Virus Removal and Inactivation Mechanisms during Iron Electrocoagulation: Capsid and Genome Damages and Electro-Fenton Reactions

Abstract

Virus destabilization and inactivation are critical considerations in providing safe drinking water. We demonstrate that iron electrocoagulation simultaneously removed (via sweep flocculation) and inactivated a non-enveloped virus surrogate (MS2 bacteriophage) under slightly acidic conditions, resulting in highly effective virus control (e.g., 5-logs at 20 mg Fe/L and pH 6.4 in 30 min). Electrocoagulation simultaneously generated H2O2 and Fe­(II) that can potentially trigger electro-Fenton reactions to produce reactive oxygen species such as •OH and high valent oxoiron­(IV) that are capable of inactivating viruses. To date, viral attenuation during water treatment has been largely probed by evaluating infective virions (as plaque forming units) or genomic damage (via the quantitative polymerase chain reaction). In addition to these existing means of assessing virus attenuation, a novel technique of correlating transmission electron micrographs of electrocoagulated MS2 with their computationally altered three-dimensional electron density maps was developed to provide direct visual evidence of capsid morphological damages during electrocoagulation. The majority of coliphages lost at least 10–60% of the capsid protein missing a minimum of one of the 5-fold and two of 3- and 2-fold regions upon electrocoagulation, revealing substantial localized capsid deformation. Attenuated total reflectance–Fourier transform infrared spectroscopy revealed potential oxidation of viral coat proteins and modification of their secondary structures that were attributed to reactive oxygen species. Iron electrocoagulation simultaneously disinfects and coagulates non-enveloped viruses (unlike conventional coagulation), adding to the robustness of multiple barriers necessary for public health protection and appears to be a promising technology for small-scale distributed water treatment.

The Effect of Zero-Valent Iron Nanoparticles (nZVI) on Bacteriophages

“…Fe ions present in the tails of bacteriophages assist in adsorption to the receptors of the host cells [ 24 ]. However, the most common mechanisms of bacteriophage titer reduction by iron-based compounds are (1) adsorption of virions on the surface of nanoparticles [ 23 ], (2) redox reactions [ 25 ], and (3) the effect of free iron ions [ 26 ].…”

“…Fe 2+ ions alone (0.1 mM) have been reported to inactivate up to 1.5log of MS2 phages compared to 4log in the case of the Fenton process (a mixture of Fe 2+ ions with H 2 O 2 ) [ 34 ]. Fe 2+ has a more substantial effect on f2 than Fe 3+ , probably owing to the limited solubility of the latter [ 25 , 36 ]. Differences in the titer reduction arise from varying susceptibility to ferrous inactivation in MS2, φ X174, and mammalian viruses.…”

Disinfection during Iron Electrocoagulation: Differentiating between Inactivation and Floc Entrapment for Escherichia coli and Somatic Coliphage ØX174

“…Regardless, reducing pH appears to be a poor means of enhancing virus disinfection during Fe-EC, while improvement of flocculation conditions is the major determinant in virus removal, mainly by enhancing irreversible floc-adsorption and separation, as has also been reported elsewhere. 17,23,39 Although inactivation by ROS is clearly an interesting pathway for disinfection during Fe-EC, the overall disinfection efficiency of either indicator was statistically the same for quenched and un-quenched conditions. This could cast doubt on the real advantage of using reduced Fe forms to conduct coagulation, as opposed to using more conventional Fe-based coagulants such as FeCl 3 for which disinfection by sorption/ sedimentation has been reported.…”

A critical review on the existing wastewater treatment methods in the COVID-19 era: What is the potential of advanced oxidation processes in combatting viral especially SARS-CoV-2?

“…Electro-Fenton process involves in-situ formation H 2 O 2 during EC utilized iron electrode in aerobic conditions. Recently, this EAOP was effectively employed by Kim et al [158] to inactivate a non-enveloped virus surrogate (MS2 bacteriophage) under slightly acidic conditions. As seen in Fig.…”