RODI filter 0 PPM Problem

[Andre Duarte]

Dear reefers.

I am struggling with my RODI unit since I am having difficulties have 0 PPM water output. My system has 1 sediment filter, 2 carbon filters, a membrane and 2 stages for resin. It started as a TMC V2Pure 100 but I later added a second carbon block to it. Finally I add two TMC V2 Pure de-Ionisation Pods (500ml) after the membrane.
To measure the result I am using a HM Dual TDS meter, calibrated with HM 342 PPM solution.
Since I was getting low results (5PPM output) I have decided to replace all filters, one DD Sediment, two DD Carbon, one Filmtec 150GPD membrane and replace the two resin filters with new FaunaMarin MB 20 resin.
Right away my TDS output went down to 0PPM, unfortunately 50 gallons later, my TDS went up to 5PPM again.
Is the resin depleted after 50 gallons? I have installed the two resin filter vertically to avoid gaps, and after a few minutes opened the filters again to make sure they were completely full.
My TDS in is about 350PPM.

Any suggestions would be appreciated.
Thank you.

 

[AllSignsPointToFish]

How old is the membrane?

 

[Andre Duarte]

New, all filters are now new. The Membrane, the sediment filter, the two carbon filters and the resin on both filters after the membrane.

 

[AllSignsPointToFish]

Have you inspected the O-rings and seal on the membrane for cuts/tears/incorrect installation? Defects in these sealing surfaces can allow high-TDS water to contaminate product water.

 

[Water Dog]

A few things...

You mentioned that your source water TDS is about 350 ppm or so, do you know what your TDS is after the RO membrane, but before the DI stage is?

Do you know what your incoming water pressure is? It is my understanding that a 150 gpd membrane will need at least 65 psi of water pressure to operate efficiently.

When you switched from a 100 gpd membrane to the current 150 gpd membrane, did you upgrade to the proper flow restrictor rated for the 150 gpd membrane?

Then lastly, I noticed those DI pods are horizontal cylinders to hold your DI resin. Those are prone to channeling, which won‘t allow the most efficient use of your DI resin. Most of us here in the states use traditional vertical canisters to hold our DI resin that allows more effluent flow through the resin without the channeling issues inherent with the horizontal DI pods that you have.

 

[lapin]

This will be hard for the US members since that system is not common here. @Water Dog just asked the questions I was going to ask

 

[Andre Duarte]

Thank you for the hits @Water Dog.

A few things...

You mentioned that your source water TDS is about 350 ppm or so, do you know what your TDS is after the RO membrane, but before the DI stage is?

Do you know what your incoming water pressure is? It is my understanding that a 150 gpd membrane will need at least 65 psi of water pressure to operate efficiently.

When you switched from a 100 gpd membrane to the current 150 gpd membrane, did you upgrade to the proper flow restrictor rated for the 150 gpd membrane?

Then lastly, I noticed those DI pods are horizontal cylinders to hold your DI resin. Those are prone to channeling, which won‘t allow the most efficient use of your DI resin. Most of us here in the states use traditional vertical canisters to hold our DI resin that allows more effluent flow through the resin without the channeling issues inherent with the horizontal DI pods that you have.

Thank you for the hits.

I have changed the TDS meter from the end of the Resins to after the membrane and the reading is
about 23 PPM. Since the input was now roughly 372 PPM this is a 93.8% rejections rate (normal?). All the o rings are new with the membrane and filters, so I am assuming there are no leaks.

The incoming pressure is around 65psi. Regarding the flow restrictor, I was not aware this should be also changed. I have attached a picture of the flow restrictor that I have. I will try to find out a new one for this membrane.

Regarding the DI pods, you are right. Here in Europe we tend to use these pods, that come with mounts to be fixed to the membrane enclosure, ie to be mounted horizontally. However, I have my DI ponds mounted vertically to avoid channeling, and the water is flowing from the top to bottom. I have opened both pods after a few minutes to fill again the pods with resin in order to avoid gaps inside. I will try to order two US vertical style canisters for my RODI system. However, I am having 23PPM before, and 5PPM after the pods. Is this rate normal?

I am assuming that my intake has a very high PPM that the system is not able to clear 100%. What else can I do?

 

[Snoopy 67]

The ratio of bad to good should be close to 4-1
4 gallons waste to 1 gallon of water from the RO.
You achieve that by adjusting the flow restrictor while running, no need to change it.
93% is a little low for a membrane, we usually get 97%, or even 99% on specific membranes

 

[Snoopy 67]

One more thing -- you are not on well water are you?

 

[Water Dog]

Pushing 23 tds water through your DI resin certainly explains why it’s exhausting so quickly. For now, I’d suggest having the flow from tour DI pods going from the bottom to the top.

As said above, you’re shooting for a 4:1 waste to product water ratio. I use a trimmed capillary flow restrictor to achieve this in my system. But for those using the set rate flow restrictors, BRS recommends a 550 ml flow restrictor for a 75 gpd membrane. Yours looks to be only a 300 ml restrictor, so I question of that is the most efficient for your 150 gpd membrane. Based on the 93% rejection rate on your new membrane, I’d say no. Get back to us with your waste to product water ratio and we’ll go from there with proper flow restrictor options.

 

[ThemytB]

For comparison sake, I have crap well water and low psi. I end up with 40 ish ppm out of RO membrane then run into a 3 stage DI(cation/anion/mixed) and get 0.3 ppm(yes my meter reads that low) System only "kills" anion resin at a rate around 1 cartridge worth every 150 or so gallons, cation and mixed bed never get touched.

 

[lapin]

800 is what I have with dual 100 gpd membranes
Not that this is your problem:
https://www.bulkreefsupply.com/membrane-flush-valve.html

 

[Andre Duarte]

One more thing -- you are not on well water are you?

No I am not. This is tap water. And apparently as a lot PPM readings. I have used a pool chlorine test on my tap water and apparently there are some chlorine in the water as well. I don't think this is a problem since the chlorine tends to evaporate from the water over time. Since I am storing the water this shouldn't be a problem.

 

[homer1475]

Chlorine will kill a membrane, this is the reason behind carbon blocks before the RO membrane.

I think you need a higher restrictor for dual membranes. On my 150GPD BRS unit(dual 75GOD DOW membranes) I have a 550 for a restrictor.

 

[Andre Duarte]

Chlorine will kill a membrane, this is the reason behind carbon blocks before the RO membrane.

I think you need a higher restrictor for dual membranes. On my 150GPD BRS unit(dual 75GOD DOW membranes) I have a 550 for a restrictor.

I did the test with two 750ml canisters and then I did a precise measurement. I got 748ml of RODI water and 525ml of waste. This give us a ratio of 1.42-1 (RO-Waste).

This is where I am confuse. If I increase my 300ml/min restriction to the 800ml/min I will further decrease the ratio by allowing more water to be wasted right?

What about the Chlorine killing the membrane? I do have two carbon filters before the membrane, should I be safe with this?

 

[Water Dog]

This is where I am confuse. If I increase my 300ml/min restriction to the 800ml/min I will further decrease the ratio by allowing more water to be wasted right?

What about the Chlorine killing the membrane? I do have two carbon filters before the membrane, should I be safe with this?

With your 300ml restrictor, I would open up the flush valve ever so slightly until you get the proper 4 to 1 waste to RO water ratio. Once you get that proper 4:1 ratio, report back with your post RO TDS.

With the two new carbon blocks before your RO membrane, it should be more than adequately protected from chlorine in your tap.

 

[homer1475]

Measure your water with a chlorine test pre RO membrane and see of any is making it past your carbon blocks. Easiest way to tell.

You should get higher waste to RO. Not the other way around. The idea is to push the water through the membrane, not allow it to trickle through. This is why the high pressure is recommended and the higher the pressure the better your production will be, up to a certain point where you'll get breakthrough of the membrane.

FYI I am certainly no expert here, and can only say what I learned when I was researching for my unit.

 

[Andre Duarte]

With your 30ml restrictor, I would open up the flipush valve ever so slightly unit you get the proper 4 to 1 waste to RO water ratio. Once you get that proper 4:1 ratio, report back with your post RO TDS.

With the two new carbon blocks before your RO membrane, it should be more than adequately protected from chlorine in your tap.

Thank you very much @Water Dog for the help.
I have tried to adjust the valve in order to have a ratio about 1 part of RODI water and 4 of waste. The valve and the tube does some noise but I think I did it.
The pressure on the membrane drops to about 30 psi. The input before the sediments filter is about 325ppm and the output after the membrane is now 13ppm, which will get an efficiency of about 96%. It is better now but not sure if acceptable readings to have before the resin.
Meanwhile I will try to get a 800ml valve.

 

[Water Dog]

Yeah, try that 800 ml flow restrictor, I’d imagine it’d be able to hold pressure better than opening up your 300ml flow meter slightly. Hopefully with the proper pressure, we can drive the efficiency of your membrane higher than the 96%. Let us know how it goes.

 

[Andre Duarte]

Yeah, try that 800 ml flow restrictor, I’d imagine it’d be able to hold pressure better than opening up your 300ml flow meter slightly. Hopefully with the proper pressure, we can drive the efficiency of your membrane higher than the 96%. Let us know how it goes.

Dear @Water Dog thank you very much for your help.
Finally I was able to get my hands on a 800 ml flow restrictor and right away the system overall seems better. (I wish a BulkReefSupply in Europe, please guys think about that).
I am currently measuring 433PPM before the sediment filter, and 10PPM right after the membrane. This is 97,69% efficiency However I am getting a 2.11-1 Waste-Filtered water ratio, far from what you have suggested 4-1. This with 58psi of pressure. Should I increase it to 1500ml flow restrictor?

What about the 10PPM out of the membrane? Is this acceptable to the resin? Maybe a will be forced to replace the resin more frequently.

Thank you.