Reverse Osmosis And Distillation Compared

Reverse Osmosis And Distillation Compared

Today, there are two leading technologies in the water purification markets, namely, reverse osmosis and distillation. Lately, however, there is a controversy a-brewing among manufacturers of these water purifying machines and devices. The following is a comparison between reverse osmosis and distillation.

First, we shall examine each of these processes.

What is reverse osmosis?

According to its proponents, reverse osmosis (also known as hyper filtration) is the finest water filtration system at the moment.

One of the contentions is that the process removes particles as small as molecular ions from a solution. It purifies water by removing dissolved salts, minerals and other impurities and brings back its taste, color and its other properties.

Its other use is purifying other fluids such as ethanol and glycol through the reverse osmosis membrane and straining out ions and contaminants.

There are other very useful uses of reverse osmosis and its technology, but the most common is in purifying water.

Reverse osmosis uses a semi-permeable membrane that allows the fluid being purified to pass through while blocking the present contaminants. These membranes have microscopic pores that are small enough only for water molecules and not the others.

Today, most of the reverse osmosis technology also employs the method called crossflow. This is where the membranes continually clean themselves. As water passes through, the rest continues downstream and sweeps the rejected substances away.

Reverse osmosis needs a driving force to pressure the fluid through the membrane, and this is done by a common pump. The higher the concentration of rejected fluid, the pressure needed grows higher as well.

At present, the technology of the reverse osmosis is capable of rejecting bacteria, salts, sugars, proteins, particles, dyes, and other constituents that have a molecular weight of greater than 150-250 daltons. Meantime, the ions are separated with the help of charged particles. Ions with charge (like salt) are rejected by the membrane and those with no charge (such as organics) are let in.

How does distillation work?

Distillation is a water purification process that uses a heat source. Water is heated and vaporized to separate it from contaminants.

The heat is kept constant to prevent the other unwanted elements from vaporizing. This is because water has a lower boiling point than salt and other mineral sediments. Distillation also separates disease-causing organisms from the water molecules.

Once all of the water has vaporized, the vapor is led into a condenser where it is cooled, and reverts back to its liquid form into a receiving container.

The remaining elements, whose boiling points are too high for vaporization, are left in the original container as sediment. Distillation is often repeated to ensure that all sediments are left behind in the process.

Many alcoholic beverages (brandy, gin, whiskey) are distilled with apparatus similar to that used in water distillation.

Because of the cost of heating in the distillation process, solar power was looked up as an efficient alternative. However, solar power only works with relatively small amounts of liquid. Multiple distillations is also out of the question because of time constraints.
More solar distillation experiments are still in progress, though.

Is a reverse osmosis unit like a distiller?

The processes are totally different. A distiller is like a tea kettle – it boils water, catches the steam, and condenses it back into water.

Reverse osmosis strains the water with a very tight semi-porous membrane. Both systems however rely on carbon filters to remove some chemicals.

Which water is purer – those produced by distillers or by reverse osmosis?

Distillers remove sodium and other common minerals better than reverse osmosis. But they are not that good in removing volatile chemicals with low boiling point.

Reverse osmosis with the carbon filters remove chloramines (the current favorite water disinfectant) best.

Both, however, produce very pure water. Actually, with reverse osmosis and distillation compared, the only difference would be the economics of ownership costs and maintenance expenses.