High TDS with Smart buddie 150 GPD and parallel 75 GPD membranes

[Muffin87]

I've installed the smart buddie 150 GPD version with two NEW 75 GPD Dow membranes, run in parallel.
After over 24 hrs of running, I get 13 TDS, even tho my tap water TDS is 310.
The booster pump is pushing about 75 PSI into the membranes.

Paradoxically, my old 100 GPD membranes in this parallel setup with the smart buddie yield 9 TDS. Suggesting this is not an insufficient pressure issue.

1. My parallel setup has the pre-filtered tapwater from the booster pump split into two using a Y-fitting, with each going into one of the two membranes
2. The waste water from the two membranes is combined into a single waste line using another Y-fitting, and then routed into the smart buddie.
3. The pure water from the two membranes is also combined into a single line using a Y-fitting, and then routed into the smart buddie.

Do you know what could be causing the High TDS?

• I've checked correct membrane placement in the membrane housings three or four times.
• I've checked the pressure gauge
• I got the same tds reading from two different tds meters.(The handheld tds meter has just been calibrated with a standard solution)
• I've checked that all the RO tubes are going to the corrected places.

Has the 150 GPD smart buddie been tested with parallel 75 GPD membranes?
I'm no expert, but the only potential problem that pops into my head is the size of the flow restrictor.

I'm attaching a picture of my setup.

Thank you very much for the help.

 

[AquaticLifeProducts]

Will be glad to help. Can you tell us the expected rejection rate of your new membranes? Typically they are 96% which a 310 ppm supply would yield 12 - 13 ppm TDS.

Higher rejection rate membranes can have lower outputs. Additionally I have seen membrane rejection rates improve as new membranes hydrate from their dry state.

Flow restrictor size is 800ml.

 

[Muffin87]

Can you tell us the expected rejection rate of your new membranes?

"The Dow Filmtec 75 GPD membrane has a 99% rejection ratio". That's reported on the Dow website, the BRS website, and others.
The minimum is certainly 96%, but I've always used Dow membranes (50 GPD or 100GPD High Rejection), and they always produced water with TDS in the range of 3 (50 GPD) to 7 (100 GPD with third party booster pump) with my tapwater.
So, I expected a rejection rate of 99% (50 GPD) or 98% (100HR) rejection.

Flow restrictor size is 800ml.

Was the 800 ml restrictor actually tested on dual 75 GPD membranes run in parallel?

The amazon.com Smart Buddy page said that configuration was fine, and that's why I bought the smart buddy and the two new Dow membranes after confirming that with you one or two weeks ago on here.

However, if it's not the flow restrictor, I don't understand why I'm not getting TDS in the range I used to get with the other Dow membranes.

I doubt that the membranes are both faulty or have both been put in the housings incorrectly, with both the membranes producing TDS higher than the 100 GPD membranes with a lower rejection rate.
I see no problem with the way the RO tubes are connected or the 75 PSI pressure, but maybe you can tell me if I'm doing anything wrong.

Thank you very much for all the help!

 

[AquaticLifeProducts]

Needed to check on the rejection rate.

As for testing, yes we only tested it with membranes in parallel. Running in series is not preferred.

Our 800 ml flow restrictor is setup to give you a ratio of 1 gallon filtered to 2 gallons waste with 150 gallons of membrane. Not sure if your previous setups are running that ratio. I believe DOW wants 15% recovery which gives you 1 gallon filtered to 5.6 gallons waste.

 

[Muffin87]

Needed to check on the rejection rate.

As for testing, yes we only tested it with membranes in parallel. Running in series is not preferred.

Our 800 ml flow restrictor is setup to give you a ratio of 1 gallon filtered to 2 gallons waste with 150 gallons of membrane. Not sure if your previous setups are running that ratio. I believe DOW wants 15% recovery which gives you 1 gallon filtered to 5.6 gallons waste.

Thank you for this.

Should I use two separate 550 ml restrictors on the wastelines of the two 75 GPD membranes, would I get a TDS more in line with Dow's predicted rejection rate?

Thanks

 

[AquaticLifeProducts]

Thank you for this.

Should I use two separate 550 ml restrictors on the wastelines of the two 75 GPD membranes, would I get a TDS more in line with Dow's predicted rejection rate?

Thanks

It’s possible. You may see a pressure drop.

Adding the restrictors to the membranes and not running to the Smart Buddie. Or you can add a bypass on the waste line to increase the waste water flow and keep the functions of the waste flush every hour.

I would need to send you tomorrow. I have it at the office.

What size were you running before?

 

[Muffin87]

It’s possible. You may see a pressure drop.

Adding the restrictors to the membranes and not running to the Smart Buddie. Or you can add a bypass on the waste line to increase the waste water flow and keep the functions of the waste flush every hour.

I would need to send you tomorrow. I have it at the office.

What size were you running before?

I was running a flushvalve, the rating is faded now, but I believe it was 800 ml.

I'm in Italy, that's why I got the smart buddy on amazon. I'm not sure you can ship all the way over here, but thanks!
I'll just buy a couple and see what happens I suppose.

 

[Muffin87]

It’s possible. You may see a pressure drop.

I've been trying to understand this but I can't seem to Google it properly.

A larger flow restrictor increases waste water, and lowers the TDS of the purified water? Is that correct?

A smaller flow restrictor reduces waste water and increases the TDS of the purified water?

 

[slingfox]

I also have a Smart Buddie with double RO membranes. I believe the preferred setup is to have the waste line from first membrane routed to the input of the second membrane. The waste line from the second membrane is then routed to the Smart Buddie membrane waste input. The clean water outputs from the two membranes is combined via a Y fitting and then routed to DI stage for further filtration.

 

[AquaticLifeProducts]

I've been trying to understand this but I can't seem to Google it properly.

A larger flow restrictor increases waste water, and lowers the TDS of the purified water? Is that correct?

A smaller flow restrictor reduces waste water and increases the TDS of the purified water?

Yes waste water will increase, may reduce the TDS of the purified water. I can only think that the low pressure is not forcing the TDS through the membrane.

Not always the case but it can increase the TDS of the filtered water as you are reducing the waste water flow, concentrating the waste water TDS.

 

[AquaticLifeProducts]

I also have a Smart Buddie with double RO membranes. I believe the preferred setup is to have the waste line from first membrane routed to the input of the second membrane. The waste line from the second membrane is then routed to the Smart Buddie membrane waste input. The clean water outputs from the two membranes is combined via a Y fitting and then routed to DI stage for further filtration.

The concern here is the TDS feed into the second membrane. Are you using the original 50 - 100 GPD Smart Buddie? What size membranes?

The problem if the membrane size is too large compared to the flow restrictor size. The original Smart Buddie is 300ml/cc. If you are using more than 100 total membrane size you could damage the membranes along with the pump.

Filtered water to waste water ratios below.
100 GPD membrane with 300ml/cc flow restrictor = 1 gallon filtered to 1.14 gallons waste.
2 x 75 = 150 membrane with 300ml/cc flow restrictor = 1 gallon filtered to 0.76 gallons waste.
2 x 100 = 200 membrane with 300ml/cc flow restrictor = 1 gallon filtered to 0.57 gallons waste.

 

[AquaticLifeProducts]

I was running a flushvalve, the rating is faded now, but I believe it was 800 ml.

I'm in Italy, that's why I got the smart buddy on amazon. I'm not sure you can ship all the way over here, but thanks!
I'll just buy a couple and see what happens I suppose.

You could test the waste water flow rate versus the filtered water flow rate too. Measure in ml and how much volume is made in 1 minute.

The Smart Buddie 150 is rated at 800ml

2 x 75 membrane should be 395 ml per minute.

Two options that we came up for customers to increase the waste water flow but keep the Flush feature on the Smart Buddie. The valve will allow you to adjust the pressure along with the waste water flow.

 

[Muffin87]

You could test the waste water flow rate versus the filtered water flow rate too. Measure in ml and how much volume is made in 1 minute.

The Smart Buddie 150 is rated at 800ml

2 x 75 membrane should be 395 ml per minute.

Two options that we came up for customers to increase the waste water flow but keep the Flush feature on the Smart Buddie. The valve will allow you to adjust the pressure along with the waste water flow.

Thanks for this. Are the connections to the RO system waste lines the same?
Upper one from the RO waste lines, lower one to the drain?

Should the 450 ml flow restrictor work with my dual 75 GPD membrane setup to create 15% recovery (1 gallon filtered to 5.6 gallons waste)?

Thanks!

 

[AquaticLifeProducts]

Yes the tubing size should all be 1/4".

Correct.

To get 1 to 5.6 or 15% recovery you would need approximately 1,000 ml flow restrictor to one 75 GPD membrane. That would be 197 ml filtered water to 1,000 ml waste water per minute. 197/1197 = 16.45%

I do not know of any companies running that high of a waster water flow but from what I can find that is the manufacturers recommendation.

If you add the flow restrictor after the membrane, you would not be able to send the waste water to the Smart Buddie. As the internal flow restrictor would then reduce back down to 800ml.