Research news

Treating wastewater through cavitation and understanding the effects of bubbles on bacterial cells

Publish Date: 29.06.2023

Category: Our contribution to sustainable development goals

Sustainable development goals: 3 Good health and well-being, 6 Clean water and sanitation, 11 Sustainable cities and communities (Indicators)

Increasing environmental pollution and drinking water shortages are a growing socioeconomic problem, in which cavitation technology can contribute to a cleaner and greener approach to wastewater treatment. Cavitation is a physical phenomenon that describes the phase change from liquid to vapour and back at constant temperature. The mechanical, thermal and chemical effects of cavitation can be utilised for various purposes, including to inactivate microorganisms in drinking water and wastewater. It has been proven that cells are subjected to damage in the immediate vicinity of a bubble. Further numerical analysis has identified the formation of microjets as a possible mechanism of bacterial cell damage.

Despite the substantial research conducted on bacterial cell inactivation, it continues to be treated as a "black box" phenomenon where it is not entirely clear what is going on at the bacterial cell scale (i.e., the micrometre scale). Incomplete understanding of this phenomenon at the fundamental level slows down the progress and optimisation of the related technology for applied purposes. 

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Figure 1: Graphical abstract of the study

In cooperation with the Biotechnical Faculty, researchers at the Faculty of Mechanical Engineering, led by Prof. Matevž Dular, studied the impact of a single cavitation microbubble on individual bacterial cells as part of the ERC research project CABUM, which has received funding from the EU Horizon 2000 programme. The researchers developed a system for generating single micrometre-size cavitation bubbles, which also uses optical tweezers and a high-speed camera for visualisation. The system made it possible to monitor the dynamics of microbubble collapse near the wall and in the proximity of bacterial cells. Fluorescence microscopy was used to identify the damaged cells. Based on experimental and numerical results, the researchers were able to define the peak hydrodynamic force required for the detachment or death of a single E. coli bacterial cell. 


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