RO wastewater

[neotekz]

is there a system out there that can reduce the amount of wastewater from a rodi system? my aquasafe uses about 2.5g per one gallon of rodi. is there any system that is more efficient? i know that a rodi system has to reject some water to work properly but is there a system out there that is more efficient? also i'm a little confused about rejection rates...what;s the difference between the higher 98% and 90%? does that mean that the 98% rejection rate RO membrane produces more wastewater per gallon?

also what is a good rodi? i was looking at the maxpure from spectrapure.com, anyone use this system?

 

[AZDesertRat]

No need to cross post, I answered in your other thread.

 

[neotekz]

yah i posted in the newbi section but i thought that it;ll get more hits here,
other thread
http://reefcentral.com/forums/showthread.php?s=&postid=9528540#post9528540

 

[30reef]

AZDesertRat is his name and Making clean water is his game!

 

[jdieck]

A couple of comments I did not see in your "other" post
a 2.5 to 1 waste to product ratio might be saving you some water but may increase the level of contaminants on the product water and shorten the life of the membrane.
If you have good inlet pressure (around 60 psi) a second membrane cartridge of the same capacity of what you have connected in series with the one you have can reduce your waste by 1/2 (waste of first membrane feeds the second and product lines of both T into a sinble line to the DI)

 

[neotekz]

so if i put a second RO stage on my rodi system it will recycle my waste water?

 

[jdieck]

<a href=showthread.php?s=&postid=9529331#post9529331 target=_blank>Originally posted</a> by neotekz
so if i put a second RO stage on my rodi system it will recycle my waste water?

It is not really recicle.
The waste water from the first membrane almost comes out of it at the same inlet pressure so it can feed the second membrane.
So basically with the waste water of a single membrane you get two product outputs.
Note that the impurities of the waste water from the first membrane increase but are still withing the specification range for inlet water. The impurities on the product water going to the DI increase a bit (1 to 3 ppm) but nothing the DI filter can't handle properly.

 

[neotekz]

yah i have tested my wastewater and its about the exact same as my tap water at 75 tds. what about using one of these pumps? http://www.spectrapure.com/St_permeate_pump.htm
i'm not sure how they work but it claims to decrease wastewater output by 80%

 

[AZDesertRat]

Permeate pumps are not miracle workers but they do speed up making water if you have a pressure tank/drinking water type system. Speeding the process up reduces the waste output by shortening the time it runs.
Your waste TDS should be 20 to 25% higher than tap water TDS or you are not removing anything. It should be concentrated from the waste being scoured off the membrane. In fact if your waste ratio is 2.5:1 like you say it should be more like 40% higher than tap water TDS! If not something is wrong.

 

[neotekz]

i'll double check the tds...so the permeate pumps doesn;t actually reduce the rate of the wastewater but just speeds up the production of the rodi water? but doesnt that mean that the pump will bring the rodi/wastewater ratio closer to each other?

 

[jdieck]

<a href=showthread.php?s=&postid=9531656#post9531656 target=_blank>Originally posted</a> by neotekz
i'll double check the tds...so the permeate pumps doesn;t actually reduce the rate of the wastewater but just speeds up the production of the rodi water? but doesnt that mean that the pump will bring the rodi/wastewater ratio closer to each other?

With an input of 75 TDS at 2.5 to 1 ratio your waste water TDS sould increase to about 100 ppm

 

[neotekz]

i just double check my waste and it's 70 in and 110 out. anyone tryed one of these pumps?

 

[jdieck]

<a href=showthread.php?s=&postid=9533676#post9533676 target=_blank>Originally posted</a> by neotekz
i just double check my waste and it's 70 in and 110 out. anyone tryed one of these pumps?

As mentioned above the permeate pump will only give results if you are using a presurized surge bladder tank to store product water. In addition the pump operates out of the flow of the waste water so you may need to adjust the restrictor to calibrate the system back to the recommended 4 to 1 ratio of waste to product which may result in increased waste at the end.
If you do not have a system that require a bladder tank like drinking faucet or such, then I would just remove the presure tank if you are using one.

 

[neotekz]

i'm not using a bladder tank. but if i get the pump i would get the bladder too. i;m even more confused now, what do u mean by adjusting the restrictor, what restrictor? so is this pump mostly just for people that have their system under the sink connected to a faucet?
is there any companies that sell an extra single RO stage?
anyother ways i can reduce wastewater?

 

[plummike]

Lowes has it all. Whirlpool systems.

 

[plummike]

Lowes has it all. Whirlpool systems.

 

[jdieck]

The bladder is a convenience, when using a faucet you do not want to wait holding the glass for 5 to 10 minutes waiting for it to be filled. Instead a small tank is used in the output of the RO/DI unit which basically contains either a rubber balloon or just some air to store clean water. As the product water is introduced to the tank the pressure inside the tank starts increasing from zero up to the pressure of the feed line or the pressure set up in a switch that shuts off the water inlet.
This small storage of pressurized water will allow your glass of water to be filled as fast as you would directly from the tap. It is also useful when connecting it to the icemaker or cold water dispenser of your fridge.
The disadvantage besides the additional cost is that as the pressure in the tank increases the production of pure water decreases but without increasing the waste flow so you may start filling the pressure tank at a ratio of 2.5 to 1 but as the tank gets close to be full your ration goes to 2.5 to almost zero. So during the time the tank is filled your waste to product ration almost doubles. The installation of a permeate pump (which does not use power but rather the pressure of the waste water to operate) increases the delivery pressure to the product line thus filling the tank faster then reducing the time your unit is operating at a high waste to product ratio.
In summary, if you do not need the bladder (because you do not use the RO for drinking then you do not need the permeate pump not the other way around.
Any supplier of RO/DI units can supply you with a membrane and membrane housing. Just need to insure that the size and type of membrane is the same capacity as what you have now. Effectively you will be doubling your capacity so you will fill your reservoir in half the time. You also must insure that your tap water pressure is 50 to 60 psi for maximum performance otherwise you may need a booster pump which will substantially increase the cost

Test results of using a second membrane:
http://thefilterguys.biz/test_results.htm

Dual membrane conversion kit:
http://thefilterguys.biz/water_saver_ro_di.htm

Piggy Back kit from Spectrapure
http://spectrapure.com/St_kits_p2.htm#piggy

 

[jdieck]

<a href=showthread.php?s=&postid=9534399#post9534399 target=_blank>Originally posted</a> by neotekz
... i;m even more confused now, what do u mean by adjusting the restrictor, what restrictor?

At the outlet connected on the waste line there is a device called the restrictor. This device maintains a back pressure inside the membrane housing on the membrane inlet side, pressure required for the membrane to operate. By adjusting the restrictor you not only change the pressure on the membrane inlet but also change the waste to product ratio as it can increase or decrease the restriction to the pasage of fwaste flow. (some are adjustable, some are for a fixed capacity and need replacement if that wants to be changed). The more restriction the lower the waste to product ratio (and the higher the impurity level on the product water) and viceversa.
By design, to maintain the structural integrity of the membrane, prevent it from carbonate deposition and fouling the design ratio for a membrane is 4 to 1 or 5 to 1
In your case given the relatively low content of impurities in your tap water (only 70 to 75 ppm) I see no problem operating the membrane at the 2.5 to 1 or 3 to 1 ratio unless you had over 80 psi pressure in your tap.
Ig your tap ipurities were over 100 ppm then I would have recommended you to change that ratio to 4 to 1 as this will improve the purity of the water exiting your membrane and doing so reducing your cost of replacement of DI cartridges.
If you install a second membrane the restrictor has to be moved to the waste exit of the second membrane. This is why it is important that the second mambrane will be of the same capacity so both are designed for the same wate to product ratio because they will be sharing the same restrictor.

 

[AZDesertRat]

The flow restrictor has very little effect on rejection rates and final TDS. It will affect the flow rate as far as GPD and it will over time affect the lifespan of the membrane and ultimately the TDS but thats when it ruptures or breaks thru due to improper flushing from having the waste ratio too low. You could actually run a membrane 0 waste for a short time but it would be pretty short once the build up solidifies on the membrane and plugs it.

 

[jdieck]

<a href=showthread.php?s=&postid=9535852#post9535852 target=_blank>Originally posted</a> by AZDesertRat
The flow restrictor has very little effect on rejection rates and final TDS. It will affect the flow rate as far as GPD and it will over time affect the lifespan of the membrane and ultimately the TDS but thats when it ruptures or breaks thru due to improper flushing from having the waste ratio too low. You could actually run a membrane 0 waste for a short time but it would be pretty short once the build up solidifies on the membrane and plugs it.

It is true that the lower the waste to product water ratio the higher the buildup of solids and the shorter life of the membrane but there is a limit to that lowering of the waste to product ratio and it is not accurate to say that a membrane can work at 0 waste not even for a short time.
For the osmosis process to occur it is required that the osmotic pressure caused by the diference in salinities between the product water and the waste water be always lower than the applied pressure at the membrane inlet.
If the percentage recovery is increased by reducing the waste to product ratio the salts in the waste feed become more concentrated and the natural osmotic pressure will increase until it is as high as the feed pressure. This can negate the driving effect of feed pressure, slowing or halting the reverse osmosis process and causing permeate flux and salt rejection to decrease and even stop all this independently of any buildup.
In other words by driving up the salt concentration in the waste side by reducing the amount of waste there is a point were the osmosis process simply stops. This limit at which the osmosis process stops depends on the amount of impurities in the feed (inlet) water. The higher the impurities the higher this limit of waste to product ratio, in other words the higher the impurities the higher the need for more waste than product.