Stimulation of aerobic and anaerobic biological processes by ultrasound

Operators of wastewater treatment plants first of all are responsible for the required good quality of the effluent before it is discharged to the environment. Today attention is being shifted more and more to optimize the operation of treatment plants not only to reduce energy consumption or other costs in an economic sense but with regard to ecological aspects like reduction of greenhouse gas emissions. So the challenge arises to improve the well established biological treatment processes targeting these goals without decreasing the quality of the effluents. First full-scale applications of high power ultrasound appeared more than ten years ago in Germany for the pre-treatment of waste activated sludge prior to anaerobic stabilization. Today about 80 treatment plants worldwide are equipped with this technology and provide confirmation on the success of this approach. Research is still carried out to better understand how ultrasound manifestations can impact also on aerobic biomass. This article reports on fundamental research as well as full-scale experience for the following applications:  Improving N removal  Reducing excess sludge  Combating filamentous microorganisms