I have a 23G with 6 membranes, i installed last year of October, the permeate flow is 5.2GPM, after 2 months the i performed the low/high PH cleaning and the GPM would only go to 4.0 and now it's down to about 3.5GPM.

What do you think, a bad membrane or anything can cause this? Also, before this i changed the membranes 4 years but this one not even a year looks like i need new membranes already.

Everything looks good my % rejection, conductivity , PH etc.

Thanks in advance for your input.

i would check to make sure that your water product has dropped. It may just be the sensor. I have had that happen before.

Did your incoming water supply pressure change? Booster pump working? Carbon, softener, or pre-filters plugged? What is you reject flow / recirc flow?? Did someone change these. I'm not sure how the 23G even works but I'm sure it's about the same as most. Did someone mess with the incoming flow restrictor? Just a few things to check. Is the backflush working? This may cause the membranes to plug easier.

Did you do a silt density check? Silt is my biggest issue here. Had the same problem and still do to a certain extent. I confirmed this with the city. Shortly after startup(before my time), they had to install an extra filter rig with 7 30" 1 micron filters in it before pretreatment. It helped, but still have some issues. Lost 6 membranes in less than a year. Multiple cleanings really had no affect. After conferring with the field rep fo my RO, now I"m changing my ro from 75% recovery to 50% to dump more down the drain. I'm hoping this will help extend my membrane even more.

Actually i did profile each membrane and i'm only getting an average of .80 GPM per membrane. Also, the drop i noticed was in a span of 2 months.

If all is perfect, the 23G membrane will produce 1.1 gpm. Perfect being a temperature of at or near 77*F, feed pressure of 200 and incoming TDS of less than 2,000. Feed water is always the first look especially the temp. You typically lose 1.5% flow per degree of temp loss. If your parameters are good then you have a membrane problem. The question is why? Does your softener last all day. Hardness whould be checked in the AM and at the end of the day. Has your drain flow changed? The 23G flow block will collect debris and cause the drain flow to decrease. When it does, the concentration of solute on the membrane rises above the solubility coefficient and scaling of the membranes is almost instant.

Anyway, there's some stuff to think about.

Just a thought here, are you sure you did the membrane cleaning in the right order? You must do the low ph(acid)cleaning first followed by a thorough rinse then do the High ph(alkali)cleaning again followed by a thorough rinse. I screwed up once when I first started in dialysis and hosed a membrane on a portable RO. I'm sure you did it right but it never hurts to have a reminder.

Just want to update everyone that responded, i changed the membranes last night, problem solved with the permeate. Still need to shipped out the old membranes so manufacturer can check it to see after a year the permeate flow had gone down.

What foulant do you suspect is in your raw water that caused the permeate flow to drop? What chemical(s) did you use to clean the membranes with?

If your permeate flow decreases after cleaning, you may be using the wrong cleaner.

Not sure what foulant is in my raw water but i'll be shipping back the old membranes to manufacturer as i said above. I used the AD20(low pH), AK110(High PH) , Minncare to disinfect.

From everyone's experience, is it possible i got a bad membrane to begin with, since the dropped i notice was after 2 month's of installation?

krutech,

I believe the membranes you received are bad, If the water pretreatment are all good,(multimedia filter, softener, carbon tanks, prefilters) especially softener there should be no problem. I have the same unit osmo 23g, and been using it for 10 years now only replaced membranes twice.

I don't know, if all 6 had the same reduced product flow I think I'd be leaning towards a foulant or change somewhere else. You may want to double check some of the posted ideas.