JOURNÉES INTERNATIONALES D'ÉTUDE

SALT REMOVAL FROM GROUNDWATER USINGREVERSE OSMOSIS

Technico-financialfeasïbility study Primeur NV, Sint-Eloois-VijveSteve Eeckhoudt - Luc Cosyns LABORELEC

1. PREAMBLE

In thé early 80' s Primeur NV was created for the freezing offresh vegetables. Until then, thé buildings were used aschick slaughterhouse and as deep freeze storage for butterand méat. In 1983 a new production hall was erected andthé required machines were bought.

Primeur NV, as a vegetable processing company, did notdevelop well at ail and after about three years it was sold toMM. Guy and Luc Van Den Broeke, owners of Van DenBroeke-Lutosa, a deep freeze products company located atLeuze, in thé Hainault région.

Early 1989 machines were installed for Ihe production ofpre-fried and deep frozen chips. By the end of Augustproduction started with a chips line capacity of 9 tons/hour.

In 1995 nearly 40.000 tons of deep frozen chips wereproduced.

The staff of Primeur NV presently amounts to 70 employéesworking in a 3-shifts System from Sunday until Friday night.

Besides investments in thé machine park, substantialenvironmental investments were made in récent years,focusing more especially on waste water recycling andprevention of stench.

Within this framework, an alternative solution enablingréduction of the groundwater consumption was alsosearched for. Having good contacts with Inter gem, PrimeurNV contacted Laborelec, the Belgian laboratory of theelectricity sector, witii long term expérience with rationaluse of water.

2. DEFINITION OF THE PROBLEM

Like in most industries, water here also is used for severalpurposes, e.g. for cooling (deep-freeze) installations, assupply water for low pressure boilers and as process fluid.Primeur NV pumps up the water with a flow-rate of 70.000rrf/year essentlally as supply water for a 15 bar steam boilerand for a cooling circuit.

The flow-rate of the make-up water of Ihis cooling circuitamounts to 5 m3/h, half of which being drained as déconcen-tration blow-off (= 2,5 m3/h). The yearly consumption ofIhis circuit is nearly 30.000 m3. As to avoid deposits andcorrosion of the heat exchangers, the water is treated with anorganic inhibitor, costing about 300.000 BEF/year.

For the boiler supply, the well water is firstly treated with

lime in order to remove the carbonates. Then HQ and aphosphate conditioning product are injected. The flow-rateof the make-up i s 5 m 3 /h and the average blow-of f I,5m3/h.The yearly consumption, including blow-off decarbonata-tion, amounts to nearly 36.000 m3. The pre-treatment andconditioning products cost 680.000 BEF/year.

As a result of the initial high sait concentration of theg r o u n d w.artumerous blow-offs are necessary as shownby the data above. A large number of blow-offs not onlymeans a high water consumption, but also a large energ yconsumption and a large consumption of chemicals.

Figure l shows Ihe composition of the groundwater. It ischaracterised by a limited présence of calcium and magne -sium. The dominant cation is sodium while the dominantanion is chlorine. The lime decarbonatation does notinfluence the chlorine content : that explains why a highblow-off rate is required.

Parameter Concentration (in mg/1)Na+

K+

Ca+

Mg++

ci-so4

2-HCO3-SiO2

TDSPH

288

1031

200

763545

9378,4

Fig. l - groundwater composition

3. TECHNICAL FEASIBILITY STUDY

It was decided to purify the pumped up water using anadequate membrane technique in order to reduce the waterconsumption. A bette r quality will indeed allo w to a doptmuch higher concentration factors.

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L'EAU ET LES TECHNIQUES MEMBRANAIRES -4-5 avril 2000

Firstly thé two membrane techniques that enable saitremoval from thé groundwater were comparée : reverseosmosis 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 thésolution with thé highest concentration. That générâtes inthé solution with thé highest concentration a hydrostaticpressure, thé so-called osmoticpressure.

In thé case of 'reverse' osmosis a pressure EXCEEDING théosmotic pressure will be applied on thé solution with théhighest 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 ofthis pressure-driven purification process.

ELECTRODIALYSIS

Hère charged membranes are used. They allow passage ofparticles either with a positive charge (cation membranes),either witii a négative charge (anion membranes). W henthese membranes are submitted in turn to an electric field,the ions of thé liquid to be treated will be moved (migrationtowards anode or cathode). As ion-sélective membranes areused hère, we become on one hand concenîrated areas andon the other hand diluîed zones. Figure 3 shows thé opéra -ting principle of electrodialysis. Hère thé sait ions areconcentrated in a volume as small as possible.

After some small-scale pilot tests and computer simulations,itbecame obvious that, comparing with electrodialysis,reverse osmosis is a more adéquate technique for purifica-tion of this spécifie groundwater . This is clearly shown byfigure 4 that compares both techniques.

Referring to the results of the analysis, reverse osmosisallows up to 30 % groundwater savings; electrodialysis only9 %. Additionally reverse osmosis will also require lessenegy and chemicals as it provides a purer permeate.Besides thé recovery is also higher.

Another significant element : using reverse osmosis, théenegry consumption for thé purification process itself issignificantly smaller.

It was decided to start a feasibility study on thé Primeur NVsite, using a reverse osmosis pilot plant.

The purpose of such a study is to corroborate the first testresults and, referring tothem, to détermine thé financialfeasibility.

Financial feasibility means, among other things :

• calculation of groundwater savings;

• calculation of lowered ener gy consumption (pumping upof groundwater, gain through reduced gas consumption asa resuit of reduced boiler blow-off);

• estimation of réduction of conditioning chemicals;

4. TECHNICAL FEASIBILITY STUDY ON PRIMEURNV SITE

The plant used when starting the test campaign on thé

1)

2) ' H : thé osmotic pressure'

3) rêva rw wsmosis

K D -m prnh r »n r-

HP pump

Fig. 2 - operating principle reverse osmosis

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JOURNÉES INTERNATIONALES D'ÉTUDE

VI KM \ AM 1 KM

Fig. 3 - Operating principle electrodialysis.

Measured

parameters

pH

Na+

Ca++

HCO3-

ci-so4

2-

Groundwater

8,4

288

3

354

200

76

Groundwater

after HC1-mjection

5,88

288

3

83

363

76

Required groundwater flow-rate (without RO/ED)

(in m3/hour)

Required purified process water flow-rate

(in m3/hour)

Required groundwater flow-rate (with RO/ED)

(in m3/hour)

Purified process water flow-rate (in m3/hour)

RECOVERY

Blow-off boiler water (in m3/hour)

Blow-off cooling water (in m3/hour)

Required electric power (in kW)

Reverse osmosis

Concentrate

6,7

1942

20

560

2485

412

Permeate

4,7

16,5

0,1

5,2

21,8

2,2

10

6

7

(= - 30 %)

6,5

93%

0,15-0,2

0,2 -0,3

8

Electrodialysis

Concentrate

6,4

1100

13

277

1406

312

Purified

solution

5,5

85

1

35

102

17

10

6

9,1

(= - 9 %)

7,3

80%

0,7

0,6

18,3

Fig.4 - Analysis results : comparison reverse osmosis - electrodialysis.

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L'EAU ET LES TECHNIQUES MEMBRANAIRES -4-5 avril 2000

Primeur NV site is a Rochem reverse osmosis module withmembranes in a disk tube System. The automatic settingvalue of thé permeate flow-rate is about 1001/hour.

The tests were per f or nie d, referring to thé pr élimina ry labstudy and thé computer simulations. Test one wasperformed with 88,5 % recovery, raised up to 94,5 % duringtest two. This resulted in a SiO 2 and CaF2 deposit. Bef orestarting test three with a 80 % recovery (new computercalculation taking into account the présence of fluorides),the membranes had to be cleaned.

In order to prevent CaC03 deposits HC1 was injected duringail tests.

4.1. TEST 1 : RECOVERY = 88,5 %

During Hiis initial test; 88,5 % recovery is obtained The averagepermeate flow-rate is 1071/hour. 7 hourslong a permeate havinga 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 392mg/1 Si02 are blown-off (via permeate and concentrate),it is obvious that thé remaining part is left in themembrane module.

That might explain thé small pressure rise from 38 up to 41bar due to SiO2 deposits on thé membranes.

Figure 5 below shows thé membrane configuration of thefirst test.

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 longthere is a permeate production with a conductivity rangingbetween 130 and 230 |/S/cm.

The analyses performed on Si02, fluorides and sulphatesclearly show that thé mass balances are not in equilibrium,

which me an s a deposit is built on thé membranes. Thatexplains once again thé pressure rise from 39 up to 46 barduring thé tests. After tins test, thé membranes hâve to becleaned before starting a third test.

4.3. TEST 3 : RECOVERY = 80 %

A new computer simulation taking into account the présenceof fluorides and sulphates gives a 80 % recovery. Theaverage permeate flow-rate is now 107 1/hour. During morethan 48 hours a permeate with a conductivity rangingbetween 80 and 90 piSIcm is produced.

The pressure is constant at an average value of 39 bars. Thisis a clear indication for thé absence of deposit of the présentsalts and minerais on thé membranes. This is corroboratedby thé analyses on SiO 2, fluorides and sulphates. The massbalances are perfectly equilibrated.

It can be assumed that thé operating conditions of test 3are appropriate for sait removal from groundwater atinduslrial scale.

Considering on one hand the present situation and, on theother hand, the operating conditions of test 3, a financialcalculation is operated in order to verify the possible annualgain such water processing might generale for the company.

That calculation is detailed hereafter.

5. FINANCIAL FEASIBILITY STUDY

As to enable Primeur NV to décide, on an economicallyjustified basis, wilh regard to a possible invesiment for areverse osmosis plant, Laborelec calculated the annualsavings on energy, water and chemicals consumption.

5.1. REDUCED WATER CONSUMPTION

As the cooling circuit and the boiler will be supplied withhigher quality water, significantly less blow-offs will be

concerrtraiteuuti

I return3331/Ti

pH-regulaflon

-Hn—

teed121 y

buffer tank

necmrery:

parnwate

=88,6^4

Fig. 5 - membrane configuration initial test on site.

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required in order to prevent sait deposits.

Practically it can be assumed that for a boiler the concentra -tion factor can be raised from 3,3 up to 20 when taking intoaccount the permeate quality for a 80 % recovery. Thelimiting factor in this case is the maximum chlorine content.

In the cooling water circuit thé concentration factor can beraised from 2 up to 10, without risk of deposits and precipi -talion on the heat exchangers.

Figure 6 shows thé required blow-of f in thé cooling and théboiler circuit as to reach respective concentration factors of9,33 and 18,5.

Considering the date above the achievable annual ground-water savings can be calculated.

Figure 7 shows the water consumption.

5.2. REDUCED ENERGY CONSUMPTION

The pre-treatment of groundwater by means of reverseosmosis will resuit in two types of energy savings :

5.2.1. SAVINGS ON PUMP ENERGY

FirsUy 11.700 m3/yea r less groundwater ha s to be pumpedup.

On an annual basis this means savings of about 32.000 BEF.

Hère the assumption i s :

• pump efficiency, ducts = 75 %• approximate kWh priée = 3 BEF• pumping height groundwater = 250 m

5.2.2. SAVINGS ON BOILER GAS CONSUMPTION

As less blow-of fs will be required, for a low pressure steamboiler less energy will be removed from thé process.

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 m3/uur• supply water température = 50 °C

5.3. REDUCED CHEMICALS CONSUMPTION

As thé number of blow-of fs is reduced, both in thé coolingand 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.

Steam boiler circuit

Cooling water circuit

20 % rétention

Total

Gain

Without RO(inm3/year)

36.000

30.000

066.000

After RO implementation Concentration factor(inm3/year)

26.640

16.800

10.860

54.300

1 1.700 m3/year (= - 17,7 %; net gain)

Cf = 9,33

Cf=18,5

22.560 m3/year (= - 34,2 %; when retentate is reused for production/transport)

Fig. 7 - Calculation gain on groundwater consumption.

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L'EAU ET LES TECHNIQUES MEMBRANAIRES -4-5 avril 2000

Steam boiler circuit

Cooling water circuit

HC1 injection

Total

Annual savings

Without RO(in BEF/year)

680.000

300.000

0

980.000

811,

After RO implementation(in BEF/year)

30.000

46.000

93.000

169.000

,000 BEF/year

Fig. 8 - Savings through reduced chemicds consumption.

September-October 1995(no RO)

September-October 1996(after 3 months RO)

Water consumption(for steam production)

Water consumption(for cooling water circuit)

3.090 rrf/month

3.200 rrf/month

1.900 rrf/month

(= - 39 %)

1.400 rrf/month

(=-55%)

Fig. 9 - Reduced water consumption in practice.

will be removed from thé production process.

Figure 8 below shows thé potential annual savings.

In brief it can be assumed that, when implementing reverseosmosis, 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 andchemicals production.

Taking into account an average investment cost, thé pay-back 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 Hieinvestment. A reverse osmosis plant with a flow-rate of 10m3/hour and a recovery of nearly 80 % was bought.

Three months after thé commissioning thé positive impactof thé reverse osmosis treatment was already évident.Figure 9 shows thé practically achieved savings on théwater consumption.

The by Laborelec alleged savings on chemicals and ener gy

consumption were also achieved.

Reverse osmosis offers also another, by yet not mentioned,advantage : thé production of stérile water, which is veryimportant in thé food industry.

7. CONCLUSION

Referring to a contact with Primeur NV in 1999 they werestill very satisfied with thé correct opération of the module.

This study shows that feasibility studies have ef fectively anadded value for thé industrial customer as they allow todécide on an economically justified basis whether an invest-ment will be made.

At the same time, it was shown that for sait removal fromsome water types (groundwater, but also main water andsurface water after an adéquate pre-treatment), membranetechnology, and more especially reverse osmosis, is a highlyrecommended technique.

Taking into account always more sévère environmentalrégulations and increasing efficiency of this technology, thénumber of economically feasible applications will certainlyincrease in thé future . . .

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