Physico-chemical factors of water at different gradient of the salt production pans (reservoir, condenser and crystallizer) of the coastal area in Cox’s Bazar were studied.Analyses of water temperature at different gradient of salt pans show almost similar values (31°C-32°C). The pH values varied from 4.9 to 7.4. The acidic pH values were recorded in Chakaria Sundarban area. Salinity ranged from 30.03‰ to 330.52‰, lowest salinity was found in reservoir pan and highest in crystallizer pan. Electric conductivity values fluctuated between 9.60 and 336.00 mmhos/cm and its values gradually increase from reservoir to crystallizer pans. Total hardness, Ca, Mg and HCO3 varied from 8000 to 213600 mg/l; 2987 to 106300 mg/l, 5013 to 107300 mg/l and 36.6 to 146.4 mg/l respectively and their values were always found to be Reservoir < Condenser< Crystallizer. Alkalinity ranged from 50-570 ppm, the lowest values were recorded in

reservoir pan and highest were found in crystallizer. Usually higher concentration of K was obtained in crystallizer pan and the highest value (15.2g/l) was recorded at Moheskhali sampling area

Kamal, Abu-Hena Mostafa

Quadery, Abrar Hossain

Zafar, Mohammad

Aquatic Commons

PHYSICO-CHEMICAL FACTORS OF SOLAR SALT FARMS
WATER IN THE COASTALAREAOF COX’S BAZAR,
BANGLADESH
Mohammad Zafar, Abu-Hena Mostafa Kamal and Abrar Hossain Quadery
Institute of Marine Sciences and Department of Physics,
University of Chittagong, Bangladesh.
ABSTRACT: Physico-chemical factors of water at different gradient of the salt
production pans (reservoir, condenser and crystallizer) of the coastal area in Cox’s Bazar
were studied. Analyses of water temperature at different gradient of salt pans show almost
similar values (31°C-32°C). The pH values varied from 4.9 to 7.4. The acidic pH values
were recorded in Chakaria Sundarban area. Salinity ranged from 30.03‰ to 330.52‰,
lowest salinity was found in reservoir pan and highest in crystallizer pan. Electric
conductivity values fluctuated between 9.60 and 336.00 mmhos/cm and its values
gradually increase from reservoir to crystallizer pans. Total hardness, Ca, Mg and HCO3
varied from 8000 to 213600 mg/l; 2987 to 106300 mg/l, 5013 to 107300 mg/l and 36.6 to
146.4 mg/l respectively and their values were always found to be Reservoir < Condenser<
Crystallizer. Alkalinity ranged from 50-570 ppm, the lowest values were recorded in
reservoir pan and highest were found in crystallizer. Usually higher concentration of K
was obtained in crystallizer pan and the highest value (15.2g/l) was recorded at
Moheskhali sampling area.
KEYWORDS: Physico-chemical factors- solar salt farm water- Bangladesh coast.
INTRODUCTION
Salt is produced by solar evaporation of sea water in Bangladesh. There are 12000 ha
of salt production area in the coastal regions of this country (Alam et al.1998), about
35000 labours are directly involve and produce more than 700000 metric tons of salt every
year. Generally salt is produced from November to April/May. The saltpans are generally
constructed of small dykes; leveling and compacting of saltpans at the onset of the dry
season in November and flooding by the beginning of December/January. Harvesting of
salt starts by the end of January and is continued until April/May (Alam et al.1998). Each
individual salt pan is fragmented into about 3-6 parallel, mostly identical salt streets. Each
salt street consists of a series of 6 consecutive pans with gradually decreasing size.
Typically, there are 3 major types of pans in the overall evaporation sequence: reservoir-
type evaporation pans, condenser and crystallizers (Fig.1). In the pans of reservoir and
condenser sea water is gradually concentrated through evaporation, whereas the
crystallizers are used for deposition of sodium chloride (Fig.2). The evaporators are
mostly not larger than 350 m2, while the crystallizer pans can be as small as 40 m2.
Intake of sea water into the evaporation pans depends on local and elevation of the
pan of either manual filling (i.e. with a water scooper or pump) and from the first
evaporation pan the water flows by gravity towards the following evaporation pans and
eventually reaches the crystallizers. During this process, generally the sea water gradually
Pakistan Journal of Marine Sciences, Vol. 10(2), 79-86, 2001.
80 Pakistan Journal of Marine Sciences, Vol. 10(2), 2001.
Fig. 1. Schematic layout of a typical salt street of Bangladesh.
Fig. 2. Deposition of salt (Sodium Chloride) in a salt farm of Bangladesh.
concentrates from about 30-40ppt in the first evaporation pan and 150-280ppt in the last
evaporator. At this point the brine is transferred to the crystallizer pan, where the salt is
deposited after further concentration of sea water to about one tenth of its original volume.
Water depth in the pan is very shallow and range from 6 to 10 cm in the first
evaporation pan to a few (<5) cm in the crystallizers. After1-2 day’s halite (NaCl) and
other salts such as calcium sulphate, potassium chloride and magnesium sulphate begin to
precipitate and salt is harvested from the crystallizers. In the natural evaporation of sea
water climatic factors play an important role in the production of salt. The most important
factors amongst these are temperature, wind velocity, relative humidity, sunshine and
rainfall. There is no scientific report on solar salt production of Bangladesh. The present
investigation is the first of its kind on physico-chemical factors of solar salt production
farm’s water from Cox’s Bazar area, Bangladesh.
Zafar et al.: Physico-chemical factors of solar salt farm water Bangladesh 81
Fig. 3. Sampling locations of the studied area of Bangladesh.
MATERIALS AND METHODS
The area of investigation is situated in the coastal districts of Cox’s Bazar is between
21º 31? and 21º 56? N latitude and 91º 50? to 92º 23? E longitude. Samples were collected
from 3 stations (Fig. 3) in the salt pans areas of Cox’s Bazar (Kuruskul), Moheskhali
(Gorakghata) and Chakaria Sundarban (Darbeskhata) in March 1995. From each station
water samples were taken from reservoir, condenser and the crystallizers pans with
replicates. Concurrently water temperature was recorded by using a thermometer. PH is
determined by digital pH meter. Salinity was obtained by standard Mohr-Knudsen method
following Barnes (1959). Electrical conductivity was recorded by conductivity meter.
Total hardness, calcium, HCO3 and total alkalinity were determined by procedures
describe by APHA (1976). K concentration was recorded by the procedure of Aitken
(1984).
RESULTS AND DISCUSSION
Water temperature:
Water temperature varied from 31 to 32ºC.Among the three sampling stations highest
(32ºC) water temperature was recorded at Moheskhali. Zafar (1994) reported that water
temperature (29ºC) in March of Kutubdia channel. Mahmood et al. (1993) recorded the
water temperature 26.93ºC in March of an aquaculture pond of Chakaria Sundarban. Ali
et al. (1985) stated that in the Moheskhali channel water temperature was recorded 27.5ºC
during this time. Mahmood et al. (1976) published that water temperature 29.69ºC in
March of Karnafuli estuary. Mahmood and Khan (1980) reported that water temperature
follows the air temperature in the parallel manner. The present investigation for reservoir
pan is close agreement with the findings of the above mentioned results.
Hydrogen ion concentration:
pH was found between 4.9 and 7.4 in the present investigated area. Very strong acidic
pH value (4.9) was found in crystallizer pond at Darbeskhata of Chakaria Sundarban area
(Table 1). Ramesh and Subramanian (1985) reported the pH value ranges from 7.8 to 8.8
at the solar salt farm near Madras. Mahmood et al. (1993) recorded the water pH 7.6 in
March of an aquaculture pond of Chakaria Sundarban. Mahmood and Saikat (1995)
reported the acidic pH values in soil of the Chakaria Sundarban area and they also
mentioned that Chakaria Sundarban area has a reach reserve of pyrite in its soil, and noted
that when acid sulfate soils are dried, oxidation takes place upon exposure to air and pH
goes down.
Salinity:
The most important feature of solar salt pans is the higher level of salinity. In the
whole investigated area salinity was varied from 30.03 to 330.52 ‰. The salinity was
gradually increasing from reservoir to crystallizer pan due to evaporation of water by solar
heat. Belaluzzaman (1995) recorded the 36.67 ‰ salinity of Cox’s Bazar coastal area in
March. Chowdhury (1995) found 28.20 ‰ salinity in March at Moheskhali channel of
Cox’s Bazar. Mahmood et al. (1993) reported the salinity of an extensive aquaculture
82 Pakistan Journal of Marine Sciences, Vol. 10(2), 2001.
Zafar et al.: Physico-chemical factors of solar salt farm water Bangladesh 83
Table
1.
Physico-chem
icalfactorsofdifferentgradientofsaltfarm
in
the
three
stations.
_______________________________________________________________________________________________________
G
radient
St.
pH
Salinity
Tem
p.
EC
Total
C
a
M
g
H
C
O
3
A
lkalinity
K
pans
N
o.
ppt
ºC
m
m
ohs/cm
hardness
m
g/L
m
g/L
m
g/L
ppm
g/L
_______________________________________________________________________________________________________
1
7.1
30.03
31.5
93.6
8000
2987
5013
36.6
120
3.4
R
eservoir
2
7
54.54
32
147.6
12500
5250
7250
48.8
140
4.97
3
6.6
53.27
31
102.6
12000
5208
7692
36.6
50
7.56
1
7.4
78.36
31.5
228
16000
7908
8092
36.6
140
4.49
C
ondenser
2
6.4
73.49
32
276
15000
7005
7995
61
240
4.65
3
5.7
84.14
31
192
23000
10500
12500
N
D
N
D
5.09
1
6.9
330.52
31.5
336
135200
65600
69600
146
570
8.87
C
rystallizer
2
6.9
325.47
32
318
142600
70300
72300
146.4
520
15.2
3
4.9
318.99
31
264
213600
106300
107300
N
D
N
D
10.67
_______________________________________________________________________________________________________
EC
=
Electric
C
onductivity
Tem
p.=
Tem
perature
N
D
=
N
otD
etected
St.=
Station
Station
1
=
C
ox’s
B
azar(K
uruskul)
Station
2
=
M
oheskhali(G
orakghata)
Station
3
=
C
hakaria
(D
arbeskhata)
pond at Chakaria Sundarban 34.84 ‰ in March. In the present investigation lower salinity
(30.03 ‰) was recorded of the reservoir at station 1 (Kuruskul). The salinity of Kuruskul
area of Cox’s Bazar is directly influenced by Bankkhali river.
Electric conductivity:
Electric conductivity was gradually increasing from reservoir to crystallizer pans due
to evaporation by solar heat (i.e. Reservoir <Condenser <Crystallizer). The minimum
value was found to be 93.6 mmohs/cm in reservoir and highest 336 mmohs/cm in
crystallizer at station 1. Ramesh and Subramanian (1985) observed that conductivity
values of salt farms showed variation from pans to pans and they also mentioned that
conductivity followed with increasing salinity because of the chemical complexity of
brines. In the salt farm of Madras they measured the conductivity range between 18 and
106 mmohs/cm, but in present study conductivity was higher in all sampling stations of
solar salt farm of Cox’s Bazar, Bangladesh than that of solar salt farm near Madras, India.
Total hardness:
The hardness of sea water from the investigated area ranged from 8000 to 213600
mg/l. The minima always recorded at reservoir pans and maxima were in crystallizer pans.
It was gradually increasing from reservoir to condenser and then crystallizer pan.
Gradually higher values of hardness of CaCO3 were found in Moheskhali Island and
Chakaria Sundarban area.
Calcium:
The Ca concentration of three sampling stations of Cox’s Bazar district varied from
2987 to 106300 mg/l. The lower concentration was recorded in reservoir pan and higher
obtained in crystallizer. Ca from reservoir to crystallizer pan was increasing (reservoir
<Condenser <Crystallizer). Ramesh and Subramanian (1985) stated that Ca concentration
varied 551 to 3608 mg/l in the solar salt farm at Madras. The present investigated area had
higher Ca concentration than Madras.
Magnesium:
Mg ion concentration in salt farm waters varied between 5013 mg/l and 107300 mg/l.
Mg was also increasing from reservoir to crystallizer. Abu-Hena et al.(2000) reported that
in an average 250.20±15.05 mg/l of Mg was present in sea water, when mean salinity
10.7±2.2 ‰ near at Bankkhali River, Bangladesh. In the present investigation Mg found
between 5013 to 7250 mg/l in reservoir pans of Cox’s Bazar salt production farms.
Bicarbonate:
The minimum concentration of HCO3 (36.6 ml/l) was recorded in Chakaria and in
this area HCO3 was not detected in the condenser and crystallizer pans. The higher
concentration of bicarbonate was recorded in the Moheskhali Island (146.4 mg/l) and its
concentration was gradually increasing (reservoir <condenser <crystallizer) at station 1
and 2. Bicarbonate was found in the solar salt farm waters, where pH value obtained
above 6.3. Ramesh and Subramanian (1985) reported that 146-582 mg/l of HCO3 was
found in the solar salt farms at Madras.
84 Pakistan Journal of Marine Sciences, Vol. 10(2), 2001.
Alkalinity:
Alkalinity values varied between 50-570 ppm in the area of investigation. It was not
detected in condenser and crystallizer pans of the Chakaria Sundarban station, where pH
ranged between 4.9 and 5.7. Belaluzzaman (1995) stated that total alkalinity content in
the intertidal water ranged from 100 to 150 ppm with a yearly mean of 127.08 ± 15.47
ppm in the sea shore of Cox’s Bazar and he also recorded the total alkalinity (70-145ppm)
in the surface waters of Bankkhali river estuary. The alkalinity concentration of reservoir
pans at Kuruskul and Gorakghata solar salt farms is more or less similar with the results
of Belaluzzaman, 1995.
Potassium:
Potassium concentration was found between 3.4 and 15.20 g/l in the investigated
area. The highest value of K was recorded in the Moheskhali Island. Ramesh and
Subramanian (1985) reported that K concentration varied from 0.825 to 5.78 g/l of the salt
farm in Madras.
CONCLUSION
The physico-chemical factors of solar salt farm of Bangladesh were recorded for the
first time during present investigation. This report would be helpful for farmers during salt
production.
ACKNOWLEDGEMENT
We are grateful to Director, Institute of Marine Sciences (IMS), University of
Chittagong for giving laboratory facilities.
REFERENCES
Abu-Hena, M. K, M. Zafar and N. Mahmood, 2000. Some aspects of ecological study on
extensive shrimp culture ponds at Cox’s Bazar, Bangladesh. Malays. Appl. Biol. 29
(1&2): 17-25.
Aitken, M.J. 1984. Thermoluminesence Dating, Academic Press, London, pp. 123.
APHA. 1976. Standard methods for the examination of water and waste water. 14th ED.
N.Y. Amer. Pub. Health Assoc. 1193pp.
Alam, M.N., M. I. Chowdhury, M. Zafar, M. Kamal, S. Ghose and A.H.M. Kamal, 1988.
Radionuclide concentrations in salt pans in the coastal area of Cox’s Bazar,
Bangladesh. J. Environ. Radioact., 44(3): 257-267.
Ali, S.S. Sukanta and N. Mahmood, 1985. Seasonal abundance of plankton in Moheskhali
Channel, Bay of Bengal. Proceedings of the Seminar on Protecting the environment
from degradation, Dhaka. Pp 128-140.
Barnes, H. 1959. Apparatus and methods of Oceanography (chemical), London and N. Y.
Acad. Press. 178-183.
Belaluzzaman, A.B. 1995. Ecology of the intertidal macrobenthic fauna in Cox’s Bazar
Zafar et al.: Physico-chemical factors of solar salt farm water Bangladesh 85
coastal area, Bangladesh. M. Sc. Thesis, Institute of Marine Sciences, University of
Chittagong, pp 146.
Mahmood, N., M. Zafar, P.K. Barua and S. Ali, 1993. Macrobenthic fauna of an
aquaculture pond of Chakaria Sundarban, Bangladesh. Pak. J. sci. ind. Res. 36(4):
156-158.
Mahmood, N. and S.Q. Saikat, 1995. On acid sulphate soils of the coastal aquaculture
ponds of Bangladesh. Pakistan Jour. Mar. Sci. 4(1): 39-43.
Mahmood, N. and Y.S.A. Khan, 1980. On the occurrence of postlarvae and juveniles of
penaeid prawn at Bankkhali estuary and adjacent coastal area of Cox’s Bazar with
notes on their utilization in aquaculture. Univ. Grants Comm. Res. Prog. Final report
22 pp.
Mahmood, N, Y.S.A. Khan and K. Ahmed, 1976. Studies on the hydrology of the
Karnafuli estuary. Jour. A. Soc. Bangladesh, Science, 2(1): 89-99.
Ramesh, R. and V. Subramanian, 1985. Water-mineral equilibria in solar salt farm near
Madras, East coast of India, India J. Mar. Sci; 14 June, 79-84.
Zafar, M. 1994. On the occurrence of Milkfish Chanos chanos (Forsskal, 1775) larvae in
the mangroves of Kutubdia Channel, Bangladesh. Mar. Res. 3(1): 41-46.
(Received: 10 August, 1999)
86 Pakistan Journal of Marine Sciences, Vol. 10(2), 2001.


Physico-chemical factors of solar salt farms water in the coastal area of Cox’s Bazar, Bangladesh

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Physico-chemical factors of solar salt farms water in the coastal area of Cox’s Bazar, Bangladesh

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