On Reverse Osmosis and Water Treatment

Reverse osmosis or RO is the process of forcing a solvent through a semipermeable membrane, from a region of high solute concentration to one that has a low solute concentration. The natural flow is the opposite, and is called the process of osmosis. Reverse osmosis only occurs when enough pressure is applied to counter the natural movement.

The most salient use of the process of reverse osmosis is in the purification and treatment of water.

Some applications require the water used to be free from contaminants and other harmful substances. The boiler water in power plants has to be pure to keep the machinery it uses free from damage.

Others need the water to have solutes mixed at certain concentrations. Most salt water aquariums are equipped with reverse osmosis filters that maintain saline, nitrogen and phosphate levels.

Reverse osmosis, however, is most applied in the production of potable water. In far-flung communities where drinkable water isn't readily available, reverse osmosis filters are used to clean the water from rivers, lakes or springs. Such filters are also used to desalinate salt water. At the same time, waste water is often treated in a process that has a reverse osmosis filter.

Cleaning the water is not achieved by a single pass through a reverse osmosis filter. In fact, there are many steps to ensure that the water ends up free of any unwanted particle or substance.

First, water for treatment is drawn in to filter out large sediments and particles. Some, more meticulous systems, would have the water pass through another sediment filter with smaller pores.

Next, the water passes through an activated or active carbon filter. Activated carbon filters, like charcoal, have very large surface areas. These substances are very porous, making them useful as filters. Activated carbon is used for water treatment not only to capture smaller organic particles, but also to absorb such substances as chlorine, which could damage the entire water treatment system.

The water is then passed through an RO membrane, often referred to as a thin film composite membrane. Referred to as TFCs, these membranes are often made from polyimides because these substances let water through, though these keep other small molecules at bay.

After passing through the TFC, water is made to flow through another RO filter as a precaution. Afterwards, the water undergoes ultra-violet light treatment to kill any organism that may have escaped prior filtering processes.

The water is then tested if any other unwanted substance has passed through. If the results are favorable, the clean water is then pumped right back into the piping system.