Seawater Chemistry and Desalination Methods Explained
This paper examines the chemical and physical properties of seawater and explains why untreated seawater is unfit for drinking. It outlines the origins of water and dissolved salts in the ocean, reviews key physical properties such as boiling point, freezing point, density, and conductivity, and discusses two primary desalination methods: reverse osmosis and thermal distillation. Real-world examples, including the Sorek plant in Israel and the Curacao Netherlands Antilles plant, illustrate how large-scale desalination overcomes cost and engineering challenges to supply fresh water from the sea.
- Introduction: Why seawater requires treatment before drinking
- Chemical and Physical Properties of Seawater: Origins, composition, salinity, and physical constants
- Desalination Methods: Reverse osmosis and thermal distillation processes compared
- Conclusion: Desalination transforms seawater into safe drinking water
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What makes this paper effective
- The paper grounds its discussion in precise quantitative data — elemental composition in parts per million, exact boiling and freezing points, and conductivity values — giving scientific credibility to its claims.
- It effectively links theoretical properties (salinity, osmotic pressure) to practical applications (desalination plant design and economics), showing cause-and-effect reasoning.
- Real-world case studies, the Sorek plant and the Curacao plant, are used to anchor abstract process descriptions in concrete, verifiable examples.
Key academic technique demonstrated
The paper demonstrates the use of compare-and-contrast structure within a thematic section. By presenting reverse osmosis and thermal distillation side by side — covering cost, process, energy use, and historical context — the writer allows readers to evaluate the trade-offs between methods without the author having to state a direct preference, which suits a descriptive scientific paper.
Structure breakdown
The paper follows a classic science-essay structure: a short introduction establishes purpose and scope; a properties section builds foundational knowledge using data and citations; an applications section translates that knowledge into process descriptions supported by case examples; and a brief conclusion synthesises the paper's purpose. The concise conclusion is appropriate for a descriptive rather than argumentative piece.
Introduction
The seas are made up of water, but that water is not drinkable, requiring treatment in desalination plants prior to distribution in drinking water systems. To understand how and why seawater is unfit for drinking, and to appreciate the complexities of desalination, it is necessary to examine the chemical and physical properties of seawater. Following this, two different desalination methods are discussed.
Chemical and Physical Properties of Seawater
Seawater is made up of water and various salts. Water, which accounts for approximately 96.5% of all seawater (Anthoni, 2006), is believed to originate mainly from water that condensed in the Earth's early atmosphere, falling to the ground as the crust of the Earth solidified (Pidwirny, 2006). Additional water has been contributed through volcanic activity, while some scientists speculate that comets entering the atmosphere may also have been a water source (Pidwirny, 2006).
The dissolved salts in seawater have a continental origin, released into water as rocks were weathered and carried to the sea by rivers (Pidwirny, 2006). There are up to 82 different elements that may be present in seawater (Turekian, 1968); however, only 6 elements make up 99% of dissolved salts, with chlorine comprising 55% of all sea salts and sodium comprising 30.6%. The main elemental constituents of seawater are detailed in the table below.
(Anthoni, 2006)
Physically, the salinity of seawater can vary, but the proportion of the different salts remains very consistent (Pidwirny, 2006). Other physical properties of seawater, however, depend on the salinity level (Pidwirny, 2006). Seawater usually boils at 100.56° Celsius at normal atmospheric pressure (Bullard, 2015). At 3.5% salinity, seawater freezes at −1.91° Celsius, with most of the salts forced out during the freezing process (Pidwirny, 2006). When frozen, water has a lighter density of between 0.84 and 0.91 Mg m⁻³ when located above the waterline, and 0.90 to 0.94 Mg m⁻³ for ice located below the waterline, which is why ice floats (Timco & Frederking, 1996).
The mean conductivity of seawater is 3.27 S m⁻¹, excluding shallow oceans. At a depth of 400 metres, conductivity increases to approximately 6% greater than at the surface (Bullard, 2015).
Conclusion
Seawater provides an excellent potential source of fresh water. Through different types of desalination, seawater may be transformed into safe drinking water by removing its salts and minerals.
References
Anthoni, J. F. (2006). The chemical composition of seawater. Retrieved from http://www.seafriends.org.nz/oceano/seawater.htm#composition
Bullard, E. (2015). Physical properties of sea water. Retrieved from
Cipollina, A., Micale, G., & Rizzuti, L. (2009). Seawater desalination: Conventional and renewable energy processes. New York: Springer.
IETC. (1997). Source book of alternative technologies for freshwater augmentation in Latin America and the Caribbean. Retrieved from http://www.oas.org/dsd/publications/unit/oea59e/begin.htm#Contents
Karagiannis, I. C., & Soldatos, P. G. (2008). Water desalination cost literature: Review and assessment. Desalination, 223(2), 448–456.
Pidwirny, M. (2006). Physical and chemical characteristics of seawater. Retrieved from http://www.physicalgeography.net/fundamentals/8p.html
Talbot, D. (2015). The world's largest and cheapest reverse-osmosis desalination plant is up and running in Israel. Retrieved from
Timco, G. W., & Frederking, R. M. W. (1996). A review of sea ice density. Cold Regions Science and Technology, 24(1), 1–6.
Turekian, K. K. (1968). Oceans. London: Prentice Hall.
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