What is Desalination? This is a desalination membrane cutaway below. As you can see, the spiral wound membrane is quite a complex component. This is the heart of the desalination process. The most important components in a desalination system, are the membranes and the high pressure pump. The membrane, is where the actual process occurs. The fresh water or (permeate) is separated from the salt solution (feed water) and directed away  from the  membrane to be collected as the 'Product' . The high pressure pump creates the pressure required, to allow the membrane to function correctly. The salt-free water, or permeate, then becomes a usable source of fresh water. In theory, this water is potable, although for human consumption, it is highly recommended that the water be treated with an Ultra Violet lamp to kill any bacteria that may be present, prior to drinking. There are many pre-treatment and post-treatment methods for desalinated water. The most appropriate method, depends on the feed water source, and the intended use of the product water. Watch the short video below, to learn how the membrane is constructed. This will help you understand more about the importance of the membrane, within this type of desalination system. Reverse osmosis is explained, briefly, on page 2 of this article...

Desalination processes are divided into (i) thermal methods, which involve heating water to produce water vapour, and (ii) membrane processes, which use a relatively permeable membrane to move either water or salt to induce two zones of differing concentrations to produce fresh water. The main thermal method employed is distillation, where saline water is progressively heated in subsequent vessels at lower pressures. Brief descriptions of the main desalination processes are provided below.

1. Distillation Processes

Multistage Flash Distillation is the most widely-used desalination method worldwide. It involves heating saline water to high temperatures and passing it though vessels of decreasing pressures to produce the maximum amount of water vapour (fresh water).

Multi-Effect Distillation operates at lower temperatures but uses the same principles as multistage flash distillation.

Vapour Compression Distillation is generally used in combination with other processes, where the heat for evaporating water comes from the compression of vapour, rather than the direct exchange of heat.

2. Membrane Processes

Reverse Osmosis is a pressure driven process which forces saline water through a membrane, leaving salts behind.

Electrodialysis is a voltage driven process and uses an electric potential to move salts selectively through a membrane, leaving fresh water behind.