Grantee Research Project Results
Final Report: Xylem Filtration: The Next Generation Approach to Accessing Clean Drinking Water
EPA Grant Number: SU836129Title: Xylem Filtration: The Next Generation Approach to Accessing Clean Drinking Water
Investigators: Landsbergen, Kim
Institution: Antioch College
EPA Project Officer: Page, Angela
Phase: I
Project Period: September 1, 2015 through August 31, 2016
Project Amount: $14,796
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet (2015) RFA Text | Recipients Lists
Research Category: P3 Awards , Pollution Prevention/Sustainable Development , Sustainable and Healthy Communities , P3 Challenge Area - Safe and Sustainable Water Resources
Objective:
A wood-based xylem filter uses a piece of a freshly collected branch to mechanically filter water through the fine xylem “pores”. This method showed potential as an emergency filter to obtain clean drinking water because it requires few, accessible, and low-cost materials. Our P3 team built on the work of Boutilier et al. (2014) to further explore the scalability, safety, ease of use of xylem filtration. Our goal was to experimentally determine if this technique could produce adequate volumes of safe drinking water, and to evaluate the practicality of the method for everyday people to use as an emergency water source.
Our experimental approach had four components:
i. Water Pre-treatments - Depending on the water source, suspended sediments may need to be removed, or the particles will clog the filter. Additions of food-safe liquid alum were evaluated and optimum doses determined for typical surface waters, as this chemical is used for this purpose in municipal drinking water treatment plants.
ii. Testing Wood Types - Only one species of wood was tested in the paper that inspired our project (white pine, Pinus strobus, from Boutilier et al. 2014). We evaluated the filtration capacities of different species of wood from trees commonly found in the eastern United States.
iii. Flow rate testing - Preliminary studies indicated that xylem can filter effectively, but low flow rates and volume might limit the practicality of the method. Our goal was to test ways to increase delivery pressure using compressed air to increase flow rates.
iv. Xylem versus other readily available filters – Lastly, we wanted to evaluate the practicality and efficacy of the xylem filter compared to other commonly used, commercially-available methods.
Summary/Accomplishments (Outputs/Outcomes):
The following summarizes the results from the four areas of investigation:
i. Water Pre-treatments - To avoid clogged filters from suspended particles in surface waters, we tested the alum method that is used in conventional water treatment facilities to flocculate or remove suspended sediments. In order to clear lake or stream water of suspended soil particles that might clog the xylem filters, we found that an optimum concentration of 2 ml L-1 of food grade alum resulted in flocculation and clearing of water as a pre-filtration treatment.
ii. Testing Wood Types - Replicate (N = 3-4) xylem filtration tests of five common tree species were tested using techniques based on Boutilier et al. 2014, in order to evaluate differences between filtration capacity per species and to rank their efficiencies. The Boutilier et al (2014) method used a particle-based dye as a test filtrate, because the particle sizes approximated the particle sizes of bacteria. Species tested and their average rank order of filtration efficiencies in removing dye from a test solution were: White pine (Pinus strobus, 82% removal), Norway spruce (Picea abies, 69% removal), sycamore (Platanus occidentalis, 55% removal), sugar maple (Acer saccharum, 39% removal) and Bur oak (Quercus macrocarpa, 18% removal). The two conifer species (pine and spruce) provided the best filtration efficiency, but their flow rates were very low, as expected in conifer xylem where the only conduits are trachieds with extremely small radii. Conversely, deciduous hardwood tree species like maple, sycamore and oak have very porous xylem (and higher flow rates) but the larger radii of the xylem vessel elements would not be capable of safely removing bacterial-sized particles.
iii. Flow rate testing - Using a flow meter and compressed nitrogen, students evaluated increasing pressure on filtration flow rates in order to maximize flow. Initial tests yielded approximately one third of a milliliter in 5 minutes on a White Pine xylem filter area of about 1 cm^2 under 1-5 psi. This yielded a rate of 0.001 ml/s, theoretically allowing the filter to provide 3.6 liters over 24 hours. Subsequent replicate tests produced similar flow rates. Hence a simple system that provided 1- 5 psi of pressure to the filtration system would make the filter usable in an emergency situation. Boutilier et al. (2014) found a higher rate of 0.05 ml/s at 1-5 psi with a same xylem filter area of about 1 cm^2.
iv. Xylem versus other readily available filters – “Do it yourself” emergency filter instructions commonly suggest that combined beds of gravel and sand might provide adequate drinking water filtration in an emergency. Over-the-counter, activated charcoal-based filtration systems also might also appear to be an adequate filtration option in times of emergency. Our fourth set of experiments tested the wood xylem filtration methods versus these two, and found that white pine xylem filter out-performed the gravel/sand and activated-charcoal cartridge methods by a factor of three (but had much lower flow rates).
Conclusions:
Ultimately, the student research team concluded that xylem filtration would not be a practical approach for emergency water filtration, because even a filter that is ~80% efficient in removing bacterial particles (such as the white pine filter we tested) would likely still place people at risk of waterborne disease. Xylem collection time, water collection, and filter assembly can take 2+ hours depending on how far xylem and water sources are, and that is under controlled laboratory conditions with ample equipment and expertise. The conifers we tested were the most effective filters due to their trachied-containing wood anatomy. However, gravity filtration did not provide enough drinking water per person per day, irrespective of wood selection. Increasing pressure increased delivery volume, but was not capable of producing the required 3 L of water per person per day. Finally, the biological materials produced variable results that would not be acceptable as a means of filtering drinking water safely.
Such a system, if needed in an emergency situation, might provide some safely-filtered water provided enough sequential systems could be deployed and some increased system pressure could be sustained. From a People, Planet, and Prosperity perspective, the potential of a safe, high-volume, xylem-based DIY-water filtration system remains an elusive goal.
Journal Articles:
No journal articles submitted with this report: View all 2 publications for this projectSupplemental Keywords:
xylem, biofilter, water, filtrationThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.