Comparison of microporous filters for concentration of viruses from wastewater

The 1-MDS Virosorb filter and the 50S and 30S Zeta-plus filters, all with a net positive charge, were compared with the negatively charged Filterite filter for concentration of naturally occurring coliphages and animal viruses from sewage effluent. When Filterite filters were used, the effluent was adjusted to pH 3.5 and AlCl3 was added before filtration to facilitate virus adsorption. No adjustment was required with the positively charged filters. Sets of each filter type were eluted with 3% beef extract (pH 9.5) or eluted with 0.05 M glycine (pH 11.5). A maximum volume of 19 liters could be passed through 142-mm diameter Filterite filters before clogging, whereas only 11, 11, and 15 liters could be passed through the 1-MDS, 50S, and 30S filters, respectively. For equal volumes passed through the filters, coliphage recoveries were 14, 15, 18, and 37% in primary effluent and 40, 97, 50, and 46% in secondary effluent for the Filterite , 1-MDS, 50S, and 30S filters, respectively. No statistically significant difference was observed in the recovery of animal viruses among the filters from secondary effluent, whereas in the Filterite and 50S filters, higher numbers of viruses from primary effluent were recovered than in the 1-MDS and 30S filters in two of three collections. Glycine was found to be a less-efficient eluent than beef extract in the recovery of naturally occurring viruses.     

Novel approach for modifying microporous filters for virus concentration from water.

Electronegative microporous filters composed of epoxyfiberglass (Filterite) were treated with cationic polymers to enhance their virus-adsorbing properties. This novel and inexpensive approach to microporous filter modification entails soaking filters in an aqueous solution of a cationic polymer such as polyethyleneimine (PEI) for 2 h at room temperature and then allowing the filters to air dry overnight on absorbent paper towels. PEI-treated filters were evaluated for coliphage (MS2, T2, and phi X174) and enterovirus (poliovirus type 1 and coxsackievirus type B5) adsorption from buffer at pH 3.5 to 9.0 and for indigenous coliphages from unchlorinated secondary effluent at ambient pH. Adsorbed viruses were recovered with 3% beef extract (pH 9). Several other cationic polymers were used to modify epoxyfiberglass filters and were evaluated for their ability to concentrate viruses from water. Zeta potentials of disrupted filter material indicated that electronegative epoxyfiberglass filters were made more electropositive when treated with cationic polymers. In general, epoxyfiberglass filters treated with cationic polymers were found to adsorb a greater percentage of coliphages and enteroviruses than were untreated filters.     

Novel approach for modifying microporous filters for virus concentration from water

Electronegative microporous filters composed of epoxyfiberglass (Filterite) were treated with cationic polymers to enhance their virus-adsorbing properties. This novel and inexpensive approach to microporous filter modification entails soaking filters in an aqueous solution of a cationic polymer such as polyethyleneimine (PEI) for 2 h at room temperature and then allowing the filters to air dry overnight on absorbent paper towels. PEI-treated filters were evaluated for coliphage (MS2, T2, and phi X174) and enterovirus (poliovirus type 1 and coxsackievirus type B5) adsorption from buffer at pH 3.5 to 9.0 and for indigenous coliphages from unchlorinated secondary effluent at ambient pH. Adsorbed viruses were recovered with 3% beef extract (pH 9). Several other cationic polymers were used to modify epoxyfiberglass filters and were evaluated for their ability to concentrate viruses from water. Zeta potentials of disrupted filter material indicated that electronegative epoxyfiberglass filters were made more electropositive when treated with cationic polymers. In general, epoxyfiberglass filters treated with cationic polymers were found to adsorb a greater percentage of coliphages and enteroviruses than were untreated filters.     

Simple method for the concentration of influenza virus from allantoic fluid on microporous filters.

Membrane filter adsorption-elution is an efficient method for concentration and partial purification of several types of viruses from various aqueous solutions. For efficient virus adsorption to negatively charged filters, the sample is adjusted to pH 3.5 and trivalent salts are added before filtration. Since influenza virus is sensitive to extremes in pH, it cannot be concentrated by ordinary filters. Zeta Plus filters, which have a net positive charge of up to 5 or 6, were evaluated for the concentration of influenza virus from infectious allantoic fluids. Influenza virus efficiently adsorbed to Zeta Plus filters at pH 6, and addition of salts was not necessary. Adsorbed virus was eluted in a small volume of 2% bovine serum albumin plus 1 M NaCl at pH 10. By this procedure, viruses in 100 ml of allantoic fluid were concentrated to a final volume of 8 ml, with an average recovery efficiency of 71.0%.     

Comparison of methods for recovering indigenous viruses from raw wastewater sludge.

Five general methods for recovering indigenous viruses from raw wastewater sludge were compared. Each method included elution, concentration, and disinfection steps. The elution method, found to consistently yield the greatest viral recovery, was a two-phase technique that involved blending sludge with Freon. Other methods, including two being tested as American Society for Testing Materials tentative standard methods, were less effective. Viral recoveries were generally greater (sometimes much greater) if samples were concentrated by high-speed centrifugation rather than by organic flocculation with 3% beef extract. Three cell lines were used to measure viral recoveries by the plaque assay. The efficiency of recovery was greatest on BGM cells, followed by RD and MA-104 cells.     

New method using a positively charged microporous filter and ultrafiltration for concentration of viruses from tap water

The methods used to concentrate enteric viruses from water have remained largely unchanged for nearly 30 years, with the most common technique being the use of 1MDS Virozorb filters followed by organic flocculation for secondary concentration. Recently, a few studies have investigated alternatives; however, many of these methods are impractical for use in the field or share some of the limitations of this traditional method. In the present study, the NanoCeram virus sampler, an electropositive pleated microporous filter composed of microglass filaments coated with nanoalumina fibers, was evaluated. Test viruses were first concentrated by passage of 20 liters of seeded water through the filter (average filter retention efficiency was ≥ 99.8%), and then the viruses were recovered using various salt-based or proteinaceous eluting solutions. A 1.0% sodium polyphosphate solution with 0.05 M glycine was determined to be the most effective. The recovered viruses were then further concentrated using Centricon Plus-70 centrifugal ultrafilters to a final volume of 3.3 (±0.3 [standard deviation]) ml; this volume compares quite favorably to that of previously described methods, such as organic flocculation (~15 to 40 ml). The overall virus recovery efficiencies were 66% for poliovirus 1, 83% for echovirus 1, 77% for coxsackievirus B5, 14% for adenovirus 2, and 56% for MS2 coliphage. In addition, this method appears to be compatible with both cell culture and PCR assays. This new approach for the recovery of viruses from water is therefore a viable alternative to currently used methods when small volumes of final concentrate are an advantage.     

Wound fiberglass depth filters as a less expensive approach for the concentration of viruses from water

Wound fiberglass depth cartridge filters (25.4 cm) with a nominal porosity of 1 micron were used to concentrate viruses from large volumes of surface water. They were found to be an excellent, less expensive alternative to the 0.2-micron pleated cartridge filters normally used for the concentration of enteric viruses from water. More than 99% of experimentally seeded poliovirus was adsorbed to these filters when the pH of the water was adjusted to pH 3.5 and aluminium chloride was added to a final concentration of 0.001 M, as recommended for electronegative filters. In comparative recovery of indigenous viruses from river water, similar results were obtained with two 1-micron or a 3-microns + 0.2-micron filter combination. The cost of the two 1-micron filters is about Can. $26, while it is about Can. $58 for the other combination.     

Concentration of poliovirus from tap water using positively charged microporous filters.

Microporous filters that are more electropositive than the negatively charged filters currently used for virus concentrations from water by filter adsorption-elution methods were evaluated for poliovirus recovery from tap water. Zeta Plus filters composed of diatomaceous earth-cellulose-"charge-modified" resin mixtures and having a net positive charge of up to pH 5 to 6 efficiently adsorbed poliovirus from tap water at ambient pH levels 7.0 to 7.5 without added multivalent cation salts. The adsorbed virus were eluted with glycine-NaOH, pH 9.5 to 11.5. Electropositive asbestos-cellulose filters efficiently adsorbed poliovirus from tap water without added multivalent cation salts between pH 3.5 and 9.0, and the absorbed viruses could be eluted with 3% beef extract, pH 9, but not with pH 9.5 to 11.5 glycine-NaOH. Under water quality conditions in which poliovirus recoveries from large volumes of water were less than 5% with conventional negatively charged filters and standard methods, recoveries with Zeta Plus filters averaged 64 and 22.5% for one- and two-stage concentration procedures, respectively. Electropositive filters appear to offer distinct advantages over conventional negatively charged filters for concentrating enteric viruses from water, and their behavior tends to confirm the importance of electrostatic forces in virus recovery from water by microporous filter adsorption-elution methods.     

Concentration of poliovirus from tap water using positively charged microporous filters.

Microporous filters that are more electropositive than the negatively charged filters currently used for virus concentrations from water by filter adsorption-elution methods were evaluated for poliovirus recovery from tap water. Zeta Plus filters composed of diatomaceous earth-cellulose-"charge-modified" resin mixtures and having a net positive charge of up to pH 5 to 6 efficiently adsorbed poliovirus from tap water at ambient pH levels 7.0 to 7.5 without added multivalent cation salts. The adsorbed virus were eluted with glycine-NaOH, pH 9.5 to 11.5. Electropositive asbestos-cellulose filters efficiently adsorbed poliovirus from tap water without added multivalent cation salts between pH 3.5 and 9.0, and the absorbed viruses could be eluted with 3% beef extract, pH 9, but not with pH 9.5 to 11.5 glycine-NaOH. Under water quality conditions in which poliovirus recoveries from large volumes of water were less than 5% with conventional negatively charged filters and standard methods, recoveries with Zeta Plus filters averaged 64 and 22.5% for one- and two-stage concentration procedures, respectively. Electropositive filters appear to offer distinct advantages over conventional negatively charged filters for concentrating enteric viruses from water, and their behavior tends to confirm the importance of electrostatic forces in virus recovery from water by microporous filter adsorption-elution methods.     

Comparison of 2 ultrafiltration systems for the concentration of seeded viruses from environmental waters

The use of ultrafiltration as a concentration method to recover viruses from environmental waters was investigated. Two ultrafiltration systems (hollow fiber and tangential flow) in a large- (100 L) and small-scale (2 L) configuration were able to recover greater than 50% of multiple viruses (bacteriophage PP7 and T1 and poliovirus type 2) from varying water turbidities (10-157 nephelometric turbidity units (NTU)) simultaneously. Mean recoveries (n = 3) in ground and surface water by the large-scale hollow fiber ultrafiltration system (100 L) were comparable to recoveries observed in the small-scale system (2 L). Recovery of seeded viruses in highly turbid waters from small-scale tangential flow (2 L) (screen and open channel) and hollow fiber ultrafilters (2 L) (small pilot) were greater than 70%. Clogging occurred in the hollow fiber pencil module and when particulate concentrations exceeded 1.6 g/L and 5.5 g/L (dry mass) in the screen and open channel filters, respectively. The small pilot module was able to filter all concentrates without clogging. The small pilot hollow fiber ultrafilter was used to test recovery of seeded viruses from surface waters from different geographical regions in 10-L volumes. Recoveries >70% were observed from all locations.     

Positively charged filters for virus recovery from wastewater treatment plant effluents.

Positively charged Zeta Plus filters were used to concentrate enteroviruses from 19 liters of effluent from activated sludge units. Neither the addition of salts nor the acidification of the effluent was required for adsorption of viruses to the filters. Viruses adsorbed to the filters were eluted by treating the filters with a solution of 4 M urea buffered at pH 9 with 0.05 M lysine. Eluted viruses were concentrated into final volumes of 1 to 2 ml by using a two-step concentration procedure that employed inorganic and organic flocculation. Approximately 50% of the viruses added to effluents could be recovered in the final sample. The procedure was used to monitor effluents from activated sludge units at two wastewater treatment plants for the presence of enteroviruses.     

Poliovirus concentration from tap water with electropositive adsorbent filters.

Simple, reliable, and efficient concentration of poliovirus from tap water was obtained with two types of electropositive filter media, one of which is available in the form of a pleated cartridge filter (Virozorb 1MDS). Virus adsorption from tap water between pH 3.5 and 7.5 was more efficient with electropositive filters than with Filterite filters. Elution of adsorbed viruses was more efficient with beef extract in glycine, pH 9.5, than with glycine-NaOH, pH 11.0. In paired comparative studies, electropositive filters, with adsorption at pH 7.5 and no added polyvalent cation salts, gave less variable virus concentration efficiencies than did Filterite filters with adsorption at pH 3.5 plus added MgCl2. Recovery of poliovirus from 1,000-liter tap water volumes was approximately 30% efficient with both Virozorb 1MDS and Filterite pleated cartridge filters, but the former were much simpler to use. The virus adsorption behavior of these filters appears to be related to their surface charge properties, with more electropositive filters giving more efficient virus adsorption from tap water at higher pH levels.     

Comparison of membrane filters for recovery of legionellae from water samples.

The procedure currently used for isolating legionellae from environmental samples recommend filtration through a 0.2-microns-pore-size polycarbonate filter. In this study we evaluated the performance of 23 other filters composed of various materials and having various pore sizes. We prefer the 0.2-micron-pore-size Gelman Supor filter because of its high level of recovery, faster filtration rate, and ease of handling.     

Simple field method for concentration of viruses from large volumes of water.

A pressure spray tank was adapted to supply positive pressure for processing water samples for concentrating viruses with microporous filters under field conditions. This low-cost system allows water to be processed in locations where electric current is not readily available or where light-weight portable equipment is required.     

Detection of respiratory viruses on air filters from aircraft

Aims: To evaluate the feasibility of identifying viruses from aircraft cabin air, we evaluated whether respiratory viruses trapped by commercial aircraft air filters can be extracted and detected using a multiplex PCR, bead‐based assay. Methods and Results: The ResPlex II assay was first tested for its ability to detect inactivated viruses applied to new filter material; all 18 applications of virus at a high concentration were detected. The ResPlex II assay was then used to test for 18 respiratory viruses on 48 used air filter samples from commercial aircraft. Three samples tested positive for viruses, and three viruses were detected: rhinovirus, influenza A and influenza B. For 33 of 48 samples, internal PCR controls performed suboptimally, suggesting sample matrix effect. Conclusion: In some cases, influenza and rhinovirus RNA can be detected on aircraft air filters, even more than 10 days after the filters were removed from aircraft. Significance and Impact of the Study: With protocol modifications to overcome PCR inhibition, air filter sampling and the ResPlex II assay could be used to characterize viruses in aircraft cabin air. Information about viruses in aircraft could support public health measures to reduce disease transmission within aircraft and between cities.     

Airborne enteric bacteria and viruses from spray irrigation with wastewater.

The relationship between bacterial concentrations in wastewater used for spray irrigation and in the air was examined. Aerosolized coliforms were detected when their concentration was 10(3)/ml or more in the wastewater. Relative humidity and solar irradiation appeared to affect viable bacteria in the air; a positive correlation was found between relative humidity and the number of aerosolized bacteria. The correlation between solar irradiation and bacterial level, on the other hand, was negative. During night irrigation, up to 10 times more aerosolized bacteria were detected than with day irrigation. Wind velocity did not play an important role in the survival of aerosolized bacteria. Echovirus 7 was isolated in 4 out of 12 air samples collected 40 m downwind from the sprinkler.     

Airborne enteric bacteria and viruses from spray irrigation with wastewater.

The relationship between bacterial concentrations in wastewater used for spray irrigation and in the air was examined. Aerosolized coliforms were detected when their concentration was 10(3)/ml or more in the wastewater. Relative humidity and solar irradiation appeared to affect viable bacteria in the air; a positive correlation was found between relative humidity and the number of aerosolized bacteria. The correlation between solar irradiation and bacterial level, on the other hand, was negative. During night irrigation, up to 10 times more aerosolized bacteria were detected than with day irrigation. Wind velocity did not play an important role in the survival of aerosolized bacteria. Echovirus 7 was isolated in 4 out of 12 air samples collected 40 m downwind from the sprinkler.     

Humic acid interference with virus recovery by electropositive microporous filters.

The effects of humic acid on poliovirus type 1 recovery from water by Zeta Plus 60S filters were investigated. The humic acid interfered by preventing virus adsorption to the filters, and the interference increased as a function of the amount of humic acid filtered. Humic acid decreased virus adsorption when filtered before the virus, but did not elute virus which had adsorbed to the filters. The effects on virus recovery were not due to alterations in virus titer or neutralizability. The addition of AlCl3, which improved virus recovery by electronegative filters in the presence of humic acid, did not aid in overall virus recovery by the Zeta Plus filters in the presence or absence of humic acid. However, the salt and humic acid in combination improved virus adsorption and concurrently reduced virus elution efficiency. The addition of NaH2PO4 had no direct effect on virus recovery and did not alter the effect of humic acid. In an attempt to identify the components of humic acid responsible for the interference, humic materials were fractionated by size by using Sephadex gel chromatography and dialysis, and the fractions were tested for interfering activity. Interference was not associated with specific size fractions of the humic materials.     

Survival of enteric viruses adsorbed on electropositive filters.

Three viruses (poliovirus type 1, rotavirus SA-11, and bacteriophage f2) adsorbed on electropositive microporous filters survived at least 5 weeks at 4 degrees C. Poliovirus type 1 and bacteriophage f2 also survived at least 6 weeks at -20 degrees C. Rotavirus SA-11 was not recovered after 1 week at -20 degrees C. The stability of viruses adsorbed on electropositive filters may enable extensive monitoring of viruses in water.     

Concentration of viruses from environmental waters using nanoalumina fiber filters

Human viral contamination in drinking and recreational water may persist for extensive periods of time and cause a significant health risk concern. The aim of this study is to evaluate a viral recovery method using a new electropositive charged nanoalumina filter and to compare results with the widely used negatively charged HAWP filter by Millipore Inc. The recovery of infectious recombinant adenovirus type 5 (rAd5) was tested using the Fluorescence-Activated Cell Sorting (FACS) assay, in parallel with viral genomes recovery assay by quantitative PCR (qPCR). The mean infectivity recoveries were 82-91% by nanoalumina filters eluted with 3% beef extract (BE, pH6.0), and 78-90% by HAWP filters eluted with 3% BE (pH 9.0), respectively, from 1 L of environmental samples seeded with 1pfu/mL rAd5. The mean genome recoveries were 16-35% by nanoalumina filters eluted with BE (pH 6.0), and 29-66% by HAWP filters eluted with NaOH (pH 10.8) from different types of water, respectively. Water quality, concentration of viruses, filters, and elution buffers are factors that determine the viral recovery efficiencies. The nanoalumina filters also had higher filtration rates than HAWP filters for large volumes of environmental water samples (up to10 L), thus, have an advantage in concentrating infectious viruses from environments without pre-filtration, adjusting pH or adding multivalent cations.