Hydrocyclones enhance oil-water separation efficiency compared to conventional separation methods. An efficient collision detection scheme with N p ln N p dependency on the number of particles is proposed. The scheme is developed to investigate the importance of particle-particle interaction for flow and particle behavior in dilute oil-water separators. However, the proposed scheme can also be used for efficient multigrid soft collision calculation with long-range particleparticle interaction models. The collision detection scheme is first validated using a case of settling spheres. Subsequently, the scheme is applied to a simplified flow field, similar to the flow fields observed in hydrocyclones.