The effort was made to screen the effect of ultrasonic waves on the purification of waste water. The ultrasonic treatment was found to be effective for the waste water purification. It was found that low intensity ultrasonic irradiation can improve the microbial activity and thus it can be used to enhance the biological treatment of wastewater and increase the treatment efficiency by improving microbial activity in the biological reactor. The biological effects of low intensity ultrasound and the mechanisms associated with the enhancement of biological activity were discussed. The applications of ultrasonic waves in bioengineering and biochemical studies are comprehensively summarized.