In order to industrialize an ultrasonic process for wastewater treatment, several works were undertaken. The first one was the study of pentachlorophenol degradation [E. Gonze, Y. Gonthier, P. Boldo and A. Bernis, Can. J. Chem. Eng. 75 (1997) 245]. Association of high-frequency ultrasound transducers was investigated [E. Gonze, Y. Gonthier, P. Boldo and A. Bernis, Entropie 204 (1997) 21] and the mapping of ultrasonic fields in various reactors was studied [E. Gonze, Y. Gonthier, P. Boldo and A. Bernis, Chem. Eng. Sci. 53 (1998) 523; V. Renaudin, N. Gondrexon, P. Boldo, C. Petrier, A. Bernis and Y. Gonthier, Ultrasonics Sonochem. 1 (1994) S81]. The third step presented here consists of considering the ultrasonic process as a preoxidation treatment before a classical biological purification. During the ultrasonic irradiation of a sodium pentachlorophenate solution (NaPCP), the concentration of NaPCP, the acute toxicity effects on bacteria (Vibrio fischeri) and on daphnids (Daphnia magna) as well as the biodegradability of the pollutant solution were simultaneously monitored. Experimental results provide evidence that an ultrasonic treatment is an efficient preoxidation step.