Low-frequency high-power ultrasound is an effective method for the separation of bacteria cells because of its strong mechanical shear stresses. Low doses of energy produce here at first a de-agglomeration; with high intensities and long exposure times the cell wall of the bacteria can also be so damaged that it causes their death. Since the required energy input is very high in the latter case, the disinfection of wastewater only with ultrasound does not yet seem economically viable.

In this work, it was investigated whether the efficiency of UV can be improved by a combined application of ultrasound and UV. Even in lab-scale tests with well clarified wastewater samples (TSS: 14 mg/L) a strong tailing effect could be observed after exposure to UV irradiation. However, preceding sonication for just 5 s resulted in a dispersion of bacteria/suspended matter and hence in a notable increase of bacteria's vulnerability to UV: Efficiency was improved by up to 1 log unit. Pilot-scale tests at a municipal sewage treatment plant (volumetric flow: 2 - 4m³/h) showed similar effects, although less pronounced. At higher concentrations of suspended matter ultrasonic pre-treatment had a more definite effect on the improvement of UV efficiency.

Furthermore, the application of chlorine was examined to find out whether a combination of ultrasound with smaller chlorine concentrations can be as efficient as what would only be possible with higher dosing of the environmentally harmful chlorine. For combined sonication/chlorination an efficiency gain up to 2.5 folds is possible, especially at very low chlorine concentrations (see figure 1). Consequently, lower dosing of the environmentally harmful chlorine is possible to obtain a specific disinfection rate, and the formation of by-products is correspondingly reduced.

Since the efficiency gain of the disinfection in our experiments was explicitly higher during the simultaneous sonication than as pre-treatment, ultrasound is not only effective with respect to the declumping of agglomerates but also on the temporary perforation of bacteria's cell walls.

• Legal notice:
  

  Copyright (c) Pielaszek Research, all rights reserved.
  The above materials, including auxiliary resources, are subject to Publisher's copyright and the Author(s) intellectual rights. Without limiting Author(s) rights under respective Copyright Transfer Agreement, no part of the above documents may be reproduced without the express written permission of Pielaszek Research, the Publisher. Express permission from the Author(s) is required to use the above materials for academic purposes, such as lectures or scientific presentations.
  In every case, proper references including Author(s) name(s) and URL of this webpage: https://science24.com/paper/8157 must be provided.

1. Improvement of Sludge Handling in Pulp and Paper Industry Using Ultrasound
2. Modification of enzymatic reaction kinetics by sonication of biomass