Characterization and optimization of a biosand filter
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More than 800 million people worldwide do not have access to clean drinking water. The number though high, has recently been reduced thanks to technologies like the biosand filter (BSF), an intermittently operated household scale slow sand filter. To date, studies have documented removal of microbiological water quality parameters and some chemical parameters. Few studies have sought to improve upon the current design of the BSF, examine its limits, or investigate its ability to remove emerging contaminants. The goal of this work was to examine a modification of the BSF, determine its operating limits, and investigate the ability of a BSF to remove emerging contaminants. Modification of the BSF was achieved by decreasing the outlet spout diameter, increasing the BSF hydraulic retention time. Turbidity, fecal coliforms (FC), dissolved oxygen (DO), pH, total organic carbon, and nitrogen data were measured in the influent and effluent water. Overall, the modification did not significantly improve water quality over the course of the experiment, though significantly greater removal of FC was observed during the startup period when comparing the 0.25” BSF to the control (unmodified) BSF. Initial startup, recovery after cleaning, maximum number of users served, and an extended pause period of the BSF were examined using the same water quality parameters as the optimization study to determine the BSFs operational limits. Results of this study indicated that the initial startup may take up to 27 days to achieve 1 log reduction of fecal coliforms, while only 17 days were needed after the first cleaning of the BSF. The maximum number of users effectively served was determined to be six, as at volumes greater than this water quality was significantly worse. Water quality was similar to the recovery period when the extended pause period of 1 week was examined, reiterating that the BSF must be used multiple times per week for best results. The removal of three endocrine disrupting compounds, estrone (E1), estriol (E3), and 17α-ethinyl estradiol (EE2) was examined by spiking a high concentration (5 mg/L) into daily BSF feed water. Results indicate the percent removal efficiency in the BSF is similar to that in slow sand filters, though the mass removal rate in the BSF was orders of magnitude greater. When the effluent was treated with household bleach, removal increased based upon Cl- dose. The BSF is a valuable technology for improving water quality, and should be used along with disinfection to protect user health.