Hydraulic Loading Rate Effect on Removal Rates in a BioSand Filter: A Pilot Study of Three Conditions
2012
Kennedy, T. J. | Hernandez, E. A. | Morse, A. N. | Anderson, T. A.
Safe drinking water is a luxury to approximately 800 million people worldwide. The number of people without access to clean water has been reduced, thanks to technologies like the biosand filter (BSF), an intermittently operated household scale slow sand filter. The BSF outlet (control diameter 0.5â³) was modified in this study by reducing the outlet diameter (0.37â³ and 0.25â³) to determine the effects of hydraulic retention time on removal rates. Filters were dosed with 20Â L of spiked lake water daily and observed for pH, dissolved oxygen (DO), fecal coliforms (FC), turbidity, nitrate, nitrite, sulfate, and ammonia until initial flow rates dropped below 0.2Â L/min. Consistent with previous studies, the average turbidity was reduced to below 1Â NTU; the average DO was reduced by 45Â %. No significant difference was observed between the modified BSFs and the control BSF. Removal efficiency of FC was not significantly different between the modified BSFs (93.3Â % and 91.9Â %) and the control BSF (89.6Â %). Mean FC reduction during the startup period (17Â days) was significantly greater in the modified 0.25â³ BSF when compared with the control during the same time period. After the first 17Â days of the experiment, the average reduction efficiency of all filters was >97Â %. While source water was below guideline values for nitrate, nitrite, ammonia, and sulfate during the course of the experiment, total nitrogen reduction was observed. The reduction indicates that the plastic BSF is capable of accomplishing limited denitrification during the filtering process.
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