Membrane permeate flow rates

[blissville maples]

Talking 8x40 membranes, what are most people seeing for flow rates on permeate in the 400 psi range, per membrane, how old is this membrane? With or without recirculation, and if with recirculation is it a side feed like d and g or end feed like CDL? I understand CDL technology 'keeps membranes from fouling' but as we all know things don't always work as well in the field as they do in the showroom, anyone have experience with cdl's reverse osmosis machine?

I've been on the fence about sending membrains out for cleaning, my machine went up to Canada last winter for upgrades and they happened to clean them. These membranes were on their first season and I took diligent care of them, I never would have guessed they were compromised as they were even after acid washing. One membrane was down 33% the other 44 which I found to be quite astonishing, however they put them through about a 15 step process which includes probably 10 rinses.

They did perform well last year but here we are again this year and they seem to be not performing like they should. I guess I've determined, and Been Told by professionals, that they need to be replaced every single year because you can't afford to lose the production. I'll probably swap them out next weekend.

I guess my question is do other peoples flow rates drop off second and third season also, regardless of being washed and rinsed diligently. When my membranes were brand new I wash them after every use and I acid washed at the end of the season I cannot imagine what else could be done to keep these performing well. I store them in their vessels with glycol and preservative, and I'm at a loss as to why this happens. Only answer I have is buy new ones, you can do all the washing you want but it's not going to get you where you want to be which is 5 to 600 gallons of flow per membrane, if I knuckle my machine down hard I'm down to 700 gph on a 2 membrane machine and still not achieving desired %.

My plan was to add vessels to this machine but I am being told it's old technology and not comparable to the newer machines like cdl's, The only difference I see is the type of recirculation and the price, they are still just electric motors and pumps!

[ecp]

The short answer to your question I see about 66% or the RO's capacity with band new membrane. Example our old 1800GPH CDL RO generally never got above 1200GPH. What I find is they rate these machine under perfect conditions (not unlike any other industry) the sap needs to be 55 degrees and pre filtered and had brand new membranes to see the flow rates they say the machine can perform at (after running it 3 times the membranes are no longer going to run at that flow even if you only put water though them). We usually run membranes for why longer than they recommend, and with the price on them coming down maybe we should change that A good rinse and soap wash after every use generally holds the flow rates the same for years. Maybe at some point we will buy the 8'' membranes at a 4 year interval, but that **** 16'' membrane is pricy.

[blissville maples]

That's pretty much where I stand. And probably true about the performance is only under ideal conditions. Kind of like when they give you miles per gallon on a pickup truck probably in a factory on a set of rollers!

I guess where I'm at is a membrane is not good for 600 gallons an hour don't ever expect that or you'll be disappointed. Probably four hundred gallons per hour like you said 66% is more like it.

[JoeJ]

I have a 2 post Lapierre RO with 7 year old membranes. I get the membranes washed at Lapierre every year costing $153. per membrane. This year's "dirty" test was 96.4% and 98.5%. Both clean were obviously at 100%. I only rinse the machine in the middle of the run on a big sap day. Other wise, at the end of each days use, I rise with 700 gallons of permeate, soap wash and then rinse with another 700 gallons. Using the Ro last Monday, the total flow was 780 gph with 43 degree sap to make 15% concentrate. I don't think that I can get any better than that with the reduced temperature from 55 degrees that the membranes are made to operate at. It always looks like I am wasting my money getting the membranes washed at Lapierre, but at least I know that they are at 100%. Still cheaper than new membranes each year.

Joe

[nas]

I have a CDL 2 post machine and I get about 850 gph getting 13-14% concentrate. I wash with just permeate after every use and only do a soap wash a couple of times a season. I have seen no noticeable drop in performance in 2 years of use. I do plan to get them professionally cleaned after this season. Keep in mind that I had 1100 taps last year and 1400 this year, so it never gets run long and gets washed often.

Nick

[ecp]

I have a 2 post Lapierre RO with 7 year old membranes. I get the membranes washed at Lapierre every year costing $153. per membrane. This year's "dirty" test was 96.4% and 98.5%. Both clean were obviously at 100%. I only rinse the machine in the middle of the run on a big sap day. Other wise, at the end of each days use, I rise with 700 gallons of permeate, soap wash and then rinse with another 700 gallons. Using the Ro last Monday, the total flow was 780 gph with 43 degree sap to make 15% concentrate. I don't think that I can get any better than that with the reduced temperature from 55 degrees that the membranes are made to operate at. It always looks like I am wasting my money getting the membranes washed at Lapierre, but at least I know that they are at 100%. Still cheaper than new membranes each year.

Joe

I like the idea of cleaning them and I would not say it was a waste of money at all because it is nice knowing. On the flip side if you didn't pay the cleaning fee you can have brand new membranes every 3 years.

[maple flats]

I can't speak for 8" membranes, but my 250 (2@ 4x40 membranes) is rated at 250 gph and I get 240-260 gph depending on sap temperature. I used my membranes cleaning them as specified in my owner's manual for 4 or 5 seasons, then I sent them to Lapierre for cleaning and testing. They came back with a report. They were passing no sugar and both were at 100-105% of new. I never figured out how they were at 105% but that's what the report said. I used it for another 5 seasons then I saw evidence that they had passed some sugar. In all previous years I had perfectly clear permeate water left in my tank (I save it to mix the sprays for my 4.5 acres of blueberries) but last summer I found some funky growth in the tank in about late July or early August. I then bought new membranes for that reason.
You say the RO's never get showroom performance, I don't know what, but somehow you are cleaning them improperly. Check with the membrane manufacturer. If the difference was only 10% it could be all related to sap temperature, but over 30% means something is wrong.

[nas]

Dave, what brix are you concentrating to? Does your ro recirculate?

Nick

[ecp]

Just adding another thing I forgot to put in. We all talk about membrane flow rates (yes I am guilty of that), but when you talk to people that design/sell/and service RO's they rate the RO on pump size which makes sense because a pump can only move so much water so if your fed pump and/or high pressure pump are only going to move lets say 900 GPH than you could put 10 membranes on there but you are only going to get a max of 900GPH as an example. Some manufacturers may spec around the membranes while others spec based on the feed pump.

[Russell Lampron]

There are a few factors that determine permeate flow. The first is sap temperature and as you know colder sap means lower flow rates. Another factor is concentration percentage. Higher percentage means lower permeate flow. Then there's pressure, higher pressure yields higher flow rates but also causes faster membrane fouling. The way that you concentrate comes into play too. Getting to 16% in one pass will yield lower flow rates while doing two passes will get you there with higher flows on the first pass with slower membrane fouling.

The machine itself has a lot to do with flow rates too. The machines like the LaPierre and CDL pro models have superior recirculation which keeps the membranes flowing at a higher rate before they foul. All of the other machines are prone to fouling and not meeting the manufacturers advertised flow capability. There's a reason that your D&G with two 8" membranes is rated for 1000 gph and the LaPierre and CDL machines with two 8" membranes are rated for 1200 gph.

The numbers that they found when they cleaned your membranes shows that your cleaning methods need improvement but part of that is the machine itself. To improve that on your end you will need to rinse and wash more frequently.

I have a LaPierre 250 Turbo which is a two membrane machine with recirculation pumps on the bottom of the towers. LaPierre invented this technology and CDL uses it. I'm using MES membranes in it. I'm starting my 3rd season with them and my flow rates are what they were when the membranes were new. This is without professional cleaning. I regularly get 280 to over 300 gph out of it at 300 psi with the concentrate set at 1.5 gph. The permeate flow is around 3.5 gph given the above factors. The concentration percentage on that pass is around 8% with 2% sap. I run 2 passes and adjust the concentrate flow to 14% on the 2nd pass. The permeate flow on that pass is much lower with total through of around 210 gph.

[DrTimPerkins]

Very nice description Russ.

[Amber Gold]

Russ, good write-up and it's how I understand it too.

I have H2O Innovation 600gph RO with a new MES membrane, but I think the numbers were about the same when I had a CDL membrane. I was running it last week, and I think these were the flow rates I was getting:
First pass
Sap @35-37F
2gpm conc.
6-6.5gpm perm.
350psi

Second Pass
Sap @42F
2gpm conc.
2-3 gpm perm.
400-450psi

[Jeff E]

I have a CDL 600, and it has a pump built into the membrane tower that agitates (recirculates) the sap, so the surface of the membrane doesnt foul as quickly. I have run up to 6000 gallons over it between wash/rinses.
My membrane is 4 years old, and still performs great, 90+% of new. Last night, after 2000 gallons I was concentrating to 12% with 7gpm permeate, 3 concentrate. ( I got higher concentrate % by recycling the concentrate back to the feed tanks).
I try and recycle my sap with leaving my concentrate a bit open, about 4 gpm. My permeate stays high that way for a long time.

[nas]

When you have a second tower, you are basically doing the same as sending it through one tower twice. It's much easier to get higher brix concentrate with two membranes because they are in series.

Nick

[blissville maples]

So a little update as to my problem something for everybody to keep in mind when things aren't adding up.

After playing with the valves and seeing my pressure at 450 PSI with my concentrate flow at 8 to 9 gallons per minute I started to question the Gage. If you're flowing over 5 gallons a minute on the concentrate it's not possible for the membrane pressure to be above 350.

I changed the pressure gauge and it was indeed wrong for the last year-and-a-half I've been running at 2 to 300 PSI wondering why I'm only getting 6%!

Now I'm running 425 and seeing 12 to 13%! Hooray, it's like I have a whole new machine just by changing the gauge!!