Effect of geometric variations in TPMS biocarriers on hydrodynamics in MBBR systems: a computational approach

Abstract Biocarriers play a critical role in enhancing biofilm growth and mass transfer in Moving Bed Biofilm Reactor (MBBR) systems. Among various designs, triply periodic minimal surface (TPMS) structures, such as gyroids, have emerged as promising biocarriers due to their high surface area-to-volume ratio, uniform porosity, and efficient flow characteristics. Despite their potential, the influence of geometric variations in gyroid biocarriers, including diameter and pore size, on hydrodynamic performance remains underexplored. In this study, a numerical investigation was conducted to assess the impact of gyroid biocarrier geometry on key hydraulic parameters, including air volume fraction, water velocity, flow patterns, and turbulence kinetic energy (TKE). Six gyroid configurations with varying diameters (20 mm, 30 mm, and 40 mm) and cell sizes (5 mm and 10 mm) were designed and simulated using computational fluid dynamics (CFD) techniques. The results revealed that smaller gyroids with narrower pores generated higher turbulence and peak water velocities, enhancing mixing and mass transfer but posing risks to biofilm stability due to increased shear forces. Conversely, larger gyroids with wider pores exhibited smoother and more uniform flow patterns, improved air distribution, and reduced turbulence, providing a stable environment for biofilm growth while slightly compromising mass transfer efficiency. These findings offer valuable insights into optimizing biocarrier design for improved performance and operational efficiency in MBBR systems.