Pretreatment using followed by household slow sand filters: technological alternatives for supplying isolated communities.

Household slow sand filter (HSSF) performance in continuous and intermittent flows was evaluated when influent water was treated with a natural coagulant extracted from . The water under study, used as influent, had a turbidity of 111 ± 17.3 NTU. When clarifying the water with , the best condition obtained was 30  mg L in natural pH (without correction), generating clarified water with turbidity satisfactory to filters operation (7.83 ± 2.32 NTU). The results indicated a better performance of continuous flow HSSF in turbidity removal (79.2% ± 8.39%) and higher efficiency of intermittent flow HSSF in the removal of (2.86 log ± 0.79 log for 12  h pause period and 2.41 log ± 0.42 log for 4  h pause period). For the sake of comparison, the evaluated HSSFs had the same production (60 L day). The impact on the interruption of the 96-h feed into the HSSFs was analysed and the results indicated a significant change in the quality of the filtered water after resuming the operation. This fragility of technology must be considered when it is implemented as lack of water can be a reality in the target communities. Acute toxicological assays with larvae showed no toxicity for pretreated and filtered water; however, more testing should be performed.