Virus removal and inactivation by iron (hydr)oxide-mediated Fenton-like processes under sunlight and in the dark

Abstract

Advanced oxidation processes (AOPs) have emerged as a promising alternative to conventional disinfection methods to control microbial water quality, yet little is known about the fate of viruses in AOPs. In this study, we investigated the fate of MS2 coliphage in AOPs that rely on heterogeneous Fenton-like processes catalyzed by iron (hydr)oxide particles. Both physical removal of viruses from solution via adsorption onto particles as well as true inactivation were considered. Virus fate was studied in batch reactors at circumneutral pH, containing 200 mg L⁻¹ of four different commercial iron (hydr)oxide particles of similar mesh sizes: hematite (α-Fe₂O₃), goethite (α-FeOOH), magnetite (Fe₃O₄) and amorphous iron(III) hydroxide (Fe(OH)₃). The effect of adsorption and sunlight exposure on the survival of MS2 was considered. On a mass basis, all particles exhibited a similar virus adsorption capacity, whereas the rate of adsorption followed the order FeOOH > Fe₂O₃ > Fe₃O₄ ≈ Fe(OH)₃. This adsorption behavior could not be explained by electrostatic considerations; instead, adsorption must be governed by other factors, such as hydrophobic interactions or van der Waals forces. Adsorption to three of the particles investigated (α-FeOOH, Fe₃O₄, Fe(OH)₃) caused virus inactivation of 7%, 22%, and 14%, respectively. Exposure of particle-adsorbed viruses to sunlight and H₂O₂ resulted in efficient additional inactivation, whereas inactivation was negligible for suspended viruses. The observed first-order inactivation rate constants were 6.6 × 10⁻², 8.7 × 10⁻², 0.55 and 1.5 min⁻¹ for α-FeOOH, α-Fe₂O₃, Fe₃O₄ and Fe(OH)₃ respectively. In the absence of sunlight or H₂O₂, no inactivation was observed beyond that caused by adsorption alone, except for Fe₃O₄, which caused virus inactivation via a dark Fenton-like process. Overall our results demonstrate that heterogeneous Fenton-like processes can both physically remove viruses from water as well as inactivate them via adsorption and via a particle-mediated (photo-)Fenton-like process.