Numerous studies have already shown that the process of cavitation can be successfully used for water treatment and eradication of bacteria. However, most of the relevant studies are being conducted on a macro scale, so the understanding of the processes at a fundamental level remains poor. In attempt to further elucidate the process of cavitation-assisted water treatment on a scale of a single bubble, the present paper numerically addresses interaction between a collapsing microbubble and a nearby compliant structure, that mechanically and structurally resembles a bacterial cell. A fluid–structure interaction methodology is employed, where compressible multiphase flow is considered and the bacterial cell wall is modeled as a multi-layered shell structure. Simulations are performed for two selected model structures, each resembling the main structural features of Gram-negative and Gram-positive bacterial cell envelopes. The contribution of two independent dimensionless geometric parameters is investigated, namely the bubble-cell distance $\delta$ and their size ratio $\varsigma$. Three characteristic modes of bubble collapse dynamics and four modes of spatiotemporal occurrence of peak local stresses in the bacterial cell membrane are identified throughout the parameter space considered. The former range from the development of a weak and thin jet away from the cell to spherical bubble collapses. The results show that local stresses arising from bubble-induced loads can exceed poration thresholds of cell membranes and that bacterial cell damage could be explained solely by mechanical effects in absence of thermal and chemical ones. Based on this, the damage potential of a single microbubble for bacteria eradication is estimated, showing a higher resistance of the Gram-positive model organism to the nearby bubble collapse. Microstreaming is identified as the primary mechanical mechanism of bacterial cell damage, which in certain cases may be enhanced by the occurrence of shock waves during bubble collapse. The results are also discussed in the scope of bacteria eradication by cavitation treatment on a macro scale, where processes of hydrodynamic and ultrasonic cavitation are being employed.

许多研究已经表明，空化过程可以成功地用于水处理和消灭细菌。然而，大多数相关研究都是在宏观尺度上进行的，因此对基本过程的理解仍然很薄弱。为了进一步阐明在单个气泡的规模上进行空化辅助水处理的过程，本文从数值上解决了坍塌的微气泡与附近的柔顺结构之间的相互作用，该结构在机械和结构上类似于细菌细胞。采用流固耦合方法，考虑可压缩多相流，将细菌细胞壁建模为多层壳结构。对两个选定的模型结构进行模拟，每个都类似于革兰氏阴性和革兰氏阳性细菌细胞包膜的主要结构特征。研究了两个独立的无量纲几何参数的贡献，即气泡距离$\delta$以及它们的尺寸比$\epsilon$. 在整个考虑的参数空间中确定了气泡破裂动力学的三种特征模式和细菌细胞膜中局部峰值应力的四种时空发生模式。前者的范围从远离细胞的弱而薄的射流发展到球形气泡破裂。结果表明，由气泡引起的载荷引起的局部应力可能超过细胞膜的穿孔阈值，并且细菌细胞损伤可以仅通过机械效应来解释，而没有热和化学效应。在此基础上，估计了单个微泡对细菌根除的破坏潜力，表明革兰氏阳性模型生物对附近的气泡破裂具有更高的抵抗力。微流被确定为细菌细胞损伤的主要机械机制，在某些情况下，泡沫破裂过程中冲击波的出现可能会增强这种影响。还讨论了在宏观尺度上通过空化处理消除细菌的结果，其中采用了流体动力学和超声空化过程。