TDS high / delta p and productivity are OK 1

[wwtp2014]

Dears

please advise the TDS of my RO becomes high after frequent CIP but delta p and productivity are good I heard there is special treatment for membrane element

Thank you

 

[bimr]

Frequent CIP should be avoided as it will shorten the lifespan of the membranes. There is nothing that can be done except for replacing the membranes.

You should concentrate your efforts to reduce the frequency of CIP.

 

[dfmorvan]

Hi

Normally, cleaning, if properly done, even frequently, should not degrade the membrane salt rejection. I would encourage you to check on your procedure. It must be adapted to the nature of foulants. Also are you doing some normalization to follow the performance reduction of your unit to decide when to clean ?
There exist some specialty chemicals to enhance membrane rejection, check with water conditonning chemicals supppliers.

 

[wwtp2014]

Dear Dfmorvan,

Thank you for your answer

In fact, we do CIP when delta P goes high
Could you please tell me more about normalization advantages

Thank you in advance

 

[dfmorvan]

Hi wwtp2014

Check membrane manufacturers sites like dow or hydranautics. They provide free spreadsheets to do this.
Delta P alone is not necessarily an accurate way to quantify fouling (even if generally speaking its upward variation indicates that something is wrong.)
The problem is that there are other factors at play. For instance temperature will play an important role due to viscosity variations. Salinity also has an influence.
Flow normalization enables you to compare your actual operating conditions to a reference (usually the starting conditions of the unit or the last time you cleaned) while removing the "seasonal" interference. That way you can have a clear view of the evolution of the performance of your unit vs time and can anticipate on the decision to clean.

 

[kybhosale]

Your membranes may be oxidized as Outlet TDS is more but dP or flow is remain same.

It is advisable to do probing test to check whether all membranes were damaged or not

Krunal Bhosale

http://waterengineer.co.in

All about Water and Wastewater Treatment

 

[Laefranz]

High TDS, higher permeate flow, deltaP normal maybe membrane broken because oxidation

Several mechanical damage of the element or permeate tubing can also allow the concentrate to penetrate the permeate.

 

[dfmorvan]

It is true that the symptoms can lead to think about membrane oxidation, so you can do a fujiwara test to check for membrane oxidation. There are some chemical treatments to try to get some rejection back, mainly based on Tannin molecule (from memory). I have never tried them so I cannot comment on their efficiency.

 

[Laefranz]

Dfmorvan: Can you give further explanation of fujiwara test and chemical treatment to get some rejection back?

Regards,
Franz

 

[bimr]

How old are the membranes?

 

[wwtp2014]

please be informed we do not inject Chlorine for oxidation we use compressed air

 

[dfmorvan]

@Laefranz

For Fujiwara test check for instance

http://www.membrane.unsw.edu.au/wp-content/uploads/Vis-Inspection.pdf

As for rejection enhancer, I think that Kurita (ex BKGiulini) used to have some specialty for that. It should be some tannin containing formulation that "coats" or adsorbs on the membrane surface.