Investigation of mini-hydrocyclone performance in removing small-size microplastics

Large amounts of microplastics (MPs) have been found in rivers and oceans, bringing great harm to aquatic animals, plants, even human beings. However, the effective removal method of MPs, especially those with small sizes (5–20 μm) is still lacking. This work presents mini-hydrocyclones to remove 10 μm (average size) diameter MPs. The removal performance of nine mini-hydrocyclones with different diameters of spigot and vortex finder is examined experimentally and numerically. The performance of the designed cyclones is evaluated in terms of recovery, water split, concentration ratio and pressure drop. The results show that mini-hydrocyclones are applicable to removing small-size MPs with the maximum concentration ratio at 2.16 and the particle recovery at 51%. The flow characteristics inside the mini-hydrocyclones are analyzed in detail. It is shown that the distributions of water axial velocity and radial velocity could collectively affect the behaviors of small-size MPs in mini-hydrocyclones. Specifically, a larger amount of water split could entrain more fine particles to underflow. Meanwhile, a less frequent alternation of radial velocity between the positive and negative directions on the same side of the cyclone should benefit the removal of small-size MPs.