Membrane Processes

Membrane separation, electrodialysis, reverse osmosis, ultrafiltration and other such processes play an increasingly important role in the treatment of waste water (Chapter 10).

A membrane is defined as a phase that can act as a barrier between other phases. It can be a solid, a solvent-swollen gel, or even a liquid.

Osmosis is defined as the spontaneous transport of a solvent from a diluted solution to a concentrated solution across a semi-permeable membrane. At a certain pressure, the so-called osmotic pressure, equilibrium is reached. The osmotic pressure varies with the concentration and the temperature, and depends on the properties of the solution.

Nitrogen compounds treated in such systems are mainly in the form of ammonium or nitrate. Electrodialysis can be expected to remove about 40 per cent of these forms; in reverse osmosis, 80 per cent.

Today the application of membrane techniques is still limited, but waste water engineers and scientists in the field of membrane processes expect a rapid growth in the use of these technologies in the very near future.

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