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Reverse osmosis lingo feels like a language unto itself sometimes, and it is easy to get a little confused.
One of the common mix-ups is between RO stages and passes. A lot of people believe they are the same thing.
In reality, they are pretty different. Let’s clarify!
So, what’s the difference between RO stages and passes?
In an RO system, the key distinction between a stage and a pass lies in their treatment of water. During a stage, the water is divided into permeate (purified water) and concentrate (wastewater). Permeate is collected for use, while concentrate is directed to a second RO membrane. Then, the second RO membrane purifies the wastewater from the first membrane, reducing overall water wastage.
A 2-pass RO system functions slightly differently. The first RO membrane separates the water as usual, but the purified water or permeate undergoes a second round of treatment by the second membrane. So the already purified water undergoes an additional level of refinement, creating ultra-pure water.
Again, the feed water enters the RO membrane as a single stream and comes out as two types of water: concentrate (dirty) and permeate (clean). The concentrate from the first stage is then used as the feed water for the second stage in a two-stage RO system. The clean water collected in the first step is mixed with the clean water obtained in the second stage.
Think of a pass as a standalone RO system. In a double-pass RO system, the clean water from the first pass becomes the feed water for the second pass. This means the water goes through two RO systems, resulting in even higher-quality clean water.
There are several pros to having a single/double pass RO system, such as:
Cons of a double pass vs a single pass:
If you have any questions about RO stages and passes please don’t hesitate to leave a comment below!
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