Date of Award
MS in Civil and Environmental Engineering
Civil and Environmental Engineering
Point-of-use (POU) drinking water treatment is a common method of providing drinking water in disaster relief situations when critical water infrastructure is damaged. In these cases, POU treatment devices can be used to treat local water until relief organizations set up more permanent water provision methods. One such POU technology is PŪR® Purifier of Water, a combined coagulation/flocculation and disinfection chemical treatment sachet produced by Procter & Gamble. PŪR® has been shown to treat contaminated water to meet water quality standards and guidelines set by the U.S. EPA for water purifiers and by the World Health Organization and The Sphere Project for emergency relief. However, the standard two-bucket method of use for PŪR® has two primary drawbacks: (1) the need for appurtenances that may not be readily available in disaster relief situations and (2) lack of a means to protect treated water from re-contamination post-treatment. An alternative to the two-bucket method is a waterbag system under development at the California Polytechnic State University, San Luis Obispo. The waterbag is a ten-liter plastic bladder with integrated filter that incorporates an all-in-one approach to drinking water treatment during emergencies. In previous studies, the first version of the waterbag consistently met World Health Organization and The Sphere Project emergency drinking water guidelines, but did not meet the pathogen reduction requirements of the U.S. EPA Guide Standard and Protocol for Testing Microbiological Water Purifiers.
A second (Mark II) version, with internal mixing baffles and a microfilter, was developed to overcome the inability of the first design to meet the U.S. EPA guidelines. The main purposes of the research presented herein were to (1) optimize the method of use and baffle configuration for the improved Mark II version of the waterbag, (2) determine ability of the waterbag to treat test waters with challenging initial water quality conditions, and (3) test the ability of the Mark II design and optimized method to meet the U.S. EPA Guide Standard and Protocol for Testing Microbiological Water Purifiers.
For the first and second objectives, the main metric of treatment performance was the extent of flocculation, which was characterized by the turbidity of waterbag supernatant after 30 minutes of settling. The waterbag procedure was varied in several ways. The variables tested were mixing duration, mixing motion type, and the effect of a mixing delay. Several waterbag baffle designs were tested to determine the physical configuration of the waterbag which resulted in best turbulence during mixing. In addition, experiments were performed to test the ability of the Mark II waterbag to treat waters with various initial qualities, such as high organic carbon content and elevated E. coli concentrations. The results of these experiments helped to prepare for a final test in meeting the pathogen removal requirements of the U.S. EPA Guide Standard and Protocol for Testing Microbiological Water Purifiers.
The procedure determined to be optimal for the Mark II waterbag treatment included five minutes of mixing using rapid 180° twisting motions at a moderate frequency of seventy 180°-twists per minute. The optimal baffle design was a 12.7 cm-wide internal mixing baffle with two cut circular holes for the promotion of turbulence during mixing. The desired post-treatment chlorine residual was achieved for different durations depending on initial organic carbon concentration. Optimal PŪR® dose to provide pathogen removals required by the U.S. EPA in the presence of Challenge Water conditions was two sachets per 10 L of water to be treated. The optimization of these design and operational procedures led to the ability of the Mark II waterbag to meet the pathogen, turbidity, pH, and non-microbiological constituent removals required by the U.S. EPA, The Sphere Project, and World Health Organization for emergency relief.