Desalination: cheap alternatives Qs

[vas]

morning all,

have some spare time waiting for my "customers" to arrive, and had a look at desalination systems. Seems that 5-6Keuro will get you a 30-60lt/h system.
Looking at it's components I realised that it's mainly a reverse osmosis membrane, similar to the one I have at home cleaning the godawful water we get on tap here and stores it to a 15lt pressurised tank for use in drinking/cooking.

Also noticed that size matters, ie a 30lt marine system has one 60cm reverse osmosis membrane/filter, whereas a 60lt system simply doubles it to two 60cm ones. Now, the 5-10lt/h (guestimage) system I have has a 20-25cm RO membrane, whole system with 3-4 pre-post filters fits nicely on a cupboard under the kitchen sink (40X30X20cm) and set me back 200euro with a set of filters good for 4yrs. (5micron, 1micron, dechlorifying, etc)

Q1: what will keep me from getting another one and a small pump and fill my tanks? OK, I could probably get a larger inverse osmosis filter and built a system that does 20lt/h for 400-500euro. Only would need a pump capable of keeping water at 4-5bar (as at home), an expansion tank to avoid having the pump running all the time and a sea strainer.
Heck, I could even buy three of the home systems and run them in parallel with a single pump for less than 500euros...
Am I missing something?
Is sea water that much different than removing all alcalic and sulfur deposits from tap water?
Mind you I'd not expect exceptional quality of water, I'd probably stick to bottled water for cooking and drinking (although that's another sad story altogether).

Q2: reverse osmosis systems remove all chlorium (chlorine, whatever that is) that sanitates water killing germs etc that is put by the water company. My home system specifically states that if not used for 3-4 days, I should empty the 15lt tank and start again.
Now, how does that work in a 500lt or 1000lt tank?
Is there some extra way of sterilising (or whatever you wish to call the process) the clean water produced or you simply have a germ infested tank to wash your teeth with?

as always open to ideas/explanations but a solution at 10-20% of marine cost albeit lower output is intriguing!

Vassilis

PS. ecosystems has some clear diagrams where I picked up my analysis from:
here

 

[yesod]

ro of salt water requires much higher pressures than for fresh. closer to 50bar.

 

[vas]

ro of salt water requires much higher pressures than for fresh. closer to 50bar.

hm, that's why I saw a company supplying a titanium high pressure raw water pump then.
I'll look around, that obviously means that I cannot reuse the normal assemblies in my home system and have to have something capable of 80-100bar

cheers

 

[vas]

my original second Q wasn't touched by anyone, so I'm repeating it (coming to think of it, I should probably change thread, but it's nice to have Q and A together...)

Q2: reverse osmosis systems remove all chlorium (chlorine, whatever that is) that sanitates water killing germs etc that is put by the water company. My home system specifically states that if not used for 3-4 days, I should empty the 15lt tank and start again.
Now, how does that work in a 500lt or 1000lt tank?

In other words, storing the water from your watermaker in a tank (not sealed, not clean of germs and other nice organisms) is a recipe for disaster (me thinks at least)
Is there something ppl do in order to keep this water clean and not full of nasties?
From my reading the marketing and engineering stuff from such companies, noone seems to bother with this!

and to add another Q, is there typically a pre-filter just before the reverse osmosis membrane to clean chlorine/iodium that (in theory) is bad for the membrane itself?

cheers

V.

 

[Brent Swain]

Desalination

I built my own RO watermaker, the one described in my book. Cost me around$700 for 540 gallons per day, engine driven. Works well. Pressure washer pumps (3gpm minimum) with ceramic plungers, are far tougher than most watermaker pumps, and cheaper, and the membranes fit perfectly in 2 1/2 inch sch 40 ss pipe from the scrapyard. The ends were easy to make up.

 

[Wiggo]

my original second Q wasn't touched by anyone, so I'm repeating it (coming to think of it, I should probably change thread, but it's nice to have Q and A together...)

Q2: reverse osmosis systems remove all chlorium (chlorine, whatever that is) that sanitates water killing germs etc that is put by the water company. My home system specifically states that if not used for 3-4 days, I should empty the 15lt tank and start again.
Now, how does that work in a 500lt or 1000lt tank?

In other words, storing the water from your watermaker in a tank (not sealed, not clean of germs and other nice organisms) is a recipe for disaster (me thinks at least)
Is there something ppl do in order to keep this water clean and not full of nasties?
From my reading the marketing and engineering stuff from such companies, noone seems to bother with this!

and to add another Q, is there typically a pre-filter just before the reverse osmosis membrane to clean chlorine/iodium that (in theory) is bad for the membrane itself?

cheers

V.

Well, most people seem not to bother. If the water is clean and sterile going in to the tank, it ought to stay that way unless it gets subsequent contamination. Can't comment on the temperatures you get in Greece, but over here most people would seem to throw a few water purification tablets in the tank every now and again. If it's really bad, then Milton Sterilizing Fluid - the stuff you use to sterilise babies' bottles...

 

[kid's inheritance]

Basically water in a pressurised system (as in mains water supply) is bacteriastatic in that it won't get any worse or better bug wise than it went in. However , water left in a tank (even if sterile to start with ) will get worse unless you add a purifying agent (like chlorine).
Those of you who leave a glass of water at your bedside might notice it tastes sweeter in the morning, that is because the pseudomonas have multiplied exponentially.
So , in short , once produced , your water , unless treated , will go downhill
Regards
Rob

 

[kid's inheritance]

pseudomonas should be in italics but the font decided to ignore me