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

Question

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.)

MOHAMMED NAZEER · Answer

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.

Terry Hughes CWS, CI, UV-CI · Answer

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?

WEI CHOEW LEE · Answer

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.

Marco Rognoni · Answer

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

Ed Hardwick · Answer

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

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