4 Stage RO/DI vs. 6 Stage RO/DI

[-Logzor]

My current RO/DI setup has been expanded over the years from the original 75 GPD system from Buckeye Hydro to include the BRS Water Savings Upgrade. This upgrade added a second RO membrane to the system. My system is driven by a booster pump that can allow the pressure to run in excess of 80 PSI.

I run the typical set of filters in the three main cartridges, sediment filter, carbon block, and DI resin. I probably only have to replace the filters every 3-4 months, maybe longer.

During the recent BRS Black Friday sale I found a 6-stage upgrade kit that added a second carbon block and DI resin cartridge. The price included an entire new set of filters so the actual cartridges that hold the filters were pretty inexpensive.

Does the expanded system from 4 stage to 6 stage buy me better water quality or just more time in between filter changes?

 

[Randy Holmes-Farley Verified Community Expert]

IMO, using two DI cartridges in series allows one to get the same 0 ppm TDS water quality while completely using the capacity of each canister of DI resin (which you cannot do with just 1)

To do that, put in the two cartridges, and monitor the TDS of the effluent (optimally also monitor between the two, if you can, but that is not critical ). When the TDS of the final effluent starts to rise above 0 ppm, remove canister #1 and discard the resin. Put canister 2 (the final one) into the place of the first one and put new DI resin in the final slot. Then run again until the TDS of the final effluent starts to rise again.

This way, you use ALL of the deionizing capability of the resin you buy.

 

[redfishbluefish]

If it is possible, here's what I'd do.....with the current unit, run a sediment filter and two carbon blocks before going through your dual membrane setup. You will need to move around the tubing. The new double chamber unit you picked up....I'd use that for two DI resin canisters.

But, I think it's best if you hear for @AZDesertRat .....he knows RO/DI.

 

[-Logzor]

IMO, using two DI cartridges in series allows one to get the same 0 ppm TDS water quality while completely using the capacity of each canister of DI resin (which you cannot do with just 1)

To do that, put in the two cartridges, and monitor the TDS of the effluent (optimally also monitor between the two, if you can, but that is not critical ). When the TDS of the final effluent starts to rise above 0 ppm, remove canister #1 and discard the resin. Put canister 2 (the final one) into the place of the first one and put new DI resin in the final slot. Then run again until the TDS of the final effluent starts to rise again.

This way, you use ALL of the deionizing capability of the resin you buy.

That's a really interesting idea, I think I might try that!

If it is possible, here's what I'd do.....with the current unit, run a sediment filter and two carbon blocks before going through your dual membrane setup. You will need to move around the tubing. The new double chamber unit you picked up....I'd use that for two DI resin canisters.

But, I think it's best if you hear for @AZDesertRat .....he knows RO/DI.

If I understand correct, I believe this is what the instructions has me do: Sediment>Carbon>Carbon>DI>DI. I'm honestly not sure if this occurs before or after the membranes, but I think it currently goes before?

 

[-Logzor]

One other question: whenever I replace my DI I always go ahead and replace my sediment and carbon. Is this necessary or am I wasting money?

 

[Randy Holmes-Farley Verified Community Expert]

That's a really interesting idea, I think I might try that!



If I understand correct, I believe this is what the instructions has me do: Sediment>Carbon>Carbon>DI>DI. I'm honestly not sure if this occurs before or after the membranes, but I think it currently goes before?

The RO membrane goes just before the DI's and after the carbon.

 

[Randy Holmes-Farley Verified Community Expert]

One other question: whenever I replace my DI I always go ahead and replace my sediment and carbon. Is this necessary or am I wasting money?

There's no need to replace a sediment filter unless it is getting clogged and the pressure is dropping too much. Do you have a pressure gauge on the RO membrane?

Carbon filters are harder to judge. They can get clogged (since they also act as sediment filters), but can also get depleted over time.

 

[AZDesertRat]

The only reason I would run two carbons is if you were using a coarse sediment filter meaning the first carbon would then be acting as an additional sacrificial sediment filter and the second carbon would actually be the one functioning to adsorb contaminants and chlorine. To me that is a total waste of both money and filter housings. Use one high quality, low micron, absolute or near absolute rated sediment filter and one high quality low micron 20,000 gallon capacity carbon block and convert that extra housing to your dual DI.
I also do not fall for BRS claims that dual membrane are water savers. If you expect to get good membrane and DI life it is critical you keep the waste ratio at the membrane manufacturers rate for your water conditions. The ONLY time you can get away with reducing the waste is when you are using naturally soft or softened water and have lower than normal TDS tap water, otherwise you are throwing money away.
Like Randy I use dual DI but I got away from two cartridges of the same resin and rotating them to the MaxCap followed by the SilicaBuster combination. For me in Phoenix with high TDS softened water, my DI life went up about 7 to 8 times, final water quality improved and cost of operation or cost per treated gallon went down significantly.

I change my sediment filter based on headloss recorded on two pressure gauges, one on the incoming raw water line and the other at the RO membrane and change my carbon based on chlorine breakthru using a low range chlorine test kit or my Hanna or Hach chlorimiter.

 

[-Logzor]

How do I change my waste ratio?

 

[AZDesertRat]

A capillary tube flow restrictor matched to your membrane gpd which you then trim with a razor blade so it is correct for your water conditions.

 

[-Logzor]

I'll have to do some research on this aspect, but as a ratio, the finished RO/DI water is maybe 40% and the waste is 60%.

Here are the old membranes, they look pretty dirty, the one has probably been in there for over 4 years. I think I replaced one about 3 years ago.

Water out of the tap is about 200 TDS.

Waste water is a bit higher but not crazy high

 

[AZDesertRat]

Excellent TDS meter! Same one I use.
If your water is not softened your waste should be at least 3 times the treated flow with 200 TDS tap. Sounds like you are only at 1.5/1 and your membranes are suffering swimming in sludge because of it.

To calculate your actual waste ratio use a measuring cup and measure first the waste then the treated for exactly one minute. You need to have approx 3 to 4 times as much waste as treated or the membranes are not sufficiently flushed by the waste velocity and flow, the solids just keep caking up.

 

[-Logzor]

I took your recommendation on this TDS meter surfing other threads!

Can you tell me more about the flow restrictor? I have these blue knobs at the end of the membrane housings, do I simply turn these?

 

[AZDesertRat]

Not sure without a photo but you may have needle valves which suck. They drift closed and ruin your membrane. Buy an untrimmed capillary tube sized to your gpd then follow the included instructions on how to measure your waste and trim the length for your exact conditions. Both Spectrapure and Buckeye Hydro sell them for $5-$6.

 

[-Logzor]

I have the knobs on the system

I tried turning the one knob all the way back and that increased my waste a ton but the waste TDS went down to nearly that of my tap water!

 

[AZDesertRat]

Those are 1/4" ball valves intended to be fully open or fully closed, they are not for regulating or throttling flows. Not precise enough.
When you have a flush kit, which is really a waste of hard earned money, you have on placed in a loop that bypasses the fixed type flow restrictor to increase the waste flow before shutting the system off. The idea is to increase flow enough to scour or cleanse the membrane but in reality the increase isn't enough to do anything but make you feel good. A capillary tube flow restrictor would insert inside the waste line like a piece of spaghetti noodles and not be seen again once you trim the length to adjust the waste flow.
At 3:1 to 4:1 waste ratio the waste TDS will be 25% to 30% higher than the tap TDS or say 250-275 in your case.

 

[-Logzor]

That makes sense, I'll check with Buckeye Hydro to get a hold of the tube flow restrictor to help fix this issue. Thanks for this information! I never fully understood the purpose of those valves.