BIOSAND FILTER REDESIGN FOR HOUSEHOLD-SCALE WATER TREATMENT IN UNDEVELOPED REGIONS

The biosand filter (BSF) made from concrete, sand, and gravel can remove nearly 100% of harmful contaminants from drinking water, and over 650,000 are estimated to have been distributed to undeveloped regions of the world since its introduction in the early 1990s. Despite its widespread popularity and successful contaminant removal rates, there are two inherent gaps in the traditional BSF design: (1) the design is oversized relative to its performance, and (2) the heavy design (350-lbs. per filter) makes it challenging to reach areas only accessible by plane, boat, or all-terrain vehicle (i.e., the design cannot fully reach the audience in need). The main objective of this study was to characterize the fluid flow and bacterial removal capabilities of two alternative designs of the v.10 CAWST biosand filter using a finite element approximation of Darcy’s law with discrete time steps and a slow sand filtration (SSF) model. A 40% and 70% reduced height filter from the traditional BSF were characterized while conserving the total filter area, reservoir volume, and vertical dimensions of the biolayer. Input parameters into the hydraulic and slow sand filtration modeling included fluid velocity, grain size of the filter media (coarse, medium-coarse, medium, and fine sand), filter bed depth, and maturation age of the biolayer. Results suggested near 100% removal for the 70% reduced height design using medium-coarse, medium, and fine sand at full depth regardless of the biolayer maturation age. The 40% reduced height redesign exhibited slightly lower values with 100% removal for only medium and fine sands at full depth after a two-week biolayer maturation period. The traditional filter design displayed the lowest efficiency of the three filters with 100% removal only using fine sand. The preliminary contaminant modeling study indicated both redesigns removed a greater portion of bacteria from the influent water compared to the traditional BSF for each media used, primarily due to the increased residence time within the filter and increased surface area of the biolayer. These results can be used to improve the overall efficiency, ease of use, and accessibility of the biosand filter for communities living with inadequate water quality.