Concentration of Brines by Natural Evaporations

8/12/2019 Concentration of Brines by Natural Evaporations

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Concentration of brines from RO desalination plantsby natural evaporation

J.M. Arnal, M. Sancho*, I. Iborra, J.M. Goza lvez, A. Santafe , J. Lora

Chemical and Nuclear Engineering Department, Polytechnic University of Valencia,Camino de Vera, s/n, 46022 Valencia, Spain

Tel. 34 963 879639; Fax34 963 877639; email: [email protected]

Received 21 January 2005; accepted 21 February 2005

Abstract

Development of desalination technologies in recent years, specially in the case of reverse osmosis process, enables

now the massive production of water with a moderate cost, providing flexible solutions to different necessities within

the fields of population supply, industry and agriculture. The great development of reverse osmosis (RO) technology

has been a consequence of several factors such as energy consumption reduction and membrane cost decrease.

Nevertheless, one of the problems of RO desalination plants is the generation of a concentrate effluent (brine) that

must be properly managed. In the case of seawater desalination plants the brine is usually discharge to the sea sincethey are placed near it. However, in the case of brackish water desalination, brine management can be specially critic

if the plants are placed far from the coast and far from any public channel or water-treatment plant where discharge

the brine. The best option in this case is to concentrate the brine by reverse osmosis up to the technical limit of the

process (around 70 g/L of salinity), and after that continue concentrating by means of evaporation until getting a

solid waste that can be valued or directly managed by an authorised company. The aim of this work is to asses the

viability of using natural evaporation (without heat supply) opposite to conventional evaporation for concentrating

brines from brackish desalination plants. The main purpose of applying natural evaporation is to reduce the energy

consumption of the treatment and the associated costs.

Keywords: Brine; Concentration; Reverse osmosis; Evaporation; Energy

1. Introduction

Desalination technologies have experienced a

great development in recent years, especially the

reverse osmosis process, which enables now the

massive production of water with a moderate

cost, providing flexible solutions to different

necessities within the fields of population supply,

industry and agriculture. The great development

Presented at the Conference on Desalination and the Environment, Santa Margherita, Italy, 2226 May 2005.

European Desalination Society.

0011-9164/05/$ See front matter 2005 Elsevier B.V. All rights reserved

*Corresponding author.

Desalination 182 (2005) 435439

doi:10.1016/j.desal.2005.02.036


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of reverse osmosis (RO) technology has been a

consequence of several factors such as energy

consumption reduction and membrane cost

decrease. Nevertheless, one of the problems of

RO desalination plants is the generation of aconcentrate effluent (brine) that mustbe properly

managed in order to avoid environmental con-

tamination. This problematic is different in

sea water desalination and in brackish water

desalination.

In the case of seawater desalination plants

the problem is solved since these plants are

usually placed near the coast, so brine can be

discharge to the sea through brine pipes or

submarine emissaries, in a place where it is

quickly diffused in the marine medium.

However, the management of brine from

brackish desalination plants can be a significant

problem in case they are placed far from the

coast (inland plants) or far from any public

channel where discharge the brine. Some of

the options for brine disposal from inland desa-

lination plants are deep well injection, evapora-

tion ponds, disposal into surface water bodies,

disposal to municipal sewers, concentration

into solid salts (evaporation) and irrigation ofplants tolerant to high salinities. The main

factors that influence the selection of a disposal

method, among others, are: the volume or

quantity of concentrate, the quality of concen-

trate, physical and geographical location of the

discharge point, capital and operational costs,

etc. [1]. The cost of brine disposal ranges from 5

to 33% of the total cost of desalination, being

the disposal cost of inland desalination plant

higher than that of plants disposing brine into

the sea [2].

We consider that one suitable option to

manage this brine from inland plants is to

concentrate it by means of reverse osmosis

up to the operational limit of the process

(around 70 g/L of salinity), and after it crys-

tallize the concentrate liquid by evaporation

until getting a solid waste that can be reused

(one application of brine is the production of

salt or other minerals with a commercial

application [3,4]) or directly managed by an

authorised company. This management option

can be extended to brine from seawaterdesalination plants and desalination of any was-

tewater from an industrial process.

Evaporation techniques are the most suita-

ble ones for concentrating brines, since their

application allow to obtain a solid waste more

easy to be managed than the original waste and

a decontaminated liquid flow that can be

directly discharged or even reused. However,

one of the main disadvantages of conventional

evaporation processes is the economical and

environmental cost associated with the produc-

tion of the thermal energy necessary for the

process. Because of that, this research work

aims to assess the viability of applying evapora-

tion without heating (under environmental

conditions) with the main purpose of reducing

energy consumption.

Evaporation under environmental condi-

tions (natural evaporation) has the disad-

vantage of requiring large earth extensions

since the productivity of the process isquite low (around 4 L . m2 . d1). This

drawback can be overcome by using wet sur-

faces (capillaries or clothes) exposed to wind

action, so surface density would be high

enough to generate a proper evaporation

flow with a minimum energy consumption

[5]. Hence, the surfaces of the system would

wet by means of capillarity and the water

would evaporate while the solids of the

brine would crystallize on the surfaces. The

final solid waste could be managed by an

authorised company or could be reused, and

the evaporated liquid, after condensation,

could be also reused or directly discharged.

In order to assess the viability of applying

natural evaporation to the concentration of

brines coming from brackish desalination

plants or from wastewater treatment, some

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experiments were carried out in which eva-

poration performance in different configura-

tions was assessed. This paper describes some

of these experiments and the main results

obtained.

2. Experimental procedure

Some experimental tests were carried out

in a laboratory scale with an industrial

wastewater with the following average

characteristics:

pH =7.5,

conductivity =27 mS/cm,

total solids =56 g/L.

Three different sets of experiments were

performed. The first set of experiments con-

sisted of natural evaporation tests in two

identical containers with 8 L of capacity

each one. One of the containers was

equipped with capillary adsorbents and the

other one without any adsorbent (represent-

ing the blank or reference). The objective of

this experiment was to assess adsorbent per-

formance from the point of view of thequantity of water that is evaporated.

Periodically, the difference of water level

from the previous measurement was taken,

as well as water conductivity and air

temperature.

In the second set of experiments, differ-

ent kind of materials and shapes were tested

as adsorbents with the aim of selecting the

most suitable one for being used in the

natural evaporation process. The following

four adsorbents were tested in these

experiments:

Adsorbent 1: cylindrical cloth made of

reprocessing cotton (80%) and synthetic

fibre (20%) with a diameter of 4 mm.

Adsorbent 2: rectangular cloth made of

viscose (80%) and polyester (20%) with a

perimeter of 26 mm.

Adsorbent 3: rectangular cloth made of

cellulose (65%) and cotton (35%) with a

perimeter of 26 mm.

Adsorbent 4: cylindrical cloth made of

polyamide with a diameter of 1.5 mm.

Each adsorbent was placed inside a flask

with a capacity of 1 L that was filled with

100 mL of wastewater. Periodically, the loss of

weight of each flask was measured, as well as

ambient temperature.

Finally, the third set of experiments consisted

of assessing the effect of air velocity in evapora-

tion performance. These tests were performed

under different environmental conditions with

air speeds varying in the rank between 1.8 and7.2 km/h. Relative humidity, air speed and tem-

perature were measured periodically, as well as

weight difference with regard to previous meas-

urement. Each experiment lasted until all the

liquid inside the flask was evaporated. The

experimental assembly was the same as the one

described in the second set of experiments.

3. Results and discussion

3.1. Effect of adsorbents

The experimental results of the first set of

experiments in which the effect of adsorbents

was assessed are shown in Fig. 1. This figure

0

5

10

15

20

25

30

35

0 100 200 300 400 500 600

Time (hours)

Volum

e(L)

Without ads orbents

With ads orbents

Fig. 1. Evaporated volume with and without adsorbents.

J.M. Arnal et al. / Desalination 182 (2005) 435439 437


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shows the evolution with time of the volume

of water that was evaporated in each con-

tainer, with and without adsorbents.

It can be clearly seen that the evaporated

volume when using adsorbents is significantlyhigher than in the case of not using adsor-

bents, especially after 170 h of test when eva-

poration with adsorbents reached values

100% higher than without adsorbents.

Furthermore, the increase of conductivity in

the container with adsorbents was also higher

than in the container without adsorbents.

According to this, it can be stated that eva-

poration improves significantly by using

adsorbents.

3.2. Selection of the most suitable adsorbent

Fig. 2 presents the main results of the

second set of experiments in which four

adsorbents were tested. This figure shows

the evolution with time of the mass inside

the flask for the four tested adsorbents. The

mass of all the flasks decreased with time due

to the quantity of water evaporated. It can be

seen that the amount of evaporated waterwas significantly higher in the case of adsor-

bent 3. This results were repeated in similar

experiments under different environmental

conditions. So, it can be said that adsorbent3 is the most suitable one for being used in

natural evaporation because increases process

productivity.

3.3. Effect of air velocity

In the third set of experiments the effect of

different air velocities were assessed. Fig. 3

shows the evolution with time of the mass

inside the flask under two different environ-

mental conditions that represent different airvelocity, v1 and v2, being v1 higher than v2.

As it can be seen in the figure, the amount

of evaporated water increases as air velocity

is higher. So it can be stated that higher air

velocity improves evaporation process, and

that improvement is even higher when using

adsorbents to increase evaporation rate.

4. Conclusions

The main conclusion of this work is that

natural evaporation is a viable process for

being applied to the concentration of brines

from desalination plants. According to the

experimental results it can be stated that:

evaporation productivity can be improved

by using adsorbents for increasing evapora-

tion surface;

0

20

40

60

80

100

120

0 50 100 150 200

Time (hours)

Mass(grams)

adsorbent 1

adsorbent 2

adsorbent 3

adsorbent 4

Fig. 2. Mass decrease due to evaporation with four

different adsorbents.

0

20

40

60

80

100

120

0 50 100 150 200 250 300

Time (hours)

Mass(g

rams)

v1

v2

Fig. 3. Effect of air velocity in the natural evapora-

tion with adsorbents.

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the most suitable adsorbent, within the tested

ones, for being used in capillary evaporation

are rectangular cloths made of cellulose (65%)

and cotton (35%) with a perimeter of 26 mm;

evaporation productivity can also beimproved increasing air velocity, although it

is limited by the blowing of solids to the eva-

porated water.

After these successful results, further

experiments have to be carried out in order to

define the characteristics of a pilot plant and to

optimise the operation parameters.

Acknowledgements

Authors would like to express their grati-tude to all the people who have participated

in this work, especially to the researchers

J. Cha fer and F. Marn.

References

[1] M. Ahmed, W.H. Shayya, D. Hoey and

J. Al-Handaly, Brine disposal from reverse osmo-

sis desalination plants in Oman and the United

Arab Emirates, Desalination, 133 (2001) 135.[2] P. Glueckstern and M. Priel, Optimized brackish

water desalination plants with minimum impact

on the environment, Desalination, 108 (1996) 19.

[3] I.S. Al-Mutaz and K.M. Wagialla, Techno-

economic feasibility of extracting minerals from

desalination brines, Desalination, 69 (1988) 297.

[4] M. Ahmed, A. Arakel, D. Hoey,

M.R. Thumarukudy, M.F.A. Goosen,

M. Al-Haddabi and A. Al-Belushi, Feasibility

of salt production from inland RO desalination

plant reject brine: A case study, Desalination,

158 (2003) 109.[5] J. Gilron, Y. Folkman, R. Savliev, M. Waisman

and O. Kedem, WAIVWind aided intensified

evaporation for reduction of desalination brine

volume, Desalination, 158 (2003) 205.

J.M. Arnal et al. / Desalination 182 (2005) 435439 439

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Concentration of Brines by Natural Evaporations