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Short guideline for limestone contactor design for large desalination plants (rev.3) 1

SHORT GUIDELINE FOR LIMESTONE CONTACTOR DESIGN FOR

LARGE DESALINATION PLANTS (REV. 3)

JUNE 11, 2005

Manuel Hernández-SuárezPh.D., M.Sc., Dipl.Ing.

Canary Islands Water Center

1 DESCRIPTION OF UP-FLOW LIMESTONE CONTACTORS WITH CONTINUOUS FEEDINGSYSTEM ......................................................................................................................................................... 2

2 CONDITIONS FOR DESIGN................................................................................................................ 4

3 SELECTION OF SUPERFICIAL VELOCITY ...................................................................................... 5

4 SELECTION OF EMPTY BED CONTACT TIME (EBCT) .................................................................. 5

5 WATER QUALITY AFTER TREATMENT........................................................................................... 6

6 DIMENSIONS OF LIMESTONE BED.................................................................................................. 7

6.1 CHARACTERISTICS OF THE LIMESTONE CELLS ................................................................................. 76.2 CHARACTERISTICS OF LARGE TANKS............................................................................................... 86.3 SUMMARY DATA FOR THE DIMENSIONS THE LIMESTONE BEDS........................................................10

7 HEAD-LOSS OF THE LIMESTONE BED .........................................................................................11

8 PERFORMANCE OF THE LIMESTONE BED AT VERY LOW FLOWRATES ..............................12

9 LIMESTONE CONSUMPTION...........................................................................................................13

10 LIMESTONE PARTICLE SIZE ......................................................................................................14

11 QUALITY OF THE LIMESTONE ...................................................................................................15

12 AUTONOMY OF THE SYSTEM ....................................................................................................16

13 LIMESTONE TREATMENT COSTS .............................................................................................16

14 SUPPLY AND LOAD OF LIMESTONE ........................................................................................17

15 FILLING OF LIMESTONE CELLS ................................................................................................17

16 CLEANING OF LIMESTONE BED WITH AIR SPARGING.........................................................17

17 ON THE USE OF SULFURIC ACID INSTEAD OF CO2 TO ENHANCE LIMESTONEDISSOLUTION .............................................................................................................................................18

18 SUMMARY OF LIMESTONE CONTACTOR CHARACTERISTICS FOR THE EXAMPLE R.O.DESALINATION PLANT .............................................................................................................................19

19 REFERENCES ...............................................................................................................................20


SHORT GUIDELINE FOR LIMESTONE CONTACTORDESIGN FOR LARGE DESALINATION PLANTS

1 DESCRIPTION OF UP-FLOW LIMESTONE CONTACTORS WITH

CONTINUOUS FEEDING SYSTEM

Passing corrosive water (i.e. with negative Langelier Saturation Index) thru a bed of crushed

limestone produces an increase in pH as well as an increase in alkalinity and hardness. In

upflow limestone contactors water moves upwards thru a bed of crushed limestone dissolving

the calcium carbonate as it rises. The reaction involves is as follow:

CaCO3 + CO2 + H20 = Ca2+ + 2HCO3- (1)

The equilibrium pH of this reaction depends on a series of factors: initial pH, CO2 content,

alkalinity, total dissolved solids, water temperature and upflow velocity, among others.

Given enough contact time inside the limestone bed, water can be saturated with calcium

carbonate. Consequently Langelier Index rises to values equal or very close to cero.

In praxis, the parameter empty bed contact time (EBCT) is used to describe the residence time

inside the bed. It is calculated by dividing the volume of the limestone bed by the flowrate,

and is given in minutes.

Large upflow limestone contactors are difficult to operate because of : () turbidity problems

in the effluent during reloading operations, () decreasing performance due to continuously

diminishing height of limestone bed between loadings, and () turbidity problems when

flushing the filter bed with air and water.

A new concept for upflow limestone contactor is proposed for this project that resolves these

problems as follow:

() Maintaining constant height of limestone bed by means of a continuous feeding system.

Limestone feeding is, grain by grain, and driven by water chemical reactions inside the bed.

() Turbidity events during re-loadings are eliminated, as re-loading is carried out inside an

in-built silo that is separated from the filter bed surface.

() A modular design allows sparging of a single module during normal operations. Since

each module treats only a fraction of the total effluent, turbidity problem is minimized, as fine

limestone particles leaving the treated module are dissolved by the much larger volume of

clear water.


The design is based on research and development work that was initiated in 2001 in the

Canary Islands (see Section 17: References).

The proposed upflow limestone contactor modules built in concrete tanks. They can be

divided into six parts, starting from the bottom: 1) the air injection system; 2) the water

distribution zone; 3) the limestone bed, 4) the still-water zone, 5) the limestone feeding zone,

and 6) the limestone silo. (see Figure 3 for details).

Part 1.- The air injection system consists of a network of PVC pipes embedded underneath

the contactor concrete base. These pipes are collected into a manifold outside the concrete

tank. The air blower is connected directly to this manifold when sparging is required.

Part 2.- The water distribution zone is located in the lower part of the tank. It consists of a

300 mm height infiltration platform. This platform consist of 996 x 996 mm2 platforms that

are placed against each other to conform an uniform infiltration surface. Contact surfaces

between platforms, as well as platforms and walls, are sealed with a plastic resin. Each

platform has three large openings on each sidewall to facilitate water distribution. They also

have internal beams to withstand more than 6,000 kg/m2. Each module has 81 nozzles,

uniformly distributed on its surface.

Part 3.- The limestone bed zone (made of crushed limestone particles 1.5-2.5 mm in

diameter) is located above the infiltration platform. The height of the limestone bed may vary

according to specifications but it is normally between 1 and 2 meters.

Part 4.- The bed surface is approximately 800 mm below perimetral spillway. This area is

called the still-water zone. This distance reduces the possibility of particles elutriation even at

high superficial velocities.

Part 5.- The limestone feeding zone is located above the still zone. It consist of a steel

supporting structure and 996 x 996 mm2 feeding plates. Each plate has 9 equally spaced

funnels. These funnels allow distribute crushed limestone particles on to the limestone the bed

surface, grain by grain and without creating turbidity. Limestone falls onto bed by gravity and

regulated by water chemical demand. Dosing pipes cross the still-water zone to reach bed

surface.

Part 6.- The feeding structure in itself makes the floor of the limestone in-built silo. The

material stored in the in-built silo falls thru the funnels on to the limestone bed below and by

gravity. The in-built silo is loaded from above thru strategically located openings.

Material supplied in regular bags or big-bags can be transported above the silos with a

moving crane and unloaded directly into them. Storage capacity of the silos allow for gives an

autonomy of several weeks.


The preliminary design presented here is for a R.O permeate flowrate of 100,000 m3/d with a

range between 92,400 m3/d and 105,600 m3/d.

2 CONDITIONS FOR DESIGN

For this preliminary study the following water characteristics are assumed:

Table 1: Chemical characteristics of the permeate

Parameter min. max.

Field Water Temperature 18 ºC 39 ºC

TDS (mg/L) 100 100

pH 4,98 4.91

Langelier Index -6.66 -6.40

CO2 29.3 29.1

Calcium (mg Ca++/L) 0.4 0.4

Alkalinity (mg CaCO3/L) 0.8 0.8

Table 2: Chemical characteristics required after

remineralization treatment

TDS (mg/L) ≤ 200

pH 7.5-8.2

Langelier ≈ +0.2

Turbidity < 0.5

Calcium (mg Ca++/L) ≥ 20

HCO3- (mg HCO3

-/L) 50-120

Other parameters such as Fe, F, Mn or B are not considered relevant for the limestone

treatment if limestone quality is such as shown on Table 8.


3 SELECTION OF SUPERFICIAL VELOCITY

Assuming a nominal flowrate of 100,000 m3/d and a range between 92,400 m3/d and 105,600m3/d the following upflow velocities can be obtained for a contactor surface of 200 m2.

Table 3: Range of upflow velocities for a contactor surface of 200 m2

Flowrate Superficial velocity (m3/d) (cm/min)

105,600 36.7 100,000 34.7 92,400 32.1

These ranges are considered adequate for limestone contactor performance according toexperience and available data.

4 SELECTION OF EMPTY BED CONTACT TIME (EBCT)

As shown on Table 1 temperature varies between 18ºC and 39ºC, consequently equilibrium

pH also varies. Figure 1 and 2 illustrate the gradual increase in pH and Langelier SI with an

increase in EBCT for 18 ºC and 39 ºC. Surface velocity was assumed to be between 32.1 and

36.7 cm/min (34.2 cm/min). The differences between the curves are mainly related to the

effect of temperature on CO2 and speed of reaction (1) of Section 1.

The curves are obtained using the simulation model of Schott (2003) and Letterman and

Kothari (1997), corrected with field data for R.O. desalinated water obtained by M.

Hernández et al., (2004).

Considering water should comply with the conditions specified on Table 2 the residence time

should be between 4 and 5 minutes.

For design purpose the EBCT will be set at 4.1 minutes.


Figure 1: Evolution of pH with increasing EBCT for RO permeate

(based on preliminary data of Table 1).

Figure 2: Evolution of Langelier Index with increasing EBCT for RO permeate

(based on preliminary data of Table 1)

5 WATER QUALITY AFTER TREATMENT

Table 4 shows the estimated characteristics of permeate after limestone treatment.

Assumptions were: 98-99% rich limestone, 1.5-2.5 mm particle size, and an upflow velocity

thru the limestone bed between 32.1 and 36.7 cm/min.

7.00

7.20

7.40

7.60

7.80

8.00

8.20

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0

EBCT (min)

pH 18 ºC

39 ºC

-1.20

-1.00

-0.80

-0.60

-0.40

-0.20

0.00

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0

EBCT (min)

Lan

geli

er

SI

18 ºC

39 ºC


Table 4: Estimated quality of the permeate after limestone treatment

Parameter 18ºC 39ºC

EBCT (min) 4.1 4.1

pH 7.9 7.8

HCO3- (mg/L) 79.9 79.8

Ca++ (mg/L) 26.3 26.2

CO2 (mg/L) 1.6 1.5

Langelier Index -0.21 -0.02

Turbidity (NTU)* < 0.5 < 0.5

* Assuming a 99% limestone has water treatment quality grade, as given on Table 8

6 DIMENSIONS OF LIMESTONE BED

Assuming a nominal flow of 100,000 m3/d, the dimension of the limestone contactor is

analyzed considering the following basic design:

• Four large concrete tanks of equal size, for treating 25,000 m3/d each, operating in parallel.

• Five small limestone cells per large tank, for treating 5,000 m3/d each, also operating in

parallel.

Details of this arrangement can be visualized on Figures 3, 4, 5, 6 and 7.

6.1 Characteristics of the limestone cells

As indicated in the previous paragraph, flowrate for each limestone cell was set at 5,000 m3/d,

equivalent to 3.47 m3/min.

Considering the selected EBCT is 4.1 minutes, the volume of cell limestone bed is: 4.1 x 3.47

= 14.2 m3. Thus, considering a surface of the cell of 10 m2 (2 x 5 m) the limestone bed height

should be 1.42 m.

However as indicated in Section 2 flowrate can go up to 105.600. To guaranty an EBCT of

4.1 minutes under those conditions bed height is set at 1.55 m

This height is considered adequate as shown in several experiments carried out by Hernández

et al., (2004).

Assuming a height for the water distribution zone of 0.30 m, adding 1.55 m for the limestone

bed, 0.8 m for the feeding structure and 1.35 for the silo, a total internal height of 4.00 m is


obtained. Figure 3 depicts a cross section with the main characteristics of the proposed

limestone bed.

6.2 Characteristics of large tanks

As indicated above, each of the large tanks will treat 25,000 m3/d and will house five

limestone cells of 10 m2 each, operating in parallel. Therefore total surface of limestone bed

for each large tank is 50 m2. The internal height of the large tank is also 4.00 m.

To allow uniform water distribution under the five limestone beds, the water entrances from

both sides of the limestone cells.

Considering there will be 4 large tanks the total surface of the limestone bed will be 200 m2.

Figures 4, 5, 6 and 7 shows a conceptual design of a 25,000 m3/d tank.

Figure 3: 3D View of a 5,000 m3/day limestone cell.Numbers correspond to the different parts described in Section 1.

1

2

3

4

5

6


INFLOW

2.0 m

OUTFLOW

Figure 4: Layout of the inflow level

Channel

LidOUTFLOW

2.0 m

Channel

INFLOW

Figure 5: Layout of the outflow level

Infiltration modular platform

Limestone dosing platform

Subterranean air sparging system

airblower

Figure 6: Cross section thru a limestone contactor cell


INFLOW

OUTFLOW

Figure 7: Individual cell sparging system

6.3 Summary data for the dimensions the limestone beds

Table 5: Summary data for the limestone beds

Flowrate to be treated 92.400- 105.600 m3

Nr. of large tanks 4

Nr. of limestone cells per large tank 5

Total number of limestone cells 20

Surface of each limestone cell 10 m2

Total surface of the limestone beds 200 m2

Height of the limestone beds 1.55 m

Total volume of the limestone beds 310 m3

Specific weight of 2-2.5 mm limestone (dry) 1.5 ton/m3

Total weight of the limestone bed (dry) 480.5 ton

EBCT 4.8 - 4.1 min

Upflow velocity 32.1 - 36.7 cm/min


7 HEAD-LOSS OF THE LIMESTONE BED

Using the correlation shown on Figure 8 (M. Hernández, unpublished) and for an average

upflow velocity of 34.7 cm/min a head-loss of 43 cm/m of bed is obtained.

Considering the bed is 1.55 m in height, the estimated head-loss would be 1.55 x 0.43 = 0.66

m (0.066bar).

The head-loss of water distribution modules (81 nozzles/m2) located below the bed is

considered irrelevant.

The total head-loss of the limestone cells is shown on Table 6.

Table 6: Head-loss inside the limestone cells

Height of the water outflow 2.65 m

Head-loss of the limestone bed 0.62 m

Total head required 3.27 m

Figure 8: Head-loss of the upflow limestone bed (particle size 2.0-2.5 mm)

y = 1.2996x - 1.8446

R2 = 0.9929

0

10

20

30

40

50

60

70

0 10 20 30 40 50 60

Superficial velocity (cm/min)

Head

-lo

ss (

cm w

ate

r co

lum

n/

m b

ed

heig

ht)


8 PERFORMANCE OF THE LIMESTONE BED AT VERY LOW FLOWRATES

For the purpose of this evaluation, it is assumed flowrate to the limestone contactor could

diminish to 13,600 m3/d (570 m3/h).

Assuming this flowrate is passed thru one large tank, i.e. thru five 2 x 5 m cells (originally

design for 25,000 m3/d) the flowrate per limestone cell would be:

Flowrate per limestone cell = 570 m3/h /5 = 114 m3/h = 1.9 m3/min

Thus the EBCT becomes: 14.2 m3/1.9 m3/min = 7.5 min.

On the other hand upflow velocity becomes:

Upflow velocity = 1.9 m3/min/10 m2 = 0.190 m/min = 19.0 cm/min

Diminishing upflow velocity has an effect on reaction (1). Decreasing water velocity around

particles slows down the reaction and consequently increases required EBCT, for same pH.

This effect has been simulated by the model and shown on Figure 9.

As before, these curves have been obtained using the simulation model of Schott (2003) and

Letterman and Kothari (1997), corrected with field data for R.O. desalinated water obtained

by M. Hernández et al., (2004).

Increasing EBCT from 4.1 to 7.5 minutes tends to compensate this effect as output of the

model suggests, and similar pH and Langelier SI can be expected than those obtained with

nominal upflow velocities of 34,7 cm/min and 4.1 EBCT.

Figure 9: Effect of upflow velocity on pH for the 18ºC conditions.

7.00

7.20

7.40

7.60

7.80

8.00

8.20

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 11.0

EBCT (min)

pH 34.7 cm/min

19.0 cm/min


Figure 10: Effect of temperature on pH with increasing EBCT at slow 19 cm/min.

Figure 11 Effect of temperature on the Langelier SI with increasing EBCT at 19 cm/min.

9 LIMESTONE CONSUMPTION

Considering reaction (1) and assuming all additional Calcium present in the permeate after

treatment comes from the Calcium Carbonate dissolved by the CO2, it can be calculated from

Tables 2 and 3 the following:

∆ Ca++ = 26.3 -0.4 = 25.9 mg/L Ca++

Assuming all the Calcium comes from the consumption of limestone it be calculated:

CaCO3 consumption = 25.9 mg Ca++/L x 2.493 mg CaCO3/Ca++ = 64.57 mg/L de CaCO3

(100%)

-0.80

-0.70

-0.60

-0.50

-0.40

-0.30

-0.20

-0.10

0.00

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 11.0

EBCT (min)

Lan

geli

er

SI

18ºC

39ºC

7.40

7.50

7.60

7.70

7.80

7.90

8.00

8.10

8.20

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 11.0

EBCT (min)

pH 18ºC

39ºC


Considering the CaCO3 is 99% pure, real consumption would be: 64.57/0.99= 65.2 mg/ L de

CaCO3 (99% rich)

Table 7: Summary of limestone consumption data

CaCO3consumption per m3 (99% rich) 65..2 g/m3

Daily CaCO3/d consumption (99% rich) 6.52 t/d (for 100,000 m3/d)

10 LIMESTONE PARTICLE SIZE

Limestone particle size affects contact surface and therefore limestone bed performance.

Figure 12 shows the relationship between particle size and limestone bed height calculated

using Letterman and Kothari (1995) model. Conditions for this example were: pH before

treatment: 5.75; saturation pH = 8.16; objective pH = 8.08; EC = 600 µS/cm; 1.23 mg Ca/L;

Alkalinity = 5.5 mg CaCO3/L, Surface velocity = 650 L/m2 and day. Limestone quality =

98% Ca CaCO3.

Figure 12: Example of relationship between particle diameter and height of the limestone bed

(see text above for details)

On Figure 13 particle size distribution recommended for this project is given. As can be seen

the size of the particle size should be between 1.25 and 2.5 mm, with an average of 2 mm.

0.5

0.75

1

1.25

1.5

1.75

2

2.25

1 1.5 2 2.5 3 3.5 4 4.5 5

Particle diameter (mm)

hei

gh

t o

f th

e lim

esto

ne

bed

(m

)


Figure 13: Recommended limestone particle diameter distribution

11 QUALITY OF THE LIMESTONE

Table 8: Recommended quality of limestone to be used for limestone contactor.

Purity 99.1 %

SiO2 0.3 %

Al2O3 0.1 %

MgO 0.2 %

SO3 0.1 %

Iron Oxide < 0.1 %

Humidity 0.14 %

pH 9.1

Hardness (Mohs) 3

Specific weight 2.7

0%

30%

60%

90%

<0,32 0,32-0,63 1,25-2,5 >2,5

screen size (mm)

% w

eig

ht


12 AUTONOMY OF THE SYSTEM

Assuming the height of the silo is 1.35 m the autonomy of the system for 100,000 m3/d can be

calculated as follow.

Table 9: Autonomy of the system

Height of the in-built silo 1.35 m

Volume of the in-built silo 270 m3

% Volume used 70 %

Volume of limestone stored 189 m3


Weight of limestone stored in silos (dry) 283.5 ton

Daily consumption (99%) 6.52 ton/day

Nr. of days of autonomy 43 days

This period of autonomy is considered adequate, as it is equivalent to approximately one

reloading per month.

13 LIMESTONE TREATMENT COSTS

The price of crushed limestone (2.5 mm) varies with location. However, assuming a price of

0.10 €/kg including freight, the treatment cost with limestone contactor can be estimated as

follow:

Table 10: Limestone treatment cost

Estimated of limestone 0.10 €/kg

Daily consumption (100% pure) 6,520 kg/d

Yearly cost 237,980 €/y

Cost per m3 0.0065 €/m3


14 SUPPLY AND LOAD OF LIMESTONE

Crushed limestone screened to diameter 1.5-2,5 mm can be obtained in big-bags (1,100 kg)

and transported in 20,000 kg container. Big-bags can be elevated above the loading area with

bridge-crane.

Picture 1: Loading limestone contactor with big-bag in South Africa

15 FILLING OF LIMESTONE CELLS

Limestone particles should always fall on water during loading operations. Limestone bed

should not be filled when no water is present inside the cell, as limestone might suffer somecompaction and consequently might tend to form clusters. When particle fall through water

they tend to settle smoothly, leaving a spongy bed.

16 CLEANING OF LIMESTONE BED WITH AIR SPARGING

Limestone may, with time, develop preferential pathways. Also some cluster may develop

here and there when bed is left to dry.

Consequently regular air sparging is recommended at least once or twice a year. Sparging

should only last for 10-15 seconds. Larger sparging may cause elutriation, i.e. particles getwashed away with water.


It is also recommended to flush the limestone bed when working with "not so pure" limestone

as it helps to wash away impurities in particular silica and iron oxides that tend to deposit on

particles surface.

The design presented in this proposal offers the possibility of sparging each cell individually(see Figures 6 and 7).

17 ON THE USE OF SULFURIC ACID INSTEAD OF CO2 TO ENHANCELIMESTONE DISSOLUTION

The addition of sulfuric acid as pretreatment to limestone contactor produce to the following

reactions:

CaCO3 + H2SO4 = CaSO4+ CO2+ H2O (2)

CaCO3 + CO2 + H20 = Ca(HCO3)2 (3)

2 CaCO3 + H2SO4= CaSO4+ Ca(HCO3) 2 (4)=(2)+(3)

As shown by recent work carried out by Hernandez, M. (2004) results agreed well with the

stochiometrical analysis. However, data suggest acid pretreatment have some limitations, as

Langelier SI does not surpass the value of -0.4 when doses are higher than 20 ppm, even after

8 minutes of EBCT. On the other hand, with the CO2 treatment Langelier SI can reached -0,1

after 4 minutes EBCT. In addition cost of treatment with the sulfuric acid treatment is higher

than with CO2 particularly because CaCO3 consumption is double (Hernandez, M., 2004)

Consequently, it is recommended that the use of sulfuric acid should be carefully evaluated

before implementing it in a large project.


18 SUMMARY OF LIMESTONE CONTACTOR CHARACTERISTICS FOR THE

EXAMPLE R.O. DESALINATION PLANT

Table 11: Summary of data for the limestone contactor characteristics for a 100,000 m3/d

desalination plant

Flowrate to be treated 92.400- 105.600 m3

Nr. of large tanks 4

Nr. of limestone cells inside per large tank 5

Total number of limestone cells 20

Surface of each limestone cell 10 m2

Total surface of the limestone beds 200 m2

Height of the limestone beds 1.55 m

Total volume of the limestone beds 310 m3


Total weight of the limestone bed (dry) 480.5 ton

EBCT 4.8-4.1 min

Upflow velocity 32.1-36.7 cm/min

Height of the water outflow 2.65 m

Head-loss of the limestone bed 0.62 m

Total head required by limestone cells 3.27 m

Height of the in-built silo 1.35 m

Volume of the in-built silo 270 m3

% Volume used 70 %

Volume of limestone stored 189 m3


Weight of limestone stored in silos (dry) 283.5 ton

Limestone consumption per m3 (99% pure) 65.2 g CaCO3/m3

Daily limestone consumption (99% pure) 6.52 ton CaCO3/d

Nr. of days of autonomy 44 days

Estimated of limestone 0.1 €/kg

Daily consumption (100% pure) 6,520 kg/d

Daily costs 652 €/d

Yearly cost 237,980 €/y

Cost per m3 0.0065 €/m3


19 REFERENCES

• Letterman, R.D. and Kothari, S (1995). Instruction for using Descon: A computer

program for the design of limestone contactor. US-EPA, Cooperative Agreement Nr.

814926.

• Letterman, R.D., (1997). Project summary: calcium carbonate dissolution rate in

limestone contactors, EPA document EPA/600/SR-95/068.

• Hernández-Suárez, M. et al., 2002. Development of a new limestone contactors with

continuous feeding system. Proceedings of the III Congress Spanish Association of

Desalination and Water Reuse, AEDyR, Málaga.

• Hernández-Suárez, M., (2003). Post-treatment of RO water for irrigation. Proceedings of

the Regional Meeting of the Euromediterranean Institute of Hydrotechnics, University of

Murcia., Spain.

• Hernández-Suárez, M. et al., (2003). Advances on remineralization of desalinated water

with limestone contactors. Proceedings of the IV Congress Spanish Association of

Desalination and Water Reuse, AEDyR, Las Palmas.

• Hernández, M. (2003). Limestone contactors in the Canary Islands, Spain in Small Public

Water System Technology Guide, Vol. II. Limestone Contactors by Azarina Jalil et al.,.

University of New Hampshire. Water Treatment Technology Assistance Center. p.26.

• Hernández, M. (2004). On the costs of remineralization (rev). Canary Islands Water

Center, available at www.fcca.es: International Section.

• Hernández, M. (2004). On the use of acids intead of CO2 to enhance performance of

limestone contactors: a comparative analysis. El Manantial, Bulletin of the Canary Islands

Water Center, December 2004, page 4, available at www.fcca.es.

• Schott, G. Limestone bed contactor corrosion control and treatment analysis. Program

V1.02 (2003). in Small Public Water System Technology Guide, Vol. II. Limestone

Contactors by Azarina Jalil et al.,. University of New Hampshire. Water Treatment

Technology Assistance Center.

• M. Hernández et. al. (2004). R&D on remineralization of desalinated waters with

limestone contactors. Canary Islands Water Center, 171 pp.

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