Science

Need to filter some water? Just go peel a pine tree

Need to filter some water? Jus...
In this false-color image, E. coli bacteria (green dots) can be seen trapped around pit membranes (red and blue) in pine sapwood
In this false-color image, E. coli bacteria (green dots) can be seen trapped around pit membranes (red and blue) in pine sapwood
View 1 Image
In this false-color image, E. coli bacteria (green dots) can be seen trapped around pit membranes (red and blue) in pine sapwood
1/1
In this false-color image, E. coli bacteria (green dots) can be seen trapped around pit membranes (red and blue) in pine sapwood

In many parts of the world, the presence of harmful bacteria makes it vitally important that water from lakes or rivers be thoroughly filtered before being consumed. While materials such as silver nanoparticles and titanium dioxide will do the job, people in developing nations or rural settings typically need something a lot cheaper and easier to manufacture. As it turns out, wood from pine trees works great.

More specifically, it's pine sapwood that traps bacteria.

It's made up of a porous material known as xylem, that is used to draw sap up from the roots and into the rest of the tree. Xylem's internal structure consists of a series of microscopic vessels, which are linked together by pores in their walls. These pores, called pit membranes, allow sap to flow from vessel to vessel along the length of the tree. They're too small for air bubbles to pass through, though – that's a good thing, as bubbles in the "sapstream" can kill a tree.

As discovered by scientists at MIT, the pit membranes also let water pass through, yet are small enough that they block the passage of bacteria. In lab tests, pieces of the sapwood were glued into the inside of rubber tubes, which E. coli-contaminated water was then flowed through. When the wood was subsequently examined, approximately 99 percent of the bacteria that had been in the water was found to be trapped around the pit membranes in the first few millimeters of the filter.

According to the researchers' calculations, a single 1.5-inch-wide (38 mm) sapwood filter could be used to produce up to four liters (1 US gal) of drinking water per day. It couldn't be allowed to dry out when not in use, however.

Additionally, although the wood can catch most types of bacteria, it likely cannot filter out viruses, due to their smaller size. Sapwood from some other types of trees has smaller pores that could presumably trap smaller microbes, however, so the scientists are planning on conducting more research.

In fact, it's not just the wood from trees that can stop bacteria. A previous study indicated the seeds of the Moringa tree are also highly effective.

A paper on the MIT research was recently published in the journal PLoS ONE.

Source: MIT

8 comments
kraftzion
I've got pine trees, can you be a little more specific.? If your trying to save the world paint by numbers is a good place to start.
Nairda
I love how these obvious kinds of mechanical filtration experiments were not even attempted, or widely published in the past.
How many lives could this have saved? And how much money did developing countries cough up for other 'advanced' chemical water treatments from first world countries.
The world we live in.
Rann Xeroxx
Would this apply to any pine trees in North America? Just wondering from a survival stand point in an emergency situation.
Slowburn
There are easier ways to sterilize water. Say boiling it over a pine needle fueled fire.
JoJuly
Nairda, Any natural discovery which can be utilized freely or cost only pence.....will not be allowed to achieve any credence by the multi-billion dollar industries...energy, cancer treatment or any other life-saving discovery. This is my feeling anyway.
ezeflyer
Years ago, a study appeared on Science News comparing wood and plastic cutting boards. The wooden boards inhibited bacteria while the plastic boards did not.
JoejustJoe
Get two buckets cloth some piping sand charcoal use the cloth to prevent sand for entering the piping and layer the sand and charcoal in inch sections and you can filter just as effectively a 100 gallons a day.
VirtualGathis
@kraftzion - If you follow the via link to the PLoS One article they have the original photos and a more detailed explaination.
The fact that it can not filter viruses is regrettable, but it is still a remarkable filter. I've seen hiking filters that can not do so well.
This would probably make a good prefilter to prolong the life of a more expensive ceramic filter. normally clogging is the reason for having to replace them after just a few filtrations, but if 99% of the contaminants were prefiltered then it would last that much longer.