Reverse Osmosis MCQ - Practice Questions & Answers

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A reverse osmosis system is designed to produce $50 \ \text{m}^3/\text{day}$ of permeate water from seawater containing 35,000 ppm of dissolved salts. The system has a water recovery rate of 70% and the applied pressure is 20 bar. If the membrane has a salt rejection coefficient of 0.97, what is the concentration of salts in the permeate water?

1050 ppm

1330 ppm

1500 ppm

1750 ppm

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Concepts Covered - 1

Reverse Osmosis

The direction of osmosis can be reversed if a pressure larger than the osmotic pressure is applied to the solution side. That is, now the pure solvent flows out of the solution through the semi-permeable membrane. This phenomenon is called reverse osmosis and is of great practical utility. Reverse osmosis is used in desalination of seawater. A schematic set up for the process is shown in Figure given below. When pressure more than osmotic pressure is applied, pure water is squeezed out of the seawater through the membrane. A variety of polymer membranes are available for this purpose.

The pressure required for the reverse osmosis is quite high. A workable porous membrane is a film of cellulose acetate placed over a suitable support. Cellulose acetate is permeable to water but impermeable to impurities and ions present in seawater. These days many countries use desalination plants to meet their potable water requirements.