Under which conditions can antiscalants cause RO membrane fouling?

Reverse Osmosis Antiscalants can cause membrane fouling in Reverse Osmosis systems under the following conditions: Fungal growth in the antiscalant –  some antiscalants contain impurities that can provide the necessary nutrients and ...

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Can I use citric acid to descale/clean a reverse osmosis (RO) Membrane?

Citric acid is an organic acid that is often used for removal of calcium carbonate scale and iron hydroxide.  Citric acid is not very effective at removing phosphate salts such as calcium and iron phosphates.  It cannot be used to dissol...

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When do we know if the cleaning of our Reverse Osmosis plant was successful?

Once the RO membrane system is placed back online after CIP, you can get a relatively good idea by comparing post-cleaning feed pressures and differential pressures for each stage to pre-cleaning values.  The most reliable method would be ...

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What is the best post-CIP flushing procedure in Reverse Osmosis systems? How do we know when flushing after a cleaning is done?

Always flush your membranes with RO permeate until the pH measured at the waste end is within a pH range of 5 – 9.  You can then proceed to flush with feed water until the pH of the water exiting the RO membrane system is similar to the ...

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Can we send the CIP solution to our deep injection well after cleaning our Reverse Osmosis membranes?

No, if a high pH RO cleaning solution is mixed with RO brine, it would result in severe scaling.  Always consult with your hydrogeologist before sending any solution to the deep injection well. See also: What is the procedure for cleaning ...

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Our RO plant doesn’t have a neutralization tank for our spent CIP solution. Can we just neutralize while circulating through the membrane system?

That is not recommended.  A high pH cleaning solution is designed to dissolve membrane fouling/scale that is soluble in basic conditions.  A low pH cleaning solution is designed to dissolve membrane fouling/scale that is soluble in acidic...

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Can we send our CIP solution direct to the waste water treatment plant after cleaning our Reverse Osmosis System?

No, pH extremes can be very disruptive to bacteria and can upset the operation of the wastewater treatment plant.  The RO cleaning solution should always be neutralized prior to sending to a wastewater treatment plant.  The solution is us...

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Why does the RO permeate pH rise when the water passes through a degasifier? Does that higher pH really stabilize the RO permeate to help prevent corrosion in the distribution system?

Bicarbonate is in equilibrium with carbonic acid, and carbonic acid is in equilibrium with carbon dioxide. [1] $${HCO{_3}{^-} \Leftrightarrow CO{_3}{^2}{^-} + H^+}$$ [2] $${H_2CO_3 \Leftrightarrow HCO{_3}{^-} + H^+}$$ [3] $${CO{_2}{_(}{_...

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A few weeks ago, we pickled all RO membranes in our trains with sodium metabisulfite for long term storage. Our membrane manufacturer recommended that we change the solution once the pH drops below 3. We measured a decrease in pH for the first two weeks, but then on the third week, the pH increased. Can you explain why the pH increased instead of decreasing?

When you mix sodium metabisulfite in water, you form a sodium bisulfite solution: $${Na_2S_2O_5 + H_2O \Leftrightarrow 2NaHSO_3}$$$${NaHSO_3 \Leftrightarrow Na^+ + HSO{_3}{^-}}$$ Bisulfite is in equilibrium with sulfite and sulfurous acid (...

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We recently installed new RO membranes in our system and observed that the permeate water tested positive for coliform bacteria. Is it possible in your experience that RO membranes could be damaged during installation and cause contamination of the water distribution system by bacteria and pathogens?

It is doubtful that the membranes were damaged inadvertently during installation.  A significant amount of effort would be required to damage RO membranes to the extent that bacteria would easily pass through.  While it’s not impossible...

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