Reducing bioaerosol dispersion from wastewater treatment and its land application: a review and analysis.

Introduction

The Federal Water Pollution Control Act Amendments of 1972, known as the Clean Water Act, set a national goal of eliminating pollutant discharges to navigable waters by 1985. Some communities, industries, and private entities have met this goal by recycling treated water to irrigate agricultural crops or open spaces. While this approach eliminates direct discharges to surface water, sewage treatment plants and spray irrigation are a potential source of bioaerosols that may disperse downwind. This literature review identifies appropriate management practices that reduce the risk to human health posed by exposure to bioaerosols from treatment and irrigation of wastewater.

Methods

A recent literature review (Brooks, Josephson, Gerba, & Pepper, 2004) provides a comprehensive examination of research on the generation of bioaerosols from the treatment and land application of wastewaters and biosolids. Bioaerosols include bacteria, fungi, viruses, and identifiable cellular remnants. In all cases, bioaerosols require a carrier for air dispersal, such as water, soil, or other particulate matter.

For the study reported here, key research reports cited in the literature review by Brooks and co-authors were examined to identify both the characteristics of the treated wastewater and the wastewater management practices that led to detected bioaerosol dispersion. This review reveals measures that may be taken to limit the generation and dispersion of bioaerosols.

Results

Teltsch and Katzenelson studied a single sprinkler that sprayed wastewater treated with a combination of primary sedimentation followed by trickling filter, sand filtration, and chlorination in sequence (1978). The reported BO[D.sub.5] level was 30 milligrams per liter (mg/L). The concentration of coliforms in the effluent was [10.sup.3] to [10.sup.5]/mL. To test for bioaerosol dispersion, Teltsch and Katzenelson introduced marker bacteria (a mutant E. coli) into the wastewater at a similar concentration ([10.sup.5]/mL).

The reporting unit for fecal-coliform testing for regulatory compliance is the number of colony-forming units (CFUs) per 100 mL of water. If all of the mutant bacteria in this experiment were viable, the effluent concentration would be [10.sup.7] CFUs/100 mL (Teltsch & Katzenelson, 1978). Common fecal-coliform standards for disinfection of wastewater used for spray irrigation in the United States range from 2.2 to 200 CFUs per 100 mL. (U.S. Environmental Protection Agency [U.S. EPA], 1992). The bacteria levels in spray effluent examined by Teltsch and Katzenelson are five to six orders of magnitude greater than the limits set by these standards.

Air samples collected 20 meters downwind of the sprinkler showed concentrations of viable bacteria in the air averaging 11 CFUs per cubic meter of air. Teltsch and Katzenelson note that the relatively short sample times (15 minutes for air samples) might have reduced the detectability of bacteria when they were at low concentrations in the effluent. Sampling for viruses in the air showed echovirus to be present in 4 of 12 samples.

That research established that low humidity and high solar radiation reduce bacteria survival in bioaerosols. Bacteria concentrations in air increased 10-fold during nighttime conditions when wind speeds and temperatures were lower, humidity was higher, and no solar radiation was present.

Teltsch and Katzenelson concluded that as the bacterial concentration in the wastewater increased, the probability of discovering bacteria in the air increased proportionally. The inverse was also true; reducing bacterial concentrations in wastewater reduced the probability of discovering bacteria in the air. They noted that bacteria were found in the air during daytime only when the concentration in wastewater was [10.sup.3]/mL or greater. No bioaerosols were detected 20 meters (66 feet) downwind when marker bacteria diminished to 3.4 to 5.7 X [10.sup.3] bacteria/mL or less (1978).

In a later report, die-away kinetics ([lambda]) of aerosolized bacteria were measured (Teltsch, Shuval, & Tadmor, 1980). In this study, the bacteria tracer was tritium, the irrigation apparatus was a jet fog sprayer with 100 percent aerosolization, and air samples were collected 20 to 40 meters downwind of the jet fogger. Complete aerosolization and a single sprayer would be expected to increase detection of downwind concentrations of microorganisms.

The report cautioned that values of [lambda] could not be used to predict downwind concentrations of microorganisms in an effluent spray irrigation field. Nevertheless, useful principles in die-away kinetics were discovered. First, in conditions of low humidity and high solar radiation, a rapid die-away of bacteria occurred in the first 10 to 20 seconds after release. There was a 90 percent reduction for every 10 seconds of travel time in the afternoon experiments. At a wind speed of 20 miles per hour, completely aerosolized water would move about 30 feet per second. Therefore, a 90 percent reduction in bacteria concentration could be predicted (ignoring Teltsch's caution) in 10 seconds, or at a travel distance of 300 feet, during "afternoon" conditions. In the 1980 report, Teltsch and co-authors also confirmed that die-away was much slower in conditions of high humidity when essentially no solar radiation was present (Teltsch, Shuval, & Tadmor).

In subsequent research, Teltsch, Kedmi, and co-authors (1980) compared the survival ratios of enterovirus, coliform, and Salmonella found in air downwind of a wastewater spray system using three different sizes of sprayers. Total-coliform levels in wastewater sprayed by the sprinklers ranged from [10.sup.6] to [10.sup.7] CFUs/100 mL. These concentrations are within the range of values reported for raw wastewater (Tchobanoglous & Burton, 1991). Salmonella concentrations in the wastewater are reported as the most probable number (MPN) per 100 mL, and they ranged from 0 to 60, with an average of 10, which is also within the range for raw wastewater (Tchobanoglous & Burton, 1991). Total-enteroviruses samples were reported as plaque forming units (PFUs) per liter and ranged from 0.0 to 8.2 X [10.sup.4] PFUs/liter, with an average of 6.9 X [10.sup.3] PFUs/liter. Samples were collected from 40 to 200 meters downwind of the various sprinklers used at the test site. Teltsch and co-authors concluded that enteroviruses and Salmonella survived downwind dispersion more successfully than total coliform.

Camann and co-authors prepared a comprehensive assessment of a Lubbock, Texas, land application system (Camann, Moore, Harding, & Sorber, 1988). Twenty-two center pivot irrigation rigs were installed and operating at the 3,665-acre Hancock Farm near Wilson, Texas, 15 miles from the source of the wastewater in Lubbock. The center pivot rigs vary in length (i.e., radius) from 307 to 476 meters (1,007 to 1,562 feet). Operations commenced in 1982. An average daily flow of 3.7 million gallons of trickling filter effluent was delivered directly to the irrigation rigs or to three storage reservoirs at the farm site.

Varieties of microorganisms were analyzed. Both upwind and downwind areas were measured to provide a comparison with background conditions. Composite wastewater samples were collected at the individual center pivots before each air-sampling exercise was conducted. Air samples were collected 10 meters upwind of collection sites, and downwind samples were collected from 50 to 400 meters from the spray apparatus. Different types of sampling apparatus were used simultaneously during the research, and various protocols were established for quality control. The report noted spray irrigation aerosol rates of 0.26 percent to 1.04 percent according to dye test samples from 25 to 80 meters downwind.

Total-organic-carbon concentrations of 105 mg/L and total-suspended-solids concentrations of 149 mg/L characterized wastewater delivered to the reservoirs. Fecal coliform levels exceeded [10.sup.6] CFUs/100 mL, and virus levels ranged from 100 to 1,000 PFU/liter. No data were provided on specific concentrations of the majority of microorganisms in pipeline water. Storage varied from as short as 60 days to as long as 180 days based on calculations taking into account flow patterns, rainfall, and other factors. The report notes that, reservoir impoundment significantly reduced the potential for exposure to microorganisms, citing reductions in coliform levels by as much as 99 percent and a lowering of viral levels to 10 PFUs/L. These observed reductions would presumably lower fecal coliform concentrations to [10.sup.4] CFUs/100 mL, a value still well in excess of limits set by common regulatory standards for treated water used for spray irrigation (2.2 to 200 CFUs per 100 mL). This value also exceeds by an order of magnitude the effluent levels observed by Teltsch and Katzenelson that produce no detectable downwind concentrations of fecal coliform (Teltsch & Katzenelson, 1978).

Camann and co-authors concluded that the effects of reservoir storage were significant and could be compared to the effects of a large buffer zone, estimated as 75 meters for fecal coliform and 300 meters for fecal streptococci, mycobacteria, coliphase, and C. perfringens. The latter three microorganisms are hardier than fecal coliform.

Frequent detection of fecal streptococci in upwind samples indicates that this bacterium may be useful for comparison of downwind and upwind areas. Upwind air samples frequently contained fecal streptococci (27 of 30 samples). The report includes precise values for fecal-streptococci concentrations in reservoir water, which are two orders of magnitude lower than those in pipeline wastewater. Interestingly, two other samples of pipeline wastewater chlorinated at the Lubbock treatment plant also contained fecal streptococci concentrations one to two orders of magnitude lower than those in pipeline water. None of the reservoir samples were subject to chlorination immediately prior to irrigation.

The fecal-streptococci data provide an interesting prediction of the effects on detectable dispersion when wastewater has been disinfected more thoroughly. Three samples (M-20, M-16, and M-19) with fecal streptococci concentrations averaging 5 CFUs/mL (or 500 CFUs/100 mL) are of interest. Two came from reservoir water, and one came from pipeline wastewater chlorinated at the Lubbock plant. When upwind samples were analyzed at the time this wastewater was sprayed, background concentrations of fecal streptococci averaged 0.2 CFU/[m.sup.3]. Earlier samples collected to determine background microorganism densities in ambient air showed fecal streptococci concentrations averaging 0.47 CFU/[m.sup.3] (Camann, Moore, Harding, & Sorber, 1988.) Therefore, at this site, background concentrations of fecal streptococci may be expected in the range of 0.2 to 0.5 CFUs/[m.sup.3].

For the three samples referenced (M-20, M-16, and M-19), the downwind concentrations of 15 of 16 fecal-streptococci samples fell within the range in the background samples. The outlying data point was a value of 0.7 CFUs/m at 40 to 59 meters downwind (131 to 169 feet). Data presented indicate that spray irrigation at the time these samples were collected often produced downwind concentrations of other microorganisms equal to or less than upwind concentrations.

Three reports by Italian researchers address dispersion of bioaerosols from wastewater treatment facilities. Carducci and co-authors reported on a yearlong experiment that measured dispersion of microorganisms at an activated sludge plant that used turbine aeration (1999). In activated-sludge facilities, wastewater is introduced to turbine aeration tanks following primary settling. Active agitation of wastewater with surface aerators (turbine aeration) would likely produce bioaerosols from an open tank.

Sampling sites were established above the tank and at locations 20 meters and 50 meters downwind. The purpose of the experiment was to clarify relationships among viruses and bacteria at different distances from the tank. No readily discernible wastewater concentration data were reported; however, several findings are of interest. First, the presence of reovirus and enterovirus at all sampling locations was a seasonal phenomenon. Measurable concentrations of these viruses were found only from June through October. Second, viral presence consistently correlated only with fecal streptococci. Third, over a distance of 50 meters, virus contamination dropped by 15 percent, while total bacteria count decreased by 88 percent, fecal streptococci by 98 percent, and coliphages by 99 percent.

In a second report, Carducci and co-authors reported on experiments at several wastewater treatment facilities in Livorno, Italy (2000). Preliminary testing identified 20 areas at the facilities with the highest likelihood of detectable microorganisms. The highest levels of contamination were found in a sewage-washing station along the collection lines, while the next highest concentrations were found near mechanical sewage-handling equipment, such as primary and secondary screens, and mechanical aeration of the grit chamber. A sludge treatment plant had mid-range levels of bacterial contamination and high frequencies of samples testing positive for viruses. The areas around the aeration tanks did not appear to be highly contaminated, a finding that Carducci and co-authors ascribed to the use of subsurface aeration. Earlier studies had shown that surface aerators (the turbine aerators mentioned above) produced high levels of contamination. For viral detection, the Carducci and co-authors recommended the reoviruses because of their frequent presence.

In a third report, also published in 2000, Brandi and co-authors reported on tests for microorganisms at facilities using different types of sludge oxygenation (2000). The first facility used mechanical agitation of sludge, while the second used a fine-bubble diffused-air system. Dramatic differences were noted in microorganism dispersion downwind of the two types of tanks. The authors concluded that "aerobic digestion with a submerged microbubble system seems to pose little risk from airborne transmission of pathogenic bacteria and fungi to waste-treatment workers or local residents. For this reason, the conversion of mechanical oxygenation systems to submerged oxygenation systems of the sludge should be considered" (Brandi et al., p. 852).

Discussion

The reports of Teltsch and Katzenelson (1978); Teltsch, Shuval, & Tadmor (1980); and Teltsch, Kedmi, and co-authors (1980) suggest that treating and disinfecting wastewater to remove fecal coliform prior to spray irrigation is an effective means of reducing potential human exposure. Furthermore, the best timing and setting for irrigation of treated wastewater is during the day in low-humidity conditions. Testing of multiple microorganisms identified variability in die-away rates and suggests that total coliform is not an appropriate predictor of downwind dispersion of other microorganisms. Fecal coliform consistently died away at faster rates than other microorganisms.

Research by Camann and co-authors supports findings that fecal coliform are less hardy than other microorganisms. Camann and co-authors also noted that all microorganism concentrations decreased as distance downwind increased, and that the highest downwind concentrations were observed when irrigation occurred at night. The report also noted higher-than-average downwind concentrations when air speed exceeded 7 meters per second, or about 16 miles per hour.

Camann and co-authors (1988) also suggest significant benefits associated with wastewater storage reservoirs in providing natural disinfection (which is likely due to settling of solids and to oxygen transfer from the atmosphere to the top layer of the stored water). In addition, their research suggests that fecal streptococci may be a better indicator organism than fecal coliform because of higher survivability and incidence in background concentrations. The relatively low downwind concentrations in water sprayed from the reservoir (or from pipeline water that had been chlorinated) indicate a substantially lower exposure risk when wastewater is more thoroughly treated.

Carducci and co-authors (1999, 2000) and Brandi and co-authors (2000) have substantiated the value of fecal streptococci as an indicator organism, noting that they were consistently associated with detection of viruses. Their work also establishes that reovirus and enterovirus contamination may be a seasonal event. Their research on bioaerosol dispersion at sewage treatment plants establishes the potential exposure risks of sludge management and the mechanical agitation of raw wastewater. Their observations regarding the reduced generation of bioaerosols when sludge is oxygenated with submerged aerators suggest that this effect is of such importance that they recommend consideration of conversion of mechanical aeration plants.

In all of these research settings, there was a poor level of disinfection in the treated wastewater. In many, fecal-coliform levels fell within the range of reported concentrations found in raw sewage. One of the cases presented (the three samples measured by Camann and co-authors) indicates that when water is disinfected more thoroughly the downwind concentrations differ little from background concentrations (1988).

Research on die-away rates indicates that viruses are long-lived, and downwind concentrations are not significantly diminished in the distances measured in the reports reviewed here. Clearly, the key to reducing viral dispersion is to reduce source concentrations to low levels.

Conclusions

This review reveals several measures necessary to reduce the generation of bioaerosols at treatment facilities and at spray irrigation sites. For treatment facilities:

1. Design facilities to avoid the direct exposure of raw wastewater to the air.

2. Avoid mechanical agitation of raw wastewater unless in a controlled area within a buffered setting.

3. Employ subsurface aeration for oxygenation tanks, lagoons, or ditches.

4. Minimize sludge generation and handling.

5. Institute infection control at facilities that lack these design features--for example, respiratory protection, frequent washing of hands, daily showers, laundry service for uniforms, and disinfection of surfaces where human contact is likely, such as desks, counter space, and cabinets.

6. Locate facilities within buffer zones.

7. Treat wastewater reused for irrigation to minimize concentrations of a wide range of microorganisms, especially viruses, which appear to have the greatest longevity of all bioaerosols.

8. Consider use of storage reservoirs for natural disinfection prior to spray irrigation of treated wastewater.

For spray irrigation facilities:

1. Use wastewater that has been disinfected to minimize all microorganisms.

2. Establish buffer zones free of human habitation.

3. To the extent possible, avoid aerosolization--for example, by directing spray downward and using coarser spray nozzles at the periphery of center pivot rigs.

4. Consider reservoir storage if it is not already provided.

5. Consider establishing background concentrations of fecal streptococci and conducting downwind monitoring to check for bioaerosol dispersion above background levels.

6. Avoid spraying in high wind conditions (>20 miles per hour).

7. Spray in daytime conditions when possible.

8. Spray in low-humidity conditions when possible.

Corresponding Author: Richard E. O'Hara, Director of Environmental Health and Safety, American Ecology, Inc., 300 East Mallard Drive, Suite 300, Boise, ID 83706. E-mail: [e-mail].

REFERENCES

Brandi, G., Sisti, M., & Amagliani, G. (2000). Evaluation of the environmental impact of microbial aerosols generated by wastewater treatment plants utilizing different aeration systems. The Society for Applied Microbiology, Journal of Applied Microbiology, 88, 845-852.

Brooks, J.P., Josephson, K.L., Gerba, C.P., & Pepper, I.L. (2004). Biological aerosol emission, fate, and transport from municipal and animal wastes. Journal of Residuals Science and Technology, 1(1), 15-28.

Camann, D.E., Moore, B.E., Harding, H.J., & Sorber, C.A. (1988). Microorganism levels in air near spray irrigation of municipal wastewater: The Lubbock infection surveillance study. Journal of the Water Pollution Control Federation, 60(11), 1960-1970.

Carducci, A., Gemelli, C., Cantiani, L., Casini, B., & Rovini, E. (1999). Assessment of microbial parameters as indicators of viral contamination of aerosol from urban sewage treatment plants. The Society of Applied Microbiology, Letters in Applied Microbiology, 28(3), 207-210.

Carducci, A., Tozzi, E., Rubolotta, E., Casini, B., Cantiani, L., Rovini, E., Muscillo, M., & Pacini, R. (2000). Assessing airborne biological hazard from urban wastewater treatment. Water Resources, 34(4), 1173-1178.

Teltsch, B., & Katzenelson, E. (1978). Aerobic enteric bacteria and viruses from spray irrigation with wastewater. Applied and Environmental Microbiology, 35(2), 290-296.

Teltsch, B., Shuval, H.I., & Tadmor, J. (1980). Die-away kinetics of aerosolized bacteria from sprinkler application of wastewater. Applied and Environmental Microbiology, 39(6), 1191-1197.

Teltsch, B., Kedmi, S., Bonnet, L., Borenzstajn-Rotem, Y., & Katzenelson, E. (1980). Isolation and identification of pathogenic microorganisms at wastewater-irrigated fields: Ratios in air and wastewater Applied and Environmental Microbiology, 39(6), 1183-1190.

Tchobanoglous, G., & Burton, F. (1991). Wastewater engineering (3rd ed.). New York: Metcalf and Eddy.

U.S. Environmental Protection Agency. (1992). Process design manual: Guidelines for water reuse. Washington, DC: Author.

Richard E. O'Hara, M.S.

Robert Rubin, Ed.D.

RELATED ARTICLE: Reducing Microorganism Concentrations in Wastewater with Submerged Aeration as a Primary Treatment Method

Abstract

Wastewater treatment systems frequently use aeration as a method of transforming organic matter into constituent elements. Some facilities use extended aeration and submerged aerators to maximize biodegradation and oxidation, and to facilitate predation. Analytical data from two facilities that use extended, submerged aeration indicate that this method effectively disinfects wastewater.

Introduction

Data are presented below from two facilities where treatment cells are oxygenated with submerged aerators providing a minimum of 2.0 pounds of oxygen per pound of five-day biochemical oxygen demand (BO[D.sub.5]). The data show that microorganism concentrations in treated wastewater may be reduced substantially through long-term aeration. At both facilities, course bubble aerators are located from 15 to 25 feet below the water surface.

The first facility is located in Timberville, Virginia, and is permitted to accept a combined flow of up to 1,923,000 gallons per day of wastewater originating from two independent poultry-processing facilities and two towns (municipalities). The combined wastewater reclamation facility provides a minimum of 30 days of detention time, and it treats wastewater in two sequential, flow-through cells. A storage reservoir with a minimum capacity of 120 days of flow is provided. The samples referenced here were collected at the storage reservoir outflow--that is, prior to chlorination (Figure 1).

The second facility (Saddlebrook Farms) treats domestic wastewater generated from a new subdivision in Round Lake Park, Illinois. This facility has a current flow of 160,000 gallons per day and uses a two-cell, flow-through design with storage integrated into each cell. No separate storage reservoir is provided (Figure 2). Cell I has 20 million gallons of capacity, and Cell II has 8.3 million gallons of capacity. The facility at Saddlebrook Farms consists of a treatment facility containing these lagoons, a disinfection system, an irrigation pump station, and a wastewater irrigation system consisting of two center pivot irrigation rigs covering a total of 62 acres of cropland.

Methods

Grab samples from the Saddlebrook site were collected on August 14, 2000, by Mark Mueller (McHenry Analytical Laboratories), Bill Pullman (Saddlebrook Farms), and Nathan Hinch (Sheaffer International). At this time, Cell I and Cell II were at relatively low levels because the irrigation season was at its peak. Total detention times would have been approximately 30 days. The following locations were sampled:

[FIGURE 1 OMITTED]

[FIGURE 2 OMITTED]

* "Influent" from the collection system manhole within the Saddlebrook Farms development;

* "Reclaimed Water Before Chlorination" from the irrigation pump station; and

* "Reclaimed Water After Chlorination" from Center Pivot Irrigation Rig #1 (since a spigot has yet to be installed at the irrigation rig to sample water, the researchers obtained this sample by loosening a flow control bolt and collecting reclaimed water as it flowed out of the bolt hole).

At the North Fork facility, Licensed Operator Delmar Reed, of SIL Cleanwater, a Sheaffer International subsidiary, collected grab samples on April 17, 2001. Mr. Reed collected influent samples at the influent manhole and collected effluent samples (before chlorination) at the irrigation pump station outlet pump overflow line, which returns excess pump flow to the storage reservoir. Chlorinated samples were not available when other grab samples were collected.

At both sites, 1-liter samples were collected in sterilized bottles provided by McHenry Analytical Laboratories. The samples were shipped overnight to the City of Milwaukee Health Department Laboratories in an insulated cooler. The sample bottles were packed inside the cooler with ice contained in separate, sealed containers. The sample collection and shipping were in accordance with the guidelines of the City of Milwaukee Health Department Laboratories. The laboratories used standard procedures for the quantification of bacteria, viruses, and protozoa present in the samples, namely, total coliform and E. coli by Colilert (IDEXX Corp.), fecal coliform and fecal streptococci by membrane filtration technology, Cryptosporidium and Giardia by U.S. Environmental Protection Agency (U.S. EPA) Method 1623, and viruses by cell culture method.

Results

Influent samples indicated that total-coliform concentrations were comparable to literature values for raw domestic wastewater (Tchobanoglous & Burton, 1991). Following treatment with extended aeration, bacterial concentrations were reduced 99.99 percent. Viruses were reduced by 94 percent or greater, and Giardia and Cryptosporidium were reduced by 98.3 percent or greater. Results are presented in Table 1. Additional treatment, by chlorination or other means of disinfection, may be necessary to meet standards for reuse or discharge of treated wastewater (U.S. EPA, 1992).

Conclusions

Extended aeration with submerged aerators is an effective means of reducing microorganism concentrations in wastewaters at the two locations tested. Additional disinfection, by chlorination or other means, may be necessary to meet standards for unrestricted reuse or discharge of treated water.

References

Tchobanoglous, G., & Burton, F. (1991). Wastewater engineering (3rd ed.). New York: Metcalf and Eddy.

U.S. Environmental Protection Agency. (1992). Process design manual: Guidelines for water reuse. Washington, DC: Author.

Richard E. O'Hara, M.S.

Robert Rubin, Ed. D.

TABLE 1 Microorganisms in Treated and Untreated Wastewater

                                                  System
Facility     Pathogen            Units            Influent

North Fork
             Cryptosporidium     Number/liter         0
             Giardia             Number/liter       230
             Fecal coliform      CFU/100 mL           4.50E + 07
             E. coli             MPN/100 mL           2.60E + 07
             Fecal streptococci  MPN/100 mL           2.90E + 06
             Adenoviruses (b)    Number isolated      1
             Adenoviruses        MPN/liter           26
Saddlebrook
             Cryptosporidium     Number/liter         2
             Giardia             Number/liter     4,000
             Fecal coliform      CFU/100 mL           2.90E + 06
             E. coli             MPN/100 mL           2.42E + 06
             Fecal streptococci  MPN/100 mL         N/A
             Reoviruses (d)      Number isolated      7
             Reoviruses          MPN/liter          179

                                 Reclaimed Water       Percent
Facility     Pathogen            Before Chlorination   Reduction

North Fork
             Cryptosporidium         0                 N/A
             Giardia                 4                  98.3%
             Fecal coliform      1,500                  99.997%
             E. coli             1,400                  99.995%
             Fecal streptococci     55.6                99.998%
             Adenoviruses (b)        0                 N/A
             Adenoviruses           <1.5               >94%
Saddlebrook
             Cryptosporidium         0                 100.0%
             Giardia                12                  99.7%
             Fecal coliform        170                  99.99%
             E. coli               161                  99.99%
             Fecal streptococci    N/A                 N/A
             Reoviruses (d)          0                 100.0%
             Reoviruses             <1 MPN/0.8 liters  >99.4%

                                 Reclaimed Water
Facility     Pathogen            After Chlorination

North Fork
             Cryptosporidium     Not sampled
             Giardia             Not sampled
             Fecal coliform      <2 CFU/100 mL (a)
             E. coli             Not sampled
             Fecal streptococci  Not sampled
             Adenoviruses (b)    Not sampled
             Adenoviruses        Not sampled
Saddlebrook
             Cryptosporidium     0
             Giardia             18
             Fecal coliform      95 (c)
             E. coli             81.6
             Fecal streptococci  Not sampled
             Reoviruses (d)      0
             Reoviruses          <1 MPN/0.8 liters

(a) April 2001 effluent test results following treatment to reduce
nutrients (oxidation ditch and clarifier) followed by chlorine contact
and dechlorination.
(b) Multiple classes and types of viruses analyzed, including three
types of reoviruses, three types of polio viruses, 70 types of
enteroviruses, and 20 to 30 types of adenoviruses. Only one type of
adenovirus was found.
(c) Four compliance samples collected from the same irrigation rig
(October 1999 to October 2000) showed fecal-coliform concentrations
ranging from 0 to 1 CFU/100 mL.
(d) Only seven types of reoviruses were identified.