Vicki Chou, Nick Farino, Chenhao Qi, Rui Zhang
Abstract
The goal of StaRS Backwash is to determine the sand grain sizes and distribution for the most efficient and effective backwash in the stacked rapid sand filters. The proper fluidization velocity for efficient backwash must first be determined. An expansion ratio of 1.3 is the current standard for the sand bed during fluidization. A sand size ratio below 1.5 is suggested for minimal segregation during backwash. The team ran experiments with sands sized by sieve combinations of 2040 and 3040 at different backwash velocities to test for segregation. Through the experiments, the team found that the 2040 sized grains always segregated at all backwash velocities, but the 3040 sand, which is under the 1.5 sand size ratio, did not segregate below backwash velocities of 15 mm/s. Current AguaClara plants use a backwash velocity of 11 mm/s, so using 3040 sand would be a good option because it should not segregate according to the data collected.
