Reverse Osmosis Theory
Reverse osmosis is a method of filtration that removes diluted solids from a feed source, leaving a much purer product. Quite often the feed is contaminated water, such as salt water, that needs to be purified to create potable drinking water.
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Osmosis
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Osmosis describes how water moves through semipermeable membranes, filtering out whatever solute (dissolved solid substance) may be present in the water. This technique is used in many industrial processes such as waste treatment and production and is also present in nearly every biological system, including the human kidneys.
How it Works
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Osmosis involves having two volumes of a liquid separated by a semipermeable membrane. The water will flow from the volume of low dilution to the volume of high dilution in an effort to equalize osmotic pressure. The amount of pressure needed on the high dilution to stop the flow and possibly reverse it is known as the "osmotic pressure" in systems where only one side has any solute at all.
Some systems have only one side with solute in them, and the other side is pure water. The force required to stop the flow of water into the side with the solute and instead filter the water into the side with less solute is called "osmotic pressure."
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Reverse Osmosis
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With reverse osmosis, osmotic pressure pushes the high dilution volume through the membrane into the low dilution volume, diluting the low dilution more and increasing the concentration of the solute in the high dilution side. This leaves the contaminated water with a higher concentration of contamination, and the clean water increases in volume. Dialysis and the process of purifying drinking water are two common uses of reverse osmosis.
Water Filtration
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Salt water can be made into potable water using reverse osmosis. A feed of salt water is put into one side of the osmotic membrane and pressure is increased until the water starts pushing through the membrane and potable water comes out the other side. Many systems use multiple passes or multiple filters.
The formula to determine how much energy is needed to produce a given volume of drinking water is given by E = pV/36, where "E" represents kilowatt hours, "p" represents bars (a measurement of pressure) and "V" stands for cubic meters.
Food Industry
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In the food industry, reverse osmosis is one of the most economical and cost-efficient ways of producing food and liquid powders, as opposed to heat treatment. Reverse osmosis can be used on heat-resistant products such as juices and on heat-sensitive products such as milk.
Kidneys and Dialysis
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Kidneys and artificial dialysis machines use reverse osmosis by straining the blood through a membrane and leaving the contaminants behind, generally in the form of urine or a removable substance.
Disadvantages
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Reverse osmosis has its drawbacks. It has a low efficiency rate, with household osmosis machines generally only being able to recover 5 to 10 percent of the feed (contaminated) liquid and large industrial setups only recovering 48 percent.
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References
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