JOURNÉES INTERNATIONALES
D'ÉTUDE
SALT REMOVAL FROM GROUNDWATER USING
REVERSE OSMOSIS
Technico-financialfeasïbility study Primeur NV, Sint-Eloois-Vijve
Steve Eeckhoudt - Luc Cosyns
LABORELEC
1. PREAMBLE
In thé early 80' s Primeur NV was created for the freezing of
fresh vegetables. Until then, thé buildings were used as
chick slaughterhouse and as deep freeze storage for butter
and méat. In 1983 a new production hall was erected and
thé required machines were bought.
lime in order to remove the carbonates. Then HQ and a
phosphate conditioning product are injected. The flow-rate
of the make-up i s 5 m 3 /h and the average blow-of f I,5m 3 /h.
The yearly consumption, including blow-off decarbonatation, amounts to nearly 36.000 m3. The pre-treatment and
conditioning products cost 680.000 BEF/year.
Primeur NV, as a vegetable processing company, did not
develop well at ail and after about three years it was sold to
MM. Guy and Luc Van Den Broeke, owners of Van Den
Broeke-Lutosa, a deep freeze products company located at
Leuze, in thé Hainault région.
As a result of the initial high sait concentration of the
g r o u n d w.artumerous blow-offs are necessary as shown
by the data above. A large number of blow-offs not only
means a high water consumption, but also a large energ y
consumption and a large consumption of chemicals.
Early 1989 machines were installed for Ihe production of
pre-fried and deep frozen chips. By the end of August
production started with a chips line capacity of 9 tons/hour.
In 1995 nearly 40.000 tons of deep frozen chips were
produced.
The staff of Primeur NV presently amounts to 70 employées
working in a 3-shifts System from Sunday until Friday night.
Figure l shows Ihe composition of the groundwater. It is
characterised by a limited présence of calcium and magne sium. The dominant cation is sodium while the dominant
anion is chlorine. The lime decarbonatation does not
influence the chlorine content : that explains why a high
blow-off rate is required.
Besides investments in thé machine park, substantial
environmental investments were made in récent years,
focusing more especially on waste water recycling and
prevention of stench.
Parameter
Na +
K+
Ca+
Mg++
Within this framework, an alternative solution enabling
réduction of the groundwater consumption was also
searched for. Having good contacts with Inter gem, Primeur
NV contacted Laborelec, the Belgian laboratory of the
electricity sector, witii long term expérience with rational
use of water.
ciso42HCO3SiO2
TDS
PH
2. DEFINITION OF THE PROBLEM
Like in most industries, water here also is used for several
purposes, e.g. for cooling (deep-freeze) installations, as
supply water for low pressure boilers and as process fluid.
Primeur NV pumps up the water with a flow-rate of 70.000
rrf/year essentlally as supply water for a 15 bar steam boiler
and for a cooling circuit.
The flow-rate of the make-up water of Ihis cooling circuit
amounts to 5 m 3 /h, half of which being drained as déconcentration blow-off (= 2,5 m3/h). The yearly consumption of
Ihis circuit is nearly 30.000 m3. As to avoid deposits and
corrosion of the heat exchangers, the water is treated with an
organic inhibitor, costing about 300.000 BEF/year.
For the boiler supply, the well water is firstly treated with
Concentration (in mg/1)
288
10
3
1
200
76
354
5
937
8,4
Fig. l - groundwater composition
3. TECHNICAL FEASIBILITY STUDY
It was decided to purify the pumped up water using an
adequate membrane technique in order to reduce the water
consumption. A bette r quality will indeed allo w to a dopt
much higher concentration factors.
132
L'EAU ET LES TECHNIQUES MEMBRANAIRES
Firstly thé two membrane techniques that enable sait
removal from thé groundwater were comparée : reverse
osmosis and electrodialysis.
REVERSE OSMOSIS
'Osmosis' is the transfer of a solvent (in most cases water)
through a semi-perméable membrane owing to a concentra tion gradient. The solvent will always migrate towards thé
solution with thé highest concentration. That générâtes in
thé solution with thé highest concentration a hydrostatic
pressure, thé so-called osmoticpressure.
In thé case of 'reverse' osmosis a pressure EXCEEDING thé
osmotic pressure will be applied on thé solution with thé
highest concentration; that will reverse thé solvent transfer .
A pure solvent flows from thé 'dirty solution' towards thé
'pure solution'. Figure 2 shows thé ope rating principle of
this pressure-driven purification process.
-4-5 avril 2000
After some small-scale pilot tests and computer simulations,
itbecame obvious that, comparing with electrodialysis,
reverse osmosis is a more adéquate technique for purification of this spécifie groundwater . This is clearly shown by
figure 4 that compares both techniques.
Referring to the results of the analysis, reverse osmosis
allows up to 30 % groundwater savings; electrodialysis only
9 %. Additionally reverse osmosis will also require less
enegy and chemicals as it provides a purer permeate.
Besides thé recovery is also higher.
Another significant element : using reverse osmosis, thé
enegry consumption for thé purification process itself is
significantly smaller.
It was decided to start a feasibility study on thé Primeur NV
site, using a reverse osmosis pilot plant.
The purpose of such a study is to corroborate the first test
results and, referring tothem, to détermine thé financial
feasibility.
Financial feasibility means, among other things :
ELECTRODIALYSIS
Hère charged membranes are used. They allow passage of
particles either with a positive charge (cation membranes),
either witii a négative charge (anion membranes). W hen
these membranes are submitted in turn to an electric field,
the ions of thé liquid to be treated will be moved (migration
towards anode or cathode). As ion-sélective membranes are
used hère, we become on one hand concenîrated areas and
on the other hand diluîed zones. Figure 3 shows thé opéra ting principle of electrodialysis. Hère thé sait ions are
concentrated in a volume as small as possible.
• calculation of groundwater savings;
• calculation of lowered ener gy consumption (pumping up
of groundwater, gain through reduced gas consumption as
a resuit of reduced boiler blow-off);
• estimation of réduction of conditioning chemicals;
4. TECHNICAL FEASIBILITY STUDY ON PRIMEUR
NV SITE
The plant used when starting the test campaign on thé
1)
K D -m prnh r »n r-
2) ' H : thé osmotic pressure'
HP pump
3) rêva rw wsmosis
Fig. 2 - operating principle reverse osmosis
133
JOURNÉES INTERNATIONALES
D'ÉTUDE
\
KM
VI
AM
1
KM
Fig. 3 - Operating principle electrodialysis.
Measured
Groundwater
Groundwater
parameters
after HC1mjection
Reverse osmosis
Concentrate
Permeate
Electrodialysis
Concentrate
Purified
8,4
5,88
6,7
4,7
6,4
solution
5,5
288
288
1942
16,5
1100
85
3
3
20
0,1
13
1
HCO3-
354
83
560
5,2
277
35
ciso42-
200
363
2485
21,8
1406
102
76
76
412
2,2
312
17
pH
Na
+
Ca++
Required groundwater flow-rate (without RO/ED)
(in m 3 /hour)
10
10
Required purified process water flow-rate
(in m 3 /hour)
6
6
7
(= - 30 %)
9,1
(= - 9 %)
6,5
7,3
93%
80%
0,15-0,2
0,7
0,2 -0,3
0,6
8
18,3
Required groundwater flow-rate (with RO/ED)
(in m 3 /hour)
Purified process water flow-rate (in m3/hour)
RECOVERY
3
Blow-off boiler water (in m /hour)
3
Blow-off cooling water (in m /hour)
Required electric power (in kW)
Fig.4 - Analysis results : comparison reverse osmosis - electrodialysis.
134
L'EAU ET LES TECHNIQUES MEMBRANAIRES
Primeur NV site is a Rochem reverse osmosis module with
membranes in a disk tube System. The automatic setting
value of thé permeate flow-rate is about 1001/hour.
The tests were per f or nie d, referring to thé pr élimina ry lab
study and thé computer simulations. Test one was
performed with 88,5 % recovery, raised up to 94,5 % during
test two. This resulted in a SiO 2 and CaF2 deposit. Bef ore
starting test three with a 80 % recovery (new computer
calculation taking into account the présence of fluorides),
the membranes had to be cleaned.
In order to prevent CaC03 deposits HC1 was injected during
ail tests.
4.1. TEST 1 : RECOVERY = 88,5 %
During Hiis initial test; 88,5 % recovery is obtained The average
permeate flow-rate is 1071/hour. 7 hourslong a permeate having
a lOOupto 130//S/cm conductivityisproduced.
S i Q-analyses show that, on the average, 760 mg/1 Si02
are introduced by thé supply flow-rate. As maximum 392
mg/1 Si02 are blown-off (via permeate and concentrate),
it is obvious that thé remaining part is left in the
membrane module.
That might explain thé small pressure rise from 38 up to 41
bar due to SiO2 deposits on thé membranes.
which me an s a deposit is built on thé membranes. That
explains once again thé pressure rise from 39 up to 46 bar
during thé tests. After tins test, thé membranes hâve to be
cleaned before starting a third test.
4.3. TEST 3 : RECOVERY = 80 %
A new computer simulation taking into account the présence
of fluorides and sulphates gives a 80 % recovery. The
average permeate flow-rate is now 107 1/hour. During more
than 48 hours a permeate with a conductivity ranging
between 80 and 90 piSIcm is produced.
The pressure is constant at an average value of 39 bars. This
is a clear indication for thé absence of deposit of the présent
salts and minerais on thé membranes. This is corroborated
by thé analyses on SiO 2 , fluorides and sulphates. The mass
balances are perfectly equilibrated.
It can be assumed that thé operating conditions of test 3
are appropriate for sait removal from groundwater at
induslrial scale.
Considering on one hand the present situation and, on the
other hand, the operating conditions of test 3, a financial
calculation is operated in order to verify the possible annual
gain such water processing might generale for the company.
That calculation is detailed hereafter.
Figure 5 below shows thé membrane configuration of the
first test.
5. FINANCIAL FEASIBILITY STUDY
As to enable Primeur NV to décide, on an economically
justified basis, wilh regard to a possible invesiment for a
reverse osmosis plant, Laborelec calculated the annual
savings on energy, water and chemicals consumption.
4.2. TEST 2 : RECOVERY = 94,5 %
During thé second test thé recovery is raised up to 94,5 %.
The average permeate flow-rate is 1051/hour . 8 hours long
there is a permeate production with a conductivity ranging
between 130 and 230 |/S/cm.
5.1. REDUCED WATER CONSUMPTION
The analyses performed on Si02, fluorides and sulphates
clearly show that thé mass balances are not in equilibrium,
concerrtraite
uuti
As the cooling circuit and the boiler will be supplied with
higher quality water, significantly less blow-offs will be
pH-regulaflon
I
return
3331/Ti
-4-5 avril 2000
-Hn—
teed
121 y
buffer tank
parnwate
necmrery:
=88,6^4
Fig. 5 - membrane configuration initial test on site.
135
JOURNÉES INTERNATIONALES
D'ÉTUDE
required in order to prevent sait deposits.
On an annual basis this means savings of about 32.000 BEF.
Practically it can be assumed that for a boiler the concentra tion factor can be raised from 3,3 up to 20 when taking into
account the permeate quality for a 80 % recovery. The
limiting factor in this case is the maximum chlorine content.
Hère the assumption i s :
• pump efficiency, ducts = 75 %
• approximate kWh priée = 3 BEF
• pumping height groundwater = 250 m
In the cooling water circuit thé concentration factor can be
raised from 2 up to 10, without risk of deposits and precipi talion on the heat exchangers.
As less blow-of fs will be required, for a low pressure steam
boiler less energy will be removed from thé process.
Figure 6 shows thé required blow-of f in thé cooling and thé
boiler circuit as to reach respective concentration factors of
9,33 and 18,5.
Considering the date above the achievable annual groundwater savings can be calculated.
Figure 7 shows the water consumption.
5.2. REDUCED ENERGY CONSUMPTION
The pre-treatment of groundwater by means of reverse
osmosis will resuit in two types of energy savings :
5.2.2. SAVINGS ON BOILER GAS CONSUMPTION
That means on an annual basis savings of about91 0.00(
BEF.
Hère thé assumption i s :
•
•
•
•
•
boiler efficiency = 90 %
gas priée = 5 BEF/Nm3
indicative energy content gas = 36 MJ/Nm3
gain on boiler blow-of f =1,3 m 3 /uur
supply water température = 50 °C
5.3. REDUCED CHEMICALS CONSUMPTION
5.2.1. SAVINGS ON PUMP ENERGY
FirsUy 11.700 m3/yea r less groundwater ha s to be pumpedup.
As thé number of blow-of fs is reduced, both in thé cooling
and in Ihe boiler water circuit, less conditioning chemicals
rewvciy
; l» %
c-oollnq
Fig. 6-Diagram water and blow-off'flow-rates
when implementing reverse osmosis.
After RO implementation
(inm 3 /year)
26.640
Concentration factor
Steam boiler circuit
Without RO
(inm 3 /year)
36.000
Cooling water circuit
30.000
16.800
Cf=18,5
20 % rétention
Total
0
10.860
66.000
54.300
Cf = 9,33
1 1.700 m3/year (= - 17,7 %; net gain)
Gain
3
22.560 m /year (= - 34,2 %; when retentate is reused for production/transport)
Fig. 7 - Calculation gain on groundwater consumption.
136
L'EAU ET LES TECHNIQUES MEMBRANAIRES
Without RO
(in BEF/year)
After RO implementation
(in BEF/year)
680.000
300.000
30.000
46.000
0
93.000
Steam boiler circuit
Cooling water circuit
HC1 injection
Total
980.000
-4-5 avril 2000
169.000
Annual savings
811, ,000 BEF/year
Fig. 8 - Savings through reduced chemicds consumption.
September-October 1995
(no RO)
September-October 1996
(after 3 months RO)
3.090 rrf/month
1.900 rrf/month
Water consumption
(for steam production)
(= - 39 %)
Water consumption
(for cooling water circuit)
3.200 rrf/month
1.400 rrf/month
(=-55%)
Fig. 9 - Reduced water consumption in practice.
will be removed from thé production process.
consumption were also achieved.
Figure 8 below shows thé potential annual savings.
Reverse osmosis offers also another, by yet not mentioned,
advantage : thé production of stérile water, which is very
important in thé food industry.
In brief it can be assumed that, when implementing reverse
osmosis, on an annual basis :
• 11.700 m3 less groundwater has to be pumped up;
• 1.753.000 BEF can be saved by a smaller energy and
chemicals production.
Taking into account an average investment cost, thé payback time of such plant is f or 2 years.
6. FOLLOW-UP CUSTOMER
Primeur NV was very satisfied with thé performed feasibi lity tests and, consequently, in 1996 decidedto make Hie
investment. A reverse osmosis plant with a flow-rate of 10
m3/hour and a recovery of nearly 80 % was bought.
Three months after thé commissioning thé positive impact
of thé reverse osmosis treatment was already évident.
Figure 9 shows thé practically achieved savings on thé
water consumption.
The by Laborelec alleged savings on chemicals and ener gy
137
7. CONCLUSION
Referring to a contact with Primeur NV in 1999 they were
still very satisfied with thé correct opération of the module.
This study shows that feasibility studies have ef fectively an
added value for thé industrial customer as they allow to
décide on an economically justified basis whether an investment will be made.
At the same time, it was shown that for sait removal from
some water types (groundwater, but also main water and
surface water after an adéquate pre-treatment), membrane
technology, and more especially reverse osmosis, is a highly
recommended technique.
Taking into account always more sévère environmental
régulations and increasing efficiency of this technology, thé
number of economically feasible applications will certainly
increase in thé future ...