Water Filtration With a Tree Branch

Taco Cowboy writes "Dirty water is a major cause of mortality in the developing world. 'The most common water-borne pathogens are bacteria (e.g. Escherichia coli, Salmonella typhi, Vibrio cholerae), viruses (e.g. adenoviruses, enteroviruses, hepatitis, rotavirus), and protozoa (e.g. giardia). These pathogens cause child mortality and also contribute to malnutrition and stunted growth of children.' People have been working on engineering cheaper and cheaper filtration systems for years, but now a group of researchers has found a promising and simple solution: a tree branch. 'Approximately 3 cm^3 of sapwood can filter water at the rate of several liters per day, sufficient to meet the clean drinking water needs of one person.' 'Before experimenting with contaminated water, the group used water mixed with red ink particles ranging from 70 to 500 nanometers in size. After all the liquid passed through, the researchers sliced the sapwood in half lengthwise, and observed that much of the red dye was contained within the very top layers of the wood, while the filtrate, or filtered water, was clear. This experiment showed that sapwood is naturally able to filter out particles bigger than about 70 nanometers.' The team tested E. coli-contaminated water, and the branch was able to filter out 99 percent of the bacterial cells."

Comments

First time?

[DogDude]

If this is true, then this is a really profound discovery that could help millions of people.

What I'm wondering, is why no other society, that we know of, has discovered this low-tech, yet seemingly incredibly useful thing previously?

Re:First time?

[i kan reed]

Ideas can be publicized, studied in more detail, or put to good use, without being truly new.

Re:First time?

[hawguy]

If this is true, then this is a really profound discovery that could help millions of people.

What I'm wondering, is why no other society, that we know of, has discovered this low-tech, yet seemingly incredibly useful thing previously?

For one thing, it doesn't filter viruses, so maybe it's already been evaluated and dicarded as a good solution. From TFA:

Karnik says sapwood likely can filter most types of bacteria, the smallest of which measure about 200 nanometers. However, the filter probably cannot trap most viruses, which are much smaller in size.

So it's of limited utility, since, as the summary says, common pathogens include viruses (e.g. adenoviruses, enteroviruses, hepatitis, rotavirus) -- for example, rotavirus is around 30nm in size, less than half the effective filtering size of the wood.

So the water will probably still need chemical or UV treatment after filtering.

Plus it's not clear how well it would work in the field, when the scientists built their filter:

They cut small sections of sapwood measuring about an inch long and half an inch wide, and mounted each in plastic tubing, sealed with epoxy and secured with clamps.

So while wood as a filter medium sounds attractive, if the user needs specialized equipment to get it to make a safe, water-tight seal, maybe it's not as useful in an area with limited resources.

Re:First time?

[Anonymous Coward]

1) Someone posts a bible verse
2) Become overjoyed at discovery of opportunity for gratuitous atheistic hate
3) Recognize poster made no claim beyond interesting anecdote, assert he did anyway
4) Realize equivalent anecdote would prompt no reaction at all for you if it weren't associatable with a religion, Christianity in particular
5) ???
6) Get eliminated by natural selection, become irrelevant

Re:First time?

[MightyYar]

When people have to hike for miles to find wood for cooking fires, I'm not sure that fresh cut wood is all that practical.

Re:Most common pathogens

[fustakrakich]

...I hope it leads to cheap and widely accessible drinking water.

Coca Cola and Pepsi will do all they can to make sure that never happens. Water is big business. That is why access is so difficult.

Re:Take That, Capitalists!

[CanHasDIY]

Filtering out "99%" of harmful bacteria may be like filtering out 99% of bullets fired at you....

So, I take it you're not a fan of Lysol or Purell?

What a silly thing to say; as if not filtering 99% of something harmful is a better idea...

Somebody Probably Thought of That

[Anonymous Coward]

"Somebody probably thought of that" is more likely to be untrue than true. You probably are the first person to think of that. And even if you aren't you might be the first person to act on the idea. And even if you aren't you might be the first person to succeed where others have failed. And even if you aren't, you might learn something. So don't ever say that, "somebody probably thought of that."

Filtering water through wafers of wood is not obvious to me. I do engineering for a living. If you are wondering why no one ever discovered something before, go back to paragraph one and repeat.

Re:Somebody Probably Thought of That

[K. S. Kyosuke]

It *is* obvious - after a fashion - since plants are generally doing just that; i.e., they use their root systems and cappilaries to absorb water including some impurities up to a certain size. The issue of "can we cut away a part of a plant tissue and filter water through it?" is probably more of a quantitative nature, rather than qualitative. As in, what is the filtering capacity? Does it clog? If it does, how often does it need to be changed? Does it rot? If so, how often does it need to be changed? The qualitative issues here seem to be "given that we're killing the plant, how does it affect the filtration process?" and "what preparation techniques can we employ to increase the practicality?". It's not that we don't have any filtration media, it's about how our knowledge and manufacturing processes make the individual filtration media more or less practical.

Re: Most common pathogens

[spune]

There already are low-cost, natural water filtration techniques being used across the world that produce clean water at a higher rate, like biosand filters. For water projects i have previously worked on, how quickly water is purified has been a significant practical concern for the folks who would benefit from the project. That was the reason that solar stills were dismissed, for example; they require more effort and materials to construct, but even then have a higher flow rate than the xylem filter. Also, how often the filter must be replaced is another big practicality issue.