Inactivation of the enveloped virus phi6 with hydrodynamic cavitation

Abstract

The COVID -19 pandemic reminded us that we need better contingency plans to prevent the spread of infectious agents and the occurrence of epidemics or pandemics. Although the transmissibility of SARS-CoV-2 in water has not been confirmed, there are studies that have reported on the presence of infectious coronaviruses in water and wastewater samples. Since standard water treatments are not designed to eliminate viruses, it is of utmost importance to explore advanced treatment processes that can improve water treatment and help inactivate viruses when needed. This is the first study to investigate the effects of hydrodynamic cavitation on the inactivation of bacteriophage phi6, an enveloped virus used as a SARS-CoV-2 surrogate in many studies. In two series of experiments with increasing and constant sample temperature, virus reduction of up to 6.3 logs was achieved. Inactivation of phi6 at temperatures of 10 and 20 °C occurs predominantly by the mechanical effect of cavitation and results in a reduction of up to 4.5 logs. At 30 °C, the reduction increases to up to 6 logs, where the temperature-induced increased susceptibility of the viral lipid envelope makes the virus more prone to inactivation. Furthermore, the control experiments without cavitation showed that the increased temperature alone is not sufficient to cause inactivation, but that additional mechanical stress is still required. The RNA degradation results confirmed that virus inactivation was due to the disrupted lipid bilayer and not to RNA damage. Hydrodynamic cavitation, therefore, has the potential to inactivate current and potentially emerging enveloped pathogenic viruses in water at lower, environmentally relevant temperatures.

Keywords: Enveloped viruses; Hydrodynamic cavitation; Phi6; SARS-CoV-2; Virus inactivation; Water decontamination.

Graphical abstract

Fig. 1

Experimental setup scheme with visible HC test-rig elements (left): (1) reservoirs, (2) Venturi constriction, (3) 5-way pneumatic valve, (4) cooling coil, (5) cooling unit, (6) thermometer Pt100 and (7) level sensor. Dimensions of the Venturi (A) and control constriction (B) are presented on the scheme on the right. ROI - region of interest.

Fig. 2

Reduction of virus concentration (log10 PFU/mL, Rv) (left) and sample temperature (right) in relation to the number of passes (Np) through Venturi (Table 2: Exp. sets HC – IT30 and HC + M – IT30) and control (Table 2: Exp. sets C – IT30 and C – IT20) constrictions. Shown data are mean ± s.d. of each experimental set. The mean initial (Np = 0) virus concentrations were between 3 × 10⁶ PFU/mL and 10 × 10⁶ PFU/mL, which corresponds to log-values between 6.5 and 7.0.

Fig. 3

Left: Reduction of virus concentration (log₁₀ PFU/mL, Rv) in relation to the number of sample passes (Np) through Venturi (solid lines, Table 2: Exp. set HC – CT) and control (dashed lines, Table 2: Exp. set C – CT) constrictions. The initial (Np = 0) virus concentrations were 6.4 × 10⁶ PFU/mL ± 4.9 × 10⁶ PFU/mL and 4.4 × 10⁶ PFU/mL ± 4.3 × 10⁶ PFU/mL for HC and control experiments, respectively. Right: HC treatment (Table 2: Exp. set HC – CT) effectiveness in comparison to the control (Table 2: Exp. set C – CT) at constant sample temperatures of 10 °C (blue), 20 °C (yellow), and 30 °C (orange). A linear model (solid line) is fitted to the data (dots). The 95 % confidence intervals of the obtained regression coefficients k are denoted by a coloured fill. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 4

High-speed visualization of cavitation in Venturi constriction at water temperature of 10, 20 and 30 °C.