Water Filtration Using Naturally-Occurring Membranes in Plant Xylem

Low-cost, accessible, point-of-use technologies for water filtration have the potential to greatly reduce the global burden of waterborne illnesses. Drawing inspiration from fluidic transport in plants, we explored the possibility of using plant xylem tissue for low-cost water filtration. The xylem tissue conducts sap in plants and has evolved porous membranes that provide low resistance to flow while arresting the spread of cavitation-induced bubbles. We demonstrate that plant xylem in the sapwood of coniferous trees can be used to effectively remove E. coli bacteria from water at high flow rates. However, a major challenge associated with the use of xylem for water filtration is the drop in permeability and deterioration in rejection ability due to the structural changes induced during drying, which is crucial in the context of transportation and shelf-life. We have developed methods to preserve the structural integrity of the xylem and to minimize the negative impacts on filtration characteristics due to drying. Further, we found that the permeability after drying is a strong function of filter length and have studied ways to design the filter to achieve an optimal balance between flow rate and rejection ability. We have also demonstrated gravity-driven filtration through the xylem and conducted fouling studies to gain insights into filter lifetime and variation in flow characteristics over time. Fabrication of the filter is simple, and the wood required for fabrication of a gravity-driven filter with a flow rate exceeding 1 L/h costs less than 1 cent and weighs only 8 grams. This work suggests the potential of plant xylem for realizing inexpensive, locally-manufacturable, and disposable point-of-use water purification devices.