connect a second membrane RO system with Permeate pump

dadarara · Jul 9, 2021

I have this Permeate pump used and I want to connect two membranes in series.
I have one membrane 100GPD and the other is 75GPD. what would be the optimum connection ?
which one first ? not exactly clear how to incorporate this Permeat pump in this scenario .
also should I have two restrictors (check valves)? one is 300ml other 420ml.
I have 60PSI pressure.

thanks

sunken3 · Jul 9, 2021

not sure what the pump is.. but from what ive read, you only want a restrictor after the second membrane (it will keep pressure for both).. not sure if you should mix and match membranes either. but if i did, i would put the 75g second.

JAC- · Jul 9, 2021

Curious why you would want to put two membranes in series? Standard configuration would be parallel. If you are having issues with TDS reduction something is likely wrong with a seal or your membrane.

In a parallel configuration you will get more RO water and both membranes will function at a higher efficiency.

sunken3 · Jul 9, 2021

JAC- said:
Curious why you would want to put two membranes in series? Standard configuration would be parallel. If you are having issues with TDS reduction something is likely wrong with a seal or your membrane.

In a parallel configuration you will get more RO water and both membranes will function at a higher efficiency.

i wasn't looking at the diagram.. however, parallel gets you more water per day, series wastes less water and is more efficient (not less).. .. if by series we are saying the first membrane's waste is fed into the second membrane. ... in "series" you use one restricotr.. in parallel you would use 2 (i think)..

note: there is a great BRS video on the difference.

mrlavalamp · Jul 9, 2021

Found a thread on the subject:

What am I really saving by using two RO membranes versus one? | BRStv Investigates

Hey guys! Another episode of BRStv Investigates is finally here! Today, we put some testing and numbers behind a single DOW Filmtec 75gpd RO Membrane versus two RO membranes and see just how much of an upgrade it is! Along with that, Ryan explores the differences between plumbing multiple...

www.reef2reef.com

sunken3 · Jul 9, 2021

mrlavalamp said:
Found a thread on the subject:

What am I really saving by using two RO membranes versus one? | BRStv Investigates

Hey guys! Another episode of BRStv Investigates is finally here! Today, we put some testing and numbers behind a single DOW Filmtec 75gpd RO Membrane versus two RO membranes and see just how much of an upgrade it is! Along with that, Ryan explores the differences between plumbing multiple...

www.reef2reef.com

that would be the one!

JAC- · Jul 9, 2021

@sunken3 I was interpreting that the intent was to run the first membranes permeate into the feed water of the second membrane. You can also recycle the brine or reject water back into your feed water to achieve this. This is the standard "re-circulation" method used by my and many other higher end RO manufactures. The math works out much better with that method.

sunken3 · Jul 9, 2021

JAC- said:
@sunken3 I was interpreting that the intent was to run the first membranes permeate into the feed water of the second membrane. You can also recycle the brine or reject water back into your feed water to achieve this. This is the standard "re-circulation" method used by my and many other higher end RO manufactures. The math works out much better with that method.

then i think i understand your comment a bit better and would agree that if you have to run 2 membranes in sequence to get your TDS down, something is wrong... normally i would see the waste water from the first membrane fed into the input line (feed) of the second membrane... and in that situation, you only need a restrictor after the second membrane.

dadarara · Jul 10, 2021

JAC- said:
Curious why you would want to put two membranes in series? Standard configuration would be parallel. If you are having issues with TDS reduction something is likely wrong with a seal or your membrane.

In a parallel configuration you will get more RO water and both membranes will function at a higher efficiency.

there is a test BRS guys did calculating the benefit of clean vs waist water in this configuration. this is what I am after. and I have two membranes so why not ?!

dadarara · Jul 10, 2021

so I understand that the restrictor should come after the second membrane. But should I put the Premate pump also after the second membrane or in between the two ? what you guys think ?

JAC- · Jul 10, 2021

dadarara said:
there is a test BRS guys did calculating the benefit of clean vs waist water in this configuration. this is what I am after. and I have two membranes so why not ?!

First off some background, I'm an engineer for a company that designs and manufactures water treatment systems for municipal, industrial and commercial applications. That isn't to say that I know better than anyone else, I'm an electrical engineer and I design the controls and other electrical components for said systems and I still learn things all the time. My point is that is I'm coming from a completely different background.

These guys are working with what they have and trying to optimize it, and cheers to them for that and sharing the knowledge in a way that definitely seems to be focused on helping people rather than just getting people to give them more money.

The primary reason I'd say why not is membrane fowling, but in my world we make RO systems that produce 30 - 100 GPM. the membranes are huge and cost 100X more. For the cost of these membranes, that is probably not a high concern for you. There are other ways to achieve the same results without putting your second membrane at such a disadvantage, but we're getting away from off the shelf components and into an area that is way beyond what is needed for your goals.

So go for it.

As for your permeate pump, the permeate lines should come together in a tee fitting and the single line would pass through that allowing your pump to create the lowest pressure possible on the permeate side of the membranes.
However looking at the diagram you have above, the brine is passing through the pump too. This makes me think it's a mechanical gear pump that is supposed to also proportion the permeate to brine ratio. That could be problematic for the configuration you are talking about. Dose the permeate pump use power?

dadarara · Sep 18, 2021

small update for posterity..
I have connected 2 membranes in series . basically based on the diagram above. the first is 100GPD and the second is 50GPD. I have very good results. The objective of the 2 membranes is to have less brine loss. nothing to do with the TDS and water quality. I presume that the second membrane might get clogged faster, we shell see.
The result of the above I am losing 40% of my water, which to me sounds fantastic. Before the second membrane was connected, I measured a ratio of 1: 3 .

BTW this premate pump is totally mechanical.

KStatefan · Sep 18, 2021

dadarara said:
The objective of the 2 membranes is to have less brine loss. nothing to do with the TDS and water quality.

If that is the goal why use a RO membrane

dadarara · Sep 27, 2021

@KStatefan
what other solution you know about? there are two that I know. one is the Premate pump and the other is two membranes. and I did both. the results are great.

KStatefan · Sep 27, 2021

You said the goal was to reduce the brine. If you did not use a membrane you would have no brine

dadarara · Sep 28, 2021

Not exactly clear what you are trying to say. In any osmosis system you must have a membrane which is the main micron grade filter. All the other Pre and post filters are additions to the membrane. 99% of system use one membrane. These systems usually have a 1:3 or 1:4 lose ratios of clean produced RO water vs the brine. Which is waste. By adding the second membrane that processes this waste water I get a total system higher volume of RO clean water for the price of a little higher TDS from the second membrane and also maybe the lower MTBF of this second membrane My setup proves to be very effective. I don’t feel any increase of TDS. Mainly because I have ion resin as the last stage which takes care of this. The cost of a membrane I buy in China is low. I don’t know how to measure any other chemicals and molecules passing through the system, so I don’t know the real effect of this second membrane in that respect.

KStatefan · Sep 28, 2021

I am saying if your goal is to reduce brine do not run a membrane. I know some people in California just run Sediment-carbon-di due to the high cost of water and water restrictions.
Jake at reefbreeders runs sediment-carbon

dadarara · Oct 2, 2021

At some point I did. Got TDS of about 240. The resin will be depleted very fast. And not sure it will be able to drop it to 0. For marina maybe it’s ok. Not for reef and not for sps.