RO unit

[prankster705]

I dont know what are they and I would really like to know what are they and how to build one...
...HELP PLEASE... ) )

 

[Lateral Line]

An RO is a passive device that uses differential water pressure across a specially produced membrane to remove impurities from water. Basically, high pressure water forces water molecules through the membrane whilst retaining the low concentration salts and organics on the other side. The result, (depending on the quality of the unit and the number of stages), is water that is, in fact, far too pure to use directly in a tank. It is very unstable and has to be re-buffered before use, (unless you are REALLY sure what you are doing).

I would never say that building anything yourself was impossible, but really, these things are made with seriously specialised components. I would expect building one would cost far more then buying one, since in "one-off" order quantities, the membranes alone would cost more then a commercial unit.

 

[sub.42]

Yep,

I agree with LL. I install and maintain these units on a daily basis. My units produce from 6 litres, to around 24 litres per minute. They run at about 15-20 bar pressure, and each membrane costs around £800. They require a massive softener, to ensure longevity, and are a huge investment in any environment.

Consider the average 9-1 reject ratio. That means for every 1 part RO, you get 9 parts of water rejected from the'solids' side of the membrane. As LL says, they literally 'strip' off the contaminents as they pass through the membrane.

Very clever stuff.

Not cheap, and not DIY. Well, unless you string about four or five DI, Carbon, 20, 10, and five micron filters together. Then you might get 2-5PPM TDS.

It's still not 0 PPM TDS. And it won't be RO.

Sorry.

sub.

 

[OohFeeshy]

Thats one thing I've wondered. The waste- can you pump it through again? Obviously there's the pressure to consider, but if you got that, would you get a better output?

 

[sub.42]

Thats one thing I've wondered. The waste- can you pump it through again? Obviously there's the pressure to consider, but if you got that, would you get a better output?

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Well, thats the whole point, reject is reject. However, some systems I use are close-loop-reject systems. Meaning that there are concerns over the whole reject thing, 9-1 is a whole load of waste water. You must consider that the reject water will carry a much higher amount of dissolved solids, and its not a good idea to ask a membrane to strip these again. What I end up doing is diluting these with the incoming water, and try to get a 5-1 mix going. It exhausts the membrane faster, and can be done, but is not a good idea.

Maybe if the water softener was up to it, I might try sending some back that way, but you are never only removing the chalky stuff. It catches stuff down to less than 1 micron and below, so you will only end up with a blocked membrane if you shove a concentrated mixture that way.

I do use a closed loop system, but it flushes the membranes for fourty seconds on startup, and then every thirty mins after. Kind of a self preservation thing.

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[prankster705]

So how much does one actualy cost and what are the benefits and downsides, and the most important is it worth it ?

 

[Lateral Line]

It is difficult to estimate the price where you are because I don't know. In England, the cheapest, which only produce ~15 liters per day and fit directly onto a tap cost less then £70, from there, the price goes up and up and up depending on the quality and the number of stages. Here in Denmark, multiply everything by 2 or 3 and you have an idea.

There may be no benefits at all if you are freshwater and your tapwater is reasonable. If your tapwater is totally unsuitable for what you want, then an RO can be useful. It provides very pure water, as I said, too pure to be much use on it's own, but it allows you to create water of exactly the parameters you want - as long as you know what you are doing. Marine tank owners tend to use RO to top up their tanks as it does not add to the dissolved salts.

Downsides, they are expensive to buy, the membranes need looking after and replacing from time to time, (not often if you look after your unit well), the stabilising salts can get quite expensive if you don't have enough chemistry to make your own, units that produce a lot of water tend to be quite large and require plumbing in, and the bypass water is a lot of water to waste if you cannot find a way to use it and you pay for water by volume.

>>> is it worth it ?

You'll have to decide that. You have not given us any indication of what you want to keep or do. If you find yourself buying loads of RO water from the lfs to do water changes or breed difficult tetras, it may be worth it. If you keep a few guppies in a 55, probably not.

 

[prankster705]

Thanks...

 

[donkey]

why not just get one from ebay .i got a 50 gall a day one for £30 brand new