ISSN 0104-6632 Printed in Brazil
www.abeq.org.br/bjche
Vol. 33, No. 04, pp. 773 - 781, October - December, 2016 dx.doi.org/10.1590/0104-6632.20160334s20150016
*To whom correspondence should be addressed
Brazilian Journal
of Chemical
Engineering
SIMULATION OF MICROALGAL GROWTH IN A
CONTINUOUS PHOTOBIOREACTOR WITH
SEDIMENTATION AND PARTIAL BIOMASS
RECYCLING
C. E. de Farias Silva
*, B. Gris and A. Bertucco
Department of Industrial Engineering, University of Padova, via Marzolo 9, 35131, Padova, Italy. E-mail: [email protected]
(Submitted: January 12, 2015 ; Revised: June 7, 2015 ; Accepted: June 24, 2015)
Abstract - Microalgae are considered as promising feedstocks for the third generation of biofuels. They are autotrophic organisms with high growth rate and can stock an enormous quantity of lipids (about 20 – 40% of their dried cellular weight). This work was aimed at studying the cultivation of Scenedesmus obliquus in a two-stage system composed of a photobioreactor and a settler to concentrate and partially recycle the biomass as a way to enhance the microalgae cellular productivity. It was attempted to specify by simulation and experimental data a relationship between the recycling rate, kinetic parameters of microalgal growth and photobioreactor operating conditions. Scenedesmus obliquus cells were cultivated in a lab-scale flat-plate reactor, homogenized by aeration, and running in continuous flow with a residence time of 1.66 day. Experimental data for the microalgal growth were used in a semi-empirical simulation model. The best results were obtained for Fw=0.2FI, when R = 1 and kd = 0 and 0.05 day-1, with the biomass production in the
reactor varying between 8 g L -1 and 14 g L-1, respectively. The mathematical model fitted to the microalgal growth experimental data was appropriate for predicting the efficiency of the reactor in producing Scenedesmus obliquus cells, establishing a relation between cellular productivity and the minimum recycling rate that must be used in the system.
Keywords: Continuous photobioreactor; Scenedesmus obliquus; Recovering; Sedimentation; Recycling rate; Downstream.
INTRODUCTION
Microalgae have gained much attention for bio-fuel production due to their high capability of storing value-added energy compounds. The chemical com-position of such compounds encompasses starches and highly saturated fatty acids convertible to neutral lipids, which play an important role in production of bioethanol and biodiesel. This feature, along with high growth rates and ease of cultivation, make mi-croalgae very promising when compared to higher plants (Rawat et al., 2013; Khan; Bahadar, 2013; Silva and Bertucco, 2016).
Scenedesmus obliquus is a microalga that has been widely studied because of its high cellular productivity and accumulation of value-added en-ergy compounds. Several works relying on its culti-vation have investigated a variety of aspects, includ-ing types of culture medium and substrate, which have been tested in bench or continuous systems, also employing different intensities of light. How-ever, studies on the efficiency of biomass recycling coupled to the photobioreactor either through simula-tion or experimental data are still required (Vigeolas
K o th fr w co u u (M ti u co o co it p th co sh ce th b m p m g w w d p co E 1 ce al in o m p ex at th g d S
Kim et al., 20 f the cellula he steps subs rom the upst way that the
onsolidated. Sedimenta ltra-filtration sed unit ope Mata et al., 2 icularly has m nit operation ontrolled pro f separating ost, mainly w t is a time-co robability of he process (R
Partial ma osts associat horten the p ellular conc he recycling r
y considerin microalgal cu roduction sy
In this wor model micro
rowth in a tw with partial b was to develo
icting the re arameters of onditions of
MA
Experimenta
S. obliquu
1 medium (R entration and lgae cultures ng agar (10 g
f S. obliquu
mately 100 hase. The s xcess condit t 8 with 10 he culture m
rowth was m ensity meas pectro, Spect
014). In orde ar production sequent to th tream to dow whole proc ation, centrif n, floculation erations for 2010). Grav many advant ns, for instan ocess, margi g supernatant when pumpi onsuming op f biomass det Rawat et al., ass recycling
ted with the production tim
entration in rate must be ng operating ulture, integ ystems.
rk, Scenedes
organism fo wo-stage pho biomass recy op a mathema ecycling rat f the microa
the bioreacto
ATERIALS A
al Part
us cultivation Rippka et al
d unlimitated were sustain g L-1) to the B
us were culti E m-2 s-1 an simplified pl tions (5% in mM HEPES medium fro monitored eac
surements at tronic Unicam
er to study th n process, a he reactor is wnstream sec
cess can be
fugation, con n and flotatio cellular bio itational sed tages in comp nce, low cost
in for scalin t with minim ng is involv peration that terioration o
2013). g could be e inoculum p
me, as well the reactor carefully tak g kinetic par rating both smus obliquu or investigat otobioreacto ycling. The atical model te as a func algal growth or.
AND METH
n was perform
l., 1979) wit d nutrients (Fi ned in solid m BG-11 mediu ivated in fla nd held in t lant was fed
air), while m S buffer in o
m acidifyin ch 24 h by m t = 750 n
m), cell coun
he sustainabi full analysis necessary, i ctions, in suc optimized a
nventional- a on are the m omass recov imentation p parison to ot for achievin ng-up, and e mum operat ed. Converse t gives rise t
ccurring dur
used to redu preparation a as obtain h r. Neverthele ken into acco
rameters of separation a
us was used a ting microal r-settler syst main object capable of p ction of kine h and operat
HODS
med using B th doubled c
igure 1). Mic medium by a um. Pre-inoc asks at appro the exponen d with CO2
maintaining order to prev ng. S. obliqu
means of opti nm (UV-visi nting in a Bur
lity s of i.e., ch a and and most very par-ther ng a ease ting ely, to a ring uce and high ess, ount the and as a lgal tem tive pre-etic ting BG- con- cro- add-cula oxi-ntial
2 in
pH vent uus ical ible rker cou we act Th So eff con HD bet use is are Fig ob Fi Ta bio unting cham eight determi The inoculu tor tank had he reactor wa ource SL 350 fective light ntinuous and D2102.1 radi
tween the re ed in the exp depicted in F e summarize
gure 1: Opti
bliquus (magn
igure 2: Sche
able 1: Vari oreactor.
Variables
θ (day) - Resid I (µE m-2 s-1)
-I
F (m3 day-1) – Culture Medium
Fg (m3 day-1)
2 CO
g
C (%) – Co CO2-air) T - Reactor Tem
mber (HGB® inations (Sfo um cellular c an optical de as illuminate 00, Photon Sy
t intensity d bench ope iometer posi eactor and la periments ha Figure 2. Th d in Table 1.
ical microsco nification of
ematic of the
ables of ma
dence Time Rea Lighting – Volumetric fl m
– Gas volume f oncentration of
mperature (°C)
®, Germany orza et al., 20 concentration
ensity of 0.5 ed with a LE System Instru
was measu erations with itioned at sam
amp. The ph ad a flat-plate he experimen
.
opic image o f 100x).
e flat-plate ph
aintenance
actor
low rate of
flow f CO2 (Mixed-
)
y), and drie 012). n within the r
at = 750 nm D lamp (Lig uments) who ured for bo h a DeltaOh me distance hotobioreact e layout whic ntal paramete
f Scenedesm
hotobioreacto
of the phot
to-st C si fo su g d tr le u S m S p st (S F v th an w to (C m Δ w tw ta is n eq S The nitrate trate) was d Carlo Erba R
ists of an ini orms a diazo ubsequent re entisic acid iazo dye. Th rophotometri ength of = sing differen
Simulation M
A photobio mass recyclin
S. obliquus cu icted in Fig tate were s Sundstrom an
Figure 3: Sch ation proces
It was ass here were no
nd that biom was approxim or was mode CSTR) by S mass balance
ΔC r
θ =
where ΔC is ween the ent ank (ΔC = C
s the rate of enti.
The net bi qual to the g
imulation of Mic
Brazilian
e concentrat determined Reagenti. The
tial reduction o after react eaction betw (2,5-dihydr he absorbanc ically measu 445 nm. The nt NaNO3 sol Model
oreactor cou ng was consi ultivation in gure 3. Oper simulated ac nd Klei, 1979
hematic of c s.
sumed that o product and mass exiting f mately zero. T
eled as a con Sforza et al
takes the ge
the differenc trance (Cin) a
Cout – Cin), θ f production
iomass produ growth rate
croalgal Growth in
Journal of Chem
ion (used as using a Kit e colorimetri
n of nitrate t ing with sul ween the diaz roxybenzoic ce of the sam ured at the
e analytical c lutions.
upled to a set idered for th a continuous rating condit
ccording to 9) with some
ontinuous S.
I I
Cx =Cp =
d biomass as from the sed The flat-plate ntinuous stirr
. (2013). Fo neral form:
ce in concen and exit (Cou
is the reside or consump
uction rate is (rx), given b
n a Continuous P
mical Engineering
s reference su t Idrimetre ic reaction c to nitrite, wh lfuric acid. T zonium salt a acid) forms mples was sp
selected wa curve was ma
tler with par he simulation s system, as tions at stea the literat e modification
obliquus cu
0
S
Cx
= = , i
process inpu dimentator’s
e photobiore red tank reac or a CSTR
ntration (C)
t) of the reac
nce time, an tion of comp
s assumed to by the Mono
Photobioreactor w
g Vol. 33, No. 04,
ub-St. on-hich The and s a pec- ave-ade rtial n of de- ady-ture ns. ulti-i.e., uts, top eac-ctor the (1) be-ctor nd r
mpo-o be od’s equ lin (B rel tio , x r x r , x r wh str rat wh sub yie (Y x Y gro giv s r tw rat R (θ rea fro Th ran tim me in c θ with Sedimentatio
, pp. 773 - 781,
uation, minu nearly propo orzani, 200 lationships b ons (2), (3) an
,t =rx–rx d,
x s
M s
k C C
K C
⋅ ⋅
+ =
,d =kd C⋅ x
here KM is th
rate S (g L-1 te (day-1), kd
hereas Cs an
bstrate and eld coefficien
/ ) x s
Y is define
/ x x s s C C Δ = = −Δ A relationsh owth rate an ven by Equat
/ 1 x s k Y K =− ⋅⎛⎜ ⎝ The recyclin ween the recy
te (FI), whic
R
I
F F
=
The solid r )
c
θ is a relatio actor tank an om the system he SRT is co
nts high proc me for the
etabolize the the reactor. U r x R w x V C F C ⋅ = ⋅
n and Partial Bio
October - Decem
us the cellula ortional to t 1). Hence, i etween the v nd (4):
he Monod sa ), k is the m is the specif nd Cx repres
biomass, re nt for substr ed by Equatio
,
, ,
(
x out
s in s o
C
C C
=
−
hip can be fo nd the subst
tion (6): . x. s
M s
k C C
K C
⎞ ⎟
+ ⎠
ng rate ( )R
cling flow ra ch is given b
retention tim on between t nd the biomas
m (Equation onsidered to cess efficien process so most part of
omass Recycling
mber, 2016
ar death rate the cellular
it is possibl variables and
aturation con maximum sp fic rate of cel sent the con espectively. rate-to-bioma on (5): ) out ound betwee trate consum
is defined as ate
( )
FR and by Equation (me (SRT) or the biomass
ss quantity th (8)) (Von Sp be adequate ncy, i.e., ther that microo f the raw-ma
7
(rx,d), which
concentratio le to establi d obtain Equ
(2
(3
(4
nstant for su pecific grow ll death (day -ncentrations
The appare ass conversio
(5
en the bioma mption rate,
(6
s a relation b d the inlet flo
(7):
(7
where Vr is the effective volume of the reactor.
The concept of wash-out time, θcwo, is very im-portant in the analysis of continuous bioprocesses.
wo c
θ is defined as the minimum residence time that allows biomass maintenance in the system. This means that θcwo is an operating limit, below which the biomass cannot be maintained in the system be-cause the wash-out rate is higher than the growth rate. From the fact that 1 x
d
c x
r k C
θ = − (biomass balance
over the system), the wash-out time θcwo can be de-termined when θc is minimun and µ x
x
r C
= is
maxi-mum for Cs =CsI. Thus:
(
)
(
)
(
)
+ =
− ⋅ −
I
M s
wo
c I
d S M d
K C
k k C K k
θ (9)
The minimum recycling rate (Rmin) can be deter-mined by combining Equations (7), (8) and (9):
(
)
(
–)
⋅ =
⋅ − ⋅
wo
w c
min wo
c w I
F R
F F
θ θ
θ θ (10)
Considering that the residence time in the reactor tank ( )θ , or hydraulic retention time (HRT) is given by Equation (11):
r
I
V F
θ = (11)
A relationship between θ and θc can be found and written as Equation (12):
. 1 1
I c
w
R F
R F
θ
θ = ⋅ +⎛⎜ ⎞⎟
+ ⎝ ⎠ (12)
From an analysis of mass balance over the system and over the settler, the substrate concentration at the exit of the reactor and the biomass concentration at the exit and recycling line of the reactor are calcu-lated by Equations (13), (14) and (15):
(
)
(
(1 1))
U M d c
s
d c
g K k
C
L k k
θ θ
⋅ +
⎛ ⎞= ⋅
− ⋅
⎜ ⎟
⎝ ⎠ − (13)
/ ( )
(1 )
I U
U x s s s c
x
d c
g Y C C
C
L k
θ
θ θ
⎛ ⎞ ⎜ ⎟
⎝ ⎠ + ⋅ ⋅
⋅ −
= (14)
1 Ux
c R
x
R C
g C
L R
θ θ ⎛ + − ⎞⋅
⎜ ⎟
⎛ ⎞ ⎜ ⎟
⎝ ⎠=⎝ ⎠ (15)
The simulation was performed using the proposed mathematical model, introducing experimental data of specific growth for S. obliquus. The cultivation experiments of this microalga in the flat-plate reactor allowed one to calculate the C CsI, , Us CUx and k coef-ficients. The value of 1.66 day for θ was used in the steady-state. The other parameters used in the simulation model are listed in Table 2. The variables
, e
U U U
s x x
C C C were predicted by varying the recy-cling rate ( )R between R=Rmin and R=1 using the MATLAB R2011 software.
Table 2: Selected parameters for S. obliquus growth simulation.
Variable/Parameter Value
I
F (m3 day-1) – Inlet volumetric flow rate 1.0
w
F (m3 day-1) – Volumetric flow rate of cell purge
0.1, 0.2, 0.3
M
K (g L-1) – Monod saturation constant for substrate
0.8
d
k (day-1) – specific death rate 0 and 0.05
r
V (m3) – Reactor volume 1.66
R – Recycling rate Rmin to 1
RESULTS AND DISCUSSION
The S. obliquus cultivation experiments were car-ried out using CO2 and nitrate (NO3-) solutions as
carbon and nitrogen sources, respectively, for the microalgae growth. CO2 was pumped in excess into
the system while NO3- solution was chosen as the
limiting substrate. Table 3 displays the values of NO3- concentration at the entrance and exit of the
reactor tank (CsIand CUs respectively), biomass con-centration (dried weight) at the reactor exit (CUx ), maximum specific growth rate ( )k and yield (Yx s/ ). It is noted that the NO3- comsumption was
approxi-mately 79%.
The high value of biomass concentration seen in Table 3 is typical of S. obliquus, which is referred as one of the most promising microalga for biofuel pro-duction. This result is in agreement with values pre-viously reported in the literature. For instance, Baky
et al. (2012) found a dried weight of 1.651 g L-1 for
S. obliquus cultivated at 25 °C in N-9 culture me-dium at 200 µE m-2 s-1 and 9% CO2 in the gas line.
af u B - 5 S re d sy ap b F th st m h T o F er S
fter 6 days sing BG-11 Breuer et al. 7 g L-1 by c 00 µE m-2
Scenedesmus
esistant agai ata also show ynthetic effi pproximately een examine Figure 4 disp
he steady-sta tate conditio month, enabl
igh cellular c
Table 3: Ex
bliquus cult
Parameter
I s C (g L-1)
U s C (g L-1)
U x C (g L-1) k (day-1)
/ (
U x
x s I U
s s
C Y
C C
= −
Figure 4: Stea ration. (a) Ce
imulation of Mic
Brazilian
of Scenedes
culture me (2013) obtai cultiving S. o
s-1. All th genus, S.
inst increase w that both iciency decr y 800 – 100 ed in detail plays values ate. It can b ons were suc ing reproduc concentration xperimental tivation proc ) U ady-state data ellular concen
croalgal Growth in
Journal of Chem
smus dimorp
edium at 51 ined a bioma
obliquus in t ese results
obliquus in es of light i
relative grow rease for co
00 µE m-2 s s by Sforza of cellular c be verified t ccessfully m cibility of th n.
l data for cess.
a for the pho ntration. (b) C
n a Continuous P
mical Engineering
phus cultivat 10 µE m-2 ass content o
the range 30 show that n particular, ntensity. Th wth and pho ncentrations s-1, which ha a et al. (201 concentration hat the stea maintained fo
he system w
the bench
Value
1.78 ± 0. 0.38 ± 0.0 5.19 ± 0.4 0.49 3.86
tobioreactor Cellular densi
Photobioreactor w
g Vol. 33, No. 04,
tion s-1. of 6 00 - the is hese of ave 14). n at ady-or 1 with S. 18 07 47 op-ity. ter ter plo P F R θ C C θ *M T P F R θ C C θ *M (ab (F of tio is con nif pli ma hig Th nev tha ob the the cal cel red rea lig eff pla de with Sedimentatio
, pp. 773 - 781,
Simulations rs listed in Ta rs are summ otted and exh
Table 4:
Parameter
w
F (m3 day-1)
min
R
c
θ (day)* U x C (g/L)*
R x C (g/L)*
wo c
θ (day)
Maximum values.
Table 5: Sim
Parameter
w
F (m3 day-1)
min
R
c
θ (day)* U x C (g/L)*
R x C (g/L)*
wo c
θ (day)
Maximum values.
The values bsence of ce
)
w
F of 0.1 a
U x
C and CxR
ons. However observed th ncentration ficantly, mak icable for the It is worth m ass concentra gh, which is he cellular g
vertheless h an 8 g L-1) a bstruction of e concentrati e shading ca lled self-shad lls located f duced, thereb actor. In this ght were not ficiency of S
ate reactor a monstrated (
n and Partial Bio
October - Decem
s were run w able 2 and 3, marized in Ta
hibited in Fig
Simulation
mulation resu
of Rmin ar ell death) wh and 0.2 m3 da
R
x also sugge
r, when kd is
at Fw strong at the steady king the con e process. mentioning t
ation at the s not encoun
rowth depen high concen re not true c the light thr ion reaches h aused by cell ding effect). farther from by decreasin
work, trans taken in acc
S. obliquus cu at 300 µE m
(Sforza et a
omass Recycling
mber, 2016
with the vari , and the resu ables 4 and gures 5, 6 an
n results for
V 0.1 0.10 9.0 32.0 58.0
ults for kd =
V 0.1 0.14 9 19 35 re satisfacto when cell pur
ay-1 were use est good oper 0.05 day-1 (s gly influence y state. Rmin
nditions for F
that, in some exit of the r untered in re nds on the l ntrations (us conditions be roughout the high levels. lls of the lig The absorpt m the light s ng the produ smission and count since a ultivation in m-2 s-1 had be
al., 2014). A
7
iables/param ulting param 5. Data we nd 7.
0 d
k = .
Value 0.2 0.3 0.25 0.50 5.0 3.6 14 6.0 22.5 9.0 2.97
= 0.05 day-1.
Value 0.2 0.3 0.38 0.90 5 3.6 8 0.9 14 1.5 3.49
ry for kd =
rge flow rat ed. The valu rational cond see Table 5), es the cellul increases si
w
F = 0.3 ina
e cases the bi reactor is ve eal condition light intensit
sually great ecause there e reactor whe
This is due ght source (s tion of light b source is the uctivity of th d absorption
a better energ a similar fla een previous A limiting co
on-ce w w in
a
d g
1 ti sp in m cr to
th m li sy an op an er fo fo v
ti ti sy T tr u te ra w re m
th v d in th m
ce d tr 1 si th
entration of where cellula weight do no ntensities bet
l., 2013; Wa itions for s eometry.
It has been .33 g L-1 and ies fixed at 1 pectively, fo n a photobio mensions. Th
reased from o self-shadin
From Figu hat Rmin inc mass remova ikely because
ystem does n n effective m perating con nd Fw= 0.1 ration, due ormer condit or microalgae
ides a huge c Ho et al. ime (HRT) o ion of Scen
ystem, which This can be
ration (1.5 vv sed by the ention time ameters. In t was used and eaching cons mately 40 h). It can be o he operating
arying the b ence time. T ng the proce he microalga maintenance a
The use o ellular conce itions witho ration of 5.1 4 g L-1 were imulated valu he model.
f 8 g L-1 is ar concentra ot exceed th tween 300 – ang et al., 20
self-shading
n reported th d 9.66 g L-1 150 µE m-2 s or cultivation oreactor with he energy
24% to 13% ng (Beraldi, 2
ure 7 and Tab creases and al is increas e the amoun not provide s microalgae g
nditions in F
or for kd = to either lo tion, or physi e growth in t cellular conce
(2013) repo of 150 hours
nedesmus o
h exceeds th explained b vm) and ligh authors, wh
used to a this work, a d a light in sequently a
observed from g conditions
biomass rem This denotes
ess before la ae growth kin
and the biom of recycling entration bec out recycling 9 g L-1, whe e obtained f ues seem to
s often repo ations expre his value fo – 1500 µE m 013). Further
also depe
at cellular co are found fo s-1 and 1000 n of Scenede
h similar ge conversion %, which wa 2013).
bles 4 and 5,
U x
C decreas sed in the s nt of cell that sufficient act rowth. It sho
w
F = 0.3 fo 0 are unreal ow cellular ical limitatio the latter con entration valu orted a hydr
(6.25 days)
obliquus in he HRT use by the lowe ht intensity ( hich justifies
achieve bett a CO2 conce
ntensity of 3 HRT of 1.66
m Figures 5, diverge sign moval rate an the importa aboratory tes netics as wel mass removal caused an in cause the exp g led to a c
ereas values for the simu
be applicabl
rted in stud essed in dr or applied li m-2 s-1 (Breuer
rmore, the c nd on reac
oncentrations or light inten 0 µE m-2 s-1,
esmus obliqu
ometry and efficiency as probably d
it can be no ses as the b system. This t remains in tive biomass ows that for r values of in terms of growth in on of the reac ndition as it p ue of 32 g L -raulic retent for the culti a continuo d in this wo er CO2 conc
(240 µE m-2 the longer er growth entration of 300 µE m-2 6 day (appro
, 6, 7 and 8 t nificantly wh nd cellular re ance of simu
sts, by obey ll as the cellu l.
ncrement in perimental c ellular conc between 6 a lated data. T le for validat
dies ried ight r et
on-ctor
s of
nsi-
re-uus
di- de-due
oted bio-s ibio-s
the for the
d
k
op-the ctor
pro-1
. tion
iva-ous ork.
cen-s-1) re- pa-2%
s-1,
oxi-that hen esi- ulat-ying
ular
the on- cen-and The ting
Fig
(R
Fig
(R
gure 5: Plot R).
gure 6: Plot R).
t of θc as a
t of CUs as a
function of
a function of
recycling ra
f recycling ra ate
F
(R
F
(R
S
Figure 7: Plo R).
Figure 8: Plo R).
imulation of Mic
Brazilian
ot of CUx as
ot of CxR as
croalgal Growth in
Journal of Chem
a function o
a function o
n a Continuous P
mical Engineering
of recycling r
f recycling r
Photobioreactor w
g Vol. 33, No. 04,
rate
rate
int can sed spe sim tem pro an dat in pu ind pri
Sc
of bio op
Rm
sid (F
ev ins as beh ma me spe sho tio
all an do tia Ma
C
θ
with Sedimentatio
, pp. 773 - 781,
The model to account th n be further dimentation ecies. Howev mulating the m with parti
ovided insig d Rmin were
ta, for instan terms of ope urge flow rate dicated 0.1 iate values o
enedesmus o
A mathema
Scenedesm
oreactor with ped in this w
min become a
dered (kd =0 )
w
F lies in th er, the recycl sufficient lev
w
F increase havior was n athematical m entation cond ecies, in suc ould be mea on is able to a
AC
The author l support pro
d welcome f ova is also a ally presented
aceiò-Alagoa
Conce Resid (HRT
n and Partial Bio
October - Decem
developed i he sedimenta controlled b conditions d ver, the prop
two stage p al biomass r ghts into the
changed, no nce the cellul
erating cond e (Fw). Fina and 0.2 m3 of Fw for the
obliquus.
CONCLU
atical model
us obliquus
h partial biom work. It was v
pplicable wh 0) and when he range of 0
led biomass vels for an ad es. Finally the not taken int model. It is ditions are de ch a way th asured to exa affect the ente
CKNOWLE
s gratefully ovided to th from the Un cknowledged d in oral form
as-Brazil.
LIST OF S
entration of c ence time or ) (day)
omass Recycling
mber, 2016
in this work ation rates;
by centrifug depend on th posed model photobioreact
recycling. Th process beh ot only in te
lar residence ditions such a
ally, the sim day-1 as the e continuous
USIONS
to simulate
s cultivation mass recycli verified that hen cell dea n the cell pu 0.1 and 0.2 m concentratio dequate micr e microalgae to account in
noteworthy ependent on t hat the sedim
amine wheth ering biomas
EDGEMENT
acknowledg his work. Th niversità degl d. This rese m at the XXX
SYMBOLS
component i
r hydraulic re
7
k did not tak however, the gation becau
he microalg was useful f tor-settler sy he model al havior as θcw
rms of kinet e time, but al
as the bioma mulation resul e more appr s cultivation
the efficienc n in a phot
ing was deve t the values ath is not co urge flow ra m3 day-1. How on decreases roalgae grow sedimentatio n the propose that the sed the microalg mentation ra her sediment ss rate.
TS
ge CAPES f he opportuni li Studi di P earch was pa XVI ENEMP
(g L-1) etention time
779
ke ey use ae for
ys-so
wo c
tic so ass lts
ro-of
cy to- el-of
on-ate
w-to wth on ed
di-ae ate
ta-for ity
Pa- ar-
r Rate of production or consumption of component i (g L-1 day-1)
KM Monod saturation constant for substrate
(g L-1)
k Maximun specific growth rate (day-1)
kd Specific rate of cell death (day-1)
w
F Cell purge flow rate (m3 day-1)
R
F Recycling flow rate (m3 day-1)
1
F Inlet flow rate (m3 day-1)
c
θ Solid retention time (SRT) (day)
wo c
θ Wash-out time (day)
Yx/s Apparent yield coefficient for
substrate-to-biomass conversion (g g-1)
Vr Effective volume of the reactor (m3)
Rmin Minimum recycling rate (-)
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