in o de o
de ach he biomass on he walls and a oid he a holing, imp o ing he
biomass collec ion. In addi ion, he du a ion o he pu ge om he i s
hickene o he second one was inc eased om 1 o 2 min. The objec i e
o his pe iod was o enhance he biomass collec ion in he second
hickene , hus imp o ing he pe o mance o he p e ious pe iods.
Al hough he esul s on Pe iod III imp o ed compa ed o he p e i-
ous pe iods, he 20 g/L a ge was no me and he e o e in Pe iod IV
(Fig. 2C) he ope a ion o he sc ape s was modi ied. In pa icula , he
ope a ing ime o bo h sc ape s was educed in o de o a oid excessi e
solids esuspension. The du a ion o he eeding e en s and pu ges
emained he same as in he p e ious pe iod. Howe e , he sc ape s did
no wo k du ing he i s and he las minu es o pu ge o each hickene ,
i.e. hey s a ed unning om he second minu e o pu ge and s opped
one minu e be o e he end o he pu ge. This way, mixing and esus-
pension o he hickened biomass we e a oided du ing he i s minu e
o he pu ge. Then, he biomass s uck o he hickene s walls was de-
ached hanks o he ac ion o he sc ape . Finally, du ing he las minu e
o he pu ge, he sc ape was s opped le ing he biomass gen ly se le
wi hou mixing. The objec i e o his pe iod was o op imize he ope -
a ional s a egy o he sc ape s aimed a inc easing he concen a ion o
TS in he collec ed biomass.
Du ing he expe imen s, he daily olumes o he in luen biomass
(coming om he lamella se le ) and he pu ge om bo h hickene s
we e moni o ed, oge he wi h he TS concen a ion in he se le pu ge
and in he biomass collec ed om he hickene s. In he o e low, he
To al Suspended Solids (TSS) concen a ion was moni o ed (ins ead o
TS) because he suspended solids concen a ion was much lowe han
he one in he ha es ed and hickened biomass.
The wa e empe a u e was moni o ed in he PBRs, which we e
equipped wi h an au oma ic empe a u e senso (Campbell Scien i ic
Inc., USA). Da a o hese pa ame e s we e aken e e y 5 s and eco ded
and s o ed each 60 s in a da alogge (Campbell Scien i ic Inc., USA). In
his s udy, he a e age daily empe a u e o he wa e was ob ained om
hese da a.
2.3. Analy ical me hods
2.3.1. Pu ge analysis
Since he beginning o he campaign (Feb ua y 21 h) un il Ap il
17 h, he concen a ion o o al solids o he pu ge we e measu ed in
o de o analyze and o imp o e he pe o mance o he hickene s.
Samples we e aken h ee imes pe week om hickene 1 in Pe iod I
(Q
u1
), and om hickene s 1 and 2 in Pe iods II, III and IV (Q
u1
and Q
u2
).
Mo eo e , in each pe iod, samples we e also aken om he pu ge o he
lamella se le (Q
i
).
In addi ion, in o de o be e analyze and unde s and he pe o -
mance o he hickene s, 50 mL samples o he pu ge o bo h hickene s
we e collec ed se e al imes a sho ime in e als o isual obse a-
ion. These samples we e aken om one pulse o he pu ges, e e y 15 s
om hickene 1 and e e y 30 s om he se le and hickene 2. These
sampling equencies we e se acco ding o he du a ion o he pulses.
Each sample was collec ed in a 50 mL lask and all o hem we e le o
se le o 10 min. Then, hey we e quali a i e analyzed o check a which
ime o he pulse he pu ge had no solids (Figs. 5, 7 and 9). Mo eo e , he
concen a ion o TS om he mix o all samples collec ed in each pulse
was measu ed by d ying a 103–105 ◦C acco ding o S anda d Me hod
2540B [25].
2.3.2. Supe na an analysis
The TSS concen a ion in he o e low was measu ed, excep in
Pe iod I due o he lack o an o e low collec ion equipmen . Daily
o e low o he wo hickene s (Q
o1
and Q
o2
) we e collec ed wice a
week in wo anks (OT-1 and OT-2 in Fig. 2), one o each hickene , and
subsequen ly analyzed. The TSS we e measu ed by means o acuum
il a ion o 100 mL o sample and d ying a 103–105 ◦C, acco ding o
S anda d Me hod 2549C [25].
2.4. Thickening pe o mance indica o s and calcula ions
Th ee pa ame e s we e used o es ima e he pe o mance o he solid-
liquid sepa a ion p ocess in he hickene s: he eco e y e iciency (RE),
he concen a ion ac o (CF), and he loss o biomass in he supe na an
(L).
The RE is de ined as he mass o solids eco e ed in he sepa a ion
p ocess ou o he o al in luen mass o solids (Eq. (1)). The CF is he
a io be ween he concen a ion o solids in he eco e ed sludge and he
concen a ion o solids in he in luen s eam (Eq. (2)) [26,9]. Sepa a ion
p ocesses wi h high RE and CF cap u e mos o he biomass wi h a good
concen a ion, and he e o e he TSS concen a ion in he o e low is
low.
Reco e y e iciency (RE,%) = 100⋅ Mass o solids eco e ed
To al in luen mass o solids (1)
Concen a ion ac o (CF,dimensionless)
=Concen a ion o solids eco e ed
Concen a ion o solids in in luen (2)
The L is de ined as he mass o solids escaping h ough he o e low ou
o he o al biomass ed o he hickene (Eq. (3)). A high L is an indica o
o he occu ence o some p oblems in he sepa a ion p ocess en ailing
excessi e escape o suspended solids in he o e low.
Biomass loss(L,%) = 100⋅ Mass o solids in he o e low
To al in luen mass o solids (3)
Acco ding o he schemes in Fig. 2, and conside ing a cons an olume,
he low balance in he i s and second hickene s esul s in equa ions
(4) and (5), espec i ely.
Qi=Qu1 +Qo1 (4)
Qu1 =Qu2 +Qo2 (5)
Table 1
Ope a ional condi ions o he hickene s du ing he ou pe iods o he s udy.*
educed ope a ing ime o he sc ape s.
Pe iod I II III IV
Du a ion (days) 7 7 14 14
Numbe o hickene s 1 2 2 2
Sc ape hickene 1 Yes Yes Yes Yes*
Sc ape hickene 2 – No Yes Yes*
Feeding o hickene 1, Q
i
(min, 9 pulses pe day) 3 3 4 4
Daily olume ed o hickene 1, Q
i
(L/d) 180 180 238 238
Feeding o hickene 2, Q
u1
(min, 9 pulses pe day) – 1 2 2
Daily olume ed o hickene 2, Q
u1
(L/d) – 59 119 119
Pu ge du a ion, Q
u2
(min, once a day) 4 4 4 4
Daily olume pu ged, Q
u2
(L) 26 26 26 26
HRT hickene 1 (h) 26.7 26.7 20.2 20.2
HRT hickene 2 (h) – 80 40.4 40.4
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5
The e o e, he pa ame e s RE, CF and L o he i s hickene can be
de e mined as shown in equa ions (6), (7) and (8).
RE1=100⋅Qu1⋅Cu1
Qi⋅Ci
(6)
CF1=Cu1
Ci
(7)
L1=100⋅Qo1⋅Co1
Qi⋅Ci
=100⋅(Qi−Qu1)⋅Co1
Qi⋅Ci
(8)
Simila ly, and acco ding o he scheme shown in Fig. 2B, he pa ame e s
RE, CF and L o he second hickene can be de e mined acco ding o
equa ions (9), (10) and (11).
RE2=100⋅Qu2⋅Cu2
Q1⋅C1
(9)
CF2=Cu2
C1
(10)
L2=100⋅Qo2⋅Co2
Q1⋅C1
=100⋅(Qu1 −Qu2)⋅Co2
Qu1⋅Cu1
(11)
Finally, he o e all RE and CF including bo h hickene s a e hose ob-
ained acco ding o equa ions (12) and (13), espec i ely.
RE =100⋅Qu2⋅Cu2
Qi⋅Ci
(12)
CF =Cu2
Ci
(13)
2.5. S a is ical analysis
Expe imen al da a ega ding he o e all CF, RE and hickened TS
concen a ion o each pe iod, we e s a is ically assessed ia mul i ac o
analysis o a iance (ANOVA) in o de o de e mine he signi icance o
he di e ences. The Tukey es (
α
=0.05) was used as a pos hoc es .
3. Resul s and discussion
3.1. Concen a ion o biomass and pe o mance o he hickene s
The amoun o mic oalgal biomass p oduced in he PBRs a ied
du ing he whole expe imen , since i was a ec ed by he ou doo
en i onmen al condi ions and he ope a ion o he PBRs. Howe e , he
Fig. 2. Scheme o ope a ion o he hickening sys em du ing Pe iods I (A), II (B), III and IV (C). Lamella se ling ank (LS); hickene 1 (TK-1); hickene 2 (TK-2);
o e low ank 1 (OT-1); o e low ank 2 (OT-2); sc ape o hickene 1 (ST-1); sc ape o hickene 2 (ST-2); pe is al ic pumps (P-1, P-2 and P-3). S eams (g een
colo ): pu ge o se ling ank (Q
i
), pu ge o hickene -1 (Q
u1
), o e low o hickene -1 (Q
o1
), pu ge o hickene -2 (Q
u2
) and o e low o hickene -2 (Q
o2
). In Pe iod I,
samples o he o e low (Q
o1
) we e no a ailable due o he lack o collec ion equipmen o he o e low. The Q alues a e exp essed in L/d. (Fo in e p e a ion o he
e e ences o colo in his igu e legend, he eade is e e ed o he web e sion o his a icle.)
A. O iz e al.

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6
concen a ion in he se ling ank pu ge was ela i ely cons an (Fig. 3).
The concen a ion o TS in he biomass in each ha es ing s ep is
p esen ed in Fig. 4. In Pe iod I, he TS concen a ion in he biomass
ha es ed om he se le (i.e. he in luen o he hickene ) anged
be ween 2.4 g/L and 4.9 g/L, while he TS o he biomass collec ed om
he hickene anged om 5.3 g/L o 7.6 g/L (Fig. 4A). This inc ease
en ails an o e all CF o 1.9 ±0.5 and RE o 28 ±8% as indica o s o he
hickening capaci y o one single ank. In spi e o he inc ease in he
concen a ion o TS, he inal concen a ion achie ed du ing his pe iod
was s ill lowe han he a ge ed objec i e (20 g/L). This a he low
concen a ion was mainly a ibu ed o an inadequa e ope a ion o he
sc ape , which could esuspend he solids du ing i s ope a ion. In
addi ion, i was obse ed ha he u bulence gene a ed by he en ance
o he in luen s eam was likely o ha e a nega i e e ec in he se ling
p ocess inside he hickene .
The e o e, a second hickening s age was added, in o de o eed i
wi h a lowe olume o biomass, bu mo e concen a ed. This way, i was
expec ed ha a g ea e amoun o biomass could each he bo om o he
second hickene , which would a o he comp ession p ocess, and
he e o e, a g ea e concen a ion o he biomass in he unde low
e luen .
In Pe iod II, he a e age TS concen a ion om he se le was
sligh ly highe han he one in he p e ious pe iod (4.3 ±1 g/L).
Howe e , he concen a ion o TS ob ained in bo h hickene s was s ill
poo (Fig. 4B). Unexpec edly, in one o he sampling days (Day 2) he TS
concen a ion in he hickene s was e en lowe han in he se ling ank.
The ins alla ion o he second hickene did no esul ed in a signi ican
inc ease o he a e age TS concen a ion (6.2 ±5.2 g/L in he i s
hickene and 5.9 ±3.6 g/L in he second one). The o e all CF and RE
we e 1.5 ±1.1 and 53 ±51%, espec i ely. These esul s show a high
a iabili y and a low pe o mance o he hickene s.
In o de o iden i y he causes o his beha io , samples o he pu ge
o he hickene s we e collec ed a egula ime in e als o isual
obse a ion, as desc ibed in sec ion 2.3.1. Fig. 5 shows pic u es o he
samples collec ed on Day 2, which was he day showing he wo s pe -
o mance. I can be obse ed ha in he i s hickene (Fig. 5A) a sig-
ni ican amoun o mic oalgal biomass was collec ed du ing he i s 30 s
o pu ge ( i s 2 samples), while du ing he emaining 30 s he amoun o
biomass was negligible. This ope a ion was epea ed o all he 9 pu ges
o he day, showing a simila beha io in e e y pu ge e en . Rega ding
he pu ge o he second hickene (Fig. 5B), a high amoun o biomass
was only obse ed du ing he i s 30 s o he pu ge, while i was
negligible du ing he emaining 3 min and 30 s. Tha was a ibu ed o
a holing: mos o he biomass was s uck o he hoppe wall and almos
clean o cla i ied wa e was pu ged om he hickene .
I should be highligh ed ha , in his expe imen al pe iod he i s
hickene was wo king wi h 9 pu ge e en s pe day and wi h a sc ape ,
which acili a ed he collec ion o he biomass du ing he pu ge, by
sc aping he inne wall o he ank and de aching he s uck biomass. On
he con a y, he second hickene was wo king wi hou sc ape and
wi h only 1 pu ge e en pe day. This is a highly p obable eason o he
low pe o mances achie ed in hickene 2.
In Pe iod III, he TS concen a ion in he pu ge om he se ling ank
was simila o he one in Pe iod II. The concen a ion achie ed in bo h
hickene s was clea ly highe han he in luen one (Fig. 4C). Mo eo e ,
as expec ed, he concen a ion achie ed in he second hickene was
highe han ha in he i s one, excep he las sampling day (Day 6), in
which a high TS concen a ion (17.3 g/L) was eached in he i s
hickene . Fig. 4C shows ha he TS concen a ion ob ained in he sec-
ond hickene ollowed a simila end o he in luen biomass concen-
a ion om he se ling ank, sugges ing ha he ope a ion o he
hickene s emained mo e s able and s eady compa ed o he p e ious
pe iods.
The concen a ion achie ed in he second hickene was always
highe han 10 g/L, wi h an a e age o 12 ±1.5 g/L (no e he ela i ely
small s anda d de ia ion). E en ually, a maximum o 13.8 g/L was
eached in Day 6. This is a sui able solids concen a ion o he subse-
quen anae obic diges ion p ocess, bu s ill lowe han he ini ial
objec i e o 20 g/L. A u he inc ease o he biomass concen a ion
would educe he amoun o wa e o be pumped and p ocessed in he
downs eam p ocesses.
The CF in bo h hickene s du ing his pe iod is shown in Fig. 6. All
he alues a e highe han 1, indica ing a success ul and s able hick-
ening, excep he las sampling day, in which CF2 was 0.8. This indica es
ha TS concen a ion dec eased in he second hickene compa ed o he
i s one, which was a ibu ed o he abo e-men ioned high TS con-
cen a ion eached in he i s hickene . The o e all CF was 3.0 ±0.7,
2.1 ±0.9 in he i s hickene and 1.6 ±0.5 in he second one. I means
ha he second hickene con ibu ed o he comp ession o he biomass,
inc easing he TS concen a ion o he hickened mic oalgal biomass by
a ac o o 1.6.
Visual obse a ion o samples o he pu ge was ca ied ou also in his
pe iod, in o de o be e analyze he imp o emen in he pe o mance o
he hickene s compa ed o he p e ious pe iods. Pic u es o he samples
collec ed in Day 6 om he i s hickene a e shown in Fig. 7. I can be
obse ed ha he biomass was success ully collec ed om bo h hick-
ene s du ing he pu ge. The concen a ion o mic oalgae was quali a-
i ely high du ing he whole pu ge in bo h hickene s. The clea
imp o emen in he mic oalgal biomass collec ion om he second
hickene was a ibu ed o he u iliza ion o he sc ape , which acili-
a ed he collec ion o biomass by sc aping he wall whe e biomass could
emain s uck and a oiding he a holing du ing he pu ge. Howe e , he
mic oalgae biomass concen a ion inside he hickene seemed o be (by
isual obse a ion) highe ha he concen a ion in he pu ge. Tha
obse a ion sugges ed ha he ope a ion o he sc ape acili a ed he
collec ion o biomass, bu a he same ime, i could esuspend some
biomass, educing he concen a ion o TS in he pu ge compa ed o he
one inside he hickene . Thus, he ope a ional s a egy o he sc ape s
could be imp o ed, as i was p oposed and es ed in he nex expe i-
men al pe iod.
In Pe iod IV, he ope a ing ime o he sc ape s was educed, and he
TS concen a ion inc eased in bo h hickene s (Fig. 4D). I should be
highligh ed ha he inc ease o he concen a ion o he hickened
biomass came along wi h an inc ease o he in luen TS concen a ion
du ing his pe iod. Indeed, he in luen concen a ion sligh ly inc eased,
wi h an a e age o 7.4 g/L, which was due o a highe p oduc ion o
biomass in he PBRs oge he wi h a s able and success ul ope a ion o
he lamella se le [15]. Ne e heless, he inc ease o TS concen a ion
in he hickene s was no iceable, achie ing an a e age alue o 10.5 g/L
in he i s hickene and 22.1 g/L in he second one. This inal alue
success ully ul illed he desi ed concen a ion o eeding he subse-
quen anae obic diges ion p ocess.
The inc ease o biomass concen a ion achie ed in bo h hickene s,
quan i ied by he CF, is p esen ed in Fig. 8. The CF emained s able o e
1 in bo h cases, apa om he wo las alues o CF1, which we e close
Fig. 3. E olu ion o he concen a ion o TS in he pu ge o he se ling ank
and he hickening p ocess du ing he ou expe imen al pe iods (no e ha
hickened biomass co esponds o he pu ge om hickene 1 in Pe iod I and o
he pu ge o hickene 2 in he o he pe iods).
A. O iz e al.
Sepa a ion and Pu i ica ion Technology 281 (2022) 119830
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o 1. In a e age, an inc ease by a ac o o 1.5 was ob ained in he i s
hickene , while i eached 2.3 in he second one. The o e all CF eached
an a e age alue o 3.6, no ably highe han hose ob ained in he
p e ious pe iods, in pa icula , almos 1 poin highe han he one in
Pe iod III.
Pic u es o he samples collec ed on Day 4 a e shown in Fig. 9.
Samples aken du ing a pu ge o he i s hickene a e shown in Fig. 9A,
while samples aken du ing he pu ge o he second hickene a e shown
in Fig. 9B. The pic u es con i m he success ul collec ion o biomass
du ing he pu ge in bo h hickene s and, pa icula ly, i was no iceable
by isual obse a ion he high concen a ion o hickened biomass om
he second hickene .
In Pe iod IV, he o e all daily olume o mic oalgal biomass ed om
he se le and he daily olume o hickened biomass collec ed in he
second hickene we e kep cons an compa ed o he p e ious pe iod.
The e o e, he su ace loading a e and HRT emained he same.
Ne e heless, bo h he hickened TS concen a ion and he CF imp o ed
in his pe iod. The inc ease o he hickened TS concen a ion could be
a ibu ed o: (i) he highe TS in luen concen a ion du ing his pe iod,
and (ii) a be e pe o mance o he hickene s. The imp o emen o he
pe o mance o he hickene s was con i med by he be e CF, and, o
he au ho s knowledge, his was no due o he inc ease in he in luen
TS load, bu a he o an imp o emen o he hickening p ocess.
The e o e, he esul s imply ha he op imiza ion o he sc ape s’
ope a ional s a egy had a posi i e e ec in he hickening p ocess. As
addi ional in o ma ion, he wa e empe a u e inc eased om he
beginning (Feb ua y) un il he end (Ap il) o he s udy abou 10 ◦C.
Wa e empe a u e was no con olled, since he expe imen al sys em
was an ou doo pilo plan a demons a i e scale, and he e ec o
empe a u e was no speci ically s udied. The empe a u e inc ease
could ha e a bene icial e ec in he se ling beha io , bu i was no
expec ed o a ec he hickening pe o mance o a g ea ex en . All in all,
i is conside ed ha he esul ing TS concen a ion has been boos ed by
bo h he highe in luen concen a ion and he op imiza ion o he
Fig. 4. TS concen a ion in he se le and hickene s pu ges in he ou expe imen al Pe iods.
Fig. 5. Samples collec ed in Pe iod II, Day 2. (A) Pu ge samples o one pulse in i s hickene , aken e e y 15 s o a minu e o pulse; (B) Pu ge samples o one pulse
in second hickene , aken e e y 30 s o ou minu es o pu ge. The samples we e a anged in ch onological o de .
Fig. 6. Concen a ion Fac o (CF) in he i s and second hickene s and o e all
CF du ing Pe iod III.
A. O iz e al.
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ope a ional s a egy. I is supposed ha he educ ion o he ope a ing
ime o he sc ape s allowed he hickened biomass o be collec ed a a
highe concen a ion. A he beginning o he pu ge, du ing he i s
minu e, he sc ape was s opped, a oiding mixing and esuspension o
he biomass. I was obse ed ha he biomass s o ed in he hoppe o he
hickene was no dis u bed and he i s laye s o hickened biomass
we e sa is ac o ily collec ed a a high concen a ion ( he olume pu ged
in 1 min co esponds o abou 30% o he olume o he hoppe ). Then,
he sc ape wo ked o 1 min in he i s hickene and 1 min in he
second one, de aching he biomass a ached o he inne walls o he
hickene s, which o he wise would be e ained inside he hickene s and
no collec ed du ing he pu ge, as was obse ed in Pe iod II. The sc ape
was u ned o one minu e be o e he end o he pu ge, in o de o educe
he mixing and esuspension caused by he ac ion o he sc ape ,
allowing he biomass o se le down and be collec ed by he pu ge om
he bo om o he ank.
3.2. Loss o biomass in he o e lows
In Pe iod I, he low balance esul ed in an o e low o 154 L/d.
Un o una ely, he concen a ion o TSS in he o e low in his pe iod
was no measu ed, he e o e, he biomass loss L h ough he o e low
was no a ailable.
In Pe iod II, acco ding o he low a es, he balance esul ed in an
o e low o 121 L/d in he i s hickene and 31 L/d in he second one.
The concen a ion o TSS in he supe na an o bo h hickene s
(Fig. 10A) was low in all he samples (25 mg/L o lowe ), excep he one
on Day 3 in he i s hickene , which eached 116 mg/L. This peak
co esponds o he lowes TS concen a ion in he pu ge o he i s
hickene (3.9 g/L, Fig. 4B), which sugges s ha he ope a ion o he
hickene su e ed mal unc ion ha day. Apa om ha day, wa e
cla i ica ion pe o med sa is ac o ily in bo h hickene s.
The o e all L was 0.8 ±1% in he i s hickene and 0.2 ±0.1% in
he second one which can be conside ed a e y small biomass loss.
In Pe iod III, he daily olume o o e low om he i s hickene
was 120 L/d, while om he second hickene i was 92 L/d. The con-
cen a ion o TSS in he o e low o bo h hickene s was measu ed wice
in his pe iod as shown in Fig. 10B. The concen a ion was low in all he
samples (80 mg/L o lowe ), gi ing a loss o biomass L1 and L2 o 0.4 ±
0.6 and 0.2 ±0.1%, espec i ely.
In Pe iod IV he o e low a es we e he same as in he p e ious
pe iod. The TSS concen a ion in he o e low o bo h hickene s was
analyzed h ee imes in his pe iod (Fig. 10C). The concen a ion o TSS
anged be ween 34 mg/L and 219 mg/L in he o e low o he i s
hickene and be ween 9 mg/L and 103 mg/L in he second one. Those
alues we e highe han in p e ious pe iods, which was a ibu ed o he
highe amoun and concen a ion o biomass in he whole sys em. In
spi e o hose highe alues, he o e all loss o biomass h ough he
o e low was s ill low, less han 1% o he in luen biomass in bo h
hickene s (L1 0.8 ±0.3% and L2 0.4 ±0.3%).
3.3. O e all discussion and p ac ical conside a ions
The p og essi e imp o emen achie ed along he s udy h ough he
di e en pe iods is e iden . The di icul ies o hickening mic oalgal
biomass in g a i y hickene s a demons a i e scale o ced he au ho s
o explo e di e en con igu a ions o he sys em and ope a ional s a-
egies in o de o op imize he pe o mance and make i easible o
collec he biomass wi h an adequa e TS concen a ion. The e olu ion o
he a e age TS concen a ion o he hickened biomass achie ed in he
consecu i e expe imen al pe iods o he s udy a e summa ized in
Fig. 11A. In Pe iod I, wi h a single hickene , he concen a ion o he
hickened biomass was a om he objec i e o 20 mg/L. The ins al-
la ion o wo hickene s in se ies in Pe iod II did no allow o achie e a
be e pe o mance han using only one hickene . A TS concen a ion o
5.8 ±3.6 g/L was ob ained wi h he second hickene compa ed o 6.3
±1.1 g/L du ing Pe iod I. Indeed, he e was no signi ican di e ence
be ween bo h pe iods. The e o e, he second hickene , wi hou sc ape ,
did no b ing an imp o emen o he o e all pe o mance. I was
Fig. 7. Samples collec ed in Pe iod III, Day 6. (A) Pu ge samples o one pulse in i s hickene , aken e e y 15 s o wo minu es o pu ge; (B) Pu ge samples o one
pulse in second hickene , aken e e y 30 s o ou minu es o pu ge. The samples we e a anged in ch onological o de .
Fig. 8. CF in he i s (CF1) and second (CF2) hickene s and o e all CF du ing
Pe iod IV.
Fig. 9. (A) Pu ge samples o one pulse in i s hickene , aken e e y 15 s o wo minu es o pu ge; (B) Pu ge samples o one pulse in second hickene , aken e e y
30 s o ou minu es o pu ge, in Pe iod IV, Day 4. The samples we e a anged in ch onological o de .
A. O iz e al.
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obse ed ha he collec ion o biomass did no pe o med sa is ac o ily,
and he ins alla ion o a sc ape was p oposed o o e come his issue.
Thus, in Pe iod III, wi h he sc ape , he pe o mance o he sys em
imp o ed, inc easing he TS concen a ion o he hickened biomass.
Despi e he s a is ical analysis does no epo signi ican di e ences
be ween his pe iod and he p e ious ones, he inc ease in TS
concen a ion seems e iden , doubling he concen a ion achie ed in
Pe iods I and II. The absence o signi ican di e ences was a ibu ed o
he high a iabili y o he esul s, which is usual in ou doo sys ems a
demons a i e scale. Ne e heless, he objec i e o 20 g/L o biomass
concen a ion was s ill no achie ed. The ope a ion o he sc ape s,
which wo ked simul aneously o he pu ge pumps and du ing he whole
pu ge e en s, was hen modi ied in he las pe iod, aimed a inc easing
he hickened biomass concen a ion. The p oposed goal o 20 g/L o TS
was achie ed du ing Pe iod IV in 70% o he sampling days h ough he
educ ion o he ope a ional ime o he sc ape s. Such modi ica ion
allowed he eco e y o he biomass a ached o he inne walls o he
hickene s, minimizing he esuspension o he biomass and achie ing a
maximum alue o 26.5 g/L o TS. The TS concen a ion du ing his
pe iod was signi ican ly highe han hose ob ained in he h ee p e ious
pe iods. Summa izing, he mul i-s age app oach in combina ion wi h
he use o sc ape s esul ed clea ly bene icial o achie e a success ul
pe o mance o he g a i y hickening.
These esul s a e con i med by he o e all CF and RE o he ou
pe iods, which a e summa ized in Fig. 11B. The o e all CF eached an
a e age alue o 3.6 in Pe iod IV, highe han hose ob ained in he
p e ious pe iods. I means ha he ope a ion o he hickene s educed
he olume o he biomass ha es ed in he se le by a ac o o 3.6,
he e o e educing he size, powe equi emen s and ope a ional cos s o
he subsequen downs eam p ocesses. In his case, no signi ican di -
e ences we e obse ed be ween he o e all CF o he di e en pe iods,
which was a ibu ed o he high a iabili y o he esul s. Howe e , as i
can be obse ed in Fig. 11B, he CF inc easing end in pe iods III and IV
is no iceable. On he o he hand, he o e all RE eached an a e age o
40% in Pe iod IV also highe han hose ob ained in he p e ious pe-
iods, bu a om a comple e eco e y o 100%. Again, he e we e no
signi ican di e ences in he o e all RE, bu he RE inc easing end in
Pe iods III and IV was clea and simila o he CF end (Fig. 11B). The
low RE alue con as s wi h he o e all loss o biomass h ough he
o e low, which was less han 1% o he in luen biomass in bo h
hickene s. This was a ibu ed o he diges e eeding a e du ing his
s udy (26.4 L/d), which was oo low o eco e all he biomass
Fig. 10. Concen a ion o TSS in he o e lows o he wo hickene s in he expe imen al Pe iods II, III and IV.
Fig. 11. (A) Concen a ion o TS in he hickened biomass achie ed in he ou
pe iods; (B) O e all Concen a ion Fac o and Reco e y E iciency achie ed in
each pe iod.
a,b
Le e s indica e a signi ican di e ence (
α
=0.05) be ween he
concen a ions and CF and RE alues o he di e en pe iods a e Tukey es .
A. O iz e al.