Abstract Description: Hydrodynamic cavitation (HC) has gained attention as a cost-effective, scalable, and chemical-free cell disruption technique for various applications including water disinfection, algae bloom control, and bioproduct processing. However, quantifying real-time cell damage at the cellular level remains challenging. Traditional methods such as cell count, microscopy, and growth tests often overlook subtle yet significant damages and other transient factors that are critical for cavitation optimization, leading to inefficiencies in HC protocols and eventually higher operational costs. This study integrated flow cytometry, fluorescent staining, and kinetic modeling to reveal the dynamic changes of cell damage and inactivation efficiency in microalgae Dunaliella viridis during HC treatment. Utilizing a bench-scale system with a Venturi cavitation device, cells in the cavitation group and a control group without cavitation were analyzed for cell count, size, viability (membrane integrity and esterase activity), chlorophyll fluorescence, and reactive oxygen species (ROS) levels, leveraging fluorescent probes such as fluorescein diacetate (FDA), erythrosine B (EB), and 2′,7′-dichlorofluorescein diacetate (DCFDA).
Results showed that HC disrupted and inactivated cells more effectively, achieving over 50% energy savings compared to the control. Cell membrane disruption was the primary HC-induced damage, leading to rapid intracellular content release. In cells with intact membranes, esterase activity and chlorophyll content remained largely unaffected, although ROS levels were reduced. Our findings suggest that for microalgae-derived bioproducts harvesting, cell membrane integrity is a more effective physiological endpoint for optimizing HC protocols. Furthermore, cells were inactivated exponentially but with a reduced rate at the early stage of HC treatment, deviating from traditional pseudo-first-order kinetics. A P-factor model, integrating two first-order rate constants modulated by the cavitation number, was developed and accurately captured the inactivation kinetics of both cavitation and control groups. The model further suggests that cavitation number alone does not fully encapsulate the complex and dynamic physical (e.g., shear stress, bubble collapse) and chemical (e.g., hydroxyl radical formation) effects essential to HC efficiency.
Our work highlights that controlling cell debris accumulation within 10–20% may sustain inactivation efficiency in early treatment stages. Overall, this study provides a foundational framework for analyzing cell inactivation via flow cytometry, offering critical insights for refining HC protocols and developing comprehensive models for applications from microorganism disinfection to bioproduct extraction.
