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End of season I rinsed 300 gal. Washed with soap. 300 more gal. Acid wash 24 hr soak. 300 gal rinse and another wash followed by 300 gal rinse. After a week I went to pull my membranes and as I pulled, 2 out 3 had snotty junk come out with them. Any thoughts? Just a home built 3 vessel 4x40.
What soap and how much did you use? When you rinse do you adjust the pressure so both concentrate and permeate flows are about equal? Which membranes do you have? What pump or pumps?
MES membrane. I open needle valve the whole way. About 4 gpm concentrate and 2 gpm permeate. CDL soap wash. I check it with ph strips. I let wash run for couple hr usually. I have a feed pump to a 330 procon. I also have a bucket heater that I turn on and allow it to heat up to around 100ish degrees. This takes a while so it washes a fairly long time.
I've seen what you describe on the outside of the membrane wrapping. (I believe the membrane itself is clean, they perform up to spec.) I run 2- 3 membrane 4x40 units. 1- MES set, 1- XLE. Can occur with either brand. I think it is happening behind the outer O-ring (not getting proper circulation when cleaning) I went from vertical to horizontal mounts. (seemed to help) I also try to run some permeate through the units every day during the season, even idle days. We have improved, but it still shows up now and then, especially if we have not removed the membranes form the housing for the entire season.
I think the problem was letting the membrane sit in permeate for a week without putting any bactericide in it.
I think it's likely 2 issues. #1, you can it with the needle valve wide ope,. that is pushing much less thru the membrane, 2x what goes thru, goes paqst without going thru. You need the flows to be closer to 50/50, if you pump 6 gpm, get about 3gpm permeate and 3gpm concentrate for a better clean.
#2, don't let that set after washing with soap, then acid (extended after season 48 hrs up to 4 weeks), then soap wash with a complete rinse between each and after the final soap wash. Then I always added preservative right away, I have read that some only use permeate, I never liked that approach.
The real problem is the space between the membrane and wall of pressure vessel is a dead space if brine seal is in place and sealing.
Commercial units with real recirculation use the gap between the membrane and pressure vessel as a flow path for recirculation and it is constantly flushed.
Nothing you can do about it , just clean things up and upgrade to a commercial unit if you can in the future.
When running properly the space between the membrane and the outer wall of the vessel is not fead space, that is where thye sap/concentrate is flowing, pressure forces the permeate thru the membrane. However that space is flowing quite slow. For example if you are removing 75% of the liquid, on a 250 gph unit, you have barely over 1 gpm in the outer flow. When you run 50/50 flow during a wash, it's about 2.25 gpm on each, in fact with the pressure quite low to get 50/50, each is likely closer to 3 gpm.
Trust me, no fluid exudes through the fiberglass outer wrap of a membrane. All fluid goes in one end and comes out the other minus the permeate.
If a membrane is in a standard housing and there is a brine seal on one end of the element there is a dead space along the entire length of the membrane.
Usually this is not a big problem but this year was particularly bad for RO cleanliness.
WMF, you have me confused. If the pump pushes 4 gal in one end and 4 gal total comes out the other, with some being concentrate and the rest permeate, how can there be a dead space/ I'll admit the concentrate is slow moving, but technically not dead, is it?