Water Spots

[Andy CWS]

All your questions are reasonable and your goals are fairly clear to me. Naturally, any RO for commercial basis must follow at least two criteria: membranes large enough with ample pressure and feed to produce adequate supplier or retention tanks large enough to provide demand water when needed...or a combination of both.

Retention for many car washes may be about 300-500 gallons at low pressure spray, with an RO that produces 1000 - 3000 gpd.

Remember that a DI resin removes both cation and anions in either a mixed bed application or separate tanks each removing anions and cations. The lower the ion count you have going into the resins beds, the longer they will last, and the cheaper they will be to maintain. An RO is very effective at removing ionized particles such as sodium, thus saving the DI resin as a “final” polishing of the water.

The RO should be preceded by a softener to convert calcium ions to sodium ions as membranes hate calcium but love sodium.

You should not use a carbon filter as a particulate filter. It will naturally, have some effect at removing particles of a given size, but that is not where their excellence lies. As for pre-filters, use as big as possible to improve flow rate and longevity.

If chlorine is to be removed then an up-flow carbon media tank would be recommended. The size, again, would be determined by the volume of water x the PPMs of Cl.

Of course, a one micron filter may serve to improve the shelf-life of DI resins but only in that the resins will not accumulate foreign matter as in a softener. But remember, those resins don’t regenerate (at your location) and are simply replaced, so the purpose of a filter that fine becomes a moot point.

I will go back to my previous statement that for spot free rinse at a commercial car wash, a properly sized RO will serve best. DI resins will be a pain and costs associated with on-going production will be regretful.

Andy Christensen, CWS

[a1certified]

Would creating the properly sized RO system result in the ability to rinse the car, let it air dry, and not have any spots? My impression is that the spots are caused by calcium and other minerals in water that get left behind as the water evaporates.

Softened water is high in Sodium and Chloride, correct? Won't these leave spots behind as the water evaporates?

[Andy CWS]

Generally speaking, yes. The RO water will be virtually void of spotting elements such as calcium and sodium. Nothing will be perfect so levels of acceptability need to be set.

The key difference between calcium and sodium spots is solubility. When water evaporates containing calcium (and other hardness salt/minerals/metals), the spots left behind cannot simply be removed by wiping with a moist towel, for example. The have 'calcified' and need to be removed by scaping or an acidic solution; both time consuming and adds expense.

Sodium spots are water soluable and a moistened towel or RO water can easily remopve them to a satisfactory degree. Softened water normally contains sodium but generally separates chlorides from the salt. So it should be sodium that you are seeing. A poorly operating softener CAN produce salty results.

Hope this helped a bit.

Andy Christensen, CWS

[a1certified]

Thanks for the clarification.

What would be your recommendation for a cost effective larger-scale solution with higher flow-through rates?

David

[Andy CWS]

There are numerous parameters to determine commecial RO usage. Source water conditions, pretreatment equipment, water and ambient temperatures, replacement parts' availability, maintenance schedules, etc., all help determine what makes it a lucrative business or hole that you pour water into.

Rule of thumb dictates that the RO product rate should be twice the expentant actual use. Storage should correspond with adequate supply and recovery. Space can be a problem for storage.

Most commecial ROs have multiple membranes that are 4" in diameter with pressure pumps and TDS meters for both product and concentrate waters.

There are calculations for car washes based on the number of vehicle per hour that would be using the spot-free rinse cycles, but I don't have them off hand.

If you visit a couple of local car washes, ask to inspect the water treatment systems and ask questions to the managers or owners. Most, I have found, are quite Ok with showing their equipment. Ask what problems they have had and how well it works. Don't present yourself as a 'competition' in thier area but more as a very interested customer and water enthusiast.

You may find some very different approaches.

Andy Christensen, CWS

[jgill]

Hard Water Woes

O.K.. You are all making a big deal out of something so simple. I live in a town that has a water hardness of 47 grains per gallon. I wash my car with softened water and yes it will leave little spots of sodium unless you dry with a chamois. For a completely spot free finish that I can let air dry, I simply fill a small Hudson sprayer(pump-up garden sprayer)(plastic is best) with R.O. water from my kitchen R.O. faucet. You could also use distilled water by the gallon from a local store. Then spray an even layer all over the car to displace the sodium laden water. By the way, you can wash the car with hard water and do the same with the R.O. or distilled water, but do so in the shade. This post may be a little late, but hopefully it will help others with extremely hard water.