Effects of physical disturbances on media and performance of household-scale slow sand (BioSand) filters

Point-of-use (POU) water treatment provides households in rural and remote communities with a means of obtaining greater control over their water quality and its effects on human health. One of the most prevalent POU interventions, the BioSand filter (BSF), is a household-scale, intermittently operated slow sand filter used by over 300,000 households. The sand and gravel media within BSFs can be housed in concrete (cBSF) or Hydraid plastic (pBSF) bodies, with the latter becoming increasingly popular due to their portability, durability, and anticipated scalability. This study evaluated whether pBSFs, which are lighter and thinner than their concrete counterparts, can maintain their integrity and performance after being subjected to disturbances that could occur in a typical household. Eight pBSFs and two cBSFs were run in parallel for 13 weeks, and three disturbances – one-time filter movement, one-time side impacts, and daily bucket impacts – were applied. Moving and side impacts affected pBSFs more dramatically than cBSFs, causing marked decreases in sand column height (6–29 mm decrease, p < 0.001) and decreases in maximum initial flow rate (18–84% decrease, p < 0.001). Brief spikes in pBSF effluent turbidity (0.98–15.2 NTU greater than mean effluent levels) also occurred immediately after disturbances.