Their paper, published in the journal PLoS ONE, is available here. It's written in fairly dry engineering context, so if you want a basic summary for the layman, I'll break it down for you:
- Filters work by passing water through microscopic holes and passages.
- Water molecules are small enough to fit through these openings, but bacteria, protozoa, and other contaminants are not.
- The wood of certain trees, such as pine trees, contains passages called xylem that move sap throughout the tree.
- These passages are between .07 and .1 micron in size, making them roughly equal to a Sawyer Mini filter element.
- The smallest bacteria are roughly .2 micron in size, and are easily caught in the filter.
|Image from http://www.offgridquest.com/813|
The wonders of science never cease!