The document describes a study that investigated using freezing as a method for desalinating seawater. Three seawater samples were collected from Boshehr beach in the Persian Gulf and subjected to three cycles of a freezing-melting process. This involved crystallization at -20°C, separation of ice crystals, surface washing, and melting. Testing showed that after three cycles, the total dissolved solids in the samples were reduced to levels making the water potable. Freezing is a potential desalination method for remote areas due to its low energy requirements compared to other processes like reverse osmosis. However, freezing also has disadvantages such as higher costs and potential water quality issues.

1. Arab J Sci Eng (2011) 36:1171–1177
DOI 10.1007/s13369-011-0115-z
RESEARCH ARTICLE - CHEMICAL ENGINEERING
Mokhtar Mahdavi · Amir Hossein Mahvi · Simin Nasseri ·
Masoud Yunesian
Application of Freezing to the Desalination of Saline Water
Received: 22 August 2009 / Accepted: 25 May 2010 / Published online: 21 October 2011
© King Fahd University of Petroleum and Minerals 2011
Abstract Freezing is one of the methods used for desalination. Although different methods, like reverse osmo-
sis and distillation, are used commercially, freezing can be used for remote areas, cold regions and for small and
remote societies. We have investigated the method of crystallization by external cooling via non-direct contact
for desalination of seawater. The steps used for the freezing-melting (FM) process included: crystallization
(at −20◦C), separation, surface washing and melting of the samples. Three samples were taken from Boshehr
beach. After three cycles of FM, the total dissolved solid (TDS) of the first sample reduced from 37,650 to
15,200, 5,059 and 1,403 mg/L, for cycles one, two and three respectively. For the second sample the TDS
reduced from 40,750 to 17,884, 5,584 and 1,487 mg/L and for the third sample with from 33,351 to 15,885,
4,850 and 1,345 mg/L. This showed that after three cycles of FM, potable water can be produced.
Keywords Desalination · Freezing · Non-direct contact freezing · Persian Gulf
M. Mahdavi · A. H. Mahvi (B) · S. Nasseri · M. Yunesian
School of Public Health and Institute for Environmental Research,
Tehran University of Medical Science, Tehran, Iran
E-mail: ahmahvi@yahoo.com
A. H. Mahvi
National Institute of Health Research, Tehran University of Medical Sciences,
Tehran, Iran
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2. 1172 Arab J Sci Eng (2011) 36:1171–1177
1 Introduction
Approximately 97.5% of the water on our planet is located in the oceans and is therefore classified as seawater.
Of the 2.5% of fresh water, approximately 70% is in polar ice and snow, and the remaining 30% is ground
water, river and lake water, and air moisture [1]. Today’s desalination technology for the production of fresh
water can be divided to two sections that depend on the mechanism used for the removal of salts. (a) Separation
processes: membrane processes that use electrical and mechanical forces, such as electro dialysis (ED) and
reverse osmosis (RO). (b) Thermal processes: changes in phase, such as distillation and freezing [2,3]. The
Danish physician Thomas Bartholinus (1616–1680) was the first to report that water obtained by melting ice
formed in seawater was fresh water. Almost at the same time, Robert Boyle reported the same observation
and foresaw the phenomenon as a source of fresh water [4]. At the end of the eighteenth century, the Italian
scientist Anton Maria Lorgna described a method to purify seawater and impure water by freezing and then
melting of the ice [5].
The method of water purification by freezing-melting (FM) was only possible in the coldest regions and
seasons, and not of practical interest, until the development of refrigerating machines. Interest in the process
of obtaining fresh water from seawater by freezing was revived in the late 1930s. The FM process was first
used commercially in the 1950s. Research in the 1960s and 70s in desalination, petroleum and food processing
applications provided many technical innovations [6].
Today, freezing processes have many applications in various areas of industry, such as the concentration
of fruit juice, dairy products, wastewater sludge and desalination. In addition, it can be used as a pretreatment
method for desalination of brackish and saline water to be further treated by other methods, like electro dialysis
and reverses osmosis [7]. In theory, the freezing process can separate water from saline and impure water by
freezing and crystallization of water. In ideal conditions the ice produced should be pure and without salts.
Fresh water can be produced by freezing of seawater, separation of crystals, surface washing and thawing of
crystals [8,7,6,5].
The three broad classes of FM processes are: direct contact freezing, non-direct contact freezing and
vacuum freezing. All of these methods involve crystallization, separation, surface washing and thawing of
the crystals. Separation of ice crystals can be performed by gravity drainage, centrifuge, filtering, and wash
columns [8,7,6,5,9].
Experimental results show that the melted ice water from a single freezing, without a wash step, has three
to six times less salt content than the feed water [10]. Nicholas showed that for frozen source water with
3,000 mg/L NaCl at an ambient temperature of −15◦C, removal of 80% of the salt was possible after melting
9% of the ice [11].
A combined RO/direct contact freezing system provides an efficient system to reduce the problem of dis-
posal of the rejected brine from inland desalination plants. Results show that the combined system can reduce
the energy consumption by about 13% and 17%, compared with separate RO and direct contact freezing plants
respectively [7]. Although the FM process isn’t widely used commercially, this process has advantages over
currently used processes. Perhaps the greatest potential advantage of desalination by freezing is the very low
energy required compared with other desalination processes. This is because the latent heat of fusion of ice is
only one-seventh the latent heat vaporization of water [12].
The freezing process also has the advantage of a low operating temperature, which minimizes scaling and
corrosion problems. Furthermore, inexpensive plastics or other low cost materials can be used at low temper-
atures [15,14,13]. Disadvantages of the freezing process include: higher initial investment and capital cost;
higher operation costs during ice separation; and the persistence of the primary odor and taste of the water
[16,17].
In this study, the effect of the freezing process on the removal of cations and anions (bicarbonate, sulfate,
chloride, calcium, magnesium, sodium and potassium), total dissolved solid (TDS) and electrical conductivity
(EC) of Persian Gulf water is investigated.
2 Materials and Methods
Three water samples from different locations at Boshehr beach in the Persian Gulf were tested. The sample
volumes were 50 L. Physicochemical characteristics of these three sample, such as bicarbonate, sulfate, chlo-
ride, calcium, magnesium, sodium, potassium ion concentration, TDS and EC, were measured according to
standard methods for examination of water and wastewater [18] (Table 1). The FM cycle was performed on
the samples according to Fig. 1. The method used for desalination was crystallization by non-direct contact
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