How to desalinate water?

Seawater desalination technology uses physical, chemical, or biological methods to remove salt and various impurities from seawater, converting saltwater into fresh water suitable for drinking, agricultural irrigation, and industrial use. Current mainstream desalination processes each have their own advantages and disadvantages, and suit different application scenarios. How to desalinate water? The following text will provide a detailed breakdown of several core technological approaches.

How does distillation desalinate water?

Distillation can desalinate water to fresh water. Distillation is the first seawater desalination technology to be successfully implemented on an industrial scale, and its core principle is similar to the natural water cycle. It works by heating seawater to induce evaporation, then cooling and condensing the resulting water vapor into fresh water, thus separating salt from water.

Advantages and disadvantages of distillation desalination

The advantages of this process include its simple operation, stable performance, and wide adaptability to varying seawater salinity levels, making it particularly suitable for areas with abundant energy resources.

Currently, the most widely used distillation technology is multi-stage flash distillation. This method introduces seawater into multiple flash chambers with progressively decreasing pressure, causing the seawater to rapidly vaporize at temperatures below its boiling point. The resulting water vapor is then condensed and collected as fresh water.
Compared to traditional single-stage distillation processes, multi-stage flash distillation significantly reduces energy consumption and requires less space. They have built several large-scale desalination plants that use this technology in energy-rich regions like the Middle East. Furthermore, low-temperature multi-effect distillation utilizes waste heat from steam to perform multiple evaporation and condensation cycles, further improving energy efficiency and making it suitable for integration with facilities such as power plants.

How does reverse osmosis desalinate water?

Reverse osmosis can be able to desalinate water to drinking water. Reverse osmosis is a seawater desalination technology that has rapidly emerged and become mainstream in recent decades. It relies on the selective permeability characteristics of reverse osmosis semipermeable membranes. Under high pressure, we force seawater through a reverse osmosis membrane that only allows water molecules to pass through, while we block salts, heavy metal ions and other impurities on the other side of the membrane, thus producing qualified fresh water.

Advantages and disadvantages of reverse osmosis seawater desalination

The core competitiveness of this technology lies in the research and application of high-performance reverse osmosis membranes. The membrane’s permeability and corrosion resistance directly affect desalination efficiency and overall cost.
Compared with distillation, reverse osmosis significantly reduces energy consumption, requiring only one-third to one-half of the energy of the former. Furthermore, the equipment is compact and has a short construction period, making it suitable for use in areas with strict limitations on space and energy consumption, such as cities and islands.

However, this technology requires high standards for seawater pretreatment, necessitating the removal of suspended solids, colloidal substances, and microorganisms from the seawater beforehand to prevent membrane pore clogging. Furthermore, the replacement cost of reverse osmosis membranes is high, and subsequent maintenance requires specialized personnel, which to some extent limits its widespread application in some less developed regions.

Other auxiliary desalination technologies

What other methods are there to desalinate water? Besides the two mainstream processes mentioned above, several other seawater desalination technologies are in the research and development or small-scale pilot application stages.
Electrodialysis utilizes the selective permeability of ion exchange membranes under the influence of an electric field to cause ions in seawater to migrate towards the electrodes, thereby achieving the separation of fresh water and salt. It is suitable for treating low-salinity seawater or brackish water and is often used in small-scale drinking water purification projects.
Solar-powered seawater desalination technology combines the advantages of renewable energy by using solar collectors to heat seawater or provide power to reverse osmosis systems. It is environmentally friendly and sustainable, making it suitable for remote areas with abundant sunlight. However, weather changes significantly impact this technology and it lacks operational stability, so we have not yet adopted it widely on an industrial scale.

In addition, new technologies such as membrane distillation and freeze desalination are continuously overcoming limitations and will likely further reduce desalination costs and improve efficiency in the future.

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Overall, the complementary application of different technologies can more accurately match the resource endowments of various regions, providing diversified solutions to the global water scarcity problem.