Miquel Duran-Ros

Accurate modeling of filter head losses is essential for the optimal design and management of microirrigation systems, particularly when treating reclaimed water. In this study, Gene Expression Programming (GEP) was applied—for the first time in the literature—to develop predictive models for head losses in disc, screen, and sand filters operating with effluents. A k-fold cross-validation procedure was adopted to rigorously evaluate model performance under both direct learning (DL) and transfer learning (TL) scenarios. GEP models achieved Scatter Index (SI) values ranging from 0.049 to 0.071 for direct learning, consistently outperforming existing empirical equations when a fair comparison using independent test sets was conducted. Under transfer learning, screen filter-derived models demonstrated superior transferability to both sand and disc filters (SI 0.058–0.101), while combining disc and sand filter data improved predictions for screen filters (SI 0.064–0.069). These results provide a novel, data-driven framework for filter head loss estimation that can support microirrigation system design when filter-specific training data are unavailable.

Drip irrigation is a widely spreading technology, mainly due to its high water-use efficiency. This technique requires a filtration process that exhibits cyclical behavior where both filtration and backwashing modes repeat. In filtration, pressure increases with time due to the particle retention up to a preset value. In backwashing, the flow is reversed to clean the filter. Different design strategies to reduce energy and water consumption have been proposed, but their practical effects are not yet clear. Here, a global analysis method based on the classification of the time evolution of the pressure curve in filtration mode was developed. Energy and water use efficiency indices were defined and evaluated under different scenarios. More design options can be undertaken to reduce the consumption of energy than of water. The decrease in the pressure drop for clean filter conditions arose as the best option to increase energy efficiency (in a realistic scenario, a reduction of 20% in the pressure drop with tap water resulted in a reduction of 7.6% in the energy consumption per volume of filtered water). Precise backwashing times and flow rates were essential to improve water use efficiency (e.g., doubling the backwashing time led to a 4.5% decrease in water use efficiency).

Sand media filters are especially recommended to prevent emitter clogging with loaded irrigation waters, but their performances rely on backwashing. Despite backwashing being a basic procedure needed to restore the initial filtration capacity, there is a lack of information about the solid removal efficiency along the media bed depth. An experimental filter with a 200 mm silica sand bed height was used to assess the effect of two operation velocities (30/45 and 60/75 (filtration/backwashing) m h⁻¹) and two clogging particles (inorganic sand dust and organic from a reclaimed effluent) on the efficiency of backwashing for removing the total suspended solids retained in different media bed slices. The average solid removal backwashing efficiency was greater with organic particles (78%) than with inorganic ones (64%), reaching its maximum at a 5–15 mm bed depth. A higher operation velocity increased the solid removal efficiency by 16%, using organic particles, but no significant differences were observed with inorganic particles. The removal efficiencies across the media bed were more uniform with organic particles (63–89%) than with inorganic (40–85%), which makes it not advisable to reduce the media height when reclaimed effluents are used. This study may contribute to future improvements in sand media filter design and management.

Pressurized sand media filters are commonly used in drip irrigation systems to prevent emitter clogging. However, the performance of these filters may be improved with more information about the retention of solids at different bed depths under different filter operation conditions and irrigation water sources. In this study, experiments in a scaled sand media filter were conducted to clog the filter with two different filtration velocities (30 and 60 m h⁻¹) and two-particle types (inorganic from A4 coarse sand dust and organic from a reclaimed effluent). The suspended solids retained in slices of 5 mm (in the first 20 mm of the bed) and 20 mm (from 20 to 200 mm depth) thick were determined following the van Staden and Haarhoff (2011) procedure. The solids retained in each slice per mass of media were significantly (p < 0.05) affected by the interaction between the filtration velocity, the bed depth, and the particle type. The solids retained in the first 5 mm of the bed were significantly higher than at other depths. Moreover, inorganic solids were retained more in upper slices than organic ones. Therefore, media depths may be adjusted depending on the irrigation water source to optimize media use.