Comparison of Laboratory and Field Methods for Biosand Filter Sand Characterization

The Centre for Affordable Water and Sanitation Technology (CAWST) (2012) recommends size standards for the effective size (ES) and uniformity coefficient (UC) of filtration media in biosand filters (BSFs) to ensure optimal effluent flow rates and contaminant removal. The recommended, laboratory-determined ES and UC ranges are also advised for field use despite differences in mass- versus volume-based protocols and no studies comparing laboratory versus field protocols to date. ES and UC values of five sand samples were compared using mass- versus volume-based measurements and lab versus field protocols. Results suggest that the use of mass- or volume-based measurements generally does not affect the ES or UC of a given method (except in cases where the density of sand grains varies significantly across the size distribution range). Differences between laboratory and field protocols, however, were found to affect ES and UC values by up to 24%. Overall, differences in laboratory and field sand size determination protocols should be further evaluated to ensure standardized field construction of BSFs and to limit potential impacts to filter efficacy and sustained, household filter usage.