Method for determining residual total suspended solids retained in pressurized sand filter media

Residual solids retained in the sand bed after backwashing are commonly used to assess the cleaning efficiency of pressurized sand filters employed in irrigation systems. However, procedures originally proposed for slow sand filters are not fully suitable for pressurized filters because these systems differ in operating conditions and bed configuration. In this study, an adapted procedure was developed to determine residual total suspended solids (TSSf) retained in pressurized sand filter media after backwashing. The method involves collecting the upper 0-100 mm layer of the sand bed, followed by drying, homogenization, controlled subsampling, sequential washing cycles under rotational agitation, and determination of suspended solids by vacuum filtration with 0.45 μm glass microfiber filters. Method validation included analysis of grain-size representativeness and reproducibility. The grain-size distribution curves obtained from different subsample masses showed Pearson correlation coefficients higher than 0.99 (p < 0.01), while coefficients of variation for TSSf determination remained below 20% for all evaluated samples. The procedure allows direct evaluation of residual solids retained in pressurized sand filters after backwashing and may be useful for comparing backwashing conditions and assessing filter cleaning performance in irrigation systems. The main features and applications of this method are as follows: • Quantification of residual solids retained in pressurized sand filter media after backwashing. • Representative sand subsampling and extraction of retained solids using sequential washing cycles. • Evaluation of backwashing performance in irrigation sand filters.