Acoustic aggregation of particles in acoustic levitation is a well-known phenomenon. However, it is only well described in the dilute regime, i.e. when particles do not interact with each other. In this study, we first demonstrate that the acoustic focusing speed can be significantly increased when dealing with particle aggregates. These results suggest that acoustic aggregation can be more efficient when dealing with relatively dense suspensions. This principle is successfully applied to microalgae suspensions. It is shown that microalgae harvesting can be accelerated without power increase using acoustically induced flocculation if the initial concentration is sufficiently high. This demonstrates that a cost-effective industrial process for acoustic microalgae harvesting is possible.