What size RO discharge holding tank to buy?

[dogwasher]

Im looking into purchasing a holding tank to hold the discharge water from my RO unit. At this time I am utilizing some of the discharge water in my holding tank for the Automatics and the rest goes down the drain.
This is a 4 ss/ 2 auto super wash. The underground spot free holding tank looks to hold about 1500-2000 gallons?
Also any ideas how other washes out there deal with this would be appreciated IE:where do "you" pump your used RO water to.
Thanks for any help

RO Capacity 4500 gal day @77 degree water
3.8 GPM Permeate flow
4.2 GPM concentrate flow
Heres another question, Should I change or clean the membranes the directions are horrible! I dont think anything has been done to them for "years"

 

[lag]

Good questions.. Holding tank size will depend on how fast you use it. We have 2 300 gallon tanks at a location with 3 self serve and 4 autos, We use a pump to send it back into the piping ,after the softener. the RO is a 10000 gallon per day unit(it has 6 membranes). the pump sends it back into the system faster than it goes into the tanks.

The other locations we are set up basically the same.

Get a TDS meter for your unit ,if the TDS is getting up there ,just replace the membranes. Membranes are alot cheaper now then they used to be. I do not believe cleaning them is worth it anymore.

Hope this helped. Lag

 

[dogwasher]

Thanks, Could you tell me how to diagnos if the membranes need replacment and if so do they change the amount of reject water?
What is a TDS meter?
I noticed Dultmier has a 1600 gallon tank, That is all I have room for. sounds like that may be big enough for my application?

 

[lag]

TDS meter is a little device to measue total dissolved solids in your spot free water. You can get them also at dultmier( around $25.00 I think). anything over 25 TDS is bad IMO. A great investment to monitor your spot free water. We check all water daily,

If TDS is high enough to warrent changing the membranes, when you order them, make sure to tell whoever you get the from ,that you use a blending valve ( I am assuming this because you stated above your water is 77 degrees). I use cold water membranes. but I had to increase my cold water piping to the units to do it.



let me claify the tank size I use at the location i spoke of above. I use two 300 gallon tanks because I use a pump to pump it back into my cold water piping ,I actually use it faster than it comes into the tank.

Your tank size will depend on how you are going to reuse the water. pump it back in ,or gravity feed an auto tank?? Maybe someone can weigh in who gravity feeds the water back in ,then you may have a better idea of tank size.

No matter how you reuse it, it is a great idea to do it. I have always wondered Why soften it, then heat some of it, only to dump it down the drain. Good luck, Lag

 

[dogwasher]

Ok now I noticed my RO unit has one of these TDS meters built into the control panel, if it works its reading 20 at this time.
The specs I listed are from the manual of the RO unit, I have cold water feeding the RO unit. That guage reads 50 degrees.
I thought I would have to buy a huge tank, due to the wieght mount it on the ground and pump the water into my gravity feed tank when its calling for water.
You say you pump your water in the street pressure line?
Here is a example of why I think I have to have a large tank: Yesturday we finally had a really good day. At 7pm with no more cars at the wash I looked into the underground spot free tank, it was 1/3 full and filling. The RO unit is operating and I can see or assume its going to run for "hours". So if the tank is 1000 gallons low Im going to reject at least 1000 gallons to get the tank back to full. Im not sure how you get away with 30 gallon tanks if there is somthing Im missing please let me know Thanks for your help!

 

[lag]

Ok.. I pump the reject water back into my piping,after the sofener, so when i am using water at the wash(even if only the RO is running) I am feeding it back into my system.

I have 900 gallons of storage, at that location ,for RO water. I have 600 total gallons of storage for reject water. those tanks(reject) have never been over half full ,never.

I do not know how you want to reuse the water , as i stated i PUMP it back into my water piping.

One big factor for me is I have a large RO unit I make water faster then I need it,so my tank never gets more than 200 gallons short. By having the large RO ststem my reject tanks never get filled for hours at a time. You may need a bigger tank, then I do.

 

[Jimmy Buffett]

I can't imagine how you are getting 1000 gallons behind with a 4500 gal/day capacity. How much sf do you use per car?

 

[MEP001]

If the manual states 77? water, then it's most likely TFC membranes, which are the most common. They produce the best quality RO, but need a soft, chlorine-free feed to last. It's not uncommon that nothing has been done to them for years and the quality is still good. It doesn't sound like you have a problem with your membranes, but it does sound like your system is almost undersized, and a large tank was used to compensate. Our 4500 GPD system is able to keep the tank filling no matter how busy it gets (6 self-serve @ 500 PSI, 1 auto).

 

[dogwasher]

How much SP used Good question I dont know, Two DS 5000 225 cars

 

[MEP001]

With the typical tips on a D&S 5000, 250 PSI from a multi-stage booster pump, avg. 50 seconds for the spot free pass, times 225 cars per day is 5025 gallons.

 

[dogwasher]

I guess that would explain my situation thats a lot of water. Do you think a 1600 gallon holding tank for the reject water would be enough for my current set up?

 

[MEP001]

It mostly depends on how you use the reject water. If you're pumping it into the wash you should have no trouble using it up during the day, but if you plan on letting gravity trickle it into a tank you'll probably keep overfilling it. If you're making 1,000 gallons of RO overnight you're going to reject at least that much. You'll need a setup that will use it quickly to minimize waste.

 

[Jimmy Buffett]

I use less than half that per car. Do most people use 20 gals. or more of sfr?

 

[dogwasher]

It mostly depends on how you use the reject water. If you're pumping it into the wash you should have no trouble using it up during the day, but if you plan on letting gravity trickle it into a tank you'll probably keep overfilling it. If you're making 1,000 gallons of RO overnight you're going to reject at least that much. You'll need a setup that will use it quickly to minimize waste.

But at nite time there is nothing running to use up the RO water.
Sounds like I need a large holding tank for night time or I need a faster regenerating RO unit so its not running all night. Problem is I dont have the room for a larger unit than I have now. Do they make them more compact than they did years ago and how much does a large on like I need cost?$$

 

[MEP001]

I should have specified that a 1,600 tank should be plenty of storage to catch and use all the RO reject. If you want to get fancy you could use a smaller tank and set it up so the RO will quit regenerating when the reject tank is full, but will come back on if the RO tank gets below a certain level. You could do that with three float switches, one to turn the RO on as it's doing now, one in the reject tank to stop the unit, and a third lower in the RO tank to guarantee it turns on before you can run out.

 

[ted mcmeekin]

we have 850 gal tank for sfr and 2200 gal for sfr reject, rain and weep--more than we need but we have lots of margin. the 2200 gal tank uses a shallow well pump to repressurize--this water is used for undercarriage and side blasters and we never waste any. the MK VII machines have check valves on both auto and ss so that if we run out of sfr or reclaim it shifts to city water source. i was a little apprehensive of check valve set up but never had failure

Ted

 

[I.B. Washincars]

The reject will be used much faster than the RO water, it's no trouble to use it up much faster than it is produced. I have three autos at one location, a Wesumat friction and two GT-700 Mark VIIs. The GT-700s have two pumps on each machine. I have the reject pump plumbed to only ONE pump on ONE of the GTs, it's even the least used auto. I store the reject in a 325 gallon tank and lose no reject water at all.

 

[rph9168]

I know a lot more about the chemistry of car washing than the equipment end and maybe I will prove that with this suggestion. If you know (or have a good idea) the ratio of how much reject water is produced for each gallon of RO water produced you should be able to size the tank based on that ratio. In addition as has been suggested, if you use the reject water for undercarriage and/or rinsing you should probably run out of it before RO water.