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Anonymous Poster #1

Single Pass vs Double Pass Reverse Osmosis (RO) Systems

11/30/2015 11:48 PM

What is diffrent single & double pass ro?

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#1

Re: Single Pass vs Double Pass Reverse Osmosis (RO) systems

12/01/2015 4:21 AM

One pass.

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#2

Re: Single Pass vs Double Pass Reverse Osmosis (RO) systems

12/01/2015 5:04 AM

"In a two-stage system the concentrate (or reject) from the first stage then becomes the feed water to the second stage. The permeate water is collected from the first stage is combined with permeate water from the second stage."

From http://puretecwater.com/what-is-reverse-osmosis.html#1-stage-vs-2-stage-reverse-osmosis-system

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#3

Re: Single Pass vs Double Pass Reverse Osmosis (RO) systems

12/01/2015 6:46 AM

Simple. The complexity of the P&ID.

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#4
In reply to #3

Re: Single Pass vs Double Pass Reverse Osmosis (RO) systems

12/01/2015 11:51 PM

How can this ?? pwslack

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#5
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Re: Single Pass vs Double Pass Reverse Osmosis (RO) systems

12/02/2015 8:02 AM

Each pass of an RO system usually consists of two stages. On occasion, three might be employed. In a single-pass RO with fresh water feed, the water passes through a first stage, where approximately 50% flows through the RO membranes and is purified to a product known as permeate. The remaining 50%, known as reject, is routed to the second stage, where again approximately half is purified to permeate. Thus, around 75% of the original makeup is converted to permeate. (This percentage can be somewhat variable depending upon the quality of the makeup.) The remaining 25% reject is a waste stream that must be disposed. (At plants with cooling towers, this stream is often sent to the cooling tower basin.) A single-pass RO unit is capable of removing 99+ percent of the ions from the makeup. With two-pass RO, the permeate from the first pass is treated in a second pass, usually also of two stages. The second pass produces a high-purity water that with some added polishing, say from an ion exchange unit, is suitable for feed to high-pressure steam generators or other processes requiring high purity water. 90% recovery is possible in the second pass, and the reject stream is typically returned to the inlet of the RO.

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#6

Re: Single Pass vs Double Pass Reverse Osmosis (RO) Systems

12/08/2015 12:24 AM

The difference between a single pass RO system and a double pass RO system is that with a double pass RO, the permeate from the first pass becomes the feed water to the second pass (or second RO) which ends up producing a much higher quality permeate because it has essentially gone through two RO systems.

Besides producing a much higher quality permeate, a double pass system also allows the opportunity to remove carbon dioxide gas from the permeate by injecting caustic between the first and second pass. C02 is undesirable when you have mixed bed ion exchange resin beds after the RO. By adding caustic after the first pass, you increase the pH of the first pass permeate water and convert C02 to bicarbonate (HCO3-) and carbonate (CO3-2) for better rejection by the RO membranes in the second pass. This can't be done with a single pass RO because injecting caustic and forming carbonate (CO3-2) in the presence of cations such as calcium will cause scaling of the RO membranes.

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