3
Microbial Contaminants in Reuse Systems

Traditionally, bacterial and other indicators have been used to evaluate the effectiveness of water and wastewater treatment systems in inactivating microorganisms. Except for special studies, relatively little occurrence information is available for the pathogens that actually pose health risks. Over the past few years, however, renewed attention has been given the health risks from microbial contamination of drinking water, and nationwide monitoring programs are being instituted. In the meantime, much of the information available on specific pathogens comes from microbial monitoring and studies of nonpotable and some potable reuse projects. Knowing the occurrence and concentration of specific pathogens in reclaimed water is critical to determining exposure and thus assessing the potential health risks of potable water reuse.

Waterborne Diseases

Microorganisms associated with waterborne disease are primarily enteric pathogens, which have a fecal-oral route of infection (either human-to-human or animal-to-human) and survive in water. These bacteria, viruses, and protozoa can be transmitted by consumption of fecal-contaminated water, but they can also be spread through person-to-person contact, contaminated surfaces, and food. Any potable water supply receiving human or animal wastes can be contaminated with microbial agents. Even pristine water supplies have been associated with disease



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--> 3 Microbial Contaminants in Reuse Systems Traditionally, bacterial and other indicators have been used to evaluate the effectiveness of water and wastewater treatment systems in inactivating microorganisms. Except for special studies, relatively little occurrence information is available for the pathogens that actually pose health risks. Over the past few years, however, renewed attention has been given the health risks from microbial contamination of drinking water, and nationwide monitoring programs are being instituted. In the meantime, much of the information available on specific pathogens comes from microbial monitoring and studies of nonpotable and some potable reuse projects. Knowing the occurrence and concentration of specific pathogens in reclaimed water is critical to determining exposure and thus assessing the potential health risks of potable water reuse. Waterborne Diseases Microorganisms associated with waterborne disease are primarily enteric pathogens, which have a fecal-oral route of infection (either human-to-human or animal-to-human) and survive in water. These bacteria, viruses, and protozoa can be transmitted by consumption of fecal-contaminated water, but they can also be spread through person-to-person contact, contaminated surfaces, and food. Any potable water supply receiving human or animal wastes can be contaminated with microbial agents. Even pristine water supplies have been associated with disease

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--> TABLE 3-1 Common Infectious Agents Potentially Present in Untreated Municipal Wastewater Agent Disease Protozoa     Entamoeba histolytica Amebiasis (amebic dysentery)   Giardia lamblia Giardiasis   Balantidium coli Balantidiasis (dysentery)   Cryptosporidium Cryptosporidiosis, diarrhea, fever Helminths     Ascaris (roundworm) Ascariasis   Trichuris (whipworm) Trichuriasis   Taenia (tapeworm) Taeniasis Bacteria     Shigella (4 spp.) Shigellosis (dysentery)   Salmonella typhi Typhoid fever   Salmonella (1700 serotypes) Salmonellosis   Vibrio cholerae Cholera   Escherichia coli (enteropathogenic) Gastroenteritis   E. coli 0157:H7 (enterohemorrhagic) Bloody diarrhea   Yersinia enterocolitica Yersiniosis   Leptospira (spp.) Leptospirosis   Legionella pneumophila Legionnaire's disease, Pontiac fever   Campylobacter jejuni Gastroenteritis Viruses     Enteroviruses (72 types)       Poliovirus Paralysis, aseptic meningitis     Echovirus Fever, rash, respiratory illness, aseptic meningitus, gastroenteritis, heart disease     Coxsackie A Herpangina, aseptic meningitus, respiratory illness     Coxsackie B Fever; paralysis; respiratory, heart, and kidney disease     Norwalk Gastroenteritis   Hepatitis A virus Infectious hepatitis   Adenovirus (47 types) Respiratory disease, eye infections   Rotavirus (4 types) Gastroenteritis   Parvovirus (3 types) Gastroenteritis   Reovirus (3 types) Not clearly established   Astrovirus (7 types) Gastroenteritis   Calicivirus (2-3 types) Gastroenteritis   Coronavirus Gastroenteritis   SOURCE: Adapted from Hurst et al., 1989; Sagik et al., 1978.

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--> outbreaks, presumably due to Giardia contamination from wildlife in the watershed. Table 3-1 shows the bacteria, viruses, and protozoan parasites potentially present in untreated municipal wastewater. Wastewater may also contain helminths (intestinal worms), but these waterborne parasites will not be discussed in this report because conventional wastewater treatment removes helminths and their relatively large ova and cysts. Other microorganisms, such as Legionella, are sometimes classified as waterborne disease agents but will not be addressed because their airborne routes of transmission are distinctly different from the transmission routes of enteric microbial agents. Concerns over particular waterborne microorganisms have changed over the years due to improved sanitary conditions, the use of preventive medicine, and improved microbiological and epidemiological methods for identifying the microorganisms responsible for outbreaks. Microorganisms were first identified as agents of waterborne disease during the cholera outbreak in England in the 1860s. In the 1920s, typhoid fever was linked to the waterborne bacterium Salmonella typhi. Giardia, a water- FIGURE 3-1 Changing trends in waterborne diseases in the United States in the twentieth century. NOTE: AGI = acute gastrointestinal illness of unknown etiology; HAV = hepatitis A virus.

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--> borne protozoan, rose as a major concern in the 1960s; rotavirus and Norwalk virus were associated with a large number of outbreaks beginning in the 1970s; and Cryptosporidium, also a protozoan, was first associated with waterborne outbreaks in the 1980s (Figure 3-1). Much of the information on the etiology of waterborne disease comes from investigations of outbreaks by state and local health departments and from voluntary reporting by physicians to the surveillance program maintained by the Centers for Disease Control and Prevention (CDC) and the Environmental Protection Agency (EPA). When an outbreak occurs and waterborne pathogens are suspected, epidemiological studies are conducted to identify whether water is the vehicle of transmission. If possible, the etiologic agent is determined by detection in clinical specimens collected from outbreak victims. For gastrointestinal illness, routine stool examinations by hospital laboratories typically include culturing for Salmonella, Shigella, and Campylobacter bacteria. At the specific request of a physician, many laboratories can also test for rotavirus, Giardia, and Cryptosporidium. Nevertheless, no specific agent is identified in many outbreaks, leaving the cause classified only as acute gastrointestinal illness of unknown etiology (AGI). Before 1982, in fact, most waterborne outbreaks reported were listed as AGI. Poor collection of clinical and/or water samples and limitations of diagnostic techniques for many enteric pathogens can prevent accurate determination of the pathogen. Clinical symptoms suggest that many of the AGI outbreaks may be due to viral agents, such as Norwalk virus and related human caliciviruses. Diseases From Enteric Bacteria Enteric bacteria are associated with human and animal feces and may be transmitted to humans through fecal-oral transmission routes. Most illnesses due to enteric bacteria cause acute diarrhea, and certain bacteria tend to produce particularly severe symptoms. As measured by hospitalization rates during waterborne disease outbreaks (that is, the percentage of illnesses requiring hospitalization), the most severe cases are due to Shigella (5.4 percent), Salmonella (4.1 percent), and pathogenic Escherichia coli (14 percent) (Gerba et al., 1994). There is now evidence suggesting that Campylobacter, Shigella, Salmonella, and Yersinia may also be associated with illness that causes arthritis in about 2.3 percent of cases (Smith et al., 1993). Most E. coli are common, harmless bacteria found in the intestinal tracts of humans and animals, but some forms of E. coli are pathogenic and cause gastroenteritis. A particular strain, E. coli 0157:H7, is enterohemorrhagic (causes bloody diarrhea), and 2 to 7 percent of infections have resulted in hemolytic uremic syndrome (HUS), in which red blood

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--> TABLE 3-2 Waterborne Bacterial Agents of Concern Bacteria Average Reported Cases in the United States Annual Case-Fatality Rate (%)a Percent Waterborneb Campylobacter 8,400,000 0.1 15 Pathogenic Escherichia coli 2,000,000 0.2 75 Salmonella nontyphoid 10,000,000 0.1 3 Shigella 666,667 0.2 10 Yersinia 5,025 0.05 35 a The number of deaths per case expressed as a percentage and based on total cases and deaths reported annually to the CDC. b Percentage of cases attributed to water contact or water consumption. SOURCE: Reprinted by permission of Elsevier Science from Bennett et al., 1987. © 1987 by American College of Preventive Medicine. cells are destroyed and the kidneys fail. HUS has one of the highest mortality rates of all waterborne diseases. The microbial reservoir for E. coli 0157:H7 appears to be healthy cattle, and transmission can occur by ingestion of undercooked beef or raw milk as well as by contaminated water. Two waterborne outbreaks of E. coli 0157:H7 have been reported in the United States (CDC, 1993). Drinking water was associated with an outbreak of E. coli 0157:H7 involving 243 cases, 32 hospitalizations, and 4 deaths in a Missouri community in 1989. Unchlorinated well water and breaks in the water distribution system were considered to be contributing factors. The other waterborne outbreak of E. coli 0157:H7 involved 80 cases in Oregon in 1991 and was attributed to recreational water contact in a lake (Oregon Health Division, 1992). Prolonged survival of E. coli 0157:H7 in water has been reported by Geldreich et al. (1992), who observed only a 2 log (99 percent) reduction after 5 weeks at 5°C. Classical waterborne bacterial diseases such as dysentery, typhoid, and cholera, while still very important worldwide, have dramatically decreased in the United States since the 1920s (Craun, 1991). However, Campylobacter, nontyphoid Salmonella, and pathogenic Escherichia coli have been estimated to cause 3 million illnesses per year in the United States (Bennett et al., 1987). Hence, enteric bacterial pathogens remain an important cause of waterborne disease in the United States. Table 3-2 shows

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--> the number of enteric bacterial illnesses, the case-fatality rate reported annually from all cases, and the percentage of illnesses attributed to contaminated water supplies, which ranges from 3 to 75 percent. Enteric bacteria caused 14 percent of all waterborne disease outbreaks in the United States from 1970 to 1990 (Craun, 1991). Diseases From Enteric Protozoa The enteric protozoan parasites produce cysts or oocysts that aid in their survival in wastewater. Important pathogenic protozoa include Giardia lamblia, Cryptosporidium parvum, and Entamoeba histolytica. (Helminth ova are present in untreated wastewater; however, they are relatively large and tend to drop out of effluent after primary and secondary treatment.) Waterborne outbreaks of amebic dysentery, caused by Entamoeba, have not been reported in the United States in over 15 years (Bennett et al., 1987). Giardia is recognized as the most common protozoan infection in the United States and remains a major public health concern (Craun, 1986; Kappus et al., 1992). The reported incidence of waterborne giardiasis has increased in the United States since 1971 (Craun, 1986). An average of 60,000 cases are reported annually, and 60 percent are estimated to be waterborne (Bennett et al., 1987). Because Giardia is endemic in wild and domestic animals, infection can result from water supplies that have no wastewater contribution. Densities of Giardia cysts in untreated wastewater have been reported as high as 3375 per liter (Sykora et al., 1991). TABLE 3-3 Illness Rates From Enteric Viruses Virus Group Annual Reported Cases in the United Statesa Case-Fatality Rate (%) Morbidity Rate (%) Enteroviruses 6,000,000 0.001 Not known Poliovirus 7 0.90 0.1-1 Coxsackievirus A Not known 0.50 50 Coxsackievirus B Not known Not known 0.59-0.94 Echovirus Not known Not known 50 Hepatitis A virus 48,000 0.6 75 Adenovirus 10,000,000 0.01 Not known Rotavirus 8,000,000 0.01 56-60 Norwalk agent 6,000,000 0.0001 40-59 a Cases reported to the CDC in 1985. SOURCE: Bennett et al., 1987; Gerba and Rose, 1993.

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--> TABLE 3-4 Emerging and Potential Waterborne Enteric Pathogens Microorganism Description Clinical Syndrome Calicivirus Group of ''small round structured viruses" approx. 27-35 nm diameter, SSa RNA. Includes Norwalk virus, Snow Mountain virus, and Hawaii virus Acute gastroenteritis, major cause of outbreaks of nonbacterial, acute gastroenteritis Astrovirus Small, round structured virus approx. 28-30 nm diameter, SS RNA, 7 serotypes Acute gastroenteritis, mainly in children and the elderly Enteric adenovirus Approx. 70-80 nm diameter, DS DNAb virus, mainly serotypes 40 and 41 Gastroenteritis with duration of 7-14 days; associated with 5-12% of pediatric diarrhea Enteric coronavirus Between 100 and 150 nm diameter, enveloped SS RNA virus; major gastrointestinal pathogens of animals, putative enteric pathogens for humans Acute gastroenteritis Torovirus Enveloped. Approx. 100-150 nm diameter, SS RNA viruses; well-established enteric pathogens for animals, putative enteric pathogens for humans Acute gastroenteritis Picornavirus Approx. 25-30 nm diameter, double-stranded RNA viruses Diarrhea Pestivirus Single-stranded RNA viruses Pediatric diarrhea Helicobacter pylori Typically, curved, gram- negative rods 3 x 0.5µm, microaerophilic Colonization of stomach causes persistent low-grade gastric inflammation; chronic infections may result in peptic ulcers and gastric cancer

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--> Evidence of Waterborne Transmission Reports of Occurrence References Numerous reports of waterborne outbreaks Methods to detect in water are currently being developed Kapikian et al., 1996 Waterborne outbreaks have been reported No methods to detect in water Matsui and Greenberg, 1996 None, but known to have fecal-oral transmission Has been recovered from sewage Foy, 1991 Petric, 1995     None, but epidemiologic evidence of fecal-oral transmission No methods to detect in water McIntosh, 1996 None No methods to detect in water Koopmans et al, 1991,1993 None No methods to detect in water Pereira et al., 1988 None No methods to detect in water Yolken et al., 1989 Probable fecal-oral transmission; some epidemiologic studies have implicated type of water supply as an important risk factor Lab studies demonstrated H. pylori survival for 10 days in freshwater; also evidence of prolonged survival as viable, nonculturable coccoid bodies. Recent report of PCR method to detect H. pylori in waterc Enroth and Engstrand, 1995 Shahamat et al., 1989 West et al., 1990

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--> Microorganism Description Clinical Syndrome Cyclospora cayetanensis Protozoa with oocysts 8-10 µm in diameter Prolonged, self-limited diarrhea with average duration of 30 days a SS RNA = single-strand RNA. b DS DNA = double-strand DNA. c PCR = polymerase chain reaction. Giardia has also been detected in treated effluent and is much more resistant to disinfection with chlorine than bacteria. Cryptosporidium was first described as a human pathogen in 1976. Cryptosporidiosis causes severe diarrhea; no pharmaceutical cure exists. Average infection rates in the United States, as measured by oocyst excretion in a population, have ranged from 0.6 to 20 percent (Fayer and Ungar, 1986). The disease can be particularly hazardous for people with compromised immune systems (Current and Garcia, 1991). Since 1985, seven reported waterborne outbreaks of cryptosporidiosis have occurred in the United States (Lisle and Rose, 1995). In 1993, Cryptosporidium was responsible for the largest waterborne disease outbreak ever recorded in the United States, causing approximately 400,000 illnesses in Milwaukee, Wisconsin. This outbreak was attributed to contamination of the surface water supply by either animal or human wastes (MacKenzie et al., 1995). All research to date suggests that the current standards for water chlorination are inadequate for inactivation of Cryptosporidium oocysts (Korick et al., 1990; Peeters et al., 1989). Cryptosporidium oocysts have been detected in municipal wastewater, but their concentrations and removal by wastewater treatment processes have not been fully evaluated (Madore et al., 1987; Rose et al., 1996; Villacorta-Martinez et al., 1992). Diseases From Enteric Viruses The enteric viruses are obligate human pathogens, which means they replicate only in the human host. Viruses are the smallest pathogenic agents. Their simple structure of a protein coat surrounding a core of

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--> Evidence of Waterborne Transmission Reports of Occurrence References Epidemiologic case- control study in Nepal implicated consumption of untreated water as a risk factor; 1990 outbreak in Chicago associated with rooftop water storage tanks Methods to detect in water are currently under development Ortega et al., 1993 Shlim et al., 1991 genetic material (DNA or RNA) allows prolonged survival in the environment. There are more than 120 identified human enteric viruses. Some of the better described viruses include the enteroviruses (polio-, echo-, and coxsackieviruses), hepatitis A virus, rotavirus, and Norwalk virus. Most enteric viruses cause gastroenteritis or respiratory infections, but some may produce a range of diseases in humans, including encephalitis, neonatal disease, myocarditis, aseptic meningitis, and jaundice (Gerba et al., 1995, 1996; Wagenkneckt et al., 1991; see Table 3-1). Cases of poliovirus are low in the United States due to almost universal immunization. Table 3-3 shows the average number of viral illnesses that occur annually in the United States for the different enteric viral groups. No general estimates exist regarding the percentage of viral illnesses attributable to contaminated water supplies. Norwalk and Norwalk-like viruses cause most waterborne viral diseases. Norwalk virus usually causes mild diarrhea that lasts on average for two days. A significant portion of the waterborne outbreaks reported as AGI are probably caused by Norwalk-like viruses that are not identified because of diagnostic limitations; Kaplan et al. (1982) suggested that such viruses may cause 23 percent of all waterborne outbreaks reported as AGI. From 1989 to 1992, contaminated drinking water was implicated in four outbreaks associated specifically with Norwalk-like viruses and hepatitis A virus (Herwaldt et al., 1992; Moore et al., 1993). During the same period, 37 waterborne outbreaks of AGI affected 15,769 people. In 85 percent of the outbreaks, the water quality met national drinking water standards for coliform bacteria.

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--> Emerging and Unknown Waterborne Pathogens One concern about potable reuse of reclaimed water is the potential health risk from little-known or unknown pathogens. In more than half of all reported outbreaks of waterborne disease, no etiologic agent was ever determined. Some outbreaks that were thoroughly investigated suggest the existence of unrecognized pathogens. For example, "Brainerd diarrhea," first described in an outbreak in Brainerd, Minnesota, in 1983 (Osterholm et al., 1986), is characterized by chronic diarrhea lasting an average of 12 to 18 months. Similar symptoms were noted in several subsequent outbreaks in seven other states where the disease etiology was associated with poor-quality or untreated drinking water (Parsonnet et al., 1989). Intense microbiological analyses failed to identify any etiologic agent for this syndrome. "Emerging" infectious diseases have been defined as those whose incidence in humans has increased within the past two decades or threatens to increase in the near future (Institute of Medicine, 1992). Some infectious agents, such as Cryptosporidium, were first described in the past 10 to 20 years but have more recently emerged as major causes of waterborne disease. Drinking water from potable reuse systems may pose a risk of exposure to emerging enteric pathogens because raw wastewater contains many enteric pathogens, the removal of which by treatment processes can only be inferred by other measures of microbial quality. The occurrence and health significance of many of these agents in finished drinking water are currently unknown. Table 3-4 summarizes information on a number of recently recognized enteric pathogens known to have waterborne transmission or to have the potential for waterborne transmission via fecal-contaminated water. The table includes the sizes of these organisms (when known), since this may be relevant to their removal by specific water and wastewater treatment processes. (Several emerging enteric waterborne pathogens that are important outside the United States e.g., hepatitis E virus, group B rotavirus, and Vibrio cholerae O139 are not discussed here because these infections have not been transmitted within the United States.) Norwalk virus and related human caliciviruses are considered emerging pathogens because new diagnostic techniques have recently identified their roles as major waterborne and foodborne pathogens. A number of other viruses are known or putative enteric pathogens. However, little or no evidence exists regarding waterborne transmission of these organisms. Methods to detect them in water and wastewater have not been developed, and little or no information exists about their survival or transmission in water. For instance, astroviruses are recently recognized

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--> Enterococci Coliphage Enterovirus Cryptosporidium Giardia -2.36 -2.62 -1.16   -1.3 99.56 99.76 93   95.3 -4.33 -4.88 -3.69 -2.63 -2.46 99.995 99.998 99.98 99.8 99.65 -3.67 -4.82 -3.56 -1.67 -2.34 99.98 99.998 99.97 97.9 99.55 -3.61 -4.57 -3.48 -3.22 -2.90 99.97 99.997 99.97 99.94 99.87 -4.67 -4.62 -3.52 -2.74   99.998 99.998 99.97 99.82   -5.27 -5.86 >-4.34 -3.53 -3.87 99.9995 99.99986 >99.995 99.97 99.986 reduction of pathogens and microbial indicators by unit process in the UOSA facility (Rose et al., 1997). The bacterial indicator Clostridium best reflects the removal of enteroviruses for secondary treatment and chemical lime treatment. Coliphage appears to better reflect the removal of viruses during the disinfection process. Reverse osmosis was found to be the single most effective barrier to cysts and oocysts. Chemical treatment was the next most effective and sand filtration the least. No studies to date have examined the disinfection of cysts and oocysts or the optimization of sand filtration in wastewater or reclaimed water.

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--> TABLE 3-16 Relative Removal of Pathogens and Coliform Indicators by Various Treatment Processes Unit Process Enterovirus Giardia Cryptosporidium Coliform Biological secondary treatment + + ND + Coagulation-flocculation-sedimentation-filtration ++ ++ + ++ Chlorination (free) +++ + - ++++ Combined chlorine + - - ++ Ozone disinfection ++++ ++ + ++++ UV disinfection ++ + ND ++++ Reverse osmosis +++ +++ +++ +++ Lime treatmenta ++ ++ ++ +++ Microfiltration + +++ ++++ ++++ Ultrafiltration ++++ ++++ ++++ ++++ NOTE: + signs indicate removal from low (+) to very high (++++); minus sign indicates no significant removal; ND indicates absence of data to make a judgment. For disinfectants, assessment is based on the rate of inactivation of organisms rather than log removals. a Chemical lime treatment adds a disinfection barrier to bacteria and viruses due to its high pH and a removal barrier to protozoa via the precipitate formed and the sedimentation process. Chemical treatment, disinfection (chlorine or ultraviolet), and reverse osmosis are effective barriers for the removal of viruses. Effective barriers for removing protozoa include chemical treatment, reverse osmosis, and, to lesser degree, sand filtration. The efficacy of disinfection, in particular ozone, awaits further evaluation for protozoa removal. Table 3-16 summarizes the relative efficiency of various unit processes in water reclamation systems as barriers to microbial pathogens. Conclusions Microbial contaminants in reclaimed water include the enteric bacteria, enteric viruses, and enteric protozoan parasites. Classic waterborne bacterial diseases, such as dysentery, typhoid, and cholera, while still important worldwide, have dramatically decreased in the United States. However, Campylobacter, nontyphoid Salmonella, and pathogenic Escherichia coli still cause a significant number of illnesses, and new emerging diseases also pose potentially significant health risks. Historically, coliforms have served as an effective indicator for many bacterial pathogens of concern. However, most recognized outbreaks of waterborne disease in the United States are caused by protozoan and

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--> viral pathogens in waters that have met current coliform standards. Table 3-17 summarizes how the three main microorganisms of concern, Giardia, Cryptosporidium, and the enteric viruses, rank with regard to their occurrence in wastewater, resistance to water treatment, adequacy of monitoring, and severity of health risk. Giardia is one of the most frequently identified microbial pathogens, occurring consistently in high numbers in untreated wastewater, secondary effluent, and secondary effluent receiving sand filtration and disinfection. However, the health threat it poses is relatively low because the resulting gastroenteritis is less severe and more amenable to treatment than infections caused by the viruses or Cryptosporidium. Cryptosporidium, which may cause severe diarrhea in immunocompromised individuals, is found in highly variable levels in wastewater. It is highly resistant to disinfection and difficult to detect in untreated wastewater with current methods. Studies in California show that disinfection standards using a concentration/contact time approach can reliably reduce enteroviruses in reclaimed waters. However, monitoring has not been conducted for other viruses of concern, such as adenoviruses, rotaviruses, and Norwalk and related human caliciviruses. Wastewater may also contain a number of newly recognized or ''emerging" waterborne enteric pathogens or potential pathogens. For some of these organisms there is no evidence of waterborne transmission, and their occurrence in wastewater is suspected but not documented. Recommendations To ensure the safety of drinking water produced from reclaimed water, planners, regulators, and operators of potable reuse systems must account for the various existing and potential health risks posed by microbial contaminants. Potable reuse systems should continue to employ a combination of advanced physical treatment processes and strong chemical disinfectants as the principal line of defense against most microbial contaminants. Some new membrane water filtration systems can almost completely remove microbial pathogens of all kinds, but experience with them is not yet adequate to depend on them alone for protection against the serious risks posed by these pathogens. Therefore, strong chemical disinfectants, such as ozone or free chlorine, should also be used, even in systems that include membrane filters. Current and future facilities should assess and report the effectiveness of their treatment processes in removing microbial pathogens so that the industry and regulators can develop guidelines and stan-

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--> TABLE 3-17 Ranking of Microbial Contaminants of Most Concern in Reclaimed Water Relative Rank Concentration in Wastewater Variation in Concentration Most concern Giardia at highest levels, always present Giardia appears to be constant Moderate concern Enteroviruses, always present Enteroviruses moderately variable Least concern Cryptosporidium sometimes present Cryptosporidium highly variable, but often undetectable dards for operations. Facilities should report number of barriers, microbial reduction performance, and the reliability or variation. They should conduct seeded tracer and pilot studies to provide data on performance in addition to information on the occurrence, concentrations, and variations in loadings of indigenous microorganisms. Appropriate disinfection studies should also be undertaken for the enteric protozoa and for some viruses. •   To provide protection against emerging pathogens, the EPA should support research to develop methods for detecting emerging pathogens in environmental samples. Research is also needed on the effectiveness of various water or wastewater treatment processes and disinfectants in removing or inactivating these pathogens. •   Both the industry and the research community need to establish the performance and reliability of individual barriers to microorgan-

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--> Resistance to Treatment Barriers Available to Control Microorganism Ability to Monitor Microorganisms or Adequate Surrogate Health Outcome Cryptosporidium most resistant Giardia by filtration and possibly disinfection (no data on wastewater or reclaimed water disinfection of cysts) Giardia cysts directly Some enteroviruses cause serious illness (e.g., heart disease, chronic sequelae) Giardia more resistant to disinfection than bacteria or viruses Enteroviruses by disinfection Enteroviruses directly; coliphage is a possible surrogate Cryptosporidium diarrhea; 1.0% hospitalization; 50% mortality in immuno-compromized population Enteroviruses more resistant than bacteria Cryptosporidium by filtration Cryptosporidium oocysts directly; Clostridium is a possible surrogate Giardia causes diarrhea, sometimes chronic; 0.45% hospitalization; 0.0001% mortality isms within treatment trains and to develop performance goals appropriate to planned potable reuse. Most present regulations and guidelines for microbial water quality and treatment performance are based on nonpotable reuse studies focusing on incidental or recreational contact with reclaimed water. Since potable reuse poses greater risks, existing state reuse regulations may not be sufficiently stringent. And while national standards for water treatment are based on scientific risk assessment procedures, they generally assume that the source water is natural surface water or ground water. Potable reuse projects, as well as water sources that are heavily impacted by upstream wastewater discharges, may need to achieve greater levels of pathogen reduction. Only California has established treatment barriers for viruses that are more protective than those used in ordinary drinking water treatment facilities. Treatment standards and goals more appropriate to potable reuse projects need

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