Available at: https://digitalcommons.calpoly.edu/theses/919
Date of Award
MS in Civil and Environmental Engineering
Civil and Environmental Engineering
Relief organizations and governments strive to provide safe drinking water to natural disaster survivors as quickly as possible. However, drinking water is typically provided either as bottled water or via mobile water treatment equipment, both of which can be difficult or expensive to transport rapidly into disaster zones. An alternative is the waterbag point-of-use treatment device developed at Cal Poly that allows survivors to produce safe drinking water from contaminated local sources. The waterbag is a 10-L bladder designed for use with Procter & Gamble Purifier of Water (PŪR®) sachets, which contain coagulant and chlorine compounds. Following treatment with PŪR®, treated water in the waterbag is flowed through an outlet port to a filter, primarily for parasitic cyst removal. Currently, the commercial version of the waterbag uses an effective but expensive hollow-fiber membrane microfilter (>$10 each). This cost will likely decrease the use of the waterbag by relief organizations responding to large disasters. The goal of the present thesis research was to develop a novel, low cost (~$5), effective, low-profile filter to be used with the waterbag in large-scale disaster relief. This new filter is referred to as an envelope filter due to its geometry and size.
Various prototype envelope filters were constructed using layers of nonwoven polypropylene filter cloth. Two types of cloth were used: a nominally-rated 1-µm pore size cloth and an absolute-rated 1-µm cloth. The filters tested were both internal and external to the waterbag and of various geometries. Filters were attached to the waterbag and used to filter defined test water after it had been treated with a PŪR® sachet. Test water for design experiments consisted of tap water with addition of standard dust (to increase turbidity) and seasalts (to increase salinity). In addition to this basic test water, mock U.S. EPA Challenge Water #2 with added bacteria and cyst surrogates (fluorescent microspheres) was used to evaluate the filter prototype designs prior to testing according to U.S. EPA Guide Standard and Protocol for Testing Microbiological Water Purifiers in a commercial laboratory.
The filter design and mock challenge experiment results indicated that a 2-ply filter with one nominal and one absolute layer was the optimal filter design. In the mock U.S. EPA challenge tests, a flowrate of 20 mL/min allowed this filter met the turbidity, bacteria, and microsphere removal requirements determined by the WHO and The Sphere Project for emergency drinking water treatment as well as the U.S. EPA Guide Standard and Protocol for Testing Microbiological Water Purifiers.. This filter design was further tested using the U.S. EPA Challenge Water #2 with triplicate waterbags at the U.S. EPA-certified BioVir Laboratories in Benicia, Calif. All three waterbags with envelope filters met the recommendations for turbidity (<5 >NTU) and for virus removal (>4-log removal). Two of the three waterbags met the bacteria and microsphere removal requirements (>6- and >3-log removal, respectively). The failure of one of the prototypes to meet the requirements could have been due to improper setting of valve that throttled the flowrate through the filter or due to a slightly leaking hose pinch valve. Future work should include incorporating more reliable valves and improving the envelope filter design and materials to achieve higher allowable flowrates.