Originally Posted by
hilltowner
Cycocommute,
Thanks for the critique of the A.M. marketing propaganda. I'm very grateful you cut through the b.s. Any comments on the study that I linked to?
(Phil)ltowner
Several things jump out about the Backpacking Light article. First, there is this:
In natural waterways, greater than 99% of bacteria exist in biofilms.
I agree whole heartedly. Bacteria need nutrients and water. Most water is going to be too low in nutrients to allow for survival of the bacteria out in the open water so it is going to anchor itself to something and take nutrients from the matrix or grab nutrients as they float by. The material that the bacteria anchor to...the matrix in the article...is most likely going to be plant based materials or perhaps other biologicals like dead animals.
But bacteria are large organism, relatively speaking. Filtration is enough to get rid of them.
We have found that the storage of filtration devices or long-term use on the trail can result in biofilm growth in the filter element that can render it useless. Most backcountry users—and manufacturers—have long assumed that filter failure is a direct result of filtering silty water. A valid reason, indeed. But they have ignored the effect of biofilm growth in the filter element, a more common-than-not means of filter failure in the absence of significant silt, soil, or undissolved organic matter in the source water.
Again, I agree but with more reservations. The growth of a biofilm depends on the nutrients available. The filter element doesn't provide any nutrients so any growth of a biofilm would depend on trapped material from the stream water being filtered. Additionally, the filter element isn't a good matrix for bacteria to set up housekeeping. Cleaning the filter after each use goes a long way towards removing nutrients and to preventing growth of bacteria. Drying it out after use or even occasionally would reduce biofilm growth.
This doesn't matter however except that the filter can become clogged. The bacteria doesn't pass through the filter...it's too big.
Chemical purification relies on an oxidant’s ability to destroy a pathogenic organism upon contact. A corollary of this is that as oxidant concentration increases, the kill-rate-per-unit time will also increase because there is more oxidant available to destroy the pathogens.
Again, I agree but this time they have missed the point. Using chemical oxidants to kill pathogens is a concentration problem. You have to have a high enough concentration of the oxidant to kill the pathogens and not have to the oxidant get involved in side reactions that are using the oxidant on material that is benign. There is also a limit to how much oxidant you can use before it becomes hazardous to consume.
Hypochlorous acid is considered to be a better bio-film disinfecting agent than either [chlorine gas] or [chlorine dioxide] because of its ability to penetrate the biofilm matrix, whereas
[chlorine gas] or [chlorine dioxide] react more strongly with matrix components and may never reach the depth of the biofilm where active cells are found.
Now the real fun begins
Hypochlorous acid forms when chlorine gas reacts with water. If you are using chlorine gas for sterilization of water, you are forming hypochlorous acid. The chlorine gas doesn't disinfect the water, it's the hypochlorous acid formed that does the job. They don't seem to understand this since the authors of the article treat them like they are two separate processes. They aren't.
They are correct that the chlorine gas, as well as the hypochlorous acid formed, and the chlorine dioxide react with the matrix that the biofilm has formed on. Therein is a large part of the concentration problem. All of these oxidants are indiscriminate. They react with anything that can be oxidized in the water mixture. If you have a bunch of twigs in the water you are treating (which also carries that biofilm), the chlorine and the chlorine dioxide will react with a component in the wood that is called lignin. Lignin in sapwood makes up about 18% of the wood but it is much higher in bark...about 25%. If you remove those twigs from the water, your chemicals will be wasted on that material. Even in "clear" water, i.e. water that appears to have nothing in it but hasn't been filtered, there can be microscopic bits floating around with biofilm all over them. That's going to suck up your chemicals. If your chemicals run out before you have killed all active organisms in the water, you risk drinking unclean water.
That's most of the reason why Aquamira is suggested for treatment of "potable" water. It's to polish the water after it has been through some other kind of treatment. I'm sure it does a great job and I have nothing against chemical treatments...as a secondary treatment. Filtering will get rid of most everything but viruses and the virus load even lower than the bacterial load in water. In certain parts of the world, filtering potable water and then treating it with a chemical oxidant would be a wise idea. The US and Europe have very good sanitation systems that keep most of the bad biologicals out of the water.
My job, by the way, often entails using chlorine dioxide to remove lignin from wood. I have to work with concentrations that are dangerous to humans because lignin can suck up a lot of chlorine dioxide. I've actually experienced a couple of the "puffs" I detailed above which are both thrilling and scary.