whats better on a ro/di setup

[Alen]

Im going to be putting together a 7 stage ro/di unit, i was wondering whats better
2 sediment filter 1st (5 micron) 2nd (1 micron) or 2 carbon filters?
as in 1 sediment (1 micron) and then 2 carbon filters, thru 2 membranes and last but not least the 2 stage di.

What do you guys think or what would you guys do?
any advice would be great

Thanks in advance

[on the spot]

single sediment, two carbons.

[Alen]

how many flow restrictors do you install on a dual membrane setup?

[on the spot]

Originally Posted by Alen

how many flow restrictors do you install on a dual membrane setup?

One. I still don't see the value of two membranes though. You'll need a booster pump to make it work well. Best of luck.

[reeferdale]

Originally Posted by on the spot

One. I still don't see the value of two membranes though. You'll need a booster pump to make it work well. Best of luck.

I have heard you get more product and less waste, less waste being the key. I have never tried it but I do have an extra memberane and cannister laying around, I should hook it up and try it out, if I do I will post results in a couple weeks.

if you are doing all this then why not just add and 8th and do 2 sediments as well?

[iyachtuxivm]

On a dual membrane you run the waste water of the one in to the input of the other one then ( Y ) the two outputs together to your di resin. The waste water of the second goes to your drain. I hooked in a second membrane works great twice the production half the waste.Still 0 tds on the inline and hand held.

[mf2055]

If you are seriously concerned with waste you can do a dirrect DI setup. No waste at all.

[Alen]

how do you do a direct di setup?

[mf2055]

Direct DI would be like bypassing the RO filter and going direct from your prefilters to DI.... Obviously not the way to go on the standard RO/DI system as it would very quickly exhaust treatment capacity. A few fish stores use them for on demand water. Eco Reef in Zeeland has something of that nature. It might be a toss up for cost efficiency for at home use on a small tank. But for larger use or commercial it gets closer to cost effective as the large canisters of exchange resign are not cheap to buy or maintain, but for anyone who pays a lot for water and might need 1000 gallons any given day the system would pay for itself over the cost of having a 1000 gallon or larger RODI storage tank taking up room.

If you could get your hands on some water softer size containers of exchange resign for a decent price I would imagine some red neck engineering could get you a somewhat more cost effective "at home" system without a drop of waste water or need for water storage.

[BuckeyeFldSup]

Why would you put together a 7 stage system?

You should think of a four stage as the default:
sediment filter -> carbon block-> RO-> DI
and add stages only if necessary to address a particualr water quality issue (e.g., heavy sediment loads, chloramines, CO2, hydrogen sulfide).

Russ

[doogle]

I'm interested in the zero/low waste setups, for sure.

[Alen]

i wanted to put together a 7 stage ro/di unit for one reason at that is to save on the waste water, i help out about four other reefers in this hobby that need ro/di water, they dont have a unit for them selves, so insted of asking for money from my friends, i will just upgrade my unit for my personal use and help others. we all win.

i have plans to add a third membrane and booster pump just to see what the out come would be. any thoughts anybody?

[BuckeyeFldSup]

In regard to adding membranes to reduce waste water, first remember that what folks call "waste water" really would be better thought of as "flush water" in that this water serves the important purpose of internally flushing the surface of the semipermeable membrane to keep the membrane from fouling/scaling.

When you configure a system with two membranes in series (the waste from the first membrane going to the "in" port on the second membrane), for this discussion let's say it's two 75 gpd membranes, the system behaves like you have a single long (75 gpd x 2) 150 gpd membrane.

Now - if you use a proper flow restrictor, that is, one for a 150 gpd membrane, you'll have about a 4:1 waste to product ratio. Sounds familiar, right?

If however you don't change the flow restrictor - meaning you keep using the same restrictor you were using when you just had one 75 gpd membrane, then you'll see a waste to product ratio much lower than 4:1. But remember that the recommendation for a ~4:1 ratio comes from the membrane manufacturer. They are telling you that you need about a 4:1 ratio to keep the membrane flushed and keep the membrane from fouling or building up scale. Run the system with a lower ratio and you will foul/scale the membrane(s) quicker than would have otherwise been the case.

Instead of adding a second membrane to lower that ratio, you could have just changed out your flow restrictor ($4) instead. A much less expensive approach to get you to the same endpoint in terms of saving on waste water.

Now, to confuse things just a bit. Filmtec specs call for the 4 to 1 ratio on the basis of assumptions about the water that will be supplied to the membrane. If you have very soft water you MAY be able to get a decent service life from the membrane running at a ratio lower than 4 to 1 (e.g., 3 to 1). Remember that the waste water from the first membrane is about 25% harder than your tap water.

Bottom line: If what you are after is reduced waste water, experiment with a different flow restrictor for $4 instead of messing around with a second membrane plumbed in series.

As a side note, you can also lower the ratio by increasing the pressure delivered to the membrane (with a booster pump), because flow restrictors are sized assuming you are providing factory spec conditions (50 psi and 77 degrees for Filmtec membranes). Increase the pressure and you'll drive more water through the membrane and viola - less waste water. But as I mentioned above, if you do this (just like over-restricting a membrane) - the lower the waste to product ratio, the shorter the lifespan on the membrane.

Makes sense?

Russ

[BuckeyeFldSup]

Originally Posted by Alen

i have plans to add a third membrane and booster pump just to see what the out come would be. any thoughts anybody?

Depending upon how you set it up, if you are using 10" x 2.5" carbon block those are typically spec'ed at a max flow rate of 1 gpm - you could easily exceed that so use more than one block. Be careful to clearly understand the spec's on the blocks you use and don't exceed their limits. Typical residential filter housings use 1/4" ports and 1/4" tubing - again depending upon how you're going to configure things consider jumping to 3/8" tubing/housings and 20" housings.

Russ

[McPuff]

This is some great information!

I will just stick to my 3 stage for now and link in a DI stage in a couple weeks. It's working well and while I hate to waste water, I don't have to make hundreds of gallons each week (maybe a couple dozen) and I'm running it at peak efficiency so it's not so bad.