The influence of pre-treatment of polyurethane sponge installed in the biologically stabilized biosand filter

Household slow sand filters are considered simple, efficient, and low-cost solutions for accessing drinking water in isolated communities. To ensure safe handling, it is essential for their operation to be simple and reliable, while requiring the lowest possible frequency of maintenance, as this will be carried out by the residents themselves. This is the first study to evaluate the performance of intermittent biosand filters (BSFs) using a polyurethane sponge positioned on top of the filter media, acting as a physical pre-treatment barrier. Two filters were compared: one with the sponge (BSF-S) and one without (BSF), analysing the effects on water quality, cleaning frequency, and material replacement. In the BSF-S, two sponges were used sequentially: BSF-S1 operated for 344 days and, after its replacement, BSF-S2 operated for an additional 189 days, while the BSF operated continuously for 533 days. No significant differences were observed among the different filter configurations in terms of turbidity, dissolved oxygen, and apparent colour. However, the study water differed significantly from all filtered samples (p < 0.05), confirming filtration effectiveness. In contrast, regarding cleaning frequency, BSF had a total of 11 filter runs, while BSF-S recorded 5 filter runs (3 with BSF-S1 and 2 with BSF-S2), demonstrating that the presence of the sponge fulfilled its role in physical pre-treatment. Incorporating the sponge at the top of the filter media improved operational performance by reducing maintenance needs without compromising water quality, supporting its use in remote households.