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Reverse Osmosis Systems and Some Popular Uses

Humans have been devising ways to free water of impurities for thousands of years with varying degrees of success. Most of the techniques employed for this purpose rely on mechanical filtration, involving passing a liquid through a porous medium: the smaller the pores, the more efficient the process. Early filter systems were limited to removing visible solids like dust and soil particles. Today, reverse osmosis (RO) systems enable filtration at a molecular level.

Filtration System RO Membrane and Control System

The process is a variation of that employed by plants to maintain rigid stems and assist the dispersion of dissolved nutrients. Plant cells contain water, and so do the spaces around them. The cell walls are semi-permeable, allowing water molecules through but nothing larger. Water will always migrate through the cell walls from areas with low levels of dissolved solids to regions of higher concentration until the levels are equal. By contrast, reverse osmosis systems employ external pressure to force a continuous flow of liquid through a synthetic membrane, preventing equilibrium and leaving the precipitated solids on its surface.

Since its introduction, RO technology has gained numerous industrial and commercial applications. Wherever water of exceptional purity is necessary, it is invariably the method of choice. For example, due to its low cost and high efficiency, it is the preferred process of the bottled water industry, recently estimated to generate worldwide annual sales worth more than US$200 billion. The pharmaceutical and semiconductor industries also rely on the exceptionally pure water produced by reverse osmosis systems.

Sometimes it’s the solute and not the solvent that’s important. For example, the technique can provide mining and chemical companies with a means to recover precious metals and other reusable materials from liquid waste. However, it now seems likely that the most vital role for RO might be to deliver the world from the looming threat of a water crisis. Few South African’s are likely to forget the “Zero Day” drought that came close to seeing Cape Town’s taps run dry. Desalination plants at Strandfontein and Monwabisi employed reverse osmosis systems to help prevent the near disaster.

Desalination is not a new idea. The first commercial plant was built in 1930 on the Caribbean island of Aruba. However, all such plants relied on evaporating the eater and collecting the condensate until relatively recently. Evaporative technology requires a lot of energy and costs more than conventional water treatments. RO requires comparatively little power, making it more cost-effective, and the future direction for desalination plants.

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