Enhancement of the Performance of a Biosand Filter Using Pumice Media and Natural Coagulant Dosing

Biosand filters (BSF) are an effective point of use technology for drinking water treatment. However, drawbacks of BSFs include slow ripening and high head losses. This paper discusses two modifications that address these drawbacks: (1) use of pumice to enhance hydraulic performance, and (2) dosing of Moringa oleifera to expedite ripening. Three filter columns with sand, pumice, and a pumice/sand beds were studied for over 3 months. Head loss, filtration rate and water quality parameters were monitored. In the first few cycles, the pumice and the dual media columns had 2-3 times greater filter run lengths compared with the sand column. The pumice column consistently had the lowest product water turbidity (< 0.23 NTU). On the other hand, the sand column had the highest organic removal (about 14.7%). The study showed that pumice had better hydraulic performance while achieving better turbidity removal. M. oleifera dosed columns ripened faster, however, continuous dosing resulted in excessive growth of biofilms, which shortened filter run times. The improvements in hydraulic performance and ripening due to the modifications can help improve acceptability of the technology by users. Further studies are necessary to find optimum doses and duration of M. oleifera application. Hydraulic modelling of the BSF showed that the experimental results (head loss and filtration rate) from the sand BSF corresponded well with model results. For pumice; however, the experimental results did not fit the model curves. This may be explained by the fact that internal pore spaces in pumice are not accounted for in the model.