Why is permeate flow reduced as I increase pressure?

[maple marc]

Deer Run EZ 125 RO in fifth season of use. Has seen 6000 gallons of sap through it. This RO has one 4x40 post. Well cared for, with hot water rinse after each run and acid and soap wash at the end of each season.

Weird behavior this year: Each run starts out well. Today with warm sap I was removing nearly 50 gallons of permeate per hour at 160 psi. After about 100 gallons of permeate my rate dropped so I increased pressure. But as I increased pressure the permeate flow actually dropped, as did the concentrate flow. This has happened during each run this run--unlike normal behavior other years.

What is going on? Permeate flow should increase as pressure increases, right?

Thanks for any ideas from you RO gurus.

[Bricklayer]

Only 2 things it could be.
1. Your membrane is fouled and needs a really good wash. I typically rinse my membranes after every use with 100-300 gallons of perm. Then a soap wash and let it sit in the soap untill the next day. If I’m not boiling within 2 days I’ll complete the wash and rinse with 200-300 gallons of permeate. Your membrane could be finished as well and un-saveable. It does happen. They do have a shelf life. Sometimes a professional from one of the big maple manufacturers can bring them back.

2. Your RO pumps are not performing as per spec. Usually with pumps the GPM falls off the higher psi they have to pump.
Check your flows perm flow + concentrate flow. They should match what your pump can pump according to its specs for the certain pressure.

[BAP]

Good recommendations from Bricklayer. Unfortunately, your maintenance routine is not necessarily “well cared for”. You need to do more than 1 soap wash per a season. Also, how hot of a water are you using to rinse? Membranes don’t want the water to be too hot. You really should be rinsing with permeate that is whatever the ambient temperature is.

[TomorrowRiverMapler]

That certainly does not make sense but I have to concur with BAP on RO care. I have a Leader Micro II (2 post 4x40). The manual says after every use to do a permeate rinse of 125 gallons, then caustic soap wash till temperature reaches 118 degrees followed by a 125 gallon permeate rinse. It's also critical to know what your permeate benchmark flow is. For Leader's Micro it is measured new using 70 degree water at 150 psi and is about 2 gpm per post. This test is then done after every use after a rinse/wash/rinse and then compared to the benchmark. That way you know when your membrane is getting plugged. If the drop is greater than 15% an acid rinse is the first step to unplug. Post back what you found out the problem was.

[SeanD]

Marc, you've gotten good advice here. Deer Run recommends processing at 275 PSI. Are you using the recirculation valve or just the large HP valve? I think the #1 thing to do is a soap wash. I think you'll see immediate results. I soap wash almost every day/run bigger than 500 gal and and definitely every time when the weather warms and the sap quality decreases. I do 2 passes, so that's 4+ hours of run time.

I've never tried letting the membrane soak in soap, but I have used 50:50 washes and rinses for the last couple of years. I picked that tip up somewhere here. It seems like it has helped keep the membranes in good condition.

Keep us updated.

[maple flats]

Another possible issue is the raw sap filter, it has a 2.5x20 filter , is it fouled? I change to a new one every day, in late season sometimes 2x a day.
Also, run a soap wash according to EZ RO's instructions, you might also need an acid wash if the soap wash doesn't get you back to proper functioning. I always run a permeate rinse daily, at times more often, then at day's end I run a perm rinse then a soap wash, then a perm rinse and then a filter change.
With a 125 RO you want to run about 125 gal of permeate rinse.

[dcast99]

I do a rinse, soap wash, rinse and acid wash every day(actually let the acid sit overnight) then another rinse. Don't like taking a chance the RO will act up when I have 700 to 1000 gal of sap to process.

[maple marc]

Thanks all for excellent advice. Bottom line is that I should be giving my RO more love. I should take into account that I use the circulation method. Only have one valve--circulate in and out of my sap tank through the RO until I get up to 8 or 10 brix. So it gets a good workout. With a 350 gallon run, that's a lot of gallons running through that RO in circulation.

I did a complete cycle of rinse--soap wash--rinse--acid wash with 24 hour soak--rinse. It did increase performance. I learned from the new owners of Deer Run that I have a 4x40 MES membrane so now I can do more research into the exact details of care. As far as a baseline goes, I find it difficult to set one because the variables are always changing--temperature especially. There is a huge difference in performance based on temperature. It's quite amazing to take off 50 gallons of permeate per hour when the sap is warm. It's very slow when working with cold sap.

One question about performance ratings. When they rate a membrane or RO system at so many gallons per hour or day, what does that mean? The number I care about is how many gallons of permeate will it take off per hour at a given temperature and brix.

Thanks again. I hope everyone had a good season. Mine was slightly below average.

[Jgranat]

I am researching to build an RO, either a single or double post 4x40 not just sure yet, I don't want to hijack this discussion but it seems like a good group to ask a question (sorry I have no answers), about the membranes. I read about guys using brackish water membranes and having good luck, is there a specific membrane one should use? I see BW membranes can be had for a little over a hundred bucks new, why not just replace it every 3 years or so?

[TapTapTap]

Interesting. I have never really looked at permeate outflow in any analytical way. I'm always too focused on the concentrate side. I'll pay more attention going forward. That's another example of how this forum makes us better sugarmakers.
Ken

[Bricklayer]

Thanks all for excellent advice. Bottom line is that I should be giving my RO more love. I should take into account that I use the circulation method. Only have one valve--circulate in and out of my sap tank through the RO until I get up to 8 or 10 brix. So it gets a good workout. With a 350 gallon run, that's a lot of gallons running through that RO in circulation.

I did a complete cycle of rinse--soap wash--rinse--acid wash with 24 hour soak--rinse. It did increase performance. I learned from the new owners of Deer Run that I have a 4x40 MES membrane so now I can do more research into the exact details of care. As far as a baseline goes, I find it difficult to set one because the variables are always changing--temperature especially. There is a huge difference in performance based on temperature. It's quite amazing to take off 50 gallons of permeate per hour when the sap is warm. It's very slow when working with cold sap.

One question about performance ratings. When they rate a membrane or RO system at so many gallons per hour or day, what does that mean? The number I care about is how many gallons of permeate will it take off per hour at a given temperature and brix.

Thanks again. I hope everyone had a good season. Mine was slightly below average.


The way manufacturers size their RO units with gph numbers is based on the hp pumps performance. Basically how much sap it can process per hour at the max PSI they recommend the pump to run at. For example. A CDL 600 gph unit will pump 10 gpm ( 600 gph ) at 500 psi. So it’s a 600 gph.
Basically if you run it at that pressure or any pressure your concentrate + permeate flow would equal what the pump is able to pump at that pressure.
A 250 or 125 is the same thing. Max pump discharge at a max pressure.

[TomorrowRiverMapler]

There certainly seems to be a shroud of secrecy around RO membranes for maple sap. Also pricing seems to be quite variable. For example, I'm thinking of replacing my Leader Micro II 4x40 membranes which are Hydranautics and cost $325. A 4x40 H2O membrane is $420. These are from the same vender selling Leader/H2O products. Is an H20 worth $100 more? Mine are 6 years old and at 85% throughput versus when new. The cost to clean is at least $100 each with no guarantees of getting them back to new condition. Probably will just buy new ones.

[Bricklayer]

Don’t think there is a maple company out there that “ makes “ their own RO membrane. They are just labeled as their own.
I’ve had great results with the MES membranes when I had a 4” unit . The person who bought my 4” RO bought new membranes off Amazon and had good results as well. I would recommend MES though. Never had any issues with those membranes.

[Jgranat]

Compared to the drinking water RO process, the maple sap desired is the "dirty" side of the process, so a cheap membrane would still work, May even seem to work better with a bit of sugar build up. This would not be the first time clever marketing was used to sell the same thing to a consumer at an inflated price.

[spike in wi]

Marc, We had a Deer Run 125 for the last 6 or 7 years. A couple things that we discovered on slower production was on sap that sat for 2 or 3 days would plug the prefilter a couple times on a run. We ran about the same taps and production that you do. We learned to run the sap daily to eliminate that problem. We did a soap wash and acid wash at the end of season and soap wash on season startup. When we first got the RO we ran at the 275 psi but eventually backed down to 250/260 or so. Really didn't notice much difference and the pump ran quieter. What others had mentioned was doing a soap wash and that helped us a couple of times. Our prefilter is 10 micron. I've heard others use 5 micron but those would plug in half the time maybe?? Our main culprit was the prefilter in most cases. My 2 cents worth!! Mike

[TapTapTap]

[QUOTE=Jgranat;418249]Compared to the drinking water RO process, the maple sap desired is the "dirty" side of the process, so a cheap membrane would still work, May even seem to work better with a bit of sugar build up. This would not be the first time clever marketing was used to sell the same thing to a consumer[QUOTE]

I'm not so sure about the cheap membrane - hopefully someone with expertise beyond me will also respond.

However, I do understand that there are some significant differences between the home drinking water RO and the maple sap RO. For one, the acceptable efficiency of the home RO is around 4 gallons of waste water per gallon of clean water. For us maple producers, our permeate can be around 10 times the volume of concentrate (a complete reversal of the home RO need, and then some). Concentrating sap to our expectations requires that we push hard on the raw sap pressure through the membrane (up to 500 psi). We also have a huge loading of impurities on the membrane. Perhaps our membranes don't need to be more efficient or robust, but I'm not sure.

I'm also not sure if the membrane works better with a little bit of sugar build up. I think the opposite - that the membrane efficiency, as measured by output at a constant pump pressure, decreases immediately and continues to decline throughout the process until the membranes are cleaned again. It's like your shop vac filter - filtration might increase with dust on it but it sucks less. In the case of the shop vac, smaller dust particles are discharged as the filtration improves. But - with the RO, filtration doesn't necessarily improve since the filtration is already sized to allow only water molecules through. There's no advantage to having more filtration.

Ken

[Jgranat]

I have some background in industrial filtration, and there are applications where the filter cake improves filtration. If it is merely a size only factor of operation, then there really could be no difference in the membranes, water molecules do not come in different sizes, one size fits all. I am still learning about this process, I would also like to hear a better explanation, hence my first question.