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Water Desalination Methods

Water Desalination Methods

Water Desalination Methods

Research suggests that nearly 98 percent of all the water on earth is salty. Through desalination, the process used to remove salt from water, over 16 billion gallons of desalinated water are produced daily, primarily for drinking. There are several methods by which this can be accomplished, but unfortunately, they’re all quite expensive.

Most methods used to filter large quantities of water produce byproducts that are considered hazardous. One such byproduct is concentrated brine, which is harmful to both animals and fresh water. Large-scale desalinization methods include:

  • Carbon Nanotube Enhanced Membrane Distillation (CNT)
  • Vapor Pressure
  • Forward Osmosis
  • Reverse Osmosis
  • Solar Desalination

Here’s a closer look at the water desalination techniques mentioned:

Carbon Nanotube Enhanced Membrane Distillation (CNT)

Carbon nanotubes are revolutionary new materials that aid in the preparation of new membranes with highly selective, low-fouling properties. In layman’s terms, carbon nanotubes exhibit ultra-high salt absorption capacity. Long carbon nanotube membranes can remove salt and any other metal or organic contaminants. Studies reveal that this method of desalination may lead to the next generation of water purification appliances and researchers are working hard to perfect the entire process.

Vapor Pressure

In this process, pressure is inserted into the thermodynamic equilibrium by vapor in its condensed state. The vapor is then subjected to pressure either in a liquid or a solid state at specific temperatures within a closed system. The liquid’s evaporation rate is indicated by the equilibrium’s vapor pressure.

With an incremental increase in temperature, vapor pressure is forced to overcome atmospheric pressure, at which point the liquid turns to vapor. The formation of vapor bubbles requires an even higher temperature, allowing pure water to escape the salt in vapor form. These vapor bubbles are then collected to form fresh water.

Forward Osmosis

Forward osmosis is a process that utilizes a semi-permeable membrane to separate water efficiently from dissolved solutes. An osmotic pressure gradient is the chief element that makes this process work.

The osmotic pressure gradient induces a net flow of water via the membrane and into the draw solution. The process effectively separates feed water from solutes.

Reverse Osmosis

As opposed to forward osmosis, reverse osmosis utilizes hydraulic pressure as the element to aid in the separation process. The hydraulic pressure actually counteracts the osmotic pressure gradient. As a result, the entire purification process uses more energy than forward osmosis.

Solar Desalination

Solar desalination is a method that utilizes the sun’s energy to remove salt from water. The two primary methods used in solar desalination are the direct method and the indirect method.

Direct solar desalination involves a solar collector joined to a distilling mechanism. The entire process takes place in a single cycle. The water produced by this method is proportional to the solar surface area.

Indirect solar desalination employs either a solar collection array or a separate conventional desalination plant. A solar collection array typically consists of fluid-based thermal collectors or photovoltaic collectors. If a separate plant is used, the separation of water and solutes is heavily dependent on the plant’s efficiency. The per-unit cost of the process goes down as the scale of the operation increases.

The processes listed above are methods currently available for large-scale water desalination. Although their high cost and hazardous byproducts are serious concerns, the earth’s growing population and changing needs have created water shortages that need to be addressed. It’s also likely that solutions to these and other problems will be uncovered by further research, at some point.