Dissolved Ammonia in Bleed Water

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We need to purify bleed water using the reverse osmosis (RO) system.

The water contains 40-60 ppm of ammonia and almost 500 ppm of sulphates.

Are these concentrations safe for RO membranes or do they need a pretreatment system other than the conventional one?

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8 Answers

  1. Is the ammonia bound and in what form is the sulphate?  What is the pH of the water.  The concern with high ammonia levels is that it will support bacterial growth and most membranes do not reduce the ammonia at the same rate as other materials.  There may be specific membranes, which do remove ammonia but they would need to be investigated.  Sulphate can be removed by RO but it is an expensive way to do it.  The simple way is to react it with hydrated lime, which then forms calcium sulphate, which then precipitates and can be removed as a solid. There is a patented system which can reduce the sulphate by the addition of a reagent, which then forms calcium alumina sulphate and can drop the sulphate down to 100 ppm.  After that RO would reduce the sulphate levels but you still have to find a way to remove the waste stream.  SO loosely, the answer, with provisos, is yes RO can reduce both ammonia and sulphate but you do need to pre-treat.  It is possible that if the pH is raised high enough with lime  and the water is passed through a scrubbing tower, the pH could be reduced prior to the RO plant.

  2. dude, don't do it.    at those levels of ammonia, your COD is like 240 to 360.    your max is 200 for RO.  too much fouling.  

    you need pretreatment.  

  3. People think RO can be designed by thumbrule calculations and standard pretreatment..it may be working for well water but your membrane life is always at risk without proper design. 

    Need complete water analysis report.

  4. These components are not detrimental to an RO membrane.  Our experience has shown that ammonia can be removed with an RO at lower pH's (4-6 is best).  A full water chemistry analysis is needed to determine what fouling effect the sulfate or other constituents will have.  Ca, Mg, Sr, and Ba are especially important along with iron.  As mentioned a good RO projection program can help with a list of analytes.  These will tell you what scaling potential you have and if an anti-scalant or other pretreatment will be needed.   Rest assured that the water with ammonia and sulfate can be effectively treated with an RO.  Depending on quality needs down stream treatment for residual ammonia may be needed such as simple softening.  We can help get to a good RO projection program or run the projections for you with some additional analysis information.

  5. The issue with ammonia is that it exists primarily as NH4+ until the pH is up to almost 8.0 and it starts to convert NH3. NH3 will air strip, the higher the pH the more ammonia you will remove. To get complete removal with air the pH must be 10.5 . As mentioned in the above posts the potential for sulphate precipitation on the membranes is significant and you you need more analysis. If you raise the pH to get rid of ammonia using air stripping you will greatly increase your potential for fouling.

    However if you keep the pH low the RO membrane will give you ok rejection of the NH4+ ionized version of ammonia. So I would avoid air stripping and use the RO for rejection. As mentioned above you need to plug the analytical data into a good RO projection program.

  6. They are sure but It is necessary confirm with a membrane projection programe which you can obtain the working conditions (pressure and recovery) So you need a complete  water inorgnic analysis including  on it Ba and Sr concentration.

  8. Depending on your RO unit, however, we have a pretreatment filter system prior to for this purpose.