Sanitizing human and animal waste (e.g., urine, fecal sludge, or grey water) is a critical step in reducing the spread of disease and ensuring microbially safe reuse of waste materials. Viruses are particularly persistent pathogens and can be transmitted through inadequately sanitized waste. However, adequate storage or digestion of waste can strongly reduce the number of viruses due to increases in pH and uncharged aqueous ammonia (NH3), a known biocide. In this study we investigated the kinetics and mechanisms of inactivation of the single-stranded RNA virus MS2 under temperature, pH and NH3 conditions representative of waste storage. MS2 inactivation was mainly controlled by the activity of NH3 over a pH range of 7.0–9.5 and temperatures lower than 40 °C. Other bases (e.g., hydroxide, carbonate) additionally contributed to the observed reduction of infective MS2. The loss in MS2 infectivity could be rationalized by a loss in genome integrity, which was attributed to genome cleavage via alkaline transesterification. The contribution of each base to genome transesterification, and hence inactivation, could be related to the base pKa by means of a Bronsted relationship. The Bronsted relationship in conjunction with the activity of bases in solution enabled an accurate prediction of MS2 inactivation rates.

(T. Kohn).A v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / w a t r e s w a t e r r e s e a r c h 4 5 ( 2 0 1 1 ) 4 9 6 0 e4 9 7 2 0043-1354/$ e see front matter ª

Treatment. DNA and dsRNA viruses were considerably more resistant than ssRNA viruses, resulting in up to 1,000-fold-longer treatment times to reach a 4-log inactivation. The apparently slower inactivation of DNA viruses was rationalized by the higher stability of DNA than that of ssRNA in HEAM. Pushing the system toward harsher pH (>9) and temperature (>35°C) conditions, such as those encountered in thermophilic digestion and alkaline treatments, led to more consistent inactivation kinetics among ssRNA and other viruses. This suggests that the dependence of inactivation on genome type disappeared in favor of protein-mediated inactivation mechanisms common to all viruses. Finally, we recommend the use of MS2 as a conservative indicator to assess the inactivation of ssRNA viruses and the stable ⌽X174 or dsDNA phages as indicators for persistent viruses. IMPORTANCEViruses are among the most environmentally persistent pathogens. They can be present in high concentrations in human excreta and animal manure (HEAM). Therefore, appropriate treatment of HEAM is important prior to its reuse or discharge into the environment. Here, we investigated the factors that determine the persistence of viruses in HEAM, and we determined the main mechanisms that lead to their inactivation. Unlike other organisms, viruses can have four different genome types (double-or single-stranded RNA or DNA), and the viruses studied herein represent all four types. Genome type appeared to be the major determinant for persistence. Single-stranded RNA viruses are the most labile, because this genome type is susceptible to degradation in HEAM. In contrast, the other genome types are more stable; therefore, inactivation is slower and mainly driven by the degradation of viral proteins. Overall, this study allows us to better understand the behavior of viruses in HEAM.

The goals of this study were to investigate the release of infective bacteriophages MS2 and FX174 (two human viral indicators) after adsorption onto an iron oxide coated sand (IOCS), and to promote viral inactivation by exploiting the photoreactive properties of the IOCS.The iron oxide coating greatly enhanced viral adsorption (adsorption densities up to w10 9 infective viruses/g IOCS) onto the sand, but had no affect on infectivity. Viruses that were adsorbed onto IOCS under control conditions (pH 7.5, 10 mM Tris, 1250 mS/cm) were released into solution in an infective state with increases in pH and humic acid concentrations. The exposure of IOCS-adsorbed MS2 to sunlight irradiation caused significant inactivation via a photocatalytic mechanism in both buffered solutions and in wastewater samples (4.9 log 10 and 3.3 log 10 inactivation after 24-h exposure, respectively). Unlike MS2, FX174 inactivation was not enhanced by photocatalysis. In summary, IOCS enhanced the separation of viruses from the water column, and additionally provided a photocatalytic mechanism to promote inactivation of one of the surrogates studied. These qualities make it an attractive option for improving viral control strategies in constructed wetlands. ª 2012 Elsevier Ltd. All rights reserved. IntroductionControlling the transmission of waterborne viruses is made difficult by the fact that viruses are incompletely removed through conventional treatment processes. Their small size helps them to bypass physical removal treatments such as sedimentation and conventional filtration (Symonds et al., 2009;Thompson et al., 2003). Even when associated with particles, viruses tend to remain in suspension and pass through granular media filters (Rao et al., 1984;Templeton et al., 2005). They also exhibit higher resistance to many disinfectants compared to other pathogens, including chlorine and UV (LeChevallier, 2004;Thompson et al., 2003). Thus, alternative processes are needed to supplement conventional removal and inactivation strategies. Natural treatment systems, such as constructed wetlands, have shown potential for virus removal. Viruses tend to adsorb poorly onto sand (Bales et al., 1991(Bales et al., , 1993, which is commonly used as wetland matrix (Brix and Arias, 2005;Hoffmann et al., 2011). The presence of metal oxides can greatly enhance adsorption. The positively-charged metal oxide surfaces naturally present on sands and soils offer favorable sites for the adsorption of negatively charged viruses and other pathogens. Similarly, pure metal oxides or * Corresponding author. Tel.: þ41 (0) 21 693 0891; fax: þ41 (0) 21 693 8070.E-mail address: tamar.kohn@epfl.ch (T. Kohn).Available online at www.sciencedirect.com j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / w a t r e s w a t e r r e s e a r c h 4 6 ( 2 0 1 2 ) 1 7 6 3 e1 7 7 0 0043-1354/$ e see front matter ª