Innovative Food Science and Emerging Technologies 49 (2018) 92–105
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Innovative Food Science and Emerging Technologies
journal homepage: www.elsevier.com/locate/ifset
Modeling of permeate flux decline and permeation of sucrose during
microfiltration of sugarcane juice using a hollow-fiber membrane module
T
Chirasmita Panigrahia, Sankha Karmakarb, Mrinmoy Mondalb, Hari Niwas Mishraa,
⁎
Sirshendu Deb,
a
b
Department of Agricultural and Food Engineering, IIT Kharagpur, Kharagpur 721302, India
Department of Chemical Engineering, IIT Kharagpur, Kharagpur 721302, India
A R T I C LE I N FO
A B S T R A C T
Keywords:
Sugarcane juice
Microfiltration
Gel layer controlling model
Removal of microorganism
Microfiltration (MF) of centrifuged sugarcane juice was used as a pre-clarification step prior to further clarification. MF was performed with the objectives of achieving maximum flux, minimum retention of sucrose and
maximum rejection of total solids as well as maximum removal of microorganisms from the permeate keeping
the nutritional and physico-chemical profile intact. In this regard, experiments were done using a polyacrylonitrile-based MF membrane of filtration area 0.027 m2 and pore size of 0.1 μm. A detailed investigation of
the effects of different operating conditions, namely transmembrane pressure TMP (35, 69, 104 and 138 kPa)
and cross flow velocity CFV (0.123, 0.246 and 0.369 m/s) on membrane productivity and juice quality was
undertaken. The steady-state permeate flux ranged from 5.41 to 6.23 l/m2∙h for the domain of the operating
conditions studied herein. Profiles of permeate flux and sucrose concentration in permeate were modeled using a
gel layer controlling model under the framework of boundary layer analysis. The optimized operating conditions
were found to be TMP of 104 kPa and CFV at 0.369 m/s, yielding a flux of 6.04 l/m2∙h and having sucrose and
polyphenols concentration of 104.8 g/l and 9.38 mg GAE/100 ml, respectively. Total solids (26%) and turbidity
(98%) were removed to a great extent during MF along with remarkable improvement of clarity (3 times).
Microbiological evaluation confirmed that, MF successfully reduced the total viable plate count by 5 log CFU/mL
scale and yeast and mold count by 4 log CFU/mL scale.
1. Introduction
Sugarcane (Saccharum officinarum L.) is an important agro-industrial
crop grown worldwide and India is the second largest producer in the
world. Sugarcane juice is a popular beverage containing mostly sucrose
(8–16%), reducing sugar, ash, fiber, and polysaccharides with the remainder as water. Higher sugar content in juice makes it a potential
natural energy drink (Yusof, Shian, & Osman, 2000). Apart from sucrose, the juice contains phytonutrients, anti-oxidants and soluble fibers
offering numerous health benefits including weight loss, improved digestion, and treating disease symptoms such as jaundice, the common
cold and heat stroke (Singh, Omre, & Gaikwad, 2014). The juice contains a relatively high level of impurities such as gums, waxes, ash,
coloring substances and soil shortening its shelf-life significantly. Microbial spoilage is another cause of juice degradation. Fresh sugarcane
juice, therefore has extremely short storage life due to its perishable
nature and heat sensitivity of its delicate flavor and sensorial components (Lo, Al-kharkhi, & Azhar, 2007). Traditional clarification
⁎
processes, like, coagulation, flocculation, addition of sulfur dioxide
followed by alkalinization fail to remove non-sugar substances, such as
gum, ash, colloids, high molecular weight proteins, colorants, oxidative
enzymes and microorganisms (Bhattacharya, Agarwal, De, & Rama
Gopal, 2001).
Methods active in stabilizing sugarcane juice include canning (Eissa,
Shehata, Ramadan, & Ali, 2010), blanching (Mao, Xu, & Que, 2007),
pasteurization (Khare, Lal, Singh, & Singh, 2012), radiation treatment
(Mishra, Gautam, & Sharma, 2011), freeze concentration (Lo et al.,
2007), acidification (Cynthia Ditchfield, 2014) and inclusion of preservatives, antioxidants and antimicrobials (Bhupinder, Sharma, &
Harinder, 1991; Sankhla, Chaturvedi, Kuna, & Dhanlakshmi, 2012).
Most of the attempts for shelf-life enhancement of sugarcane juice are
focused on thermal processes, but they have usual demerits of heatinduced thermal damages and accelerated sugar degradation, resulting
in dark color and burnt flavor (“jaggery” flavor in case of sugarcane)
that greatly alter the organoleptic character of juice. Radiation has
deleterious effects on color, flavor and nutrient value (Chauhan, Singh,
Corresponding author.
E-mail address: sde@che.iitkgp.ernet.in (S. De).
https://doi.org/10.1016/j.ifset.2018.07.012
Received 22 February 2018; Received in revised form 16 July 2018; Accepted 18 July 2018
Available online 25 July 2018
1466-8564/ © 2018 Elsevier Ltd. All rights reserved.
Innovative Food Science and Emerging Technologies 49 (2018) 92–105
C. Panigrahi et al.
empirical resistance-in-series model (Ferreira, Cozar, & Schmidt, 2016;
Makardij, Farid, & Chen, 2002). Total resistance against solvent flux
was considered to be constituted as individual resistances in series, like,
membrane resistance, pore-blocking resistance and polarized layer resistance. Polarized layer resistance was assumed to vary with time
following a particular function and constants involved in the function
were correlated with operating conditions. Since, these models were
based on correlations, their predictive capability was poor beyond the
range of operating conditions. Another feature of these models was that
only decline in permeate flux was quantified without estimating the
permeation of sucrose.
Additionally, it may be noted that all the above works were carried
out in small laboratory test kits and therefore are not directly scalable
and there was no attempt to develop appropriate theoretical framework
to model the system performance for further scale-up based on first
principle models. The present work is undertaken to fill this gap.
Centrifuged sugarcane juice was treated by scalable hollow fiber MF
membrane module to remove impurities and microorganisms. Effects of
operating conditions, namely, cross flow rate and transmembrane
pressure drop were investigated in detail. A theoretical model based on
boundary layer framework was developed from first principle for MF of
sugarcane juice in order to predict both permeate flux (process
throughput) and sucrose concentration in filtrate for subsequent scaleup.
Tyagi, & Balyan, 2002). Chemically manufactured artificial preservatives are regarded as carcinogenic, since they pose health risks
causing digestive and respiratory problems (Parke & Lewis, 1992).
Therefore, an effective preservation method eliminating the potent sites
for microbial growth as well as retaining the freshness must be developed which would enhance the quality of the juice ensuring its long
shelf-life, wider distribution and availability. Moreover, increase in
consumer demand for fresh-like nutritional products has induced research in field of non-thermal preservation techniques.
Membrane based technologies, being easily scalable, non-thermal,
and physical in nature without using any external additives can be attractive alternative in enhancing the shelf-life of sugarcane juice.
Microfiltration (MF) membranes having pore size varying from 0.1 to
10 μm can remove colloids, emulsion, high molecular weight impurities, including microorganisms. Microfiltration is used as a primary
clarification step for many fruit juice and extracts (Biswas, Mondal, &
De, 2016; Chaparro et al., 2016; Das Purkayastha et al., 2012; Oliveira
et al., 2016; Sagu, Karmakar, Nso, & De, 2014; Vaillant et al., 2005).
Moreno, de Oliveira, & de Barros, 2012 compared clarification by MF in
tubular module with traditional coagulants, like, powdered activated
carbon and slaked lime, and established superior performance of MF in
reducing turbidity, color and concentration of reducing sugar. Gaschi,
Gaschi, Barros, and Pereira (2014) pretreated sugarcane juice by MF
before final polish filtration by ultrafiltration (UF). MF was observed to
remove larger sized impurities, thereby reducing fouling of subsequent
UF membranes significantly. Superior clarification ability of MF compared to traditional clarification by liming and addition of sulfur dioxide and subsequent improvement of quality of treated sugarcane juice
was established by many researchers (Farmani, Haddadekhodaparast,
Hesari, & Aharizad, 2008; Rezzadori, Serpa, Penha, Petrus, & Petrus,
2014; Sim, Shu, Jegatheesan, & Phong, 2009). On the other hand,
pretreatment of sugarcane juice before subjecting MF was also advocated by researchers (Abbara, Abdel-rahman, & Bayoumi, 2004;
Doherty, Rackemann, & Steindl, 2010; El Rayess et al., 2012) to mitigate membrane fouling and consequent reduction of throughput.
One of the major factors limiting the use of membrane filtration is
membrane fouling caused by concentration polarization during juice
processing leading to decline of permeate flux. The rate and extent of
membrane fouling are typically the function of solute content in the
feed stream and operating conditions. Modeling of flux profile during
filtration allows identifying the fouling mechanism and provides a
predictive tool for successful scale-up. Many researchers worked on
modeling flux decline during MF and concluded that formation of gel
type layer over the membrane surface was the primary cause of flux
decline although pore blocking might have played important role
during initial period of filtration (Nourbakhsh, Emam-Djomeh,
Mirsaeedghazi, Omid, & Moieni, 2014; Pagliero, Ochoa, & Marchese,
2011; Tarleton & Wakeman, 1994; Todisco, Peña, Drioli, & Tallarico,
1996). However, reports involving modeling of MF performance of
sugarcane juice are scant in literature and most of these works were
2. Theory
Constituents of sugarcane juice are grouped in three categories,
namely, high molecular weight solutes (HMW, like, proteins, polysaccharides, etc.), sucrose and low molecular weight solutes (LMW,
which have molecular weight less than sucrose). It is assumed that
HMW solutes are completely retained by the membrane forming a gel
type layer which grows with filtration time. Sucrose was partially retained by gel layer and membrane and LMW solutes are freely permeable through the membrane. Similar assumptions were adapted by
Mondal, Chhaya, and De (2012).
The schematic of flow geometry, formation of gel layer by HMW
solutes and transport of LMW solutes are presented in Fig. 1.
2.1. Transient model
Considering a mass balance of gel-forming component in the mass
transfer boundary layer (0 < y < δ) can be written as (De &
Bhattacharya, 1997),
ρg (1 − εg )
dH
dC
= vw C1 − D1 1
dt
dy
(1)
Subjected to boundary condition,
at y = 0, C1 = C1b
Fig. 1. Schematic of the flow geometry.
93
(1a)
Innovative Food Science and Emerging Technologies 49 (2018) 92–105
C. Panigrahi et al.
over the membrane surface, the steady state permeate flux is derived
dH
from Eq. (4) by putting dt = 0 .
where, ρg is gel layer density, εg is gel porosity, H is gel layer
thickness and vw is permeate flux at any time t, C1 is concentration of
HMW solute. D1 is its effective diffusivity. C1b and C1g are concentration
of HMW solute in bulk and in gel layer, respectively. Solution of Eq. (1)
is,
ρg (1 − εg ) dH
v y
⎛⎜1 − exp ⎛ vw y ⎞ ⎞⎟
C1 (y ) = C1b exp ⎛ w ⎞ +
D
vw
dt ⎝
⎝ 1⎠
⎝ D1 ⎠ ⎠
⎜
⎟
⎜
C1g ⎞
vw = k1 ln ⎛
⎝ C1b ⎠
⎜
(2)
Evaluating the concentration C1 at y = δ where, C1 = C1g, the following equation is resulted.
⎜
⎟
⎜
1
Sh =
⎟
(3)
( )
( )
(4)
k1
μ w = μ0 e α1 C1g
r2
r2
g
vw H
εg D 2
⎛⎜ μ ⎞⎟ = e−α1 (C1g − C1b)
⎝ μw ⎠
H
1
+ εD
k2
g 2
r2
w
1
k2
2
1
⎜
2.3. Model parameters and numerical solution
Parameters relevant to the system geometry, operating conditions,
solute and solution properties, membrane performance parameters and
model parameters are presented in Table 1. Since, the HMW solutes are
a complex mixture of various components, its effective diffusivity (D1)
and gel concentration C1g are difficult to estimate. Thus, α, D1 and C1g
are three parameters of Eq. (14), which are determined using the optimization routine of interior point algorithm following a trust region
method (Byrd, Gilbert, & Nocedal, 2000), by minimizing the sum of
square of errors of the steady state permeate flux of all the experiments.
Sum of square error is defined as,
(8)
(9)
where, Rm is hydraulic resistance of membrane and μ is viscosity of
permeating solution.
Rg is defined as,
Rg = βH
(17)
(7)
where, B1 = 3770; B2 = 38.8 and B3 = −0.04.
Permeate flux at any point of time can be written as,
ΔP − Δπ
μ (Rm + Rg )
⎟
In an ideal gel controlling filtration model, the mass transfer coefficient is independent of transmembrane pressure drop (Trettin &
Doshi, 1980).
(6)
where, πm and πp are osmotic pressure of the solution at the membrane
surface and permeate side, respectively. Solution osmotic pressure due
to sucrose is expressed as (Sourirajan & Agrawal, 1969),
vw (t ) =
(16)
u 0 D12 ⎞ 3 −α1 (C1g − C1b ) 0.14 ⎛ C1g ⎞
(e
) ln
vw = 1.62 ⎜⎛
⎟
⎝ C1b ⎠
⎝ dL ⎠
The osmotic pressure difference of solution due to concentration of
sucrose across the membrane is given as,
Δπ = B1 C2m Rr 2 + B2 C22m {1 − (1 − Rr 2 )2} + B3 C23m {1 − (1 − Rr 2 )3}
3
Using Eq. (14) the steady state flux can be expressed as,
C2p
Δπ = Δπm − Δπp
1
u 0 D1 ⎞
(e−α1 (C1g − C1b ) )0.14
k1 = 1.62 ⎜⎛
⎟
⎝ dL ⎠
H
εg D 2
where, γg is the partition coefficient of sucrose across the gel layer and
mass transfer boundary layer. It is defined as, C2(δ−) = γgC2(δ+). Real
retention (Rr2) of sucrose can be expressed as,
C2m
(15)
The expression of mass transfer coefficient can be presented as,
(5)
Rr 2 = 1 −
(14)
Using Eqs. (11) and (12) the following result is obtained,
(
) ⎤⎦
γ R + (1 − R )(γ − 1) exp (
) + (1 − R ) exp ⎡⎣v ( + ) ⎤⎦
g
(13)
Viscosity at the wall becomes,
C2m
C2b exp ⎡vw
⎣
(12)
μ = μ0 e α1 C
In above equation, k1 (D1/δ) is the film mass transfer coefficient of
HMW component.
Next, a mass balance of sucrose in mass transfer boundary layer and
gel layer has been carried out. The detailed derivation in presented in
Appendix 1. The final expression of sucrose at the membrane surface is
given as
=
0.14
inside a fiber, d is inner diameter of the hollow fiber, μ is bulk solution
viscosity, ρ is solution density. Reynolds number was calculated as 83,
166 and 249 for cross flow velocity of 0.123, 0.246 and 0.369 m/s,
respectively, hence, the flow was assumed to be laminar.
Following exponential variation of viscosity is assumed,
vw
C1g − C1b exp k
dH
1
= vw
vw
dt
1 − exp
k1 d
d 3 μ
= 1.62 ⎛Re Sc ⎞ ⎛⎜ ⎞⎟
D1
L ⎠ ⎝ μw ⎠
⎝
ρu d
μ
where, Re = μ0 , Sc = ρD , ρ is solution density, u0 is cross flow velocity
1
Rearranging Eq. (3), the governing equation of gel layer thickness is
obtained.
ρg (1 − εg )
(11)
where, k1 is the mass transfer coefficient of HMW solutes, C1g and C1b
are gel layer and bulk solute concentration. Mass transfer coefficient
under laminar flow conditions is calculated using Leveque's equation
(Blatt, Dravid, Michaels, & Nelsen, 1970),
⎟
ρg (1 − εg ) dH
v
⎛⎜1 − exp ⎛ vw ⎞ ⎞⎟
C1g = C1b exp ⎛ w ⎞ +
k
vw
dt ⎝
⎝ 1⎠
⎝ k1 ⎠ ⎠
⎟
N
2
i
i
exp
⎡ vw,exp − vw, cal ⎤
S0 = ∑ ⎢
⎥
vwi,exp
i=1 ⎣
⎦
(18)
where, Nexp is the number of experiments conducted.
Eqs. (4)–(6), (8), (9), and (10) constitute a set of differential–algebraic equation (DAE). In this set, the parameters are β, γg, ρg
and εg. Real retention of sucrose (Rr2) is independently estimated as
described in experimental section. Diffusivity of sucrose is available in
literature (Linder, Nassimbeni, Polson, & Rodgers, 1976). Four parameters, namely, β, γg, ρg and εg are estimated by comparing the sum of
square errors between the calculated and experimental data with respect to permeate flux and time averaged permeate concentration.
(10)
where, β = α(1 − εg)ρg, is constant as it is a characteristic of gel layer.
2.2. Steady state model
The experiments are conducted in hollow fiber membrane set up in
total recycle mode. A steady state is attained for every set of operating
condition. Since, HMW solutes are assumed to form a thick gel layer
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Innovative Food Science and Emerging Technologies 49 (2018) 92–105
C. Panigrahi et al.
3.1.3. Chemicals
Folin–Ciocalteu reagent, anhydrous sodium carbonate, and sodium
hydroxide (analytical grade) were purchased from Merck Specialties
Pvt. Ltd., Mumbai, India. Gallic acid standard was obtained from Loba
Chemie, Mumbai, India. Glass bottles were obtained from Borosil Glass
Works Ltd. (India). All chemicals used in experimentation and analysis
were of analytical grade.
Table 1
System geometry, characterization and model parameters.
Parameters relevant to system geometry
Number of hollow fibers
Length of fibers (cm)
Inner diameter of fibers (μm)
Filtration area (m2)
Parameters relevant to operating conditions
Feed concentration of HMW (kg/m3)
Feed concentration of sucrose (kg/m3)
Cross flow rate (l/h)
Velocity (m/s)
Reynolds number
Transmembrane pressure drop (kPa)
Solute properties
Diffusivity of sucrose (m2/s)
Membrane performance parameters
Intrinsic membrane resistance for nascent membrane
(Rm) (m−1)
Real retention of sucrose by the membrane (Rr2)
Model parameters
Gel layer concentration (Cg) (kg/m3)
Effective diffusivity of HMW solutes (D) (m2/s)
Viscosity coefficient (α1) (m3/kg)
Gel layer characteristic resistance (β) (m−2)
Partition coefficient of sucrose between bulk and gel
layer (γg)
Gel layer porosity (εg)
Gel layer density (ρg) (kg/m3)
2
80
18
600
0.027
30 ± 0.4
128
10, 20, 30
0.123, 0.246,0.369
83, 166, 249
35, 69, 104, 138
3.2. Pretreatment with centrifugation
Pre-filtration prior to membrane separation increases the yield and decreases the fouling of subsequent MF. Centrifugation aids in separation of
impurities like sand, mud, etc., and produces a clear juice suited to be fed
into the membrane system. Centrifugation was carried out in a laboratory
centrifuge (Model number CPR 30 Plus, supplied by M/s, Remi
International Ltd., Mumbai, India) under batch mode of operation at room
temperature (303K). The centrifugation capacity was 200 ml per batch with
centrifugation speed 3780 g and time 20 min. These conditions were selected based on preliminary studies so that maximum clarity and sediment
deposition were obtained. After centrifugation, the supernatant clear juice
was collected and analyzed to determine its characteristics.
(4.3 ± 0.3) × 10−10
2.36 × 1012
0.02
(65 ± 0.5)
(3.9 ± 0.3) × 10−11
(3 ± 0.2) × 10–3
(3.5 ± 0.5) × 1017
2 ± 0.05
3.3. Membrane characterization
0.5 ± 0.004
1400 ± 20
Hollow fiber membranes were characterized in terms of permeability, pore size distribution, surface morphology and surface chemistry.
2
Nexp N
Nexp
j
j
ij
ij
⎡ C2p,exp − C2p, cal ⎤
⎡ vw,exp − vw, cal ⎤
S0 = ∑ ∑ ⎢
+
∑
⎥
⎢
⎥
vwij,exp
C2jp,exp
j=1 i=1 ⎣
j=1 ⎣
⎦
⎦
3.3.1. Membrane permeability
The permeate flux is calculated by measuring the volume of filtrate
collected for fixed interval of time.
(19)
In above equation, Nexp is number of experiments, N is number of
data points in jth experiment. vw, expij is experimental data of permeate
flux at ith time instant of jth experiment and vw, calij is corresponding
calculated flux values. It may be noted that sucrose concentration in
permeate was not measured experimentally at different time points,
however, it was measured at the end of the experiment, containing the
cumulative permeate. Thus, the sucrose concentration in the permeate
is calculated as a time averaged value,
Jp =
Q
A × Δt
(21)
where, Jp is permeate flux; Q is filtrate volume collected in time Δt; A is
effective membrane surface area. Permeate flux was measured at different transmembrane pressure drop (TMP) using distilled water and
variation of permeate flux with TMP was linear through origin. The
slope of this straight line indicated the membrane permeability.
t
C2p =
1
(1 − Rr 2 )
C2m dt
t
0
∫
3.3.2. Real retention of sucrose
Real retention value of sucrose was estimated experimentally under
low polarization conditions, i.e., high CFR (40 l/h), low TMP (14 kPa)
and low feed concentration of sucrose (20 mg/l). The observed retention under these conditions was equal to real retention assuming
complete mixing (Mondal & De, 2016).
(20)
Based on above definition, the sum square on sucrose concentration
in permeate represented by second term in right hand side of Eq. (20) is
defined. C2p, expj is experimental value of sucrose concentration in
permeate and C2p, calj is corresponding calculated value.
3.3.3. Membrane morphology
The surface morphology of membranes was studied at different
views (cross section view, inner and outer surface) by field emission
scanning electron microscope (FESEM) (JSM-7610 F, JEOL, Japan). The
membranes were dried in dessicator overnight. For cross sectional
images, membranes were fractured by dipping in liquid nitrogen and
for inner and outer surface views, the fibers were cut with a blade
longitudinally along the midline.
3. Materials and methods
3.1. Materials
3.1.1. Raw material
Sugarcane juice was procured from a vendor in local market, Indian
Institute of Technology, Kharagpur, West Bengal, India. The juice was
collected in containers, stored in deep freezer immediately and was
thawed each time before use.
3.3.4. Membrane surface chemistry
The surface chemistry of fresh and used membranes was conducted
by Perkin Elmer Spectrum-100 instrument based on the principle of
Fourier Transform Infrared Spectroscopy (FTIR).
3.1.2. Membrane
A membrane cartridge having 80 polyacrylonitrile-based microfiltration (MF) grade hollow fibers (HF) having internal diameter
600 μm and wall thickness 300 μm with effective filtration area of
0.026 m2 was used. The average pore diameter of hollow fibers was
0.1 μm. The hollow fiber cartridge was supplied by M/s, Technoquips
Separations Pvt. Ltd., Kharagpur, India.
3.4. Microfiltration
3.4.1. Estimation of feed concentration of HMW solutes
The microfiltration feed essentially contains various components and they
can be grouped into high molecular weight components (HMW) and low
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Innovative Food Science and Emerging Technologies 49 (2018) 92–105
C. Panigrahi et al.
before the experiment and after the cleaning procedure once the run
was over.
3.5. Physico-chemical analysis of juice
Various streams (raw juice, juice after centrifugation and MF) were
analyzed in terms of total solids (TS), total soluble solids (TSS), color,
clarity, turbidity, sucrose and total poly-phenol concentration. Additional parameters, viscosity, titratable acidity, vitamin C, reducing and
total sugar were also determined.
The gravimetric method was adopted to measure the total solid
content of the sample kept in a hot air dried oven at 104 ± 2 °C until
attainment of constant weight (Ranganna, 1986). ABBE type refractometer (Excel International, Kolkata, India) was used for determining TSS of the juice. Color (in terms of absorbance) and clarity
(expressed as % transmittance) were determined with the help of a
UV–Vis spectrophotometer (M/s Perkin Elmer, Connecticut, USA) by
noting the absorbance at 420 nm and transmittance at 660 nm
(Karmakar & De, 2017). Turbidity of juice was determined by using a
turbidity meter (Model: 331, supplied by M/s, EI Products, Parwanoo,
India). Titratable acidity was determined by titration with 0.1 M NaOH
using phenolphthalein as indicator. Viscosity of juice was determined
by using an Ostwald viscometer (Pisco, Kolkata, India) at constant
temperature.
Total polyphenol was measured using a modified Folin and
Ciocaltaeu method (Vasco, Ruales, & Kamal-Eldin, 2008). The results
were expressed as mg of Gallic acid equivalent per 100 ml (mg GAE/
100 ml).
Vitamin C was determined by 2, 6-dichlorophenol indophenol visual
titration method. Sucrose, reducing sugar and total sugar were determined by the method of Lane and Eynon (Ranganna, 1986).
Particle size of the fresh and microfiltered sugarcane juice was
measured by Zetasizer (model: Zetasizernano ZS90) supplied by M/s,
Malvern Instruments, Worcestershire, UK.
Fig. 2. Schematic diagram of hollow fiber experimental unit. 1: Feed tank; 2:
suction pipe; 3: booster pump; 4: bypass valve; 5: bypass pipe; 6 and 6′: pressure
gauge (at the upstream and downstream of the membrane module); 7: membrane module; 8: back pressure valve; 9: rotameter; 10: outlet flow pipe line
from rotameter (retentate line); 11: permeate line.
molecular weight components (LMW). Components with lower molecular
weight, less than sucrose are grouped as LMW solutes. It is considered that
the HMW solutes were completely retained, LMW solutes were freely
permeable and sucrose is partially retained by gel layer and membrane. Using
this categorization, the amount of HMW and LMW solutes present in the feed
can be estimated. Thus, TSfeed = LMWfeed + HMWfeed + Sucrosefeed and,
TSper = LMWper + Sucroseper. Since, LMWfeed is freely permeable, it is equal
to LMWper, therefore HMW in feed can be estimated as HMWfeed =
(TSfeed − TSper) − (Sucrosefeed − Sucroseper). LMW in permeate can be estimated by TSper − Sucroseper. The percentage of LMW in feed was around
200 kg/m3 (20%) and for HMW it was around 150 kg/m3 (15%).
3.4.2. Experimental setup
The schematic of the microfiltration setup is shown in Fig. 2. The
microfiltration system consists of a feed tank, a membrane module, a
booster pump, two pressure gauges (at the inlet and outlet of the
membrane module), two valves, and one rotameter. The bypass valve
and back pressure regulating valve in the retentate line were used to
adjust and maintain the desired transmembrane pressure and cross flow
rate independently.
3.6. Microbial examination
Microbial examination was done to check the efficacy of microfiltration in clarifying sugarcane juice.
3.6.1. Viable bacterial count
Centrifuged and microfiltered juice samples were analyzed for CFU
count to assess the microbial stability. To calculate the colony-forming
unit, 1 ml of sample was diluted to 101, 102, 103, 104 and 105 times in a
test tube. An aliquot of 0.1 ml of the diluted sample was aseptically
transferred to agar plates and carefully spread using a spreader. The
plates were incubated at 37 °C for 24 h. This process was repeated for
three plates. Each plate was observed for growth and colonies were
counted visually. The average values of CFU/ml were reported. The
following equation was used to calculate the colony forming units:
3.4.3. Experimental procedure
The experiments were done in a controlled environment (293 K
temperature and nitrogen environment in a clean laminar hood) arresting the growth of bacteria in the retentate stream. Since these
conditions were maintained, the chance of bacterial fermentation is
minimal. Each experiment was conducted using 500 ml of centrifuged
juice. The experiments were done under total recycle mode with recycling of both permeate and retentate into the feed tank to maintain
uniform feed concentration. By controlling the bypass and retentate
valves, transmembrane pressures (TMP) and cross flow rates (CFR)
were set independently. Different TMPs (35 to 138 kPa) and CFRs (10 to
30 l/h) were applied. Reynolds number (Re) for corresponding CFR is
83, 166 and 249, respectively. A small quantity of permeate (clarified
juice) was collected for its characterization. Permeate flux profiles for
each operating condition was also measured. Each run was for 60 min
ensuring steady state. Once the experiment was over, after circulating
the tap water for 30 min through the flow circuit, an acid solution
(0.1 N HCl) was first used to wash the membrane for 40 min. Then, an
alkaline wash (0.2 N NaOH) was carried out for another 40 min. At the
end of the washing procedure, distilled water was re-circulated through
the module for 10 min. The permeability of the membrane was measured thereafter. The membrane fouling, expressed as a percentage
drop in water permeability, was estimated by measuring the water flux
CFU
ml =
CFU per plate × Dilution factor
Volume of sample taken (ml)
(22)
A very small amount from the plates were put into individual slides
and observed under microscope for obtaining focused images of bacterial growth.
3.6.2. Yeast and mold count
Yeast malt agar of 20 g was suspended in 500-ml distilled water for
preparation of culture medium. It was heated to boiling for about 2 min
in order to dissolve the medium completely. The flask containing the
agar media was sterilized with steam at 1 bar for about 45 min. After
removing, it was mixed well and 20–25 ml of media was poured into
each sterile petri-plate. For plating the sample, serial dilutions (10−1,
10−2, 10−3 and 10−4) for centrifuged juice and (10−1 and 10−2) for
MF juice were made and aliquots of 1 ml were added to each duplicate
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Fig. 3. SEM images of (a) cross section, (b) macrovoids, (c) inner surface of the fresh membrane and (d) inner surface and (e) macrovoids of the used membrane.
4.2.1. Membrane characterization
Scanning electron micrograph images of the cross section of the
pristine hollow fiber and used one are presented in Fig. 3. It can be
observed from Fig. 3(a) that the hollow fiber has a thin dense skin
followed by finger like pores spreading all across the cross section. The
macrovoids are presented in Fig. 3(b). SEM views of the inner surface of
the pristine hollow fiber and the used one were shown in Figs. 3(c) and
(d), respectively. It is observed from Fig. 3(c) that the inner surface is
really very dense with visible smaller pores. But, these pores become
invisible completely in case of used membrane, confirming the deposited layer on the surface (Fig. 3d). Fig. 3(e) presents the magnified
views of macrovoids in the cross-section of hollow fibers. Comparing
Figs. 3(b) and 3(e), it is clearly visible that there were prominent depositions inside the used fibers.
petri-dish. The inoculum was mixed in the agar by gentle shaking and
using a V-glass rod. It was allowed to stand for some time and then
incubated in inverted position at 25 °C for 72 h. After incubation, colonies were counted and YMC/ml was noted.
4. Results and discussion
4.1. Centrifugation
The raw sugarcane juice was subjected to centrifugation at 3780 g
for 20 min at room temperature (30 °C). Centrifugation as a pretreatment method was very effective in terms of clarity improvement from
3.5%T to 32.6%T (8 times) and turbidity reduction from 192.6 NTU to
20.2 NTU (90%). The centrifuged juice was then subjected to MF.
4.2.2. Particle size analysis
Particle size distribution of the centrifuged juice and the MF
permeate is shown in Fig. 4(a). It can be observed from this figure, that
a multimodal distribution profile is present in the feed sample indicating two distinct size distributions of the particles: (i) ranging from
0.75 to 2.3 μm (ii) ranging from 2.5 to 3.7 μm. The average membrane
pore diameter is 0.1 μm. It is clear from the particle size distribution of
4.2. Microfiltration
Microfiltration eliminates larger-sized, high molecular weight gel
forming materials from the feed itself. Also, MF reduces the microbial
count in the feed.
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Centrifuged juice (Feed for MF)
Microfiltered permeate
25
Intensity (%)
20
(a)
15
10
5
0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
Particle size ( m)
(b)
Raw Juice
Centrifuged Juice
Microfiltered Juice
Fig. 4. (a) Particle size analysis of feed and microfiltered juice; (b) Representative diagram of the raw, centrifuged and microfiltered juice (at optimum operating
condition).
permeate that particles with size more than 0.35 μm are not present in
the filtrate. However, the intensity of peak is maximum at 0.12 μm
which is comparable to membrane average pore diameter. Thus,
smaller-sized fraction of the particles in the feed are easily permeated
through the membrane and larger-sized fraction (beyond 0.35 μm) is
arrested on membrane surface causing the growth of the fouling layer.
The photographic representation of raw, centrifuged and microfiltered
juice is presented in Fig. 4(b). As evident from the figure, reduction in
color occurred after centrifugation and the juice become clear after
microfiltration.
4.2.4. Effects of operating conditions
Parameters of the model were estimated as described in Section 2
and presented in Table 1. Once the parameters are estimated, Eqs. (7)
and (8) are solved to get the profiles of permeate flux and growth of gel
layer and these are presented in Fig. 6. It can be observed from this
figure that gel layer thickness (H) increases with TMP at fixed Reynolds
number. For example, H increases from 140 μm to 280 μm at the end of
60 min as TMP increases from 35 to 138 kPa at Re = 83. Bigger sized
solutes are convected towards the membrane surface at higher pressures making the gel layer thicker, thereby increasing the gel layer
resistance (βH in Eq. 7). However, increase in gel layer resistance with
pressure (increasing denominator of Eq. 7) is squarely compensated by
increase in TMP value (numerator of Eq. 7), thereby making steady
state permeate flux (vw) almost invariant with TMP. For example,
permeate flux after 60 min of filtration remains almost same 7.5 l/m2∙h
at Re = 83 and in TMP from 35 to 138 kPa. This trend is same for all
Reynolds number independent of TMP. This observation confirms that
the permeate flux at steady state is pressure-independent as reported in
literature (Karmakar & De, 2017).
Effect of Reynolds number is apparent from this figure. Increase in
cross flow rate imparts sufficient shear on the gel layer thereby preventing its uncontrolled growth, reducing its thickness. For example, at
TMP 35 kPa, gel layer thickness is reduced from 140 to 90 μm (1.56
times reduction) after 60 min with increase in Re from 83 to 249 (3
times). Same trend is observed for other TMP values 69, 104 and
138 kPa. However, at higher pressures, extent of reduction of gel layer
thickness is reduced from 280 μm to 210 μm (1.33 times) after 60 min
4.2.3. FTIR analysis
The FTIR analysis of the fresh MF membrane and the membrane
after filtration is represented in Fig. 5. From Fig. 5, it can be inferred
that the fresh MF membrane has intense peaks at 1458, 1670, 2254 and
2944 cm−1. These peaks correspond to the alkane, amine, nitrile and
hydroxyl groups, respectively and these are the functional groups present in PAN membrane. Increase in peak intensity at wavelength
1620–1570 cm−1for the used membrane is due to deposition of protein
molecules (amine groups) on the membrane surface. Also, it may be
noted that, at wave number between 3300 and 2900 cm−1, the intensity is higher in used membrane which might be due to adherence of
–OH bond of polyphenol compounds present in the juice. It may also be
noted that for the used membrane some peaks are subdued at various
points due to hindrance of absorption spectra by deposition on the
membrane surface.
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almost 99% of the values are included in ± 1.5σ. Variation of parameters, like, sucrose content and turbidity, with operating condition is
also statistically insignificant. The values of turbidity and sucrose
content ranged from 0.4 to 0.7 NTU and 98.7 to 108.7 g/l, respectively.
The mean values were 0.48 NTU for turbidity and 102.86 g/l for sucrose with standard deviation 0.15 and 2.84, respectively. As evident
from Tables 2, 75% of the values for sucrose and turbidity lie
within ± σ and for turbidity, effect of operating condition are insignificant as all the values lie with ± 1.5σ. Also, for sucrose, around 92%
(11 out of 12) of the values lie within ± 1.5σ. Hence, the variation is
statistically insignificant.
The optimum operating condition was selected judiciously on the
basis of productivity and some physico-chemical properties like, sucrose content, clarity, polyphenols content and TSS. Although, the
highest flux was observed in case of 138 kPa TMP and Re 249, however,
the flux was comparable in case of 104 kPa and Re 249 (3% decrease)
and also parameters like, TSS, sucrose and polyphenol are comparable,
whereas, color and clarity had improved. Hence, 104 kPa TMP and Re
249 was selected as optimum operating conditions based on color,
clarity, TSS, sucrose content, polyphenol content and productivity at
steady state.
Detailed physical characteristics and nutritional parameters are
compared between centrifuged juice (CJ) and microfiltered juice (MFJ
at optimum operating condition) and reported in Table 3. It can be
concluded by observing results in Table 3 that MF reduces the total
solids of sugarcane juice without significant reduction in soluble sugars
making it one of the most appropriate pre-clarification processes.
The profiles of sucrose concentration in permeate at different operating conditions are presented in Fig. 7. General trend is sucrose
concentration decreases with time. As filtration progresses, gel layer
grows in thickness (as shown in Fig. 6) acting as a dynamic membrane,
thereby rejecting more sucrose leading to lowering in its concentration
in permeate. For fixed TMP, at the same time of filtration, sucrose
concentration increases with Reynolds number (Fig. 7). For example, at
35 kPa TMP, at 30 min, sucrose concentration in permeate increases
from 102 g/l to 107 g/l with change in Re from 83 to 249. Gel layer
thickness decreases with Reynolds number due to enhanced shear
(Fig. 6), thereby offering less resistance against solute transport and as a
result, permeate concentration of sucrose increases. At fixed Re, sucrose
concentration in permeate increases with TMP. For example, at the end
of 60 min, sucrose concentration increases from 100 g/l to 110 g/l (at
Re = 249) with change in TMP from 35 to 138 kPa. Solute transport
through gel layer increases both by convection and diffusion at enhanced TMP, thereby increasing sucrose concentration in permeate.
Time averaged sucrose concentration in filtrate is calculated from Eq.
18 and presented along with the experimental data for various operating conditions in Fig. 7(e). It is observed that there exists reasonable
agreement between calculated and experimental data.
Microfiltration membrane (Used)
200
Transmittance (% T)
150
100
110
Microfiltration membrane (Fresh)
105
100
95
5000
4000
3000
2000
1000
0
-1
Wavenumber (cm )
Fig. 5. FTIR analysis of MF membrane before and after filtration of sugarcane
juice.
over the same change in Re from 83 to 249. At higher TMP, the gel layer
becomes more compact and equivalent magnitude of shear in range of
83–249, is less effective to reduce the thickness of gel layer. Although,
reduction of gel layer is significant (1.33 to 1.56 times reduction) with
Re, its effect on profiles of permeate flux is marginal as observed from
Fig. 6. This anomaly can easily be understood by considering the order
of magnitude of membrane hydraulic resistance (Rm) and gel layer resistance (Rg) in Eq. 7. Variation of gel layer thickness is reflected in gel
layer resistance for different operating conditions. Although membrane
and gel layer resistances are in the same order, gel layer resistance is
2–3 times the membrane resistance in the range of operating conditions
studied herein. Gel layer resistance decreases with tube Reynolds,
however, effects of cross flow rate on gel layer resistance are not significant leading to marginal variation of permeate flux as displayed in
Fig. 6. Comparisons between calculated steady state permeate flux and
experimental data is presented in Fig. 6(e). It is clear that the calculated
data of steady state flux is within ± 20% of the experimental values.
Variation of nutritional parameters with microfiltration operating
conditions is tabulated in Table 2. It may be mentioned that other
parameters like solution viscosity, titratable acidity, vitamin C, total
sugar, reducing sugar have marginal variation with operating conditions. Major parameters are presented in this table. It can be observed
from Table 2 that, there is a significant decrease in the total solid
content after microfiltration (26%), but, with the variation of operating
parameters the change is insignificant. The mean value for TS is 14.73%
with a standard deviation (σ) of 0.32. As evident from the results, 85%
of the values lie within ± σ and all the values fall within ± 1.5σ, hence,
the variation of TS with operating condition are statistically insignificant (Sagu, Karmakar, Nso, Kapseu, & De, 2014). Similar trend is observed for TSS, color, clarity and total polyphenols, where the mean
values are, 12.72, 0.39, 89.47 and 9.13, respectively, with the corresponding standard deviation of 0.56, 0.08, 1.42 and 0.36. In all these
cases, the variation of the physico-chemical properties with operating
conditions is insignificant as almost 85% of the values fall with ± σ and
4.3. Membrane cleaning
The membrane resistance increases significantly from the nascent
membrane due to irreversible fouling. The membrane resistance varied
from 2.36 × 1012 to 2.51 × 1013 m−1. Also, the membrane resistance
remains almost constant after eight runs, suggesting saturation of irreversible fouling.
4.4. Microbial examination of raw and MF sugarcane juice
4.4.1. Total plate count
The microbial contamination of centrifuged sugarcane juice was
4.3 × 106 colonies per ml of juice. However, the microbial population
drastically reduced after microfiltration and the filtrate had counts of
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60
1
TMP=35 kPa
& 1: Re: 83
& 2: Re: 166
& 3: Re: 249
Symbol: Experimental
Solid Lines: Calculated
20
10
60
30
0
Permeate Flux (l/m2h)
90
10
20
30
40
Time (min)
50
10
160
120
80
40
5
0
0
10
20
30
40
50
0
10
20
30
40
50
60
70
80
80
40
0
300
1
Error bar: ± 10%
120
20
0
2
250
3
200
TMP=138 kPa
& 1: Re: 83
& 2: Re: 166
& 3:Re: 249
Symbol: Experimental
Solid Lines: Calculated
10
0
70
60
120
0
10
20
30
40
50
60
150
100
50
Gel layer thickness ( m)
200
3
15
TMP=69 kPa
& 1: Re= 83
& 2: Re: 166
& 3: Re: 249
Symbol: Experimental
Solid Lines: Calculated
160
Gel layer thickness ( m)
240
TMP=104 kPa
& 1: Re: 83
& 2: Re: 166
& 3: Re: 249
Symbol: Experimental
Solid Lines: Calculated
160
Time (min)
2
80
200
(d)
1
Error bar: ± 10%
2
3
10
0
280
100
1
Error bar: ± 10%
60
120
(c)
(b)
60
20
0
0
Permeate Flux (l/m2h)
Permeate Flux (l/m2h)
2
3
50
Gel layer thickness ( m)
Error bar: ± 10%
80
120
Gel layer thickness ( m)
(a)
Permeate Flux (l/m2h)
240
150
0
Time (min)
Time (min)
Calculated permeate flux (l/m2h)
10
-11
D1= (3.9±0.3) ×10
2
m /s
C1g= (65±0.5) g/l
8
= (3±0.2) ×10-3 l/g
6
+20%
(e)
4
-20%
2
0
0
2
4
6
8
10
Experimental permeate flux (l/m2h)
Fig. 6. Effect of (a) 35 kPa, (b) 69 kPa, (c) 104 kPa, (d) 138 kPa on the productivity of the membrane along with gel layer thickness and (e) validation of calculated
steady state flux with the experimental values.
2.7 × 101 CFU/ ml, achieving 5-log reduction which is common in case
of MF (Fauquant, Beaucher, Sinet, Robert, & Lopez, 2014). Most bacteria are in the size range of 0.5–100 μm. Hence, MF removes all the
bacteria from the feed stream and allows a very negligible part to pass
through it. Since, these bacteria are much larger in size than the
membrane average pore size (0.1 μm), they are placed together under
HMW contributing to the formation of gel layer. However, due to a
varied pore size distribution a negligible amount of microorganism is
found to be present in the permeate stream. There is a significant cutback in growth of microorganisms due to MF operation. Growth of
bacteria with whitish close patches or clusters was found in plates
having centrifuged juice. These close patches of bacterial colony growth
resemble the structure of Leuconostoc species. On the other hand, very
thinner strands of Leuconostoc slime growth were observed in the microscopic image of microfiltered juice sample. These bacteria are very
harmful and need to be removed, since they play dominant role in
causing microbial fermentation and biodegradation of sugarcane juice
by converting sucrose and fructose into exopolysaccarides like, dextran
and mannitol, respectively.
These results certainly reflect the rejection of the bacteria by MF
(0.1 μm) to a larger extent, hence reducing the chance of havoc created
by this bacteria through cane deterioration in sugar industry and
thereby, extensively ensuring the stability of the juice during storage
and crystallization.
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Table 2
Comparison of quality parameters among process conditions of microfiltration for optimization.
Sample
Total solids (%)
TSS (°Brix)
Color (abs)
Clarity (%T)
Turbidity (NTU)
Sucrose (g/l)
Total polyphenols (mg GAE/
100 ml)
Steady state flux (l/
m2∙h)
CJ⁎
19.8 ± 0.16
14.5 ± 0.01
2.31 ± 0.03
32.6 ± 0.66
20.2 ± 0.43
128 ± 4.2
17.28 ± 0.85
–
14.74 ± 0.16
14.69 ± 0.33
14.76 ± 0.16
14.66 ± 0.23
14.43 ± 0.23
14.79 ± 0.16
14.47 ± 0.33
14.37 ± 0.23
14.91 ± 0.33
14.40 ± 0.33
15.05 ± 0.16
15.49 ± 0.16
12.5 ± 0.02
12.6 ± 0.02
12.8 ± 0.06
12.4 ± 0.01
12.9 ± 0.06
13.0 ± 0.03
12.1 ± 0.02
13.2 ± 0.06
13.2 ± 0.06
11.4 ± 0.06
13.2 ± 0.02
13.3 ± 0.02
0.35 ± 0.02
0.35 ± 0.03
0.36 ± 0.03
0.31 ± 0.05
0.33 ± 0.05
0.38 ± 0.05
0.43 ± 0.02
0.32 ± 0.01
0.46 ± 0.02
0.37 ± 0.02
0.52 ± 0.03
0.53 ± 0.05
91.33 ± 0.33
90.79 ± 0.46
89.27 ± 0.26
87.11 ± 0.46
87.85 ± 0.26
88.62 ± 0.26
89.30 ± 0.67
91.68 ± 0.46
90.32 ± 0.33
90.34 ± 0.16
88.45 ± 0.16
88.61 ± 0.26
0.4 ± 0.02
0.5 ± 0.03
0.3 ± 0.03
0.6 ± 0.02
0.7 ± 0.03
0.7 ± 0.05
0.6 ± 0.05
0.3 ± 0.02
0.5 ± 0.05
0.4 ± 0.03
0.3 ± 0.02
0.5 ± 0.02
98.7 ± 1.9
99.2 ± 1.3
100.9 ± 1.3
101.7 ± 1.8
102.4 ± 1.9
104.2 ± 1.2
101.3 ± 2.2
102.3 ± 1.6
104.8 ± 2.6
104.4 ± 1.9
105.7 ± 1.6
108.7 ± 1.1
9.1 ± 0.33
9.16 ± 0.26
9.25 ± 0.26
9.04 ± 0.26
9.26 ± 0.13
9.35 ± 0.13
8.63 ± 0.26
9.36 ± 0.26
9.38 ± 0.49
8.22 ± 0.13
9.37 ± 0.16
9.39 ± 0.26
5.41 ± 0.06
5.6 ± 0.03
5.72 ± 0.05
5.65 ± 0.05
5.84 ± 0.03
5.97 ± 0.05
5.79 ± 0.05
5.89 ± 0.03
6.04 ± 0.02
5.87 ± 0.02
6.07 ± 0.02
6.23 ± 0.01
MFJ⁎
TMP
(kPa)
Re
35
35
35
69
69
69
104
104
104
138
138
138
94
182
288
94
182
288
94
182
288
94
182
288
⁎
CJ = Centrifuged Juice, MFJ = Microfiltered Juice.
were reported at 45 °C. Masse, Shu, Jegatheesan, Gros, and Phong
(2013) pretreated the sugarcane juice by liming to pH 7.5 followed by
screening using 250 mm and 150 mm mesh and then diluted the juice to
15°Brix. The resultant juice was subjected was subjected to ceramic
tubular membrane of average pore diameter 0.1 μm at 3 m/s cross flow
velocity at 60 °C and 100 kPa TMP. The average permeate flux was
reported as 46 l/m2∙h∙bar with 95% and 98% recovery of TSS and sucrose, respectively. Moreno et al. (2012) pretreated the sugarcane juice
by liming to pH 8 at 65 °C followed by coagulation by 60 mg/l polyaluminium sulfate. The supernatant juice was subjected to ceramic
tubular membrane of average pore size 0.4 μm at 35 °C and 200 kPa
TMP. The average permeate flux was 32 l/m2∙h∙bar and 83% and 80%
recovery of TSS and sucrose were reported.
The present work employed polyacrylonitrile (PAN) based 0.1-μm
average pore sized hollow fiber membrane to treat the centrifuged sugarcane juice. At 104 kPa TMP, 20 °C and 0.37 m/s cross flow velocity,
the steady state specific permeate flux was about 6 l/m2∙h∙bar that is
higher than the data at 25 °C and comparable with data at 45 °C reported by Rezzadori et al. (2014). Average flux of the present work
(10 l/m2∙h∙bar at 104 kPa TMP and 0.37 m/s) is less than those of Masse
et al. (2013) and Moreno et al. (2012) since there was extensive pretreatment of raw sugarcane juice carried out by those researcher
thereby improving the average permeate flux. Extent of recovery of TSS
in the present work is better than that of Moreno et al. (2012) and
comparable with Rezzadori et al. (2014) and Masse et al. (2013). Recovery of sucrose in present work is comparable with Moreno et al.
(2012).
Table 3
Detailed physical characteristics and nutritional parameters determined at the
optimized points.
Parameters
Centrifuged juice (CJ)
Microfiltered juice
(MFJ)
TS (%)
TSS (°Brix)
Color (abs value)
Clarity (%T)
Turbidity (NTU)
Viscosity (cP)
Titratable acidity (% citric
acid)
Vit C (mg ascorbic acid/
100 ml)
Total sugars (%)
Sucrose (%)
Reducing sugars (%)
Total polyphenols (mg GAE/
100 ml)
19.8 ± 0.16
14.5 ± 0.01
2.31 ± 0.03
32.6 ± 0.66
20.2 ± 0.43
1.19 ± 0.03
0.15 ± 0.05
14.91 ± 0.33
13.2 ± 0.06
0.46 ± 0.02
90.32 ± 0.33
0.5 ± 0.00
0.94 ± 0.003
0.12 ± 0.001
1.28 ± 0.032
1.08 ± 0.02
14.5 ± 0.26
12.8 ± 0.15
1.7 ± 0.04
17.28 ± 0.33
11.87 ± 0.4
10.48 ± 0.26
1.39 ± 0.01
9.38 ± 0.49
4.4.2. Yeast and mold count
The initial counts for yeast and mold in centrifuged sugarcane juice
were 6.6 × 104 CFU/ ml. However, the YMC reduced significantly (less
than 10 CFU/ ml) after microfiltration. Hence, it can be inferred that
the juice would remain quite safe and stable for long months if stored at
low temperature due to declined rate of fermentation owing to large
reduction in population of yeasts and molds.
4.5. Comparative study
5. Conclusions
Performance of MF of sugarcane juice in the present work is compared with some of the recent reports in this section. It may be noted
that researchers adopted different pretreatment techniques and conducted MF using various membranes (ceramic or polymeric) at different
operating conditions. Rezzadori et al. (2014) reported MF of sugarcane
juice using 0.4-μm average pore sized hollow fiber membrane. They
reported a steady state specific permeate flux of 8.2 l/m2∙h∙bar at 45 °C
and 4.6 l/m2∙h∙bar at 25 °C with cross flow velocity of 0.87 m/s and
200 kPa TMP. 95% and 99% recovery of total soluble solids and sucrose
Centrifuged sugarcane juice was clarified using hollow fiber MF. A
gel layer controlled model coupled with mass transfer boundary layer
was proposed from first principles to simulate the profiles of permeate
flux as well as sucrose concentration in permeate. The gel layer characteristics and other transport parameters were estimated by comparing
the simulated results with the experimental data. Sucrose was retained
partially by the gel layer. Model predictions showed, although gel layer
thickness increased significantly with TMP thereby increasing gel layer
resistance, increase in driving force resulted in more convection and
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C. Panigrahi et al.
(a)
Sucrose concentration in permeate (g/l)
Sucrose concentration in permeate (g/l)
130
1: Re: 94
2: Re: 182
3: Re: 288
TMP: 35 kPa
120
110
3
2
100
1
0
10
20
30
40
50
130
(b)
120
110
3
2
60
0
Sucrose concentration in permeate (g/l)
Sucrose concentration in permeate (g/l)
1: Re: 94
2: Re: 182
3: Re: 288
120
110
3
2
1
100
0
10
20
30
40
10
20
30
40
50
60
70
80
Time (min)
130
TMP: 104 kPa
1
100
Time (min)
(c)
1: Re: 94
2: Re: 182
3: Re: 288
TMP: 69 kPa
50
60
130
(d)
1: Re: 83
2: Re: 166
3: Re: 249
TMP: 138 kPa
120
3
110
2
1
100
70
0
Time (min)
10
20
30
40
50
60
Time (min)
Sucrose concentration (predicted) (g/l)
130
(e)
120
+10%
110
100
-10%
90
80
80
90
100
110
120
130
Sucrose concentration (experimental) (g/l)
Fig. 7. Predicted sucrose concentration profile in permeate at different TMP (a) 35 kPa, (b) 69 kPa, (c) 104 kPa and (d) 138 kPa (e) Validation of predicted sucrose
concentration with the experimental values.
derived at these particular conditions showed appreciable physical
characteristics, like, least solid content, high clarity, low turbidity, high
TSS with sufficient productivity. The developed model can, therefore,
be used as a predictive tool to design scaled up MF filtration system.
The current work is found to be an appropriate pre-clarification step
for further polished filtration of sugarcane juice aiming at longer shelflife.
almost evenly compensated the gel layer resistance leading to pressure
independent permeate flux.
Nutritional qualities of the centrifuged juice in terms of TSS, sucrose, vitamin C were retained in microfiltered permeate. Five log reduction of microbial load and four log reduction of yeast and mold
count were obtained by MF. The operating parameter of 104 kPa and Re
249 was selected as the optimum operating condition since, juice
102
Innovative Food Science and Emerging Technologies 49 (2018) 92–105
C. Panigrahi et al.
ρg
εg
γg
μ
μ0
μw
μb
πm
πp
ρ
T
Nomenclature
A
C1
C
C1b
C1g
C2p
C2m
C2m
d
D1
D2
H
Jp
k1
k2
L
N
Nexp
Q
Re
Rg
Rm
Rr2
S0
Sc
Sh
T
T
u0
vw
y
Effective membrane surface area, m2
Concentration of HMW solutes, kg/m3
Bulk concentration of solution, kg/m3
Bulk concentration of HMW solutes in bulk, kg/m3
Gel layer concentration of HMW solutes, kg/m3
Sucrose concentration in permeate, kg/m3
Membrane surface concentration of sugar, kg/m3
Bulk concentration of sugar, kg/m3
Inner diameter of the hollow fiber, m
Effective diffusivity of the HMW components in water, m2/s
Diffusivity of sugar, m2/s
Gel layer thickness, m
Permeate flux, m3/m2∙s
Film mass transfer coefficient of HMW components (D1/δ),
m/s
Mass transfer coefficient of sucrose, m/s
Length of the membrane module, m
Number of data points in jth experiment
Number of experiments
Volume of filtrate collected
Reynolds no, (ρu0d/μ)
Gel layer resistance, m−1
Membrane hydraulic resistance, m−1
Real retention of sugar
Sum of square of errors in Eq. (18 and 19)
Schmidt number (μ/ρD1)
Sherwood number (kd/D), Eq. (12)
Time, s−1
Temperature, K
Cross flow velocity inside a fiber, m/s
Steady state permeate flux, m3/m2∙s
Dimension normal to membrane surface, m
Abbreviation
Abs
CFR
CFU
CFV
DAE
FTIR
GAE
HCl
HF
HMW
LMW
MWCO
MF
NaOH
NTU
PAN
SEM
TMP
TS
TSS
UF
YMC
Greek symbols
α
α1
β
δ
σ
ΔP
Δπ
Δt
Gel layer density, kg/m3
Gel porosity
Partition coefficient of sugar
Viscosity of the permeating solution, Pa∙s
Viscosity of water, Pa∙s
Viscosity at the wall, Pa∙s
Viscosity of the bulk solution, Pa∙s
Osmotic pressure of the solution at the membrane surface, Pa
Osmotic pressure of the solution at the permeate side, Pa
Density of solution, kg/m3%
Percentage transmittance
Absorbance value
Cross flow velocity
Colony forming unit
Cross flow velocity
Differential Algebraic Equation
Fourier Transform Infrared Spectroscopy
Gallic acid equivalent
Hydrochloric acid
Hollow fiber
High molecular weight solute
Low molecular weight solute
Molecular weight cut off of the membrane
Microfiltration
Sodium hydroxide
Nephelometric Turbidity Unit
Polyacrylonitrile
Scanning electron microscopy
Transmembrane pressure
Total solid
Total soluble solids
Ultrafiltration
Yeast & mold count
Acknowledgement
Specific gel layer resistance, m/kg
Proportionality constant
Gel layer characteristics parameter, m−2
Mass transfer boundary layer thickness, m
Standard deviation
Transmembrane pressure, Pa
Osmotic pressure difference, Pa
Sampling time, s
This work is partially supported by a grant from the SRIC, IIT
Kharagpur under the scheme no. IIT/SRIC/CHE/SMU/2014-15/40,
dated 17-04-2014. The authors would also like to thank Mrs. Munmun
Mukherjee for her contribution in antibacterial study. Any opinions,
findings and conclusions expressed in this paper are those of the authors.
Appendix 1
A mass balance for the LMW solute in the concentration boundary layer gives,
vw C2p = vw C2 − D2
dC2
dy
(A1)
In the bulk, the boundary condition is,
at y = 0, C2 = C2b
(A2)
Solution of Eq. (A1), subject to the boundary condition, Eq. (A2) is,
C2 (y ) − C2p
v y
= exp ⎛ w ⎞
⎝ D2 ⎠
⎜
C2b − C2p
⎟
(A3)
A mass balance of LMW solute in the gel layer gives, for δ < y < δ + H,
vw C2p = vw C2 − εg D2
dC2
dy
(A4)
The boundary conditions for Eq. (A4) at the membrane surface is,
at y = δ + H , C2 = C2m
(A5)
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Innovative Food Science and Emerging Technologies 49 (2018) 92–105
C. Panigrahi et al.
The LMW solute gets adsorbed in the gel layer. Its concentration at the boundary layer and gel layer interface remains at equilibrium and is
dictated by the partition coefficient between the boundary and gel layer. Therefore, a linear relationship may be described as,
C2 (δ−) = γg C2 (δ +)
(A6)
where, γg is the partition coefficient of sucrose across the gel layer and mass transfer boundary layer. Solution of Eq. (A4) with boundary condition,
Eq. (A6) is,
v (y − δ ) ⎞ C2p (1 − γg ) + (C2b − C2p) exp(vw / k2 )
C2 (y ) − C2p = exp ⎜⎛ w
⎟ ×
γg
⎝ εg D 2 ⎠
(A7)
where, k2(=D2/δ) is the mass transfer coefficient for the LMW solute. Using the boundary condition Eq. (A5) we get,
C2p (1 − γg ) + (C2b − C2p) exp(vw / k2 )
v H
C2m − C2p = exp ⎜⎛ w ⎟⎞ ×
γg
⎝ εg D 2 ⎠
(A8)
Real retention (Rr2) of sucrose can be expressed as,
Rr 2 = 1 −
C2p
(A9)
C2m
Putting Eq. (A9) in Eq. (A8) and eliminating C2p we obtain, after rearrangement
C2m
( + ) ⎤⎦
=
γ R + (1 − R )(γ − 1) exp (
) + (1 − R ) exp ⎡⎣v ( + ) ⎤⎦
C2b exp ⎡vw
⎣
g
r2
r2
g
vw H
εg D 2
1
k2
H
εg D 2
r2
w
1
k2
H
εg D 2
(A10)
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