Reverse Osmosis Filtration Stages

By | March 14, 2017

One common customer dilemma nowadays is the issue with what contaminants RO systems protect us from. In a conversation with a salesman who wants to replace his RO system filters, one customer was in shock when he found out that a reverse osmosis system’s semi-permeable membrane cannot filter chlorine. We don’t know how many more customers had their eyes popped wide open when a similar scenario happened.

Truth be told, the salesman was just being honest about it. However, he himself has been misinformed about how a modern RO water purifier works. To clear the confusion, here is a comprehensive list of stages that a modern reverse osmosis water filtration system has.

Sediment Stage

This stage employs a sediment pre-filter, which does the job of removing sand, rust, turbidity, as well as particulates. These are usually the ones that are largest in size, and some of these can be observed through the naked eye.

Carbon Stage

To solve the customer dilemma that was mentioned above, let me present to you the activated carbon pre-filter. This filter is very important in the entire RO system unit. While every stage has an important role to play, but this one serves as a filter, as well as a protective shield for the semi-permeable membrane. Chlorine is very dangerous, not just for our bodies, but also for the semi-permeable membrane, since it can destroy the thing itself. That is the reason why this stage is very important. It filters chlorine, disinfectants, herbicides and pesticides, and different volatile organic compounds (VOCs), which can damage the reverse osmosis membrane. I know it is a shock to you, but yes, disinfectants and pesticides can also be present in the water that comes out of our faucets. That is also why you cannot just entrust safe drinking water to ordinary tap water filters.

Reverse Osmosis Stage

This is the core of the entire reverse osmosis filtration. By the use of a semi-permeable membrane, everything that has a larger molecule than water will not pass through. That means that salts, heavy metals, microorganisms, and everything else will not pass through from here. Bulk of the entire purification is accomplished here.

There are two common types of household reverse osmosis membranes that are being used today: the Thin Film Composite (TFC) Membrane, and the Cellulose Triacetate (CTA) Membrane. These are equally efficient in their own right: Thin Film Composite (TFC) Membrane can guarantee a staggering 98% filtration success, but cannot withstand chlorine, thus has to be protected by a carbon pre-filter. If the pre-filter is torn, or does not function properly, you can assure that the TFC membrane will get destroyed. On the other hand, CTA membrane can filter up to 93% of the contaminants, but can resist chlorine.

Remineralisation Stage

Water that has passed through the semi-permeable membrane tends to be highly pure and acidic. This stage helps to improve the taste of the water, and to balance the pH.

Optional or Application-Specific Treatment Stage(s)

Other RO units have additional stages which perform different functions, like to kill microorganisms that are small enough to pass through the semi-permeable membrane. And for those other contaminants that have escaped from the filters, these stages provide a second check.

Final Carbon Stage

This is usually the last stage in filtration, and is called the “polishing” phase, wherein any other impurities are removed, while the final product water’s taste and pH is improved.

Once water has successfully passed through all these stages, we can guarantee up to 99% water purity.

Leave a Reply

Your email address will not be published. Required fields are marked *