States
nental Protection
EPA 600-1-81-006
:fi and Development
Hsaltn Effects Research
Laboratory
Cincinnati OH 45268
POTENTIAL HEALTH EFFECTS FROM VIABLE EMISSIONS AND TOXINS
ASSOCIATED WITH WASTEWATER TREATMENT PLANTS AMD
LAND APPLICATION SITES
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POTENTIAL HEALTH EFFECTS FROM VIABLE EMISSIONS AND TOXINS
ASSOCIATED WITH WASTEWATER TREATMENT PLANTS AND
LAND APPLICATION SITES
by
Vimala A. Majeti and C. Scott Clark
Department of Environmental Health
University of Cincinnati Medical Center
Cincinnati, Ohio 45267
Grant No. R-805445
Project Officer
Herbert R. Pahren
Epidemiology Division
Health Effects Research Laboratory
Cincinnati, Ohio 45268
HEALTH EFFECTS RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
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DISCLAIMER
This report has been reviewed by the Health Effects Research Laboratory,
U.S. Environmental Protection Agency, and approved for publication. Approval
does not signify that the contents necessarily reflect the-views and policies of
the U.S. Environmental Protection Agency, rior does mention of trade names or
commercial products constitute endorsement or recommendation for use.
n
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FOREWORD
The U.S. Environmental Protection Agency was created because of increasing
public and governmental concern about the dangers of pollution to the health and
welfare to the American people. Noxious air, foul water, and spoiled land are
tragic testimony to the deterioration of our national environment. The
complexity of that environment and the interplay between its components require
a concentrated and integrated attack on the problem.
Research and development is that necessary first step in problem solution
and it involves defining the problem, measuring its impact, and searching for
solutions. The primary mission of the Health Effects Research Laboratory in
Cincinnati (HERL) is to provide a sound health effects data base in support of
the regulatory activities of the EPA. To this end, HERL conducts a research
program to identify, characterize, and quantitate harmful effects of pollutants
that may result from exposure to chemical, physical, or biological agents found
in the environment. In addition to the valuable health information generated by
these activities, new research techniques and methods are being developed that
contribute to a better understanding of human biochemical and physiological
functions, and how these functions are altered by low-level insults.
This report presents an overview of the literature on potential health
problems associated with microbiological contaminants during wastewater treat-
ment or disposal. It is hoped that this review will provide a better
understanding of the problem so that adequate measures may be taken to avoid
disease.
Director
Ith Effects Research Laboratory
i11
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ABSTRACT
This report summarizes the potential health effects from viable emissions.
and toxins associated with wastewater treatment plants and land application
facilities to the workers and nearby populations. The different types of
microorganisms present in wastewater and sludge and the effectiveness of the
various treatment processes in their removal or inactivation is discussed
briefly. The monitoring of microorganisms and toxins in aerosols generated at
wastewater treatment plants and land application sites, the disadvantages in
using coliform organisms as indicators to represent the actual levels of
pathogenic microorganisms in aerosols, and the various mathematical models that
are used to predict the microorganism levels in aerosols are also reviewed. The
levels of microorganisms detected in aerosols at wastewater treatment plants
and land application facilities from some of the recent studies are presented.
Diseases attributed to the pathogenic microorganisms are summarized.
Results from several recent epidemiologic studies of workers at wastewater
treatment- plants and land application sites and' an nearby residents are
evaluated. The different methods that can be used to reduce the microorganism
levels in aerosols and to suppress and/or to reduce the generation of aerosols
are also discussed.
The review concludes that although pathogenic microorganisms have been
detected in aerosols at wastewater treatment plants and land application
facilities, the existing evidence from health effects studies does not indicate
a significant health hazard to the workers from infectious disease agents and
that a health risk to nearby populations has not been demonstrated. The fact
that exposure to pathogenic microorgansims in wastewater aerosols is not a
unique way of i-nitiating enteric infections, makes it difficult to detect the
effect, if any, of a wastewater facility. The report also concludes that the
mathematical models that are used to predict the microorganism levels in
aerosols are not perfected enough to replace actual field monitoring. Recom-
mendations are made concerning suitable microorganisms other than coliform
organisms as indicators of pathogen levels in aerosols and regarding monitoring
requirements of water samples at land application facilites for microorganisms.
Recommendations "are also made concerning guidelines (minimum treatment re-
quirements) "for land application and buffer or safety zones.
This report was submitted in partial fulfillment of Grant No. R805445 by
the Department of Environmental Health, University of Cincinnati, under the
sponsorship of the U.S. Environmental Protection Agency. This report covers the
period February 22, 1978 to May 21, 1980.
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CONTENTS
Foreword 111
Abstract ]v
Figures and Tables vii
Acknowledgments viii
1. Introduction 1
2. Conclusions 3
3. Recommendations 5
Pol icy/guidel ines 5
Further research - 6
4. Occurrence and Persistence of Microorganisms, and
Toxins in Wastewater and S1 udge , 7
Microorganisms and Toxins 'Present in Waste-
water and Sludge 7
___.Microorganisms 7
Tox i ns 10
Microorganism and Toxin Persistence During Waste-
water and Sludge Treatment... 11
; Wastewater : 11
; Sludge... 13
.._._ .. _._ ; Toxins. 15
5. Microorganisms and Toxins in Aerosols Generated at
Wastewater Treatment Plants and Land Application Sites 16
Aerosols , , 16
Microorganism monitoring in aerosols 18
Sampling of microorganisms in aerosols -.' * 18
Indicator organisms 19
Monitoring endotoxins in dust and aerosols 20
Microorganisms in aerosols at wastewater -
treatment plants and vicinity .'. 21
Microorganisms in aerosols at wastewater land
application sites and vicinity 25
Survival and dispersion of microorganisms
in aerosoIs 30
6. Models for Predicting Microorganism Levels in
Aerosols. 32
Pasquill's Model... 33
Turner' s Model 33
Camann' s Model 36
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7. Effects of Pathogenic Microorganisms Present in
Wastewater and Wastewater Aerosols 39
Diseases attributed to pathogenic microorganisms
present in wastewater and aerosols 39
Bacterial diseases 41
Viral diseases 42
Protozoan diseases 43'
Parasitic diseases 43
Epidemiology of wastewater treatment plant workers
and populations living in the vicinity 44
Epidemiology of workers at land application sites and
populations living in the vicinity 49
8. Control of Aerosols _._ 52
Vegetative Barriers .~ 52
Buffer/Safety Zones 53
Disinfection 61
Spray Equipment 61
Covering Aeration Basins 61
References 62
VI
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.. FIGURES AND TABLES
Number Figures Page
1 Varability of deposition of particles in the respiratory
tract 17
Tables
1 Major Organisms of Health Concern That May Be Present in
Sewage from U.S. Communities 8
2~ Removal of Microorganisms From Wastewater by
Disinfection With Chlorine..... 12
3 Inactivation of Microorganisms by Anaerobic
Digestion; 14
4 Bacteria Concentrations in Aerosols at Specified
Distances From Trickling Filters and Activated Sludge
Units. 22
5 Bacteria and Virus Concentrations in Aerosols at Specified
; Distances From Wastewater Spray Irrigation Sites 27
6 Summary Information on Reported Waterborne Diseases in
the United States 40
7 Buffer/Safety Zones Recommended by Some States for Safe
Application of Wastewater (W) and/or Sludge (S) to
Land Compi led From Mai 1 Survey 54
i i
8 Guidelines Established by Some States for Safe Land
Application of Wastewater (W) and/or Sludge (S)
Compiled From Mail Survey 56
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ACKNOWLEDGMENTS
Mr. A. Komrichwarakool, Ms. H. K. Weir, and Mr. A. I. Carson, graduate
students in the Department of Environmental Health, University of Cincinnati,
provided assistance in searching and partial evaluation of the literature
pertaining to this report.
Ms. K. Brenner, Ms. W. Davis-Hoover, and Dr. P. V. Scarpino of the De-
partment of Civil and Environmental Engineering, University of Cincinnati,
prepared the material from which Section 6 on predictive models was adapted.
Mr. T. L. Huge, Biostatistician, Department of Environmental Health, Uni-
versity of Cincinnati, helped provide an understanding of the basic principles
and limitations of the predictive"models. " "
The assistance provided by Ms. M. J. Onslow and Ms. S. F. Humiston,
Department of Environmental Health, University of Cincinnati, in preparing and
providing editorial assistance for the manuscript, respectively, is gratefully
acknowledged. ;
The comments and suggestions provided by Dr. R. L. Ward of the Sandia
Laboratories, Albuquerque, New Mexico, and Dr. J. J. Bertucci, of the Metro-
politan Sanitary District of Greater Chicago, 'in their reviews of this document
:are sincerely appreciated. \
We are also thankful to the Health Effects Research Laboratory, U.S.
Environmental Protection Agency, Cincinnati, Ohio, for providing financial
;support for this work.
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SECTION 1
INTRODUCTION
A large variety of potential disease-causing microorganisms and viruses
are present in municipal wastewaters. The workers at the wastewater treat-
ment plants are potentially exposed to these pathogenic microorganisms and
viruses through ingestion as well as inhalation of the aerosolized pathogens.
Furthermore, the populations living in the vicinity of the wastewater treat-
ment plants may be exposed to low densities of these pathogenic microor-
ganisms and viruses that are airborne.
"As a result of legislative actions, such as the 1972 Clean Water Act
and its 1977 amendments, land application of wastewater and sludge is gaining
renewed interest as an alternative means to the more conventionally used
disposal methods, such as ocean and surface water dumping, and incineration.
Land application represents a recycling process in which water and plant
nutrients are returned to the soil. However, wastewater treatment does not
completely remove pathogens and many become concentrated in the sludge.
The potential health effects on workers from exposure to airborne patho-
gens and toxins, at wastewater treatment plants and land application sites,
and on the populations living in the vicinity of the treatment plants and
land application sites, will be discussed in this report. Also, recommen-
dations regarding methods to control human exposure will be made.
Information regarding human health risks resulting from contact with
wastewater and sludge brought about by occupational exposure or by residing
near wastewater treatment plants and/or land application facilities, is
limited. Several health effects studies have been initiated in the past few
years on the health risks of pathogens in wastewater and aerosols generated
at the wastewater treatment plants.
The reports of Hickey and Reist (1), Sepp (2), Parsons et al. (3),
Clark et al. (4), the Proceedings of the Conference on Risk Assessment and
Health Effects of Land Application of Municipal Wastewater and Sludges (5),
the International Symposium on the State of Knowledge in Uand Treatment of
Wastewater (6), SCS Engineers report (7) and the State of California's report
on State-of-the-Art Review of Health Aspects of Wastewater Reclamation
for Groundwater Recharge (8), all form the background material for parts of
this report.
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In order to assess the potential health risks from exposure to viable
and nonviable pathogens in aerosols generated at wastewater treatment plants
and land application sites, three topics are first discussed.
Occurrence and persistence of microorganisms and toxins in
wastewater and sludge (Section 4).
Microorganisms and toxins in aerosols generated at wastewater treatment
plants and land application sites (Section 5).
Models for predicting microorganism and virus levels in aerosols
(Section 6).
Following this background, diseases attributed to pathogens for wastewater
and sludge are discussed along with the results of several recent epidemi-
ologic studies of populations with wastewater exposure in a section en-
titled:
Effects of pathogenic microorganisms and viruses present in wastewater
and wastewater aerosols (Sectfon 7).
The final section of the report addresses the need for the control of aerosols
and methods applicable to their control (Section 8).
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_ _ _ SECTION Z. -
CONCLUSIONS
Members of each group of the microorganisms - bacteria, protozoa,
helminths, and viruses survive standard wastewater treatment processes, al-
though in reduced numbers, and are concentrated in sludge.
Pathogenic bacteria are present in aerosols in detectable levels at
wastewater treatment plants and spray application facilities, and inhalation
is a possible route of exposure. Animal viruses have been detected, but
only by. sampling relatively^large volumes of.air. . .. _ ...
Coliform organisms do not survive wastewater aerosolization as well as
the other microorganisms such as Streptococcus faecal is and,therefore,have
limited usefulness as indicators of pathogens in aerosols. The use of coli-
form organisms-as indicators would tend to underestimate the potential effect
on workers as well as nearby populations.
Because of the lack of a standard method- for viral monitoring, comparison
of data from two or more laboratories must consider differences in sample
handling, concentration,.and method of measurement. Because of the dif-
ficulties involved in routinely detecting airborne viruses at wastewater
itreatment plants and spray irrigation facilities, it is presently not possible
to validate atmospheric dispersion models for their prediction.
For bacteria the models appear to have some usefulness, but have not
been perfected enough to replace the field monitoring.
Information is not available on minimum infective dose of airborne
microorganism levels for the inhalation route.
- ; i
A number of epidemiological studies have recently been performed on
workers at wastewater treatment plants, and spray irrigation facilities and
on populations living adjacent to these sites who would generally be ex-
posed to lower levels of the pathogens. Data on health effects from the
existing epidemiological studies do not show any correlation between the
airborne pathogenic microorganism levels at wastewater treatment plants and
incidence of disease in treatment plant workers or in nearby populations.
However, the worst case of exposure of either the workers or the nearby
populations has probably not yet been investigated. No adverse health
effects have been reported in workers or in nearby populations at wastewater
jspray application facilities. From the data on health effects from the
existing epidemiological studies, it is concluded that exposure to pathogenic
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microorganisms in wastewater aerosols is not a unique way of initiating
enteric infections. The existence of the other possible pathways of infection
could tend to make more difficult the detection of a wastewater facility
effect if indeed one exists.
Studies reported from Sweden attribute responses such as elevated
immunoglobulins and excess gastrointestinal symptoms in workers at con-
ventional wastewater treatment plants to the effects of exposure to endo-
toxins.
Investigators in Copenhagen, Denmark, showed that sewer workers had
elevated levels of immunoglobulin, IgG and hepatitis A antibodies compared to
a control group.
Buffer zones, vegetative barriers, design of spray equipment, use.of
subsurface injection, covering aeration tanks, etc. can suppress or reduce
the aerosols and/or the levels of microorganisms in aerosols. These
measures could serve to control the exposure of nearby populations, and in
some cases, but to a lesser extent, that of the workers.
Data from viral and bacterial monitoring of wastewater and aerosols
indicate that buffer or safety zones may not be necessary between waste-
water treatment plants or spray application facilities and the surrounding
population centers.
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SECTION 3
RECOMMENDATIONS
POLICY/GUIDELINES
1. For aesthetic reasons, a minimum vegetative barrier or buffer zone is
recommended around wastewater treatment plants and spray irrigation
facilities to control the possible release of foam and water droplets.
2. For spray application, low pressure downward spray equipment is
generally preferred instead of high pressure upward spray equipment.
Ridge and furrow irrigation or "subsurface injection should be practiced
whenever possible, instead of spray application.
3. Spray application of wastewater without appropriate prior treatment is
not recommended under conditions which increase the viability of air-
borne microorganisms such as very high relative humidity, night-time or
at other times when there is no solar radiation, winter months in colder
regions, etc.
4. Only stabilized sludge should be permitted to be applied on land.
5. Wastewater must be pretreated prior to application on land. The pre-
treatment requirements should be based on the type of land use, type of
crops grown, etc. as shown:
(a) A minimum of primary treatment should be required for the
irrigation of forest land, sod farms, fodder crops, pasture land
and other non-food crops, and for irrigation of lands that are
remote from and not easily accessible to the general public.
(b) A minimum of secondary treatment or sufficient elapsed time for
microorganism die-off should1 be required for agricultural irri-
gation of food crops processed for human consumption.
(c) A minimum of secondary treatment followed by disinfection should
be required for the irrigation of public areas such as golf courses
and public parks.
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6. Water'samples (leachates and runoff) at land application facilities
should be monitored for microorganisms to ensure protection of ground
and surface waters.
7. Resistant microorganisms such as Streptococcus faecal is should be used
as indicators of pathogen levels in ambient air.
FURTHER RESEARCH
A standard method should be developed for the concentration and de-
tection of viruses in wastewater and in aerosols to facilitate virus
monitoring and to enable comparison of results obtained in different
laboratories.
Epidemiology of health effects of workers involved in worst-case sewer
activities and wastewater and sludge treatment operations should be con-
ducted.
Existing covers on aeration basins used to control odors should be
evaluated for their usefulness irr suppression- of aerosols.
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SECTION 4
OCCURRENCE AND PERSISTENCE OF MICROORGANISMS
AND TOXINS IN WASTEWATER AND SLUDGE
Microorganisms present in wastewater and sludge and their survival
during treatment have been discussed thoroughly recently by several authors
(9-16) and, therefore, will only be summarized here briefly.
MICROORGANISMS AND TOXINS PRESENT IN WASTEWATER-AND SLUDGE
Microorganisms __ ._. _ _ . .._
The major groups of microorganisms present in municipal wastewater and
sludge are bacteria, viruses, protozoa and helminths. Some of these micro-
organisms, the diseases that are attributed to them, and known reservoirs of
infection are shown in Table 1 (9).
Bacteria. The enteric bacteria are the most common microorganisms
present in wastewater. Escherichia coTi frequently are present at a concen-
tration of about 10^/1iter and streptococcus faecal is, at about 10^/1iter of
wastewater. Salmonella are the most prevalent pathogenic bacterial species
present in wastewater and densities of 5000/1iter have been reported in raw
wastewater (11)., Shi gel la and pathogenic strains of _£. coli also occur in
wastewater. ] \
i
Protozoa. The protozoan agents present in wastewater are in the form
of cysts which are excreted in large numbers of the feces. The most patho-
genic of these is Entamoeba histolytica. Salantidium coli and Giardia
1amb1i a are also, found in wastewater. It is estimated that protozoan cysts
in wastewater do^ not exceed 5000/1iter (17).
; Helminths. A large number of parasitic helminths are present in waste-
water in the form of eggs. The helminths are of major public health concern
because of the extreme persistence of the eggs to a wide range of environ-
mental conditions. The various parasitic ova most commonly found in waste-
water are Ascaris lumbricoides, Trichuris trichiura, Hymenolepis species,
Taem'a saginata, Enterobius verrm'cularis, a'nd'Necator americanus. Levels of
parasitic eggs have been predicted to be about 62/1iter of raw wastewater in
the U.S. (18). Since a significant amount of animal wastes reach municipal
wastewater, the parasites of animal origin are also of concern.
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TABLE 1. MAJOR ORGANISMS OF HEALTH CONCERN THAT MAY BE PRESENT IN
SEWAGE FROM U.S. COMMUNITIES (9)
Organisms
Disease
Reservoir(s;
I. Bacteria
Salmonellae
(Approx. 1700 types)
Shigellae (4 spp.)
Escherichia coli
(enteropathogenic types)
II. Enteric viruses
Enteroviruses
(67 types)
Rotavirus
Parvovirus-like agents
(at least 2 types)
Hepatitis A virus
Adenoviruses
(31 types)
Typhoid fever
Salmonellosis
Shigellosis
(bacillary dysentary)
Gastroenteritis
Gastroenteritis, heart
anomalies, meningitis,
others
Gastroenteritis
Gastroenteritis
Infectious hepatitis
Respiratory disease,
conjunctivities, other
Man, domestic and
wild animals and
birds
Man
Man, domestic
animals
Man, possibly
lower animals
Man, domestic
animals
Man
Man, other
primates
Man
Balantidiasis
Amebiasis
Giardiasis
III. Protozoan
Balantidium coli
Entamoeba histolytica
Giardia 1amb1i a
IV. Helminths
Nematodes (roundworms)
Ascaris lumbricoides Ascariasis
Ancylostoma duodenale Ancylostomiasis
(continued)
Man, swine
Man
Man, domestic and
wild animals?
Man, swine?
Man
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TABLE 1 (continued)
Organisms
Disease
Reservoir!s)
Necator americanus
Ancylostoma braziliense
(cat hookworm]
Ancylostoma caninum
(dog hookworm")
Necatorlas is Man
Cutaneous larva migrans Cat
Cutaneous larva mi grams Dog
Enterobius vermicularis Enterobiasis
(pinworm)
Strongyloldes stercoralis
(threadworm)
Toxocara cati
(cat roundworm)
Toxocara can is
(dog roundworm)
Trichuris trichiura
(whip worm")
Cestodes,(tapeworms)
Taenfa saginata
(beef tapeworm)
Taenia soli urn
(pork tapeworm)
Hymenolepis nana
(dwarf tapeworm)
Ecninococcus granulosue
(dog tapeworm)
EchinocQCCus
multlTocularie
Strongyloidiasis
Man
Man, dog
Visceral larva migrams Carnivores
Visceral larva migrams Carnivores
Trichuriasis
Man
Taen i as is
Taeniasis
Taen i as i s
Unilocular
echinococcosis
Alveolar hydratid
disease
Man
Man
Man, rat
Dog
Dog, carnivore
Reprinted from "Health Hazards Associated with Wastewater Effluents and
Sludge: Microbiological Considerations" by Akin et al. In: Proceedings of
the Conference on Risk Assessment and.Health Effects of Land Application of
Municipal Wastewater and Sludges, B. P. Sagik and C. A. Sorber, eds., University
of Texas at San Antonio, San Antonio, Texas, 1978, pp. 9-26, with permission
of the editors.
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Viruses--
About 100 different enteric virus species are associated with human
waste. About 80% of the viruses isolated from wastewater are enteroviruses.
Other groups found include adenovirus, rotavirus, reovirus, parvovirus-1ike
agents, and hepatitis A virus. The numbers of viruses isolated from waste-
water are undoubtedly lower than the actual levels due to the limited
sensitivity of detection methods. The average enteric virus density in the
United States has been estimated to be about 7000 viruses per liter of raw
wastewater (19) and most reports indicate virus levels of 1 to 2000 per
liter in secondary treated wastewater.
Bertucci et al. (20) studied the relationship between confirmed virus
plaques and unconfirmed plaques in primary and secondary wastewater effluent
samples from three midwestern U.S. cities. They found that the virus con-
centrations for individual samples ranged from 0-80.0 pfu per liter of waste-
water and that infective viruses were present in 16.5% of the plaques. The
authors believe that failure to confirm plaques as being virus induced may
result in overestimation of virus content of wastewater samples. Since
Bertucci et al. (20) confirmed 16.5% of all plaques, they would have over-
estimated the virus content of wastewater samples by an average factor of
six if they had not confirmed the plaques.
Toxins
The dust generated at the wastewater treatment plants during sludge
heat-treatment operations and at land application sites may contain signif-
icant quantities of toxins which may represent a potential health risk to
the workers. The toxins of concern are endotoxins derived from bacteria and
mycotoxins produced by the fungi. Endotoxins are derived from viable and
nonviable gram-negative bacteria whichv are present in wastewater and sludges.
They are the lipopolysaccharide component of the bacterial cell wall and are
usually known as the lipopolysaccharides (IPS). Endotoxins are released
when the cell wall is disrupted. Acute and chronic inflammation observed in
workers exposed to dust generated at a sewage treatment plant in Gothenburg,
Sweden, were attributed to exposure to endotoxins in sewage dust by Rylander
et al. (21,22).
Among the mycotoxins, aflatoxin produced by the fungus Aspergillus
flavus a known human carcinogen, may be of concern for workers involved in
sludge composting operations. Composting is a thermophilic process which
encourages proliferation of thermophilic fungi. Detroy et al. (23) have
shown that the optimal conditions that: favor aflatoxin production (i.e.,
moisture content, humidity, temperature, incubation time, aeration, and
nitrogen and carbohydrate content) parallel the conditions present in sludge
composting operations. They have also shown that aflatoxin is not destroyed
by temperatures of 60-80°C and therefore would not be detoxified by the
temperatures generated during composting (40-60°C).
10
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MICROORGANISMS AND TOXIN PERSISTENCE DURING WASTEWATER AND SLUDGE TREATMENT
Wastewater
Several factors affect microorganism survival during wastewater treat-
ment-pH, operating temperature, oxygen demand, ammonia concentration, etc.
Primary Treatment. Primary treatment involves physical processes such
as screening, grit removal and sedimentation. The microorganisms may settle
out by their density or by being adsorbed to solids. Because of their rela-
tively small size, viruses are less easily removed from wastewater than
bacteria, protozoa or helminths. Viruses do not settle out unless adsorbed
to solids. The removal of parasitic ova and protozoan cysts during primary
treatment is usually not very efficient due to their low specific densities
(11). An exception are Ascaris ova which have been reported to be up to
100% removed by primary wastewater treatment (24). The percentage of
efficiency of removal of some of the microorganisms during primary treatment
is about 50% (7,12,13).
Secondary Treatment. Secondary treatment is a biological degradation
process. Activated sludge treatment, trickling filters, aerated lagoons and
ponding are some of the secondary treatment processes. Each of these proc-
esses requires subsequent sedimentation which may be incorporated within the
latter two methods. The percentage of efficiency of removal of some of the
microorganisms during secondary treatment is about 90% (7,12-14).
Tertiary Treatment. Chemical treatment, filtration, adsorption, ion
exchange, nitrogen removal, etc. are tertiary treatment processes. There is-
not very much information available on.the survival of microorganisms in the
various tertiary treatment processes. Available information indicates that
microorganisms are not completely removed from wastewater by tertiary treat-
ment (7).
Disinfection. Chlorination and ozonation are two of the methods used
for the disinfection of wastewater effluents. Chlorination is most commonly
used (7,15). Disinfection is very effective in achieving a decrease of up
to three orders of magnitude in the number of bacteria and viruses (25). The
effectiveness of disinfection by chlorine is dependent on the concentration
of the chlorine used, free chlorine residual, pH, time, temperature, the
microorganisms under consideration, and the presence of particulate
material. Viruses are not inactivated as fast as bacteria and require free
chlorine residuals (7,15). The efficiency of chlorine disinfection in
inactivating the microorganisms and viruses in wastewater is shown in Table
2 (7,14). Some pathogens such as amoebic cysts, helminth ova, and some viruses,
are considerably more resistant to Chlorination than coliforms or total
aerobic bacteria.
11
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TABLE 2. REMOVAL OF MICROORGANISMS FROM WASTEWATER BY
DISINFECTION WITH CHLORINE (7.14)
Group
Virus
Bacteria
Nematodes
Others
Organism
Infectious
hepatitis
Coxsackie
Coxsackie
Echo
Poliovirus I
Coliphage B
Theiler phage
M. tuberculosis
E. coli
Coliforms
Total count
Diplogaster
Cheilobus
S. mansoni
Chlorine
residual
(mq/1)
.1
15
5
1.0
1.95
0.53
0.03
0.03
1-5
2
1
0.14
0.03
1-1.2
Some
2.5-3
15-45
0.2-0.6
Time
min.
30
30
2.5
3
6.5
14
10
10
120
.30
30
3
10
15
15
120
1
30
Efficiency
Survived
Inactivated
Survived
99.6% Inactivated
Survived
Survived
20% Survival
Inactivated
99% Killed
99% Killed
Destroyed
99.9% Killed
52% Killed
99% Killed
98-99% Killed
Survived and
Mobile
Killed
(ova and
miracidia)
S. japonicum
(ova and
miracidia)
0.2-0.6
30 Killed
12
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Sludge
Each of the sedimentation processes described earlier produces a sludge.
The microorganisms that survive the various stages of the treatment may
accumulate in these sludges and if so, are present in much higher concen-
tration than in wastewater (26). Bacteria (27) and viruses (28,29) adsorb
to particulate materials and remain infectious. The activated sludge process
sequesters a major portion of the viruses in the sludge (30). Poliovirus in
wastewater are mostly associated with the sludge and their presence in
wastewater effluents is inversely proportional to the solid content in waste-
water (31). Considerable quantities of Mycobacterium may occur in primary
sludge. Tubercle bacilli showed a 67-fold increase in concentration in
primary sludge as compared to influent wastewater (32). The range of protozoan
cysts in sludge is estimated to be about 310-410/liter (18).
Stabilization of sludge by treatment prior to land application is usually
necessary to reduce the levels of pathogenic microorganisms and putrescible
organic matter. Anaerobic digestion, aerobic digestion, chemical treatment,
heat-drying, and composting are some of the methods that can be used to
stabilize the sludge. - ~ -
Anaerobic digestion is the biolog.ical decomposition in the absence of
free oxygen. Sufficient inactivation of microorganisms including enteroviruses
may be obtained in anaerobic digestion depending on the temperature and re-
tention time (16,33,34). The efficiency of inactivation of some of the
microorganisms and viruses present in sludge by anaerobic digestion is shown
in Table 3 (15,35-38). Virus inactivation by anaerobic digestion is de-
pendent on temperature and retention time. Renters et al. (39) showed that
virus inactivation rates varied' in proportion to temperature over a range of
20-35°C. They also showed that among the components of anaerobically digested
sludge, sludge supernatant had the greater impact on virus inactivation.
Aerobic digestion process is a biochemical oxidative stabilization of
sludge. Pathogen inactivation by aerobic digestion is less efficient under
normal design conditions but 100% pathogen destruction can be achieved under
auto-heated design conditions (33). Although heat drying is generally re-
garded as an effective sludge stabilization method, high concentrations of
viable airborne bacteria have been measured in a sludge heat-drying facility
indicating the potential for pathogen survival (40). These bacteria must
have been released from the sludge stream before or without heating since
the temperatures reached in the heat drying units are adequate to kill
bacteria. ;
Composting is a thermophilic aerobic decomposition process. Two types
of composting processes are generally in use in the U'.S.A. windrow and
forced aeration pile system (33,41). The windrow system consists of long,
low piles which are turned periodically. Forced aeration pile system consists
of a stationary compost pile constructed over an aeration system. A blower
is used to draw air through the pile. Temperatures in the range of 55°-65°C
are usually attained during the composting process (33). One of the most
-important objectives of composting is to obtain high, uniform temperatures
'throughout..the sy.stem./.pr_jufljcjent_dur_atipn so as to penetrate the entire
13
-------
TABLE 3. INACTIVATION OF MICROORGANISMS BY
ANAEROBIC DIGESTION3
Organism
Virus
Coxsackie A9
Coxsackie A9
Echo 11
Echo 11
Coxsackie 84
Coxsackie 84
Temperature
(°C)
35
35
35
35
35
35
Time
(Days)
1
2
1
2
1
2
System
Bench
Bench
Bench
Bench
Bench
Bench
%
Inactivation
97.6
99.7
54.5
92.5
91.25
98.99
Reference
35,
35
35
35
35
35
Bacteria
Tubercle Not given
bacilli
-Salmonella Not given
Helminths
Taenia 85
saginata eggs
(beef tapeworm)
35 Plant and 70-85 36
Bench
60-90 Plant . 25- 37 ;
180 Bench 50+ 38
a. Adapted from 0.. J. Sproul "The Efficiency of Wastewater Unit Processes
in Risk Reduction." IN: Proceedings of the Conference on Risk
Assessment and Health~TTffects of Land Application of Municipal Waste-
water and Sludges, B. P. Sagik and C. A. Sorber, eds. University of
Texas at San Antonio, San Antonio, Texas, 1978. pp. 282-296
14
-------
mass. A well-run composting process can inactivate the microorganisms in-
cluding viruses provided the mixing or aeration is efficient. However,
windrow or aerated pile operations have not achieved a sufficiently uniform
internal temperature to inactivate all microorganisms (33). Surge et al.
(42) showed that windrow system was less effective than the aeration pile
system in destroying pathogenic microorganisms. This was attributed to the
greater probability of non-uniform heat within the windrow where mixing
moves the material from outside of the mound to the center and also possibly
due to the potential regrowth of bacteria in the cooler portion of the
windrows.
Toxins
As mentioned before, endotoxins are derived from the lipopolysaccharide
component of the bacterial cell wall. Any treatment process that results in
destruction of bacteria in wastewater and sludge is expected to result in
increased amounts of endotoxin. Similarly, the conditions present in sludge
composting, a thermophilic process, are believed to be conducive to the pro-
duction of aflatoxin, a mycotoxin, from the fungus Aspergillus flavus.
SUMMARY
In conclusion, the existing data indicate that some of the microorganisms
survive during wastewater and sludge treatment; and that the amount of endo-
toxins may increase during treatment processes that result in destruction of
bacteria. Workers at wastewater treatment plants and land application sites
will, therefore, be potentially at risk of exposure to pathogenic bacteria,
viruses and endotoxins.
15
-------
SECTION 5
MICROORGANISMS AND TOXINS IN AEROSOLS GENERATED AT WASTEWATER
TREATMENT PLANTS AND LAND APPLICATION SITES
AEROSOLS
Some of the microorganisms present in wastewater and sludge, especially
bacteria and viruses, can become airborne (43). Major sources of the aer-
osols are the aeration basins of the activated sludge treatment units,
trickling filters, and land application sites that use spray irrigation.
Aerosols are particulate materials in either solid or liquid form and may
also include gases and vapors that are adsorbed or contained in airborne
particles or liquid droplets. Inhalation is a possible route of infection
because the viruses and most pathogenic bacteria are in the respirable size
range. The health hazard posed by aerosolized particles depends on their
ability to deposit in the lungs. The most important factor in lung de-
position is the size of the particle.
The particle size is usually expressed as mass median or aerodynamic
diameter-. The aerodynamic diameter is a function of both the physical di-
ameter and the density of the particle. It is defined as the diameter of a
unit density sphere having the same settling velocity as the particle in
question of whatever shape and density. Figure 1 shows the deposition
pattern in the various regions of the respiratory system by different sized
particles (44,45). Particles with an aerodynamic diameter greater than 30
jum do not enter the nasal passage, those with an aerodynamic diameter ranging
from 5-30 Aim are deposited in the naso-pharyngeal region. Particles ranging
in aerodynamic diameter from l-5>um are usually deposited in the tracheobron-
chial region by sedimentation. Particles less than 1 ,um in aerodynamic di-
ameter are deposited in the pulmonary or alveolar region by diffusion. It
is the last category of particles that may constitute a health hazard by
inhalation. Particles deposited in the tracheobronchial region can be re-
moved by mucociliary action (spiral movement of the mucus by ciliated
epithelium) toward the trachea and pharynx where the material is swallowed
or expectorated. The swallowed particles then pos'e a health hazard via
ingestion by exposing the gastrointestinal tract to the pathogens.
Bacteria and viruses may be concentrated in the aerosolized droplet.
The concentration of Escherichia coli and bacteriophage were found to be 30
and 50 times, respectively, greater in the aerosols than in the suspending
fluid (46).
16
-------
Figure 1.
0.01 Q050.I 0.5'1.0 5 10 50100
Mass Median diameter (/jm)
Variability of deposition of particles in the
respiratory tract (44,45).
Each shaded area (envelope) indicates the variability of
deposition for a given mass median (aerodynamic) diameter Gum)
in each compartment when the distribution parameter varies
from 1.2 to 4.5 and the tidal volume is 1450 ml, and at the
rate of 15 respirations per minute.
Reprinted from "Task Group on Lung Dynamics, International
Commission of Radiologic Protection," Health Physics, 12,
173-207 (1966), with permission of Pergamon Press, Ltd., New
York, N.Y. and the Health Physics Society.
17
-------
MICROORGANISM MONITORING IN AEROSOLS
Sampling of Microorganisms in Aerosols
Airborne microorganisms are usually collected by the Andersen air sam-
pler (47,48), all glass impinger (47,49), or high volume air sampler (47,50).
The Andersen air sampler collects and separates particles into different
size ranges and thus provides a good size distribution of the particles.
The Andersen sampler is good only when particle concentrations are high,
since it has a limited sampling rate of 28.3 liters/min. It also requires a
large number of plates. The all glass impinger also has a low sampling rate
(6- 12,5 liters/min) and, therefore, is not well adapted to low concentrations
of microbial particles. The high volume air sampler can sample large quan-
tities of air with a high collection efficiency for all particle sizes, but
it does not provide a size distribution of the particles.
- Viruses in aerosols are less well studied than bacteria mainly due to
technical limitations in sampling and in obtaining accurate measurement of
viruses in air. Large volumes of air must be sampled for virus monitoring
in aerosols"because of low levels of viruses"present in wastewater and waste-
water aerosols., For the low levels of viruses present in wastewater,
Johnson et al. (51,52) believe that monitoring of viruses in air near waste-
water treatment plants and spray irrigation sites is not feasible except by
using extraordinary methods. They suggest that "a more practical approach
would be to measure the levels in wastewater and then to utilize a pre-
dictive model to estimate their concentrations in the air at various
distances." '
Moore et al. (53) showed that in order to detect aerosolized viruses,
extremely- large air volumes have to be sampled, and additional concentration
of aerosol sample collection fluids was also found to be necessary. For
example, Moore et al. (53) sampled 1440 m^ (4716 ml of collection fluid) and
2340 m3 (7820 ml of collection fluid) of air to detect significant numbers
of viruses in aerosols at a spray irrigation site in Pleasanton, California.
In order to be able to collect such large volumes of air, eight high volume
samplers close to each other at the appropriate downwind distance were used
The samples were operated simultaneously for six to eight consecutive 30-
minute periods. :
The techniques used for concentrating and quantifying bacteria may be
found in Standard Methods for Analysis of Water and Wastewater (54). Bac-
terial cell count is usually performed by determining the number of cells in
the sample capable of forming colonies on a suitable agar medium. It is re-
ported either as standard plate count or colony forming units (cfu). Vi-
ruses are usually replicated in suitable tissue cell monolayer and are " - .
quantified as plaque forming units (pfu). Viruses are also reported in
terms of endpoint dilution such as most probable number (MPN). As mentioned
in an earlier section, Bertucci et al. (20) studied the relationship between
virus levels as measured by the plaque assay and actual virus populations in
wastewater samples from three midwestern areas. Although virus populations
-tn excess of 104 pfu/liter have been reported in untreated municipal waste
18
-------
water, Bertucci et al. (20) found infective viruses in only 16.5% of the
plaques. The authors agree that all viruses which are present in an en-
vironmental sample will not be detected by any one particular assay system
and that plaque'lesions or cytopathic effects may be induced by agents other
than viruses. Bertucci et al. (20) conclude that virus populations reported
only in terms of pfu without plaque confirmation may be grossly overestimated.
""The viable aerosol sampling protocol should take into consideration
several meteorological factors such as air temperature, relative humidity,
solar radiation, wind velocity, wind direction, evaporation, precipitation,
time of day, etc. since microbial survival is dependent on these factors.
It is recommended, in general, that sampling be done under stable atmospheric
conditions (55). Schaub et al. (56) recommend that simultaneous, continuous
meteorological information is required to insure valid sampling and also for
predictive mathematical aeroso.l modeling.
Indicator Organisms
Coliform bacteria and coliphage viruses are generally used as indicators
of fecal contamination in water, because they are considered to reflect
pathogen levels. Coliform is a general term used to describe the non-spore
forming facultative anaerobic gram-negative rods which ferment lactose.
These bacteria inhabit the intestinal tract of humans and other animals.
The coliform group includes Escherichia, Klebsiella, Enterobacter and
Citrobacter. The use of coliform organisms as indicators meets many if not
all of the requirements for drinking water standards (57). Usually labora-
tory cultures are seeded as indicator organisms. Selection of the indicator
organism depends on the prevalence of the organism in the substrate, avail-
ability of methods for quantifying the organism, and resistance of the or-
ganism relative to other organisms in the group it represents. Conditions
,that may destroy a laboratory strain may not harm a naturally occurring
strain. i
Coliform organisms are also used as indicators of pathogen levels in
the monitoring of aerosols. The absence of coliform organisms is often
interpreted as meaning that the specific environment or medium under con-
sideration is free of pathogens. This practice is being questioned in the
recent years as to its accuracy. It is believed that the traditional col.iform
indicators for water pollution are very poor models for the evaluation of
microbial transport in wastewater aerosols (58). For instance, it has been
shown that the disinfection by chlorination is often more effective in re-
ducing the levels of coliform organisms than the viruses and certain other
bacteria (59-62). It has also been shown that pathogens such as fecal
streptococci, Pseudomonas, and Clostridium perfringens survive longer in
aerosols (59-62) than E. coli which has an extremely short life span in the
aerosolized form (60,6TT64).
From extensive environmental monitoring studies conducted at a spray
irrigation site in Pleasanton, California, Johnson et al. (51) have shown
that the indicator microorganisms, especially total coliforms and fecal
califonns die-off more rapidly with aerosol age than do the pathogenic
19
-------
bacteria. They also found that coliphage levels, which are used as indicators
of airborne animal and human viruses, tend to decay much faster than the
hardier human viruses in the aerosol state. Johnson et al. (51) concluded
that the use of the traditional col-iform organisms as indicators of patho-
genic microorganism levels in aerosols results in an extreme underestimation
of actual pathogen levels.
Monitoring for total airborne bacteria instead of only for coliform
organisms has been suggested by several workers as a faster and a more re-
liable method of indicating pathogen levels in aerosols because coliform
organisms such as Escherichia, Klebsiella, and Enterobacter species accounted
for only 5% of the total aerosolized bacterial population (65,66). Monitoring.
of total bacterial count has the advantage of not having to preselect the
indicator organism in wastewater, but it may not be representative of the
pathogenicity of the aerosol. Encapsulated organisms such as Klebsiella
have been shown to survive longer in aerosol state than noncapsulated or-
ganisms such as E. coli (67). Johnson et al. (51) recommend that fecal
streptococci wouTd be a more suitable indicator than coliform organisms be-
cause of the relative ease of the assay, the levels found in wastewater, its
relative hardiness~during aerosolization/ and its relatively low viability
decay rate.
The hardiness of viruses is shown in studies where they were detectable
in a primary effluent containing 3 mg/liter of chlorine as a disinfectant
(68). Coliphages-have been suggested as indicators of airborne animal viral
contamination (68), and they are also more stable than coliform bacteria in
the airborne state. The human enteric viruses ar%e hardier than col iphages;
however, the monitoring of these viruses is not very practical because large
volumes of air (>300 m^) must be sampled and monitoring cannot be done at
a distance greater than 100 m from the source in the case of spray irri-
gation facilities (51,52). I
MONITORING ENDOTOXINS IN OUST AND AEROSOLS
One of the limitations to the accurate monitoring of endotoxin levels
in environmental samples is the lack of a sensitive and specific assay for
endotoxins. Assay methods currently available include the rabbit pyrogenicity
assay (69), tumor necrosis assay (69), and the mouse lethality or the Limulus
lysate assay (70). All these assays require endotoxin to be pure and free
from contaminants which may give false positive reactions. Endotoxins in
dust or aerosol samples are usually extracted and purified by Westphal's
method (71). However, the yield of endotoxin extracted by this method is
only about 1% based on the dry weight of bacteria or cell walls extracted.
Rylander £t al. (72) have reported detecting endotoxins in aerosols at
conventional wastewater treatment plants in Sweden. Samples for endotoxin
analysis were collected from air on Millipore filters using personal air
samplers, which were carried by workers over a four-hour period while per-
forming routine work. Levels of endotoxins were determined using the Limulus
20
-------
lysate assay method (70). Values of endotoxins found ranged from 0 to 0.2
jug/nn (73).
MICROORGANISMS IN AEROSOLS AT WASTEWATER TREATMENT PLANTS AND VICINITY
As indicated before, two of the secondary treatment processes - activated
sludge treatment units and trickling filters are shown to be the main sources
of aerosols at most wastewater treatment plants (74) and about 50% of the
particles generated are found to be 5>im in diameter (67). Hickey and
Reist (1) have made an extensive survey of the microorganisms emitted at
wastewater treatment plants as well as spray irrigation sites. SCS Engineers
(7) also reviewed the microorganism emissions at wastewater treatment plants
and spray irrigation facilities.
For lack of standardized sampling methods and suitable indicator or-
ganisms, it is difficult to interpret the literature on airborne levels of
microorganisms. Most researchers to date, have relied upon coliforms as in-
dicator organisms. Because of the many variables involved, quantitative
results among the various investigations may be compared only in general
terms.
The bacteria and virus concentrations in aerosols generated from some
activated sludge units and trickling filters are listed in Table 4. Aerosol
sampling protocols generally included collection of air samples at or near
the source and sometimes also at specified downwind distances. Samples
collected upwind were used as controls.
Some of the factors affecting the emission of viable aerosols besides
aeration from wastewater are shown to be aeration bubble size, microorganism
concentration in wastewater, total solid content in the aerated liquid drop-
let and wind velocity. Smaller aeration bubble size, increased microorganism
concentration in wastewater, increase in total solid content in the aerated
liquid droplets and higher wind velocity have all been shown to increase
emission of viable aerosols (1,43,75-78). Blanchard et al. (79) report that
in the process of droplet formation at the surface of aerated liquids, the
droplet scavenges organic material and microorganisms, with the result that
the aerosol particles may contain a bacterial or virus concentration 100 or
more times greater than that of the ambient water. This suggests that
bubbles formed during aeration processes of sewage treatment such as the
activated sludge method may lead to the formation of droplets containing
very much higher concentrations of pathogens than the wastewater itself
(16).
The recovery of microorganisms in air samples was dependent upon
aerosol die-off, deposition, diffusion between the source and the sampling
location, wind velocity, relative humidity, solar radiation, air temperature,
etc. (65,76-78, 80). The pattern of recovery of microorganisms was found to
be similar with all studies. The concentrations of the microorganisms per
unit volume of air were relatively high at or near the source and much lower
21
-------
TABLE 4. BACTERIA CONCENTRATIONS IN AEROSOLS AT SPECIFIED DISTANCES FROM
. TRICKLING FILTERS AND ACTIVATED SLUDGE UNITS '
Sampling
Aerosol distance
source downwind
Trickling Filter <5 m
>5 m
1_5 m
>5 m
<5 m
>5 m
Activated Sludge Near the
source
Micro-
organism
sampled
Coliphage Virus
Coliphage Virus
Coliphage Bacteria
Total Bacteria
Concentration
in the aerosol
0.32/m3
0.24/m3
0.25/m3
0*1 ft \
. 1 6/nr
210/m3
14/m3
30,700/m3
1,170/m3
Klebsiella, Aerobacter, 10.5% of
ro
(V)
Activated Sludge 45 m
Activated Sludge 0 m
45 m
Trickling Filter 0 m
45 m
Activated' Sludge On-plant
site
800 m
On-plant
site
800 m
Proteus
Total Bacteria
Col i form
Col i form
Total Viable .
Particles
Total Coli forms
total
bacteria
106/m3
99; 770/m3
7; 1088/m3
106; 1053/m3
7; 141/m3
376/m3
198/m3
6.87/m3
1.1 5/m3
(continued)
Comments Ref.
Average most probable number. 68
Only col i forms show a
statistically significant
decrease with distance.
Andersen Sampler 1,7,
All -glass impinger 80
Known respiratory tract
pathogens
Same as concentration 45 m 1,7,
upwind. No observable effect 65
at >45 m downwind.
50% particles <5 ym in , 7,67
diameter
Mean concentration 83
Mean concentration
-------
TABLE 4 (continued)
Aerosol
source
Activated Sludge
Sampling
distance
downwi nd
30-50 m
Micro-
organism
sampled
Total Colt form
Pseudomonas
Coliphage
Enterovirus
Concentration
in the aerosol
5.8 cfu/m3
7.0 cfu/m3
0.7 pfu/rn3
<9.0 x 10~4
Comments Ref.
Geometric mean concentration 85
Activated Sludge 20- 25 m
ro
CO
250-300 m
1000-2000 m
Fecal Streptococcus
Mycobacterium
Proteus
Fecal Streptococcus
Salmonella
Shigella
Klebsiella
Enterovirus
Proteus
Fecal Streptcoccus
Salmonella
Shigella
Klebsiella
Enterovirus
Proteus
Fecal Streptococcus
Salmonella
Shigella
Klebsiella
Enterovirus
pf u/m3
2.0 cfu/m3
9.1 cfu/m3
<17 cfu/m3
<17 cfu/m3
<17 cfu/rn3
<17 cfu/rn3
Possibly isolated
<0.7 pfu/m3
<15 cfu/m3
<15 cfu/m3
<15 cfu/m3
<15 cfu/m3
Isolated
<0.76 pfu/m3
<17 cfu/m3
<17 cfu/m3
<17 cfu/m3
<17 cfu/m3
Not isolated
<0.47 pfu/m3
High volume air sampler.
Maximum concentrations at
the distance indicated.
5-day plaques
84
5-day plaques
5-day plaques
(continued)
-------
TABLE 4 (continued)
Aerosol
source
Activated sludge
Sampling
distance
downwind
on-plant
site
Micro-
organism
sampled
Standard plate
count
Total coli form
Fecal coli form
Fecal streptococci
Concentration
in the aerosol
81 2/m3
8/m3
1/m3
Comments Ref.
Geometric mean concentrations 86
at the aeration basins
Activated sludge
on-plant Standard plate count
site Total coliform
Fecal coliform
Fecal streptococci
253/m
6/m3
2/m3
iCtivated sludge on-plant
site
-
iCtivated sludge on-plant
site
Activated sludge on-plant
s i te
Standard plate
count
Total coli form
Fecal coli form
Fecal streptococci
Standard plate
count
Total coli form
Fecal coli form
Fecal streptococci
Standard plate
count
Total coli form
Fecal coli form
Fecal streptococci
3
292/mJ
4/m3
3/m
2/m3
n
735/mJ
43/rn3
12/m3
55/m3
o
583/mJ
68/m3
45/m3
66/m3
Geomi
at tl
Geomi
at tl
Geomi
at t
Geometric mean concentrations 86
at the aeration basins
Geometric mean concentrations 86
at the aeration basins
Geometric mean concentrations 86
at the aeration basins
Geometric mean concentrations 86
at the aeration basins
-------
as the downwind sampling distance increased. Hickey and Reist (1) noted
that the downwind viable aerosol concentrations generally diminished to
upwind concentrations within a few meters of the source, although coliforms
have been reported to have been recovered 1.29 Km downwind from a trickling
filter (78). They attributed such recoveries at greater downwind distances
to normal sampling variations. Hickey and Reist (1) as well as SCS Engineers
(7) concluded that the activated sludge and trickling filter generate micro-
organisms, some of which are pathogenic, in aerosols and that the aerosols
may also contain low levels of animal viruses. Fannin et al. (81) and Slote
(82) also concluded, from independent investigations, that the aerosols
emitted from activated sludge units and trickling filters are continuous
sources of low levels of animal viruses. Some of the recent studies that
have been reported since the reviews of Hickey and Reist (1) and the SCS
Engineers (7) are discussed below.
The activated sludge unit of the wastewater treatment plant in Skokie,
Illinois was shown to be a source of aerobic bacteria containing particles
and total coliforms at the treatment plant and in the vicinity by Carnow et
al. (83). The concentration of the microorganisms decreased with downwind
distance from the plant. At 0.8 Km downwind, the concentration of total
viable particles was found to be 45% greater than that at a similar location
upwind.
Aerosol monitoring conducted at and in the vicinity of wastewater treat-
ment plant near Chicago, Illinois, by Johnson et al. (84) showed that the
aeration basin is probably the source of airborne indicator bacteria, coli-
phage, pathogenic bacteria, and enteroviruses. However, in the neighboring
residential areas at a distance of'400 meters, microorganism levels in air,
soil and water samples were found to be indistinguishable from the background
levels. Johnson et aU (85) also measured the microorganism levels in aerosols
at the aeration and surge basins at the Durham advanced treatment plant in
Tigard, Oregon. They found that the microorganism levels in aerosols were
higher at the aeration basin than at the surge basin. The aeration basin
and the surge basin were located within 400 m of the classroom area and 50 m
of the school playground, respectively, from an elementary school. The
daily peak dose to which the school children may be exposed on any one school
day per year was estimated to be about 9 cfu of mycobacteria and 3.5 cfu of
fecal streptococci.
The airborne microorganism levels measured by Clark et al. (86) at the
center of aeration tanks at treatment plants in three midwestern U.S. cities
are listed in Table 4.
MICROORGANISMS IN AEROSOLS AT WASTEWATER LAND APPLICATION- SITES AND
VICINITY
Wastewater application methods (87,88) play an important role in the
emission of aerosols at land application sites. The choice of the method
depends on the individual land application facility, geographic location and
climate. Of the various methods of land application, spray or sprinkler
irrigation is believed to generate the maximum amount of aerosols.
25
-------
The type of spray equipment and type and spacing of nozzles would also
affect the emission of aerosols at spray irrigation sites. Between 0.1% and
1% of the wastewater sprayed is transformed into aerosol depending on the
type of spray device, the pressure and the wind speed. Increased pressure
is reported to increase the emission of smaller particles (89). The concen-
tration of microorganisms in aerosols, as has been shown before, is directly
proportional to the concentration in the wastewater. Airborne E,. coli were
detected only when the effluent concentration was 104 organisms/ml or greater
(90).
The concentration of microorganisms in aerosols at spray irrigation
sites would also depend on the degree of treatment received by the waste-
water or the sludge. Microbial concentration in aerosols decreases as the
treatment process received by the wastewater increases. The experience of
European countries with raw or partially treated wastewater supports this
statement (2). The coliform organisms generated in aerosols from the use of
raw wastewater could be detected at 400 m downwind, when the wind velocity
was 16-32 kilometers per hour (Kph) (91). Under favorable meteorological
conditions such as high humidity and wind and little or no sunlight, coli-
form organisms were found to be dispersed as far-as 1200 m from the source
when settled raw sewage was used (92). The bacteria and virus concentrations
in aerosols generated at some wastewater spray irrigation sites are shown in
Table 5.
Katzenelson et al. (90,93) reported that coliform bacteria were found
in the air 350 m downwind from the wastewater spray sprinklers. They also
reported detecting a colony of Salmonella in one sample, a known human
pathogen, 60 m downwind from the spray source. The authors calculated that
at a distance of 100 m downwind from this wastewater sprinkler, a person may
inhale about 36:coliform organisms in 10 minutes. It must be emphasized
:that the effluent sprayed on these fields was from partially-treated undisin-
fected municipal wastewater and levels of coliform bacteria in the effluent
were approximately the same as those seen in raw wastewater present in the
United States, and raw wastewater is not sprayed in the United States.
Sorber et al. (25) and Bausum et al. (94,95) conducted two field studies
,at Ft. Huachuca, Arizona where chlorinated secondary municipal effluent was
used to irrigate a golf course. Field testing was also conducted with un-
chlorinated effluent to determine the effect of chlorine disinfection on the
ilevels of microorganisms in wastewater aerosols. In the first study (25),
bacterial aerosol levels that were significantly above background levels
were measured out to 200 m downwind of the spray line, the greatest distance
tested. Klebsiella was the most commonly found pathogen. Bacteriophage was
used as a tracer in the second study conducted at Ft. Huachuca (94,95). The
study showed that bacteriophage can be recovered at a distance of 562 m
downwind from the spray nozzle. The study also showed that total aerobic
bacteria reached levels in excess of 10,000/m^ at 46 m downwind and that
Klebsiella formed a large part of coliform population at 46 m downwind from
the source when unchlorinated effluent was used. The concentration of the
microorganisms in aerosols from the two studies at Ft. Huachuca are listed
in-Table 5.
26
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TABLE 5. BACTERIA AND VIRUS CONCENTRATIONS IN AEROSOLS AT SPECIFIED DISTANCES
FROM WASTEWATER SPRAY IRRIGATION SITES
Concentration
in
wasfeewater
3.7 x 105/rnla
1.4 x 105/mla
2-4 x 105/mla
Sampling
distance
downwind
47 m
152 m
47 m
152 m
46 m
Micro-
organism
sampled
Aerobic bacteria
Col i form-like
bacteria
Aerobic bacteria
Klebsiella
Concentration
in the aerosol " Comments
1630/m3
100/m3
330/m3
q
30/m
>10%3
~50/mJ
Ref.
25
94,95
2.5 x 105/mlb'c
563 m Tracer bacterio-
phage
Recovered, con-
centrations not
indicated
105-106/mld
104-105/mle
5.8 x 103 - 6.6 x
104/mlf
10 m
70 m
10 m
100 m
400 m
60 m
30 m
100 m
200 m
30 m
50 m
100 m
Total col i form
Total col i form
Total col i form
Total col i form
Total col i form
Salmonella 1
Total col i form
Total col i form
Total col i form
Standard plate count
425/m3
102/mJ
496/m3
88/m3
. 4/mJ
colony found
452/m3
5/mJ
4/tn3
485 cfu/m3
417 cfu/m3
37 cfu/m3
(continued)
All glass impinger
Maximum concentrations
Andersen sampler
Maximum concentrations
Andersen sampler
Maximum concentrations
75% particles<5
in diameter
Mean value for airborne
bacteria bearing particles
above background
93
93
97
-------
TABLE 5 (continued)
no
oc
Concentration
: in
wastewater
699,000/mla
7500/mla
800/mla
220/mla
67/mla
1050/mla
390/mla
54/mla
46/mla
0.12/mla
Sampling
distance
downwi nd
5- 20 m
100-200 m
5- 20 m
100-200 m .
5- 20 m
100-200 m
5- 20 m
100-200 m
5- 20 m
100-200 m
5- 20 m
100-200 m
5- 20 m
100-200 m
5- 20 m
100-200 m
50 m
100 m
50 m
100 m
Micro-
organism
sampled
Standard plate count
Total col i form
Fecal col i form
Coliphage
Fecal streptococci
Pseudomonas
Klebsiella
Clostridium
perfringens
Mycobacteria
En terovi ruses
(3 and 5 day)
Concentration
in the aerosol Comments Ref.
2570/m3 Geometric mean concentrations 51,52
880/m3
5.7 MFC/m3
1.2 MFC/mJ
1.0 MFC/m3
<0.3 MFC/m3
0.34 pfu/m3
0.18 pfu/m3
1.4 cfu/m3
1.9 cfu/m3
72 cfu/m3
43 cfu/m3
<5 cfu/m3
<5 cfu/m3
1.5 cfu/m^
1.1 cfu/mj
0.80 cfu/m3
0.82 cfu/m3
0.014 pfu/m3
a. Secondary treated wastewater
b. Lagoon effluent, unchlorinated
c. Tracer bateriophage concentration at the spray nozzle
e. Aerated ponds
f.' Ponded, chlorinated wastewater
-------
Sorber et al. (25) and Bausum et al. (94,95) also showed that disin-
fection of the effluent by terminal chlorination was effective in reducing
the bacterial concentration in aerosols to near background levels, but was
much less effective in reducing the dissemination of the bacteriophage. The
studies also showed that under nighttime conditions, characterized by lower
wind speeds and increased atmospheric stability, microorganism levels in
aerosols were slightly greater than under daytime conditions.
Sorber et al. (61) calculated predicted levels of bacteria and viruses
downwind of spray irrigation sites using modification of the Turner's
atmospheric dispersion model. They determined that an individual working
200 m downwind from a center pivot spray rig with a 300 m radius could
inhale as many as 20 infectious airborne viruses in 10 minutes. Teltsch and
Katzenelson (96) recovered Echovirus 7 in 4 out of 12 air samples taken at
40 m downwind from the source at a spray irrigation site in Israel. As
mentioned before, the microbial content of effluents sprayed in Israel is
approximately the same as that found in raw wastewater and the case in
Israel is not representative of situations in the United States since raw
wastewater is not sprayed in the United States.
Bausum et al. (97) monitored the bacterial levels in aerosols generated
at a spray irrigation site at Deer Creek Lake, Ohio, a demonstration land
wastewater treatment site for U.S. Army Corps of Engineers recreational
areas. They observed a mean value of 485 cfu/m^ for standard plate count
at 30 m downwind. This value was reduced by 15% and 92% at 50 m and 200 m,
respectively. The median diameter of the bacteria - bearing particles was
found to be 2.6Mm at 30 m downwind, and 75% of these particles had a di-
ameter that ranged from l-5jjm. A number of spray heads were used in this
study compared to only a single spray head or a line source used, in general,
in their previous studies (25,94,95).
Johnson et al. (51,52) conducted extensive monitoring of the aerosols
generated at a spray irrigation facility in Pleasanton, California,for
microorganism levels at the downwind edge of the spray irrigation site and
at several downwind locations. The levels of microorganisms in aerosols at
100-200 m downwind are, as expected, found to be lower than at the downwind
edge of the spray irrigation site. Aerosols sampling was performed out to
600 meters downwind of the spray fields, extending into the populated areas.
Detectable levels above background were noted for standard plate count,
fecal streptococci, and mycobacteria. Microbial levels observed in the
aerosols at night were twice -those seen-in the daytime. The levels found
in aerosols of a number of microorganisms, standard bacterial plate count,
total coliform, fecal coliform, fecal streptococci, Pseudomonas, Klebsiella,
Clostridium perfri'ngens, coliphages, and enteroviruses, are shown in Table 5.
Based on the reported enterovirus density, a worker on duty 8 hours per day
at 50 meters would inhale only one enterovirus each nine days.
Baubinas and Vloda.vets (98) have reported recovering enteric pathogens
from grass and aerosols at a distance of 200, 250, and 400 meters from a
spray irrigation site in Russia.
29
-------
Brenner et al. (99) and Davis-Hoover et al. (100) have carried out
environmental-monitoring for airborne animal viruses and pathogenic bacteria
at the spray irrigation facility of the Muskegon Wastewater Management System
1 in Michigan. The Muskegon County Wastewater Management System is an
aeration, lagoon impoundment, and spray irrigation facility which treats
about 102,000 cubic meters of wastewater per day and irrigates 2160 hectares
of corn land. During the growing season, wastewater is applied using center-
pivot irrigation rigs. Although viruses were present in the raw influent
wastewater and sometimes in the storage lagoon, no animal viruses were de-
tected either in the lagoon wastewater just prior to spray application or in,
the aerosol samples collected at the aeration basin. Enterobacter cloacae,
Klebsiella pneumoniae and aerogenes were some of the bacteria isolated in
the air samples collected at the facility. Klebsiella was found to be the
most predominant of the gram-negative rod pathogens. The numbers of bacteria
isolated adjacent to the spray irrigation rigs as well as aeration basins
were found to be higher than those found upwind. Their findings also showed
that the number of bacteria isolated adjacent to the aeration basins were
higher than those found adjacent to the spray irrigation rigs. The bacterial
levels found upwind of the aeration basin appeared to be about the same as
those detected 18 m downwind of spray irrigation rigs. The authors calculated
that an average adult breathing 500 ml of air per breath and 20 breaths per
minute, standing downwind of the aeration basin would inhale about 10 total
bacteria colony forming units (cfu) per minute.
In summary, the available data indicate that the microorganisms in
aerosols generated at spray irrigation sites may remain viable and be dis-
persed- for several hundred meters from the spray source.
SURVIVAL AND DISPERSION OF MICROORGANISMS IN AEROSOLS
Some of the variables that affect the survival and dispersion of micro-
organisms in aerosols are die-off, deposition, and diffusion (65,66), and
have been discussed in detail recently (1,101,102) and, therefore, will only
be summarized briefly. In general, a higher viable aerosol decay rate was
observed initially followed by a much lower decay rate. The high initial
decay rate of microorganisms in aerosols was attributed to organism die-off
from the stress of droplet evaporation. Die-off, deposition, and diffusion
of the microorganisms in aerosols are affected by the following environmental
factors.
Relative Humidity: Microorganisms in aerosols survive longer at high
relative humidities such as those occurring at night. High relative
humidity delays droplet evaporation and retards organism die-off (101).
Wind Velocity: The dispersion of microorganisms in aerosols is
directly proportional to wind velocity (101).
Sunlight: Sunlight promotes decay of airborne microorganisms. It has
been shown that the concentration of the microorganisms in air samples taken
at nighttime were generally higher than those taken during the daytime (51).
30
-------
Temperature: Increased temperature reduces the viability of micro-
organisms in aerosols. The effect of the temperature is not usually
apparent until it is 80°F or more. Increased temperature also increases
droplet evaporation (102).
Open Air: Airborne microorganisms are shown to be inactivated more
rapidly in the.actual field conditions compared to those generated under
controlled conditions in the laboratory (102).
31
-------
Continuous emission from the source, so that diffusion in the
direction of transport may be neglected.
The material was a stable gas or aerosol (less than. 20 microns
in diameter) which remained suspended in the air over lonq
periods of time.
None of the material emitted was removed from the plume as
it was moved downwind, and there was complete reflection at
the ground, thus no deposition or chemical/biological reactions.
The mean wind direction specified the X-axis, and a mean wind
speed representative of the diffusing layer was chosen.
Except where mentioned, the plume constituents were distributed
normally in both the vertical and cross wind directions.
The model held for ten minute intervals.
These equations were to be used when the mean wind speed and direction
could be determined, but when the measurements of turbulence were
not available. If these were available, then Pasquill's equations
-would be more- accurate-. ....... - ........ -- - -- .......... - - - .....
These equations should be used for only sources of ground level
to 20 meters in height.
Turner's equations were used by Katzenelson et. al (90, 93) directly
without any modification and by Ken line et. al (65, 66), Sorter et. al
.jil_.(.9_7l_and Johnson et. al (107) with modifications to
__-_ ..
''.determine, the .concentration jif_ microorganisms in aerosols at wastewater
treatment plants and wastewater spray irrigation facilities.
The work of Katzenelson, et al. (90,93). was based on Turner's equations.
Air samples were taken in the field of Kibbutz Tsorah and near the agricul-
tural school at En Kerem, using Andersen six-stage cascade impactor and
AGI-30 impingers. The equation used was Turner's (104) line source equation,
derived from Sutton (109). The assumptions were the same as in Turner's work
with one additional assumption, that the quantity of aerosols was 1% of the
total output of the sprinkler for all meteorological conditions. There was
no modification of the equation to make it applicable to viable-particles £ttiat is,
to account for die-off) or to account for relative humidity which is thought to
be critical for viable partrci-e survival . The authors beHeved that the difference
in the observed and predicted -Values was probably due to these factors.
, Turner's equations were modified by Kenline and Scarpino (65, 66). They
tried to account for the deficiencies in Turner's equations, such as deposi-
tion and die-off, and derived a new equation, using many ideas from Sutton
(109) and Chamberlain (HO). Their equation for an area source (an aeration
basin at a conventional secondary sewage treatment plant) was achieved by
34
-------
summing Button's line source equation. They included a term for microDial
dep_o_siti_qn_ and die-off, atmospheric diffusion and height above the ground.
By exposing petri dishes containing solid media at ground level adjacent to the
Andersen sampler, they were able to calculate the velocity of deposition. Al-
though Kenline felt that relative humidity was important in the survival of
bacteria, this was not taken into account directly in the equation. Kenline's
equation assumes Turner's stability class B (T04) and a mean wind speed of ~
2 m/sec. He found that while diffusion and die-off were dependent on distance,
deposition was not. With a limited number of samples, there is a good correl-
ation between the predicted values and measured values. Kenline felt that his
. average vertical difference of 10%, with a range of 1 to 21%, and an average
horizontal difference of 13%, with a range of 1 to 25%, was within the accept-
able ranges of sampling error.-
Work done by Sorber, Schaub, and Bausum (61) eventually led to the dev-
elopment of Camann's early model (25). This study used Turner's equations
without any measured aerosol data. The study was done on aerosolization pro-
duced by center pivot rigs and was admittedly a "gross approximation". Pre-
liminary data suggested that the aerosolization efficiency was 0.1 to 1%.
The authors stated that the achievement of more than a 3 log reduction
in viruses by filtration and disinfection is superior, in protecting the
environment, to a buffer zone of 800m which only achieves a 2 log reduction.
The next application of Turner's equations by Sorber, Bausum and Schaub
(95). was used in a study of, the Ft. Huachuca .Golf Course,, which was irrigated
' with secondary treated domestic sewage. They used f^ phage as a tracer, a
questionable procedure as other phage in the wastewater can grow in the host
and give a positive result in the fo test, thus leading to possibly misleading
elevated results,. Andersen six-stage samplers with disposable plastic petri.
dishes were used to collect total aerobic bacteria and coliphage, and high
volume a~ir samplers were also used to determine total viable bacteria. All
measurements were taken at five foot elevation for 30 to 40 minutes. When the
wastewater was chlorinated, they found a Cowering of viable counts by three
and a half orders of magnitude (a factor of !QOMD, where OMD = the numbers of
orders of magnitude, in this case !03-5) for total aerobic bacteria and one
order of magnitude for the fg phage.
The equations used by Sorber et aT. (95) assume 100% aerosol ization, 100%
sampler efficiency, and zero decay, ihus, they accurately predicted that the
computed values would usually be higher than the actual values. The predicted
to observed ratios ranged from 0/1 to 9750/1. Using a d.ye as a tracer, they
found that about 0.32% of wastewater solids escaped the wetted zone as an
aerosol.
The model developed by Sorber et. al (25) in their later work was
based on Turner's adaptation (104) of Pasquill's diffusion equation (103).
The equation used specific wind velocities instead of the mean wind velocity
and incorporated separate calculations of concentrations of microorganisms
in the atmosphere for eac-h one minute interval throughout the sampling
period. These concentrations were then summed and used in a new multi-
plicative equation to find the adjusted sampler recovery. Variables con-
35
-------
sidered were the summed model prediction from Turner's equation, efficiency
of aerosolization and sampler collection, a decay factor, and a "factor of
fit." Using this model, estimates of the buffer zone required to reduce the
total aerobic bacterial aerosol population to 5 organisms/m^ above back-
ground were made. A study of terminal disinfection showed that the reduction
in aerosol bacterial levels was somewhat less than the reduction in waste-
water bacterial levels, but the authors (25) felt that terminal chlorination
would probably be a. more practical and economical measure than buffer zones.
The next development was seen in the first phase of the Pleasanton
study by Johnson et al. (108). The assumptions were the same as Turner's
assumptions with one addition, that measurements must be made on a level
terrain. Johnson et al. (108) explained that the estimates would be
greater than the observed values, as the assumption of no deposition was
probably invalid. The wastewater dye source strength and the percent
aerosolization were calculated. The latter ranged from 0.43 to 0.75%.
There were no data to show how close the observed values were to the
estimated values. A second model was proposed for Andersen samplers, using
bacterial survival factors, such as temperature, relative humidity, solar
radiation, and sampling period, as variables, but there was no data showing
how these estimated results related to the observed results.
CAMANN'S MODEL
A dispersion model based on an extensive aerosol monitoring study
(51) at the City of Pleasanton, California, spray irrigation site using
all-glass impingers, LEAP and Litton M Large-Volume air samplers, and
Rotorod samplers, was developed by Camann (51, 52, 56, 58, 106, lllj. The
study consisted of two ptiase-s-: phase I ('tOS^was designed to select a
suitable site and to develop optimum methods for sampling and analysis of
wastewater and aerosol samples; Phase II (51) was designed tc
perform extensive environmental monitoring and to develop a dispersion
model that could be applied to other wastewater spray irrigation sites.
Camann's dispersion model (57) incorporated three parameters, partially
developed in the earlier multiplicative model of Sorber et al. (25). These
parameters are (1) a site specific parameter for aerosolization efficiency,
i.e., the fraction of the sprayed wastewater that is aerosolized during
a run, (2) a microbiological impact factor, i.e., the proportion of the
aerosolized microorganisms of a group that remain viable at some downwind
distance, and (3) a microbiological age decay rate, i.e., the rate at which
microorganisms of a group die-off with aerosol age.
Several assumptions were made in the development of this model. First,
the major biological and physical processes affecting microorganism levels
in aerosols from spray irrigated wastewater were adequately represented
by the multiplicative dispersion model. Second, aerosol microorganism
die-off was caused by factors such as meteorological conditions that have
the same effect at any spray irrigation site. Last, the microbiological
aerosol concentrations from field studies vary with the sampling, shipping
and assay procedures used. Hence, the aeroso.l concentrations predicted
by the model assume the" use of the' Pleasanton procedures.
36
-------
Camann found that the preponderance of model predictions were within
one order of magnitude of the net measured values, and most were within a
factor of 5. This model was developed from selected Pleasanton data and
was validated for indicator organisms with the remaining data and data from
additional studies at a Ft. Huachuca, Arizona, golf course soray irrigation
site (25,95) and the Deer Creek Lake State Park, Ohio, campground spray
fields (97). Camann suggested that the use of limited sampling and the
predictions from this microbiological dispersion model may be a preferable
alternative to extensive field sampling when sprayed wastewater was not
chlorinated.
Sorber and Sagik (58) suggested that the model developed at Pleasanton
(51) may be used to estimate the level or dose of aerosolized pathogens to
which treatment plant workers and nearby residents may be exposed. They
point out, however, that it cannot be used to determine the threshold levels
of pathogens in aerosols and is not predictive of the health risks asso-
ciated with spray irrigation.
Schaub et. al (56), in detailed discussion of the methodology of
aerosol monitoring, suggested that a major limitation in verifying Camann's
model has been the lack of reliable methods for obtaining microorganism
concentrations in effluent and aerosol samples. They suggested that refine-
ments in the model may be needed to separate the individual components of
the microbiological impact factor. In addition, standard indicator organ-
isms, used in the-development of-the model, were not representative indi-
cators of the pathogen content of the wastewater aerosols.
In aerosol studies (85) conducted at the Durham Advanced Wastewater
Treatment Plant in Tigard, Oregon, using Litton Model M Large Volume air
samplers, Camann's model was used to predict the daily dose of aerosolized
mycobacteria'and fecal streptococci received by Durham elementary school
children. In order to use the model, the authors assumed that the waste-
water quality and meteorological conditions during the week of aerosol
sampling were representative of both the mean levels and the variability
occurring over the two school years of interest and that the extrapolation
procedure used was valid. Examination of the school attendance records
revealed no adverse effects from the operation of the treatment facility,
located adjacent to the school. However, it was suggested that the students
may have received a peak daily dose of 9 cfu of mycobacteria and 3-.5 cfu of
fecal streptococci about one day per year. These values exceed the usual
seven-hour outdoor background dose by two orders of magnitude for fecal
streptococci and by three or more orders of magnitude for mycobacteria.
The authors admitted that the extrapolation procedure used may have caused
uncertainty in the predicted microorganism concentrations of one or more
orders of magnitude.
CONCLUSIONS
To date, dispersion models have limited usefulness in the prediction
of aerosol concentrations of microorganisms for various reasons. Some of
the limitations of dispersion models are the following:
37
-------
(1) Models make assumptions in their development
which may, in reality, be only partially valid or
may only be valid for a specific site and set of
conditions.
(2) Models may contain considerable error or imprecision
due to extrapolations, interpolations, partially valid
or invalid assumptions, and the inadequacies of the
measurement of various equation parameters.
(3) Models may not incorporate all factors necessary for
.the .determination of the. actual microorganism concen-
tration in aerosols, such as aerosolization efficiency,
deposition, die-off, relative humidity, and solar
radiation.
»
(4) Models may be used for purposes not originally intended
at the time of their development.
(5) Models may not be sufficiently validated.
(6) Insufficient or inappropriate techniques may be used
in. the mathematical or other types of analysis of the
model.
(7) Models are based on and validated, by data collected
using sampling methods limited by the current state-
of-the-art.
. The predictions of microorganism concentration in aerosols by the
present models contain one of more of the limitations listed above. However,
for bacteria the models appear to have some usefulness but have not been
developed enough to replace actual field monitoring. More research is
needed to test and improve present models or to develop new ones.
38
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SECTION 7
EFFECTS OF PATHOGENIC MICROORGANISMS PRESENT IN WASTEWATER
AND WASTEWATER AEROSOLS
Details about the pathogenic microorganisms present in wastewater that
have adverse effects on human health, the various routes of their infection,
the relative risk associated with each potential mechanism, sewage-related
diseases of concern, their symptoms and severity, current incidence, etc.
have been discussed extensively recently and will only be summarized here
(1,4,7,9,112-114). Disease incidents related to contamination of water
supplies by untreated wastewater and abuse of commonly accepted wastewater
management practices have been summarized by Sepp (2) and Bryan (13) and,
therefore, will not be discussed here.
DISEASES ATTRIBUTED TO PATHOGENIC MICROORGANISMS PRESENT IN WASTEWATER AND
AEROSOLS
Pathogenic microorganisms generated at wastewater treatment plants and
land application sites can be transmitted via inhalation, skin,contact, and
ingestion via poor hygiene. Infection may result in disease depending on
the degree of exposure as well as other factors such as pathogen density
minimum infective dose, virulence of the organism, and susceptibility of
the exposed individual.
The dose of a particular organism that is required to produce an in-
fection or disease in a healthy individual is referred to as the minimum
infective dose. It depends on the particular strain of the organism, its
virulence under the conditions of exposure and the susceptibility of the
individual. It is very difficult to define dose-response to low densities
of pathogenic microorganisms. Low density refers to a density capable of
causing disease in only a small fraction of the exposed population. Under
special circumstances, an infection can develop from a single virus, pro-
tozoan or helminth. The minimum infective dose for bacteria ranges from
100 to 100 million, depending on species (13). While the 50 percent in-
fective dose for Giardia lamblia is between 25 and 100 cysts (115). A
summary of available information on the reported waterborne diseases in the
U.S. is shown in Table 6 (114). A brief discussion of the diseases attributed
to the pathogenic microorganisms present in wastewater and wastewater aerosols
is presented below.
39
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TABLE 6. SUMMARY INFORMATION ON REPORTED WATERBORNE DISEASES IN THE
UNITED STATES (114)
Resulting
Wastewater constituent disease
Disease incidents
1961-1974
Reported no. Reported no.
of outbreaks of cases
Reported
untreated
wastewater
concentration
No./100 ml
Indicator organisms
Total coliforms
Fecal coliforms
Bacteria
Shigella sp
Salmonella typhi
Salmonella "sp^
Escherichia coli
Virus
NS
Hepatitis virus A
Parasites
Entamoeba histolytica
Giardia lamb! i a
Miscellaneous
NS
Chemical agents
NA
NA
Shigellosis
Typhoid fever
Salmonellosis
NS
Hepatitis A
Amoebiasis
Giardiasis
Gastroenteriti
Chemical
poisoning
NA
NA
32
18
11
t
4b
NA
43
3
15C
sd 85
9e
NA ,
NA.
4,413
326
16,743
188
NA
1,254
39
5,303C
34,538
474e
1Q9
103
ND
f* "t
106 to 4xl03
600
ND
700 to 1,900
4X10-1
ND
ND
ND
Note: NA - not applicable; ND = no data; NS = not specified.
a. Excludes 5. typhi.
b. None reported during 1971-1974.
c. Incomplete reporting for major incidents only.
d. May include other disease previously reported.
e. For the time interval 1971-1974.
40
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Bacterial Diseases
The important classes of bacteria and the diseases attributed to them
are shown below:
'Shigella sp. - -
Salmonella sp.
Vibrio cholerae
Mycobacterium tuberculosis
Leptospira icterohemorrhagiae
Escherichia coli (enteropathogenic)
Disease
Shigellosis
Salmonellosis
Cholera
Tuberculosis
Leptospirosis
Gastroenteritis
Shige Hosis. Shigellosis, also known as bacillary dysentery is an
acute bacterial diarrheal disease and is caused by Shigella organisms.
Shigellosis is an intestinal disese and is limited to man and higher apes.
Infection is primarily due to ingestion and spreads rapidly under improper
sanitary conditions. Waterborne spread of the organisms can cause outbreaks
of shigelTosis. Recovery is usually spontaneous. Most Shi gel!a infections
are subclinical with no manifested symptoms.
Salmons 1losis. Salmonellosis is caused by a large variety of species
of Salmonella and is characterized by diarrhea, abdominal cramps, fever,
nausea and vomiting. The disease is usually mild and even asymptomatic.
Infection usually occurs as a result of ingestion of contaminated food.
Typhoid fever is usually obtained from' drinking water or eating food con-
taminated with Salmonella typhi. The duration of the illness is about
.three weeks. In untreated cases, a mortality rate of 10% is observed (112,116)
'Salmonella typhi has been shown to be responsible for incidents of typhoid
fever associated with wastewater contaminated drinking water (117). Other
members of the Salmonella group are associated with paratyphoid fever and
acute gastroenteritis.
Cholera. Cholera is caused by the bacterium Vibrio cholerae. It is a
serious acute intestinal disease characterized by acute diarrhea, vomiting,
dehydration, and lowered body temperature and blood pressure. Death can
occur within a few hours of the onset of the disease. Infection can spread
from person to person via contaminated, food and water. Occurrence of cholera
in Israel in 1970 was attributed to the practice of irrigating vegetable
crops with untreated wastewater (118).
Tuberculosis. Tuberculosis is caused by the bacterium Mycobacterium
tuberculosis.Tnfection is primarily due to inhalation of infective bacteria.
Tuberculosis manifests itself in two forms, primary and post-primary.
Primary tuberculosis is characterized by acute respiratory debilitation
either healing or progressing to more serious illness and death. Post-primary
tuberculosis is a chronic illness.
Leptospiroris. Leptospirosis, also known as Weil's disease is caused by
41
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the bacterium Leptospira icterohemorrhagiae and can be transmitted to man
by rodents. Symptoms include chills, high fever, headache, photophobia and
muscular pain. The infection is usually sufaclinical but, on occasion it
can be fatal. Outbreaks of the disease have been linked to water contam-
inated by urine from humans, pet animals, and livestock.
Gastroenteritis. Gastroenteritis can be caused by a number of bacteria,
in particular, by enteropathogenic strains of Escherichia cpli. It is
characterized by diarrhea, nausea, prostration, dehydration, and usually
the lack of febrile response (119). In general, the illness is not severe
and recovery is spontaneous. The disease can be spread via sewage-contam-
ination of drinking water (120).
Viral Diseases
Viruses consist of a nucleic acid genome' enclosed in a protective
protein coat. Viruses that are shed in fecal matter, referred to as enteric
viruses, are characterized by their ability to infect tissues in the throat
and gastrointestinal (GI) tract. These viruses include the enteroviruses
(polio-, echo-, and coxsackie- viruses), reoviruses, adenoviruses and rota-
viruses, as well as the agent of infectious hepatitis. They can cause a
wide variety of diseases, such as paralysis, meningitis, respiratory illness,
myocarditis, congenital heart anamolies, diarrhea, eye infections, liver
disease and gastroenteritis. Almost all of these viruses also produce
nonclinical infections thus making it difficult to recognize them as being
waterborne. Known cases of waterborne viral diseases have largely been
limited to infectious hepatitis. Some viral diseases that may be transmitted
via wastewater and their etiologic agents are discussed below.
Infectious Hepatitis. Infectious hepatitis is caused by Hepatitis A
virus and is a common viral disease transmissible via wastewater. Water-
borne outbreaks of hepatitis are known to occur (117). Foodborne outbreaks
from harvesting of sea food from sewage contaminated water have also been
reported (121).
Poliomyelitis. Poliomyelitis is caused by poliovirus types 1, 2 and
3. It is a viral disease that affects the central nervous systems. Symptoms
include fever, malaise, headache, etc. Paralysis of the voluntary muscles
can occur in severe cases. Infection occurs following ingestion of viable
virus particles. ;
Gastroenteritis. A number of viruses are known to cause gastroenteritis.
Enteric viruses such as coxsackie, Echo and Hepatitis A viruses, parvovirus-like
agent, rotavirus and adenovirus all cause gastroenteritis.
42
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Gastroenteritis is a relatively mild illness, often sufaclinical, and of
short duration. Rotavirus infection is of particular interest because of
its prevalence in infants. It is often stated that a single virus particle
is capable of initiating infection in a susceptible individual (122). Min-
inum infective dose for normal persons is in the range of 10 to 200 viruses.
Since viruses do not replicate in the external environment, asymptomatic
individuals can act as an important reservoir for viral replication and
thus increase the likelihood of" initiating disease in susceptible individuals,
Protozoan Diseases
Protozoans pathogenic to man and capable of transmission via wastewater
are Entamoeba histolylica, which causes amebic dysentery or amoebiasis, and
Giardia Iambiia which causes giardiasis. These diseases can result from
fecal contamination of drinking water. The organisms are obligate parasites
and do not survive outside the human host.
Amebic Dysentery. Amebic dysentery is caused by the organism Entamoeba
histolytica. The organism infects the human colon causing erosion of the
superficial mucous membranes.-- It may eventually invade the tissue with
subsequent ulceration. Symptoms include abdominal discomfort, diarrhea,
nausea, and in some cases liver abscesses.
Giardiasis. Giardiasis is an intestinal disease caused by the infection
of the gut by the protozoan Giardia lamblia. The disease ranges from sub-
clinical to clinical malabsorption. Symptoms include abdominal pain, loss
of appetite, apathy, headache and diarrhea alternating with constipation.
Outbreaks of giardiasis due to consumption of contaminated drinking water
have been reported (112).
Parasitic Diseases !
The parasitic organisms of most concern are Ascaris lumbricoides,
Necator americanus (hookworm), Trichuris trichiura (whipworm) and Taerri_a
saginata {beef tapeworm). These parasitic organisms can cause infection
via skin contact. The severity of infestation depends on the number of
ingested eggs.
Ascariasis. Ascariasis results from ingestion of the eggs of A.
lumbricoides.The larvae of this organism hatch in the small intesYine and
penetrate through the wall to infiltrate the blood stream. The symptoms
are variable depending on the number of infecting organisms present. They
include abdominal pain, acute colic pain, vomiting, diarrhea, and mild
fever. The worms do not reproduce inside a human host and, therefore, the
severity of symptoms is directly related to the number of eggs ingested.
The infection is usually self limiting, but migration of the larvae in
large numbers through the lung can cause hemorrhage and pneumonia.
Trichuriasis. Whipworm infestation is caused by Trichuris trichiura
e99s-ihese eggs are not hardy and require special environmental conditions
-in-order to mature to an infective stage (112,123).
43
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Necatoriasis. Hookworm infestation is caused by skin penetration by
the larvae of N. americanus. The .eggs of this organism must hatch in the
soil and develop to the third stage larvae in order to be infective to
humans (112,123). The larvae penetrate the skin on contact and follow the
cardiopulmonary pharyngeal route to the intestine. Hookworms cause mal-
nutrition and anemia (119). Workers involved in the transportation of
sludge and those at land application sites are potentially at risk to in-
fection via skin penetration. The organism is not common in the U.S.
Taeniasis. Taeniasis is caused by Taenia saginata (Beef tapeworm)
and/or Taenia solium (pork tapeworm). These helminths can be present in
contaminated animal flesh and in water. The symptoms of taeniasis are
abdominal pain, digestive disturbance and weight loss.
EPIDEMIOLOGY OF WASTEWATER TREATMENT PLANT WORKERS AND POPULATIONS LIVING
IN THE VICINITY
Clark et al. (4) reviewed the literature concerning the possible health
effects of workers exposed to municipal wastewater via physical and aerosol
routes of exposure to pathogenic microorganisms. They stated that only a
few studies to date (1975) had been conducted on the health status of waste-
water workers. These studies were mostly retrospective in nature and,
therefore, do not permit determination of whether the specific disease con-
dition existed before exposure to wastewater. Also, most of the studies
mentioned in their work were from outside of the United States. They found
that no correlation had been made between specific microorganism levels and
the incidence of selected disease. They concluded that in order to evaluate
the disease risk associated with occupational exposure to wastewater, the
disease incidence of the comparable general population group must be known
as well as worker health status, and length and degree of exposure. They
recommend that more definitive studies of occupational risks associated
with sewage collection and treatment should be carried out.
A number of studies on the health effects of wastewater exposure have
been initiated in recent years. The studies usually consisted of two
general types --
(1) retrospective medical history questionnaire surveys or
examination of medical records, and
*
(2) prospective clinical and laboratory evaluation of the health
status of treatment plant workers and populations residing
near treatment plants.
Some of the recent studies are discussed in this section.
44
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Cincinnati, Ohio; Chicago, Illinois; and Memphis, Tennessee (86). A
prospectiveseroepidemlological study of municipal wastewater workers with
controls in three metropolitan areas -- Cincinnati, Ohio; Chicago, Illinois;
and Memphis, Tennessee -- was carried out by Clark et al. (86). The study
group consisted of more than 100 workers recruited when they began work at
activated sludge treatment plants. In addition, in Cincinnati about 50
sewer maintenance workers and 50 primary wastewater treatment plant workers
were also included in order to differentiate between aerosol exposure and
exposure associated with primary wastewater treatment. The study involved
quarterly collection of sera, throat and rectal swabs, annual multiphasic
and physical examinations; monthly collection of illness information and
environmental monitoring. Clinical illness surveys did not show an in-
crease in respiratory, gastrointestinal or other illness in workers exposed
to wastewater. Clinical laboratory examination showed no evidence of in-
creased bacterial or parasitic infections in wastewater workers. Liver
function tests and immunoglobulin determinations (IgA, IgG and IgM) also
did not show consistent abnormalities in the wastewater workers. Although
more enteroviruses were recovered from wastewater workers, the authors
found that the recovery rates were not significantly different. Preliminary
analysis of viral serology data also failed to show a significant dif-
ference in the prevalence of antibodies specific to viruses. However, in
one of the cities in 1977, there were significantly more seroconversions in
experienced wastewater treatment plant workers than in inexperienced workers
and controls when the results of testing for 31 viruses were evaluated
together. Viral serology of the family members of the study participants
also did not reveal any significant differences between workers and family
members. Additional testing for antibodies to Hepatitis A and Legionella
pneumophila is planned. The study did show an increase in minor gastro-
intestinal illness in inexperienced wastewater workers compared to experi-
enced workers and controls. However, these illnesses did not correspond to
enteroviral infections.
Gartside and Clark et al. (124) carried out a mortality study of former
employees of the Metropolitan Sanitation District of Greater Chicago
(MSDGC). Preliminary analysis of about 400 death certificates showed no
significant departures from expected death rates for several major disease
groupings for the workers as a whole or for several employee subgroups,
or the length of employment. They did, not find any correlation between
cause of death and exposure to wastewater.
Winnipeg, Manitoba, Canada (125). A prospective epidemiological
study of wastewater treatment plant workers was conducted in Winnipeg,
Manitoba by Sekla et al. (125). The study was initiated as a result of
frequent complaints of headache, fatigue, lassitude, dysentery, and nausea
by the workers. The symptoms were noted when workers were taken out of
their work environment; thus illness was of short duration. Comprehensive
hematological, biochemical, serological and immunological profiles of the
workers were compared with those of suitable controls. The study concluded
that clinical laboratory results obtained from the wastewater exposed
workers did not differ from those of the controls. However, sinusitis was
detected among the wastewater workers that started upon exposure to the
45
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work environment and diminished after leaving work. They suggest that an
allergen might be involved. An excess of nasal disorders was also detected.
Gothenburg, Sweden (72). ' Rylander et al. (72) carried out a pro-
spective epidemiological study of workers in conventional sewage treatment
plant, at a plant where the sludge was heat-treated and at another plant
where household waste and sewage sludge was composted. The study involved
interviewing workers to determine the frequency of clinical symptoms and
chemical and immunological evaluations of workers' sera. A high proportion
of workers in conventional sewage treatment plants and in the compost plant
had gastrointestinal symptoms. Workers exposed to sewage dust, especially
at heat-treated sludge operations were found by Rylander and his co-workers
(21) to suffer from acute episodes of fever.and eye discharges. Sewage-ex-
posed workers were found to have elevated levels of immunoglobulins (IgG,
IgM and IgA), in addition to a higher percentage of elevated levels of
C-reactive protein and fibrinogen degradation products. Rylander et al.
(72) attribute the clinical symptoms as due to exposure to endotoxins present
in the wastewater treatment process, especially the dust generated during
the sludge-drying operations.
Copenhagen, Denmark (126,127). Investigators in Copenhagen conducted
a health survey of Copenhagen sewer workers, who were noted to have a higher
death rate than a comparable control population. The study was initiated
at the request of the sewer workers and consisted of analysis of death
statistics and sick leave records, administration of a health questionnaire,
medical consultation, and blood and urine chemistry. The study showed that
a high proportion of deaths occur within the year of retirement. The death
rate was found to be greater in those working for 9-16 years than in those
employed for" less than nine years. A limitation of this study is that-only
33 deaths were evaluated. Absenteeism was found to be significantly higher
in workers over 50 years of age than in office workers of the same age.
However, there is no difference in absenteeism rate in sewer workers when
compared to other manual workers. The study also showed that sewer workers
experience a high rate of acute gastrointestinal disorders including nausea,
vomiting, and diarrhea. Clinical laboratory analyses showed that sewer
workers have elevated levels of the immunoglobulin, IgG, but no other signif-
icant differences from control groups. Higher levels of antibodies to
Hepatitis A were also reported in sewer workers but not to Hepatitis B.
Hepatitis A results correlated better with age than with length of employment.
Other investigators have shown that the presence of antibody to Hepatitis A
increases with age (128).
Honolulu, Hawaii (129). A retrospective epidemiological study of the
assessment of health risks to sewer workers was carried out by Root et al.
(128). The study involved examination of medical and sick leave records
of the workers for a two-year period. Analysis of individual sick leave
records showed that total number of days lost in a year are 2.5 times
greater for workers frequently exposed to raw wastewater than for those
who were rarely exposed. Symptoms included colds, flu, stomach upsets,
and a variety of aches and pains. A review of annual physical examination
46
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records showed no differences in the exposed and rarely exposed groups.
Root at al. (129) state that from sick.leave record analysis, it would
appear that there is a significant relationship between frequency of ex-
posure to sewage and number of sick days taken. They concede that their
conclusions should be based on more than a two-year study and recommend
that a more detailed analysis be carried out over a greater time period.
They do, however, conclude that sewer workers were at no greater risk than
the general population. -- - --....
Egan Plant, Chicago, Illinois (84). A prospective epidemiological
study of households within a 5 Km radius of a new wastewater reclamation
plant located near Chicago, Illinois was carried out by Johnson et al.
(84). The study consisted of environmental monitoring, household health
survey to examine the incidence of respiratory and gastrointestinal diseases,
and clinical evaluation of biological specimens to isolate pathogenic bacteria,
viruses and parasites, and to determine viral antibody titers. The study
showed that the microorganism and chemical levels in the air, water and
soil samples in the neighborhood were not distinguishable from the back-
ground levels. The household health survey showed that there is an increased
incidence-of skin disease, nausea, vomiting, and diarrhea among residents
living close to the wastewater treatment plant. The authors believe that
these symptoms may be associated with the nearby operation of the waste-
water treatment plant. However, they mention that the evidence obtained
from the household health survey is non-medical and possibly subjective.
Clinical laboratory evaluations did not show evidence of an adverse health
effect from the wastewater treatment plant. They concluded-that there is no
public health hazard for populations living beyond 400 meters from the
plant, this distance being the closest that any people resided. The authors,
however, point out that the area surrounding the plant was developed further
after their study started and that the new residents were not included in
the study.
Skokie, Illinois (83). A prospective epidemiological health survey of
a population living within 1.6 Km of an activated sludge treatment plant in
Skokie, Illinois was carried out by Carnow et al. (83). The study consisted
of collection of throat swabs, stool specimens, blood samples for pathogenic
bacteria and virus analysis, immunological evaluation for viral antibodies;
maintenance of health diaries, and environmental monitoring. The study
included 269 households living at about 600-800 meters from the center of
the wastewater treatment plant. The study failed to show a correlation
between exposure and the rate of illnesses reported or of bacterial or
viral infection rates, even though the plant has been shown to be a source
of viable bacteria and viruses. They concluded that there are no adverse
health effects on residents potentially exposed to viable aerosols. The
authors, however, concede that only a very small number of people were
exposed to the highest pollution levels and hence the results are not con-
clusive.
Tecumseh, Michigan (130). The potential health effects of an activated
sludge treatment plant on residents of a community living within a series
.of 600 meter concentric rings from the plant were studied by a retro-
spect ive_ study by admin iste_rj_ng a_ questionnaire by Fannin et al. (130).
47
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The objective of the study was to find the incidence of total, res-
piratory, and gastrointestinal illnesses. They found differences in
disease incidence during the period May through October at varying distances
from the wastewater treatment plant. Persons living within a 600 m radius
were found to have a greater than expected risk to respiratory and gastro-
intestinal illnesses, when specified for income and education. The authors
conclude that the higher illness rates may be related to higher densities
of lower socioeconomic families than to the wastewater treatment plant.
Persons living around a second 600 m concentric ring were used as controls.
Tigard, Oregon (85). Johnson et al. (85) analyzed the attendance data
at an elementary school that was located next to a wastewater treatment
plant in Tigard, Oregon,as a part of the first phase of a potential health
hazard evaluation. The aeration basin of the plant was located within 400
m of the classrooms and the surge basin was found to be located within 50 m
of the school playground. The study also included environmental monitoring.
Camaan et al. (Ill) using a model, calculated that the students would receive
a peak dose of about 9 cfu of mycobacteria and 3.5 cfu of fecal streptococci.
Small exposure levels would be encountered several dozen days per year.
The-study-concluded that illness, as represented by school attendance, did
not show evidence of adverse health effects from wastewater treatment plant
operations at these exposure doses. The authors concede that the analysis
of school attendance data was a relatively insensitive measure.
Summary
The following conclusions can be drawn from the epidemiology of workers
at the wastewater treatment plants, and populations living in the vicinity
and are- based mostly on the comments from the pane3 at the USEPA
Symposium (131). The survival and dispersion of viable particles in aerosols
are dependent on a variety of factors as mentioned earlier. Finding a cor-
relation between airborne microorganism levels and incidence of disease in
exposed workers or in nearby populations is rather difficult because of the
complexity of the variables involved. Also, there is no information avail-
able on minimum infective dose of airborne microorganism levels for in-
halation route., Although pathogenic microorganisms have been detected in
aerosols and inhalation is a possible route of exposure, the health effects
studies carried out so far do not indicate any increased health risk due to
exposure to wastewater aerosols. However, in the words of Oliver "negative
epidemiologic evidence is even less persuasive than most other kinds of
negative evidence." Oliver recommends that "people should not venture
closer than necessary to a source of wastewater aerosol." He also notes
that people visiting sewage treatment plants regularly stand in the "aerosol
cloud" of the activated sludge tanks without perceptible ill effects (132).
The panel at the USEPA symposium concluded that wastewater
treatment plant workers' hazard, if any, is small from infectious disease
agents, hazards to nearby residents is almost nonexistent and that the
exposure to pathogenic microorganisms in aerosols is not a unique way of
initiating enteric infections. The panel recognized, however, that the
.worst case exposure of either the worker or the populations has not yet
been investigated (131),.
48
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The absence of a recognizable disease hazard due to exposure to waste-
water aerosols in wastewater treatment plant workers may be explained as
due to the possible immunity developed by being regularly exposed to low
levels of viruses and pathogenic bacteria that can cause infection but not
clinical illness (133).
EPIDEMIOLOGY OF WORKERS AT LAND APPLICATION SITES AND POPULATIONS LIVING IN
THE VICINITY
There are only a limited number of studies on health effects of workers
at land application sites and populations living in the vicinity, some of
these studies are still being carried at present.
Israel (134). A retrospective epidemiological study was carried out
in Israel by Katzenelson et al. (133). The incidence of enteric communicable
disease in 77 kibbutzim (cooperative agricultural settlements) where crop
irrigation was practiced with partially treated, nondisinfected wastewater,
was compared with that of 130 kibbutzim not practicing such irrigation.
The incidence of shigellosis, salmonellosis, typhoid fever, and infectious
hepatitis was found to be 2-4 times higher in the kibbutzim practicing
wastewater spray irrigation. The study populations lived from 100 to 3000
m from the spray irrigation fields. The study seemed to provide some
evidence for an increased risk for enteric communicable disease among popu-
lations living near wastewater spray irrigation sites. The pathways of
infection, that is, direct contact or aerosol exposure, are not clear. The
study also did not directly relate spray irrigation with the elevated in-
cidence of diseases. The authors concede that the study has serious
methodology problems and that there-were other sources of disease besides
the wastewater pathogens.
A follow-up retrospective epidemiological study was carried out by
Shuval et al. (135) in 83 kibbutzim. Preliminary analysis of data showed
that there is no apparent difference in overall enteric disease incidence
between kibbutzim practicing wastewater sprinkler irrigation and those that
do not. In those kibbutzim which irrigated with wastewater for only two
out of a four-year perio_d, the study also showed no difference in enteric
disease incidence for the period when wastewater irrigation was practiced
compared to the period when they did not. Although these conclusions are
based on preliminary analysis of data only, it appears that aerosols are
probably not an important pathway of infection in the kubbutz populations.
A prospective epidemiological study is planned which is aimed at further
elucidation of the possible routes of transmission of pathogens from spray
irrigation sites to the adjacent communities (135).
*
Melbourne, Victoria, Australia (136). Wastewater from the city of
Melbourne has been applied to agricultural lands at the Melbourne and
Metropolitan Board of Works Werribee Farm since 1896. Land filtration,
grass filtration, and lagooning are some of the treatment processes used
prior to land application of the raw wastewater, depending on the season.
49
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The workers involved in the land application and the residents on the farm
would be expected to be at risk from exposure to pathogens and chemicals in
the wastewater. Even' though the farm had been in operation for the past 80
years, according to an official of the farm, the health of the workers as
well as the residents of the farm "has been as good as that of the commu-
nity generally and no epidemics of diseases have occurred." It appears, in
the absence of supporting evidence, that such a conclusion was a personal
observation made by the official and was probably not based on an actual
health effects study (health questionnaire survey or clinical investigation),.
No special precautions were taken during the whole of this period other
than normal hygiene practices. There were, however, complaints of ob-
jectionable odor, but they report that the degree of offense or inconve-
nience has been minimal.
India (137). A prospective epidemiological study of the health status
of sewage farm workers and a suitable control population was carried out in
India by Krishnamoorthi et al. (137). The study consisted of a clinical
evaluation and collection of stool specimens for the analysis of protozoan
parasites, cysts, and helminthic eggs. Ascaris lumbricoides (round worm)
and Ancyloma duodenale (hook worm) were the most dominant parasites while
Entamoeba histolytica was the most dominant protozoan found among the sewage
farm workers. The study results show that the incidence of infection was
about 20-27% higher in the sewage farm workers compared to the control
populations and the multiplicity and intensity of infection were found to
be more predominant in sewage farm workers than the control population;
thus indicating a clear health hazard to the workers involved in the land
.application of raw sewage. It must be emphasized that the experience in
India involves land application of untreated sewage "and, therefore, does
not represent situations in the United States.
Ohio State Farm Bureau (138). A prospective epidemiological study of
the health effects of farm families utilizing municipal sludge for land
application is being carried out by Ohio Farm Bureau Federation and the
United States Environmental Protection Agency in cooperation with the Ohio
State University Research Foundation, the Ohio Agricultural Research and
Development Center, the Ohio Cooperative Extension Service, the Ohio De-
partment of Health and the Ohio Environmental Protection Agency (138, 139).
Muskegon, Michigan (140). A short-term prospective seroepidemio-
logical study of the workers at a wastewater spray irrigation facility in
Muskegon, Michigan is being carried out by Clark et al. (140).
Stanford et al. (141) carried out a study of morbidity risk factors
from irrigation with treated wastewater. They found that no instance of
disease was reported from the spray irrigation of chlorinated secondary
effluents.
Summary
The following conclusions can be drawn from the limited information
available on the epidemiology of workers and populations at land
application sites. Althougn pathogenic microorganisms are present in
50
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aerosols In detectable levels, there Is no recognized disease transmission
that can be attributed to airborne pathogens to either workers or popu-
lations at land application facilities. It is believed that the health
hazard from sprinkling wastewater is limited to direct contact with un-
evaporated droplets. There is, however, a potential for contamination of
food crops grown on wastewater or sludge treated lands which should be
taken into consideration when formulating guidelines or recommendations. It
has been shown that viruses concentrate in sludge because of their tendency
to adsorb to particulate material, which also prolongs their survival.
Once crops are harvested, enteric viruses can survive for long periods
during storage at low temperature. There is also a possibility that
vegetables consumed after thorough cooking might have been infected by
contact with kitchen surface, utensils and hands contaminated by raw crops.
51
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SECTION 8
CONTROL OF AEROSOLS
Major sources of aerosols are, as has been mentioned earlier, aeration
basins, trickling filters, and land application sites that practice spray
application. Some of the factors that affect the microbial concentration
in aerosols are:
viable microorganism levels in wastewater
-- aerosolization efficiency i.e., the proportion of wastewater
that enters the aerosol state.
aerosol decay rate
-- volume of the wastewater sprayed per unit time
atmospheric stability and other meteorological parameters
such as wind speed, relative humidity, solar radiation,
temperature, etc.
Once aerosolized, the survival of airborne microorganisms is reduced by
increased temperature, lower relative humidity, and solar radiation. Air-
borne microorganism levels are also reduced by diffusion by high wind '
speed. However, neither meteorlogical conditions nor diffusion by high
wind speed would provide reliable reduction in airborne microorganism
levels.
Some of the techniques which may be used to control or suppress aerosols
and/or the levels of microorganisms in aerosols are:
use of vegetative barriers to intercept, filter, and disperse aerosol;
use of suitable buffer/safety zones
disinfection of wastewater effluents and sludge prior to
land application
selection of proper spray equipment
covering the aeration basins.
Adaptation of some or all or a combination of these techniques would help
suppress the aerosols and/or microorganism levels in aerosols. The
effectiveness of the various techniques is discussed below briefly.
Vegetative Barriers. The effectiveness of the vegetative barrier was
evaluated by the Metropolitan Sanitary District of Greater Chicago (MSDGC)
by using dense coniferous and deciduous vegetation (142,143). The extent
of filtration as a function of vegetation density and wind velocity was
studied in a low-speed wind tunnel. Filtration effectiveness was
determined by reduction in the levels of Bacillus subtilis, var. niger
52
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and E_. coll in aerosols. The study showed that the levels of microorganisms
in aerosols were reduced by 50% and concluded that strategically-placed
vegetation would effectively reduce aerosols generated at wastewater
treatment plants. This would be expected to be true atspray irrigation
facilities also.
Buffer/Safety Zones. A buffer or safety zone is a space between the
wastewater treatment plant or the edge of the wetted area of spray irrigation
site and adjacent land uses that ensures adequate protection of populations
from potential health hazards or aesthetic insult of exposure to pathogenic
microorganisms in aerosols, and water supplies from contamination with
pathogenic microorganisms present in wastewater and sludge used for land
application.
The buffer zones recommended by several states for safe land application
of municipal wastewater and sludge are listed in Table 7. The distance
recommended for human inhabitation ranged from about 61 meters (Iowa,
surface spreading of stabilized sludge) to 400 meters (Minnesota and South
Dakota, spray application of secondary wastewater). The data shown in
Table 7 are compiled from information/literature received in response to a
mail survey from states and U.S. territories. The guidelines established
by some states for safe land application of wastewater and sludge are
shown in Table 8. The data shown in Table 8 are obtained from the same
source used for compiling the data in Table 7. As can be seen from Table
8, some states have adapted quite stringent requirements depending on the
type of the use of the land. Although most states permitted grazing of
pasture lands by dairy cows after a certain number of days following waste-
water or sludge application, some states.do not permit such use. As can
be seen from Tables 7 and 8, none of the states permit land application of
raw wastewater or unstabilized sludge. When queried regarding the basis
for the guidelines, responses ranged from "none" to "intuition" to
published literature, United States Department of Agriculture (USDA) studies
and EPA Manuals. As can be seen from Table 8, the greater the potential
hazard (i.e., the more intimate the public contact with the treated waste-
water), the more stringent are the regulations. None of the states have
based their guidelines on a health effects survey or on known health effects.
It was mentioned earlier that Sorber et al. (61) calculated predicted
levels of bacteria and viruses downwind of spray irrigation sites using a
modification of Turner's atmospheric dispersion model. They determined
that an individual working 200 m downwind from a center pivot spray rig
with a 300 m radius could inhale as many as 20 infectious airborne viruses
in 10 minutes. From this, they estimated that an 800 m buffer zone should
be used around a spray irrigation site as a safe distance for normal human
inhabitation. Bertucci et al. (20) calculated that a total of about 1340
hectares (3348 acres) would be required to provide an 800 m buffer zone,
as recommended by Sorber et al. (61), around a 400 hectare (100 acres)
spray irrigation site. But based on the reported enterovirus density by
Johnson et al. (51,52) at a spray irrigation site in Pleasanton, California,
a worker on duty 8 hours per day at 50 meters would inhale only one entero-
virus every nine days.
53
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TABLE 7. BUFFER/SAFETY ZONES RECOMMENDED BY SOME STATES FOR SAFE APPLICATION OF
WASTEWATER (W) AND/OR SLUDGE (S) TO LAND COMPILED FROM MAIL SURVEY3 (METERS)
State
Floridab (S)
Florida (W)
Georgia (W)
Idahob (S)
Idaho0 (S)
Illinoisb (S)
Illinois°»d (S)
Illinois0*6 (S)
Indianab (S)
Iowab (S)
Kansas0 (W & S)
Maineb (S)
Maineb (S)
Michiganb (S)
Minnesotab (S)
Minnesota0 (S))
Minnesota (W)
Nebraska (W) ,.
Nebraska5 (S) .
New Yorkb (S)
New York0 (S)
Ohio (S) '
Pennsylvania (S)'
Minimum
treatment
required
Stabilized
Secondary &
disinfection
Secondary
Stabilized
Stabilized
Digested
Digested
Digested
Stabilized
Stabilized
Secondary
Stabilized
Untreated
Stabilized
Stabilized
Stabilized
Secondary & '
disinfection
Pretreatmenr
Digested
Untreated
Digested
Digested or
stabilized
Digested
Nearest water Nearest Nearest
Supply Public inhabited
Well Surface road area
304 91.2..
60.8 60.8
60.8 30.4
152 91.2
152 152
45.6 60.8
45.6 304
45.6 60.8
91.2 91.2
152
60.8 60.8
30.4 30.4
91.2 91.2
60.8 60.8
60.8 60.8
60.8 91.2
400 . 400
91,2 15.2
60'. 8 60.8
60.8
--i- 60.8
- 91.2
91.2 30.4
: 91.2
--
45.6
15.2
152
6.08
304
60.8
91.2
-. _
Reasonable Dist.
60.8
7.6
91.2
15.2
--
--
91.2
--
91.2
91.2
152
60.8
304
60.8
91.2
60.8
_ _
91.2
152
60.8
395.2
400
364.8
304
152
91.2
Nearest
residential
development
--
__
__
^
456
152
152
182.4
790.4
400
364.8
_ _
'
_..
Nearest
property
line
._
--
45.6
30.4
7.6
__
__
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15.2
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Bertucci et al. (20) examined the recommendation of Sorber et al. and
suggested that no buffer zones are required around wastewater treatment
plants based on their study of the relationship between confirmed virus
plaques and unconfirmed plaques in primary and secondary wastewater.
Bertucci et al. (20) suggest that other agents present in wastewater
might mimic the effects of virus in such assays resulting in an overestimation,
They found that in recent literature, a consistent ratio of confirmed
virus colonies to pfu has not been established. Because of the very low
average ratios found, they concluded that no buffer zones would be necessary
between wastewater treatment plants or spray irrigation sites and the
surrounding population centers. The health effects studies described in
Section 7 also seem to lend support to such a conclusion.
In Russia, buffer/sanitary protection zones of 100-1000 meters are
required around agricultural fields that are irrigated by spray application
of wastewater (98).
Disinfection. It was discussed earlier that disinfection of wastewater
effluents is very effective in reducing the levels of microorganisms in
wastewater by 2-3 orders of magnitude. The levels of airborne microorganisms
are directly proportional to their levels in wastewater. Sorber et al.
(25) and Johnson et al. (51,52) have shown that disinfection of wastewater
prior to spray application reduced the levels of airborne microorganisms
to nondetectabla levels.
Spray Equipment. The type of spray equipment and type and spacing of
nozzles affect the emission of aerosols at spray irrigation sites. Selection
of proper spray equipment can be employed to effectively reduce the gen-
eration of aerosols. This was demonstrated in a Russian study in which
bacterial aerosols have been found to spread up to 250 m when short spray
equipment was used compared to 450 m and 600 m when medium and far spray
equipment, respectively, were used (98). In the United States, the spray
technology is changing in the past five years from the use of high pressure
upward spray to low pressure downward spray equipemnt and more recently to
subsurface injection.
Covering Aeration Basins. Removable covers installed on top of the
aeration basins would suppress aerosols as well as control odors. Existing
covers used for the suppression of odors should be examined for their
utility in suppressing aerosols.
Summary '
In conclusion, adaptation of any or all or a combination of these
techniques would help suppress the aerosols and/or microorganism levels in
aerosols. But care must be taken in the examination of the various tech-
niques for aerosols control or suppression to insure that workers are not
subjected to undue safety risks as well as other hazards.
61
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95. Bausum, H. T., S. A. Schaub, and C. A. Sorber. Viral and Bacterial
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74
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TECHNICAL REPORT DATA
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Potential Health Effects from Viable Emissions and
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September 1980
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