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Title: Department of Food Science and Technology University of Tuscia, Viterbo, Italy


1
Department of Food Science and Technology
University of Tuscia, Viterbo, Italy
Premio Lerici Udine, June, 20th, 2005
  • PhD Thesis in Food Biotechnology EXPERIMENTAL
    PROCEDURE
  • TO MODEL THE RECOVERY
  • OF SOME FERMENTATION PRODUCTS
  • BY ELECTRODIALYSIS

Marcello Fidaleo
(Tutor Mauro Moresi)
2
ED is a unit operation for the separation or
concentration of ions in solutions based upon
their selective electromigration through
semipermeable membranes under the influence of
a potential gradient
3
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4
These membranes are essentially sheets of
ion-exchange resins. The heterogeneous
membranes usually hold higher electrical
resistances and more uneven distribution of fixed
charges than the homogeneous ones.
5
These membranes allow intrusion and exchange
of COUNTER-IONS from an external source, but
exclusion of the co-ions.
The main characteristics of the commercially
available ion-exchange membranes are reported
on-line (htpp//phychem.kjist.ac.kr?312.pdf).
6
  • An ED system consists of the following items
  • ED stacks,
  • a D.C. generator,
  • pumps, piping, tanks,
  • measuring devices for P, T, pH, c, QV.

7
ED stacks can be subdivided into two basic types
8
ED stacks can be subdivided into two basic types
Ionics Inc. (Watertown, MA, US)
9
ED stacks can be subdivided into two basic types
Ionics Inc. (Watertown, MA, US)
Sheet-flow
10
ED stacks can be subdivided into two basic types
Sheet-flow
Astom Co. (Minato-Ku, J) Asahi Glass Eng. Co.
(Chiyoda-ku, J) Du Pont Co. (Fayetteville, NC, US)
Ionics Inc. (Watertown, MA, US)
11
The simplest ED stack arrangement is the batch
desalination process.
The solution is circulated through the stack from
a storage vessel until the desired degree of ion
depletion or enrichment is achieved. To prevent
scaling of carbonates and hydroxides, the pH in C
is controlled by automatic acid addition.
12

An ED process may be run in
  • the continuous single-passage
  • or
  • feed-and-bleed mode

13
Whatever the operating mode, an ED unit can
work with
CONSTANT or REVERSED POLARITY
The ED reversal process (EDR) was firstly
proposed by Ionics Inc. (Watertown, MA, US) in
the early 70s to minimise membrane fouling or
scaling as due to the organic or inorganic
substances present in brackish water during
desalination processes.
14
By inverting the polarities of the electrodes
periodically (2-4 times per h), and the hydraulic
flow streams, fouling or scaling constituents are
removed or re-dissolved in the NEXT CYCLE, when
the concentrating comp.s are reverted to the
diluting ones.
15
  • Aims of this PhD thesis

(1) To point out some critical aspects in ED
modelling with specific reference to the recovery
of some target electrolytic solutes sodium
acetate (Na-A) sodium lactate (Na-L)
from aqueous solutions. sodium propionate
(Na-P)
(2) To assess the really important process
engineering parameters useful to design
optimise ED units dedicated to the downstream
processing of acidic fermentation broths.
16
Present ED applications in the FOOD INDUSTRY
17
WHEY DEMINERALIZATION
The SERUM OF MILK is the major by-product of
cheese making (whey cheese ratio 9-11).
18
The optimum process for WHEY DEMINERALISATION
may combine EDR, IER NF.

HYBRID PROCESSES RECOMMENDED by EURODIA/AMERIDIA
19
WHEY DEMINERALIZATION PLANTS
Nestlé SA (Wyeth-Ayerst, CH) Bristol-Myers
Squibb.
Lactofrance (Baleycourt, F)
20
TARTRATE STABILIZATION OF WINE
TA (H2T) ? 1- 3 Grapes contain high levels
of g/l K ?
0.8-1.5 Tartaric acid is a weak dicarboxylic one
that dissociates into tartrate and bitartrate
forms H2T ? HT- H HT-
? T H It can precipitate as
THK (not very soluble) TCa (insoluble).
Both salt solubility of varies with T, pH,
alcohol content. Some wine components
(polysaccharides, mannoproteins) slow down the
precipitation process.
21
The effective use of ED for tartrate
stabilisation of wines is well established and
dates back to the tests performed by Paronetto as
early as 1941. Experiments had been more
systematically carried out since the 70s and have
given rise to the automatic method and device for
tartaric stabilization of wines developed by
Escudier et al. (1995) at the French National
Agronomic Research Institute (INRA) in
co-operation with Ameridia.
ED treatment has been recognized by the
International Wine Office (OIV) as a "good
manufacturing practice" and has been APPROVED for
commercial use by the EU regulatory
n 2053/97.
22
A unit for tartaric STABILIZATION of WINE
consists of an ED stack, with two tanks and
circulation pumps for the fluids (wine and brine)
in and out of the stack.
Tartaric wine stabilization plant (9 m3 h-1)
(Skalli, Sete, F).
23
For winery capacities up to 45,000 hl/yr the ED
unit is compact, can be installed on a truck and
moved to offer treatment services on rent from
vineyard to vineyard at less than c10 per
bottle.
24
FERMENTATION INDUSTRY
  • ED appears to be useful to recover
  • Microbial Electrolytic Metabolites that
  • inhibit microbial growth and/or metabolic
    activity
  • or
  • are dissolved in raw media difficult to purify.

25
  • DOWNSTREAM PROCESSING may consists of several
    operations
  • ? Liming to precipitate the metabolite as the
    calcium salt,
  • ? Washing the precipitate with water to remove
    soluble impurities,
  • ? Acidification via strong acids to convert the
    salt in its free acid form
  • ? Demineralisation of the acidic liquor using
    IERs,
  • ? Decolourisation using active carbons,
  • ? Concentration under vacuum,
  • ? Crystallisation.

Since the use of ED simplifies such a complex
sequence of recovery techniques, ED is generally
regarded as an environmentally-friendly
alternative to the conventional bioproduct
recovery processes.
26
POTENTIAL APPLICATIONS of ED to recover microbial
metabolites from fermentation media
27
  • MATHEMATICAL MODELLING

To DESIGN or OPTIMISE an ED process SEVERAL
PARAMETERS are to be take into account, namely
? STACK construction and SPACER configuration,
? OPERATION mode, ? MEMBRANE
perm-selectivity, ? FEED and PRODUCT
concentration, ? FLOW velocities, ? CURRENT
density VOLTAGE applied to the
electrodes, ? RECOVERY rates, etc.
28
The MAXWELL-STEFAN (MS) EQUATION represents the
simplest mathematical tool for linking the flux
of a generic species through the membrane with
its interfacial concentrations at the membrane
left- and right-sides, with the external
electrical voltage applied to the ED electrodes
(Krishna Wesselingh, 1997).
29
The main bottleneck in the application of the
MS-based mass transfer model to ED processes is
the lack of available diffusivities either in
the free solution or membrane phase and
thermodynamic properties.
30
(Yen Cheryan, 1993 Boniardi et al., 1997
Lee et al., 1998 Bailly et al., 2001 Nikonenko
et al., 2002 Fidaleo Moresi, 2004 Ibanez et
al. 2004)
The main advantage of NP equation is that it
contains two terms expressing the contribution of
diffusion and electro-migration. in
31
THE BASIC MATHEMATICAL MODEL CONSISTS OF
  • WATER SOLUTE MASS BALANCES
  • WATER SOLUTE MASS TRANSFER EQUATIONS
  • VOLTAGE EQUATION FOR THE ED LOOP CONCERNED.

32
FLOW DIAGRAM for an ED unit, simplified
concentration profiles in an ED cell pair the
analogous electrical circuit.
33
NP-based mathematical modeling of an ED stack
34
The OHMIC RESISTANCES of the BULK SOLUTIONS in
the concentrating (C), diluting (D), or electrode
rinsing solution (ERS) compartment can be
ESTIMATED via the 2nd Ohms law
35
Experimental procedure set up for parameter
identification.
36
Experimental apparatus
PVC thank
ED stack
Electrodialyzer Aqualyzer P1 (Corning EIVS)
Graphite electrodes
AMV and CMV membranes (Asahi Glass)
Direct current generator (0-5 A, 0-60 V)
37
This procedure also involved a sequential
assessment of several physical properties of the
salt solutions undergoing ED processing, that is
  • density,
  • viscosity,
  • osmotic pressure,
  • electric conductivity,
  • mean molal activity coeff.,
  • diffusivity

via the open literature or direct measurements.
38
Conductivity measurements

-
39

-
40
  • ZERO-CURRENT
  • LEACHING, OSMOSIS DIALYSIS TESTS

Net increment or decrement in water mass (DnWk)
in C or D tank vs. time (q) at different DcB
?,? ? 1.28 kmol m-3 ?, ? ? 0.71 ?,
? ? 0.29
C/D (closed/open symbols)
41
  • ZERO-CURRENT
  • LEACHING, OSMOSIS DIALYSIS TESTS

Net increment or decrement in solute mass (DnBC)
in C or D tank vs. time (q) under different DcB
Net increment or decrement in water mass (DnWk)
in C or D tank vs. time (q) at different DcB
?,? ? 1.28 kmol m-3 ?, ? ? 0.71 ?,
? ? 0.29
?, ? ? 1.32 kmol m-3 ?, ? ? 0.41 ?,
? ? 0.23
C/D (closed/open symbols)
42
The contribution of solute diffusion (LB) at zero
current was of the same order of magnitude of the
experimental error and can be regarded as
negligible with respect to that of
electro-migration. LB ?0 The contribution of
solvent diffusion (LW) tended to grow as the
solute concentration difference at the membrane
sides increased or current density was reduced.
LW ? 0 unless a min deviation between the
exp. and calc. solute concentrations in C at the
end of ED recovery processes performed at low
current densities is searched for.
43
  • ELECTRO-OSMOSIS TESTS
  • DESALINATION TESTS

I1 A
I1 A
Water mass increment Solute mass
increment
were linear function of the ideal number of
solute moles transferred ( ) and
independent of current intensity
44
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45
iv) CURRENT-VOLTAGE TESTS

-





c c c
A single type of membranes is installed (Nm19,
N9).
Potential difference across the stack is measured
by varying I (0-5 A) at different levels of -
Superficial velocity (v) 3-9
cm/s - Electrolyte concentration (c)
0.02-0.05 M
46
Current-voltage relationship generally exhibits
a typical 3-region pattern. 1) E ? I (ohmic
region) As E increases, the solute
concentration at the membrane surface reduces. As
it falls to zero the E vs. I plot exhibits a
first deviation from the linear trend. 2)
Plateau region DE yields a smaller
DI 3) Over-limiting region as E is increased, I
tends to increase again In conventional ED
stacks, as the limiting current is exceeded, the
apparent resistance of the cell rises sharply,
the pH of the dilute falls, the pH of the
concentrate increases, the Coulomb efficiency
falls.
47
Voltage-current curves
Na-L
  • By correlating E vs. I via the least squares
    method for any cB vS, it was possible to
    estimate
  • the resistance of the stack (RS)
  • - electrode potential (Eel).

48
Voltage-current curves
Na-L
If RMP is independent of vS in any compartment,
it is an indirect confirmation of negligible
polarisation effects.
For all trials examined Eel ? 2.20.3 V.
49
Voltage-current curves
Na-L
As cB reduces, RMP increases
50
Cowan and Brown plot
Ilimit f(cB,vS) RMP f(cB)
RMP ? the intercept of the straight line Eel
? the slope.
51
Effect of the bulk solute concentration (cB) on
Ilima (open symbols) Ilim,c (closed symbols)
at different vS values
?,? 3.4 cm s-1 ?, ? 4.3 ?, ? 5.1
?, ? 5.9
52
For dconst vS const, the ratio between these
limiting current intensities or densities becomes
53
Neglecting polarization effects we have
RMP vs. (1/?)
vS 3 cm/s
Main results of limiting current tests for NaA
(?, ?), NaL (?, ? ) and NaP (?,?) referred to c
or a membranes (closed or open symbols)
54
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55
  • The membrane surface area (ame) effectively
    utilised was found to be
  • about 2/3 of the geometrical one
  • just 10 greater than the exposed surface area
    of electrodes.

This confirmed the general rule that recommends
to provide the electrodes with bases with the
highest degree of open area in the direction
perpendicular to the membrane faces so as to
maximise utilisation of membrane area minimise
the electrical resistance of stack.
56
Mass transfer coefficient estimation
Knowledge of the effective membrane surface area
(ame) allows the mass transfer coefficient
kmDB/d to be estimated from Cowan Brown
definition of limiting current density as a
function of Q, cB and type of electro-membrane
used
57
Effect of Re on the ratio Sh/Sc1/3 referred to ED
stacks composed of anionic (?) or cationic (?)
membranes.

(Sonin Isaacson,1974)
(Kraaijeveld et al., 1995)
(Kuroda et al., 1983)
(Moresi Fidaleo, 2005)
58
v) VALIDATION TESTS
The contribution of solute polarisation, namely
the electric resistance (Rf) junction
potential difference (Ej) across any boundary
layer, was found to be negligible. The
Donnan potential difference (ED) in any cell
pair, which behaves as a direct current generator
with inverted polarities with respect to those of
the external DC generator, has to be accounted
for as DcB at both sides of the anionic and
cationic membranes increases
59
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60
CONCLUSIONS
Thanks to the aforementioned 5-step experimental
procedure, the overall mathematical model here
developed allowed basic ED phenomena, such as
LIMITING CURRENT DENSITY, DIFFUSION OHMIC
POTENTIALS.
to be simulated accurately up to NaCl or organic
acid concentrations of about 1.7 or 1.2 kmol
m-3, respectively
61
PRESENT PROBLEMS FUTURE PROSPECTS
  • The present ED industry has experienced a steady
    GROWTH rate of about 15 since 15 years.
  • Although ED PROCESSING POTENTIALITIES are
    numerous, ED APPLICATION is still too marginally
    extended to the FOOD INDUSTRY.

What are the REASONS for such a SCARCE
DIFFUSION?
62
  • There are a number of PROBLEMS that undoubtedly
    LIMIT
  • ELECTRO-MEMBRANE SALES
  • MEMBRANE fouling PROBLEMS,
  • DESIGN considerations,
  • CLEANABILITY,
  • invest. membr. replacement COSTS,
  • competing TECHNOLOGIES (NF IER).

63
  • THE INCOMPLETE COMPREHENSION
  • OF MASS TRANSFER MECHANISMS
  • IN MEMBRANE SYSTEMS
  • MAKES DIFFICULT THE DESIGN OF
  • MEMBRANE PLANTS
  • AND HAMPER THEIR DIFFUSION.

64
  • By tradition, the
  • TECHNICAL PROGRESS
  • of FOOD INDUSTRY
  • has generally proceeded quite slowly
  • with 20-30 year delay
  • with respect to that of
  • the chemical and pharmaceutical industries
    (Cantarelli, 1987).

65
  • To overcome such PROBLEMS,
  • long-term lab- and pilot-scale experiments are
    NEEDED
  • to assess the membrane process PERFORMANCE
    RELIABILITY.

66
  • For instance, in the food biotechnology sector
    ED applications are still in their infancy.
  • Practically none of the processes
  • studied in laboratory- and pilot-scales
  • have been converted into industrial realities,
    except for the recovery of Na-L from clarified
    fermentation broths.

67
  • This means that ED processing potentialities have
    not been completely exploited so far probably
    because of
  • the high specific electro-membrane costs or
  • their short lifetime.

68
  • Thus, any attempt
  • to enhance ion mobility through the ED
    membranes
  • or
  • to extend their service life
  • 1) would minimise the overall surface of ED
    membranes to be installed (thus reducing plant
    investment and maintenance costs)
  • 2) would ensure further growth beyond
    desalination and salt production foster ED
    applications in the food sector, as well as in
    the chemical, pharmaceutical municipal
    effluent treatment areas.

69



T
  • hank you for your attention

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