Abstract: A system for changing a concentration of at least one group of particles in a fluid, which includes a first container and a second container; a first transfer device and a second transfer device, and an element for keeping the volume of fluid in the first and second containers constant. The first container is fluidly connected to an inlet of the first transfer device, and the second container is fluidly connected to an inlet of the second transfer device. The first and second transfer devices include a chamber associated with at least one acoustic wave generator for generating acoustic waves within the chamber; at least two outlets including a first outlet for fluid enriched with the particles and a second outlet for fluid depleted of the particles; the first outlet being fluidly connected to the first container and the second outlet being fluidly connected to the second container.