The recently developed flexible fiber filters (3Fs) are modular filtration units, which can satisfactorily remove solids at high filtration rates. Normally built with polyamide fibers, it is supposed that natural fibers can be used alternatively. This paper evaluated the performance of 3Fs using as filtering media sisal fibers in lieu of the polyamide ones. The sisal fibers were evaluated by means of scanning electronic microscopy and through solubility assays in hydrochloric acid and sodium hydroxide. Six filters with 28 mm of internal diameter were built, varying their length (25, 60, and 100 cm) and porosity (85 and 93%). The filtration system was fed with synthetic water, in-line coagulation was applied by the addition of 22.5 mg/L of aluminum sulfate, and filtration rates from 20 to 80 m/h were evaluated. Only the filter with 100 cm of length and 85% of porosity could work within the limit established (1 NTU), operating at 20 and 40 m/h. For all the studied configurations, the pressure drop was considerably low (less than 0.5 mH2O) when compared with 3Fs built with polyamide, which shows the potential of using this kind of filter as pre-filtration units or for less restrictive uses. This study showed that 3Fs can be adapted to include different configurations and materials, reducing their cost and making them appropriate for low-income countries.

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