Increased pH of permeate water in Reverse Osmosis plant with 25 m3/d capacity.

Hello All

The pH input to the reverse osmosis system is7.5
While the pH of the output water (permeate) reaches 8.9.

Note:
1- Only acidic antiscalants are injected.
2-This RO system designed in a room that its has a high temperature approximately in the range of 33-38 ° C.

Questions:
What is the cause of the pH increase?
A- Temperature has increased the pH?
B- Does microbial contamination can increase pH?(Chlorine injections have not been applied, which makes the water bad smell. membranes has also been infected with microbial contamination.)
 

Taxonomy

• Reverse Osmosis
• Scale & Corrosion
• Chemistry
• Reverse Osmosis

8 Answers

1. Hello.Membrane was fouled.Good pretreatment required.Increase in PH in reject water is Ok but if permeat PH increase big issue.Your item 2 applicable.

2. While some of previous answers have merit, it could be your membranes are plumbed wrong and you're actually getting concentrate or a portion of it from the permeate side. Your pH should always be reduced after passing thru an RO! Have you checked both permeate and concentrate sides for TDS and pH?

   1 Comment

   1. Have you checked both permeate and concentrate sides for TDS and pH?

      TDS and pH for permeate are 6 ppm and 8.9 respectively.

      Unfortunately, output water (concentrate sides) data is not available.

      1 Comment reply

      1. Arsalan, What is your incoming raw water pH? Is it high?

3. RO permeate is acidic normally if no pH adjustment. Therefore, microbial contamination is likely the case. Please check the physical condition of membrane whether it is slimy or pressure build up.

   1 Comment

   1. Thanks

4. Dear Arsalan,

   please check your question. I expect permeate to be rather acid and pH more than 8 for rejected brine (not permeate).

   Please inform the concentration of bicarbonates in the feeding salty water

   1 Comment

   1. Please check ​your question.

       

      I am sure of the question.

       

      Please inform....   (OK, I measure and report it)

5. You need to supply a full water analysis with a cation anion balance. 

6. It is the slippage of more cations (Na) causes for high pH.

   How you are operating the RO plant with out microbial control. It affects the membrane and product quality.

   Go for C2/Hypo - SMBS dose at appropriate locations to have control.

    

   1 Comment

   1. Thanks.

      How you are....(Unfortunately, the company that launched it does not have a chlorine injection system.)

7. I believe the pH may have increased as a result of some microbial effect, similar to the increase of pH when the algae strip out the carbon atom from alkalinity sources resulting in producing the hydroxyl ion, and consequently increasing the pH. The Bad odour may be associated with Grosmin or MIB in the final water. 

8. It depends on the TDS of permeate. If the TDS is high water will evaporate and pH will increase. What is the temperature of permeate. At warm conditions even the microbial activity is increase .This also could a possible reason. 

   Dr. Syed Naimathulla 

   1 Comment

   1. The ​temperature of ​permeate is 32 °C.