Research on multi-factor regulation of expansion characteristics in upflow activated carbon filters

The expansion degree (ED) of upflow activated carbon (AC) filters is a critical hydraulic parameter governing contact efficiency and carbon loss, yet its dependence on multiple factors-including particle size, material, shape, temperature, and aging-remains inadequately quantified. This study provides a first systematic quantification and mechanistic analysis of these dependencies through controlled experiments. Results reveal particle size as the dominant factor: at 12 m/h, 40×60 mesh AC posed a severe carbon loss risk (72% ED), whereas 20×40 mesh AC maintained an optimal range (35%∼40%). The distinct coupling mechanisms of material and shape were uncovered; crushed AC exhibited >30% greater fluidizability than cylindrical AC. Furthermore, less dense coal-based crushed AC (455 g/L) showed 6% higher ED than denser coconut shell AC (589 g/L), with this gap widening to 18% as flow increased. Operational impacts were also quantified: a 5 °C temperature rise reduced ED by 2.5%-3%, while aged AC (5%∼15% higher wear) exhibited a lower minimum fluidization velocity, increasing ED at constant flow. Notably, microbial growth was found to exert a negligible impact on the overall expansion degree, underscoring physical and hydraulic parameters as the primary drivers of bed expansion. Based on these insights, 20×40 mesh coal-based crushed AC at 12 m/h is recommended to ensure operational stability. The study further delivers modified fluid mechanics formulas, providing predictive tools for terminal settling velocity and filter ED to guide optimized AC selection and filter design in water treatment practice.