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|Scooped by Cait Madera|
The lack of clean drinking water free of dangerous pathogens has been a long-term battle for many developing countries, where such water borne diseases are leading cause of death. Pathogens, disease-causing microorganisms, such as bacteri and viruses include the largest health risk, in most part of the world and are generally spread through human or animal feces. The World Health Organization reports that these pathogens cause gastrointestinal infections in the form or diarrhea, killing around 2.2 million people globally each year most of which are children in developing countries. The barriers for such low-income communities to achieve the necessary quantity of safe potable water are staggering. Some techniques of water disinfections have been used in the past with success, however smaller communities that cannot afford large-scale filtration systems are suffering. Even simple methods of cleansing water such as boiling require an unrealistic quantity of fuel resources that an average family would struggle coming up with.
A group of researchers from MIT offer an innovative and shockingly low-tech approach to an affordable and realistic model of water filtration. Taking a step back and looking to nature for inspiration the MIT team proposes that the solution to filtration is in the porous material within a plant; xylem. The xylem of a plant is the system of tube like tissues that circulates water and dissolved minerals. With simplicity as the theme, the materials involved in the study are minimal. MIT researches picked white pine saplings, using the young bark as the constant throughout the experiment. Construction of the filtration system starts with sapling bark cut into 1 inch long sections. The outer layer of bark was then peeled off and the remaining wood was then sealed into a clear tube with epoxy and a metal clamp. The now filter device, is then flushed with 10ml of deionized water to ensure the optimal moisture of the spongy xylem.
Before experimenting with actual contaminated water, the group first tested water mixed with red ink ranging from 70 to 500 nanometers in size, to represent the various sizes in bacteria found in contaminated water. After all the liquid passed through, the researchers sliced the sapwood in half, the found that much of the red dye was confined within the very top layers of the wood, while the resulting filtered water, was clear, a good sign that the contaminants did not go through. They then filled the tube with 5 milliliters of water, under pressure that would be equivalent to the natural gravitational pressure that would occur in the field using this device. The water filtered through at a rate equal to more than 4 liters per day, enough drinking water to sustain a person for a day.
This experiment showed that sapwood is naturally able to filter out particles larger than about 70 nanometers. With this said, in another experiment, the team found that sapwood was unable to separate out 20-nanometer particles from water thus potentially harmful material that are smaller than that could pass through risking some waterborne diseases. Inherently there are some limitations to this kind of filtration. A misguidedly simple one is that the wood must be freshly cut to work as an effective filter. The team explains that the channels in wood that has dried become blocked and so don’t work as filters. This is potentially a serious problem if these are to be distributed to developing countries as personal filtration system. Another potential set back not included in the experiment is how often the sapling would need to be changed out to maintain freshly filtered water.
Karnik and co. conclude in their study, “The simple construction of xylem filters, combined with their fabrication from an inexpensive, biodegradable, and disposable material suggests that further research and development of xylem filters could lead to their widespread use and greatly reduce the incidence of waterborne infectious disease in the world.”