RODI membrane

[knee]

I'm currently using Aquatic Life RO Buddie 50 gpd with DI and I make 15g of RODI water weekly. My waste waste water is 60g more or less and I want to reduce that if possible. I do use it to water my outdoor plants but that's only less than 5g cause I don't have much.

Questions:

• Can I add another membrane to my current setup?
• If I can add another membrane, then I'd be connecting the "waste" output tube of membrane #1 to the input of membrane #2 giving me two outputs of clean water. Is there a way I can connect both outputs to the DI so I only have one output of water?
• Do I really need DI if i'm running two membranes?

[ScottieB]

Hi! I see your idea and I think its great your using the waste water for something. 

In that particular RO setup, or any for that matter I don't believe you can make it more efficient by adding a second membrane (unfortunately) in the way you describe.

The biggest thing that comes to mind is pressure, the waste water doesn't have enough pressure to drive it through a membrane. There are more efficient ones, up to 1.5:1 (or even 1:1) units but those are designed to maintain high pressure though the single or double membrane.

Also, the DI is used to reduce your TDI (total dissolved solids) to essentially 0. The water coming out of the membrane might be close to 0 depending on your source water but the DI membranes finish off whatever small charged ions are left in the water. So yeah, even with a super efficient RO and multiple membranes small charged ions still make it through. So if 0 TDS is the goal then DI is still needed.

Here is an example an efficient "water saver" unit for some more info: https://www.bulkreefsupply.com/4-stage-value-150-gpd-water-saver-ro-di-system-bulk-reef-supply.html

[knee]

On 3/9/2023 at 12:09 PM, ScottieB said:

There are more efficient ones, up to 1.5:1 (or even 1:1) units but those are designed to maintain high pressure though the single or double membrane.

I'd love to get an RODI unit from BRS but my space is so limited that's why I opted for the Aquatic life unit. I really prefer the bigger units and I used them before, but now I can't crowd the sink too much cause I also have a roommate and I don't wanna take all the space in the kitchen. 

Will it help with the pressure if I added a booster pump?

 

[ScottieB]

Ok, I see. I have mounted them under the sink, or used piggy back valves to plumb them in other locations but if you renting or just don't want to mess with plumbing thats totally understandable. 

A booster pump will help increase pressure on the inlet, some people on well water or in certain areas don't have the ideal minimum water pressure of like 60psi. They need a booster pump to kick up that pressure from like 30-40psi to something that can push through the membrane. 

Honestly I cant think of a way to pressurize the waste water without doing something way too elaborate. You may have to just stick to what you've got unfortunately. Wish I could be of more help.

 

[knee]

On 3/9/2023 at 1:25 PM, ScottieB said:

Honestly I cant think of a way to pressurize the waste water without doing something way too elaborate. You may have to just stick to what you've got unfortunately. Wish I could be of more help.

 

I really appreciate the help! Thank you 🙂

[Procrypsis]

Capture your waste in buckets and use it to flush toilets.

[Andy's Fish Den]

I am not familiar with the unit that you have, so I can't help much concerning it. I have used a RODI unit for years, using it to make pure water for my reef tanks and now I use it when needed in my freshwater tanks as well. I have had a 75 gallon per day unit from Bulk Reef Supply for a long time, and I was in the same boat you are, of having about 5-6 gallons waste water to every gallon of RODI water. I got a booster pump kit from BRS, it boosts the water pressure up to 80 PSI and now when I use it is like 1.5-2 gallons waste to one gallon RODI water. I have noticed that I am not using the DI resin as fast as well. 

[Pepere]

Flushing toilets would be excellent use of the waste water.  
 

using buckets to do it would get old quickly…. And I dont  know that the cost savings could amortize the plumbing costs to automate it.

[gardenman]

If your water pressure is low a booster pump would certainly help. My old well had a 20/40 pressure switch. The pump would run whenever the water pressure got under 20 PSI and stop at 40 PSI. If you've got a well, there's a pressure switch in the system and a gauge to show the pressure. There should be markings on the switch showing its rating, but if not simply turn on a faucet and watch the gauge. If it falls to 20 PSI then rebounds to 40, you've got a 20/40 switch. If it goes down to 40 then up to 60, you've got a 40/60 switch. There are also 30/50 pressure switches. The 40/60 switches seem the most common, but even with those and many RO/DI systems wanting 60 or more PSI a booster pump could be a good investment. You'd only be getting 60 PSI for a very short period.

[knee]

On 3/10/2023 at 3:30 AM, Andy's Fish Den said:

I got a booster pump kit from BRS, it boosts the water pressure up to 80 PSI and now when I use it is like 1.5-2 gallons waste to one gallon RODI water. I have noticed that I am not using the DI resin as fast as well. 

I might just try adding a booster pump if that will help reduce my waste water. I've used RO a few times but have never tried attaching a booster pump. Hopefully I don't mess it up 😂

 

On 3/10/2023 at 6:18 AM, gardenman said:

If your water pressure is low a booster pump would certainly help.

To be honest with you, I don't even know my water pressure. The ro buddie doesn't have a water pressure gauge but I do want to get one so I can get an accurate number, and make it easier for me and other people trying to help to figure things out. Is there one you'd recommend?

[egruttum]

What you are describing is very common in industrial RO units where you have a primary unit and a secondary recovery unit that takes the reject stream from the first membrane.  They run at much higher than 65 PSI pressure and typically these basic ones get 75% recovery, meaning 3 gallons of clean permeate per 1 gallon of rejected water.  If you do it this way you will not be able to tie the primary and secondary membrane permeate streams together as they will be at much different pressures.  You will have to run them separately to your permeate tank.  Do you need DI?  It all depends on how low of TDS you want in your water.  If you want zero you will have to run DI.  If you just want low, like 1-10, then RO should be just fine alone. 

Low pressure industrial boilers will use RO water as their feedwater without any issue.  Once you get up to high pressure super-heated steam boilers for turbines you have to do DI after RO to remove everything, especially the really hard to remove silica minerals that will plate out on your turbine blades.

[knee]

On 3/11/2023 at 5:31 PM, egruttum said:

Do you need DI?

I don't really need the DI because I mix 50/50 RODI/tap anyway. I only bought the 4 stage because it was the only one in stock on amazon and the price wasn't much different from the 3 stage version. I haven't tested just the RO water TDS tho which I know I should've right when I set it up. I'll definitely check tomorrow.

 

On 3/11/2023 at 5:31 PM, egruttum said:

What you are describing is very common in industrial RO units where you have a primary unit and a secondary recovery unit that takes the reject stream from the first membrane.  They run at much higher than 65 PSI pressure and typically these basic ones get 75% recovery, meaning 3 gallons of clean permeate per 1 gallon of rejected water.  If you do it this way you will not be able to tie the primary and secondary membrane permeate streams together as they will be at much different pressures.  You will have to run them separately to your permeate tank.

Really appreciate this info. I'll stick to my current setup for now and will probably try this when I have more space. Do you think this is better than getting those units that have a 1.5:1 ratio?

[egruttum]

Based on what I am reading you saying I would not run DI.  DI is for people that want zero dissolved substances in their water so what they make is 100% by design.  The difference between RO and RODI is so small that I think it's mostly a sales gimmick by companies to sell more product.  I'm sure there are some tiny use cases where DI makes sense but I think the vast majority of users use it because a company says it's better for your aquarium.  When you take your RODI water and mix it with tap water anything that the DI took out goes right back in.  Using DI will only help the resin supply companies with their bottom line.

My knowledge of home RO isn't great because I only use it industrially so this answer won't be the best.  But if I were looking at buying an additional RO membrane for a homemade secondary recovery vs buying an entirely new unit with higher recovery I would carefully look at costs and my conditions.  Inlet pressure is critical on an RO to create the proper pressure differential from the inlet of the RO membrane to the permeate side.  With a low inlet pressure you won't have the driving force to push water through the membrane which will result in low recovery like you are seeing.  If my water source was a low or inconsistent pressure I would look at a booster pump on the inlet.  That will help your existing unit as well as help with any modifications or future purchases you make.  If that doesn't get you the recovery you want I would probably look at the cost of a higher performance unit.  But first I would consider what you are trying to optimize.  For me personally I try to optimize my cost.  I would look at the cost of a new unit vs the cost of water with the really low recovery you are seeing.  If it's a really long pay back period I would save the upfront cost and just deal with the higher water cost.  But if you are worried about your environmental impact and wasting water your calculation may be much different than mine.

Hope this helps a little.