Assessment methodology of backwash in pressurized sand filters

The objective of this study was to apply a methodology based on sampling sand from contaminated filter beds, to evaluate the performance of the backwash process in pressurized sand filters used in irrigation. Backwash trials were conducted in an experimental module with three new sand filters of the same commercial model. The evaluations were conducted after filtration processes performed using four filtration rates and three separate sand particle sizes (fine - 0.55 mm; medium - 0.77 mm, and coarse sand - 1.04 mm diameter), repeated in three subsequent cycles. After reaching a fixed expansion of 25% of the filter bed height, the backwash processes were performed for 15 min. Backwash cleaning efficiency was evaluated in all trials based on the mass of removed solids for different filter bed layers and throughout the entire filter bed. The backwash assessment methodology is effective and has potential to be a practical tool for farmers in the evaluation of the performance of pressurized sand filters used in irrigation.