Virus Removal by Rapid Sand Filtration, Tucson Water Reuse Project

Transcription

1 Virus Removal by Rapid Sand Filtration, Tucson Water Reuse Project Item Type text; Proceedings Authors De Leon, Ricardo; Sing, Shri N.; Rose, Joan B.; Mullinax, Rebecca L.; Gerba, Charles P. Publisher Arizona-Nevada Academy of Science Journal Hydrology and Water Resources in Arizona and the Southwest Rights Copyright, where appropriate, is held by the author. Download date 23/04/ :53:18 Link to Item

2 VIRUS REMOVAL BY RAPID SAND FILTRATION, TUCSON WATER REUSE PROJECT by Ricardo De Leon, Shri N. Singh, Joan B. Rose, Rebecca L. Mullinax and Charles P. Gerba Department of Microbiology University of Arizona Tucson, Arizona INTRODUCTION The Proposed Regulations for Reuse of Wastewater for irrigation or golf courses from the Arizona Department of Health Services set a maximum of 125 pfu of enteric viruses per 40 liters as a limit. To meet this limit or further improve the quality of effluent from Tucson's Roger Road Wastewater Treatment Plant two sand filters have been installed. A study was conducted which evaluated the performance of the sand filters with regards to the effluent's ph, enteric virus and coliform content, turbidity and presence of Ascaris lumbricoides. This paper reports only the virological analysis. The Roger road Wastewater Treatment Plant is a secondary treatment plant including sceening, grit removal, primary clarification, bio-filtration, secondary clarification and chlorination. The added filter systems would provide tertiary treatment of water consisting of rapid sand filtration and floculation. Waterborne hepatitis has been recognized in the United States for several decades, but only recently has it become evident that enteric viruses are a major cause of nonbacterial gastroenteritis. Concern about enteric viruses in water arises from their lower infectious dose than pathogenic bacteria and greater resistance to inactivation by chlorination (Berg, 1983). Enteric viruses also Often survive longer in wastewater and other types of water than either coliform bacteria or pathogenic bacteria (Gerba et al, 1975). In addition, viruses can persist in soils during land application of sewage and penetrate into the subsurface to contaminate ground water (Keswick and Gerba, 1980). There are currently over 120 different types of human pathogenic viruses which can occur in domestic sewage. The most easily isolated and identified viruses are the enteroviruses; i.e., poliovirus, echovirus, and coxsackievirus. Rotaviruses, which are a common cause of diarrhea, and hepatitis virus can 175

3 also be identified in sewage, but require special methods. No methods are currently available for the detection of Norwalk virus which has been responsible for at least 32 outbreaks of waterborne disease in the United States in recent years (Gerba, 1983). Methods used in this study are described in Standard Methods for the Examination of Water and Wastewater (APIA, 1980) and the forthcoming EPA Manual on Virus Analysis of Water. They are designed primarily for the isolation of enteroviruses. Surprisingly few studies have been done on the removal of viruses by rapid sand filtration of sewage effluents. Most have been laboratory studies with laboratory grown viruses (Leong, 1983). Virus removal by sand filters is usually considered inefficient, unless preceded by coagulation. Sand particles are essentially poor adsorbents of viruses. Sand -virus interaction is governed by the physicochemical properties of the suspending medium, the size of the sand particles, and by the flow rate (Bitton, 1980). Most of the virus removal which occurs by sand filtration is probably due to retention of solid particles or to flocs onto which the virus is already associated. This is probably especially true of chlorinated wastewater effluents, where much of the surviving virus is solid- associated because of the protective effect of solids (Hejkal et al, 1979; Gerba et al, 1978). In wastewater between 0 and 99.8% removal of virus has been reported by rapid sand filtration (Leong, 1983). Safferman and Morris (1976) studied the removal of seeded f2 coliphage from tertiary treated sewage by mixed media filters. Virus reduction averaged 18.2% and varied 0 to 48 %. This erratic picture of virus removal by sand filters has been observed in other studies as well (Chang, 1968). Because of the expected low level of human enteric viruses in the chlorinated wastewater, several surrogate viruses were used to more quantitatively evaluate the filter performance. Coliphage, bacterial viruses which infect coliform bacteria, are abundant in sewage and can be easily and inexpensively detected in sewage. Coliphages have been used extensively in the evaluation as models of human enteric virus behavior during treatment processes (Leong, 1983), and were evaluated in this study. The coliphage f2 adsorbs poorly to almost any surface (Gerba et al, 1981) less than any studied animal virus. Thus it could be considered a worst case example when evaluating removal processes which depend upon adsorption. Rotaviruses, a cause of waterborne diarrhea in man also poorly adsorb to surfaces and processes which involve adsorption to aluminum flocs are known to be less efficient for removal of this group of viruses (Gerba, 1981). The removal efficiency of these viruses by the treatment process was studied to provide an idea of a worst case example for the evaluation of the filtration system. The simian rotavirus SA -11, which is structurally and antigenically closely related to the human rotavirus,but not known to cause disease in man, was used in this study. 176

4 Materials and Methods Filters. The two pilot sand filters consist of a 6 ft steel column, 10 in. diameter with 36 in. high of filtering components each. One filter, dual media, contains 18 in. of mm filter sand and on top 18 inches of mm anthracite coal. The second filter, tri media, contains first 3 in. of 0.21 mm effective size garnet, then 15 in. of mm filter sand and on top 18 in. of mm anthracite coal. The filter runs were conducted at a filtration rate of 5.5 gpm/ft sq. The coagulants and polymer were added by means of two chemical metering pumps into the filter influent line. In -line static mixers were used for homogenizing water and coagulants. Alum (A1203) at a concentration of 1.5 mg /1, ferric chloride (FeC13) at 2.0 mg /1 and polymer L691E (Calgon) at concentrations of 0.25, 0.3 and 0.5 mg/1 were used as coagulants for the different runs. The pilot filters required daily backwashing which was conducted at 5.5 gpm/ft sq for 5-6 min. Phages and phage assays. The bacteriophage f2 used in this study was obtained from American Type Culture Collection and was grown and assayed with the host bacterium, E. coli B (ATCC 15597). Both naturally occuring phages and f2 were assayed by the PFU method. The host E. coli B(ATCC 15597) was also used for the naturally occuring phage assays. Culture and assay procedures were similar to those described by Adams (1959); Davis and Sinsheimer (1963); and Ravozzo and Burke (1973). SA -11 stock and assays. The simian rotavirus SA -11 was prepared and assayed in MA -104 cells by the PFU method as described by Smith et al, (1979). The MA -104 cells were obtained from Bruce Keswick, University of Texas, Houston, and used between passages Enterovirus assays. Wastewater concentrates were assayed for human enterovirus using the buffalo green monkey kidney (BGM) cell line which was passaged, grown and maintained by previously described methods (Melnick et al, 1979). Samples were divided into two aliquots. One aliquot was assayed by the plaque- forming -units (PFU) method (Melnick et al, 1979), by inoculation of 2 mas onto a monolayer of BGM cells in 75 an area sq. flasks. A 90 to 120 min adsorption period was allowed before the cells were overlaid with agar. The overlaid cell cultures were incubated at 37 C and were examined daily for 7-14 days for the presence of plaques. The other aliquot was divided with 2 ml being inoculated in five 75 an sq. flasks and 0.2 and a 1:10 dilution being inoculated into each of five sets of flasks. The BGM cell monolayers were observed for days for the presence of cytopathogenic effects. The concentration of virus was determined by a most probable- number test. 177

5 Enteric virus concentration. Enteric viruses were concentrated from water by adsorption -elution from microporous filters. The method is described in detail by Gerba et al (1978). In this study, the water to be sampled was first collected in a 100 gallon plastic tank and dechlorinated by addition of sodium thiosulfate. The sewage was then adjusted to ph 3.5 by addition of HC1 and A1C13 added to a final concentration of M. The sewage was then pumped through a 0.45 um nominal pore size 10 inch pleated Filterite fiberglass filter. Viruses which were adsorbed to the filter were eluted by passage of one liter of beef extract adjusted to ph 9.5. Viruses in this eluate were reconcentrated to a final volume of ml by the bioflocculation procedure of Katzenelson et al (1976) with FeC1 used as a flocculating aid. 3 Determination of coliphage f2 and rotavirus removal by filtration. A 100 gallon plastic tank with dechlorinated wastewater was seeded with either 103 PFU of SA -11 or 106 PFU of f2. The wastewater was dechlorinated with sodium thiosulfate. the effluent was mixed and passed through one of the filter columns. The same flow rate of 5.5 gpm/ft sq was used. Approximatedly 50 ml samples of influent and effluent from the filter column were collected after various times until the 100 gallons were utilized.the sampling procedure was repeated for the second filter column. Results and Discussion The virological analysis included naturally occuring coliphage and enteric viruses plus the surrogates f2 phage and the SA -11 simian rotavirus. The influent and the effluent from both filters were tested to observe efficiency differences between the dual and the tri media filters. Backwash samples were also collected on a few occasions. Coliphage. Filtration without the addition of coagulant appeared to be largely ineffective in naturally occuring coliphage removal. The addition of 2.0 mg /1 of ferric chloride or 0.3 mg /1 of anionic polymer did not appear to significantly affect coliphage removal. With 1.5 mg /1 of Alum and 0.25 mg /1 of polymer L691E addition, the dual media removed 41% of the coliphage and the tri media removed 36% (Table 1). 178

6 Table 1. Naturally Occuring Coliphage Removal by Filtration. Treatment None 0.3mg/1 Polymer L691E 2.0mg /1 Ferric chloride 2.0mg /1 FeC mg /1 1.5mg /1 Alum mg /i Average Percentage Coliphage Removal Dual Media Tri Media Polymer 0 Polymer Coliphage f2 removal. Surrogate coliphage f2 removal was strikingly similar to that observed for the naturally occurring coliphage present in the sewage (Table 2). Coliphage f2 removal averaged 38% for the dual media and 35% for the tri media. Table 2. Coliphage f2 Removal by Filtration with 1.5 mg /1 Alum and 0.25 mg /i Polymer L691E Addition. Trial Sample time* (min) Dual media % removal Tri media % removal 1 6 NS ** Mean *Time after beginning of passage of coliphage seeded sewage through the filters. * *NS = No Sample Rotavirus. Surrogate SA -11 rotavirus removal was somewhat less than that observed for the coliphages (Table 3). Removal for the dual media averaged 21% and for the tri media 27 %. Naturally occuring rotavirus was not tested. 179

7 Table 3. Effect of 1.5 mg /1 of Alum and 0.25 mg /1 Polymer Addition on Rehoval of Rotavirus by Filtration. Trial 1 Sample time* Dual media Tri media (min) % removal % removal Mean *Time after begining of passage of seeded sewage through the filters. rotavirus Enteric virus. As expected, detection of human enteric virus in the chlorinated sewage discharge from the Roger Road plant was erratic (Table 4). The highest concentration of virus in the sewage was 7.9 PFU per 40 liters which is well below the recommended limit of 125 PFU /40 liters for effluent reused for noncontact recreation and irrigation on non -foof crops. Removal of enteric viruses by filtration with alum addition ranged from 0 to 92 %, but viruses were isolated on too few occasions to draw meaningful) conclusions on percent of virus removal. Additional treatment would be required to achieve i PFU /40 liters if the wastewater was to be used for food crop irrigation. Much of the virus removal which occurs during sand filtration is most likely due to retention of particulates on which viruses are adsorbed. The association of viruses to solids is best illustrated by the high concentration of enteric viruses in the backwash (Table 5). 180

8 Table 4. Enterovirus Removal by Filtration. Date Influent PFU or MPN /40 L Dual Media Effluent PFU or MPN /40 L Tri Media Effluent PFU or MPN /40 L Free Chlorine mg /L Coagulants 8/ None 8/ None 8/ None 8/ Alum+Polymer 8/ Alum+Polymer 8/ Alum+Polymer 8/ Alum+Polymer 9/ Alum+Polymer 9/ Alum+Polymer 9/ Alum+Polymer 9/ Alum+Polymer Table 5. Enterovirus Ocurrence in Filter Backwash Dual Media Tri Media Date PFU or MPN /40 1 PFU OR MPN /40 1 8/ / Filtration by itself clearly had little effect on coliphage removal as did the addition of anionic polymer prior to filtration. Viruses adsorb poorly to sand particles and anionic polyelectrolytes are known to actually decrease virus removal by coagulation (Bitton, 1980). In drinking water treatment, coagulation and sedimentation with alum and ferric chloride can result in appreciable virus removal. Virus removals exceeding 90% or greater can be achieved by addition of 10 to 60 mg/1 of these coagulants (Bitton, 1980). Most of the removal occurs during coagulation and sedimentation, but additional removal occurs during sand filtration by entrapment of the floc particles. Much smaller quantities of coagulate were added during the present study because of the absence of a sedimentation step which would be required to prevent rapid clogging of the filters. The simian rotavirus SA -11 removal in the presence of alum and polymer averaged 21% for the dual media filter and 27% for the tri media, which was less than that observed for the 181

9 coliphages. Rotaviruses adsorb to a lesser degree to alum flocs than enteroviruses and perhaps other viruses (Farrah et al, 1978). Thus they probably reflect a worst possible situation as far as animal virus is concerned. The concentration of human pathogenic viruses may vary greatly in domestic sewage depending on the time of year, the incidence of enteric virus disease in a community, the social economic status of the community, etc. The most easily detected human enteric viruses are the enteroviruses which were the ones most likely detected in this study because of the methods employed. The peak concentration of enteroviruses in domestic sewage in the United States occurs in the late summer and early fall. Thus this study was conducted at the same time as the peak enterovirus concentration would be expected. Enteroviruses represent only about 30-40% of all the enteric viruses which could occur in domestic sewage. Rotaviruses, for example, can occur at concentrations equal to or greater than those observed for enteroviruses and may be more chlorine resistant (Gerba, 1981). Viruses are known to be protected by inactivation by turbidity (Hejkal et al, 1979). Filtration will help ensure some additional removal of virus, but more importantly, greater efficiency of virus inactivation by chlorine. Conclusions From these results it was concluded that 1) At the concentrations used in this study, ferric chloride was not as effective as alum and polymer in the removal of naturally occuring coliphage. 2) Removal of naturally occuring coliphage and f2 coliphage was similar upon alum and polymer addition and averaged about 38 %. 3) Considering the SA -11 and the f2 removal as worst possible cases and average removal of between 21% to 38% can probably be expected by sand filtration after the addition of 1.5 mg /1 of alum and 0.25 mg /1 of polymer. 4) The filter effluents met current standards of enteric virus concentration for golf course irrigation and noncontact recreation in Arizona of less than 125 PFU /40 liters. Additional treatment would be required for the 1 PFU /40 liters required for contact recreation or food crop irrigation. 5) Removal of particular matter by the added filtration will help in reducing the viral content of the effluent, but also the efficiency of viral deactivation by chlorination will be enhanced due to decreased interference by the particulates. References Cited American Public Health Association Standard Methods for Examination of Water and Wastewater. Amer. Public Hlth. Assoc., Washington, D. C. Adams, M. H Bacteriophages. John Wiley and Sons, New York. 182

10 Bitton, G Introduction to Environmental Virology, John Wiley and Sons, New York. Davis, J. E., and R. L. Sinsheimer The replication of bacteriophage MS -2. J. Mol. Biol., 6: Farrah, S. R., S. M. Goyal, C. P. Gerba, R. H. Conklin and E. M. Smith Comparison between adsorption of poliovirus and rotavirus by aluminum hydroxide and activated sludge flocs. Appl. Environ. Microbiol., 35: Gerba, C. P., S. M. Goyal, I. Cech and G. F. Bogdan Quantitative assesnent of the adsorption behavior of viruses to soil. Environ. Sci. Technol., 15: Gerba, C. P., C. H. Stagg and M. G. Abadie Characterization on sewage solid- associated viruses and behavior in natural waters. Water Res., 12: Gerba, C. P Virus survival in wastewater treatment. In Viruses and Wastewater Treatment, M. Goddard and M. Bulter (eds.), pp Pergamon Press, New York. Gerba, C. P., S. M. Goyal Methods in Environmental Virology. Marcel Dekker, New York. Gerba, C. P., S. R. Farrah, S. M. Goyal, C. Wallis and J. L. Melnick Concentration of enteroviruses from large volumes of tapwater, treated sewage and seawater. Appl. Environ. Microbiol., 35: Keswick, B. H. and C. P. Gerba State of knowledge and significance of viruses in ground water. Environ. Sci. Technol., 14: Katzenelson, E., B. Fattal and T. Hostovesky Organic flocuulation: an efficient second -step concentration method for the detection of viruses in tapwater. Appl. Environ. Microbiol., 32: Leong, L. Y. C Review: Removal and inactivation of viruses by treatment processes for potable water and wastewater. Water. Sci. Technol., 15: Rovozzo, G. C., and C. N. Burke A manual of basic virological techniques. pp Prentice -Hall, Inc., Englewood Cliffs, N. J. Safferman, R. S. and M. E. Morris Assesment of virus removal by multi -stage activated sludge process. Water. Res., 10: Smith, E. M., M. K. Estes, D. Y. Graham and C. P. Gerba A plaque assay for simian rotavirus SA -11. J. Gen. Virol., 43: