Sustainable sand filtration strategies for microplastic removal in irrigation water

Microplastic contamination in irrigation water poses a growing threat to agricultural ecosystems. While sand filters are widely used in irrigation systems, their efficiency and optimization parameters for microplastic removal remain insufficiently explored. This study evaluated the performance of sand filters with different media sizes (0.5-1.0, 1.0-1.5, and 1.5-2.0 mm) in removing microplastics of various morphotypes (fibers, fragments, particles) and sizes (500-5000, 200-500, 100-200 μm) from irrigation water, as well as backwash efficiency at varying flow rates (0.007-0.017 m/s) and durations (1-10 min). Results showed that the removal efficiency increased as the filter media particle size decreased, achieving removal rates of 89.9 %, 79.9 %, and 55.6 % for 0.5-1.0 mm, 1.0-1.5 mm, and 1.5-2.0 mm media, respectively. While sand filtration was highly effective for larger microplastics (81 % removal rate for 500-5000 μm), its efficiency declined significantly for smaller fractions, with only 17.3 % removal for 100-200 μm particles. Fibrous microplastics (∼85 %) were removed more effectively than particulate forms (∼30 %). Furthermore, backwashing performance improved with higher flow rates, reaching optimal efficiency at 0.017 m/s, while a 3-min duration was sufficient to maintain filter cleanliness without excessive energy consumption or media loss. This study recommends using 0.5-1.0 mm filter media combined with a backwash flow rate of 0.017 m/s and a 3-min backwash duration for optimal microplastic removal. Additionally, secondary filtration is suggested to enhance the removal of small-sized and particle-shaped microplastics. These findings provide critical operational insights for sand filtration systems, contributing to effective microplastic mitigation in agricultural irrigation and promoting sustainable land management.