An ultrasonic treatment chamber and a process for ultrasonically treating a liquid in an ultrasonic treatment chamber include an elongate, generally tubular housing having an inlet and an outlet spaced longitudinally from the inlet. Liquid is directed into the housing at the housing inlet for longitudinal flow within the housing to the housing outlet. Mechanical ultrasonic vibration is generated within the housing in direct contact with the liquid flowing within the housing, with the direct contact being upstream of the housing outlet. A standing acoustic wave is produced within the housing with the standing acoustic wave having a node spaced longitudinally from the housing outlet.