Sapwood, like pine, can filter e. coli and other bacteria from water, according to researchers from the Massachusetts Institute of Technology (MIT).
Campers out in the woods can safely clean water of contaminants by straining it through a piece of pine or other sapwood, from which the bark has been removed. The wood from one branch can clean up to a gallon of water a day. This is enough to satisfy the needs of one person in the wilderness.
Freshly-cut sapwood can remove up to 99 percent of e. coli from contaminated water, according to the study, published in PLOS ONE. Within pores in the wood are xylem tissues, which normally assist in the transport of sap upwards in trees.
Recent discoveries in water filters made from graphene, a form of carbon, show great promise for the industry. But, this new finding may suggest such high-tech solutions for water filtration may be unnecessary.
"Today's filtration membranes have nanoscale pores that are not something you can manufacture in a garage very easily. 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," Rohit Karnik, study co-author, said.
Other water filtration methods are dogged by problems for those in the wilderness. Commercial filters are expensive, many require a pump or battery, and all filters can become clogged. Boiling water means burning a lot of fuel, in the form of propane or wood. Supplies of dry, flammable material in the wilderness can be hard to find, especially after a massive storm. This natural alternative could provide low-cost, safe drinking water.
Sapwood filters would also be fully biodegradable, making them even more appealing for environmentally-minded campers, and for use in rural commercial systems. Much of the developing world cannot afford commercial filtration systems using chlorine or oxygen. Poor water quality is a leading cause of death in much of the world, so a system suitable to use in these regions could save millions of lives.
"[T]he sapwood of coniferous trees - a readily available, inexpensive, biodegradable, and disposable material - can remove bacteria from water by simple pressure-driven filtration... The results demonstrate the potential of plant xylem to address the need for pathogen-free drinking water in developing countries and resource-limited settings," the researchers wrote.
To make the filters, researchers cut branches into segments one inch long. They then inserted the pieces of wood into plastic tubes, and filled one end with water, containing a known concentration of bacteria. After sealing the tube, water was allowed to drain through the wood, and the samples were re-tested for E.coli contamination. Analysis of the filters showed most bacteria were trapped within the first one-eighth inch.
Only fresh, not dried, sapwoods have the ability to filter the water.