water purification without chlorine?

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homer

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We are heading to places where water has to be purified and there are, of course, tablets etc. which can be popped in the tank. However, our water tanks are aluminium and, as I understand it, contact with chlorine is best avoided. Are there any treatments available which do not contain chlorine? (We already have a carbon filter but this does not kill all bugs.)
 
As mentioned, I already have a carbon filter but, as we are heading for Eritrea, a belt and braces approach seems sensible. It looks like it will be Elsil! Thanks for input.
 
Several points. Mrs AntarcticPilot happens to be a chemist majoring on water purification, so I hope this is pretty reliable.

  1. Filters WON'T necessarily remove infective material , and certainly not reliably. They will remove solids and dissolved gases, making the water taste better, but as they can act as reservoirs of infective organisms, they are not a reliable way of ensuring safe water. Of course, some include disinfecting material (e.g. silver), but the length of time this will remain active is not apparent to the user. Taste is NOT a reliable guide to safety.
  2. Chlorine based methods are probably the simplest and most reliable for use in "field" conditions.
  3. Chlorine reacts with some contaminants (e.g. humic acids) to form carcinogenic compounds.
  4. Oxygen based methods are very good, but require a source of ozone or hydrogen peroxide, which is not readily available, and which has a short shelf-life.
  5. My wife has worked on methods using photo-electrocatalysis, which uses sunlight and a small amount of electricity to sterlize water. Unfortunately this technique, which would be ideal for yachts, is a long way from being ready for market.

Probably the best method with current technology is to dose the tank with purifying tablets or Milton, then pass it through a carbon filter to remove taste and excess chlorine. That's what we shall probably end up with, when finances permit getting a decent filter!
 
AntarcticPilot said:
[*]Oxygen based methods are very good, but require a source of ozone or hydrogen peroxide, which is not readily available, and which has a short shelf-life.
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I'm surprised you say H2O2 is not readily available? Can't you get it from any chemist?
Alternatively there are several products around on the lines of Elsil from chandlers and camping shops. I think Elsil (which also incorporates a silver compound - a chelate? - for more persistent protection) claims to have a shelf life of a year.
It's dearer than bleach - but tasteless even in tea. :)
 
Troubadour said:
I'm surprised you say H2O2 is not readily available? Can't you get it from any chemist?
Alternatively there are several products around on the lines of Elsil from chandlers and camping shops. I think Elsil (which also incorporates a silver compound - a chelate? - for more persistent protection) claims to have a shelf life of a year.
It's dearer than bleach - but tasteless even in tea. :)
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Yes, you can get it in civilized places readily enough, but as it has a definite shelf-life which decreases with temperature, it is unlikely to be readily available in some countries, especially hot countries. The OP specified he was going to hot countries. You'd also want to be sure that the stuff you bought was free of nasty impurities; as most hydrogen peroxide solution is sold for bleaching rather than for disinfection, that might not necessarily be true of all supplies.


Hydrogen peroxide (10%) attacks nitrile, neoprene, copper, delrin and nylon, all likely to be found in a boat's fresh-water system. It also attacks Hypalon; maybe not something you want to spill in your dinghy!

Water purification plants using ozone usually generate the ozone on-site, which takes power.
 
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homer said:
We are heading to places where water has to be purified and there are, of course, tablets etc. which can be popped in the tank. However, our water tanks are aluminium and, as I understand it, contact with chlorine is best avoided. Are there any treatments available which do not contain chlorine? (We already have a carbon filter but this does not kill all bugs.)
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Could you treat the water in plastic containers first?
 
I've seen swimming pool installations that use ultra violet light to sterilise water. While I don't know of any specifically yottie kit that works like this, it shouldn't be too difficult to adapt / rig something up.
 
Could you use one of these aboard ?, I know nothing about this subject, but water sterilisers are used for koi ponds and some fish tanks to keep bacterial levels in check, but this one seems to be suitable for drinking water.

How about combining a carbon filter, with this gadget to make the water safe ?

ultraviolet-water-sterilizer-system
 
DaveS said:
I've seen swimming pool installations that use ultra violet light to sterilise water. While I don't know of any specifically yottie kit that works like this, it shouldn't be too difficult to adapt / rig something up.
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It is an enhanced version of that, using visible light, that my wife is working on. It will use much less power. UV only systems are power hungry, and also UV is not a safe thing to have around in a non-industrial environment.

I should have said, UV at disinfecting wavelengths is not nice to have around without elaborate safety systems to ensure the light is never on when people might be exposed to it.
 
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As AP has said, filtration is problematic but does work if you maintain them properly. But doing filtration from a tank won't work without a booster pump as to get water through a 5 and 0.2 micron filter will need 3 bar if the water is bad quality. An easier way is a water maker. These are , in essence , a self contained mini reverse osmosis plant. Not cheap but if you are only producing drinking water , you can get the smaller sized (and cheaper ) ones
Regards
Rob
 
AntarcticPilot said:
It is an enhanced version of that, using visible light, that my wife is working on. It will use much less power. UV only systems are power hungry, and also UV is not a safe thing to have around in a non-industrial environment.

I should have said, UV at disinfecting wavelengths is not nice to have around without elaborate safety systems to ensure the light is never on when people might be exposed to it.
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The UV unit that TopDonkey linked to is metal cased (stainless?) so I would have thought adequately shielded. While its electrical rating is not quoted, it claims that the daily running cost (from the mains) is "pennies" which would suggest not too high a loading.
 
DaveS said:
The UV unit that TopDonkey linked to is metal cased (stainless?) so I would have thought adequately shielded. While its electrical rating is not quoted, it claims that the daily running cost (from the mains) is "pennies" which would suggest not too high a loading.
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I'm getting out of my depth here, but I think that the point is that my wife is looking at industrial scale water purification, capable of dealing with community level water supplies. I don't know why, but unaided UV is not considered viable; the method she is researching uses visible sunlight and a tiny amount of electricity. As her work starts from a technique that uses UV with a catalyst, I assume there's a good reason why UV alone is regarded as insufficient. However, I can imagine that a small-scale installation would be OK.

However, it is true that one means of purifying water is to leave it in a suitable UV transparent bottle exposed to full sun for long enough.
 
I was out of my depth ages ago !, my ex wife's father was a bore hole engineer and dealt with water extraction and purification every day, but i cant ask him anything now

All i know is that when i kept a tropical reef tank, i used a UV water steriliser like the one i linked to because thats what i was advised at the time by fish experts, i believe they consume about half an amp at 24 volts if my memory serves me right and it ran constantly day and night on the output of one of my huge filter units
 
A few extra considerations are...
The chlorine smell and taste can be removed by adding sodium thiosulphate to treated water.
Humic acids, usually from peat usually form a very noticeable malodour, e.g. TCP so you’ll probably not want to drink water smelling like that anyway, thus avoiding any other by-products.

One low cost, low energy UV option for drinking water is often used by overland back-packers and seems to be held in high regard. http://www.steripen.com/
 
i treat water for drinking on a remote base and would suggest chloriinating and storing in plastic drum or even a large waterbutt.chlorine concentration should be assesed on a daily basis and should not drop below 0.1% chlorine to water and not be above 0.5% for drinking.i test with a photometer for chlorine /iron /aluminium /hazen etc.
we use calcium hypochlorite crystals for chlorinating .the water collected comes off small streams.100grammes would treat about 50 000 litres as a guide to achieve a 0.15% reading.
 
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