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Harvard Forest REU Symposium Abstract 2012

• Title: What is the response of turbidity and pathogen levels to variations in sand depths in filters?
• Author: Tefiro K Serunjogi (Grinnell College)
• Abstract:

  My project this summer considered ways in which safe water could be made available to people in areas like my village that lack access to safe water sources. It encompassed aspects pertaining to community water supply, household filtration, and the development of hand-held sand filters. After realizing that research into household sized filters was quite comprehensive, I switched my focus to the development of hand-held filters. My interest was in using locally available materials like sand and gravel for the filtration process and then coupling it with chlorination using regular bleach (sodium hypochlorite).
  
  
  
  Chlorination as a means of water disinfection has been on the rise in Uganda in recent years but its effectiveness is greatly reduced by the turbidity that is often present in the water sources. Therefore, I focused on a three step process (settling, filtration, and chlorination) that aimed to rid the water of as much turbidity as possible (by settling & filtration) and so allow for the chlorination process to be as effective as possible.
  
  
  
  I designed a range of bottle-sized sand filters with varying sand depths: 3inches, 4inches, 5inches, and 6inches. My first test involved one replicate of filters that I tested with a very dirty source-water from a tub that I artificially contaminated with dirt and cow waste-which I later discontinued, given the considerable amount of biological matter that had developed in the source over time. The second test tested 5 replicates of all 4 sand depths using turbid water from a local river with more natural pathogen levels (I spiked it with more coliform-containing water). A sub-sample of each filtrate was chlorinated. I tested source water, blanks, filtrates, and chlorinated filtrate for pathogen indicators (Total Coliforms and Escherichia coli (E. coli)) using membrane filtration and the m-coli blue24 method (Hach Company). I also tested for the turbidity of the samples using the Non-Filterable Residue technique (formerly known as the Total Suspended Solids (TSS) technique) by filtration through a glass fiber filter. My third experiment looked at the effectiveness of filters over time by pouring source water through one 6 inch filter on a daily basis and observing pathogen removal and TSS.
  
  
  
  The investigation showed; a) that the hand-held filters were up to 88% effective in pathogen removal provided pathogen levels were not too high, b) that the filters removed a considerable amount of suspended solids, c) that chlorination after filtration was effective, d) that increased sand depth gave the filters greater effectiveness in the removal of pathogens (ANOVA, p. = 0.08) as well as the removal of suspended solids, and e) that filters could reduce pathogen levels for at least 3 days. However, more tests would need to be run to provide a greater understanding of the effect of the varying sand depths on the pathogen counts and the statistical significance of the relationship between the two variables.
  
  
  
  This study’s conclusions may eventually help improve access to safe water for people where developed water sources are not available. My hope is that these results will help to better the lives of people in my community and, possibly, around the world.

• Research Category: International Research Projects


• Figures:
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