Upgrading system to 2 Membranes + Booster?

[richfavinger]

I'm considering upgrading my existing SP2000/MaxCap 90gpd 5 Stage to a Dual (2x) 90gpd Membrane and adding a booster pump for higher production and less waste... Would less waste be a correct assumption?

2x 90gpd MB would = about 180gpd? Yes?
Adding a booster pump would be OK, and also better for the 2x system?

Would I get less waste if I stay with the 90gpd and still add the booster?
Manual Booster Pump = I switch it on or plug it in when running the system?
Auto Booster is controlled by a Float?

My rejection is around 3.5:1 and about 50-55psi Line pressure.

[SpectraPure]

Booster pumps are for low-pressure situations, not for saving water. Your 50-55psi will benefit marginally with a pump. You need to have the same wasteroduct ratio, regardless of how many GPD you are making. The TDS of the tap water has a bigger effect on the waste ratio you can get away with. What is your tap water TDS?

The proper way to control a booster pump is with our BPHF-PS-250/4-115 kit, seen here:

http://spectrapure.com/St_kits_p3.htm

Then, a float valve will turn everything on and off.

Scott
SpectraPure, Inc.

[SpectraPure]

also-
Another perspective on Booster Pumps for RODI systems

We often are asked the questions, “If you operate your RODI system at less than optimum tap water pressures, what is the downside? Is there a negative?”

To help answer these questions, I have provided data (below) that shows the actual results of various pressures applied to a typical RO membrane.


Membrane Pressure GPD Measured % Rejection % Increase
35 39.3 97.5
45 55.2 98.2 0.7
55 67.9 98.3 0.8
65 81.8 98.3 0.8
75 97.7 98.5 1.0
85 111.5 98.7 1.2

Note: 80.8 F, .932 TCF, 950ppm TDS, 1150 uS,
OPCF 7 psi; corrected psi 67


Generally speaking, production rate is directly proportional to operating pressure. It can be seen in this example that raising the pressure by the use of a booster pump from 35 pounds (a commonly found pressure in many homes and offices, especially as demand fluctuates during busy periods) to 75 pounds increases production rate by a whopping 2.5 times! This is the primary and most common reason for adding a booster pump to your system (either an RO or an RODI system)
you want to make more water faster! In cold-water locations, a booster pump can also increase the production rate, as production rate is proportional to water temperature.

Another reason for booster pumps that is often over looked, is that in hard water locations (many places in the country) % rejection improves significantly with the increase in pressure provided by a booster pump. Our data above shows a rejection performance increase from 97.5% to 98.5%, or about 1%. How important is 1%? The rule of thumb for DI resin capacity is for every 1% RO membrane rejection improvement you get a 25% increase in DI cartridge life (due to the reduced ionic load). Thus, with this particular RO membrane as an example (they do vary somewhat), you can see that operating an RODI system at higher pressures (75 psi) will gain a 25% increase in cartridge life over lower pressures (35 psi). In other words, with a 25% gain, every fifth DI cartridge is free! As DI cartridge changes are a significant cost of producing DI water over the life of your system, a 25% increase in cartridge life can add up fairly quickly.

bh

[richfavinger]

Production rate never bothered me much. And yes, after I posted this and did a little more reading (and a little thinking) I did realize the ratios remain the same 3:1, 4:1 in water. Water saving efforts was the key.

My tap water TDS is around 180-200tds... off the membrane is 1tds, and of course off the DI's is 0tds.

[SpectraPure]

Hi
I had a thought for you, with water like yours (at least, based on the indicated TDS) you may be able to run your membrane(s) at 2:1 without greatly comprimising the life or rejection if your goal is to reduce your waste stream. Hopefully, your waste is being used on your yard, or trees, or the many other uses people have come up with to use the reject water and thus not "waste" it. :-)
Optimal membrane life/performance is usually experienced at lower ratios like 4:1 or 5:1.
However, if you are the experimenting sort who likes to monitor his system performance, you may try the reduced waste while closely monitoring for scaling effects (losing rejection will accelerate your DI consumption radically) to optimize your overall system performance and cost of ownership.
Enjoy! On my system at home, I run it much harder (low waste) and closely monitor for rejection loss (and production to a lesser extent) and change my membrane when I see a 2% drop in rejection. In my situation (my well water and my septic system) I can afford to change my membrane a litle more frequently in return for low DI consumption and less "waste" even though I run my reject line to my pine trees (they love it).
Just a thought.
Bruce