Virus concentration from sewage

Optimal conditions for concentrating poliovirus from large volumes of raw sewage were established. Solids 1 μm or larger, present in the raw sewage, were removed by textile clarifying filters without significant retention of virus. By acidification of the clarified sewage and addition of salts to enhance virus attachment to the adsorbent, virus in the sewage was concentrated on a fibre glass depth filter, with subsequent elution of virus into small volumes suitable for assay. An 80–95 per cent efficiency of virus concentration was effected.     

A comparison of current methods of poliovirus concentration from tap water

The efficiency of concentration of poliovirus from Jerusalem tap water was investigated for several types of “electronegatively-charged” and “electropositively-charged” microporous filters. In addition, the efficiency of organic flocculation as a procedure for reconcentrating poliovirus from filter eluates was investigated. The Balston and Cox filters had similar recovery efficiencies from tap water, with recovery of approx. 90% of the input virus, both after filtration and after organic flocculation. Decreasing the concentration of beef extract in the eluent from 3 to 1% did not negatively influence virus recovery. However, recovery of low virus numbers from large volume samples by Cox filters was variable. Balston filters were used in a series of high volume experiments to test the efficacy of the tentative standard method for virus recovery using a proportioner pump with two additive pumps. The method was inefficient without a simple modification, the addition of a second mixing chamber, which increased the virus recovery to an acceptable level. The Zeta Plus electropositively-charged type of filter had a high efficiency of virus recovery in the eluate, but approximately half of the virus was lost during organic flocculation. This may indicate the need for modification of the organic flocculation method when used with filters.     

Biofiltration for removal of BOM and residual ammonia following control of bromate formation

Nitrification was developed within a biological filter to simultaneously remove biodegradable organic matter (BOM) and residual ammonia added to control bromate formation during the ozonation of drinking water. Testing was performed at pilot-scale using three filters containing sand and anthracite filter media. BOM formed during ozonation (e.g., assimilable organic carbon (396-572 microg/L), formaldehyde (11-20 microg/L), and oxalate (83-145 microg/L)) was up to 70% removed through biofiltration. Dechlorinated backwash water was required to develop the nitrifying bacteria needed to convert the residual ammonia (0.1-0.5 mg/L NH(3)-N) to nitrite and then to nitrate. Chlorinated backwash water resulted in biofiltration without nitrification. Deep-bed filtration (empty-bed contact time (EBCT) = 8.3 min) did not enhance the development of nitrification when compared with shallow-bed filtration (EBCT = 3.2 min). Variable filtration rates between 4.8 and 14.6 m/h (2 and 6 gpm/sf) had minimal impact on BOM removal. However, conversion of ammonia to nitrite was reduced by 60% when increasing the filtration rate from 4.8 to 14.6 m/h. The results provide drinking water utilities practicing ozonation with a cost-effective alternative to remove the residual ammonia added for bromate control.     

Concentration of virus from tap water at ambient salt and pH levels using positively charged filter media

Positively charged filter media were used to recover bacteriophage f2 and poliovirus 1 from tap water at ambient pH level 7.8 without added multivalent cations. Recoveries from 201. vol of water with Carlson-Ford type 4 asbestos filters averaged 65% for the phage and 68% for the poliovirus after elution with alkaline nutrient broth.     

Selection of an adsorbent for lead removal from drinking water by a point-of-use treatment device

The removal of lead from drinking water was investigated to develop a point-of-use water filter that could meet the regulation imposed by the new European Directive 98-83 lowering lead concentration in drinking water below 10 μg L⁻¹. The objective of this research was to assess the potential of different adsorbents (zeolites, resins, activated carbon, manganese oxides, cellulose powder) to remove lead from tap water with a very short contact time. To begin, the repartition of the lead species in a tap water and a mineral water was computed with the computer model CHESS. It showed that in bicarbonated waters lead is mainly under lead carbonate form, either in the aqueous or in the mineral phase. Batch experiments were then conducted to measure the equilibrium adsorption isotherms of the adsorbents. Then, for five of them, dynamic experiments in micro-columns were carried out to assess the outlet lead concentration level. Three adsorbents gave rise to a leakage concentration lower than 10 μg L⁻¹ and were then selected for prototypes experiments: chabasite, an activated carbon coated with a synthetic zeolite and a natural manganese oxide. The proposed method clearly showed that the measurement of equilibrium isotherms is not sufficient to predict the effectiveness of an adsorbent, and must be coupled with dynamic experiments.     

Methods for concentrating viruses from large volumes of estuarine water on pleated membranes

The efficiency of cartridge filters with pleated membranes was determined for the recovery of poliovirus from large volumes of seawater. Flow rates of about 6 gal min⁻¹ were obtained when a combination of a 3- and a 0.45-μm pleated filter were incorporated into the Wallis—Melnick virus concentrator. The filters adsorbed poliovirus when water was acidified at pH 3.5 and aluminum chloride added at a final concentration of 0.0015 m. The filters retained their capacity to adsorb virus particles, even after 600 gal (22681.) of very turbid estuarine water had been filtered. Viruses were eluted from the pleated filters with pH 11.5 glycine buffer and reconcentrated by precipitation with ferric chloride or aluminum chloride. Virus from 100-gal samples was concentrated into a final eluate volume of 20–100 ml, with virus recovery of about 50% being achieved in the material that had been concentrated 20,000–100,000 times.     

The effect of filter pore size on the evaluation of aluminum coagulants to remove fulvic acid from water

Evaluation of aluminum coagulants to remove fulvic acid from water depends on the process of separating the precipitate from the liquid phase. Membrane filters are often used for this purpose. The degree of separation was found to depend on the filter pore size. Differences in removal efficiencies of up to 80% were observed when membrane filters with pore sizes of 0.45 and 0.10 μm were used for the solid-liquid separation. Membrane filters with a pore size of 0.45 μm under certain experimental conditions demonstrated deep-filter characteristics in the sense that in the initial steps of filtration, when the filter was clean, small particles were filtered through, but as the filter pores became clogged, the efficiency of the filter improved.     

Detection of viruses in large volumes of natural waters by concentration on insoluble polyelectrolytes

A method is described for recovering small amounts of virus from very large volumes of water. When poliovirus was added to large volumes of tap water, it could be recovered by adsorbing the virus onto thin layers of an insoluble polyelectrolyte (a crosslinked copolymer of isobutylene maleic anhydride), with subsequent concentration into small volumes of eluent for assay purposes. Virus contained in 25, 50, 75 and 100 gal of water was recovered with efficiencies ranging from 60 to 80 per cent. Poliovirus added to a 17,000-gal swimming pool was recovered with an efficiency of about 40 per cent by passing 300 gal of the pool water through a thin 3 mm polyelectrolyte layer 293 mm in diameter, with subsequent elution of the virus from the layer, and reconcentration into a smaller volume for assay.     

Comparison of positively charged membrane filters and their use in concentrating bacteriophages in water

Virus adsorption-elution studies and physical measurements were performed on four electro-positive membrane filters (Virosorb 1MDS, Posidyne N66, Zeta plus C-30 and Seitz S). The relative hydrophobicity of the membrane filters was determined by measuring the contact angle of carbon tetrachloride with the filters and by measuring the rate of rise of hexadecane and water in the filters. Viruses adsorbed to the least hydrophobic filter (Virosorb 1MDS) could be eluted by using a solution of salt (NaCI or NaEDTA) alone to disrupt electrostatic interactions between the viruses and the filter. Solutions containing both salt and detergent were required to elute virus adsorbed to two of the more hydrophobic filters (Posidyne N66 and Zeta plus C-30), indicating that both electrostatic and hydrophobic interactions were responsible for viral adsorption to these filters. A two-step procedure for recovering bacteriophages from water was developed that employed different filters for each step. Virosorb 1MDS was used to adsorb indigenous phage in water samples. Adsorbed virus could be recovered by treating the filter with a solution of 1.0 M NaCl. Phages in this solution could be further concentrated by a second adsorption-elution step that used Seitz S filters.     

On the measurement of particulate association of americium in freshwater

A laboratory investigation tested various filtration methods to study the particulate-water fractionation of ²⁴¹Am added to filtered freshwater (Monaco tap water) adjusted to different pH's. By using a system of washed Nuclepore polycarbonate filters, the particulate association (>0.2 or >1 μm) was found to increase hyperbolically with pH and with time, so that less than 1% of the Am was filterable (i.e. retained by a filter) at pH 4.2 and about 5% was filterable at pH 8.2 after 1 day; light had no apparent effect on the filterability of the Am. These values are somewhat greater than those for particle association of Am in seawater but substantially lower than previous estimates of Am particulate association in filtered freshwater. Filter adsorption problems are identified for other filtration systems commonly employed to assess metal particulate association. The results suggest that Am in freshwater is unlikely to form particles to an appreciable extent at pH's ?8.     

Removal of viruses from surface water and secondary effluents by sand filtration

The filtration of phi X 174, MS2, and T4 bacteriophages out of tap water and secondary effluents was performed by rapid sand filtration. The viruses were characterized, and the influence of their microscopic characteristics on filterability was examined by comparing retention values, residence times, attachment, and dispersion coefficients calculated from an advection-dispersion model and residence time variation. The only factor observed to influence retention was virus size, such that the larger the virus, the better the retention. The difference was due to the more effective transport of viruses inside the media, an observation that runs counter to currently accepted filtration theory. Cake formation on top of the filter during the initial stages of secondary effluent filtration significantly increased headloss, eventually resulting in shorter filtration cycles. However, deep filters contain buffering zones where the pressure drop is amortized, thus allowing for continued filtration. After the effluent passed through the buffer zone, regular filtration was observed, during which considerable virus retention was achieved.     

Design and evaluation of a filter-based chairside amalgam separation system

This study evaluated the ability of a chairside filtration system to remove particulate-based mercury (Hg) from dental-unit wastewater. Prototypes of the chairside filtration system were designed and fabricated using reusable filter chambers with disposable filter elements. The system was installed in five dental operatories utilizing filter elements with nominal pore sizes of 50 microm, 15 microm, 1 microm, 0.5 microm, or with no system installed (control). Daily chairside wastewater samples were collected on ten consecutive days from each room and brought to the laboratory for processing. After processing the wastewater samples, Hg concentrations were determined with cold vapor atomic absorption spectrometry (USEPA method 7470A). Filter systems were exchanged after ten samples were collected so that all five of the configurations were evaluated in each room (with assignment order balanced by a Latin Square). The numbers of surfaces of amalgam placed and removed per day were tracked in each room. In part two, new filter systems with the 0.5 microm filter elements were installed in the five dental operatories and vacuum levels at the high-velocity evacuation cannula tip were measured with a vacuum gauge. In part three of the study, the chairside filtration system utilizing 0.5 microm and 15 microm filter elements was evaluated utilizing the ISO 11143 testing protocol, a laboratory test of amalgam separator efficiency utilizing amalgam samples of known particle size distribution. Mean Hg per chair per day (no filter installed) was 1087.38 mg (SD = 993.92 mg). Mean Hg per chair per day for the 50 microm, 15 microm, 1 microm, 0.5 microm filter configurations was 79.13 mg (SD = 71.40 mg), 23.55 mg (SD = 23.25 mg), 17.68 mg (SD = 17.35 mg), and 4.25 mg (SD = 6.35 mg), respectively (n = 50 for all groups). Calculated removal efficiencies from the clinical samples were 92.7%, 97.8%, 98.4%, and 99.6%, respectively. ANCOVA on data from the four filter groups, with amalgam-surfaces-removed included as a significant covariate, was statistically significant (P < 0.0001). Tukey post-hoc comparisons (P < or = 0.05) indicated that the 50 microm filter removed less mercury than all other filters and the 0.5 microm removed more mercury than the 50 microm and 15 microm filters. Chairside vacuum measured on chairs with the 0.5 microm filters installed were minimally affected at the time of installation, and then gradually diminished as the filters became loaded with debris. The 0.5 microm configuration passed the ISO 11143 testing protocol at 96.8% efficiency.     

Sensory pollution from bag filters, carbon filters and combinations

Used ventilation filters are a major source of sensory pollutants in air handling systems. The objective of the present study was to evaluate the net effect that different combinations of filters had on perceived air quality after 5 months of continuous filtration of outdoor suburban air. A panel of 32 subjects assessed different sets of used filters and identical sets consisting of new filters. Additionally, filter weights and pressure drops were measured at the beginning and end of the operation period. The filter sets included single EU5 and EU7 fiberglass filters, an EU7 filter protected by an upstream pre-filter (changed monthly), an EU7 filter protected by an upstream activated carbon (AC) filter, and EU7 filters with an AC filter either downstream or both upstream and downstream. In addition, two types of stand-alone combination filters were evaluated: a bag-type fiberglass filter that contained AC and a synthetic fiber cartridge filter that contained AC. Air that had passed through used filters was most acceptable for those sets in which an AC filter was used downstream of the particle filter. Comparable air quality was achieved with the stand-alone bag filter that contained AC. Furthermore, its pressure drop changed very little during the 5 months of service, and it had the added benefit of removing a large fraction of ozone from the airstream. If similar results are obtained over a wider variety of soiling conditions, such filters may be a viable solution to a long recognized problem. PRACTICAL IMPLICATIONS: The present study was designed to address the emission of sensory offending pollutants from loaded ventilation filters. The goal was to find a low-polluting solution from commercially available products. The results indicate that the use of activated carbon (AC) filters downstream of fiberglass bag filters can reduce the degradation of air quality that occurs with increasing particle loading. A more practical solution, yet comparably effective, is a stand-alone particle filter that incorporates AC. In either case, further testing under a variety of conditions is recommended before making design decisions regarding the type of filters best suited to efficient building operation.     

Optimization of the extended terminal subfluidization wash (ETSW) filter backwashing procedure

The increased passage of particles and microorganisms through granular media filters immediately following backwashing is a common problem known to the water treatment community as filter "ripening" or maturation. While several strategies have been developed over the years to reduce the impact of this vulnerable period of the filtration cycle on finished water quality, this research involves a recently developed filter backwashing strategy called the extended terminal subfluidization wash (ETSW). ETSW is a method of terminating the backwash cycle with a subfluidization wash for a period of time sufficient to pass one theoretical filter-volume of water upward through the filter. ETSW was shown to remove significantly greater quantities of backwash remnant particles thereby reducing the magnitude of filter ripening turbidity and particle count spikes. Optimum ETSW flow rates were determined for deep-bed anthracite and granular activated carbon filters herein by monitoring filter effluent turbidities and particle counts during the filter ripening period. Optimality of the coagulation process was also shown to influence the magnitude of filter ripening particle passage. ETSW was found to be equally effective for biological and conventional deep-bed anthracite filters.     

Stability of commercial metal oxide nanoparticles in water

The fate of commercial nanoparticles in water is of significant interest to health and regulatory authorities. This research investigated the dispersion and stability of metal oxide nanoparticles in water as well as their removal by potable water treatment processes. Commercial nanoparticles were received as powder aggregates, and in water neither ultrasound nor chemical dispersants could break them up into primary nanoparticles. Lab-synthesized hematite was prepared as a primary nanoparticle (85 nm) suspension; upon drying and 1-month storage, however, hematite formed aggregates that could not be dispersed completely as primary nanoparticles in water. This observation may explain why it is difficult to disperse dry commercial nanoparticles. Except for silica, other nanoparticles rapidly aggregated in tap water due to electric double layer (EDL) compression. The stability of silica in tap water is related to its low Hamaker constant. For all these nanoparticles, at an alum dosage of 60 mg/L, coagulation followed by sedimentation could remove 20-60% of the total nanoparticle mass. Filtration using a 0.45 microm filter was required to remove more than 90% of the nanoparticle mass.     

Concentration of adenovirus from seawater

Factors influencing adenovirus 5 recovery from seawater by virus concentrator methods were determined. A 19,000-fold concentration of 25 gal samples with a theoretical recovery efficiency of 90% was possible with input multiplicities of 1000 TCID₅₀ units ml⁻¹. Pre-treatment of orlon and cellulose acetate filters with beef extract or tween 80 solutions promoted adenovirus passage during sample clarification. Adenovirus adsorbed to textile and epoxy fiberglass filters at acid pH. Adsorption to textile filters was enhanced by 0–05 m MgCl₂. No salt enhancement was necessary for adsorption to epoxy fiberglass filters. Adenovirus was recovered from adsorbent filters following elution with 3% beef extract solution adjusted to pH 9.0. Adenovirus was reconcentrated from beef extract eluates by aqueous polymer phase separation. Actual recovery of 106 PFU of adenovirus from 50 gal of a waste treatment plant effluent was made with the modified virus concentrator procedure developed in the study.     

Evaluation of procedures for recovery of viruses from water—II detection systems

Three filter media were evaluated for their suitability in recovering seeded poliovirus type 2 from tap and river water. The importance of the presence of aluminium cations was also examined. Fibreglass filters gave best recoveries in this evaluation when used with 0.0005 M AlCl₃6H₂O, being up to 4 × more efficient than filters used without Al³⁺. No such Al³⁺ requirement was found for cellulose nitrate membrane filters. A procedure was arrived at suitable for the recovery of enteroviruses from tap and river water. The efficiency of the organic flocculation procedure as a secondary concentration method varied with viral serotype.     

Initial studies of oxidation processes on filter surfaces and their impact on perceived air quality

Used filters can be a strong sensory pollutant source. Oxidation processes, especially those initiated by ozone, may contribute to the pollutants emitted from such filters. In the present study, ozone was added to the airstream passing through used ventilation filters. Two flow rates were examined. While the upstream ozone concentration was approximately 75 ppb, the concentrations downstream of the filter were initially 35-50% lower. However, within an hour downstream concentrations were only 5-10% lower than those upstream. These filter samples were then placed for 48 h in nitrogen, ambient air containing less than 5 ppb ozone, or ambient air at an elevated temperature. This resulted in partial regeneration of the ozone removal capability of the filter. In analogous experiments, lower ozone removal occurred when the filter samples were first ventilated for 24 h with ozone-free air before making the measurements. Samples from a new filter removed <10% of the ozone in the airstream, and removal remained relatively constant over time. In companion studies, human subjects assessed the air passing through various used filter samples. In the initial evaluation each of the four filter samples, taken from the same filter and ventilated for 24 h, were assessed to be equivalent. The next evaluation was immediately after the samples had been kept for 24 h in either nitrogen, air, air at an elevated temperature or ozone. The nitrogen-treated filter was assessed to be best, while the ozone-treated filter was assessed to be the worst. The final evaluation occurred after ambient air had passed through the 'treated' filters for 2 h. All such ventilated filters were assessed to be more acceptable than immediately after the 24-h treatments; the ozonized and air-treated filters were the most polluting of the four. Practical Implications The present paper supports previous findings that loaded ventilation filters can be significant sources of sensory pollution. Replacing a loaded filter with a new filter temporarily removes this source of pollution. However, the present study does not provide an answer to how frequently changes are needed under different conditions. The results indicate that in cases of intermittent operation of ventilation systems, the airflow through the polluted filters should be restarted in sufficient time prior to occupancy to purge odorous pollutants that have accumulated on the filter surface. Removal of ozone upstream of the particle filters may further improve perceived air quality in the space downstream of the filter bank. Future efforts related to the development and application of low-polluting filtration systems are warranted.     

Evaluation of procedures for recovery of viruses from water—1 concentration systems

Three filter media were evaluated for their suitability in recovering seeded poliovirus type 2 from tap and river water. The importance of the presence of aluminium cations was also examined. Fibreglass filters gave best recoveries in this evaluation when used with 0.0005 M AlCl₃6H₂O, being up to 4 × more efficient than filters used without Al³⁺. No such Al³⁺ requirement was found for cellulose nitrate membrane filters. A procedure was arrived at suitable for the recovery of enteroviruses from tap and river water. The efficiency of the organic flocculation procedure as a secondary concentration method varied with viral serotype.     

DBPs removal in GAC filter-adsorber

A rapid sand filter and granular activated carbon filter-adsorber (GAC FA) were compared in terms of dissolved organic carbon (DOC) and disinfection by-products (DBPs) removal. A water treatment plant (WTP) that had a high ammonia concentration and DOC in raw water, which, in turn, led to a high concentration of DBPs because of a high dose of pre-chlorination, was investigated. To remove DBPs and DOC simultaneously, a conventional rapid sand filter had been retrofitted to a GAC FA at the Buyeo WTP in Korea. The overall removal efficiency of DBPs and DOC was higher in the GAC FA than in the sand filter, as expected. Breakthrough of trihalomethanes (THMs) was noticed after 3 months of GAC FA operation, and then removal of THMs was minimal (<10%). On the other hand, the removal efficiency of five haloacetic acids (HAA(5)) in the GAC FA was better than that of THMs, though adsorption of HAA(5) decreased rapidly after 3.5 months of GAC FA operation. And then, gradual improvement (>90%) in HAA(5) removal efficiency was again observed, which could be attributed to biodegradation. At the early stage of GAC FA operation, HAA(5) removal was largely due to physical adsorption, but later on biodegradation appeared to prevail. Biodegradation of HAA(5) was significantly influenced by water temperature. Similar turbidity removal was noticed in both filters, while better manganese removal was confirmed in the sand filter rather than in the GAC FA.