Experimental study on plastic retention & hydraulic loss at drum racks

This study investigates macroplastic retention and the hydraulic performance at elevated drum racks, thereby providing essential data for engineering design of sustainable river clean-up technologies. Prototype-scale experiments were conducted to analyse the interaction between the rack and 23 plastic particle types of different polymer and shape characteristics under varying hydraulic conditions. Hydraulic analysis revealed system-scale head loss coefficients ranging between 2 and 4.5 for the elevated drum-rack configuration, exhibiting a distinct Reynolds-number dependence that differs from classical planar trash rack formulations. The complex drum geometry caused head loss to depend on submergence ratio and bar spacing (sb), which also affected plastic fragment retention. While 3D items were effectively retained, fragment retention was dependent on particles’ properties and hydraulic load. Specifically, depth distribution and flexural rigidity were identified as relevant factors for the retention of suspended fragments. Particle orientation, reorientation and deformation processes strongly affected retention ratios of smaller fragments (particle length Lp < 0.1 m) within the transitional geometric regime of 2 < Lp/sb < 4. Beyond this zone, high retention ratios were achieved largely independent of particle type. This study demonstrates that retention ratios strongly depend on the particle transport regimes and can be optimized through appropriate configuration of cleaning systems, balancing effective retention and hydraulic impact.