Water treatment by cavitation: Understanding it at a single bubble - bacterial cell level. (1st June 2023)

• Record Type: Journal Article
• Authors: Pandur, Žiga; Zevnik, Jure; Podbevšek, Darjan; Stojković, Biljana; Stopar, David; Dular, Matevž
• Is Part Of: Water research. Volume 236(2023)
• Publication Date: 2023-06-01
• Subjects: Cavitation -- Microbubble -- Bacteria -- Surface cleaning -- Water treatment -- Disinfection; Water -- Pollution -- Research -- Periodicals; 363.7394
• DOI: 10.1016/j.watres.2023.119956
• Languages: English
• ISSNs: 0043-1354

Abstract

Highlights: Methodology to study bubble-bacteria interaction on a nano- to microscale resolution in both space and time is presented. A single cavitation microbubble can cause detachment and death of wall-bound bacterial cells. The water jet resulting from the near-wall bubble implosion is the primary mechanism of wall-bound cell damage. Very high likelihood of cell detachment and cell death for cells directly under the center of a bubble. A peak force of 0.8 and 1.2 μN is needed for reliable detachment and death of E. coli bacteria. Abstract: Cavitation is a potentially useful phenomenon accompanied by extreme conditions, which is one of the reasons for its increased use in a variety of applications, such as surface cleaning, enhanced chemistry, and water treatment. Yet, we are still not able to answer many fundamental questions related to efficacy and effectiveness of cavitation treatment, such as: "Can single bubbles destroy contaminants?" and "What precisely is the mechanism behind bubble's cleaning power?". For these reasons, the present paper addresses cavitation as a tool for eradication and removal of wall-bound bacteria at a fundamental level of a single microbubble and a bacterial cell. We present a method to study bubble-bacteria interaction on a nano- to microscale resolution in both space and time. The method allows for accurate and fast positioning of a single microbubble above the individual wall-bound bacterial cell with optical tweezers and triggering of a violent microscale cavitation event, which either results in mechanical removal or destruction of the bacterial cell. Results on E. coli bacteria show that only cells in the immediate vicinity of the microbubble are affected, and that a very high likelihood of cell detachment and cell death exists for cells located directly under the center of a bubble. Further details behind near-wall microbubble dynamics are revealed by numerical simulations, which demonstrate that a water jet resulting from a near-wall bubble implosion is the primary mechanism of wall-bound cell damage. The results suggest that peak hydrodynamic forces as high as 0.8 μN and 1.2 μN are required to achieve consistent E. coli bacterial cell detachment or death with high frequency mechanical perturbations on a nano- to microsecond time scale. Understanding of the cavitation phenomenon at a fundamental level of a single bubble will enable further optimization of novel water treatment and surface cleaning technologies to provide more efficient and chemical-free processes. Graphical abstract: Image, graphical abstract