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Enhancing the Solar Water Disinfection (SODIS) Method Using a Fresnel Lens

  • Author(s): Awad, Christina
  • Advisor(s): Matsumoto, Mark
  • et al.
Abstract

Currently, about one in seven people worldwide lack access to clean water, and meeting the needs of a growing population will only further stress our existing resources (Gleick 2002). It is for these reasons that sustainable, cost effective, efficient water disinfection systems are needed. Therefore, the subject of this research is to explore a possible method of enhancing the Solar Water Disinfection (SODIS) method by using a Fresnel lens to concentrate solar energy, with the goal of attaining pasteurization temperatures to reduce holding times for disinfection. This method will be referred to as "PULSE" - Pasteurization Using a Lens and Solar Energy. The hypotheses are that pasteurization temperatures can be reached using a Fresnel lens and, secondly, that the Fresnel lens will accelerate the rate of disinfection by causing a rapid temperature rise during the solar disinfection process.

To test the first hypothesis, a Fresnel lens was used under varying weather conditions to determine its heating capabilities and conditions under which it is able to reach pasteurization temperatures. In testing the second hypothesis, disinfection rate as a function of temperature increase was established using a hot plate. Following demonstration that disinfection increases with temperature increase, an experiment utilizing PET bottles (typically employed in the SODIS method) (SODIS: How does it work? 2011) filled with water spiked with E. coli, was carried out to determine bacterial inactivation rates. Each condition (Dark, Hotplate, SODIS, and PULSE) was tested, but SODIS and PULSE were done over the summer months, when weather conditions would be similar, to ensure reproducibility of results. Temperature and E. coli numbers were monitored as a function of time. The rates of bacterial inactivation in each of the PET bottles were compared to confirm how temperature affects disinfection rates and to determine whether the Fresnel lens will speed up the solar disinfection process. The goal was to demonstrate that by achieving pasteurization temperatures, a Fresnel lens could significantly increase disinfection rates, thereby providing clean water in a much shorter amount of time.

In exploring this technology approach, this research sought to lay a foundation in which the mechanism, application, and relevance of lens-enhanced solar disinfection can be more closely studied. Better designs, better materials, and a better understanding of the fundamental principles governing disinfection can be brought to the forefront with the examination of existing designs, materials, and current data that this research looks to elucidate. Ultimately, it is towards this end in which this research is directed - to help mitigate human suffering due to something well within our capability.

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