Water treatment by cavitation: Understanding it at a single bubble - bacterial cell level

Žiga Pandur; Jure Zevnik; Darjan Podbevšek; Biljana Stojković; David Stopar; Matevž Dular

doi:10.1016/j.watres.2023.119956

Water treatment by cavitation: Understanding it at a single bubble - bacterial cell level

Water Res. 2023 Jun 1:236:119956. doi: 10.1016/j.watres.2023.119956. Epub 2023 Apr 8.

Authors

Žiga Pandur¹, Jure Zevnik², Darjan Podbevšek³, Biljana Stojković², David Stopar⁴, Matevž Dular⁵

Affiliations

¹ Faculty of Mechanical Engineering, University of Ljubljana, Askerceva 6, 1000 Ljubljana, Slovenia; Biotechnical Faculty, University of Ljubljana, Jamnikarjeva 101, 1000 Ljubljana, Slovenia.
² Faculty of Mechanical Engineering, University of Ljubljana, Askerceva 6, 1000 Ljubljana, Slovenia.
³ Faculty of Mechanical Engineering, University of Ljubljana, Askerceva 6, 1000 Ljubljana, Slovenia; Advanced Science Research Center at The Graduate Center of the City University of New York, 85 Saint Nicholas Terrace, New York, USA.
⁴ Biotechnical Faculty, University of Ljubljana, Jamnikarjeva 101, 1000 Ljubljana, Slovenia.
⁵ Faculty of Mechanical Engineering, University of Ljubljana, Askerceva 6, 1000 Ljubljana, Slovenia. Electronic address: matevz.dular@fs.uni-lj.si.

PMID: 37087917
DOI: 10.1016/j.watres.2023.119956

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.

Keywords: Bacteria; Cavitation; Disinfection; Microbubble; Surface cleaning; Water treatment.

MeSH terms

Bacteria
Escherichia coli*
Hydrodynamics
Microbubbles
Water Purification*