Mt. Whitney Portal Store & Hostel Forums General Mt. Whitney Portal Store Message Board Use of UV: Oxidation in Water Purification

Now and then, the topic of UV water purification systems appears on the board; a physicist buddy of mine forwarded this interesting technical brief:

Use of UV: Oxidation in Water Purification

For the Production of High Purity Water

more here

Haven't read it yet (thanks Bee), but every time I see, or hear, about this, I think back to the documentary that I saw a long time ago where they were pumping really dirty Colorado mine water thru a UV system and drinking it from the other end. I hope this paper confirms that it works!

Has anyone seen a study on the sun's effectiveness in sterilizing water? I use a steripen. But I wonder, for example, whether anyone has tested whether you can simply take a clear bag such as a ziplock, platypus or nalgene, fill it with water and leave it out in the sun for some requisite period of time to let the sun's UV rays bombard the organic impurities in the water to stop their ability to reproduce. I have read on this and other boards the general principle that taking water from the top of relatively still but moving water would probably yield a sterilized sample. I just wonder if you can improve the odds with a clear bag, and if so, how long it needs to sit out.

Brent

The plastic bag (carbon-carbon, carbon-hydrogen, etc. bonds)is going to be absorbing the UV. Spectal transmittance of the UV will be nil.

Hi Bee,
(Getting rained on?)

What's glossed over is:



I still see people desperately trying to zap a Nalgene full of floaters (east end of Trail Pond, anyone?) thinking that somehow the "organic" matter is going to just dissolve into purity. (Better bring a lot of batteries...)

UV irradiation is usually only a final "polishing" step in (laboratory) water purification and is generally preceeded by demineralization, reverse osmosis, and ion exchange of tap water. ( See the Millipore site referenced in the article for more information. Also, here is another reference source on the subject: http://thermo.dirxion.com/waterbook/WebProject.asp?CodeId=7.1.1.1 ) . As the Tech. Brief states, the UV is used to kill off algae and reduce the Total Organic Carbon (TOC).

I don't think that anyone in their right mind would remotely conceive of drinking mine water, Colorado or otherwise, that was ONLY subjected to UV irradiation.

Hardly glossed over - that is prominently presented as the second sentence in the three sentence introduction.

The reason that this article was sent to Bee is because she is a chemist and, in a previous thread on the subject, stated that she had not really seen any literature discussing the mechanism of UV irradiation for the treatment of organics. A basic understanding of chemistry and physics is helpful in appreciating the article.

The article was lifted from the website of Millipore, which is one company involved in the manufacture of systems for the production of highly purified water (DI water - deionized water) for a variety of laboratory uses. As the first sentence of the introduction points out, UV irradiation is only one step in the process.

(Better bring a lot more than batteries... no magic bullets here.)

P.S. Actually, I'm also primarily a chemist, but with an extensive physics bent. I usually carry a MIOX unit in case I decide that I don't trust a water source - primarily because I almost never use it and don't want to drag along my filter unit if it is just going to end up as dead weight.

That would be true if the monomers used in the plastic are aromatics (such as phthalate-based plastics), but it would not be true for polyethylene or similar plastics. And even then, if the aromatics in the plastic do not absorb UV at the critical wavelengths, it is not an issue.

Sunlight exposure of water in plastic containers has been proven to be an effective means of sterilizing water, and this method is being used in third world countries to neutralize pathogens in drinking water. A six hour exposure in bright sunlight zaps all the bugs. Look up SODIS:

http://www.matternetwork.com/2008/8/sodis-water-purification-made-easy.cfm

Many of these briefs will not address controversy/ambiguity on the layman's level (I am not trying to sound like a snob)as the basic premise mentioned -- UV being only part of the connective process of ultra-purifying water -- is already well-known and assumed in the lab environment. In that the emphasis/purpose of the article was to expand on the mechanics of the UV process, expanding on the rest of the steps towards purification was irrelevent (in the context of the brief, itself, which allows the release to remain....brief)

Thank you very much for this article, Len, it is one of the best that I have seen on the subject!

Really hot day, dry mouth, come upon a flowing streamlette, PUR filter out, pump, one minute later a liter of nice cold water, chug with water spilling down my front. Ah, refreshed.

Or,

swizzle electric thing in water, then drink wondering if it really works.

Or,

Mix swimming pool pellets with water and then drink it.

What is also glossed over, is the sentence before that:
"for the chemical,
food and beverage, pharmaceutical
and semiconductor industries."

In other words, what is being discussed is for a COMMERCIAL operation, not individual water use (which is, of course, why we would be talking about it.)

I only posted the brief because it was one on the first articles that I have seen on UV technology that realy explains the mechanism -- no matter the application, commercial or otherwise.

I got LIGHTENINGED on today!!

I totally agree with you about the floaters; even though the technology is sound, I do not want any pulp in my water (I hate pulped orange juice!)

This is a great thread as finally some science is referenced.

A couple of things that have always confused me about this topic.

First, if the sun's UV is so potent, why isn't air sterile?

And second, why the focus on standing pools of water? Am I to believe the bacteria and viruses in running streams out-run radiation at the speed of light?

The UVC wavelengths discussed in the referenced article (and emitted by the Steri-Pen) do not make it through the atmosphere.

The UVA and UVB wavelengths that reach the Earth's surface do not penetrate very far in water, so only the top layer of a lake is sterilized at all. Someone else will have to answer the question of exactly what is killed off by those wavelengths.

Well that would explain why air is not sterile. But, if the atmosphere blocks the sun's UV, then why should we expect any effect of the sun's UV on surface water at all, whether running or pooled?

What about the snow layer ... the stuff that's been in the atmosphere and hasn't melted off into the streams yet? Does it need treatment?

UV covers a wide range of wavelengths. Generally, the atmosphere passes the longer wavelengths well and the shorter ones poorly. At the wavelength used by, say, the SteriPen, the atmosphere is pretty opaque. whatever the sun does to surface water is done by longer wavelengths. Even UVA has some sterilization potential.