In this study, the separation behaviors of particles in highway rainfall runoff using a Ø7.5 cm hydrocyclone were examined. The volume fraction and the total suspended solids concentrations in the overflow and underflow from the hydrocyclone were analyzed. The results indicated that the overflow volume fraction increased with increasing operational pressure, but decreased with decreasing ratio of underflow outlet to inlet sizes (Du/Di), while the underflow volume fraction showed contrary behavior. The TSS concentration ratio between the overflow and inflow (TSSover/TSSin) decreased as a function of the operational pressure, while the corresponding ratio of underflow to inflow (TSSunder/TSSin) increased. There was no visible difference in the TSSover/TSSin ratio with increasing Du/Di ratio but the TSSunder/TSSin decreased sharply. The particle removal efficiency was affected mainly by the particle size. The hydrocyclone can work well using 1.6 m natural water head, and it is more space saving and more efficient in the separation of fine particles than the sedimentation method.
Keywords: highway particulates, hydrocyclone, particle number concentration, rainfall runoff, separation efficiency