Building a Chlorine-Free Desert Swimming Pool

Maybe an ozone or ultraviolet treatment along with these others?

UV treatment will probably be the better option. Bromides and QAC's have lasting effects and would only be absorbed back into the system by dilution. Chlorine could work if you drained the pool to a separate resevoir and let the sun take care of the Chlorine before re-introducing it back into the river. regards.

You can also use a low power DC electrolysis unit with copper terminals. This will introduce copper ions that will kill the bacteria into the water.

Diatomaceous earth

You could use one of the new salt water filters they have out there. They're a little expensive but I was thinking about getting one myself. They say you don't need any chemicals at all running this sort of system. Worth checking out don't you think?

Are you sure it can't be chlorinated?

My thinking is, that since it's short term, a gallon of household bleach could be added at night when the pool is closed. It would kill the germs, and it is very quickly neutralized by sunlight, rendering it harmless.

Environmental impact would be zero. http://en.wikipedia.org/wiki/Bleach

Bromine is often used as an alternative to chlorine. It performs well in hot water which you will have following the first day in the sun. You might add aerators that could be run at night thus cooling the water to help reduce the ideal conditions for algae growth. Gary

Use a UV of 14m3/hr and a cartridge filter instead of sand filter with a pump of discharge at 14m3/hour.

I have installed several pools without chlorine, but very good residual antibacterial potent. You must to change few technical inputs, and then users will give you best advertise you could get (no chlorine smell, no itching, no hair or swimming suits damage). Also, no any danger for swimmers lung (trichalomethanes, asthma etc). Electrolytically dissolved copper could cause and lead to green hair in swimmers, forget it. Ozone and UV are just great, but there are no long term action. Pool MUST have long term protection. UV destroy "active" chlorine in pool very quickly. So there must be added cyanurate. However, destroyed active chlorine, dont mean that pool water are free of chlorine. It is free from "active chlorine". Miroslav

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That sensitivity to the local environment is going to cost plenty.

There goes the Spanish economy.. of fear

..is all of the fuss to keep chlorine from being pumped back into the river when all is done?

Sodium Chlorite works well and has no known side effects.Derived from common salt and reduces back to salt. As for the dust, dirt and sediment there are lots of good suggestions already.

Filtration is NEVER enough to sanitize water against all potential organic contaminants.

I would highly suggest using either a copper/silver based sanitizer system and or an ozone system.

A quick search on the net will list many sources

Im JUST speaking from my personal experience. Filtration are very, very , very important, truly not enough. Sliver copper are good if know to use it, but slow action and could create several problems if you overuse it. 14,5 m3 are very easy to keep in perfect conditions without chlorine, and exchange water only once per season. Miroslav

Try this link http://www.triogen.com/

They have all the UV and ozone equipment you will need for this pool.

The site also have some nice application notes that should answers all of your questions.

Wow, what a great response. Thanks to everyone who replied. I'll go through the responses that looked promising below, then post any new questions that have sprung up as I've read:

REPLIES:

Tornado: I'm considering ultraviolet. It seems energy efficient and pretty simple. As far as I'm aware Ozone requires there to be chlorine in the water to function?

Leonf: I'm being lazy here by not doing some more research myself, but will chlorine really break down to become inert? How long does the process take? Theoretically I could close the pool at night and treat it with chlorine but it would need to be chlorine-free within a few hours of sun-up. The organisers are being quite firm about people swimming in any chemicals!

DVader1000 & mrclean: I will look into electrolysis and salt water filters :)

gcoffing: The idea is to keep the water chemical free if possible. I will look into aerators though as the water is likely to be pretty warm after a day in the sun.

waterparks: What makes you suggest a cartridge filter rather than a sand filter? The little bit I've learned so far suggested that the cartridges will clog with desert dust quite quickly and that a sand filter (either before or instead of a cartridge filter) would be better as it can be regularly flushed. Would love to know more. Maybe you know more than I do!

cwarner7_11: A very helpful post. Thank you! Ozone sounds more fiddly to get right and in a harsh environment I'd be concerned about errors or breakdowns that could potentially pollute the water or the air. This would not go down well with the organisers.

UV seems like a definite, especially as the presence of run-off in the river water is highly likely as it passes through cultivated land before reaching the desert. Am I right in thinking a carbon filter will neutralise any traces of pesticides?

marcot: Very helpful link. Triogen suggest that ozone systems don't perform well in smaller pools with high flow rate. I'm aiming for the highest flow rate achievable to counteract the dust that will be entering the water. That suggests that UV is definitely the way to go.

Sandman: Again, cheers for a helpful post. I'm hesitant with salt water generators as I'd be releasing 14 tons of sea water into the desert. Ideally I'd love (and the organisers have requested) that only river-quality fresh water go back into the water table. Admittedly, salt water better than a chemical cocktail so I'm not dismissing it. There is likely to be considerable dust going into the water, and possibly bits of costume. A vortex filter sounds an excellent idea, though would you say it was necessary with a flushable sand filter?

Looking up an LED fountain now - will be sure to post pictures up for you guys :D

NEW Questions:

Carbon filters - nobody has really mentioned these? Are they as useful at getting rid of contaminants as I've read or is the silence an indication that sand & cartridge filters + UV is sufficient?

Cheers to all!

Tass

Carbon filters are very effective at removing all sorts of volatile contaminants (those that have noxious odors/tastes)- mostly organic compounds. One would have to look at the specific chemical composition of any pesticide/chemical fertilizer to determine if carbon filtration would be advantageous or overkill. Were we talking about drinking water, carbon filtration as the last stage before consumption is a standard practice for all of the potable water systems I spec...

Ozone does not require chlorine to work. EPA has documented the efficacy of ozone as a biocide, rating it as the most effective oxidizer available ("EPA Guidance Manual, Alternative Disinfectants and Oxidants", available for direct download by searching for the phrase "Alternative Disinfectants and Oxidants Guidance Manual - EPA 815-R". This document covers most commonly used disinfectant strategies, but does not discuss saltwater chlorination or ion exchange, if memory serves. This may also be a newer version than the one I have been using).

For your limited time frame, however, UV would most likely be far more cost effective. You do have to insure that the water has sufficient exposure time (a function of the flow rate).

Looking forward to the pictures...Be sure to include pictures of the mechanical installation (pumps, filters, etc)- some of us find that more invigorating than pictures of nearly naked women we can not touch...

Well a UV requires a filter size of 5-10 microns to be effective and since sand filter will only best give 20-25 microns Hence choice of the cartridge filter.

You may build-in a Ultra-Violet lamp in your filter system as well to ensure your water keeps clear during the 10 days of use. Such filter systems are generally used for ponds but I know they sometimes also use it for swimming-pools.

New info: Pool has been downsized to a 10 foot shallower pool holding 6500 ltrs as the cost involved in hauling 14 tons of water was just too great. This makes little difference as far as I can see, except to the flow rate. Based on your suggestions I'm working to the following spec:

Backwashable Sand Filter > 20 micron sediment filter > Carbon Filter > UV Filter

The flow rate is 6500ltrs/h (the entire pool)

Questions: I've been working on sourcing components for 6 hours now, trying to match the flow rates of the various different filters. This is proving a nightmare! How necessary is it to cycle the water fully every hour? I'm struggling to find filters with high enough flow rates. At the moment I'm looking at 9 carbon filters to meet the 108ltrs per min required rate, for example. With filter housings and pipework that works out pretty expensive. Would a 2h cycle time make a huge difference?

Are pleated 20 micron filters very much different to solid spun ones? I can get much better flow rates from the pleated ones but the difference is so great (2 pleated cartridges vs 14 spun ones) that I am suspicious about their effectiveness.

How does one moderate the pressure in a pool filter system? Again, differing filters require different pressures. Is it simply a case of moderating the pump pressure as best you can at the start, is it possible to change the pressure to specific filters?

You guys are amazing! Looking forward to showing you pics of the fruits of your labour. Now if any of you are in spain in July... ;)

Tass

This is a glorified hot tub at this point. I would think a two hp pump at full flow would be sufficient. One turnover per hour is very aggressive and requires oversized piping and multiple drains or skimmers to assure safety. You might end up with a vortex whirlpool. How far from the pool to the equipment? Gary

Trying to filter the entire pool every hour is going to drive your costs through the roof. A complete change in four hours would most likely be excessive, but much easier to match equipment to the flow rate. There is most likely a health standard for public pools in Spain that can offer you guidance.

The recommended cycle time when I was helping to rebuild the school pool some years ago was 3 hours. It was a 60 m3 pool, and we used the usual sand filter (massive & expensive, but effective & cheap to run) and a 2hp (I think) pump giving about 22-23 m3/hr flowrate. I was hoping to get away from chlorine, but alternatives at that time were either too expensive, or not acceptable to the wary school caretaker who would be maintaining the pool. I don't think you should be too concerned with the fineness of the filters. 20 micron sounds a bit excessive to me.

Thanks gcoffing cwarner7_11 and Holzfeller. Thats exactly what I wanted to hear. I was going on waterparks recommendation in post #7 but I think thats going to be beyond my finances. Apparently the recommended turnover for domestic pools is 6-12 hours, but that seems far too long to clear the dust from the water. I'm aiming for 3 hour now.

gcoffing: haha, my glorified hot-tub is actually 12ft. I measured it myself this time! The litre-age is correct though. The filter station will likely be mounted to a pallet and camoflaged right next to the pool

Holzfeller: 20 micron filters were recommended by a guy who built a pool at Burning Man festival in the Nevada desert, USA. Apparently desert dust is so fine it can pass through a sand filter.

I can see the point of the 20 micron filters now. Desert dust is not a sight we see in this neck of the woods.

There are so many "i would like to..." opinions. Your pump must be in function minimum 8-9 h/day. DON'T even think to use active carbon filter (unless it is VERY necessary). You have create biofilm garden for microbes. Any who recommend it to you, are pool amateur. UV&the same are good on site disinfection (in the tube), bu water are unprotected in pool (from dust, swimmers etc). 20 microns are not too bad, bus 5 microns are better (but you need stronger pump). Sand, itself have not enough capacity to hold all pollutant's. You have good possibility, great chance, (as i see open door), but bad strategy. Good luck

I agree with #3. When you are still hesitate about which one to choose, Why not try Diatomaceous earth. It's completely biological and highly efficient.