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Post by Deleted on Nov 22, 2021 11:42:33 GMT
Hello all, I am at a loss. I have a cwp that the % Rejection has dropped to 93% from 98% the other day it was running at 91.7% I did a ph cleaning followed by minncare and it came back up to 93.8%. I was contemplating doing another ph cleaning and seeing if I can get it back to normal or if I'm s.o.l and should go ahead and get new membranes? We have crap city water and they dump A LOT of stuff in that the pretreatment does not take out such as alum. so for them to get clogged is not normal but for them to have such a big drop in % rej. is new, any suggestions?
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Post by joey on Nov 22, 2021 15:18:09 GMT
What is your recovery rate?
Do you have 1 micron prefilters in place?
Are you doing low pH first or high?
How often do you usually do a pH cleaning?
Did you get a lab result for your tap water and maybe get one from your municipality?
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lost
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Post by lost on Nov 22, 2021 15:57:17 GMT
Do you perform regular pH cleanings? We've found that areas that perform regular pH cleanings(versus only if needed), see a higher rate of failed RO membranes.
I have no data to support this but it's just something a lot of us have noticed across a few regions.
I'll add to Joeys questions..
What's your incoming water temperature? Temperature can have a significant impact on your membrane efficiency and we are getting into the colder part of the year.
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Post by gfreely on Nov 23, 2021 18:36:01 GMT
Do you perform regular pH cleanings? We've found that areas that perform regular pH cleanings(versus only if needed), see a higher rate of failed RO membranes. I have no data to support this but it's just something a lot of us have noticed across a few regions. I'll add to Joeys questions.. What's your incoming water temperature? Temperature can have a significant impact on your membrane efficiency and we are getting into the colder part of the year. Last pH cleaning I did on ours resulted in an expedited membrane change. Not a fan and will use ONLY as a last resort now.
Agree w/ the temp. When I took over my unit they were maintaining the blending valve at around 75°F with RR% in low 90s. Researched/tweaked a little and found that our units prefer a spot around 60°F. Brought the RR% into the upper 90s. (MarCor says they can handle as low as 5°C but not ready to call THAT bet with our system)
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Post by Chuck Weddle on Nov 23, 2021 23:20:12 GMT
jay,
I agree with lost and gfreely, I don't believe in routine membrane cleanings either. IMHO, the only time they should be cleaned is if they show signs of being scaled over or otherwise fouled. I don't think aluminum sulfate (alum) is your problem because it shouldn't foul the membranes and an RO is the best way to remove it from the water.
Low temperature wouldn't be a cause because it would cause the membranes to be tighter resulting in a better water quality.
Your lower % Rejection is indicative of membrane damage (possibly from cleaning) or a leaky o-ring. In either case, you should see slightly higher product water production. Another possibility is if your softener is letting some calcium get through.
What is your % Recovery? What is it supposed to be?
What is your product water flow rate? What was it before?
What is your waste water flow rate? What was it before?
What is your product water conductivity? What was it before?
Have you sent a sample to the lab for an AAMI analysis? If you do, make sure you compare its results with those of about the same time of year as they can vary a good bit with the seasons.
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Post by Deleted on Nov 26, 2021 12:24:33 GMT
AAMI's of product water are great city water is crap. I ended up replacing the membranes thanksgiving day my percent rejection is now at 95.6% i normally run at 98%. I tuned in all the pressures and reject rates. Today I am going to call Cantel and see if it is a pump issue or just need a bigger hammer. lol I will let you know what comes of this after the call.
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Post by Chuck Weddle on Nov 26, 2021 12:48:12 GMT
AAMI's of product water are great city water is crap. I ended up replacing the membranes thanksgiving day my percent rejection is now at 95.6% i normally run at 98%. I tuned in all the pressures and reject rates. Today I am going to call Cantel and see if it is a pump issue or just need a bigger hammer. lol I will let you know what comes of this after the call. Jay, If by "bigger hammer" you mean a larger pump, the answer is NO. If you can obtain the spec'd pressure with some adjustment to spare there is nothing wrong with your pump. Running a higher pump pressure will make your % Rejection lower as it will force more contaminants through the membranes. Another very likely problem could be the accuracy of one of the temperature/conductivity probes (most likely the feed water probe). I have had a number of them go bad on our 4400's. They were reading a higher temperature throwing off the temperature compensation which resulted in false low % Rejection calculations. |
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Post by joey on Nov 26, 2021 14:17:45 GMT
jay, I agree with lost and gfreely, I don't believe in routine membrane cleanings either. IMHO, the only time they should be cleaned is if they show signs of being scaled over or otherwise fouled. I don't think aluminum sulfate (alum) is your problem because it shouldn't foul the membranes and an RO is the best way to remove it from the water. Low temperature wouldn't be a cause because it would cause the membranes to be tighter resulting in a better water quality. Your lower % Rejection is indicative of membrane damage (possibly from cleaning) or a leaky o-ring. In either case, you should see slightly higher product water production. Another possibility is if your softener is letting some calcium get through. What is your % Recovery? What is it supposed to be? What is your product water flow rate? What was it before? What is your waste water flow rate? What was it before? What is your product water conductivity? What was it before? Have you sent a sample to the lab for an AAMI analysis? If you do, make sure you compare its results with those of about the same time of year as they can vary a good bit with the seasons.Chuck, how often do you do your membranes? As needed? Quarterly? |
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lost
Junior Member
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Post by lost on Nov 26, 2021 19:03:26 GMT
My 2 cents on cleaning membranes.
If my rejection is good (mid to high 90s), I don't do cleanings. At all. So I guess "as needed" is the answer.
Weekly Minncare does enough passive cleaning as long as you don't have extreme scaling.
That being said... I watch my pretreatment like a hawk. Water softener and brine system is dialed in and my staff are well educated to alert me of anything outside of normal.
Most water system issues can be prevented on the front end. Very important to have a well functioning Pre-treatment system.
If you DO have to change membranes, pay good attention to the o-rings, as Chuck suggested. Any deterioration, chips, etc can cause waste to mix with product and you WILL have a decrease in % rejection.
Good o-ring lubrication is also a must.
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Post by Chuck Weddle on Dec 4, 2021 17:52:08 GMT
Something else for everyone to keep in mind is...% Rejection tells you NOTHING about water quality. IMHO, there should not even be a required minimum percentage. I have seen a RO producing 2.8 uS water and be alarming for low % rejection. With direct feed systems becoming more common because of heat disinfection, I predict this will be seen more often.
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lost
Junior Member
Posts: 82
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Post by lost on Dec 5, 2021 2:53:41 GMT
Something else for everyone to keep in mind is...% Rejection tells you NOTHING about water quality. IMHO, there should not even be a required minimum percentage. I have seen a RO producing 2.8 uS water and be alarming for low % rejection. With direct feed systems becoming more common because of heat disinfection, I predict this will be seen more often. This is very true. We have a location in our area with like 180-200ish uS on the incoming side. The product is usually like 2-3 but the % rejection stays barely over 90% most of the time. It's definitely an anomaly for us (most water in our area is 800-1100 uS incoming), but everyone at that clinic is on board with this abnormality so no one ever freaks out about it. % rejection is still nice though because it can provide a secondary frame of reference for the end users to report to their area biomeds. Hopefully that provides a little more context for someone. |
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Post by joey on Dec 7, 2021 19:06:25 GMT
Something else for everyone to keep in mind is...% Rejection tells you NOTHING about water quality. IMHO, there should not even be a required minimum percentage. I have seen a RO producing 2.8 uS water and be alarming for low % rejection. With direct feed systems becoming more common because of heat disinfection, I predict this will be seen more often. Chuck do you clean them on a schedule or just keep an eye on numbers? I know when DOH came when in my earlier years we were cleaning and disinfecting quarterly and he made me show him the manual and it said as needed and he said "well industry standards are pushing towards monthly" We didn't get cited though and I still do not clean them monthly....we do quarterly to have it on a schedule and sometimes I do it sooner...........and I agree about rejection....the higher the feed the less safe the 90% number is and during the winter with our last system our feed went down to 60 so we dip below 90% sporadically.
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Post by Chuck Weddle on Dec 7, 2021 21:49:52 GMT
Chuck do you clean them on a schedule or just keep an eye on numbers? I know when DOH came when in my earlier years we were cleaning and disinfecting quarterly and he made me show him the manual and it said as needed and he said "well industry standards are pushing towards monthly" We didn't get cited though and I still do not clean them monthly....we do quarterly to have it on a schedule and sometimes I do it sooner...........and I agree about rejection....the higher the feed the less safe the 90% number is and during the winter with our last system our feed went down to 60 so we dip below 90% sporadically.
Joey, The only times I've performed cleanings was once about 15 years ago our product water flow rate dropped by almost a gpm over just a few days. Another time was we had to run without our water softener for about a week so we did a cleaning because of likely scale. |
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Post by joey on Dec 7, 2021 21:55:11 GMT
Great thanks
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Post by stephenccarr on Dec 8, 2021 21:01:31 GMT
When the feedwater conductivity is low the calculated rejection is typically less than the actual ionic rejection because any CO2 is concentrated in the product water. This CO2 can come from both any free amount present in the feed water and by the breakdown of the carbonate ion. This also makes the product water pH less than the feedwater.
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