MIT researchers have discovered a simple method of removing bacterial contaminants from water using nothing but a stick of wood. The new discovery can be used to make an improvised water filter that can be used during camping trips or even during survival situations.
The low-tech but ingenious water filtration system is very easy to make using pine or sapwood. Simply take a fresh branch from a nearby pine tree and take off the bark. Once the bark has been removed, carefully pour lake or river water through the length of the stick and collect the water using a clean container. The exposed surface of the branch will be able to remove bacteria from the water to provide clean water that is suitable for drinking. A single branch and be used to filter around 4 liters of water, which is enough to fill the fluid requirements of a single person for a day.
The team for the Massachusetts Institute of Technology (MIT) published their findings in the online journal PLOS One. To conduct the study, the researchers used a small piece of sapwood to filter water contaminated by E. coli bacteria. The team found that their simple water filter was able to remove over 99 percent of the bacteria present in the water.
The researchers found that the pores on the wooden branch were the perfect size for trapping bacteria while letting water pass through. Once the bark is removed, the branch's xylem tissues are also exposed. Xylem tissues are responsible for moving tree saps throughout the tree and can be used to trap bacteria in a manner similar to commercially available filters.
"Today's filtration membranes have nanoscale pores that are not something you can manufacture in a garage very easily," said Rohit Karnik, an associate professor of mechanical engineering from the MIT and one of the co-authors of the study.. "The idea here is that we don't need to fabricate a membrane, because it's easily available. You can just take a piece of wood and make a filter out of it."
While there are numerous water filtration systems available in the market today, many of these products are often expensive. Filtration systems meant for large scale use often rely on chlorine. While there are portable options, these smaller filters can be costly and they can get clogged after a while.
"Plants have had to figure out how to filter out bubbles but allow easy flow of sap," Karnik said. "It's the same problem with water filtration where we want to filter out microbes but maintain a high flow rate. So it's a nice coincidence that the problems are similar."
Campers and survival experts often recommend boiling water to kill of bacterial agents. However, boiling water requires fuel, which may not be practical in a number of situations. Using wooden branches as filters is cheap, easy to make and reliable.
"There's huge variation between plants," Karnik says. "There could be much better plants out there that are suitable for this process. Ideally, a filter would be a thin slice of wood you could use for a few days, then throw it away and replace at almost no cost. It's orders of magnitude cheaper than the high-end membranes on the market today."
