Microbial reductions and physical characterization of chitosan flocs when using chitosan acetate as a cloth filter aid in water treatment

The World Health Organization (WHO) estimates 2.1 billion people lack access to safely managed water. Cloth filtration is often employed in rural and developing communities of South Asia for point-of-use water treatment, but bacteria and viruses are too small for efficient removal by this filtration method. Chitosan is a biodegradable, cationic, organic polymer derived from the chemical treatment of chitin that acts as a coagulant and flocculant of contaminant of microbes and other particles in water, thereby facilitating filtration of microbes. This research 1) evaluated the use of chitosan acetate as a pre-treatment coagulation-flocculation process followed by cloth filtration for microbial reductions and 2) assessed floc particle size under three stirring conditions. E. coli KO11 bacteria and MS2 coliphage virus removals were quantified using culture-based methods. Chitosan acetate coagulation-flocculation pre-treatment of water, followed by cloth filtration, met or exceeded the protective (2-star) WHO performance levels for bacteria (2 log10 reduction) and viruses (3 log10 reduction), and filtrate turbidity was consistently reduced to < 1 NTU, meeting United States Environmental Protection Agency (EPA) and WHO targets.

Sediment re-suspension as a potential mechanism for viral and bacterial contaminants

Pathogenic enteric viruses and bacteria tend to occur in higher concentrations and survive longer in aquatic sediments than suspended in the water column. Re-suspension of these organisms can result in a significant degradation of overlying water quality. Additionally, the re-suspension of microbial pathogens in artificial irrigation canals could endanger the consumption of fresh and ready-to-eat produce. Irrigation water has been implicated in numerous fresh produce outbreaks over the last 30 years. This study aimed to quantify the proportions of bacterial and viral re-suspension from sediment in a recirculating flume with varying velocities. MS2 coliphage and Escherichia coli were found to re-suspend at rates that were not significantly different, despite organism size differences. However, E. coli re-suspension rates from sand and clay were significantly different. This suggests that likely sediment-associated particles were recovered with the organisms attached. Similar re-suspension rates are hypothesized to be due to the dynamics of sediment transport, rather than that of the organisms themselves. This study also indicated that the re-suspension of sediment at very low velocities (e.g., less than 10 cm/s), could impact the microbiological quality of the overlaying water. Results from this study conclude that sediment could be a viable mechanism for irrigation water contamination.

Transport of bacteriophage MS2 and PRD1 in saturated dune sand under suboxic conditions

Soil passage of (pretreated) surface water to remove pathogenic microorganisms is a highly efficient process under oxic conditions, reducing microorganism concentrations about 8 log¹⁰ within tens of meters. However, under anoxic conditions, it has been shown that removal of microorganisms can be limited very much. Setback distances for adequate protection of natural groundwater may, therefore, be too short if anoxic conditions apply. Because removal of microorganisms under suboxic conditions is unknown, this research investigated removal of bacteriophage MS2 and PRD1 by soil passage under suboxic conditions at field scale. At the field location (dune area), one injection well and six monitoring wells were installed at different depths along three suboxic flow lines, where oxygen concentrations ranged from 0.4 to 1.7 mg/l and nitrate concentrations ranged from 13 to 16 mg/L. PRD1 and MS2 were injected directly at the corresponding depths and their removal in each flow line was determined. The highest bacteriophage removal was observed in the top layer, with about 9 log removal of MS2, and 7 log removal of PRD1 after 16 meters of aquifer transport. Less removal was observed at 12 m below surface, probably due to a higher groundwater velocity in this coarser grained layer. MS2 was removed more effectively than PRD1 under all conditions. Due to short travel times, inactivation of the phages was limited and the reported log removal was mainly associated with attachment of phages to the aquifer matrix. This study shows that attachment of MS2 and PRD1 is similar for oxic and suboxic sandy aquifers, and, therefore, setback distances used for sandy aquifers under oxic and suboxic conditions provide a similar level of safety. Sticking efficiency and the attachment rate coefficient, as measures for virus attachment, were evaluated as a function of the physico-chemical conditions.

Effect of the Shellfish Proteinase K Digestion Method on Norovirus Capsid Integrity

Norovirus outbreaks are associated with the consumption of contaminated shellfish, and so efficient methods to recover and detect infectious norovirus in shellfish are important. The Proteinase K digestion method used to recover norovirus from shellfish, as described in the ISO 15216, would be a good candidate but its impact on the virus capsid integrity and thus infectivity was never examined. The aim of this study was to assess the impact of the Proteinase K digestion method, and of the heat treatment component of the method alone, on norovirus (genogroups I and II) and MS2 bacteriophage capsid integrity. A slightly modified version of the ISO method was used. RT-qPCR was used for virus detection following digestion of accessible viral RNA using RNases. MS2 phage infectivity was measured using a plaque assay. The effect of shellfish digestive glands (DG) on recovery was evaluated. In the presence of shellfish DG, a reduction in MS2 phage infectivity of about 1 log₁₀ was observed after the Proteinase K digestion method and after heat treatment component alone. For norovirus GII and MS2 phage, there was no significant loss of genome following the Proteinase K digestion method but there was a significant 0.24 log₁₀ loss of norovirus GI. In the absence of shellfish DG, the reduction in MS2 phage infectivity was about 2 log₁₀, with the addition of RNases resulting in a significant loss of genome for all tested viruses following complete Proteinase K digestion method and the heat treatment alone. While some protective effect from the shellfish DG on viruses was observed, the impact on capsid integrity and infectivity suggests that this method, while suitable for norovirus genome detection, may not completely preserve virus infectivity.

Evaluation of the suitability of a plant virus, pepper mild mottle virus, as a surrogate of human enteric viruses for assessment of the efficacy of coagulation-rapid sand filtration to remove those viruses

Here, we evaluated the removal of three representative human enteric viruses - adenovirus (AdV) type 40, coxsackievirus (CV) B5, and hepatitis A virus (HAV) IB - and one surrogate of human caliciviruses - murine norovirus (MNV) type 1 - by coagulation-rapid sand filtration, using water samples from eight water sources for drinking water treatment plants in Japan. The removal ratios of a plant virus (pepper mild mottle virus; PMMoV) and two bacteriophages (MS2 and φX174) were compared with the removal ratios of human enteric viruses to assess the suitability of PMMoV, MS2, and φX174 as surrogates for human enteric viruses. The removal ratios of AdV, CV, HAV, and MNV, evaluated via the real-time polymerase chain reaction (PCR) method, were 0.8-2.5-log₁₀ when commercially available polyaluminum chloride (PACl, basicity 1.5) and virgin silica sand were used as the coagulant and filter medium, respectively. The type of coagulant affected the virus removal efficiency, but the age of silica sand used in the rapid sand filtration did not. Coagulation-rapid sand filtration with non-sulfated, high-basicity PACls (basicity 2.1 or 2.5) removed viruses more efficiently than the other aluminum-based coagulants. The removal ratios of MS2 were sometimes higher than those of the three human enteric viruses and MNV, whereas the removal ratios of φX174 tended to be smaller than those of the three human enteric viruses and MNV. In contrast, the removal ratios of PMMoV were similar to and strongly correlated with those of the three human enteric viruses and MNV. Thus, PMMoV appears to be a suitable surrogate for human enteric viruses for the assessment of the efficacy of coagulation-rapid sand filtration to remove viruses.

Development of an efficient viral aerosol collector for higher sampling flow rate

Viral aerosol infection through cough generates large amounts of viral aerosol and can result in many adverse health effects such as influenza flu and severe acute respiratory syndrome (SARS). To characterize the coughed viral aerosol, the sampler needs to sample at higher flow rate and possess high physical collection efficiency as well as high viral preservation. However, most current inertia-based high flow bioaerosol samplers are not suited for viral aerosol sampling since the viability will be lost doing the sampling process. Current condensation growth methods only have good physical collection efficiency and viral preservation at low flow rate (< 10 LPM). In this study, we developed a viral aerosol sampling system using a cooler and steam-jet aerosol collector (SJAC) for bioaerosol collection for the first time. The system is based on mixing condensation growth method and has high viral preservation at a higher flow rate (12.5 LPM). We control the inlet aerosol flow temperature and the SJAC mixing reservoir temperature to improve the physical collection efficiency and viability preservation of the viral aerosol. Results indicate that the physical collection efficiency is 70-99% for aerosol 30-100 nm when the aerosol flow and mixing reservoir temperature was 19 and 50 °C, respectively. In addition, the system was 7 and 22 times more efficient for viability preservation of MS2 bacteriophage than the commonly used All Glass Impinger 30 (AGI-30) and BioSampler®, respectively. Finally, the system can be applied to sample at a lower concentration (105 PFU/m3), and results shows the system was 4.7 times more efficient for viability preservation than using AGI-30 alone. The developed viral collection system will improve our understanding of the characteristics of coughed aerosol and can be used for future evaluation of respiratory protective equipment and environmental sampling.

Removal of model viruses, E. coli and Cryptosporidium oocysts from surface water by zirconium and chitosan coagulants

The present work evaluates the effect of contact filtration, preceded by coagulation with zirconium (Zr) and chitosan coagulants, on model microorganisms and waterborne pathogens. River water intended for potable water production was spiked with MS2 and Salmonella Typhimurium 28B bacteriophages, Escherichia coli, and Cryptosporidium parvum oocysts prior to coagulation. The hygienic performance demonstrated by Zr comprised 3.0-4.0 log₁₀ removal of viruses and 5.0-6.0 log₁₀ removal of E. coli and C. parvum oocysts. Treatment with chitosan resulted in a removal of 2.5-3.0 log₁₀ of viruses and parasites, and 4.5-5.0 log₁₀ of bacteria. A reference coagulant, polyaluminium chloride (PACl), gave a 2.5-3.0 log₁₀ removal of viruses and 4.5 log₁₀ of E. coli. These results indicate that both Zr and chitosan enable adequate removal of microorganisms from surface water. The present study also attempts to assess removal rates of the selected microorganisms with regard to their size and surface properties. The isoelectric point of the Salmonella Typhimurium 28B bacteriophage is reported for the first time. The retention of the selected microorganisms in the filter bed appeared to have some correlation with their size, but the effect of the charge remained unclear.

Comparison of internal process control viruses for detection of food and waterborne viruses

Enteric viruses are pathogens associated with food- and waterborne outbreaks. The recovery of viruses from food or water samples is affected by the procedures applied to detect and concentrate them. The incorporation of an internal process control virus to the analyses allows monitoring the performance of the methodology. The aim of this study was to produce a recombinant adenovirus (rAdV) and apply it together with bacteriophage PP7 as process controls. The rAdV carries a DNA construction in its genome to differentiate it from wild-type adenovirus by qPCR. The stability of both control viruses was evaluated at different pH conditions. The rAdV was stable at pH 3, 7, and 10 for 18 h. PP7 infectious particles were stable at pH 7 and showed a 2.14 log reduction at pH 10 and total decay at pH 3 after 18 h. Three virus concentration methods were evaluated: hollow-fiber tap water ultrafiltration, wastewater ultracentrifugation, and elution-PEG precipitation from lettuce. Total and infectious viruses were quantified and their recoveries were calculated. Virus recovery for rAdV and PP7 by ultrafiltration showed a wide range (2.10-84.42 and 13.54-84.62%, respectively), whereas that by ultracentrifugation was 5.05-13.71 and 6.98-13.27%, respectively. The performance of ultracentrifugation to concentrate norovirus and enteroviruses present in sewage was not significantly different to the recovery of control viruses. For detection of viruses from lettuce, genomic copies of PP7 were significantly more highly recovered than adenovirus (14.74-18.82 and 0.00-3.44%, respectively). The recovery of infectious virus particles was significantly affected during sewage ultracentrifugation and concentration from lettuce. The simultaneous use of virus controls with dissimilar characteristics and behaviors might resemble different enteric viruses.

Investigation of enteric adenovirus and poliovirus removal by coagulation processes and suitability of bacteriophages MS2 and φX174 as surrogates for those viruses

We evaluated the removal of enteric adenovirus (AdV) type 40 and poliovirus (PV) type 1 by coagulation, using water samples from 13 water sources for drinking water treatment plants in Japan. The behaviors of two widely accepted enteric virus surrogates, bacteriophages MS2 and φX174, were compared with the behaviors of AdV and PV. Coagulation with polyaluminum chloride (PACl, basicity 1.5) removed AdV and PV from virus-spiked source waters: the infectious AdV and PV removal ratios evaluated by means of a plaque-forming-unit method were 0.1-1.4-log10 and 0.5-2.4-log10, respectively. A nonsulfated high-basicity PACl (basicity 2.1) removed infectious AdV and PV more efficiently than did other commercially available PACls (basicity 1.5-2.1), alum, and ferric chloride. The MS2 removal ratios tended to be larger than those of AdV and PV, partly because of differences in the hydrophobicities of the virus particles and the sensitivity of the virus to the virucidal activity of PACl; the differences in removal ratios were not due to differences in the surface charges of the virus particles. MS2, which was more hydrophobic than the other viruses, was inactivated during coagulation with PACl. Therefore, MS2 does not appear to be an appropriate surrogate for AdV and PV during coagulation. In contrast, because φX174, like AdV and PV, was not inactivated during coagulation, and because the hydrophobicity of φX174 was similar to or somewhat lower than the hydrophobicities of AdV and PV, the φX174 removal ratios tended to be similar to or somewhat smaller than those of the enteric viruses. Therefore, φX174 is a potential conservative surrogate for AdV and PV during coagulation. In summary, the surface hydrophobicity of virus particles and the sensitivity of the virus to the virucidal activity of the coagulant are probably important determinants of the efficiency of virus removal during coagulation.

Competitive Coadsorption Dynamics of Viruses and Dissolved Organic Matter to Positively Charged Sorbent Surfaces

Adsorption onto solid-water interfaces is a key process governing the fate and transport of waterborne viruses. Although negatively charged viruses are known to extensively adsorb onto positively charged adsorbent surfaces, virus adsorption in such systems in the presence of negatively charged dissolved organic matter (DOM) as coadsorbate remains poorly studied and understood. This work provides a systematic assessment of the adsorption dynamics of negatively charged viruses (i.e., bacteriophages MS2, fr, GA, and Qβ) and polystyrene nanospheres onto a positively charged model sorbent surface in the presence of varying DOM concentrations. In all systems studied, DOM competitively suppressed the adsorption of the viruses and nanospheres onto the model surface. Electrostatic repulsion of the highly negatively charged MS2, fr, and the nanospheres impaired their adsorption onto DOM adlayers that formed during the coadsorption process. In contrast, the effect of competition on overall adsorption was attenuated for less-negatively charged GA and Qβ because these viruses also adsorbed onto DOM adlayer surfaces. Competition in MS2-DOM coadsorbate systems were accurately described by a random sequential adsorption model that explicitly accounts for the unfolding of adsorbed DOM. Consistent findings for viruses and nanospheres suggest that the coadsorbate effects described herein generally apply to systems containing negatively charged nanoparticles and DOM.

Electrochemical disinfection of toilet wastewater using wastewater electrolysis cell

The paucity of proper sanitation facilities has contributed to the spread of waterborne diseases in many developing countries. The primary goal of this study was to demonstrate the feasibility of using a wastewater electrolysis cell (WEC) for toilet wastewater disinfection. The treated wastewater was designed to reuse for toilet flushing and agricultural irrigation. Laboratory-scale electrochemical (EC) disinfection experiments were performed to investigate the disinfection efficiency of the WEC with four seeded microorganisms (Escherichia coli, Enterococcus, recombinant adenovirus serotype 5, and bacteriophage MS2). In addition, the formation of organic disinfection byproducts (DBPs) trihalomethanes (THMs) and haloacetic acids (HAA5) at the end of the EC treatment was also investigated. The results showed that at an applied cell voltage of +4 V, the WEC achieved 5-log10 reductions of all four seeded microorganisms in real toilet wastewater within 60 min. In contrast, chemical chlorination (CC) disinfection using hypochlorite [NaClO] was only effective for the inactivation of bacteria. Due to the rapid formation of chloramines, less than 0.5-log10 reduction of MS2 was observed in toilet wastewater even at the highest [NaClO] dosage (36 mg/L, as Cl2) over a 1 h reaction. Experiments using laboratory model waters showed that free reactive chlorine generated in situ during EC disinfection process was the main disinfectant responsible for the inactivation of microorganisms. However, the production of hydroxyl radicals [OH], and other reactive oxygen species by the active bismuth-doped TiO2 anode were negligible under the same electrolytic conditions. The formation of THMs and HAA5 were found to increase with higher applied cell voltage. Based on the energy consumption estimates, the WEC system can be operated using solar energy stored in a DC battery as the sole power source.

Efficient collection of viable virus aerosol through laminar-flow, water-based condensational particle growth

AIMS

State-of-the-art bioaerosol samplers have poor collection efficiencies for ultrafine virus aerosols. This work evaluated the performance of a novel growth tube collector (GTC), which utilizes laminar-flow water-based condensation to facilitate particle growth, for the collection of airborne MS2 viruses.

METHODS AND RESULTS

Fine aerosols (<500 nm) containing MS2 coliphage were generated from a Collison nebulizer, conditioned by a dilution dryer and collected by a GTC and a BioSampler. The GTC effectively condensed water vapour onto the virus particles, creating droplets 2-5 μm in diameter, which facilitated collection. Comparison of particle counts upstream and downstream revealed that the GTC collected >93% of the inlet virus particles, whereas the BioSampler's efficiency was about 10%. Viable counts of the GTC-collected viruses were also one order of magnitude higher than those of the BioSampler (P = 0·003).

CONCLUSION

The efficiency of the GTC for the viable collection of MS2 viruses exceeds that of industry standard instrument, the BioSampler, by a factor of 10-100.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study reveals that the GTC is an effective collector of viable MS2 aerosols, and concludes the instrument will be an effective tool for studying viable virus aerosols and the inhalation risks posed by airborne viruses.

Virus removal and integrity in aged RO membranes

Membrane ageing reduces the quality of the filtered water. Therefore, in order to warrant public health, monitoring membrane performances are of utmost importance. Reverse osmosis (RO) membranes are generally used to remove viruses and salt. However, there is no detailed study demonstrating the impact of aged membrane on the rejection of viruses and of membrane integrity indicators. In this paper, the impact of hypochlorite induced RO ageing on the rejection of a virus surrogate (MS2 phage) and four membrane integrity indicators (salt, dissolved organic matter, rhodamine WT and sulphate) was evaluated. Hypochlorite exposure was either active (under filtration) or passive (soaking), and the changes of the membrane surface chemistry were characterised using several autopsy techniques. Under this accelerated ageing condition, the introduction of chlorine in the membrane chemistry and the breakage of amide bonds caused an increase of the water permeability and a decrease of the virus surrogate's and indicators' rejection. Ageing resulted in a more negatively charged membrane and also in a higher hydrophobicity, which lead to the adsorption of MS2 phage. Despite severe physical membrane damage leading to a reduction of salt rejection to 1.2 log (94%), the minimum rejection of MS2 phage stayed on or above 4 log.

Application of F⁺RNA Coliphages as Source Tracking Enteric Viruses on Parsley and Leek Using RT-PCR

The objective of this study was to identify sources of fecal contamination in leek and parsley, by using four different F(+)RNA coliphage genogroups (IV, I indicate animal fecal contamination and II, III indicate human fecal contamination). Three different concentrations (10(2), 10(4), 10(6) pfu/ml) of MS2 coliphage were inoculated on the surface of parsley and leek samples for detection of phage recovery efficiency among two methods of elution concentration (PEG-precipitation and Ultracentrifugation) by performing double agar layer (DAL) assay in three replications. Highest recovery of MS2 was observed in PEG method and in 10(6) inoculation concentration. Accordingly, the PEG method was used for washing and isolation of potentially contaminated phages of 30 collected samples (15 samples from the market and 15 samples from the farm). The final solutions of PEG method were tested for the enumeration of plaques by DAL assay. Total RNA was then extracted from recovered phages, and RT-PCR was performed by using four primer sets I, II, III, and IV. Incidence of F(+)RNA coliphages was observed in 12/15 (80 %) and 10/15 (66/6 %) of samples were obtained from farm and market, respectively, using both DAL and RT-PCR test methods. Different genotypes (I, II, and IV) of F(+)RNA coliphages were found in farm samples, while only genotype I was detected in market samples by using the primer sets. Due to the higher frequency of genotype I and IV, the absence of genotype III, and also the low frequency of genotype II, it is concluded that the contamination of vegetable (parsley and leek) in Neyshabour, Iran is most likely originated from animal sources.

Enteric Viral Surrogate Reduction by Chitosan

Enteric viruses are a major problem in the food industry, especially as human noroviruses are the leading cause of nonbacterial gastroenteritis. Chitosan is known to be effective against some enteric viral surrogates, but more detailed studies are needed to determine the precise application variables. The main objective of this work was to determine the effect of increasing chitosan concentration (0.7-1.5% w/v) on the cultivable enteric viral surrogates, feline calicivirus (FCV-F9), murine norovirus (MNV-1), and bacteriophages (MS2 and phiX174) at 37 °C. Two chitosans (53 and 222 kDa) were dissolved in water (53 kDa) or 1% acetic acid (222 KDa) at 0.7-1.5%, and were then mixed with each virus to obtain a titer of ~5 log plaque-forming units (PFU)/mL. These mixtures were incubated for 3 h at 37 °C. Controls included untreated viruses in phosphate-buffered saline and viruses were enumerated by plaque assays. The 53 kDa chitosan at the concentrations tested reduced FCV-F9, MNV-1, MS2, and phi X174 by 2.6-2.9, 0.1-0.4, 2.6-2.8, and 0.7-0.9 log PFU/mL, respectively, while reduction by 222 kDa chitosan was 2.2-2.4, 0.8-1.0, 2.6-5.2, and 0.5-0.8 log PFU/mL, respectively. The 222 kDa chitosan at 1 and 0.7% w/v in acetic acid (pH 4.5) caused the greatest reductions of MS2 by 5.2 logs and 2.6 logs, respectively. Overall, chitosan treatments showed the greatest reduction of MS2, followed by FCV-F9, phi X174, and MNV-1. These two chitosans may contribute to the reduction of enteric viruses at the concentrations tested but would require use of other hurdles to eliminate food borne viruses.

Use of a Hand Sanitizing Wipe for Reducing Risk of Viral Illness in the Home

This study determined whether a hand sanitizing wipe can reduce virus transmission in households, and could reduce the probability of infection by rhinovirus and rotavirus. Bacteriophage MS-2 (a marker virus) was used to assess viral transmission in five households having at least two children of ages 2-18. Hands of one female adult were inoculated with ~10(8) PFU MS-2 bacteriophages in each home, and after 8 h, hands of all family members and select fomites were sampled to determine baseline contamination without intervention. This sequence was repeated with the intervention, where all family members were instructed to use a quaternary ammonium compound-based sanitizing wipe at least once per day. A significant reduction of virus after the intervention occurred on inoculated hands (95.3%; p = 0.0039), all fomites combined (74.5%; p < 0.005), and non-inoculated hands and fomites combined (73.5%; p < 0.005). However, viral reduction on non-inoculated hands was not significant, likely due to small sample size. Using rhinovirus and rotavirus as models it was estimated that infection risk was reduced by ~30 to 89% with the use of sanitizing wipes once per day depending on the starting concentration of these viruses on hands of susceptible individuals. Therefore, using a hand sanitizing wipe can significantly reduce viral transmission and risk of illness in homes. Previous studies have shown other hand hygiene interventions, such as alcohol-based hand sanitizers, are even more effective for reducing risk of illness in homes; however the sanitizing wipe used in this study is appropriate to use for microbial reduction.

DLVO and XDLVO calculations for bacteriophage MS2 adhesion to iron oxide particles

In this study, batch experiments were performed to examine the adhesion of bacteriophage MS2 to three iron oxide particles (IOP1, IOP2 and IOP3) with different particle properties. The characteristics of MS2 and iron oxides were analyzed using various techniques to construct the classical DLVO and XDLVO potential energy profiles between MS2 and iron oxides. X-ray diffractometry peaks indicated that IOP1 was mainly composed of maghemite (γ-Fe2O3), but also contained some goethite (α-FeOOH). IOP2 was composed of hematite (α-Fe2O3) and IOP3 was composed of iron (Fe), magnetite (Fe3O4) and iron oxide (FeO). Transmission electron microscope images showed that the primary particle size of IOP1 (γ-Fe2O3) was 12.3±4.1nm. IOP2 and IOP3 had primary particle sizes of 167±35nm and 484±192nm, respectively. A surface angle analyzer demonstrated that water contact angles of IOP1, IOP2, IOP3 and MS2 were 44.83, 64.00, 34.33 and 33.00°, respectively. A vibrating sample magnetometer showed that the magnetic saturations of IOP1, IOP2 and IOP3 were 176.87, 17.02 and 946.85kA/m, respectively. Surface potentials measured in artificial ground water (AGW; 0.075mM CaCl2, 0.082mM MgCl2, 0.051mM KCl, and 1.5mM NaHCO3; pH7.6) indicated that iron oxides and MS2 were negatively charged in AGW (IOP1=-0.0185V; IOP2=-0.0194V; IOP3=-0.0301V; MS2=-0.0245V). Batch experiments demonstrated that MS2 adhesion to iron oxides was favorable in the order of IOP1>IOP2>IOP3. This tendency was well predicted by the classical DLVO model. In the DLVO calculations, both the sphere-plate and sphere-sphere geometries predicted the same trend of MS2 adhesion to iron oxides. Additionally, noticeable differences were not found between the DLVO and XDLVO interaction energy profiles, indicating that hydrophobic interactions did not play a major role; electrostatic interactions, however, did influence MS2 adhesion to iron oxides. Furthermore, the aggregation of iron oxides was investigated with a modified XDLVO model. This model included magnetic interactions between the particles in order to predict the aggregation of iron oxides. Even though iron oxide particle aggregation could occur under experimental conditions, the DLVO model results using primary particle size were more suitable for the interactions between MS2 and the iron oxides because of fast sorption of MS2 onto the surfaces of iron oxides.

Adsorption of Rotavirus, MS2 Bacteriophage and Surface-Modified Silica Nanoparticles to Hydrophobic Matter

Adsorption to aquifer media is an important process in the removal of viruses from groundwater. Even though hydrophobic interactions have been shown to contribute to adsorption, little is known about the hydrophobicity of viruses found in groundwater. In this study, the hydrophobicity of rotavirus, MS2 bacteriophage and DNA-labelled silica nanoparticles (SiNPs) coated with glycoprotein, protein A and alpha-1-microglobulin/bikunin precursor (AMBP) was investigated. The hydrophobicity was experimentally determined by using a modified microbial adhesion to hydrocarbons (MATH) assay. The results were compared with the theoretical hydrophobicity of the viral capsid proteins and the proteins used to coat the nanoparticles, and with the results of adsorption tests with unmodified and organosilane-coated (hydrophobic) silica sand. While most theoretical protein hydrophobicity values were similar, the results of the MATH assay suggested fundamental differences in the hydrophobicity of the viruses and the SiNPs. MS2 was found to be highly hydrophobic as based on the MATH hydrophobicity and a significantly enhanced adsorption to hydrophobic sand, whereas rotavirus was relatively hydrophilic. The MATH assay revealed that protein-coating of SiNP introduced some degree of hydrophobicity to hydrophilic SiNPs, enabling them to more closely mimic viral hydrophobicity. Our study also demonstrated that the protein-coated SiNPs better mimicked rotavirus adsorption to sand media (coated or not coated with hydrophobic organic matter) than the MS2. This further supports previous findings that these surface-modified SiNPs are useful surrogates in mimicking rotavirus retention and transport in porous media.

Investigation of E. coli and Virus Reductions Using Replicate, Bench-Scale Biosand Filter Columns and Two Filter Media

The biosand filter (BSF) is an intermittently operated, household-scale slow sand filter for which little data are available on the effect of sand composition on treatment performance. Therefore, bench-scale columns were prepared according to the then-current (2006-2007) guidance on BSF design and run in parallel to conduct two microbial challenge experiments of eight-week duration. Triplicate columns were loaded with Accusand silica or crushed granite to compare virus and E. coli reduction performance. Bench-scale experiments provided confirmation that increased schmutzdecke growth, as indicated by decline in filtration rate, is the primary factor causing increased E. coli reductions of up to 5-log10. However, reductions of challenge viruses improved only modestly with increased schmutzdecke growth. Filter media type (Accusand silica vs. crushed granite) did not influence reduction of E. coli bacteria. The granite media without backwashing yielded superior virus reductions when compared to Accusand. However, for columns in which the granite media was first backwashed (to yield a more consistent distribution of grains and remove the finest size fraction), virus reductions were not significantly greater than in columns with Accusand media. It was postulated that a decline in surface area with backwashing decreased the sites and surface area available for virus sorption and/or biofilm growth and thus decreased the extent of virus reduction. Additionally, backwashing caused preferential flow paths and deviation from plug flow; backwashing is not part of standard BSF field preparation and is not recommended for BSF column studies. Overall, virus reductions were modest and did not meet the 5- or 3-log10 World Health Organization performance targets.

Aerosolization of a Human Norovirus Surrogate, Bacteriophage MS2, during Simulated Vomiting

Human noroviruses (NoV) are the leading cause of acute gastroenteritis worldwide. Epidemiological studies of outbreaks have suggested that vomiting facilitates transmission of human NoV, but there have been no laboratory-based studies characterizing the degree of NoV release during a vomiting event. The purpose of this work was to demonstrate that virus aerosolization occurs in a simulated vomiting event, and to estimate the amount of virus that is released in those aerosols. A simulated vomiting device was constructed at one-quarter scale of the human body following similitude principles. Simulated vomitus matrices at low (6.24 mPa*s) and high (177.5 mPa*s) viscosities were inoculated with low (108 PFU/mL) and high (1010 PFU/mL) concentrations of bacteriophage MS2 and placed in the artificial "stomach" of the device, which was then subjected to scaled physiologically relevant pressures associated with vomiting. Bio aerosols were captured using an SKC Biosampler. In low viscosity artificial vomitus, there were notable differences between recovered aerosolized MS2 as a function of pressure (i.e., greater aerosolization with increased pressure), although this was not always statistically significant. This relationship disappeared when using high viscosity simulated vomitus. The amount of MS2 aerosolized as a percent of total virus "vomited" ranged from 7.2 x 10-5 to 2.67 x 10-2 (which corresponded to a range of 36 to 13,350 PFU total). To our knowledge, this is the first study to document and measure aerosolization of a NoV surrogate in a similitude-based physical model. This has implications for better understanding the transmission dynamics of human NoV and for risk modeling purposes, both of which can help in designing effective infection control measures.

Control of the spread of viruses in a long-term care facility using hygiene protocols

BACKGROUND

Approximately 50% of norovirus cases in the United States occur in long-term care facilities; many incidences of rotavirus, sapovirus, and adenovirus also occur. The primary objectives of this study were to demonstrate movement of pathogenic viruses through a long-term care facility and to determine the impact of a hygiene intervention on viral transmission.

METHODS

The coliphage MS-2 was seeded onto a staff member's hands, and samples were collected after 4 hours from fomites and hands. After 3 consecutive days of sample collection, a 14-day hygiene intervention was implemented. Hand sanitizers, hand and face wipes, antiviral tissues, and a disinfectant spray were distributed to employees and residents. Seeding and sampling were repeated postintervention.

RESULTS

Analysis of the pre- and postintervention data was performed using a Wilcoxon signed-rank test. Significant reductions in the spread of MS-2 on hands (P = .0002) and fomites (P = .04) were observed postintervention, with a >99% average reduction of virus recovered from both hands and fomites.

CONCLUSION

Although MS-2 spread readily from hands to fomites and vice versa, the intervention reduced average MS-2 concentrations recovered from hands and fomites by up to 4 logs and also reduced the incidence of MS-2 recovery.

Adsorption of MS2 on oxide nanoparticles affects chlorine disinfection and solar inactivation

Adsorption on colloidal particles is one of the environmental processes affecting fate, transport, viability or reproducibility of viruses. This work studied colloidal interactions (adsorption kinetics and isotherms) between different oxide nanoparticles (NPs) (i.e., TiO2, NiO, ZnO, SiO2, and Al2O3) and bacteriophage, MS2. The results shows that that all oxide NPs exhibited strong adsorption capacity for MS2, except SiO2 NPs, which is supported by the extended Derjaguin and Landau, Verwey and Overbeek (EDLVO) theory. Moreover, the implication of such colloidal interactions on water disinfection is manifested by the observations that the presence of TiO2 and ZnO NPs could enhance MS2 inactivation under solar irradiation, whereas NiO and SiO2 decreased MS2 inactivation. By contrast, all of these oxide NPs were found to mitigate chlorine disinfection against MS2 to different extent, and the shielding effect was probably caused by reduced free chlorine and free MS2 in the solution due to sorption onto NPs. Clearly, there is a pressing need to further understand colloidal interactions between engineered NPs and viruses in water to better improve the current water treatment processes and to develop novel nanomaterials for water disinfection.

Modeling of human viruses on hands and risk of infection in an office workplace using micro-activity data

Although the number of illnesses resulting from indirect viral pathogen transmission could be substantial, it is difficult to estimate the relative risks because of the wide variation and uncertainty in human behavior, variable viral concentrations on fomites, and other exposure factors. The purpose of this study was to evaluate the micro-activity approach for assessment of microbial risk by adapting a mathematical model to estimate probability of viral infection from indirect transmission. To evaluate the model, measurements of phage loading on fomites and hands collected before and after implementation of a Healthy Workplace Project intervention were used. Parameter distributions were developed from these data, as well as for micro-activity rates, contact surface areas, phage transfer efficiencies, and inactivation rates. Following the Monte Carlo simulations (n = 1,000), the estimated phage loading on hands was not significantly different from the loading of phage on hands measured in the experimental trials. The model was then used to demonstrate that the Healthy Workplace Project intervention significantly reduced risk of infection by 77% for rotavirus and rhinovirus. This is the first published study to successfully evaluate a model focused on the indirect transmission of viruses via hand contact with measured data and provide an assessment of the micro-activity approach to microbial risk evaluation.

Effect of hydraulically reversible and hydraulically irreversible fouling on the removal of MS2 and φX174 bacteriophage by an ultrafiltration membrane

The effect of membrane fouling on the removal of enteric virus surrogates MS2 and φX174 bacteriophage by an ultrafiltration membrane was assessed under simulated full-scale drinking water treatment operating conditions. Filtration experiments of up to 8 days using either river or lake water ascertained how the membrane fouling layer affected virus removal. Organic carbon fractionation techniques identified potential foulants, including biopolymers, in the feed water and in the permeate. Hydraulically irreversible fouling could greatly improve the removal of both viruses at moderate and severe fouling conditions by up to 2.5 logs. Hydraulically reversible fouling increased virus removal only slightly, and increased removal of >0.5 log for both phage were only obtained under severe fouling conditions. The increase in virus removal due to irreversible and reversible fouling differed between the two water sources. As the degree of fouling increased, differences between the removal of the two phage decreased. Maintenance cleaning partially removed membrane foulants, however virus removal following maintenance cleaning was lower than that of the fouled membrane, it remained higher than that of the clean membrane.

MS2 bacteriophage reduction and microbial communities in biosand filters

This study evaluated the role of physical and biological filter characteristics on the reduction of MS2 bacteriophage in biosand filters (BSFs). Three full-scale concrete Version 10 BSFs, each with a 55 cm sand media depth and a 12 L charge volume, reached 4 log10 reduction of MS2 within 43 days of operation. A consistently high reduction of MS2 between 4 log10 and 7 log10 was demonstrated for up to 294 days. Further examining one of the filters revealed that an average of 2.8 log10 reduction of MS2 was achieved within the first 5 cm of the filter, and cumulative virus reduction reached an average of 5.6 log10 after 240 days. Core sand samples from this filter were taken for protein, carbohydrate, and genomic extraction. Higher reduction of MS2 in the top 5 cm of the sand media (0.56 log10 reduction per cm vs 0.06 log10 reduction per cm for the rest of the filter depth) coincided with greater diversity of microbial communities and increased concentrations of carbohydrates. In the upper layers, "Candidatus Nitrosopumilus maritimus" and "Ca. Nitrospira defluvii" were found as dominant populations, while significant amounts of Thiobacillus-related OTUs were detected in the lower layers. Proteolytic bacterial populations such as the classes Sphingobacteria and Clostridia were observed over the entire filter depth. Thus, this study provides the first insight into microbial community structures that may play a role in MS2 reduction in BSF ecosystems. Overall, besides media ripening and physical reduction mechanisms such as filter depth and long residence time (45 min vs 24 ± 8.5 h), the establishment of chemolithotrophs and proteolytic bacteria could greatly enhance the reduction of MS2.

Transport and removal of bacteriophages MS2 and PhiX174 in steel slag-amended soils: column experiments and transport model analyses

The aim of this study was to investigate the removal of bacteriophages MS2 and PhiX174 in soils amended with converter furnace steel slag. Column experiments were performed to examine the bacteriophage removal in slag-amended (slag content: 0%, 25%, and 50%) loam soils. For comparison, column experiments were also conducted with Escherichia coli. In addition, chloride (Cl) was used as a conservative tracer to determine transport characteristics. Results showed mass recoveries of Cl of 98.6 +/- 3.5%, indicating that the experiments were conducted successfully. The mass recovery of MS2 was 86.7% in no slag (100% soil), decreasing to 0% in slag contents of 25% and 50%. The mass recovery of PhiX174 decreased from 87.8% to 51.5% with increasing slag content from 0% to 50%. In the case of E. coli, the mass recoveries decreased from 47.0% to 10.5% with increasing slag content from 0% to 50%. In the transport models analyses, the HYDRUS-1D code was used to quantify the sorption parameters from breakthrough curves. For the 100% soil column, a one-site kinetic sorption model was fitted to the data, whereas a two-site kinetic sorption model was fitted for slag-amended (25% and 50% slag) soil data. Results demonstrate that the addition of steel slag to soil enhances the removal of bacteriophages due to the presence of FeO in the steel slag. However, CaO could not contribute to the bacteriophage removal in our experimental conditions because the effluent pH (7.7-8.9) in slag-amended (25% and 50% slag) soils was not high enough to promote the bacteriophage inactivation.

Bacteria and virus removal effectiveness of ceramic pot filters with different silver applications in a long term experiment

In 2012 more than 4 million people used a ceramic pot filter (CPF) as household water treatment system for their daily drinking water needs. In the normal production protocol most low cost filters are impregnated with a silver solution to enhance the microbial removal efficiency. The aim of this study was to determine the role of silver during the filtration and subsequent storage. Twenty-two CPFs with three different silver applications (non, only outside and both sides) were compared in a long-term loading experiment with Escherichia coli (K12 and WR1) and MS2 bacteriophages in natural challenge water under highly controlled laboratory circumstances. No significant difference in Log Removal Values were found between the filters with different silver applications. The results show that the storage time in the receptacle is the dominant parameter to reach E. coli inactivation by silver, and not the contact time during the filtration phase. The hypothesis that the absence of silver would enhance the virus removal, due to biofilm formation on the ceramic filter element, could not be confirmed. The removal effectiveness for viruses is still of major concern for the CPF. This study suggests that the ceramic pot filter characteristics, such as burnt material content, do not determine E. coli removal efficacies, but rather the contact time with silver during storage is the dominant parameter to reach E. coli inactivation.

Comparison of high-volume air sampling equipment for viral aerosol sampling during emergency response

OBJECTIVE

This study compared the performance of two high-volume bioaerosol air samplers for viable virus to an accepted standard low-volume sampler. In typical bioaerosol emergency response scenarios, highvolume sampling is essential for the low infective concentrations and large air volumes involved.

DESIGN

Two high-volume air samplers (XMX/2LMIL and DFU-1000) were evaluated alongside a lowvolume sample (BioSampler). Low and high concentrations (9.3-93.2 agent containing particles per liter of air [ACPLA]) of male-specific coliphage 2 (MS2) virus were released into a 12 m3 aerosol test chamber and collected using the air samplers. The collection media from the samplers were then processed and viable virus was assessed via plaque assay.

SETTING

Aerosol test chamber.

SUBJECTS, PARTICIPANTS

None.

INTERVENTIONS

Collection media and flow rate were modified for the XMX/2L-MIL sampler for viable analysis.

MAIN OUTCOME MEASURES

Concentration estimates in units of plaque forming units per liter of air (PFU/liter) assessed by the samplers as compared to the levels inside the chamber as evaluated with a slit to agar plate in units of ACPLA. Comparison was made via one-way analysis of variance.

RESULTS

Both the XMX/2L-MIL and DFU-1000 achieved collection effectiveness equal to or greater than the low-volume air sampler for the evaluated MS2 concentrations. The XMX/2L-MIL reliably collected quantifiable low concentrations of MS2, but the DFU-1000 was unable to do so.

CONCLUSIONS

For emergency response to suspected bioaerosols, the evaluated high-volume samplers are as effective as the standard low-flow sampler and should be considered in conducting a health risk assessment. If low concentrations are expected, then high-flow samplers using liquid collection are preferred.

Intermittent versus continuous operation of biosand filters

The biosand filter is a household-scale point-of-use water filtration system based on slow sand filtration, but modified for intermittent operation. Studies on slow sand filters show that intermittent operation reduces filter effectiveness. However, continuous versus intermittent operation of biosand filters has never been compared. Eight 10-cm diameter columns were constructed to represent field biosand filters. Five were operated intermittently with a 24-h residence period, while the remaining three were operated continuously. Continuous operation of the filters resulted in significantly better reduction of Escherichia coli (3.71 log10 versus 1.67 log10), bacteriophage MS2 (2.25 log10 versus 0.85 log10), and turbidity (96% versus 87%). Dissolved oxygen levels at 5 and 10 cm of media depth in intermittent filters reached an average of 0 mg/L by 24 h of residence time on day 60 of the experiment. A simple numerical model was developed to describe E. coli removal during ripening from days 0-58 for continuously operated versus intermittent filters. This research confirms that although biosand filters were developed for intermittent operation, the filters perform significantly better when operated continuously. However, both operational modes resulted in a significant reduction of microbial indicators.

Mechanisms of MS2 bacteriophage removal by fouled ultrafiltration membrane subjected to different cleaning methods

An ultrafiltration unit with a polyvinylidene fluoride (PVDF) membrane of 40 nm nominal pore size was used to study bacteriophage MS2 removal under different membrane conditions: pristine membrane, membrane fouled by soluble microbial product (SMP) extracted from membrane bioreactor (MBR) feedwater, backwashed membrane, and chemically cleaned membrane. The order of MS2 removal by these membranes was as follows: fouled membrane > backwashed membrane > chemically cleaned membrane ≈ pristine membrane. A linear correlation between membrane relative permeability and MS2 removal was found. Mass balance analysis showed a high percentage of MS2 in the concentrate for the fouled membrane as compared with the pristine membrane. Quartz crystal microbalance (QCM) results showed faster kinetics of MS2 adhesion to the pristine membrane than to the SMP-fouled membrane. In agreement with QCM results, an attractive force between MS2 and the pristine membrane was detected using an atomic force microscope (AFM), whereas a repulsive force was detected for the interaction between MS2 and the fouled membrane. The presence of SMP on the membrane surface led to higher rejection of MS2 due to both pore blocking and repulsion between MS2 and the SMP layer. Chemical cleaning removed most of the SMP foulant and as a result led to a lower MS2 removal.

Effect of temperature and sunlight on the stability of human adenoviruses and MS2 as fecal contaminants on fresh produce surfaces

Determining the stability, or persistence in an infectious state, of foodborne viral pathogens attached to surfaces of soft fruits and salad vegetables is essential to underpin risk assessment studies in food safety. Here, we evaluate the effect of temperature and sunlight on the stability of infectious human adenoviruses type 2 and MS2 bacteriophages on lettuce and strawberry surfaces as representative fresh products. Human adenoviruses have been selected because of their double role as viral pathogens and viral indicators of human fecal contamination. Stability assays were performed with artificially contaminated fresh samples kept in the dark or under sunlight exposure at 4 and 30°C over 24h. The results indicate that temperature is the major factor affecting HAdV stability in fresh produce surfaces, effecting decay between 3 and 4 log after 24h at 30°C. The inactivation times to achieve a reduction between 1 and 4-log are calculated for each experimental condition. This work provides useful information to be considered for improving food safety regarding the transmission of foodborne viruses through supply chains.

Impact of milk components on recovery of viral RNA from MS2 bacteriophage

Noroviruses are responsible for approximately 44 % of outbreaks involving dairy products for which causative agents are reported. Recovery of viruses from milk and dairy products is a difficult task. The role of different components of milk in the recovery of viral RNA was evaluated in this study. Four model milk formulations (A-D) were prepared by mixing different combinations of lactose, whey protein, casein, and fat in water. Each model formulation was spiked with five concentrations of bacteriophage MS2. The phenol-guanidine thiocyanate-chloroform protocol was used for extracting viral RNA from the model milk formulations and then extracted RNA was measured by a nanodrop spectrophotometer in ng/μl. The results showed that casein and whey protein had the highest negative impact on RNA yield, especially when the number of MS2 was less than 1.3 pfu/ml. The highest RNA recovery was obtained from the model milk formulation containing all four components; lactose, whey protein, casein, and fat. The amount of extracted RNA was closely correlated with the dry matter content of each formulation and the spiked concentration of coliphage using response surface modeling (R²:0.93). It was determined that milk fat is the most effective component in facilitating RNA extraction and the highest RNA yield can be achieved via elimination of whey protein and casein from milk by centrifugation at 40,000×g for 60 min. To achieve the highest viral RNA recovery efficiency by the proposed method, milk fat must be recombined with the supernatant of the centrifuged sample and then homogenized before performing the extraction protocol.

Sweep flocculation and adsorption of viruses on aluminum flocs during electrochemical treatment prior to surface water microfiltration

Bench-scale experiments were performed to evaluate virus control by an integrated electrochemical-microfiltration (MF) process from turbid (15 NTU) surface water containing moderate amounts of dissolved organic carbon (DOC, 5 mg C/L) and calcium hardness (50 mg/L as CaCO3). Higher reductions in MS2 bacteriophage concentrations were obtained by aluminum electrocoagulation and electroflotation compared with conventional aluminum sulfate coagulation. This was attributed to electrophoretic migration of viruses, which increased their concentrations in the microenvironment of the sacrificial anode where coagulant precursors are dissolved leading to better destabilization during electrolysis. In all cases, viruses were not inactivated implying measured reductions were solely due to their removal. Sweep flocculation was the primary virus destabilization mechanism. Direct evidence for virus enmeshment in flocs was provided by two independent methods: quantitative elution using beef extract at elevated pH and quantitating fluorescence from labeled viruses. Atomic force microscopy studies revealed a monotonically increasing adhesion force between viruses immobilized on AFM tips and floc surfaces with electrocoagulant dosage, which suggests secondary contributions to virus uptake on flocs from adsorption. Virus sorption mechanisms include charge neutralization and hydrophobic interactions with natural organic matter removed during coagulation. This also provided the basis for interpreting additional removal of viruses by the thick cake formed on the surface of the microfilter following electrocoagulation. Enhancements in virus removal as progressively more aluminum was electrolyzed therefore embodies contributions from (i) better encapsulation onto greater amounts of fresh Al(OH)3 precipitates, (ii) increased adsorption capacity associated with higher available coagulant surface area, (iii) greater virus-floc binding affinity due to effective charge neutralization and hydrophobic interactions, and/or (iv) additional removal by a dynamic membrane if a thick cake layer of flocs is deposited.

A mathematical model for removal of human pathogenic viruses and bacteria by slow sand filtration under variable operational conditions

Slow sand filtration (SSF) in drinking water production removes pathogenic microorganisms, but detection limits and variable operational conditions complicate assessment of removal efficiency. Therefore, a model was developed to predict removal of human pathogenic viruses and bacteria as a function of the operational conditions. Pilot plant experiments were conducted, in which bacteriophage MS2 and Escherichia coli WR1 were seeded as model microorganisms for pathogenic viruses and bacteria onto the filters under various temperatures, flow rates, grain sizes and ages of the Schmutzdecke. Removal of MS2 was 0.082-3.3 log10 and that of E. coli WR1 0.94-4.5 log10 by attachment to the sand grains and additionally by processes in the Schmutzdecke. The contribution of the Schmutzdecke to the removal of MS2 and E. coli WR1 increased with its ageing, with sticking efficiency and temperature, decreased with grain size, and was modelled as a logistic growth function with scale factor f0 and rate coefficient f1. Sticking efficiencies were found to be microorganism and filter specific, but the values of f0 and f1 were independent of microorganism and filter. Cross-validation showed that the model can be used to predict log removal of MS2 and ECWR1 within ±0.6 log. Within the range of operational conditions, the model shows that removal of microorganisms is most sensitive to changes in temperature and age of the Schmutzdecke.

A mathematical model for removal of human pathogenic viruses and bacteria by slow sand filtration under variable operational conditions

Slow sand filtration (SSF) in drinking water production removes pathogenic microorganisms, but detection limits and variable operational conditions complicate assessment of removal efficiency. Therefore, a model was developed to predict removal of human pathogenic viruses and bacteria as a function of the operational conditions. Pilot plant experiments were conducted, in which bacteriophage MS2 and Escherichia coli WR1 were seeded as model microorganisms for pathogenic viruses and bacteria onto the filters under various temperatures, flow rates, grain sizes and ages of the Schmutzdecke. Removal of MS2 was 0.082-3.3 log10 and that of E. coli WR1 0.94-4.5 log10 by attachment to the sand grains and additionally by processes in the Schmutzdecke. The contribution of the Schmutzdecke to the removal of MS2 and E. coli WR1 increased with its ageing, with sticking efficiency and temperature, decreased with grain size, and was modelled as a logistic growth function with scale factor f0 and rate coefficient f1. Sticking efficiencies were found to be microorganism and filter specific, but the values of f0 and f1 were independent of microorganism and filter. Cross-validation showed that the model can be used to predict log removal of MS2 and ECWR1 within ±0.6 log. Within the range of operational conditions, the model shows that removal of microorganisms is most sensitive to changes in temperature and age of the Schmutzdecke.

Evaluation of concentration efficiency of the Pseudomonas aeruginosa phage PP7 in various water matrixes by different methods

Enteric viruses monitoring in surface waters requires the concentration of viruses before detection assays. The aim of this study was to evaluate different methods in terms of recovery efficiencies of bacteriophage PP7 of Pseudomonas aeruginosa, measured by real-time PCR, using it as a viral control process in water analysis. Different nucleic acid extraction methods (silica-guanidinium thiocyanate, a commercial kit (Qiagen Viral RNA Kit) and phenol-chloroform with alcohol precipitation) exhibited very low recovery efficiencies (0.08-4.18 %), being the most efficient the commercial kit used for subsequent experiments. To evaluate the efficiency of three concentration methods, PBS (as model for clean water) and water samples from rivers were seeded to reach high (HC, 10(6) pfu ml(-1)) and low concentrations (LC, 10(4) pfu ml(-1)) of PP7. Tangential ultrafiltration proved to be more efficient (50.36 ± 12.91, 17.21 ± 9.22 and 12.58 ± 2.35 % for HC in PBS and two river samples, respectively) than adsorption-elution with negatively charged membranes (1.00 ± 1.34, 2.79 ± 2.62 and 0.05 ± 0.08 % for HC in PBS and two river samples, respectively) and polyethylene glycol precipitation (15.95 ± 7.43, 4.01 ± 1.12 and 3.91 ± 0.54 %, for HC in PBS and two river samples, respectively), being 3.2-50.4 times more efficient than the others for PBS and 2.7-252 times for river samples. Efficiencies also depended on the initial virus concentration and aqueous matrixes composition. In consequence, the incorporation of an internal standard like PP7 along the process is useful as a control of the water concentration procedure, the nucleic acid extraction, the presence of inhibitors and the variability of the recovery among replicas, and for the calculation of the sample limit of detection. Thus, the use of a process control, as presented here, is crucial for the accurate quantification of viral contamination.

Improved virus removal in ceramic depth filters modified with MgO

Ceramic filters, working on the depth filtration principle, are known to improve drinking water quality by removing human pathogenic microorganisms from contaminated water. However, these microfilters show no sufficient barrier for viruses having diameters down to 20 nm. Recently, it was shown that the addition of positively charged materials, for example, iron oxyhydroxide, can improve virus removal by adsorption mechanisms. In this work, we modified a common ceramic filter based on diatomaceous earth by introducing a novel virus adsorbent material, magnesium oxyhydroxide, into the filter matrix. Such filters showed an improved removal of about 4-log in regard to bacteriophages MS2 and PhiX174. This is explained with the electrostatic enhanced adsorption approach that is the favorable adsorption of negatively charged viruses onto positively charged patches in an otherwise negatively charged filter matrix. Furthermore, we provide theoretical evidence applying calculations according to Derjaguin-Landau-Verwey-Overbeek theory to strengthen our experimental results. However, modified filters showed a significant variance in virus removal efficiency over the course of long-term filtration experiments with virus removal increasing with filter operation time (or filter aging). This is explained by transformational changes of MgO in the filter upon contact with water. It also demonstrates that filter history is of great concern when filters working on the adsorption principles are evaluated in regard to their retention performance as their surface characteristics may alter with use.

Combination of microalgae cultivation with membrane processes for the treatment of municipal wastewater

The treatment of wastewater by microalgae cultivation has attracted more and more attention. However, the way to harvest microalgae cells from the wastewater and the treatment of the large quantity of residual solution have become critical issues. In this work, a new approach for the treatment of municipal wastewater is presented. The combination of flocculation for removing mainly microalgae and thereafter membrane filtration for chemical oxygen demand (COD) and conductivity reduction of the residual solution after flocculation is discussed. The COD concentration of the wastewater decreased from 260 to 84 mg/L after flocculation by chitosan. Five ultrafiltration (UF) membranes and two nanofiltration (NF) membranes were used for filtration to find a suitable membrane for COD and conductivity reduction. Among the five UF membranes, GR82PE showed the best performance, whose permeate flux and COD retention at 4 bar were 189.66 L/(m(2)·h) and 43.03%, respectively. NF membranes showed higher COD and conductivity retentions than UF membranes. The COD retention of Desal5-DK reached 98.3% at 20 bar. Lastly, the flux recovery after the filtration test of each membrane is also discussed.

Microorganism inactivation by an ozonation step optimized for micropollutant removal from tertiary effluent

This paper demonstrates the additional benefit of the microbicidal efficacy of an ozonation plant implemented for micropollutant removal from tertiary effluent. Due to the low amount of viruses and protozoa in the tertiary effluent, bacteriophage MS2 and spores of Bacillus subtilis were dosed as surrogates. At specific ozone consumptions of 0.6 and 0.9 g O3/g dissolved organic carbon (DOC) a 2-log colony forming unit (CFU) reduction was achieved for indigenous Escherichia coli and enterococci, and the limits of the European bathing water directive for the excellent quality of inland waters were met. Higher removal was impeded by the shielding effect of suspended solids in the effluent, which implies the combination of ozonation with a preceding filtration step if higher microbicidal performances are required. The surrogate virus MS2 was reduced by 4-5 log while no significant inactivation was detected for B. subtilis spores. Additionally, the impact of ozonation on the biochemical oxygen demand (BOD) was studied. The BOD5 measurement was not adversely affected despite the reduced concentration of microorganisms after ozonation. The intrinsic increase in BOD5 averaged 15% at 0.6-0.7 g O3/g DOC. The impact of the projected increase on the surface water quality is generally not considered a problem but has to be assessed on a case-by-case approach.

Microbiological effectiveness of mineral pot filters in Cambodia

Mineral pot filters (MPFs) are household water treatment (HWT) devices that are manufactured and distributed by the private sector, with millions of users in Southeast Asia. Their effectiveness in reducing waterborne microbes has not been previously investigated. We purchased three types of MPFs available on the Cambodian market for systematic evaluation of bacteria, virus, and protozoan surrogate microbial reduction in laboratory challenge experiments following WHO recommended performance testing protocols. Results over the total 1500 L testing period per filter indicate that the devices tested were highly effective in reducing Esherichia coli (99.99%+), moderately effective in reducing bacteriophage MS2 (99%+), and somewhat effective against Bacillus atrophaeus, a spore-forming bacterium we used as a surrogate for protozoa (88%+). Treatment mechanisms for all filters included porous ceramic and activated carbon filtration. Our results suggest that these commercially available filters may be at least as effective against waterborne pathogens as other, locally available treatment options such as ceramic pot filters or boiling. More research is needed on the role these devices may play as interim solutions to the problem of unsafe drinking water in Cambodia and globally.

Alumoxane/ferroxane nanoparticles for the removal of viral pathogens: the importance of surface functionality to nanoparticle activity

A bi-functional nano-composite coating has been created on a porous Nomex® fabric support as a trap for aspirated virus contaminated water. Nomex® fabric was successively dip-coated in solutions containing cysteic acid functionalized alumina (alumoxane) nanoparticles and cysteic acid functionalized iron oxide (ferroxane) nanoparticles to form a nanoparticle coated Nomex® (NPN) fabric. From SEM and EDX the nanoparticle coating of the Nomex® fibers is uniform, continuous, and conformal. The NPN was used as a filter for aspirated bacteriophage MS2 viruses using end-on filtration. All measurements were repeated to give statistical reliability. The NPN fabrics show a large decrease as compared to Nomex® alone or alumoxane coated Nomex®. An increase in the ferroxane content results in an equivalent increase in virus retention. This suggests that it is the ferroxane that has an active role in deactivating and/or binding the virus. Heating the NPN to 160 °C results in the loss of cysteic acid functional groups (without loss of the iron nanoparticle's core structure) and the resulting fabric behaves similar to that of untreated Nomex®, showing that the surface functionalization of the nanoparticles is vital for the surface collapse of aspirated water droplets and the absorption and immobilization of the MS2 viruses. Thus, for virus immobilization, it is not sufficient to have iron oxide nanoparticles per se, but the surface functionality of a nanoparticle is vitally important in ensuring efficacy.

Combination of crossflow ultrafiltration, monolithic affinity filtration, and quantitative reverse transcriptase PCR for rapid concentration and quantification of model viruses in water

We present a rapid and effective adsorption-elution method based on monolithic affinity filtration (MAF) for the concentration and purification of waterborne viruses. The MAF column consists of a hydrolyzed macroporous epoxy-based polymer. High recoveries were achieved by columns for the bacterial virus (bacteriophage) MS2 110 (±19)%, as model organism, as well as for human adenoviruses 42.4 (±3.4)% and murine noroviruses 42.6 (±1.9)%. This new concentration and purification method was combined with crossflow ultrafiltration (CUF). Because of the adsorption of the examined viruses to the macroporous surface of the MAF column at pH 3, concentrated matrix components by CUF can be removed. Bacteriophages MS2 were spiked in tap water and concentrated with the new CUF-MAF concentration method by a volumetric factor of 10(4) within 33 min. Furthermore, the detection limit for quantification of bacteriophage MS2 by quantitative reverse transcriptase PCR (qRT-PCR) could be improved from 79.47 to 0.0056 GU mL(-1) by a factor of 1.4 × 10(4). In a first study, we have shown that this method could also be applied for river water containing naturally MS2 and MS2-like phages.

Effects of relative humidity and spraying medium on UV decontamination of filters loaded with viral aerosols

Although respirators and filters are designed to prevent the spread of pathogenic aerosols, a stockpile shortage is anticipated during the next flu pandemic. Contact transfer and reaerosolization of collected microbes from used respirators are also a concern. An option to address these potential problems is UV irradiation, which inactivates microbes by dimerizing thymine/uracil in nucleic acids. The objective of this study was to determine the effects of transmission mode and environmental conditions on decontamination efficiency by UV. In this study, filters were contaminated by different transmission pathways (droplet and aerosol) using three spraying media (deionized water [DI], beef extract [BE], and artificial saliva [AS]) under different humidity levels (30% [low relative humidity {LRH}], 60% [MRH], and 90% [HRH]). UV irradiation at constant intensity was applied for two time intervals at each relative humidity condition. The highest inactivation efficiency (IE), around 5.8 logs, was seen for DI aerosols containing MS2 on filters at LRH after applying a UV intensity of 1.0 mW/cm(2) for 30 min. The IE of droplets containing MS2 was lower than that of aerosols containing MS2. Absorption of UV by high water content and shielding of viruses near the center of the aggregate are considered responsible for this trend. Across the different media, IEs in AS and in BE were much lower than in DI for both aerosol and droplet transmission, indicating that solids present in AS and BE exhibited a protective effect. For particles sprayed in a protective medium, RH is not a significant parameter.

Thermostable DNA polymerase from a viral metagenome is a potent RT-PCR enzyme

Viral metagenomic libraries are a promising but previously untapped source of new reagent enzymes. Deep sequencing and functional screening of viral metagenomic DNA from a near-boiling thermal pool identified clones expressing thermostable DNA polymerase (Pol) activity. Among these, 3173 Pol demonstrated both high thermostability and innate reverse transcriptase (RT) activity. We describe the biochemistry of 3173 Pol and report its use in single-enzyme reverse transcription PCR (RT-PCR). Wild-type 3173 Pol contains a proofreading 3′-5′ exonuclease domain that confers high fidelity in PCR. An easier-to-use exonuclease-deficient derivative was incorporated into a PyroScript RT-PCR master mix and compared to one-enzyme (Tth) and two-enzyme (MMLV RT/Taq) RT-PCR systems for quantitative detection of MS2 RNA, influenza A RNA, and mRNA targets. Specificity and sensitivity of 3173 Pol-based RT-PCR were higher than Tth Pol and comparable to three common two-enzyme systems. The performance and simplified set-up make this enzyme a potential alternative for research and molecular diagnostics.

Removal of MS2, Qβ and GA bacteriophages during drinking water treatment at pilot scale

The removal of MS2, Qβ and GA, F-specific RNA bacteriophages, potential surrogates for pathogenic waterborne viruses, was investigated during a conventional drinking water treatment at pilot scale by using river water, artificially and independently spiked with these bacteriophages. The objective of this work is to develop a standard system for assessing the effectiveness of drinking water plants with respect to the removal of MS2, Qβ and GA bacteriophages by a conventional pre-treatment process (coagulation-flocculation-settling-sand filtration) followed or not by an ultrafiltration (UF) membrane (complete treatment process). The specific performances of three UF membranes alone were assessed by using (i) pre-treated water and (ii) 0.1 mM sterile phosphate buffer solution (PBS), spiked with bacteriophages. These UF membranes tested in this work were designed for drinking water treatment market and were also selected for research purpose. The hypothesis serving as base for this study was that the interfacial properties for these three bacteriophages, in terms of electrostatic charge and the degree of hydrophobicity, could induce variations in the removal performances achieved by drinking water treatments. The comparison of the results showed a similar behaviour for both MS2 and Qβ surrogates whereas it was particularly atypical for the GA surrogate. The infectious character of MS2 and Qβ bacteriophages was mostly removed after clarification followed by sand filtration processes (more than a 4.8-log reduction) while genomic copies were removed at more than a 4.0-log after the complete treatment process. On the contrary, GA bacteriophage was only slightly removed by clarification followed by sand filtration, with less than 1.7-log and 1.2-log reduction, respectively. After the complete treatment process achieved, GA bacteriophage was removed with less than 2.2-log and 1.6-log reduction, respectively. The effectiveness of the three UF membranes tested in terms of bacteriophages removal showed significant differences, especially for GA bacteriophage. These results could provide recommendations for drinking water suppliers in terms of selection criteria for membranes. MS2 bacteriophage is widely used as a surrogate for pathogenic waterborne viruses in Europe and the United States. In this study, the choice of MS2 bacteriophage as the best surrogate to be used for assessment of the effectiveness of drinking water treatment in removal of pathogenic waterborne viruses in worst conditions is clearly challenged. It was shown that GA bacteriophage is potentially a better surrogate as a worst case than MS2. Considering GA bacteriophage as the best surrogate in this study, a chlorine disinfection step could guaranteed a complete removal of this model and ensure the safety character of drinking water plants.

Mechanisms of virus control during iron electrocoagulation--microfiltration of surface water

Results from a laboratory-scale study evaluating virus control by a hybrid iron electrocoagulation - microfiltration process revealed only 1.0-1.5 log MS2 bacteriophage reduction even at relatively high iron dosages (≈ 13 mg/L as Fe) for natural surface water containing moderate natural organic matter (NOM) concentrations (4.5 mg/L dissolved organic carbon, DOC). In contrast, much greater reductions were measured (6.5-log at pH 6.4 and 4-log at pH 7.5) at similar iron dosages for synthetic water that was devoid of NOM. Quantitative agreement with Faraday's law with 2-electron transfer and speciation with phenanthroline demonstrated electrochemical generation of soluble ferrous iron. Near quantitative extraction of viruses by dissolving flocs formed in synthetic water provided direct evidence of their removal by sorption and enmeshment onto iron hydroxide flocs. In contrast, only approximately 1% of the viruses were associated with the flocs formed in natural water consistent with the measured poor removals. 1-2 logs of virus inactivation were also observed in the electrochemical cell for synthetic water (no NOM) but not for surface water (4.5 mg/L DOC). Sweep flocculation was the dominant destabilization mechanism since the ζ potential did not reach zero even when 6-log virus reductions were achieved. Charge neutralization only played a secondary role since ζ potential → 0 with increasing iron electrocoagulant dosage. Importantly, virus removal from synthetic water decreased when Suwanee River Humic Acid was added. Therefore, NOM present in natural waters appears to reduce the effectiveness of iron electrocoagulation pretreatment to microfiltration for virus control by complexing ferrous ions. This inhibits (i) Fe(2+) oxidation, precipitation, and virus destabilization and (ii) virus inactivation through reactive oxygen species intermediates or by direct interactions with Fe(2+) ions.

Mg/Al layered double hydroxide for bacteriophage removal in aqueous solution

The objective of this study was to investigate the removal of bacteriophages in Mg/Al layered double hydroxide (LDH). Batch experiments were performed with bacteriophage MS2 in a powder form of Mg/Al LDH under various LDH doses. Column experiments were also performed under flow-through condition with bacteriophages MS2 and phiX174 in Mg/Al LDH immobilized on sand surfaces. Batch tests demonstrated that the powder form of Mg/Al LDH was effective in removing MS2 with the removal capacity of 2.2 × 10(8) plaque forming unit (pfu)/g under the given experimental conditions (LDH dose = 2 g/L; initial MS2 concentration = 4.61 × 10(5) pfu/mL). Column experiments showed that the log removal of phiX174 was 4.40 in columns containing 100% Mg/Al LDH-coated sand while it was 0.05 in 100% quartz sand. These findings indicated that Mg/Al LDH-coated sand was effective in removing bacteriophages compared with sand. A more than 4 log removal (=5.44) of MS2 was achieved in 100% Mg/Al LDH-coated sand. This study demonstrates the potential application of Mg/Al LDH for virus removal in water treatment.

Performance of conventional and antimicrobial-treated filtering facepiece respirators challenged with biological aerosols

This study evaluated the filtration performance of four commercially available models of National Institute of Occupational Safety and Health (NIOSH)-certified filtering facepiece respirators (FFR) against both biological and inert aerosols at a flow rate of 85 L/min. Conventional N95 and P100 FFRs and two antimicrobial (AM)-treated FFRs (an N95 and a P95, both with iodine-based AM treatments) were tested for both physical penetration (PEN(P)) and viable penetration (PEN(V)) with three different bioaerosols, including MS2 bacteriophage virus, and the spores and vegetative cells of Bacillus atrophaeus bacteria, in addition to inert sodium chloride (NaCl) aerosol. For each FFR model, the PEN(P) measured with NaCl was predictive of its MS2 PEN(P), and it was observed that spores and bacteria aerosols were also filtered similarly to the inert aerosol. For both conventional FFRs, up to a 1-log reduction in PEN(V) in comparison with PEN(P) was observed and attributed to the experimental variability of the test system. For both models of AM-FFRs, no statistically significant differences between PEN(V) and PEN(P) for any of the three different bioaerosol challenges were observed. Thus, no bioaerosol filtration enhancement over the conventional FFRs was detected for either iodine-based AM-FFR. In the absence of any standardized test methods, we recommend that future studies evaluating the filtration performance of AM-treated FFRs incorporate the experimental best practices described herein.

Occurrence and removal of microbial indicators from municipal wastewaters by nine different MBR systems

Nine different membrane bioreactor (MBR) systems with different process configurations (submerged and external), membrane geometries (hollow-fiber, flat-sheet, and tubular), membrane materials (polyethersulfone (PES), polyvinylidene fluoride (PVDF), and polytetrafluoroethylene (PTFE)) and membrane nominal pore sizes (0.03-0.2 μm) were evaluated to assess the impact of influent microbial concentration, membrane pore size and membrane material and geometries on removal of microbial indicators by MBR technology. The log removal values (LRVs) for microbial indicators increased as the influent concentrations increased. Among the wide range of MBR systems evaluated, the total and fecal coliform bacteria and indigenous MS-2 coliphage were detected in 32, 9 and 15% of the samples, respectively; the 50th percentile LRVs were measured at 6.6, 5.9 and 4.5 logs, respectively. The nominal pore sizes of the membranes, membrane materials and geometries did not show a strong correlation with the LRVs.

[Water treatment from viruses using heterogeneous sensitizer based on polycationic aluminum phthalocyanine]

The authors propose a new heterogeneous photo sensitizer containing aluminum tetrakis [bis(cholinyl)phenylthio)] phthalocyanine grafted onto silica as an active phase. A poliovirus type 1 LSc2ab and RNA-containing phage MS2 model was used to show that the sensitizer had photo decontaminating activity against viruses and may be used to purify water from viral contamination. The mechanism for removal of viruses from water is two-step and involves the adsorption of the virus on the heterogeneous sensitizer particles and the photodynamic inactivation of the adsorbed virus.