Abstract: A freeze concentration method separates the nucleation and the growth processes at least to the extent necessary to enable nucleation and crystal growth to occur at different temperatures. Nucleation, however, is triggered by a sonicator, i.e., ultrasonic radiation. This provides excellent control of the process since the variables of the input sonic energy are adjusted easily. Most importantly, the use of ultrasound permits nucleation at low supercooling. The consequences of this are: an inexpensive plain--as opposed to the more complex and expensive scraped-surface--heat exchanger can be used since the coolant temperature is only slightly lower than that of the solution, preventing ice scaling in the heat exchanger; the higher coolant temperature leads to savings also in the operation costs. In addition ultrasonic nucleators are easily scaled-up to treating the large-volume effluents from industrial plants. The only way to scale-up scraped-surface nucleators is by using multiple nucleators in parallel.