Reducing RO waste ratio

[danielevan]

Hey all --

I've got an Aqua Safe 6-stage RO/DI units, and just for kicks, I filled up a drinking glass with clean water, and collected the waste water.

The amount of waste was unconscionable!

Is there a way to reduce the waste ratio? Would a more restrictive flow restrictor on the waste line push more water across the membrane, and less out the waste line?

[j_mccen]

The ratio should be about 4 to 1......

[danielevan]

By design, it's 4:1. That doesn't make it responsible!

[j_mccen]

Thats just the way the system works.....use the discharged water to put on your flowers or something.

[aqua_obs]

I had the same concerns and people suggested lawn/flowers/laundry/distill it! Make some moonshine!

[Benthic Explorer]

you get some waste.

[David P]

well, you can run a secon ro unit from the waste, a lot of money and still alot of waste. I run the waste to water flowers and top off my pool and pond. You may want to look into a cold sterile unit. No waste and makes water much faster.

[salmon alley]

I asked a similar question regarding the waste water. You can check out the replies here:
http://archive.reefcentral.com/forums/showthread.php?s=&threadid=186730

[Mako]

I thought the ratio was more like 3:1. You can obtain an adjustable flow restrictor for fine tuning your system from ARS.

[dendronepthya]

If you want zero waste water, run a large DI unit rather than an RO unit.

[salmon alley]

dendronepthya-
Can you obtain the same kind of purity with DI only?
Also, what's the difference in cost between running an RO/DI unit vs. DI (I'm assuming you mean separate cation and anion chambers)

Thanks
SA

[dendronepthya]

I don't know whether the water is more pure or not. There are ways to test it, but I never have. You can do so with either a conductivity meter or a total dissolved solids meter. I really don't think that getting the most pure water is a big issue when you consider all the other inputs that go into the tank's water such as supplements and feeding.

The price is between $200 and $500 depending on the size you are looking for.

[SAT]

A DI filter removes all the inorganic ions and will yield a "zero" result using a TDS meter, just like RO/DI. However, the carbon stage & RO membrane remove some compounds (including fine sediment and some organics) that a DI stage will pass through.

It's a fallacy, BTW, that a TDS meter measures all the impurities in water. What it measures is conductivity. There are many impurities that do not affect conductivity, some of which are quite toxic. A TDS meter very effective for telling you when the DI resin needs replacement. It is not very effective at measuing total water quality.

In any case, you'll be using 10-20X as much DI resin if you don't prefilter the water with the RO membrane. Now the question: is it better to waste 75% of the water or is it better to waste the DI resin? Bear in mind that a lot of resources went into making that DI resin.

[dendronepthya]

You can recharge DI resin. For large scale operations, you really cannot afford the 4:1 of waste water. In a month, it's possible the facility would go through a couple thousand gallons of waste water.

Out of curiosity, what would you recommend using for testing the purity of tap water? Very few people even bother using a TDS meter in the first place.

[SAT]

Originally posted by dendronepthya
Out of curiosity, what would you recommend using for testing the purity of tap water? Very few people even bother using a TDS meter in the first place. If it's city water, you can get a report from the water company which covers everything the EPA considers important. An equivalent test for well water would be expensive. In practice, the output of an RO/DI filter is almost certainly OK provided the unit is working properly.

If you're concerned about RO waste, I suggest a combination of sediment, carbon & DI stages. You'll still go through DI quickly, and a few pollutants will go through, but if the water was safe to drink to begin with you're probably OK.

[MalHavoc]

conductivity and TDS are indicators of purity, and my DI unit produces water that is just as pure as RO/DI units. The only catch is that you have to replace the membranes more often, since DI cartridges don't seem to last as long. But, there's no waste water.

[salmon alley]

I love the idea of not having waste water, and we have pretty good city water to begin with, so I think the DI system would work in my situation.

My main concern is: How difficult is it for the average hobbyist to recharge the resins?
Is it an all day affair requiring highly toxic chemicals?

It seems that the somewhat higher cost of the DI resins would be offset by a savings in water (and therefore water bill)

Tanks!

SA

[dendronepthya]

From everything I've read, recharging DI resin is not a pleasant experience. The chemicals used are strong acids and bases that must be handled with extreme caution. I think it makes sense if you are purifying large quantities of water, but it might not make sense on a hobby scale. It really depends on your application.

[Wolverine]

Here's a link for how to recharge, at least specifically in regards to the TWP; procedures for other resins are chemically similar, but often easier because you can buy completely separate cationic and anionic resins, so you don't have to worry about the separation steps:
http://www.reefs.org/library/article/twp_recharge.html

The purity of DI is comparable to RO/DI, but the resin will not last as long.

The waste water: purewater ratio varies depending on several things, including the quality of the setup and how dirty the membranes are. Some mediocre ones have about 10:1, while some of the top-notch ones have about 1:1. The disadvantage of those units with 1:1 is that they are very expensive, anywhere from 3-10X what the more common 4:1 units.

Dave